WO2021172361A1 - Light source device - Google Patents

Abstract

A light source device (10) is provided with a light source (11) that generates excitation light (Lp) having an excitation wavelength (λp), and a quasi phase matching element (12) having a polarization period (Λ). The quasi phase matching condition in the quasi phase matching element is fulfilled by a first photon pair (G1) emitted from the quasi phase matching element in response to the incidence of the excitation light on the basis of the polarization period and the excitation wavelength, and is fulfilled by a second photon pair (G2) emitted in the same direction as that of the first photon pair on the basis of the same polarization period and excitation wavelength as those of the first photon pair. The first photon pair has a first wavelength (λn1) within the range of a first wavelength band, and a second wavelength (λm1) within the range of a second wavelength band different from the first wavelength band. The second photon pair has a third wavelength (λn2) different from the first wavelength within the range of the first wavelength band, and a fourth wavelength (λm2) different from the second wavelength within the range of the second wavelength band.

Description

Translated fromJapanese

光源装置Light source device

　本開示は、例えば量子的に相関した光子の対を生成する光源装置に関する。The present disclosure relates to, for example, a light source device that generates quantum-correlated photon pairs.

　近年、量子テレポーテーションや量子センサを構築するための光を用いた量子情報の基礎技術として、量子相関によりもつれ合った光子対を生成する技術が研究されている。In recent years, as a basic technology of quantum information using light for constructing quantum teleportation and quantum sensors, a technology for generating entangled photon pairs by quantum correlation has been studied.

　特許文献１は、非縮退の偏光量子もつれ光子対を効率よく簡便に生成することを目的とした非縮退偏光量子もつれ光子対生成装置を開示している。この装置は、互いに周期が異なる第１及び第２周期分極反転構造をその内部に形成した量子もつれ光子対生成体と、第１周期分極反転構造を通過した後に第２周期分極反転構造を通過するように光を量子もつれ光子対生成体に入射させる入射手段とを備える。第１周期分極反転構造の周期は、ある角周波数ω１を持たせた光子が第１の偏光を有し、別の角周波数ω２を持たせた光子が第２の偏光を有するように調整される。第２周期分極反転構造の周期は、角周波数ω１の光子が第２の偏光を有し、角周波数ω２の光子が第１の偏光を有するように調整される。Patent Document 1 discloses a non-degenerate polarized quantum entangled photon pair generator for the purpose of efficiently and easily generating a non-degenerate polarized quantum entangled photon pair. This device passes through a quantum entangled photon pair producer in which first and second periodic polarization inversion structures having different periods are formed therein, and a second period polarization inversion structure after passing through the first period polarization inversion structure. As described above, it is provided with an incident means for incident light on a quantum entangled photon pair producer. The period of the first period polarization inversion structure is adjusted so that a photon having a certain angular frequency ω1 has a first polarization and a photon having another angular frequency ω2 has a second polarization. .. The period of the second period polarization inversion structure is adjusted so that the photon having the angular frequency ω1 has the second polarization and the photon having the angular frequency ω2 has the first polarization.

国際公開第２００９／０９３３９１号International Publication No. 2009/093391

Ariel Bruner et al., "Temperature-dependent Sellmeier equation for the refractive index of stoichiometric lithium tantalate", OPTICS LETTERS Vol. 28, No. 3 February 1, 2003Ariel Bruner et al., "Temperature-dependent Sellmeier equation for the refractive index of stoichiometric lithium tantalate", OPTICS LETTERS Vol. 28, No. 3 February 1, 2003

　特許文献１の装置では、角周波数ω１，ω２と第１及び第２の偏光とのもつれ合いによる２種類の光子対が、量子もつれ光子対生成体の中で第１周期分極反転構造が設けられた場所と、第２周期分極反転構造が設けられた場所とにおいて別々に生成されることから、量子的なもつれかどうかには議論がある。又、第１及び第２周期分極反転構造の各々の周期を精密に調整した装置構成を要する一方で、角周波数ω１，ω２の違いは僅かであり、生成される光子対の波長帯は近赤外領域中の限られた一部に留まる。In the apparatus ofPatent Document 1, two types of photon pairs due to the entanglement of the angular frequencies ω1 and ω2 and the first and second polarized light are provided with a first periodic polarization inversion structure in the quantum entangled photon pair producer. Whether it is quantum entanglement or not is controversial because it is generated separately at the location and at the location where the second periodic polarization inversion structure is provided. Further, while the device configuration in which the respective periods of the first and second periodic polarization inversion structures are precisely adjusted is required, the difference between the angular frequencies ω1 and ω2 is slight, and the wavelength band of the generated photon pair is near red. Remains in a limited part of the outer region.

　本願発明者は、こうした光子対の生成技術について鋭意研究を重ね、従来技術とは異なった複数の波長帯による新規の量子もつれ２光子状態を見出した。この知見から、本願発明者は、新規の量子もつれ光源だけでなく広帯域光源としても活用できる技術を考案するに到った。The inventor of the present application has conducted extensive research on such a photon pair generation technique, and has found a new quantum entangled two-photon state with a plurality of wavelength bands different from the conventional technique. From this knowledge, the inventor of the present application has come up with a technique that can be utilized not only as a novel quantum entangled light source but also as a wideband light source.

　本開示は、簡単な装置構成において複数の波長を有する光子対を生成できる光源装置を提供する。The present disclosure provides a light source device capable of generating photon pairs having a plurality of wavelengths in a simple device configuration.

　本開示に係る光源装置は、励起波長を有する励起光を生成する光源と、光源から励起光が入射するように配置され、周期的に分極が反転する分極周期を有する結晶で構成される擬似位相整合素子とを備える。擬似位相整合素子において規定される擬似位相整合条件が、励起光の光軸に沿った分極周期及び励起波長に基づき、励起光の入射に応じて擬似位相整合素子から出射する第１の光子対により充足され、且つ第１の光子対と共通の分極周期及び励起波長に基づき、第１の光子対と共通の方向に出射する第２の光子対により充足される。第１の光子対は、第１の波長帯の範囲内の第１波長と、第１の波長帯とは異なる第２の波長帯の範囲内の第２波長とを有する。第２の光子対は、第１の波長帯の範囲内で第１波長とは異なる第３波長と、第２の波長帯の範囲内で第２波長とは異なる第４波長とを有する。The light source device according to the present disclosure is a pseudo-phase composed of a light source that generates excitation light having an excitation wavelength and a crystal having a polarization period in which excitation light is incident from the light source and the polarization is periodically reversed. It is equipped with a matching element. The pseudo-phase matching condition defined in the pseudo-phase matching element is based on the polarization period and excitation wavelength along the optical axis of the excitation light, and is determined by the first photon pair emitted from the pseudo-phase matching element in response to the incident of the excitation light. It is satisfied and is satisfied by the second photon pair that emits in the same direction as the first photon pair, based on the polarization period and excitation wavelength common to the first photon pair. The first photon pair has a first wavelength within the range of the first wavelength band and a second wavelength within the range of the second wavelength band different from the first wavelength band. The second photon pair has a third wavelength that is different from the first wavelength within the range of the first wavelength band and a fourth wavelength that is different from the second wavelength within the range of the second wavelength band.

　本開示によると、第１から第４の波長を有する第１及び第２の光子対が、擬似位相整合条件を充足するような励起波長及び分極周期を有する光源及び擬似位相整合素子という簡単な装置構成において、複数の波長を有する光子対を生成できる光源装置を提供することができる。According to the present disclosure, a simple device such as a light source and a pseudo-phase matching element having an excitation wavelength and a polarization period such that the first and second photon pairs having the first to fourth wavelengths satisfy the pseudo-phase matching condition. In the configuration, it is possible to provide a light source device capable of generating photon pairs having a plurality of wavelengths.

本開示の実施形態１に係る光源装置の構成を例示する模式図Schematic diagram illustrating the configuration of the light source device according to the first embodiment of the present disclosure.実施形態１に係る光源装置における特性曲線を例示するグラフA graph illustrating a characteristic curve in the light source device according to the first embodiment.図２よりも励起波長が長い場合の特性曲線を例示するグラフA graph illustrating a characteristic curve when the excitation wavelength is longer than that in FIG.図２よりも励起波長が短い場合の特性曲線を例示するグラフA graph illustrating a characteristic curve when the excitation wavelength is shorter than that in FIG.実施形態１に係る光源装置における放射特性曲線を例示するグラフA graph illustrating a radiation characteristic curve in the light source device according to the first embodiment.実施形態１の光源装置における分極周期依存性の分極周期１７．０２５μｍでの理論計算を示すグラフA graph showing a theoretical calculation at a polarization period of 17.025 μm, which is dependent on the polarization period in the light source device of the first embodiment.実施形態１の光源装置における分極周期依存性の分極周期１６．９２３μｍでの理論計算を示すグラフA graph showing a theoretical calculation at a polarization period of 16.923 μm, which is dependent on the polarization period in the light source device of the first embodiment.実施形態１の光源装置における分極周期依存性の分極周期１６．８２１μｍでの理論計算を示すグラフA graph showing a theoretical calculation at a polarization period of 16.821 μm, which is dependent on the polarization period in the light source device of the first embodiment.実施形態１の光源装置における分極周期依存性の分極周期１６．７１９μｍでの理論計算を示すグラフA graph showing a theoretical calculation at a polarization period of 16.719 μm, which is dependent on the polarization period in the light source device of the first embodiment.実施形態１の光源装置における分極周期依存性の図６Ａに対応する実験結果を示すグラフA graph showing the experimental results corresponding to FIG. 6A of the polarization period dependence in the light source device of the first embodiment.実施形態１の光源装置における分極周期依存性の図６Ｂに対応する実験結果を示すグラフThe graph which shows the experimental result corresponding to FIG. 6B of the polarization period dependence in the light source apparatus ofEmbodiment 1.実施形態１の光源装置における分極周期依存性の図６Ｃに対応する実験結果を示すグラフA graph showing the experimental results corresponding to FIG. 6C of the polarization period dependence in the light source device of the first embodiment.実施形態１の光源装置における分極周期依存性の図６Ｄに対応する実験結果を示すグラフA graph showing the experimental results corresponding to FIG. 6D of the polarization period dependence in the light source device of the first embodiment.実施形態１の光源装置における角度依存性の角度０．８０°での理論計算を示すグラフA graph showing theoretical calculation at an angle-dependent angle of 0.80 ° in the light source device of the first embodiment.実施形態１の光源装置における角度依存性の角度０．７１°での理論計算を示すグラフA graph showing theoretical calculation at an angle-dependent angle of 0.71 ° in the light source device of the first embodiment.実施形態１の光源装置における角度依存性の角度０．６２°での理論計算を示すグラフA graph showing theoretical calculation at an angle-dependent angle of 0.62 ° in the light source device of the first embodiment.実施形態１の光源装置における角度依存性の角度０．５３°での理論計算を示すグラフA graph showing theoretical calculation at an angle-dependent angle of 0.53 ° in the light source device of the first embodiment.実施形態１の光源装置における角度依存性の図８Ａに対応する実験結果を示すグラフThe graph which shows the experimental result corresponding to FIG. 8A of the angle dependence in the light source apparatus ofEmbodiment 1.実施形態１の光源装置における角度依存性の図８Ｂに対応する実験結果を示すグラフThe graph which shows the experimental result corresponding to FIG. 8B of the angle dependence in the light source apparatus ofEmbodiment 1.実施形態１の光源装置における角度依存性の図８Ｃに対応する実験結果を示すグラフThe graph which shows the experimental result corresponding to FIG. 8C of the angle dependence in the light source apparatus ofEmbodiment 1.実施形態１の光源装置における角度依存性の図８Ｄに対応する実験結果を示すグラフThe graph which shows the experimental result corresponding to FIG. 8D of the angle dependence in the light source apparatus ofEmbodiment 1.実施形態２の光源装置における分極周期依存性の理論計算を示すグラフA graph showing the theoretical calculation of the polarization period dependence in the light source device of the second embodiment.実施形態２の光源装置における角度依存性の理論計算を示すグラフA graph showing the theoretical calculation of the angle dependence in the light source device of the second embodiment.実施形態２の光源装置における励起波長の最適化を説明した図The figure explaining the optimization of the excitation wavelength in the light source apparatus ofEmbodiment 2.実施形態２における光源装置の構成例を示す図The figure which shows the structural example of the light source apparatus inEmbodiment 2.実施形態２の光源装置におけるＰＰ結晶素子の構成例を示す図The figure which shows the structural example of the PP crystal element in the light source apparatus ofEmbodiment 2.実施形態２の光源装置における分極周期依存性の実験結果を示すグラフA graph showing the experimental results of polarization period dependence in the light source device of the second embodiment.実施形態２の光源装置における分極周期依存性の理論計算と実験結果との対応関係を示すグラフA graph showing the correspondence between the theoretical calculation of the polarization period dependence and the experimental results in the light source device of the second embodiment.実施形態２の光源装置における角度依存性の実験結果を示すグラフA graph showing the experimental results of angle dependence in the light source device of the second embodiment.実施形態２の光源装置における角度依存性の理論計算と実験結果との対応関係を示すグラフA graph showing the correspondence between the theoretical calculation of the angle dependence and the experimental results in the light source device of the second embodiment.変形例の光源装置における分極周期依存性の理論計算を示すグラフGraph showing the theoretical calculation of polarization period dependence in the light source device of the modified example変形例の光源装置における角度依存性の理論計算を示すグラフGraph showing the theoretical calculation of angle dependence in the light source device of the modified example

　以下、添付の図面を参照して本開示に係る光源装置の実施の形態を説明する。なお、以下の各実施形態において、同様の構成要素については同一の符号を付している。Hereinafter, embodiments of the light source device according to the present disclosure will be described with reference to the attached drawings. In each of the following embodiments, the same reference numerals are given to the same components.

（実施形態１）
　実施形態１では、量子もつれ光源を非常に簡単な構成で実現し、且つ中赤外領域等の広帯域光源としても機能する光源装置の一例について説明する。(Embodiment 1)
In the first embodiment, an example of a light source device that realizes a quantum entangled light source with a very simple configuration and also functions as a wideband light source in the mid-infrared region will be described.

１．装置構成
　実施形態１に係る光源装置の構成について、図１を用いて説明する。図１は、本実施形態に係る光源装置１０の構成を例示する模式図である。1. 1. Device Configuration The configuration of the light source device according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram illustrating the configuration of thelight source device 10 according to the present embodiment.

　本実施形態に係る光源装置１０は、例えば図１に示すように、レーザ光源１１と、ＰＰ（周期分極）結晶素子１２とを備える。レーザ光源１１は、ＰＰ結晶素子１２に供給する励起光Ｌｐを生成する光源の一例である。ＰＰ結晶素子１２は、周期的に分極を反転させた結晶で構成される擬似位相整合素子の一例である。Thelight source device 10 according to the present embodiment includes, for example, alaser light source 11 and a PP (periodic polarization)crystal element 12 as shown in FIG. Thelaser light source 11 is an example of a light source that generates excitation light Lp to be supplied to thePP crystal element 12. ThePP crystal element 12 is an example of a pseudo-phase matching element composed of a crystal whose polarization is periodically inverted.

　本実施形態の光源装置１０は、レーザ光源１１及びＰＰ結晶素子１２という簡単な装置構成において、本願発明者の鋭意研究により見出された複数の波長帯による量子もつれ２光子状態（後述）を実現する。これにより、本実施形態の光源装置１０は、新規の量子もつれ光源および広帯域光源として機能する。Thelight source device 10 of the present embodiment realizes a quantum entangled two-photon state (described later) with a plurality of wavelength bands found by the diligent research of the inventor of the present application in a simple device configuration of alaser light source 11 and aPP crystal element 12. do. As a result, thelight source device 10 of the present embodiment functions as a novel quantum entangled light source and a wideband light source.

　レーザ光源１１は、例えば各種半導体レーザで構成される。例えば、レーザ光源１１は、予め設定された励起波長λｐにピーク波長を有するレーザ光を励起光Ｌｐとして生成する。レーザ光によると、励起光Ｌｐにコヒーレント性を持たせることができる。励起波長λｐは、本実施形態では可視領域において設定され、例えばλｐ＝０．６μｍ～０．８５μｍである。Thelaser light source 11 is composed of, for example, various semiconductor lasers. For example, thelaser light source 11 generates laser light having a peak wavelength at a preset excitation wavelength λp as excitation light Lp. According to the laser beam, the excitation light Lp can be made coherent. The excitation wavelength λp is set in the visible region in this embodiment, and is, for example, λp = 0.6 μm to 0.85 μm.

　励起光Ｌｐは、例えばレーザ光源１１を出射後にＰＰ結晶素子１２に入射してから進行する方向に沿った光軸を有する。以下、光源装置１０における励起光Ｌｐの光軸の方向をＺ方向とし、Ｚ方向に垂直で且つ互いに直交する２方向をＸ，Ｙ方向とする。又、励起光Ｌｐに含まれる光子Ｇｐを「励起光子Ｇｐ」という場合がある。The excitation light Lp has, for example, an optical axis along a direction in which thelaser light source 11 is emitted, is incident on thePP crystal element 12, and then travels. Hereinafter, the direction of the optical axis of the excitation light Lp in thelight source device 10 is defined as the Z direction, and the two directions perpendicular to the Z direction and orthogonal to each other are defined as the X and Y directions. Further, the photon Gp contained in the excitation light Lp may be referred to as "excitation photon Gp".

　ＰＰ結晶素子１２は、例えばタンタル酸リチウム（ＬｉＴａＯ_３）の結晶に周期分極構造を設けて構成される。周期分極構造は、特定の方向に沿って結晶の分極が、予め設定された分極周期Λ毎に反転した構造である。本実施形態の光源装置１０では、ＰＰ結晶素子１２が、周期分極構造の方向をＺ方向に向けて配置される。分極周期Λは、本実施形態ではＰＰ結晶素子１２内で一定の値に設定され、例えば１６μｍ～２５μｍである。また、ＰＰ結晶素子１２のサイズＬ１２は、所謂コヒーレント長Ｌよりも短く設定され、例えば数ｃｍである。ThePP crystal element 12 is_{configured by providing, for example, a crystal of lithium tantalate (LiTaO 3} ) with a periodic polarization structure. The periodic polarization structure is a structure in which the polarization of a crystal is reversed along a specific direction for each preset polarization period Λ. In thelight source device 10 of the present embodiment, thePP crystal element 12 is arranged so that the direction of the periodic polarization structure is directed to the Z direction. In the present embodiment, the polarization period Λ is set to a constant value in thePP crystal element 12, and is, for example, 16 μm to 25 μm. Further, the size L12 of thePP crystal element 12 is set shorter than the so-called coherent length L, for example, several cm.

　以上のように構成される光源装置１０によると、図１に示すように、レーザ光源１１からの励起光Ｌｐの入射に応じてＰＰ結晶素子１２内で量子もつれ２光子状態が生じ、例えば同じ場所で２種類の光子対Ｇ１，Ｇ２が生成され得る。According to thelight source device 10 configured as described above, as shown in FIG. 1, a quantum entangled two-photon state occurs in thePP crystal element 12 in response to the incident of the excitation light Lp from thelaser light source 11, for example, at the same location. Can generate two types of photon pairs G1 and G2.

２．量子もつれ２光子状態について
　本実施形態の光源装置１０における量子もつれ２光子状態について、図１を用いて説明する。2. Quantum entangled two-photon state The quantum entangled two-photon state in thelight source device 10 of the present embodiment will be described with reference to FIG.

　量子もつれ２光子状態は、例えば励起光Ｌｐと同軸方向すなわちＺ方向に出射する光に関して、次式（１０）のように表される。
｜ψ＞＝｜ωｎ１＞｜ωｍ１＞＋｜ωｎ２＞｜ωｍ２＞　　…（１０）The quantum entangled two-photon state is expressed by the following equation (10) with respect to light emitted in the coaxial direction, that is, in the Z direction, for example, with respect to the excitation light Lp.
｜ ψ ＞ ＝ ｜ ωn1 ＞｜ ωm1 ＞ ＋ ｜ ωn2 ＞｜ ωm2 ＞… (10)

　上式（１０）において、左辺は量子もつれ２光子状態の波動関数を示す。右辺の第１項は、第１の光子対Ｇ１による２光子状態を示し、第２項は第２の光子対Ｇ２による２光子状態を示す。In the above equation (10), the left side shows the wave function of the quantum entangled two-photon state. The first term on the right side shows the two-photon state by the first photon vs. G1, and the second term shows the two-photon state by the second photon vs. G2.

　２光子状態は、パラメトリック過程の一種であるパラメトリック下方変換等により、１つの励起光子Ｇｐが、２つの光子からなる光子対に変換された状態である。２光子状態は、例えば上式（１０）の第１項（又は第２項）のように、光子対Ｇ１（又はＧ２）における１つ目の光子Ｇｎ１（又はＧｎ２）の量子状態と、２つ目の光子Ｇｍ１（又はＧｍ２）の量子状態との積により記述される。本実施形態では、所謂ｔｙｐｅ－０の位相整合を想定しており、励起光子Ｇｐの偏光状態と、各光子対Ｇ１，Ｇ２における各々の光子Ｇｎ１～Ｇｍ２の偏光状態とは同じである。The two-photon state is a state in which one excited photon Gp is converted into a photon pair consisting of two photons by parametric downward conversion, which is a kind of parametric process. There are two two-photon states, for example, the quantum state of the first photon Gn1 (or Gn2) in the photon pair G1 (or G2), as in the first term (or second term) of the above equation (10). It is described by the product of the photon Gm1 (or Gm2) of the eye with the quantum state. In this embodiment, so-called type-0 phase matching is assumed, and the polarization state of the excited photon Gp is the same as the polarization state of each photon Gn1 to Gm2 in each photon pair G1 and G2.

　量子もつれ２光子状態は、例えば式（１０）に示すように、複数の２光子状態の和つまり重ね合わせで記述される。量子もつれ２光子状態によると、１つの励起光子Ｇｐから生成される光子対の候補として複数の２光子状態が存在することから、例えば１つの光子対が生成されたときに、当該光子対のうちの一方の光子の状態が観測されるまで他方の光子の状態は判明しない。その一方で、当該光子対のうちの一方の光子の状態が観測されると、他方の光子の状態も同時に判明することとなる。The quantum entangled two-photon state is described by, for example, as shown in equation (10), the sum or superposition of a plurality of two-photon states. According to the entangled two-photon state, there are a plurality of two-photon states as candidates for the photon pair generated from one excited photon Gp. Therefore, for example, when one photon pair is generated, among the photon pairs. The state of one photon is unknown until the state of one photon is observed. On the other hand, when the state of one of the photon pairs is observed, the state of the other photon is also known at the same time.

　式（１０）において、ωｎ１，ωｎ２は各光子対Ｇ１，Ｇ２における１つ目の光子Ｇｎ１，Ｇｎ２の角周波数であり、ωｍ１，ωｍ２は他方の２つ目の光子Ｇｍ１，Ｇｍ２の角周波数である。本実施形態において、角周波数ωｎ１，ωｎ２はそれぞれ近赤外領域において別々の波長λｎ１，λｎ２に対応し、角周波数ωｍ１，ωｍ２はそれぞれ中赤外領域において別々の波長λｍ１，λｍ２に対応する。In equation (10), ωn1 and ωn2 are the angular frequencies of the first photon Gn1 and Gn2 in each photon pair G1 and G2, and ωm1 and ωm2 are the angular frequencies of the other second photon Gm1 and Gm2. .. In the present embodiment, the angular frequencies ωn1 and ωn2 correspond to different wavelengths λn1 and λn2 in the near infrared region, and the angular frequencies ωm1 and ωm2 correspond to different wavelengths λm1 and λm2 in the mid-infrared region, respectively.

　従来の量子もつれ２光子状態に関する研究は、近赤外領域において盛んに行われている。また、一般的に良く知られた２光子状態には、光子対における各光子の波長が互いに同一の縮退状態がある。特許文献１の縮退偏光量子もつれ光子対生成装置は、２光子状態において偏光状態の違いに伴い各光子の波長を、１．５８μｍと１．５２μｍというように近赤外領域の範囲内で僅かに異ならせている。Conventional research on quantum entangled two-photon states is being actively conducted in the near-infrared region. Further, in the generally well-known two-photon state, there is a degenerate state in which the wavelengths of the photons in the photon pair are the same as each other. The reduced polarization quantum entangled photon pair generator ofPatent Document 1 slightly changes the wavelength of each photon in the two-photon state within the near infrared region such as 1.58 μm and 1.52 μm due to the difference in the polarization state. It's different.

　本実施形態の量子もつれ２光子状態は、各光子対Ｇ１，Ｇ２において近赤外領域の光子Ｇｎ１，Ｇｎ２と中赤外領域の光子Ｇｍ１，Ｇｍ２とがペアリングされた新規のもの（理論解）である。本願発明者は、近赤外領域だけでなく中赤外領域にまで及ぶ広範囲に亘って、励起光Ｌｐの入射に応じてＰＰ結晶素子１２中で量子もつれ２光子状態を生じ得る理論解を探索することにより、本実施形態の光源装置１０を想到するに到った。The quantum entangled two-photon state of the present embodiment is a novel one in which photons Gn1 and Gn2 in the near-infrared region and photons Gm1 and Gm2 in the mid-infrared region are paired in each photon pair G1 and G2 (theoretical solution). Is. The inventor of the present application has searched for a theoretical solution that can generate a quantum entangled two-photon state in thePP crystal element 12 in response to the incident of excitation light Lp over a wide range not only in the near infrared region but also in the mid-infrared region. As a result, thelight source device 10 of the present embodiment was conceived.

２－１．擬似位相整合条件について
　量子もつれ２光子状態は理論的に、次式（１ａ），（１ｂ）のような擬似位相整合条件を充足する光子対が複数、在る場合に実現される。2-1. Pseudo-phase matching condition The quantum entangled two-photon state is theoretically realized when there are a plurality of photon pairs satisfying the pseudo-phase matching condition as in the following equations (1a) and (1b).

　擬似位相整合条件は、光子対の基となる励起光子Ｇｐと、光子対との（平面波解等における）位相の整合性から要求される。以下では式（１ａ），（１ｂ）の総称を式（１）という場合がある。The pseudo-phase matching condition is required from the phase matching (in a plane wave solution, etc.) between the excited photon Gp, which is the basis of the photon pair, and the photon pair. In the following, the generic names of the equations (1a) and (1b) may be referred to as the equation (1).

　式（１ａ）は、励起光子Ｇｐと光子対とにおけるエネルギーの保存則に関し、励起波長λｐに対応する角周波数ωｐに基づいている。ωｎは光子対における一方の光子の角周波数であり、ωｍは同光子対における他方の光子の角周波数である。本実施形態において、ωｎ＝ωｎ１又はωｎ２であり、ωｍ＝ωｍ１又はωｍ２である。Equation (1a) is based on the angular frequency ωp corresponding to the excitation wavelength λp with respect to the energy conservation law between the excitation photon Gp and the photon pair. ωn is the angular frequency of one photon in the photon pair and ωm is the angular frequency of the other photon in the same photon pair. In this embodiment, ωn = ωn1 or ωn2, and ωm = ωm1 or ωm2.

　式（１ｂ）は、励起光子Ｇｐと光子対とにおける運動量の保存則に関する。上式（１ｂ）に上付きで表記した矢印「→」は、以下では省略するが、空間座標（Ｘ，Ｙ，Ｚ）における３次元ベクトルを示す。ｋｐは、励起光子Ｇｐの波数ベクトルを示す。ｋｎは、光子対における角周波数ωｎの光子の波数ベクトルを示し、ｋｍは、同光子対における角周波数ωｍの光子の波数ベクトルを示す。ｅは、ＰＰ結晶素子１２の周期分極構造の方向を示す基準ベクトルであり、絶対値｜ｅ｜＝１に規格化されている。Δｋは、ミスマッチを示すベクトルであり、コヒーレント長Ｌと次式（１１）の対応関係を有する（πは円周率）。
Ｌ＝２π／｜Δｋ｜　　　…（１１）Equation (1b) relates to the law of conservation of momentum between the excited photon Gp and the photon pair. The arrow “→” superscripted in the above equation (1b) is omitted below, but indicates a three-dimensional vector in spatial coordinates (X, Y, Z). kp represents the wave vector of the excited photon Gp. kn indicates a wave vector of a photon having an angular frequency ωn in a photon pair, and km indicates a wave vector of a photon having an angular frequency ωm in the same photon pair. e is a reference vector indicating the direction of the periodic polarization structure of thePP crystal element 12, and is standardized to an absolute value | e | = 1. Δk is a vector indicating a mismatch, and has a correspondence relationship between the coherent length L and the following equation (11) (π is the pi).
L = 2π / | Δk |… (11)

　本実施形態では、励起光Ｌｐの光軸すなわち励起光子Ｇｐの進行方向をＺ方向としていることから、波数ベクトルｋｐ＝（ｋｐｘ，ｋｐｙ，ｋｐｚ）においてＺ成分ｋｐｚ以外のＸ，Ｙ成分ｋｐｘ，ｋｐｙは「０」である。又、ＰＰ結晶素子１２の基準ベクトルｅも、上述したようにＺ方向に向いており、ｅ＝（０，０，１）である。In the present embodiment, since the optical axis of the excitation light Lp, that is, the traveling direction of the excitation photon Gp is the Z direction, the X and Y components kpx and kpy other than the Z component kpz in the wave vector kp = (kpx, kpy, kpz). Is "0". Further, the reference vector e of thePP crystal element 12 is also oriented in the Z direction as described above, and e = (0,0,1).

　各種の角周波数ω（＝ωｐ，ωｎ，ωｍ）と波数ベクトルｋ（＝ｋｐ，ｋｎ，ｋｍ）とは、ＰＰ結晶素子１２の内部ではその屈折率ｎ（λ，Ｔ）を用いて、次式（１２）の関係を有する。
ω＝ｃ｜ｋ｜／ｎ（λ，Ｔ）　　　…（１２）The various angular frequencies ω (= ωp, ωn, ωm) and the wave vector k (= kp, kn, km) are expressed by the following equations using their refractive index n (λ, T) inside thePP crystal element 12. It has the relationship of (12).
ω = c | k | / n (λ, T) ... (12)

　上式（１２）において、ｃは光速であり、｜ｋ｜は波数ベクトルｋの絶対値であり、ＴはＰＰ結晶素子１２の温度である。なお、各種の波長λ（＝λｐ，λｎ，λｍ）と波数ベクトルｋとは、λ＝２π／｜ｋ｜の関係を有する。また、真空中の角周波数ωと波長λとの対応関係は、ω＝２πｃ／λである。In the above equation (12), c is the speed of light, | k | is the absolute value of the wave vector k, and T is the temperature of thePP crystal element 12. The various wavelengths λ (= λp, λn, λm) and the wave vector k have a relationship of λ = 2π / | k |. The correspondence between the angular frequency ω and the wavelength λ in vacuum is ω = 2πc / λ.

　ＰＰ結晶素子１２の屈折率ｎ（λ，Ｔ）は、光（或いは光子）の波長λに応じて変動する特性を有する。こうした特性は、温度変動の特性と共に経験則的に知られた次式（１３）のようなＳｅｌｌｍｅｉｅｒの分散式により表される（非特許文献１参照）。

The refractive index n (λ, T) of thePP crystal element 12 has a characteristic of fluctuating according to the wavelength λ of light (or photon). These characteristics are represented by the cellmeier's dispersion formula such as the following formula (13), which is empirically known together with the characteristics of temperature fluctuation (see Non-Patent Document 1).

　本願発明者は、擬似位相整合条件の式（１）に関して、ＰＰ結晶素子１２の屈折率ｎ（λ，Ｔ）の波長依存性が影響するような幅広い波長帯にわたり量子もつれ２光子状態の理論解を探索した。上式（１３）におけるパラメータＡ～Ｈ及び温度関数ｂ（Ｔ），ｃ（Ｔ）としては、本実施形態のＰＰ結晶素子１２に関してＳＬＴ（リチウムタンタレート）を用いる際に、非特許文献１に従い下記の値を採用した（Ｔは摂氏温度）。
Ａ＝４．５０２４８３
Ｂ＝０．００７２９４
Ｃ＝０．１８５０８７
Ｄ＝－０．０２３５７
Ｅ＝０．０７３４２３
Ｆ＝０．１９９５９５
Ｇ＝０．００１
Ｈ＝７．９９７２４
ｂ（Ｔ）＝３．４８３９３３×１０^－８（Ｔ＋２７３．１５）^２
ｃ（Ｔ）＝１．６０７８３９×１０^－８（Ｔ＋２７３．１５）^２The inventor of the present application has a theoretical solution of a quantum entangled two-photon state over a wide wavelength band in which the wavelength dependence of the refractive index n (λ, T) of thePP crystal element 12 affects the equation (1) of the pseudo-phase matching condition. I searched for. The parameters A to H and the temperature functions b (T) and c (T) in the above equation (13) are in accordance withNon-Patent Document 1 when SLT (lithium tantalate) is used for thePP crystal element 12 of the present embodiment. The following values were adopted (T is the temperature in degrees Celsius).
A = 4.502483
B = 0.007294
C = 0.185087
D = -0.02357
E = 0.073423
F = 0.199595
G = 0.001
H = 7.997424
b (T) = 3.483933 ×^10-8 (T + 273.15)²
c (T) = 1.607838 ×^10-8 (T + 273.15)²

２－２．同軸解について
　以下では、各光子対Ｇ１，Ｇ２が励起光Ｌｐの光軸と同軸方向に出射する場合の理論解について、図２～４を用いて説明する。この場合、対応する波数ベクトルｋｎ，ｋｍは、ｋｎ＝（０，０，｜ｋｎ｜），ｋｍ＝（０，０，｜ｋｍ｜）となる。2-2. Coaxial solution In the following, the theoretical solution when each photon pair G1 and G2 emits in the coaxial direction with the optical axis of the excitation light Lp will be described with reference to FIGS. 2 to 4. In this case, the corresponding wave vector kn, km is kn = (0,0, | kn |), km = (0,0, | km |).

　図２は、実施形態１に係る光源装置１０における特性曲線Ｃ１を例示するグラフである。横軸は、光子対Ｇ１，Ｇ２における１つの光子の波長λ（μｍ）を示す。縦軸は、ＰＰ結晶素子１２における分極周期Λ（μｍ）を示す。FIG. 2 is a graph illustrating the characteristic curve C1 in thelight source device 10 according to the first embodiment. The horizontal axis represents the wavelength λ (μm) of one photon in photon pairs G1 and G2. The vertical axis represents the polarization period Λ (μm) in thePP crystal element 12.

　特性曲線Ｃ１は、（励起波長λｐを固定して）分極周期Λが可変と仮定した際に、式（１）を充足する光子の波長を示す。図２では、励起波長λｐをλｐ＝０．７６μｍに設定して、擬似位相整合条件の式（１）の数値計算を行った。The characteristic curve C1 shows the wavelength of a photon satisfying the equation (1), assuming that the polarization period Λ is variable (fixing the excitation wavelength λp). In FIG. 2, the excitation wavelength λp was set to λp = 0.76 μm, and the numerical calculation of the equation (1) under the pseudo-phase matching condition was performed.

　図２に例示する場合において、特性曲線Ｃ１は、近赤外領域（ＮＩＲ）と中赤外領域（ＭＩＲ）との間において部分的に下に凸となる谷部分Ｃ１０を有し、谷部分Ｃ１０の外部では全体的に上に凸である。特性曲線Ｃ１では、近赤外領域におけるピーク波長λ＝λｎａにて分極周期Λが極大値Λｍａｘとなり、且つ中赤外領域におけるピーク波長λ＝λｍａにて分極周期Λが極大値Λｍａｘとなる。又、特性曲線Ｃ１の谷部分Ｃ１０では、近赤外のピーク波長λｎａと中赤外のピーク波長λｍａとの間の境界波長λ＝λａにて分極周期Λが極小値Λｍｉｎとなる。In the case illustrated in FIG. 2, the characteristic curve C1 has a valley portion C10 that is partially convex downward between the near infrared region (NIR) and the mid-infrared region (MIR), and the valley portion C10. Outside of, it is generally convex upwards. In the characteristic curve C1, the polarization period Λ has a maximum value of Λmax at the peak wavelength λ = λna in the near infrared region, and the polarization period Λ has a maximum value of Λmax at the peak wavelength λ = λma in the mid-infrared region. Further, in the valley portion C10 of the characteristic curve C1, the polarization period Λ becomes the minimum value Λmin at the boundary wavelength λ = λa between the peak wavelength λna in the near infrared and the peak wavelength λma in the middle infrared.

　上記のような特性曲線Ｃ１は、図２に示すように、Λｍｉｎ＜Λ＜Λｍａｘの範囲内で分極周期Λの固定値を示す直線Ｌ１に対して、近赤外のピーク波長λｎａと境界波長λａと中赤外のピーク波長λｍａとの各々の前後にて４交点ｐ１，ｐ２，ｐ３，ｐ４を有する。こうした４交点ｐ１～ｐ４は、エネルギーの保存則等から２つずつにペアリングされることにより、式（１）を充足する２つの光子対Ｇ１，Ｇ２に対応する。As shown in FIG. 2, the characteristic curve C1 as described above has a near-infrared peak wavelength λna and a boundary wavelength λa with respect to a straight line L1 showing a fixed value of the polarization period Λ within the range of Λmin <Λ <Λmax. It has four intersections p1, p2, p3, and p4 before and after each of the mid-infrared peak wavelength λma. These four intersections p1 to p4 correspond to two photon pairs G1 and G2 satisfying the equation (1) by being paired with each other according to the law of conservation of energy and the like.

　具体的に、近赤外のピーク波長λｎａ前の交点ｐ１と中赤外のピーク波長λｍａ後の交点ｐ４とが第１の光子対Ｇ１に対応しており、近赤外のピーク波長λｎａ後の交点ｐ２と、中赤外のピーク波長λｍａ前の交点ｐ３とが、第２の光子対Ｇ２に対応している。即ち、谷部分Ｃ１０外部の２交点ｐ１，ｐ４が示す波長λｎ１，λｍ１のペアと、谷部分Ｃ１０内部の２交点ｐ２，ｐ３が示す波長λｎ２，λｍ２のペアとが、それぞれ式（１）の理論解を構成する。Specifically, the intersection p1 before the near-infrared peak wavelength λna and the intersection p4 after the mid-infrared peak wavelength λma correspond to the first photon pair G1 and after the near-infrared peak wavelength λna. The intersection p2 and the intersection p3 before the mid-infrared peak wavelength λma correspond to the second photon pair G2. That is, the pair of wavelengths λn1 and λm1 indicated by the two intersections p1 and p4 outside the valley portion C10 and the pair of wavelengths λn2 and λm2 indicated by the two intersections p2 and p3 inside the valley portion C10 are the theory of equation (1), respectively. Construct a solution.

　以上のように、特性曲線Ｃ１の谷部分Ｃ１０を通るような分極周期Λの設定により、擬似位相整合条件を充足する第１及び第２の光子対Ｇ１，Ｇ２が得られ、近赤外領域の波長λｎ１，λｎ２と、中赤外領域の波長λｍ１，λｍ２とによる量子もつれ２光子状態を実現できる。As described above, by setting the polarization period Λ so as to pass through the valley portion C10 of the characteristic curve C1, the first and second photon pairs G1 and G2 satisfying the pseudo-phase matching condition are obtained, and the first and second photon pairs G1 and G2 in the near infrared region can be obtained. A quantum entangled two-photon state with wavelengths λn1 and λn2 and wavelengths λm1 and λm2 in the mid-infrared region can be realized.

　上記のような分極周期Λの設定範囲は、極大値Λｍａｘ未満で且つ極小値Λｍｉｎよりも大きい。Λ＝Λｍａｘになると、第１の光子対Ｇ１の波長λｎ１，λｍ１と第２の光子対Ｇ２の波長λｎ２，λｍ２とが、それぞれ縮退してしまう（λｎ１＝λｎ２＝λｎａ，λｍ１＝λｍ２＝λｍａ）。Λ＝Λｍｉｎになると、第２の光子対Ｇ２の波長λｎ２，λｍ２同士が縮退してしまう（λｎ１＝λｍ２＝λａ）。The setting range of the polarization period Λ as described above is less than the maximum value Λmax and larger than the minimum value Λmin. When Λ = Λmax, the wavelengths λn1, λm1 of the first photon pair G1 and the wavelengths λn2, λm2 of the second photon pair G2 are degenerated (λn1 = λn2 = λna, λm1 = λm2 = λma). .. When Λ = Λmin, the wavelengths λn2 and λm2 of the second photon pair G2 are degenerated (λn1 = λm2 = λa).

　本願発明者は、以上のような量子もつれ２光子状態に関する励起波長λｐを設定可能な範囲についても確認した。この点について、図３，４を用いて説明する。The inventor of the present application has also confirmed the range in which the excitation wavelength λp related to the above-mentioned quantum entangled two-photon state can be set. This point will be described with reference to FIGS. 3 and 4.

　図３は、図２の場合よりも励起波長λｐが長い場合の特性曲線Ｃ１を例示する。図４は、図２の場合よりも励起波長λｐが短い場合の特性曲線Ｃ１を例示する。具体的に、図３では励起波長λｐ＝０．８５μｍに設定し、図４では励起波長λｐ＝０．６μｍに設定した。FIG. 3 illustrates a characteristic curve C1 when the excitation wavelength λp is longer than that in the case of FIG. FIG. 4 illustrates a characteristic curve C1 when the excitation wavelength λp is shorter than that in the case of FIG. Specifically, in FIG. 3, the excitation wavelength λp = 0.85 μm was set, and in FIG. 4, the excitation wavelength λp = 0.6 μm was set.

　図３の場合、特性曲線Ｃ１の谷部分Ｃ１０が、図２の場合よりも小さくなっており、分極周期Λの設定範囲Λｍａｘ～Λｍｉｎが狭くなっている。このことから、本実施形態の光源装置１０において、励起波長λｐは、０．８５μｍ以下であることが望ましい。更に励起波長λｐを長くすると、谷部分Ｃ１０が無くなり、各ピーク波長λｎａ，λｍａ及び境界波長λａが縮退してしまう。この場合、第２の光子対Ｇ２の理論解が無くなり、上述した量子もつれ２光子状態は取り得なくなる。In the case of FIG. 3, the valley portion C10 of the characteristic curve C1 is smaller than that in the case of FIG. 2, and the setting range Λmax to Λmin of the polarization period Λ is narrowed. Therefore, in thelight source device 10 of the present embodiment, the excitation wavelength λp is preferably 0.85 μm or less. If the excitation wavelength λp is further lengthened, the valley portion C10 disappears, and the peak wavelengths λna, λma and the boundary wavelength λa are degenerated. In this case, the theoretical solution of the second photon vs. G2 disappears, and the above-mentioned quantum entangled two-photon state cannot be taken.

　また、図２～４においてＰＰ結晶素子１２に用いたＬｉＴａＯ_３においては、吸収波長が５μｍよりも長波長側にある。よって、量子もつれ２光子状態において各光子対Ｇ１，Ｇ２の生成効率を均等に保つ観点からすると、第１及び第２の光子対Ｇ１，Ｇ２における最長の波長λｍ１が５μｍ以下であることが望ましい。_{Further, in LiTaO 3} used for thePP crystal element 12 in FIGS. 2 to 4, the absorption wavelength is on the longer wavelength side than 5 μm. Therefore, from the viewpoint of keeping the generation efficiency of each photon pair G1 and G2 uniform in the quantum entangled two-photon state, it is desirable that the longest wavelength λm1 of the first and second photon pairs G1 and G2 is 5 μm or less.

　図４の場合では、特性曲線Ｃ１において中赤外のピーク波長λｍａが５μｍよりも僅かに小さいことから、第１及び第２の光子対Ｇ１，Ｇ２における最長の波長λｍ１も、５μｍ以下に設定することが可能である。このことから、本実施形態の光源装置１０において、励起波長λｐは、０．６μｍ以上であることが望ましい。これよりも励起波長λｐを短くすると、波長λｍ１を５μｍ以下に設定し難くなる。In the case of FIG. 4, since the peak wavelength λma in the mid-infrared region is slightly smaller than 5 μm in the characteristic curve C1, the longest wavelength λm1 in the first and second photon pairs G1 and G2 is also set to 5 μm or less. It is possible. Therefore, in thelight source device 10 of the present embodiment, it is desirable that the excitation wavelength λp is 0.6 μm or more. If the excitation wavelength λp is made shorter than this, it becomes difficult to set the wavelength λm1 to 5 μm or less.

　以上のように、本実施形態の光源装置１０は、励起波長λｐが０．６μｍ～０．８５μｍの範囲内で機能することが確認された。又、本実施形態の光源装置１０は、特に上記生成効率を考慮しない用途にも適用可能である。この場合、特性曲線Ｃ１に谷部分Ｃ１０を持たせるように励起波長λｐを設定し、谷部分Ｃ１０に関する極大値Λｍａｘと極小値Λｍｉｎ間を通るように分極周期Λを設定して、光源装置１０が構成されてもよい。As described above, it was confirmed that thelight source device 10 of the present embodiment functions in the range of the excitation wavelength λp of 0.6 μm to 0.85 μm. Further, thelight source device 10 of the present embodiment can be applied to an application in which the above generation efficiency is not particularly considered. In this case, the excitation wavelength λp is set so that the characteristic curve C1 has the valley portion C10, the polarization period Λ is set so as to pass between the maximum value Λmax and the minimum value Λmin with respect to the valley portion C10, and thelight source device 10 sets thelight source device 10. It may be configured.

２－３．角度依存性と広帯域光源
　本願発明者は、同軸方向から種々の角度θで放射される光子対Ｇ１，Ｇ２の理論解についても確認した。本実施形態の光源装置１０は、比較的小さい有限角度の範囲内で広帯域の光を放射できる。この点について、図５を用いて説明する。2-3. Angle Dependence and Wideband Light Source The inventor of the present application has also confirmed the theoretical solution of photons vs. G1 and G2 emitted from the coaxial direction at various angles θ. Thelight source device 10 of the present embodiment can emit a wide band of light within a range of a relatively small finite angle. This point will be described with reference to FIG.

　図５は、本実施形態に係る光源装置１０における放射特性曲線Ｃ２を例示するグラフである。図５では、図２の場合（λｐ＝０．７６μｍ）において様々な角度θに関して式（１）の数値計算を行った。この際、分極周期Λは、Λ＝２０．６μｍに設定した。FIG. 5 is a graph illustrating the radiation characteristic curve C2 in thelight source device 10 according to the present embodiment. In FIG. 5, in the case of FIG. 2 (λp = 0.76 μm), the numerical calculation of the equation (1) was performed for various angles θ. At this time, the polarization period Λ was set to Λ = 20.6 μm.

　放射特性曲線Ｃ２は、式（１）を充足する光子対Ｇ１，Ｇ２における１光子が、種々の方向に放射される際の角度θと波長との関係を示す。放射特性曲線Ｃ２は、図５に示すように、中赤外のピーク部分Ｃ２０と、近赤外のピーク部分Ｃ２１とを有する。The radiation characteristic curve C2 shows the relationship between the angle θ and the wavelength when one photon in the photon pair G1 and G2 satisfying the equation (1) is emitted in various directions. As shown in FIG. 5, the radiation characteristic curve C2 has a mid-infrared peak portion C20 and a near-infrared peak portion C21.

　中赤外のピーク部分Ｃ２０は、上述した同軸方向（即ちθ＝０°）の場合の中赤外領域における第１の光子対Ｇ１の波長λｍ１（本例では略５μｍ）から第２の光子対Ｇ２の波長λｍ２（本例では略２μｍ）までに及ぶ。角度θが０°から増えるにつれて、第１の光子対Ｇ１の波長λｍ１は減少する一方、第２の光子対Ｇ２の波長λｍ２は増大している。角度θ＝５°程度に到ると、中赤外領域における各光子対Ｇ１，Ｇ２の波長λｍ１，λｍ２はピーク波長λｍｂに縮退している（λｍ１＝λｍ２＝λｍｂ）。The mid-infrared peak portion C20 has a wavelength λm1 (approximately 5 μm in this example) of the first photon pair G1 in the mid-infrared region in the above-mentioned coaxial direction (that is, θ = 0 °) to the second photon pair. It extends to the wavelength λm2 of G2 (approximately 2 μm in this example). As the angle θ increases from 0 °, the wavelength λm1 of the first photon vs. G1 decreases, while the wavelength λm2 of the second photon vs. G2 increases. When the angle θ = 5 °, the wavelengths λm1 and λm2 of each photon pair G1 and G2 in the mid-infrared region are degenerated to the peak wavelength λmb (λm1 = λm2 = λmb).

　本例の光源装置１０によると、波長２μｍ～５μｍという広帯域に亘り連続した帯域を有する中赤外光が、同軸方向から５°程度という比較的小さな角度範囲に放射される。本実施形態では、光源装置１０にレーザ光源１１を用いており、放射する光のスポット径を絞り易い。光源装置１０は、外部の集光レンズに光を放射してもよいし、集光レンズと一体的に構成されてもよい。本実施形態の光源装置１０は、様々な用途に適用可能な広帯域の中赤外光源として利用できる。According to thelight source device 10 of this example, mid-infrared light having a continuous band over a wide band with a wavelength of 2 μm to 5 μm is radiated in a relatively small angle range of about 5 ° from the coaxial direction. In the present embodiment, thelaser light source 11 is used as thelight source device 10, and the spot diameter of the emitted light can be easily narrowed down. Thelight source device 10 may radiate light to an external condensing lens, or may be integrally configured with the condensing lens. Thelight source device 10 of the present embodiment can be used as a wideband mid-infrared light source applicable to various applications.

　本実施形態の光源装置１０によると、同軸方向に出射する場合の中赤外領域における第１の光子対Ｇ１の波長λｍ１から第２の光子対Ｇ２の波長λｍ２までの連続した帯域を有する中赤外光が、有限角度θの放射において得られる。こうした帯域は、上記の例に限らず、分極周期Λ及び励起波長λｐ等の設定に応じて制御できる。According to thelight source device 10 of the present embodiment, medium red having a continuous band from the wavelength λm1 of the first photon vs. G1 to the wavelength λm2 of the second photon vs. G2 in the mid-infrared region when emitting in the coaxial direction. External light is obtained in radiation at a finite angle θ. Such a band is not limited to the above example, and can be controlled according to settings such as the polarization period Λ and the excitation wavelength λp.

　また、近赤外のピーク部分Ｃ２１は、同軸方向の場合の近赤外領域における第１の光子対Ｇ１の波長λｎ１から第２の光子対Ｇ２の波長λｎ２までに及ぶ。角度θが増えるにつれて、第１の光子対Ｇ１の波長λｎ１が増大する一方、第２の光子対Ｇ２の波長λｎ２は減少する。近赤外領域における各光子対Ｇ１，Ｇ２の波長λｎ１，λｎ２は、図５の例で中赤外領域が縮退した角度５°よりも小さい角度θにおいて、ピーク波長λｎｂに縮退している（λｎ１＝λｎ２＝λｎｂ）。Further, the near-infrared peak portion C21 extends from the wavelength λn1 of the first photon pair G1 to the wavelength λn2 of the second photon pair G2 in the near-infrared region in the coaxial direction. As the angle θ increases, the wavelength λn1 of the first photon vs. G1 increases, while the wavelength λn2 of the second photon vs. G2 decreases. The wavelengths λn1 and λn2 of each photon pair G1 and G2 in the near-infrared region are degenerated to the peak wavelength λnb at an angle θ smaller than theangle 5 ° in which the mid-infrared region is degenerated in the example of FIG. 5 (λn1). = Λn2 = λnb).

　以上より、本実施形態の光源装置１０は、必ずしも中赤外領域に限らず、近赤外領域においても連続した帯域を有する赤外光を、比較的小さな角度範囲で放射できる。From the above, thelight source device 10 of the present embodiment can emit infrared light having a continuous band not only in the mid-infrared region but also in the near-infrared region in a relatively small angle range.

２－４．確認実験について
　以上のような理論解について、本願発明者は確認実験を行った。この点について、図６Ａ～９Ｄを用いて説明する。2-4. Confirmation experiment The inventor of the present application conducted a confirmation experiment on the above theoretical solution. This point will be described with reference to FIGS. 6A-9D.

　図６Ａ～６Ｄは、本実施形態の光源装置１０における分極周期依存性の理論計算を示すグラフである。図７Ａ～７Ｄは、分極周期依存性の実験結果を示すグラフである。6A to 6D are graphs showing the theoretical calculation of the polarization period dependence in thelight source device 10 of the present embodiment. 7A-7D are graphs showing the experimental results of polarization cycle dependence.

　図６Ａ～６Ｄでは、励起波長λｐ＝０．６３９μｍに設定して、同軸方向の特性曲線Ｃ１を数値計算した。この数値計算に関して、分極周期Λを極大値Λｍａｘ近傍で変化させた場合の実験を行った。In FIGS. 6A to 6D, the excitation wavelength λp = 0.639 μm was set, and the characteristic curve C1 in the coaxial direction was numerically calculated. For this numerical calculation, an experiment was conducted in which the polarization period Λ was changed near the maximum value Λmax.

　図６Ａは、分極周期Λが１７．０２５μｍ（＝Λｍａｘ）の状態を例示する。同様に、図６Ｂ，６Ｃ，６Ｄは、それぞれ分極周期Λが１６．９２３μｍ，１６．８２１μｍ，１６．７１９μｍ（＜Λｍａｘ）の状態を例示する。図７Ａ，７Ｂ，７Ｃ，７Ｄは、それぞれ図６Ａ，６Ｂ，６Ｃ，６Ｄに対応する実験結果の波長スペクトルを示す。FIG. 6A exemplifies a state in which the polarization period Λ is 17.025 μm (= Λmax). Similarly, FIGS. 6B, 6C, and 6D exemplify the states in which the polarization periods Λ are 16.923 μm, 16.821 μm, and 16.719 μm (<Λmax), respectively. 7A, 7B, 7C and 7D show the wavelength spectra of the experimental results corresponding to FIGS. 6A, 6B, 6C and 6D, respectively.

　図７Ａ～７Ｄの実験では、レーザ光源１１として上記の励起波長λｐをレーザ光の発振波長とするＣＷ型の半導体レーザ（出力２００ｍＷ）を用い、ＰＰ結晶素子１２として、周期分極Ｍｇ添加ＬｉＴａＯ_３結晶（ＰＰＳＬＴ）であって、ファンアウト型のＰＰＳＬＴ（オキサイド社製）を用いた。ファンアウト型のＰＰＳＬＴにおいて対応する分極周期Λの箇所を通るようにレーザ光を照射し、ＰＰＳＬＴから許容角度１°以内で同軸方向に出射する光の波長スペクトルを、近赤外領域で計測した。In the experiments of FIGS. 7A to 7D, a CW type semiconductor laser (output 200 mW) having the above excitation wavelength λp as the oscillation wavelength of the laser light was used as thelaser light source 11, and the periodic polarization Mg-added LiTaO₃ crystal was used as thePP crystal element 12. (PPSLT), a fan-out type PPSLT (manufactured by Oxide Corporation) was used. In the fan-out type PPSLT, the laser beam was irradiated so as to pass through the corresponding polarization period Λ, and the wavelength spectrum of the light emitted from the PPSLT in the coaxial direction within a permissible angle of 1 ° was measured in the near infrared region.

　本実験によると、例えば図７Ｄの場合、近赤外領域の波長０．７３５μｍと波長０．７８５μｍとに同等の強度でパラメトリック蛍光ピークが確認された。この結果は、理論計算から予想されるとおりである（図７Ｄ参照）。また、図７Ｄ，７Ｃ，７Ｂ，７Ａに示すように、分極周期Λを長くするにつれて、２つの蛍光ピークが近づくことが確認できる。図７Ａの場合には蛍光ピークが縮退しており、このことは図６Ａに示すように分極周期Λ＝Λｍａｘの理論計算と合致する。According to this experiment, for example, in the case of FIG. 7D, a parametric fluorescence peak was confirmed with the same intensity as the wavelength of 0.735 μm and the wavelength of 0.785 μm in the near infrared region. This result is as expected from the theoretical calculation (see FIG. 7D). Further, as shown in FIGS. 7D, 7C, 7B, and 7A, it can be confirmed that the two fluorescence peaks approach each other as the polarization period Λ is lengthened. In the case of FIG. 7A, the fluorescence peak is degenerate, which is consistent with the theoretical calculation of the polarization period Λ = Λmax as shown in FIG. 6A.

　図８Ａ～８Ｄは、本実施形態の光源装置１０における角度周期依存性の理論計算を示すグラフである。図９Ａ～９Ｄは、角度周期依存性の実験結果を示すグラフである。8A to 8D are graphs showing the theoretical calculation of the angle period dependence in thelight source device 10 of the present embodiment. 9A-9D are graphs showing the experimental results of the angle period dependence.

　図８Ａ～８Ｄでは、図６Ａ～６Ｄと同じ励起波長λｐにおいて、種々の角度θにおける特性曲線Ｃ１を数値計算した。分極周期Λは、Λ＝０．６３９μｍに設定した。In FIGS. 8A to 8D, the characteristic curves C1 at various angles θ were numerically calculated at the same excitation wavelength λp as in FIGS. 6A to 6D. The polarization period Λ was set to Λ = 0.639 μm.

　図８Ａは、角度θ＝０．８０°の状態を例示する。同様に、図８Ｂ，８Ｃ，８Ｄは、それぞれ角度θ＝０．７１°，０．６２°，０．５３°の状態を例示する。図８Ｄの状態と、図６Ｄの状態とは同様である。図９Ａ，９Ｂ，９Ｃ，９Ｄは、それぞれ図８Ａ，８Ｂ，８Ｃ，８Ｄに対応する実験結果の波長スペクトルを示す。FIG. 8A illustrates a state where the angle θ = 0.80 °. Similarly, FIGS. 8B, 8C, and 8D exemplify the states at angles θ = 0.71 °, 0.62 °, and 0.53 °, respectively. The state of FIG. 8D and the state of FIG. 6D are the same. 9A, 9B, 9C and 9D show the wavelength spectra of the experimental results corresponding to FIGS. 8A, 8B, 8C and 8D, respectively.

　図９Ａ～９Ｄでは、図７Ａ～７Ｄと同様の環境において、図８Ａ～８Ｄの数値計算を確認するための実験を行った。図９Ａ～９Ｄでは、それぞれ図８Ａ～８Ｄに対応する角度θから角度範囲０．９°分の光を波長スペクトルの計測対象とした。本実験によると、図９Ｄ，９Ｃ，９Ｂ，９Ａに示すように、角度θを大きくするにつれて、２つの蛍光ピークが近づくことが確認できた。In FIGS. 9A-9D, an experiment was conducted to confirm the numerical calculation of FIGS. 8A-8D in the same environment as in FIGS. 7A-7D. In FIGS. 9A to 9D, light for an angle range of 0.9 ° from the angle θ corresponding to FIGS. 8A to 8D was measured for the wavelength spectrum. According to this experiment, as shown in FIGS. 9D, 9C, 9B, and 9A, it was confirmed that the two fluorescence peaks approached as the angle θ was increased.

　以上のように、近赤外領域において第１及び第２の光子対Ｇ１，Ｇ２の波長λｎ１，λｎ２の分極周期依存性及び角度依存性が確認できた。又、このことから、それぞれ中赤外領域において対応する波長λｍ１，λｍ２の光も同時に得られることが理論的に分かる。更に、各々の場合においてコヒーレント長Ｌを理論計算すると、数ｃｍを超える程度であった。このことから、コヒーレント長Ｌ以下のサイズＬ１２のＰＰ結晶素子１２も実用上、容易に得られる。As described above, the polarization period dependence and angle dependence of the wavelengths λn1 and λn2 of the first and second photon pairs G1 and G2 were confirmed in the near infrared region. From this, it can be theoretically understood that light having the corresponding wavelengths λm1 and λm2 can be obtained at the same time in the mid-infrared region, respectively. Further, the theoretical calculation of the coherent length L in each case was about several cm or more. From this, aPP crystal element 12 having a size L12 having a coherent length L or less can be easily obtained in practical use.

　また、式（１３）に示すように、ＰＰ結晶素子１２の屈折率ｎ（λ，Ｔ）は温度Ｔに依存することから、特性曲線Ｃ１の温度依存性も理論的に把握できる。このことから、光源装置１０においてＰＰ結晶素子１２の温度Ｔを適切に設定する、例えば摂氏０度から摂氏３００度の間に設定することにより、２種類の光子対Ｇ１，Ｇ２を生成し易くすることも可能である。Further, as shown in the equation (13), since the refractive index n (λ, T) of thePP crystal element 12 depends on the temperature T, the temperature dependence of the characteristic curve C1 can be theoretically grasped. Therefore, by appropriately setting the temperature T of thePP crystal element 12 in thelight source device 10, for example, setting it between 0 degrees Celsius and 300 degrees Celsius, it becomes easy to generate two types of photon pairs G1 and G2. It is also possible.

３．まとめ
　以上のように、本実施形態に係る光源装置１０は、励起波長λｐを有する励起光Ｌｐを生成する光源の一例であるレーザ光源１１と、擬似位相整合素子の一例であるＰＰ結晶素子１２とを備える。ＰＰ結晶素子１２は、レーザ光源１１から励起光Ｌｐが入射するように配置され、周期的に分極が反転する分極周期Λを有する結晶で構成される。ＰＰ結晶素子１２において規定される擬似位相整合条件が、励起光Ｌｐの光軸に沿った分極周期Λ及び励起波長λｐに基づき、励起光Ｌｐの入射に応じてＰＰ結晶素子１２から出射する第１の光子対Ｇ１により充足され、且つ第１の光子対Ｇ１と共通の分極周期Λ及び励起波長λｐに基づき、第１の光子対Ｇ１と共通の方向に出射する第２の光子対Ｇ２により充足される。第１の光子対Ｇ１は、第１の波長帯（例えば近赤外領域）の範囲内の波長λｎ１（第１波長）と、第１の波長帯とは異なる第２の波長帯（例えば中赤外領域）の範囲内のλｍ１（第２波長）とを有する。第２の光子対Ｇ２は、第１の波長帯の範囲内で波長λｎ１とは異なる波長λｎ２（第３波長）と、第２の波長帯の範囲内で波長λｍ１とは異なるλｍ２（第４波長）とを有する。3. 3. Summary As described above, thelight source device 10 according to the present embodiment includes alaser light source 11 which is an example of a light source that generates an excitation light Lp having an excitation wavelength λp, and aPP crystal element 12 which is an example of a pseudo-phase matching element. To be equipped. ThePP crystal element 12 is arranged so that the excitation light Lp is incident from thelaser light source 11, and is composed of a crystal having a polarization period Λ in which the polarization is periodically reversed. The first pseudo-phase matching condition defined in thePP crystal element 12 is emitted from thePP crystal element 12 in response to the incident of the excitation light Lp, based on the polarization period Λ along the optical axis of the excitation light Lp and the excitation wavelength λp. Is satisfied by the first photon pair G1 and is satisfied by the second photon pair G2 that emits in the same direction as the first photon pair G1 based on the polarization period Λ and the excitation wavelength λp common to the first photon pair G1. NS. The first photon pair G1 has a wavelength λn1 (first wavelength) within the range of the first wavelength band (for example, the near infrared region) and a second wavelength band (for example, medium red) different from the first wavelength band. It has λm1 (second wavelength) within the range of (outer region). The second photon pair G2 has a wavelength λn2 (third wavelength) different from the wavelength λn1 within the range of the first wavelength band and a wavelength λm2 (fourth wavelength) different from the wavelength λm1 within the range of the second wavelength band. ) And.

　以上の光源装置１０によると、種々の波長λｎ１～λｍ２を有する第１及び第２の光子対Ｇ１，Ｇ２が、擬似位相整合条件を充足するような励起波長λｐ及び分極周期Λを有するレーザ光源１１及びＰＰ結晶素子１２という簡単な装置構成において、複数の波長を有する光子対を生成することができる。According to the abovelight source device 10, thelaser light source 11 has an excitation wavelength λp and a polarization period Λ such that the first and second photon pairs G1 and G2 having various wavelengths λn1 to λm2 satisfy the pseudo-phase matching condition. In a simple device configuration of thePP crystal element 12 and thePP crystal element 12, photon pairs having a plurality of wavelengths can be generated.

　本実施形態の光源装置１０において、第１の波長帯は、境界波長λａなどの上限値を有してもよく、第２の波長帯は、第１の波長帯の上限値以上において設定されてもよい（図２参照）。第２の光子対Ｇ２による第３波長λｎ２は、第１の波長帯の範囲内で第１の光子対Ｇ１による第１波長λｎ１よりも長い。第２の光子対Ｇ２による第４波長λｍ２は、第２の波長帯の範囲内で第１の光子対Ｇ１による第２波長λｎ２よりも短い。こうした第２の光子対Ｇ２が、第１の光子対Ｇ１とは別途存在することにより、量子もつれ２光子状態を実現することができる。In thelight source device 10 of the present embodiment, the first wavelength band may have an upper limit value such as the boundary wavelength λa, and the second wavelength band is set at the upper limit value or more of the first wavelength band. It may be good (see FIG. 2). The third wavelength λn2 due to the second photon pair G2 is longer than the first wavelength λn1 due to the first photon pair G1 within the range of the first wavelength band. The fourth wavelength λm2 due to the second photon pair G2 is shorter than the second wavelength λn2 due to the first photon pair G1 within the range of the second wavelength band. Since such a second photon pair G2 exists separately from the first photon pair G1, the quantum entangled two-photon state can be realized.

　本実施形態の光源装置１０において、第１の波長帯は、例えば近赤外領域であり、例えば波長７００～９００ｎｍである。第２の波長帯は、例えば中赤外領域であり、例えば波長２～５μｍである。各波長帯の光子Ｇｎ１～Ｇｍ２を有する第１及第２の光子対Ｇ１，Ｇ２によると、近赤外領域の光子Ｇｎ１，Ｇｎ２と中赤外領域の光子Ｇｍ１，Ｇｍ２とは、光学的に容易に分離可能であることから、量子情報のためのシステムを容易に構築できる。例えば、計測が容易な近赤外領域の光子Ｇｎ１，Ｇｎ２の波長を観測することにより、対応する中赤外領域の光子Ｇｍ１，Ｇｍ２を簡単に検知することができる。In thelight source device 10 of the present embodiment, the first wavelength band is, for example, a near infrared region, for example, a wavelength of 700 to 900 nm. The second wavelength band is, for example, a mid-infrared region, for example, a wavelength of 2 to 5 μm. According to the first and second photon pairs G1 and G2 having photons Gn1 to Gm2 in each wavelength band, the photons Gn1 and Gn2 in the near infrared region and the photons Gm1 and Gm2 in the mid-infrared region are optically easy. Since it can be separated into two, a system for quantum information can be easily constructed. For example, by observing the wavelengths of the photons Gn1 and Gn2 in the near-infrared region, which are easy to measure, the corresponding photons Gm1 and Gm2 in the mid-infrared region can be easily detected.

　本実施形態の光源装置１０においては、例えば、励起光Ｌｐの光軸を基準として５°以内などの所定の角度範囲内で、励起光Ｌｐの入射に応じてＰＰ結晶素子１２から出射する光は、第１及び第２の光子対Ｇ１，Ｇ２が光軸に沿って出射した場合における、第１波長λｎ１から第３波長λｎ２までと、第２波長λｍ１から第４波長λｍ２までとを含む帯域を有する（図５参照）。ＰＰ結晶素子１２から出射する光の帯域は、波長２μｍから５μｍまでという、中赤外領域における広帯域を含み得る。In thelight source device 10 of the present embodiment, for example, the light emitted from thePP crystal element 12 in response to the incident of the excitation light Lp within a predetermined angle range such as within 5 ° with respect to the optical axis of the excitation light Lp. , The band including the first wavelength λn1 to the third wavelength λn2 and the second wavelength λm1 to the fourth wavelength λm2 when the first and second photon pairs G1 and G2 are emitted along the optical axis. Has (see FIG. 5). The band of light emitted from thePP crystal element 12 may include a wide band in the mid-infrared region having a wavelength of 2 μm to 5 μm.

　本実施形態の光源装置１０において、第１の光子対Ｇ１は、互いに同じ偏光方向を有する２つの光子Ｇｎ１，Ｇｍ１を含んでもよい。第２の光子対Ｇ２は、第１の光子対Ｇ１と同じ偏光方向を有する２つの光子Ｇｎ２，Ｇｍ２を含んでもよい。第１及び第２の光子対Ｇ１，Ｇ２の偏光方向と、励起光Ｌｐの偏光方向とが同じであってもよい。こうしたｔｙｐｅ－０の位相整合において、量子もつれ２光子状態を実現できる。例えば、量子情報のためのシステムにおいて、偏光方向に基づき量子もつれ２光子状態のフィルタを容易に設けられる。In thelight source device 10 of the present embodiment, the first photon pair G1 may include two photons Gn1 and Gm1 having the same polarization direction as each other. The second photon pair G2 may include two photons Gn2, Gm2 having the same polarization direction as the first photon pair G1. The polarization directions of the first and second photon pairs G1 and G2 may be the same as the polarization directions of the excitation light Lp. In such type-0 phase matching, a quantum entangled two-photon state can be realized. For example, in a system for quantum information, a filter in a quantum entangled two-photon state can be easily provided based on the polarization direction.

　本実施形態の光源装置１０において、擬似位相整合条件が第１及び第２の光子対Ｇ１，Ｇ２によって充足されるように、励起波長λｐ、分極周期Λ、励起光Ｌｐの光軸の向き、及びＰＰ結晶素子１２の温度のうちの少なくとも一つが設定されてもよい。例えば、励起光Ｌｐの光軸の向きを変えることにより、励起光Ｌｐの光軸に沿った分極周期Λの大きさが変わる。このことから、実質的にＰＰ結晶素子１２の分極周期Λを変更した場合と同様の調整を行うことも可能である。In thelight source device 10 of the present embodiment, the excitation wavelength λp, the polarization period Λ, the direction of the optical axis of the excitation light Lp, and the direction of the optical axis of the excitation light Lp so that the pseudo-phase matching conditions are satisfied by the first and second photon pairs G1 and G2. At least one of the temperatures of thePP crystal element 12 may be set. For example, by changing the direction of the optical axis of the excitation light Lp, the magnitude of the polarization period Λ along the optical axis of the excitation light Lp changes. From this, it is possible to make substantially the same adjustment as when the polarization period Λ of thePP crystal element 12 is changed.

　本実施形態の光源装置１０において、擬似位相整合条件は、上述した式（１）によって表される。ここで、ωｐは励起波長λｐに対応する角周波数であり、ωｎは第１波長又は第３波長に対応する角周波数であり、ωｍは第２波長又は第４波長に対応する角周波数であり、ｋｐは角周波数ωｐを有する光子の波数ベクトルであり、ｋｎは角周波数ωｎを有する光子の波数ベクトルであり、ｋｍは角周波数ωｎを有する光子の波数ベクトルであり、Λは分極周期Λであり、ｅは結晶における向きを示す基準ベクトルであり、Δｋはミスマッチを示すベクトルである。In thelight source device 10 of the present embodiment, the pseudo-phase matching condition is represented by the above-mentioned equation (1). Here, ωp is an angular frequency corresponding to the excitation wavelength λp, ωn is an angular frequency corresponding to the first wavelength or the third wavelength, and ωm is an angular frequency corresponding to the second wavelength or the fourth wavelength. kp is the wavelength vector of the photon having the angular frequency ωp, kn is the wavelength vector of the photon having the angular frequency ωn, km is the wavelength vector of the photon having the angular frequency ωn, and Λ is the polarization period Λ. e is a reference vector indicating the orientation in the crystal, and Δk is a vector indicating a mismatch.

　本実施形態の光源装置１０において、ＰＰ結晶素子１２に用いる結晶は、ＬｉＴａＯ_３結晶である。この場合、励起波長λｐは、０．６μｍ以上０．８５μｍ以下の範囲内に設定可能である。In thelight source device 10 of the present embodiment, the crystal used for thePP crystal element 12 is a LiTaO₃ crystal. In this case, the excitation wavelength λp can be set within the range of 0.6 μm or more and 0.85 μm or less.

（実施形態２）
　実施形態１では、光源装置１０の理論計算及び実験結果の一例を説明した。実施形態２では、更なる光源装置１０の理論計算及び実験結果の例について説明する。以下、実施形態１とは同様の説明を適宜省略して、実施形態２を説明する。(Embodiment 2)
In the first embodiment, an example of the theoretical calculation and the experimental result of thelight source device 10 has been described. In the second embodiment, an example of the theoretical calculation and the experimental result of thelight source device 10 will be described. Hereinafter, the second embodiment will be described by omitting the same description as that of the first embodiment.

　図１０は、実施形態２の光源装置１０における分極周期依存性の理論計算を示すグラフである。図１１は、本実施形態の光源装置１０における角度依存性の理論計算を示すグラフである。FIG. 10 is a graph showing the theoretical calculation of the polarization period dependence in thelight source device 10 of the second embodiment. FIG. 11 is a graph showing the theoretical calculation of the angle dependence in thelight source device 10 of the present embodiment.

　図１０，１１では、励起光Ｌｐを励起波長λｐ＝０．６３８μｍに設定して、実施形態１と同様にＰＰＳＬＴの擬似位相整合条件の理論計算を行った。図１０の縦軸は分極周期Λ（μｍ）であり、図１１の横軸は出射する光の角度θ（°）である。図１０，１１における横軸について、各図中の上側に中赤外領域の波長λｍ（μｍ）を示し、下側に近赤外領域の波長λｎ（ｎｍ）を示す。以下では、各光子対Ｇ１，Ｇ２において中赤外光に対応する光子をアイドラ光子といい、近赤外光に対応する光子をシグナル光子という場合がある。In FIGS. 10 and 11, the excitation light Lp was set to the excitation wavelength λp = 0.638 μm, and the theoretical calculation of the pseudo-phase matching condition of PPSLT was performed in the same manner as in the first embodiment. The vertical axis of FIG. 10 is the polarization period Λ (μm), and the horizontal axis of FIG. 11 is the angle θ (°) of the emitted light. Regarding the horizontal axis in FIGS. 10 and 11, the wavelength λm (μm) in the mid-infrared region is shown on the upper side of each figure, and the wavelength λn (nm) in the near-infrared region is shown on the lower side. In the following, the photon corresponding to the mid-infrared light in each photon pair G1 and G2 may be referred to as an idler photon, and the photon corresponding to the near-infrared light may be referred to as a signal photon.

　図１０では、図２～４と同様の特性曲線Ｃ１において、アイドラ光子に対応する中赤外領域近傍の部分Ｃ１ｍと、シグナル光子に対応する近赤外領域近傍の部分Ｃ１ｎとを重ねて図示している。同様に、図１１では、図５と同様の放射特性曲線Ｃ２において、アイドラ光子に対応する部分Ｃ２ｍと、シグナル光子に対応する部分Ｃ２ｎとを重ねて図示している。In FIG. 10, in the characteristic curve C1 similar to FIGS. 2 to 4, the portion C1m in the vicinity of the mid-infrared region corresponding to the idler photon and the portion C1n in the vicinity of the near-infrared region corresponding to the signal photon are superimposed and shown. ing. Similarly, in FIG. 11, in the radiation characteristic curve C2 similar to that in FIG. 5, the portion C2m corresponding to the idler photon and the portion C2n corresponding to the signal photon are superimposed and shown.

　上記の励起波長λｐにおいては、図１０に示すように、分極周期Λ＝１６．８８μｍにおいて、量子もつれ２光子状態のアイドラ光子に対応する波長λｍ１＝５．６μｍ及び波長λｍ２＝３．５μｍが、同時に擬似位相整合条件を満たす。また、図１０に示すように、波長λｍ＝３．５～５．６μｍの中赤外光が出射する角度が４°の範囲内に収まっている。At the above excitation wavelength λp, as shown in FIG. 10, at the polarization period Λ = 16.88 μm, the wavelength λm1 = 5.6 μm and the wavelength λm2 = 3.5 μm corresponding to the idler photon in the entangled two-photon state are set. At the same time, the pseudo phase matching condition is satisfied. Further, as shown in FIG. 10, the angle at which the mid-infrared light having a wavelength of λm = 3.5 to 5.6 μm is emitted is within the range of 4 °.

　図１２は、本実施形態の光源装置１０における励起波長λｐの最適化を説明した図である。図１２の縦軸は励起波長λｐを示し、横軸はアイドラ光子の波長λｍを示す。図１２では、上述した量子もつれ２光子状態の擬似位相整合条件について、様々な励起波長λｐにおいて求解し、解が得られた領域Ｒ１を図示している。領域Ｒ１の求解においては、各励起波長λｐについて、分極周期Λ及び開口数ＮＡといったパラメータについては可変とした。FIG. 12 is a diagram illustrating optimization of the excitation wavelength λp in thelight source device 10 of the present embodiment. The vertical axis of FIG. 12 indicates the excitation wavelength λp, and the horizontal axis indicates the wavelength λm of the idler photon. In FIG. 12, the region R1 in which the above-mentioned entangled two-photon state pseudo-phase matching condition is solved at various excitation wavelengths λp and the solution is obtained is shown. In the solution of the region R1, parameters such as the polarization period Λ and the numerical aperture NA were made variable for each excitation wavelength λp.

　図１２中の破線は、励起波長λｐ＝０．６３８μｍ、分極周期Λ＝１６．８８μｍ、開口数ＮＡ＝０．０７の場合に量子もつれ２光子状態の解が得られた範囲を例示している。図１２の領域Ｒ１によると、例えば励起波長λｐ＝０．７８μｍにおいて、λｎ＝２～５μｍを含む広帯域の赤外光が得られている。以上のような理論計算の結果を確認するべく、本実施形態では、光源装置１０についての実験を行った。The broken line in FIG. 12 illustrates the range in which the solution of the quantum entangled two-photon state is obtained when the excitation wavelength λp = 0.638 μm, the polarization period Λ = 16.88 μm, and the numerical aperture NA = 0.07. .. According to the region R1 of FIG. 12, for example, at an excitation wavelength λp = 0.78 μm, a wide band infrared light including λn = 2 to 5 μm is obtained. In order to confirm the result of the theoretical calculation as described above, in this embodiment, an experiment was conducted on thelight source device 10.

　図１３は、本実施形態における実験的な光源装置１０の構成例を示す。本例において、光源装置１０は、レーザ光源１１及びＰＰ結晶素子１２に加えて、レーザ光源１１とＰＰ結晶素子１２間に配置されるレンズ１３と、ＰＰ結晶素子１２の出射側（＋Ｚ側）に順番に並ぶ絞り１４、レンズ１５、波長フィルタ１６およびレンズ１７を備える。本構成例の光源装置１０は、例えば光ファイバなどの伝送光学系を介してシリコンＣＣＤ２０に接続される。FIG. 13 shows a configuration example of the experimentallight source device 10 in this embodiment. In this example, in addition to thelaser light source 11 and thePP crystal element 12, thelight source device 10 has alens 13 arranged between thelaser light source 11 and thePP crystal element 12 and an emission side (+ Z side) of thePP crystal element 12. It includes anaperture 14, alens 15, awavelength filter 16 and a lens 17 arranged in order. Thelight source device 10 of this configuration example is connected to thesilicon CCD 20 via a transmission optical system such as an optical fiber.

　本構成例のレーザ光源１１は、ＣＷ型で励起波長λｐ＝６３８ｎｍを有し、平均パワー５０ｍＷを有する。レンズ１３は、例えば焦点距離１００ｍｍを有し、レーザ光源１１からの励起光ＬｐをＰＰ結晶素子１２に導光する。絞り１４は、予め設定される各種の開口数において、ＰＰ結晶素子１２から出射する光を規制する。レンズ１５は、例えば焦点距離２００ｍｍを有し、絞り１４を通過した光のうちの透過可能な光を導光して、例えば中赤外光を遮断する。波長フィルタ１６は、例えば波長７００ｎｍよりも大きい波長の光を選択的に通過させ、例えば励起光Ｌｐ等を遮断する。レンズ１７は、例えば焦点距離５０ｍｍを有し、波長フィルタ１６を通過した光（例えば近赤外光）を、伝送光学系の一端等に集光する。Thelaser light source 11 of this configuration example is a CW type, has an excitation wavelength of λp = 638 nm, and has an average power of 50 mW. Thelens 13 has, for example, a focal length of 100 mm, and guides the excitation light Lp from thelaser light source 11 to thePP crystal element 12. Thediaphragm 14 regulates the light emitted from thePP crystal element 12 at various numerical apertures set in advance. Thelens 15 has, for example, a focal length of 200 mm, guides the transmissible light among the light passing through thediaphragm 14, and blocks, for example, mid-infrared light. Thewavelength filter 16 selectively passes light having a wavelength larger than, for example, 700 nm, and blocks, for example, excitation light Lp. The lens 17 has, for example, a focal length of 50 mm, and collects light that has passed through the wavelength filter 16 (for example, near-infrared light) on one end of a transmission optical system or the like.

　シリコンＣＣＤ２０は、伝送光学系の他端に接続され、ＰＰ結晶素子１２において生成されたアイドラ光子およびシグナル光子の光子対のうちのシグナル光子を観測することができる。本実施形態の光源装置１０において、シグナル光子の波長帯は、シリコンＣＣＤ２０等のシリコン製の検出器で検出可能な波長帯にて適宜、設定されてもよく、可視光領域を含んでもよい。この場合のアイドラ光子の波長帯は、例えば赤外領域においてシグナル光子の波長帯と対応するように設定される。Thesilicon CCD 20 is connected to the other end of the transmission optical system, and can observe the signal photon among the photon pairs of the idler photon and the signal photon generated in thePP crystal element 12. In thelight source device 10 of the present embodiment, the wavelength band of the signal photon may be appropriately set to a wavelength band that can be detected by a silicon detector such as a silicon CCD20, or may include a visible light region. The wavelength band of the idler photon in this case is set so as to correspond to the wavelength band of the signal photon, for example, in the infrared region.

　図１４は、本実施形態の光源装置１０におけるＰＰ結晶素子１２の構成例を示す。本構成例のＰＰ結晶素子１２は、ファンアウト型のＰＰＳＬＴで構成され、例えばＺ方向におけるサイズ１１ｍｍ及びＸ方向におけるサイズ５ｍｍを有する。ＰＰ結晶素子１２は、図中の上側（＋Ｘ側）では比較的短い分極周期Λ１を有し、下側（－Ｘ側）では比較的長い分極周期Λ２を有する（例えばΛ１＝１６．６μｍ、Λ２＝１８．３μｍ）。こうしたＰＰ結晶素子１２によると、Ｘ方向に沿ってスライドさせることにより、励起光Ｌｐが入射する位置を変更して、利用する分極周期Λの大きさを可変にすることができる。FIG. 14 shows a configuration example of thePP crystal element 12 in thelight source device 10 of the present embodiment. ThePP crystal element 12 of this configuration example is composed of a fan-out type PPSLT, and has, for example, a size of 11 mm in the Z direction and a size of 5 mm in the X direction. ThePP crystal element 12 has a relatively short polarization period Λ1 on the upper side (+ X side) in the drawing and a relatively long polarization period Λ2 on the lower side (−X side) (for example, Λ1 = 16.6 μm, Λ2). = 18.3 μm). According to such aPP crystal element 12, by sliding along the X direction, the position where the excitation light Lp is incident can be changed, and the magnitude of the polarization period Λ to be used can be made variable.

　以上のように構成される光源装置１０を用いて行った実験について、図１５～１８を用いて説明する。The experiments performed using thelight source device 10 configured as described above will be described with reference to FIGS. 15 to 18.

　図１５は、実施形態２の光源装置１０における分極周期依存性の実験結果を示すグラフＳ１１～Ｓ１７である。図１５の実験では、図７Ａ～７Ｄの実験と同様に、同軸上の過程について分極周期Λを変えながらシグナル光子に対応する近赤外領域における波長λｎのスペクトルを計測した。FIG. 15 is graphs S11 to S17 showing the experimental results of the polarization cycle dependence in thelight source device 10 of the second embodiment. In the experiment of FIG. 15, the spectrum of the wavelength λn in the near infrared region corresponding to the signal photon was measured while changing the polarization period Λ for the coaxial process, as in the experiments of FIGS. 7A to 7D.

　図１５において、グラフＳ１１は分極周期ΛをΛ＝１７．２６μｍに設定した場合におけるシグナル光子の波長スペクトルである。同様に、グラフＳ１２はΛ＝１７．１８μｍであり、グラフＳ１３はΛ＝１７．０９μｍであり、グラフＳ１４はΛ＝１７．００μｍであり、グラフＳ１５はΛ＝１６．９２μｍであり、グラフＳ１６はΛ＝１６．８３μｍであり、グラフＳ１７はΛ＝１６．７５μｍであった。In FIG. 15, graph S11 is a wavelength spectrum of signal photons when the polarization period Λ is set to Λ = 17.26 μm. Similarly, graph S12 has Λ = 17.18 μm, graph S13 has Λ = 17.09 μm, graph S14 has Λ = 17.00 μm, graph S15 has Λ = 16.92 μm, and graph S16 has Λ = 16.83 μm, and graph S17 was Λ = 16.75 μm.

　図１６は、本実施形態における分極周期依存性の理論計算と実験結果との対応関係を示すグラフである。本実施形態において、同軸上の過程(Collinear process)についての分極周期依存性の理論計算(Theoretical calculation)は、図１５の実験結果として得られる実験データ(Experimental data)と、図１６に示すように良く整合していることが確認された。FIG. 16 is a graph showing the correspondence between the theoretical calculation of the polarization cycle dependence and the experimental results in the present embodiment. In the present embodiment, the theoretical calculation of the polarization period dependence for the coaxial process is as shown in the experimental data (Experimental data) obtained as the experimental result of FIG. 15 and FIG. It was confirmed that they were well aligned.

　図１７は、実施形態２の光源装置１０における角度依存性の実験結果を示すグラフＳ２０～Ｓ２５である。図１７の実験では、開口数ＮＡ＝０．０７として、図９Ａ～９Ｄの実験と同様に、出射する角度範囲毎に近赤外領域における波長λｎのスペクトルを計測した。FIG. 17 is graphs S20 to S25 showing the experimental results of the angle dependence in thelight source device 10 of the second embodiment. In the experiment of FIG. 17, the numerical aperture NA = 0.07, and the spectrum of the wavelength λn in the near infrared region was measured for each emission angle range as in the experiments of FIGS. 9A to 9D.

　図１５において、グラフＳ２０は角度範囲をθ≧０．６６°に設定した場合におけるシグナル光子の波長スペクトルである。同様に、グラフＳ２１はθ＝０．５４～０．６６°であり、グラフＳ２２はθ＝０．４２～０．５４°であり、グラフＳ２３はθ＝０．３０～０．４２°であり、グラフＳ２４はθ＝０．００～０．３０°であった。又、全ての角度範囲を含めた結果をグラフＳ２５に示す。In FIG. 15, graph S20 is a wavelength spectrum of signal photons when the angle range is set to θ ≧ 0.66 °. Similarly, graph S21 has θ = 0.54 to 0.66 °, graph S22 has θ = 0.42 to 0.54 °, and graph S23 has θ = 0.30 to 0.42 °. , Graph S24 was θ = 0.00 to 0.30 °. Further, the result including the entire angle range is shown in the graph S25.

　図１８は、本実施形態における角度依存性の理論計算と実験結果との対応関係を示すグラフである。本実施形態において、角度依存性の理論計算(Theoretical calculation)も、図１７の実験結果として得られる実験データ(Experimental data)と、図１８に示すように良く整合していることが確認された。FIG. 18 is a graph showing the correspondence between the theoretical calculation of the angle dependence and the experimental result in the present embodiment. In the present embodiment, it was confirmed that the theoretical calculation of the angle dependence is also well matched with the experimental data obtained as the experimental result of FIG. 17 as shown in FIG.

（他の実施形態）
　上記の実施形態１，２においては、擬似位相整合素子の一例としてＬｉＴａＯ_３結晶を用いたＰＰ結晶素子１２を例示したが、本開示は特にこれに限定されない。本実施形態において、擬似位相整合素子は、周期分極構造を設けられる各種結晶で構成可能であり、例えばニオブ酸リチウム（ＬｉＮｂＯ_３）結晶を用いて構成されてもよい。ＬｉＮｂＯ_３結晶（ＰＰＬＮ）を用いた場合、励起波長λｐは、０．６５μｍ以上０．９５μｍ以下に設定可能である。また、本実施形態の擬似位相整合素子は、ニオブ酸カリウム（ＫＮｂＯ_３）、またはチタン酸リン酸カリウム（ＫＴｉＯＰＯ_４）等の結晶で構成されてもよい。こうした変形例の一例を、図１９，２０を用いて説明する。(Other embodiments)
_{In the above-described first and second embodiments, the PP crystal element 12 using the LiTaO 3} crystal has been illustrated as an example of the pseudo-phase matching element, but the present disclosure is not particularly limited thereto. In the present embodiment, the pseudo-phase matching element can be composed of various crystals provided with a periodic polarization structure, and may be composed of, for example, a lithium niobate (LiNbO₃ ) crystal. When a LiNbO₃ crystal (PPLN) is used, the excitation wavelength λp can be set to 0.65 μm or more and 0.95 μm or less. Further, the pseudo-phase matching element of the present embodiment may be composed of crystals such as_{potassium niobate (KNbO 3} ) or potassium titanate (KTIOPO_4). An example of such a modification will be described with reference to FIGS. 19 and 20.

　図１９は、上記のような光源装置の変形例における分極周期依存性の理論計算を示す。図２０は、本変形例の光源装置における角度依存性の理論計算を示す。本変形例の光源装置は、実施形態１，２の光源装置１０と同様の構成において、ＰＰＳＬＴの擬似位相整合素子の代わりに、ＰＰＬＮの擬似位相整合素子を備える。FIG. 19 shows the theoretical calculation of the polarization period dependence in the modified example of the light source device as described above. FIG. 20 shows the theoretical calculation of the angle dependence in the light source device of this modification. The light source device of this modification has a configuration similar to that of thelight source devices 10 of the first and second embodiments, and includes a PPLN pseudo-phase matching element instead of the PPSLT pseudo-phase matching element.

　図１９では、図２等の特性曲線Ｃ１と同様に、ＰＰＬＮにおいて擬似位相整合条件を満たす場合における特性曲線Ｃ３(PPLN QPM curve)を例示する。図２０では、上記の場合における、図５の放射特性曲線Ｃ２と同様の放射特性曲線Ｃ４においてアイドラ光子に対応する部分を例示する。この際の励起光Ｌｐは、励起波長λｐ＝０．８μｍに設定した。又、図２０の理論計算では、分極周期Λ＝２１μｍを用いた。FIG. 19 illustrates a characteristic curve C3 (PPLN QPM curve) when the pseudo-phase matching condition is satisfied in PPLN, similarly to the characteristic curve C1 in FIG. FIG. 20 illustrates a portion corresponding to an idler photon in the radiation characteristic curve C4 similar to the radiation characteristic curve C2 in FIG. 5 in the above case. The excitation light Lp at this time was set to an excitation wavelength λp = 0.8 μm. Further, in the theoretical calculation of FIG. 20, the polarization period Λ = 21 μm was used.

　図１９に示すように、ＰＰＬＮの擬似位相整合素子においても、別々の波長帯において２つのピークを有する特性曲線Ｃ３が得られ、実施形態１，２と同様に量子もつれ２光子状態を実現できることが確認された。また、ＰＰＬＮの擬似位相整合素子においては、図２０に示すように、励起波長λｐ＝０．８μｍに基づき、中赤外領域の波長λｍ＝２～５μｍにわたる広帯域の赤外光が、開口数ＮＡ＝０．１程度で得られることが確認できた。As shown in FIG. 19, even in the pseudo-phase matching element of PPLN, the characteristic curve C3 having two peaks in different wavelength bands can be obtained, and the quantum entangled two-photon state can be realized as in the first and second embodiments. confirmed. Further, in the PPLN pseudo-phase matching element, as shown in FIG. 20, a wide band infrared light having a wavelength λm = 2 to 5 μm in the mid-infrared region is emitted with a numerical aperture NA based on the excitation wavelength λp = 0.8 μm. It was confirmed that it can be obtained at about 0.1.

　また、実施形態１では、擬似位相整合素子の一例として分極周期Λが一定のＰＰ結晶素子１２を例示した。本実施形態において、擬似位相整合素子の分極周期Λは、擬似位相整合素子の内部で変化してもよい。例えば、同軸方向に沿って分極周期Λが変化するチャープ型の周期分極構造により、擬似位相整合素子が構成されてもよい。この場合、分極周期Λの変化に応じて、同軸方向に出射する光の帯域を広帯域にすることができる。また、本実施形態において、擬似位相整合素子の周期分極構造は、種々の構成であってもよく、例えばチャープ型に限らず、ファンアウト型、シングルグレーティング型、マルチグレーティング型、或いはハイブリッド型等であってもよい。Further, in the first embodiment, thePP crystal element 12 having a constant polarization period Λ is illustrated as an example of the pseudo-phase matching element. In the present embodiment, the polarization period Λ of the pseudo-phase matching element may change inside the pseudo-phase matching element. For example, a pseudo-phase matching element may be configured by a chirp-type periodic polarization structure in which the polarization period Λ changes along the coaxial direction. In this case, the band of light emitted in the coaxial direction can be widened according to the change in the polarization period Λ. Further, in the present embodiment, the periodic polarization structure of the pseudo-phase matching element may have various configurations, for example, not limited to the chirp type, but may be a fan-out type, a single grating type, a multi-grating type, a hybrid type, or the like. There may be.

　また、上記の各実施形態では、光源装置１０における光源の一例としてレーザ光源１１を例示した。本実施形態において、光源装置１０における光源は、レーザ光源と各種の波長変換素子との組み合わせで構成されてもよい。こうした波長変換素子は、例えばＰＰ結晶素子１２と一体的に構成されてもよい。また、本実施形態において光源装置１０における光源は必ずしもレーザ光源をに限らず、種々の固体光源を含んでもよい。また、光源装置１０における励起波長λｐは、特に可視領域に限らず、適宜設計に応じて種々の波長帯にて設定可能である。Further, in each of the above embodiments, thelaser light source 11 is exemplified as an example of the light source in thelight source device 10. In the present embodiment, the light source in thelight source device 10 may be composed of a combination of a laser light source and various wavelength conversion elements. Such a wavelength conversion element may be integrally configured with, for example, thePP crystal element 12. Further, in the present embodiment, the light source in thelight source device 10 is not necessarily limited to the laser light source, and may include various solid-state light sources. Further, the excitation wavelength λp in thelight source device 10 is not particularly limited to the visible region, and can be appropriately set in various wavelength bands according to the design.

　また、上記の各実施形態では、ｔｙｐｅ－０の位相整合による量子もつれ２光子状態を説明した。本実施形態はｔｙｐｅ－０に限らず、例えばｔｙｐｅ－ＩＩ又はｔｙｐｅ－Ｉの位相整合も利用可能である。この場合においても、各々の偏光方向における屈折率等を用いて実施形態１と同様の理論計算が適用でき、光源装置１０の各種パラメータを適宜設計可能である。Further, in each of the above embodiments, the quantum entangled two-photon state due to the phase matching of type-0 has been described. The present embodiment is not limited to type-0, and for example, phase matching of type-II or type-I can also be used. Also in this case, the same theoretical calculation as in the first embodiment can be applied by using the refractive index and the like in each polarization direction, and various parameters of thelight source device 10 can be appropriately designed.

　本開示は、例えば量子情報技術に適用可能であるが、これに限定されるものではない。例えば、本開示は、赤外線を利用した分光／分析といった様々な分野にも適用可能である。The present disclosure is applicable to, for example, quantum information technology, but is not limited thereto. For example, the present disclosure is also applicable to various fields such as spectroscopy / analysis using infrared rays.

Claims (10)

Translated fromJapanese

　励起波長を有する励起光を生成する光源と、
　前記光源から前記励起光が入射するように配置され、周期的に分極が反転する分極周期を有する結晶で構成される擬似位相整合素子とを備え、
　前記擬似位相整合素子において規定される擬似位相整合条件が、
　前記励起光の光軸に沿った分極周期及び励起波長に基づき、前記励起光の入射に応じて前記擬似位相整合素子から出射する第１の光子対により充足され、且つ
　前記第１の光子対と共通の分極周期及び励起波長に基づき、前記第１の光子対と共通の方向に出射する第２の光子対により充足され、
　前記第１の光子対は、第１の波長帯の範囲内の第１波長と、前記第１の波長帯とは異なる第２の波長帯の範囲内の第２波長とを有し、
　前記第２の光子対は、前記第１の波長帯の範囲内で前記第１波長とは異なる第３波長と、前記第２の波長帯の範囲内で前記第２波長とは異なる第４波長とを有する
光源装置。A light source that produces excitation light with an excitation wavelength,
It is provided with a pseudo-phase matching element composed of crystals arranged so that the excitation light is incident from the light source and having a polarization period in which the polarization is periodically reversed.
The pseudo-phase matching condition defined in the pseudo-phase matching element is
Based on the polarization period and excitation wavelength along the optical axis of the excitation light, it is filled with the first photon pair emitted from the pseudo-phase matching element in response to the incident of the excitation light, and is filled with the first photon pair. Based on a common polarization period and excitation wavelength, it is filled with a second photon pair that emits in the same direction as the first photon pair.
The first photon pair has a first wavelength within the range of the first wavelength band and a second wavelength within the range of the second wavelength band different from the first wavelength band.
The second photon pair has a third wavelength different from the first wavelength within the range of the first wavelength band and a fourth wavelength different from the second wavelength within the range of the second wavelength band. Light source device having and.　前記第１の波長帯は、上限値を有し、
　前記第２の波長帯は、前記第１の波長帯の上限値以上において設定され、
　前記第３波長は、前記第１の波長帯の範囲内で前記第１波長よりも長く、
　前記第４波長は、前記第２の波長帯の範囲内で前記第２波長よりも短い
請求項１に記載の光源装置。The first wavelength band has an upper limit value and has an upper limit value.
The second wavelength band is set above the upper limit of the first wavelength band, and is set.
The third wavelength is longer than the first wavelength within the range of the first wavelength band.
The light source device according to claim 1, wherein the fourth wavelength is shorter than the second wavelength within the range of the second wavelength band.　前記第１の波長帯は近赤外領域であり、前記第２の波長帯は中赤外領域である
請求項２に記載の光源装置。The light source device according to claim 2, wherein the first wavelength band is a near-infrared region, and the second wavelength band is a mid-infrared region.　前記光軸を基準とする所定の角度範囲内で、前記励起光の入射に応じて前記擬似位相整合素子から出射する光は、
　前記第１及び第２の光子対が前記光軸に沿って出射した場合における、前記第１波長から前記第３波長までと、前記第２波長から前記第４波長までとを含む帯域を有する
請求項１～３のいずれか１項に記載の光源装置。Within a predetermined angle range with respect to the optical axis, the light emitted from the pseudo-phase matching element in response to the incident of the excitation light is
A claim having a band including the first wavelength to the third wavelength and the second wavelength to the fourth wavelength when the first and second photon pairs are emitted along the optical axis. Item 3. The light source device according to any one of Items 1 to 3.　前記擬似位相整合素子から出射する光の帯域は、波長２μｍから５μｍまでを含む
請求項４に記載の光源装置。The light source device according to claim 4, wherein the band of light emitted from the pseudo-phase matching element includes a wavelength of 2 μm to 5 μm.　前記第１の光子対は、互いに同じ偏光方向を有する２つの光子を含み、
　前記第２の光子対は、前記第１の光子対と同じ偏光方向を有する２つの光子を含み、
　前記第１及び第２の光子対の偏光方向と、前記励起光の偏光方向とが同じである
請求項１～５のいずれか１項に記載の光源装置。The first photon pair contains two photons having the same polarization direction as each other.
The second photon pair contains two photons having the same polarization direction as the first photon pair.
The light source device according to any one of claims 1 to 5, wherein the polarization directions of the first and second photon pairs are the same as the polarization directions of the excitation light.　前記擬似位相整合条件が前記第１及び第２の光子対によって充足されるように、前記励起波長、前記分極周期、前記光軸の向き、及び前記擬似位相整合素子の温度のうちの少なくとも一つが設定される
請求項１～６のいずれか１項に記載の光源装置。At least one of the excitation wavelength, the polarization period, the orientation of the optical axis, and the temperature of the pseudo-phase matching element so that the pseudo-phase matching conditions are satisfied by the first and second photon pairs. The light source device according to any one of claims 1 to 6, which is set.　前記擬似位相整合条件は、下記の式によって表され、

　ここで、ωｐは前記励起波長に対応する角周波数であり、ωｎは前記第１波長又は第３波長に対応する角周波数であり、ωｍは前記第２波長又は第４波長に対応する角周波数であり、ｋｐは角周波数ωｐを有する光子の波数ベクトルであり、ｋｎは角周波数ωｎを有する光子の波数ベクトルであり、ｋｍは角周波数ωｎを有する光子の波数ベクトルであり、Λは前記分極周期であり、ｅは前記結晶における向きを示す基準ベクトルであり、Δｋはミスマッチを示すベクトルである
請求項１～７のいずれか１項に記載の光源装置。The pseudo-phase matching condition is expressed by the following equation.

Here, ωp is an angular frequency corresponding to the excitation wavelength, ωn is an angular frequency corresponding to the first wavelength or the third wavelength, and ωm is an angular frequency corresponding to the second wavelength or the fourth wavelength. Yes, kp is the wavelength vector of the photon having the angular frequency ωp, kn is the wavelength vector of the photon having the angular frequency ωn, km is the wavelength vector of the photon having the angular frequency ωn, and Λ is the polarization period. The light source device according to any one of claims 1 to 7, wherein e is a reference vector indicating the orientation in the crystal, and Δk is a vector indicating a mismatch.　前記結晶は、タンタル酸リチウム結晶又はニオブ酸リチウム結晶である
請求項１～８のいずれか１項に記載の光源装置。The light source device according to any one of claims 1 to 8, wherein the crystal is a lithium tantalate crystal or a lithium niobate crystal.　前記励起波長は、０．６μｍ以上で且つ０．９５μｍ以下である
請求項１～９のいずれか１項に記載の光源装置。The light source device according to any one of claims 1 to 9, wherein the excitation wavelength is 0.6 μm or more and 0.95 μm or less.

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