Disclosure of Invention
The invention aims to provide an adjustable surface type volume Bragg grating and a spectral imager, wherein the surface type of the adjustable surface type volume Bragg grating can be adjusted, so that a plurality of volume Bragg gratings with different surface types can be replaced, and in the surface type changing process, the adjustable surface type volume Bragg grating does not need to be taken out from an optical path, so that the optical path does not need to be adjusted again in the surface type changing process, the cost can be reduced, and the working efficiency can be improved.
The invention is realized by the following technical scheme:
the surface-adjustable volume Bragg grating comprises a volume Bragg grating and a surface-adjustable layer covering the upper surface of the volume Bragg grating, wherein the surface shape of the volume Bragg grating is changed by adjusting the refractive index of the surface-adjustable layer.
The surface type of the existing volume Bragg grating is fixedly formed in the manufacturing process and cannot be changed subsequently, so that a plurality of volume Bragg gratings need to be configured in an optical path system needing to use volume Bragg gratings with different surface types, the cost is increased, the optical path needs to be readjusted in the process of replacing the volume Bragg gratings with different surface types, the optical path debugging time is greatly wasted, and the working efficiency is reduced. Based on the above, the application provides an adjustable surface type volume bragg grating, which has a surface type adjusting layer, and the surface type of the volume bragg grating is changed by adjusting the refractive index of the surface type adjusting layer, so that a plurality of volume bragg gratings with different surface types can be replaced by one adjustable surface type volume bragg grating, and the cost is effectively reduced; in the surface shape changing process, the adjustable surface type volume Bragg grating does not need to be taken out of the optical path, so that the optical path does not need to be readjusted in the surface shape changing process, and the working efficiency can be effectively improved.
Preferably, the surface type adjusting layer comprises a substrate layer, a first electrode layer, a first orientation layer, a liquid crystal layer, a second orientation layer and a second electrode layer which are sequentially arranged from top to bottom, the second electrode layer is arranged on the upper surface of the volume bragg grating, and the first electrode layer is connected with an external driving circuit.
Preferably, the first electrode layer is configured as a strip electrode array, and each strip electrode in the strip electrode array is connected to the external driving circuit.
Preferably, the second electrode layer is provided as a bulk electrode.
A spectral imager comprises an imaging lens, a photosensitive element and the adjustable surface type volume Bragg grating; and the light beam of the observed target is collected by the imaging lens and then transmitted to the adjustable surface type volume Bragg grating, and the light beam is transmitted to the photosensitive element for imaging display after being diffracted by the adjustable surface type volume Bragg grating.
The volume Bragg grating narrow-band filtering imaging technology is a new way for realizing staring type spectral imaging, has the advantages of high spectral transmittance, wide spectral tuning range and the like, and has wide application prospect in the fields of space optics, information optics and the like. However, in practical system applications, the filter spectral width needs to be further reduced, and the system structure needs to be further simplified. Based on the above, the application provides a spectral imager, wherein the surface type structure of the adjustable surface type volume bragg grating is adjustable, and the volume bragg grating can have a certain curvature by adjusting the surface type of the adjustable surface type volume bragg grating, so that the angular spectrum distribution of light beams in the volume bragg grating can be adjusted, the filter spectrum width is further reduced, the color blur of an image surface is reduced, and the imaging spatial resolution is improved; meanwhile, by adopting the volume Bragg grating with certain curvature distribution, the functions of incident beam angular spectrum transformation, spectral filtering and imaging can be realized without a beam shaping light path and an imaging light path, the system structure can be effectively simplified, and the robustness and the environmental adaptability of the system can be improved.
Preferably, the optical fiber surface-adjustable volume bragg grating further comprises a reflector, and the reflector is arranged between the imaging lens and the adjustable surface volume bragg grating; when the light beam of the observed target is collected by the imaging lens and transmitted to the reflector, the light beam is reflected by the reflector and transmitted to the adjustable surface type volume Bragg grating.
Preferably, the adjustable optical diaphragm is arranged between the imaging lens and the adjustable surface type volume bragg grating, when a light beam of an observed target is collected by the imaging lens, the light beam is transmitted to the adjustable optical diaphragm, and the light beam is transmitted to the adjustable surface type volume bragg grating after the light beam is acted by the adjustable optical diaphragm.
Preferably, the tunable surface type volume bragg grating further comprises an absorption black cavity, and the absorption black cavity is arranged on the rear surface of the tunable surface type volume bragg grating.
Preferably, the optical fiber further comprises a displacement device for changing the angle of the tunable facet-type volume bragg grating and/or the position of the photosensitive element.
Preferably, the displacement device comprises a driving device, a rotating platform, a two-dimensional displacement platform and a control terminal, wherein the rotating platform is electrically connected with the driving device;
the adjustable surface type volume Bragg grating is arranged on the rotating platform, and the photosensitive element is arranged on the two-dimensional displacement platform; when the control terminal generates a control command, the driving device responds to the control command to drive the rotating platform to rotate and/or the two-dimensional displacement platform to move.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the adjustable surface type volume Bragg grating is provided with a surface type adjusting layer, and the surface type of the volume Bragg grating is changed by adjusting the refractive index of the surface type adjusting layer, so that one adjustable surface type volume Bragg grating can be used for replacing a plurality of volume Bragg gratings with different surface types, and the cost can be effectively reduced;
2. in the surface shape changing process, the adjustable surface type volume Bragg grating does not need to be taken out of the optical path, so that the optical path does not need to be readjusted in the surface shape changing process, and the working efficiency can be effectively improved;
3. the volume Bragg grating has certain curvature by adjusting the surface shape of the adjustable surface type volume Bragg grating, so that the angular spectrum distribution of light beams in the volume Bragg grating can be adjusted, the filter spectrum width is further reduced, the color blur of an image surface is reduced, and the imaging spatial resolution is improved;
4. the volume Bragg grating with certain curvature distribution is adopted, the functions of incident beam angular spectrum transformation, spectral filtering and imaging can be realized without a beam shaping light path and an imaging light path, the system structure can be effectively simplified, and the robustness and the environmental adaptability of the system can be improved.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
The embodiment provides a tunable surface type volume bragg grating, which comprises avolume bragg grating 17 and a surface type adjusting layer covering the upper surface of the volume bragg grating 17, wherein the surface type of thevolume bragg grating 17 is changed by adjusting the refractive index of the surface type adjusting layer.
The surface type of the existingvolume bragg grating 17 is fixed and molded in the manufacturing process, and cannot be changed subsequently, so that a plurality ofvolume bragg gratings 17 need to be configured in an optical path system needing to usevolume bragg gratings 17 with different surface types, the cost is increased, the optical path needs to be readjusted in the process of replacingvolume bragg gratings 17 with different surface types, the optical path debugging time is greatly wasted, and the working efficiency is reduced. Based on this, the present application provides a tunable surface-type bragg grating, wherein the tunable surface-type bragg grating 4 has a surface-type adjusting layer, and the surface type of thevolume bragg grating 17 is changed by adjusting the refractive index of the surface-type adjusting layer, so that a plurality ofvolume bragg gratings 17 with different surface types can be replaced by one tunable surface-type bragg grating 4; in the surface shape changing process, the adjustable surface shape Bragggrating 4 does not need to be taken out of the optical path, so that the optical path does not need to be readjusted in the surface shape changing process, the cost can be reduced, and the working efficiency can be improved.
Specifically, the surface type adjustment layer in this embodiment is as shown in fig. 1, and includes asubstrate layer 11, afirst electrode layer 12, afirst alignment layer 13, aliquid crystal layer 14, asecond alignment layer 15, and asecond electrode layer 16, which are sequentially disposed from top to bottom, where thesecond electrode layer 16 is disposed on an upper surface of a volume bragg grating 17; in this embodiment, thesecond electrode layer 16 is configured as a block electrode, thefirst electrode layer 12 is configured as a strip electrode array, as shown in fig. 2, and each strip electrode in the strip electrode array is connected to an external driving circuit, which may be a power chip, and a plurality of output terminals on the power chip are electrically connected to each strip electrode, that is, the output terminals correspond to the strip electrodes one to one, so as to implement independent control of the voltage loaded on each electrode.
The principles of the present application are explained below:
each independent strip electrode above theliquid crystal layer 14 and the block electrode layer below form a certain electric field distribution, the electric field intensity of the electric field is related to the voltage loaded on each independent electrode, and the electric fields with different intensities regulate and control the director distribution of liquid crystal molecules, so that the refractive index of the liquid crystal is changed. Therefore, by changing the voltage distribution on the strip electrode array, the refractive index distribution at different positions of theliquid crystal layer 14 can be realized. It should be noted that the shape of thefirst electrode layer 12 is not limited to the strip-shaped electrode array, and may be reasonably arranged according to the required surface structure.
The following describes an implementation of the spherical surface type bragg grating 17:
to realize the spherical surfacetype bragg grating 17, theliquid crystal layer 14 is required to have spherical phase distribution for the light wave, and the voltage distribution required to be loaded on the strip electrode array can be obtained by calibrating the voltage-phase delay relationship of theliquid crystal layer 14.
It should be noted that the thickness of theliquid crystal layer 14 is typically a few microns and the phase retardation capability is greater than 2 pi, but not too great. Thus, if the phase delay of the desired load exceeds 2 π, then the amount of phase delay is modulo 2 π (i.e., the amount of phase delay is divided by 2 π, taking the remainder). The phase distribution obtained by the treatment has the phase delay amount within the range of 0-2 pi, but does not influence the phase distribution of the curved surface to be simulated.
The above is an example of a spherical surface, and the spherical surfaces with different curvatures are different in phase distribution in nature, and the voltage distribution can be changed. By analogy, other aspheric surface shapes which are difficult to process can be realized by the method.
Example 2
The present embodiment provides a spectral imager based onembodiment 1, as shown in fig. 3, including animaging lens 1, aphotosensitive element 6, and a tunable surface-type bragg grating 4 provided inembodiment 1; theimaging lens 1 may be a single lens or a lens group as long as the collection of the light beam of the observed target can be achieved; thelight sensing element 6 may be provided as a CCD sensor or a cmos sensor as long as image display of the light beam is realized. In specific implementation, in order to ensure the imaging definition and improve the imaging spatial resolution, thephotosensitive element 6 is installed at the focus of the adjustable surface-type bragg grating 4, and the focus position is always located on the photosensitive surface of thephotosensitive element 6.
It is to be noted that the real shape of the tunable facet-type volume bragg grating 4 in fig. 3 is a plane, as shown in fig. 1; in the present embodiment, since it is necessary to adjust the voltage applied to the tunable surface-type volume bragg grating 4 so that theliquid crystal layer 14 has a spherical phase distribution with respect to the optical wave, for convenience of understanding, the surface of the tunable surface-type volume bragg grating 4 is equivalently drawn as a curved surface in the present embodiment, as shown in fig. 3.
The principle of this solution is explained as follows:
light beams of an observed target are collected by theimaging lens 1 and transmitted to the surface type adjusting layer of the surface type adjustable volume Bragg grating 4, and are refracted by the surface type adjusting layer and enter the medium of the volume Bragg grating 17 to become collimated light beams; if the angle of the collimated light beam meets the Bragg condition of the volume Bragg grating 17, the collimated light beam is diffracted in the volume Bragg grating 17, the diffracted light beam reaches the surface type adjusting layer from the interior of the volume Bragg grating 17 at a certain diffraction angle, and after being refracted by the surface type adjusting layer, the diffracted light beam is focused and imaged on thephotosensitive element 6.
The volume Bragg grating 17 narrow-band filtering imaging technology is a new way for realizing staring type spectral imaging, has the advantages of high spectral transmittance, wide spectral tuning range and the like, and has wide application prospect in the fields of space optics, information optics and the like. However, in practical system applications, the filter spectral width needs to be further reduced, and the system structure needs to be further simplified. Based on this, the application provides a spectral imager, the surface type structure of the adjustable surface type volume Bragg grating 4 in the application is adjustable, the adjustable surface type volume Bragg grating 4 can be changed into a curved surface volume Bragg grating with a certain curvature by adjusting the voltage acting on the adjustable surface type volume Bragg grating 4, so that the angular spectrum distribution of light beams in the volume Bragg grating 17 can be adjusted, the filter spectrum width is further reduced, the color blur of an image surface is reduced, and the spatial resolution of imaging is improved; meanwhile, when the light beam reaches the adjustable surface type body Bragg grating 4, the light beam is converted into collimated light after being transmitted by the surface type adjusting layer, so that the functions of incident light beam angular spectrum transformation, spectral filtering and imaging can be realized without arranging a light beam shaping light path and an imaging light path, the system structure can be effectively simplified, and the robustness and the environmental adaptability of the system can be improved.
Further, in order to reduce the optical path length and the volume of the spectrometer, the present embodiment further provides areflector 2 between theimaging lens 1 and the tunable surface-typevolume bragg grating 4, and the light beam collected by theimaging lens 1 is reflected to the surface-type adjusting layer of the tunable surface-type volume bragg grating 4 through thereflector 2, that is: when the adjustable surface type Bragg grating and theimaging lens 1 are arranged in different rows, the length of the light path can be effectively shortened when the adjustable surface type Bragg grating 4 and theimaging lens 1 are arranged in the same row compared with the case that thereflector 2 is not arranged.
Further, in order to change the filter spectrum width, the present embodiment is further provided with an adjustable diaphragm 3 whose diaphragm aperture size can be adjusted, and the field angle range is changed by adjusting the size of the adjustable diaphragm 3, so that the size of the light beam passing through the adjustable diaphragm 3 can be changed. In specific implementation, the adjustable diaphragm 3 is arranged between thereflector 2 and the adjustable surface typevolume bragg grating 4, and the light beam reflected by thereflector 2 is transmitted to the adjustable surface type volume bragg grating 4 through the adjustable diaphragm 3. The adjustable diaphragm 3 is preferably disposed at the focal plane of theimaging lens 1 and the front focal point of the adjustable surfacevolume bragg grating 4.
Furthermore, after the light beams are incident into the volume Bragg grating 17, the narrow-band spectrum can be diffracted to form diffracted light beams, and the diffracted light beams reach the surface type adjusting layer from the interior of the volume Bragg grating 17 at a certain diffraction angle; while other spectral components pass through the rear surface of the volume bragg grating 17, in order to prevent strong transmitted light from interfering with weak diffracted light and to improve the signal-to-noise ratio, the present embodiment further provides an absorptionblack cavity 10 for absorbing the transmitted light passing through the rear surface of the tunable surfacevolume bragg grating 4.
Further, considering that the central wavelength of the diffracted light formed in the volume bragg grating 17 is angle-dependent, the central wavelength of the filtered light can be changed by changing the incident angle of the light beam and the tunable surface-typevolume bragg grating 4, and based on this, a displacement device is further provided in this embodiment, and the displacement device is used for changing the angle of the tunable surface-typevolume bragg grating 4 and/or the position of thephotosensitive element 6, so as to ensure that the focus of the diffracted light is always on the photosensitive surface of thephotosensitive element 6 after the angle of the tunable surface-type volume bragg grating 4 is changed.
Specifically, the displacement device in the present embodiment includes adriving device 8, and a rotating table 5, a two-dimensional displacement platform 7, and a control terminal 9 electrically connected to thedriving device 8;
the adjustable surface type Bragg grating 4 and the absorptionblack cavity 10 are both arranged on therotating platform 5, thephotosensitive element 6 is arranged on the two-dimensional displacement platform 7, and the photosensitive surface of thephotosensitive element 6 faces the adjustable surface type Bragg grating 4; when the control terminal 9 generates a control instruction, the drivingdevice 8 responds to the control instruction and drives therotating platform 5 to rotate and/or the two-dimensional displacement platform 7 to move, so that the angle of the light beam inside the medium of the volume Bragg grating 17 is changed, and the focus of the diffracted light is always positioned on the photosensitive surface of thephotosensitive element 6.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.