Tile-level line cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation and controlTechnical Field
The invention relates to the field of single-frequency fiber lasers, in particular to a tile-level line cavity single-frequency fiber oscillator based on dynamic refractive index grating regulation.
Background
The single-frequency optical fiber oscillator has good monochromaticity, longer coherence length, lower noise characteristic and other excellent performances, and becomes an important laser source in the application fields of scientific research, detection, communication and the like. The main characteristic of the single-frequency optical fiber oscillator is that the single-longitudinal mode operation provides a great challenge for the design of the oscillator, which limits the output power of the single-frequency optical fiber laser, most of the current single-frequency optical fiber lasers have the output power of the order of hundreds of milliwatts, and less of the single-frequency optical fiber lasers can reach the order of hundreds of milliwatts or watts, and the main reason is that the better frequency selecting performance cannot be kept with the increase of the power level.
The current frequency selecting mode in the oscillator comprises an ultra-short line cavity, a cascade subchamber, a compound line cavity, a saturable absorber and the like. The frequency selection of the ultra-short wire cavity is that a larger free spectrum range is ensured by means of a shorter cavity length, the shorter cavity length also greatly limits the length of a gain medium although the compact structure and the superior performance of inhibiting mode hopping are achieved, the length of the gain medium is generally limited by adopting a highly doped active optical fiber as the gain medium for obtaining higher output power, but the small change of the cavity length caused by temperature change of the gain medium seriously weakens the frequency selection capacity of an oscillator along with the improvement of laser power, so that the frequency selection mode based on the low doped optical fiber oscillator is widely studied, the principles of a cascade subchamber and a composite wire cavity are both based on vernier effect, so that the free spectrum range of the oscillator is increased, the complexity of a system is increased, the accuracy requirement on the cavity length is higher on the other hand, the method of selecting a Saturable Absorber (SA) is generally realized by adopting an unpumped active optical fiber, the refractive index modulation grating is obtained by periodically modulating the refractive index of a standing wave field formed in a saturable absorber along with the improvement of laser power, and further, the single-mode operation of a single-mode laser with the single-mode can be realized by using a single-mode, and the single-mode operation can be realized by a single-mode operation mode, but the high-level laser power can be realized by a single-mode operation, and the single-mode can be realized by a single-mode operation, and the high-mode can be realized by a single-mode operation, and the laser can be saturated, and a high frequency mode can be realized.
In summary, the current single-frequency laser frequency selection method cannot keep the effective frequency selection of the laser under the higher output power under the high-power operation, and in order to obtain the higher single-frequency laser output power, development of a more effective frequency selection method is needed to ensure the stable single-frequency laser output above the watt-level output power.
Disclosure of Invention
The invention provides a tile-level linear cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation, which improves the frequency selection performance in a single-frequency laser and ensures single longitudinal mode operation under high power condition under the condition of not adding special devices, and is described in detail below:
A tile-level linear cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation comprises two sections of active optical fibers which are pumped by two pumping sources respectively,
The two sections of active optical fibers still remain unpumped parts while absorbing pumping power;
The standing wave effect in the linear cavity laser generates narrow-band refractive index modulation gratings in the unpumped parts of the two sections of active optical fibers to generate a frequency selection effect, and the vernier effect is formed by the narrow-band refractive index modulation gratings in the two sections of active optical fibers to further strengthen the frequency selection effect.
Further, the oscillator includes four cavity-type structures.
In a first scheme, the two sections of active optical fibers are:
The first active optical fiber is positioned at one side of the first high reflection optical fiber grating, the second active optical fiber is positioned at one side of the first low reflection optical fiber grating, the first high reflection optical fiber grating and the first low reflection optical fiber grating provide laser feedback, the first active optical fiber and the second active optical fiber are respectively reversely pumped by a first pump source and a second pump source, pump laser output by the first pump source is coupled and injected into the first active optical fiber through a first pump coupling device, and pump laser output by the second pump source is coupled and injected into the second active optical fiber through a second pump coupling device.
In a second scheme, the two sections of active optical fibers are:
the third active optical fiber and the fourth active optical fiber are respectively and positively pumped by a third pump source and a fourth pump source through a third pump coupling device and a fourth pump coupling device.
In a third scheme, the two sections of active optical fibers are:
the fifth active optical fiber is reversely pumped by the fifth pump source through the fifth pump coupling device, and the sixth active optical fiber is positively pumped by the sixth pump source through the sixth pump coupling device.
In a fourth scheme, the two sections of active optical fibers are:
the seventh active optical fiber is positively pumped by a seventh pump source through a seventh pump coupling device, and the eighth active optical fiber is reversely pumped by an eighth pump source through an eighth pump coupling device;
and a section of passive optical fiber with matched size is added between the seventh active optical fiber and the eighth active optical fiber, and the passive optical fiber is used for isolating the narrow-band refractive index modulation grating formed in the seventh active optical fiber and the eighth active optical fiber so as to form a vernier effect.
The two sections of active optical fibers are active optical fibers doped with the same or different rare earth ions, and the two sections of active optical fibers have an emission section and an absorption section at the central wavelengths of the high-reflection fiber grating and the low-reflection fiber grating.
The active optical fiber is single-clad optical fiber, double-clad optical fiber or three-clad optical fiber, and the central wavelengths of the high-reflection fiber grating and the low-reflection fiber grating are consistent.
Preferably, the two pump sources are solid state lasers, fiber lasers, or semiconductor lasers, the two pump sources are single longitudinal mode lasers or multi-longitudinal mode lasers, and the two pump sources are single transverse mode lasers or higher order transverse mode lasers.
The technical scheme provided by the invention has the beneficial effects that:
1. based on the technical means, the frequency selection performance in the single-frequency laser can be improved under the condition of not adding special devices, and the single longitudinal mode operation under the high-power condition is ensured;
2. Based on the technical means, a feasible single-frequency operation scheme is provided for the active optical fiber which is in a special wave band, namely has no stronger absorption in the wave band as SA;
3. The SA in the scheme has lower requirement on the absorption section of the signal light, can expand the application wave band of the SA, realizes the optimization of single longitudinal mode performance based on the regulation and control of the dynamic refractive index modulation grating, has simple and compact structure and strong laser longitudinal mode stability;
4. the scheme can realize a high-power single-frequency optical fiber laser without depending on a highly doped active optical fiber, and has wide application range.
Drawings
FIG. 1 is a schematic diagram of a first structure of a Watt-level linear cavity single-frequency fiber oscillator based on dynamic refractive index grating modulation;
FIG. 2 is a schematic diagram of a second structure of a Watt-level linear cavity single-frequency fiber oscillator based on dynamic refractive index grating modulation;
FIG. 3 is a schematic diagram of a third structure of a Watt-level linear cavity single-frequency fiber oscillator based on dynamic refractive index grating modulation;
Fig. 4 is a fourth structural schematic diagram of a watt-level line cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation.
In the drawings, the list of components represented by the various numbers is as follows:
in fig. 1:
1.2, a first active optical fiber;
3. a first pump coupling device; 4, a first pumping source;
5. a second active optical fiber, a second pump coupling device;
7. the first low reflection fiber grating;
in fig. 2:
9. 10, a third pumping source;
11. 12, a third active optical fiber;
13. 14, a fourth pump coupling device;
15. 16, a second low reflection fiber grating;
In fig. 3:
17. 18, a fifth active optical fiber;
19. 20, a fifth pump source;
21. a sixth pump source, 22, a sixth pump coupling device;
23. 24, third low reflection fiber gratings;
In fig. 4:
25. 26, a seventh pumping source;
27. 28, a seventh active optical fiber;
29. 30, eighth active optical fiber;
31. 32, an eighth pump source;
33. and a fourth low reflection fiber grating.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail below.
1. Design principle:
A tile-level linear cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation comprises two sections of active optical fibers which are pumped by two pumping sources respectively, the two sections of active optical fibers still keep unpumped parts while absorbing pumping power, and a standing wave effect existing in a linear cavity laser can generate a narrow-band refractive index modulation grating in unpumped parts of the two sections of active optical fibers, so that the two sections of active optical fibers serve as gain media to provide laser gain on one hand and serve as SA to generate a frequency selection effect on the other hand, and the narrow-band refractive index modulation grating in the two sections of active optical fibers forms a vernier effect to strengthen frequency selection so as to meet the requirement of tile-level output power.
In the embodiment of the invention, the narrow-band refractive index modulation grating formed in the two sections of active optical fibers is a key for realizing single-frequency operation, and the bandwidth of the narrow-band refractive index modulation grating is related to the strength and the length of the refractive index modulation grating, so that the power ratio of the two pumping sources can be controlled to regulate the refractive index modulation gratings in the two sections of active optical fibers, thereby realizing optimal frequency selection effect under different power levels and stable single-frequency operation.
2. Classification of laser oscillator cavity structures
The cavity structure of the laser oscillator in the embodiment of the invention has four types according to different pumping directions:
1. First cavity type structure:
the first high reflection fiber grating 1 and the first low reflection fiber grating 8 provide laser feedback, the first active fiber 2 is positioned on one side of the first high reflection fiber grating 1, the second active fiber 5 is positioned on one side of the first low reflection fiber grating 8, the first active fiber 2 and the second active fiber 5 are respectively reversely pumped by the first pump source 4 and the second pump source 7, pump laser output by the first pump source 4 is coupled and injected into the first active fiber 2 through the first pump coupling device 3, and pump laser output by the second pump source 7 is coupled and injected into the second active fiber 5 through the second pump coupling device 6.
2. The second cavity type structure:
the required device is identical to the first cavity type structure. In this configuration, the third active optical fiber 12 and the fourth active optical fiber 15 are each forward pumped by the third pump source 10 and the fourth pump source 13 via the third pump coupling device 11 and the fourth pump coupling device 14, respectively.
3. Third cavity type structure:
The required device is identical to the first cavity type structure. In this configuration, the fifth active optical fiber 18 is back pumped by the fifth pump source 20 through the fifth pump coupling device 19, and the sixth active optical fiber 23 is forward pumped by the sixth pump source 21 through the sixth pump coupling device 22.
4. Fourth cavity type structure:
The required device is identical to the first cavity type structure. In this configuration, the seventh active optical fiber 28 is forward pumped by the seventh pump source 26 through the seventh pump coupling device 27, the eighth active optical fiber 30 is reverse pumped by the eighth pump source 32 through the eighth pump coupling device 31, and a length of size-matched passive optical fiber 29 is added between the seventh active optical fiber 28 and the eighth active optical fiber 30. The passive optical fiber 29 is used to isolate the narrow band index modulated gratings formed in the seventh active optical fiber 28 and the eighth active optical fiber 30, thereby creating a vernier effect.
3. Preference of the device
In the embodiment of the invention, the two sections of active optical fibers can be the same or different rare earth ion doped active optical fibers, and can be the same or different under the condition of the same rare earth ion doped active optical fibers, and only the condition that the two sections of active optical fibers have emission sections at the central wavelengths of the high-reflection fiber grating and the low-reflection fiber grating and have certain absorption sections is satisfied.
The active optical fiber in the embodiment of the invention can be a single-cladding optical fiber or a double-cladding optical fiber, and only needs to ensure that two sections of active optical fibers can provide laser gain and serve as SA.
In the embodiment of the invention, the two matched pump sources can be solid lasers, fiber lasers, semiconductor lasers and the like, so long as the laser with the wavelength can be generated. It may be a single longitudinal mode laser or a multiple longitudinal mode laser, which is not limited in this embodiment of the present invention. The laser may be single transverse mode laser or high-order transverse mode laser, so long as the laser can be coupled into an optical fiber laser system for transmission and absorption, and the embodiment of the invention is not limited thereto.
In the embodiment of the invention, the center wavelengths of the high-reflection fiber grating and the low-reflection fiber grating are consistent, and the reflectivity and the bandwidth only need to realize the oscillation of laser, so the embodiment of the invention is not limited.
In the embodiment of the invention, the pump coupling device can be a wavelength division multiplexer or a pump beam combiner, and the pump coupling device only needs to couple pump laser into the resonant cavity to pump the active optical fiber.
Example 1
A watt-level linear cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation is shown in a typical embodiment in figure 1.
The oscillator comprises a first high reflection fiber grating 1, a first active optical fiber 2, a first pump coupling device 3, a first pump source 4, a second active optical fiber 5, a second pump coupling device 6, a second pump source 7 and a first low reflection fiber grating 8 which are connected in sequence.
The first high reflection fiber grating 1 has a center wavelength of 2050nm, a reflectivity of 99.9% and a half-width of 0.5nm, the first active fiber 2 and the second active fiber 5 are thulium-holmium co-doped single-clad fibers, the fiber core and the cladding have a size of 8 μm and 125 μm respectively, an absorption coefficient at 1570nm is 150dB/m, the lengths of the fiber cores and the cladding are 6m, the first pump source 4 and the second pump source 7 are 1570nm erbium ytterbium co-doped fiber lasers, the center wavelength of the first low reflection fiber grating 8 is 2050nm, the reflectivity of 50% and the half-width of 0.09nm, the first pump coupling device 3 and the second pump coupling device 6 are all 1570nm/2000nm wavelength division multiplexers, and the wavelength division multiplexers are used for coupling 1570nm and 2000nm band lasers.
Example 2
A watt-level linear cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation is shown in a typical embodiment in fig. 2.
The oscillator comprises a second high reflection fiber grating 9, a third pump source 10, a third pump coupling device 11, a third active fiber 12, a fourth pump source 13, a fourth pump coupling device 14, a fourth active fiber 15 and a second low reflection fiber grating 16 which are connected in sequence.
The second high reflection fiber grating 9 has a center wavelength 1950nm, a reflectivity of 99.9% and a half-width of 0.5nm, the third active fiber 12 is a thulium-doped double-clad fiber, a core/cladding size of 10/130 μm, an absorption coefficient of 800dB/m at 1570nm, the fourth active fiber 15 is a thulium-doped single-clad fiber, a core/cladding size of 9/125 μm, an absorption coefficient of 150dB/m at 1570nm, the third pump source 10 and the fourth pump source 13 are 1570nm erbium ytterbium co-doped fiber lasers, and the second low reflection fiber grating 16 has a center wavelength 1950nm, a reflectivity of 70% and a half-width of 0.05nm. The third pump coupling device 11 and the fourth pump coupling device 14 are 1570nm/1950nm wavelength division multiplexers.
Example 3
A watt-level line cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation is shown in a typical embodiment in fig. 3.
The oscillator comprises a third high reflection fiber grating 17, a fifth active optical fiber 18, a fifth pump coupling device 19, a fifth pump source 20, a sixth pump source 21, a sixth pump coupling device 22, a sixth active optical fiber 23 and a third low reflection fiber grating 24 which are connected in sequence.
The third high reflection fiber grating 17 has a center wavelength of 1064nm, a reflectivity of >99.9% and a half-width of 0.3nm, the fifth and sixth active fibers 18 and 23 are ytterbium-doped single-clad fibers, the core/clad size is 5/125 μm, the absorption coefficient at 976nm is 1500dB/m, the fifth and sixth pump sources 20 and 21 are 976nm high-power semiconductor lasers, and the third low reflection fiber grating 24 has a center wavelength of 1064nm, a reflectivity of 70% and a half-width of 0.05nm. The fifth pump coupling device 19 and the sixth pump coupling device 22 are 976nm/1064nm wavelength division multiplexers.
Example 4
A watt-level line cavity single-frequency optical fiber oscillator based on dynamic refractive index grating regulation is shown in a typical embodiment in FIG. 4.
The oscillator comprises a fourth high reflection fiber grating 25, a seventh pump source 26, a seventh pump coupling device 27, a seventh active fiber 28, a passive fiber 29, an eighth active fiber 30, an eighth pump coupling device 31, an eighth pump source 32 and a fourth low reflection fiber grating 33 which are connected in sequence.
Wherein the center wavelength 2800nm, the reflectivity >99.9% and the half-width 0.3nm of the fourth high reflection fiber grating 25, the seventh active fiber 28 and the eighth active fiber 30 are erbium-doped ZBLAN fibers, the core/cladding size is 15/125 μm, the absorption coefficient at 976nm is 150dB/m, the seventh pump source 26 and the eighth pump source 32 are 976nm high power semiconductor lasers, and the center wavelength 2800nm, the reflectivity 70% and the half-width 0.1nm of the fourth low reflection fiber grating 33. The seventh pump coupling device 27 and the eighth pump coupling device 31 are 976nm/2800nm wavelength division multiplexers.
The embodiment of the invention does not limit the types of other devices except the types of the devices, so long as the devices can complete the functions.
Those skilled in the art will appreciate that the drawings are schematic representations of only one preferred embodiment, and that the above-described embodiment numbers are merely for illustration purposes and do not represent advantages or disadvantages of the embodiments.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.