CN215811240U - High-resolution optical system based on acousto-optic tunable filter - Google Patents
High-resolution optical system based on acousto-optic tunable filter Download PDFInfo
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- CN215811240U CN215811240U CN202120907492.8U CN202120907492U CN215811240U CN 215811240 U CN215811240 U CN 215811240U CN 202120907492 U CN202120907492 U CN 202120907492U CN 215811240 U CN215811240 U CN 215811240U
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Abstract
The utility model relates to the technical field of spectral imaging, in particular to a high-resolution optical system based on an acousto-optic tunable filter, which comprises a hybrid filter unit, wherein the hybrid filter unit comprises an acousto-optic tunable filter, a first optical lens group, a planar holographic diffraction grating, a second optical lens group and a third optical lens group; a first light path and a second light path which enable the acousto-optic tunable filter and the planar holographic diffraction grating to respectively perform two-time diffraction are formed in the hybrid filter unit; the high-resolution optical system provided by the utility model has the advantages that the acousto-optic action distance of the system is multiplied, and the spectral resolution is improved.
Description
Technical Field
The utility model relates to the technical field of spectral imaging, in particular to a high-resolution optical system based on an acousto-optic tunable filter.
Background
The spectrum analysis technology is a representative of 'green detection technology', and has the advantages of effectively improving analysis efficiency and reducing labor and production cost, so that rapid development is achieved. At present, the spectral imaging technology is an important branch of the spectral analysis technology, plays an increasingly important role in the field of analysis and testing, especially in the field of on-line analysis and testing and industrial control, and is widely applied to many fields including agriculture and animal husbandry, food, chemical industry, petrochemical industry, pharmacy, tobacco and the like.
An Acousto-optic tunable filter (AOTF for short) is a narrow-band tunable filter as an important device of a spectrum analysis technology, and is also a light splitting device manufactured according to an Acousto-optic action principle; the working principle of the acousto-optic tunable filter is as follows: when a beam of polychromatic light passes through a high-frequency vibrating crystal with optical elasticity, monochromatic light with a certain wavelength can be diffracted inside the crystal and is emitted out of the crystal at an angle, and the undiffracted polychromatic light directly transmits through the crystal along the propagation direction of original light, so that the purpose of light splitting is achieved; the split wavelength is selected by varying the frequency of the rf drive applied to the crystal to achieve wavelength scanning.
In addition, the acousto-optic tunable filter has better force and thermal characteristics due to the all-solid-state structure, has flexible spectrum selection performance due to the electric tuning spectrum filtering, has the advantages of controllable spectrum sampling interval, quick wavelength scanning and the like, is very suitable for the requirements of spectrum detection on flexible and efficient data acquisition, and is researched more and more.
AOTF spectral imaging detection techniques must be based on high spectral resolution, which requires acousto-optic tunable filters with narrow spectral bandwidths. The spectral resolution of the existing spectral imaging detection technology adopting a single acousto-optic tunable filter can be controlled to a certain extent by designing a proper incident light polar angle and an acousto-optic interaction distance, but the method has a limited degree of improving the spectral resolution and is not flexible in an adjusting process.
Disclosure of Invention
The utility model aims to overcome the defects of the prior art and provide a high-resolution optical system based on an acousto-optic tunable filter, on one hand, the acousto-optic acting distance of the system is multiplied on the premise that the acousto-optic acting distance of an acousto-optic crystal is not changed, and on the other hand, the high spectral resolution is obviously improved by adopting a mode of combining the acousto-optic tunable filter and a planar holographic diffraction grating.
In order to achieve the purpose, the utility model adopts the following technical scheme:
a high-resolution optical system based on an acousto-optic tunable filter comprises a hybrid filter unit, wherein the hybrid filter unit comprises an acousto-optic tunable filter, a first optical lens group, a planar holographic diffraction grating, a second optical lens group and a third optical lens group; a first light path and a second light path which enable the acousto-optic tunable filter and the planar holographic diffraction grating to respectively perform two-time diffraction are formed in the hybrid filter unit;
the first light path is: an incident beam enters the acousto-optic tunable filter and emits a first diffracted beam from the acousto-optic tunable filter, the first diffracted beam enters the first optical lens group and emits a first emergent beam from the first optical lens group, the first emergent beam enters the planar holographic diffraction grating and emits a second diffracted beam from the planar holographic diffraction grating, and the second diffracted beam enters the second optical lens group and emits a second emergent beam from the second optical lens group;
the second light path is: the second emergent beam is incident to the plane holographic diffraction grating and emits a third diffracted beam from the plane holographic diffraction grating, the third diffracted beam is incident to the third optical lens group and emits a third emergent beam from the third optical lens group, and the third emergent beam is incident to the acousto-optic tunable filter and emits a fourth diffracted beam from the acousto-optic tunable filter.
Preferably, the first optical lens group includes a collimating and focusing lens group, and the first emergent light beam is a parallel light beam.
Preferably, the second optical lens group comprises a mirror group for collimating and focusing the second diffracted light beam.
Preferably, the third optical lens group includes a shaping focusing lens group and a turning lens, the third diffracted light beam passes through the shaping focusing lens group and the turning lens in sequence and is emitted as a third emergent light beam by the turning lens, and the third emergent light beam is incident into the acousto-optic tunable filter.
Preferably, the first diffracted light beam and the fourth diffracted light beam are +1 order diffracted light beams in diffracted light emitted by the acousto-optic tunable filter; and the second diffracted light beam and the third diffracted light beam are + 1-order diffracted light beams in diffracted light emitted by the plane holographic diffraction grating.
Preferably, the high-resolution optical system further includes a wavelength coupling unit, the wavelength coupling unit includes a rotation axis linked with the planar holographic diffraction grating, and the planar holographic diffraction grating rotates around the rotation axis to make the center wavelength of the third outgoing beam equal to the center wavelength of the first outgoing beam.
Preferably, the incident light beam has an incident light polar angle θ with respect to the acousto-optic tunable filteri0The polar angle of the diffracted light of the first diffracted light beam in the acousto-optic tunable filter is thetad0The first diffracted light beam has a dielectric external diffraction angle beta relative to the acousto-optic tunable filter0(ii) a The polar angle of the third emergent light beam relative to the incident light of the acousto-optic tunable filter is thetai1The diffraction light polar angle of the fourth diffraction light beam in the acousto-optic tunable filter is thetad1The medium external diffraction angle of the fourth diffracted light beam relative to the acousto-optic tunable filter is beta1(ii) a And satisfies the following conditions: thetai0＝θi1，θd0＝θd1，β0＝β1；
Preferably, an included angle between a projection of a chief ray of the first outgoing beam on the main cross section of the planar holographic diffraction grating and a normal of the planar holographic diffraction grating is α0The projection of the principal ray of the second diffracted light beam on the main section of the planar holographic diffraction grating and the normal of the planar holographic diffraction grating form an included angle phi0The included angle between the principal ray of the first emergent beam and the main section of the planar holographic diffraction grating is xi1Center of the second diffracted beamWavelength of λ2；
The projection of the chief ray of the second emergent beam on the main section of the plane holographic diffraction grating and the normal of the plane holographic diffraction grating form an included angle phi1The projection of the chief ray of the third diffracted beam on the main section of the plane holographic diffraction grating and the normal of the plane holographic diffraction grating form an included angle alpha1The included angle between the principal ray of the second emergent beam and the main section of the planar holographic diffraction grating is xi2The central wavelength of the third diffracted beam is lambda3(ii) a And satisfies the following conditions: alpha is alpha0＝φ1，λ2＝λ3＝λ。
Preferably, the angle of the first outgoing beam incident on the planar holographic diffraction grating and the angle of the second outgoing beam incident on the planar holographic diffraction grating are in a symmetrical relationship.
Preferably, the rotation center line of the rotation shaft is coplanar with the main plane of the planar holographic diffraction grating, and the extension direction of the rotation shaft is the same as the extension direction of the grooves on the planar holographic diffraction grating.
Preferably, the acousto-optic crystal of the acousto-optic tunable filter has an acousto-optic structure capable of anomalous bragg diffraction, and an incident light beam entering the acousto-optic tunable filter meets the condition of anomalous bragg diffraction.
Preferably, the acousto-optic structure comprises an acousto-optic crystal made of TeO2Crystal with ultrasonic polar angle of 78 deg. and corresponding incident light polar angle thetai024 degrees, and the acousto-optic interaction distance L is 4.2 mm.
Preferably, the condition that the incident light beam satisfies anomalous bragg diffraction includes that the incident light beam is a convergent light beam having an aperture angle, and the incident light polar angle of the principal ray is θi0，θi0Is at 24 °
Compared with the mode that the existing target light beam only passes through the acousto-optic tunable filter once, the acousto-optic tunable filter based high-resolution optical system has the advantages that the target light beam undergoes acousto-optic interaction twice in the acousto-optic tunable filter, the acousto-optic action distance of the optical system is multiplied, the spectral bandwidth of the target light beam is obviously narrowed after the target light beam undergoes dispersion twice in the planar holographic diffraction grating and undergoes filtering color separation twice in the acousto-optic crystal, and the spectral resolution of the high-resolution optical system is obviously improved by the combination of the acousto-optic tunable filter and the planar holographic diffraction grating; and the target light beam passes through the same acousto-optic tunable filter twice, and only the radio frequency drive of the acousto-optic tunable filter needs to be controlled once, so that the problem that the control is not easy to synchronize when the target light beam passes through different acousto-optic tunable filters is solved. In addition, the acousto-optic tunable filter can emit spectra with different central wavelengths according to different frequencies of radio frequency signals, and the planar holographic diffraction grating can rotate to enable the central wavelength of the spectrum emitted by the planar holographic diffraction grating to be the same as the central wavelength of the spectrum emitted by the acousto-optic tunable filter, so that the high-resolution optical system based on the acousto-optic tunable filter can flexibly and effectively improve the spectral resolution.
Drawings
FIG. 1 is a schematic structural diagram of a high-resolution optical system based on an acousto-optic tunable filter according to the present invention;
FIG. 2 is a schematic diagram of the transmission path of the pre-diffraction beam and the post-diffraction beam of the present invention on a planar holographic diffraction grating;
Detailed Description
The following embodiments are given in conjunction with fig. 1-2 to further illustrate the embodiments of the acousto-optic tunable filter based high resolution optical system of the present invention. The acousto-optic tunable filter based high resolution optical system of the present invention is not limited to the description of the following embodiments.
The utility model relates to a high-resolution optical system based on an acousto-optic tunable filter, which comprises a hybrid filter unit, wherein the hybrid filter unit comprises an acousto-optic tunable filter 1, a first optical lens group, a planar holographic diffraction grating 3, a second optical lens group and a third optical lens group; a first light path and a second light path which enable the acousto-optic tunable filter 1 and the planar holographic diffraction grating 3 to respectively diffract twice are formed in the hybrid filter unit;
the first light path is: an incident beam enters the acousto-optic tunable filter 1 and is emitted out of a first diffracted beam by the acousto-optic tunable filter 1, the first diffracted beam enters the first optical lens group and is emitted out of a first emergent beam by the first optical lens group, the first emergent beam enters the planar holographic diffraction grating 3 and is emitted out of a second diffracted beam by the planar holographic diffraction grating 3, and the second diffracted beam enters the second optical lens group and is emitted out of a second emergent beam by the second optical lens group;
the second light path is: the second emergent beam is incident to the plane holographic diffraction grating 3 and emits a third diffracted beam from the plane holographic diffraction grating 3, the third diffracted beam is incident to the third optical lens group and emits a third emergent beam from the third optical lens group, and the third emergent beam is incident to the acousto-optic tunable filter 1 and emits a fourth diffracted beam from the acousto-optic tunable filter 1.
Referring to FIG. 1, the acousto-optic tunable filter 1 adopts TeO2When the crystal and the incident light beam only pass through the acousto-optic tunable filter 1 once, the polar angle of the incident light is assumed to be thetaiThe polar angle of the diffracted light is thetadThe external diffraction angle of the medium is beta, and the central light wavelength of the incident beam is lambda0The center wavelength of the diffracted light beam (i.e. the first diffracted light beam in the present application) is λ (the center wavelength λ and the spectral width of the diffracted light beam of the acousto-optic tunable filter 1 vary correspondingly with the frequency of the radio frequency signal applied to the acousto-optic tunable filter 1), the acousto-optic interaction distance is L, and the refractive indexes of the incident light beam and the diffracted light beam are n, respectivelyiAnd ndConsider TeO2The crystal has optical activity, then:
the spectral bandwidth of the diffracted beam (first diffracted beam) is:
the diffraction efficiency of the incident beam after passing through the acousto-optic tunable filter 1 is as follows:
η＝η0sin2[-brL(λ-λ0)/2λ0 2]/[-brL(λ-λ0)/2λ0 2]2；
wherein eta is0The peak diffraction efficiency is determined by the crystal properties, the geometric dimension and the ultrasonic power of the acousto-optic tunable filter 1, and the eta is determined by the dimension of the crystal and the system0Is a constant value.
It can be seen that, if the spectral resolution of the acousto-optic tunable filter is to be improved, the following two paths can be used: on the first path, the polar angle theta of the incident light is increasediHowever, ultrasonic attenuation is increased when a high-frequency radio-frequency signal is transmitted in the crystal of the acousto-optic tunable filter 1, and the difficulty in manufacturing the transducer of the acousto-optic tunable filter 1 is increased; on the other hand, the acousto-optic interaction distance L is increased, but the incident light aperture is inversely proportional to the acousto-optic interaction distance L, so that the collected energy of the target light signal is reduced along with the increase of the acousto-optic interaction distance, and even the normal response of the detector to the light signal is influenced. Also, the incident light polar angle θiOnce the parameters such as the acousto-optic interaction distance L are selected, the spectral resolution of the acousto-optic tunable filter 1 is also determined, and the spectral resolution cannot be flexibly improved again.
Compared with the mode that the existing target light beam only passes through the acousto-optic tunable filter once, the acousto-optic tunable filter based high-resolution optical system has the advantages that the target light beam undergoes acousto-optic interaction twice in the acousto-optic tunable filter, the acousto-optic action distance of the optical system is multiplied, the spectral bandwidth of the target light beam is obviously narrowed after the target light beam undergoes dispersion and splitting twice in a crystal of the acousto-optic tunable filter and is subjected to filtering and splitting twice in a plane holographic diffraction grating, and the spectral resolution of the high-resolution optical system is obviously improved by the combination of the acousto-optic tunable filter and the plane holographic diffraction grating; and the target light beam passes through the same acousto-optic tunable filter twice, and only the radio frequency drive of the acousto-optic tunable filter needs to be controlled once, so that the problem that the control is not easy to synchronize when the target light beam passes through different acousto-optic tunable filters is solved.
Preferably, as shown in fig. 1, the high-resolution optical system of the present invention further includes a wavelength coupling unit, the wavelength coupling unit includes a rotation axis coupled to the planar holographic diffraction grating 3, and the planar holographic diffraction grating 3 rotates around the rotation axis to make the center wavelength of the third outgoing beam equal to the center wavelength of the first outgoing beam. The acousto-optic tunable filter can emit spectra with different central wavelengths according to different frequencies of radio frequency signals, and the planar holographic diffraction grating can rotate to enable the central wavelength of the spectrum emitted by the planar holographic diffraction grating to be the same as the central wavelength of the spectrum emitted by the acousto-optic tunable filter, so that the high-resolution optical system based on the acousto-optic tunable filter can flexibly and effectively improve the spectral resolution; and the planar holographic diffraction grating 3 can also enhance the intensity of the light beam.
It should be noted that, on the one hand, in order to obtain better spectral resolution, the planar holographic diffraction grating 3 is required to have a smaller spectral range to narrow the spectral width as much as possible; on the other hand, in order to obtain a stronger optical signal, the planar holographic diffraction grating 3 is required to have a larger spectral range so as to improve the diffraction efficiency; therefore, the two cases are considered together to select the planar holographic diffraction grating 3 having the proper spectral range so that both the spectral width and the diffraction efficiency are in the better range.
The high-resolution optical system based on the acousto-optic tunable filter of the present invention will be further described with reference to the drawings and specific embodiments.
As shown in fig. 1, the high-resolution optical system based on an acousto-optic tunable filter of the present embodiment includes a hybrid filter unit, which includes an acousto-optic tunable filter 1(AOTF), a first optical lens group, a planar holographic diffraction grating 3, a second optical lens group, and a third optical lens group; a first light path and a second light path which enable the acousto-optic tunable filter 1 and the planar holographic diffraction grating 3 to respectively diffract twice are formed in the hybrid filter unit;
the first light path is: an incident beam enters the acousto-optic tunable filter 1 and is emitted out of a first diffracted beam by the acousto-optic tunable filter 1, the first diffracted beam enters the first optical lens group and is emitted out of a first emergent beam by the first optical lens group, the first emergent beam enters the planar holographic diffraction grating 3 and is emitted out of a second diffracted beam by the planar holographic diffraction grating 3, and the second diffracted beam enters the second optical lens group and is emitted out of a second emergent beam by the second optical lens group;
the second light path is: the second emergent beam is incident to the plane holographic diffraction grating 3 and emits a third diffracted beam from the plane holographic diffraction grating 3, the third diffracted beam is incident to the third optical lens group and emits a third emergent beam from the third optical lens group, and the third emergent beam is incident to the acousto-optic tunable filter 1 and emits a fourth diffracted beam from the acousto-optic tunable filter 1.
It should be noted that the center wavelengths of the first diffracted beam, the first outgoing beam, the second diffracted beam, the second outgoing beam, the third diffracted beam, the third outgoing beam, and the fourth diffracted beam are the same.
Preferably, as shown in fig. 1, the high-resolution optical system of the present invention further includes a wavelength coupling unit, the wavelength coupling unit includes a rotation axis coupled to the planar holographic diffraction grating 3, and the planar holographic diffraction grating 3 rotates around the rotation axis to make the center wavelength of the third outgoing beam equal to the center wavelength of the first outgoing beam. Further, the rotation center line of the rotation axis of the wavelength coupling unit is coplanar with the main plane of the planar holographic diffraction grating 3 (the main plane of the planar holographic diffraction grating 3 refers to the plane where the first outgoing beam enters the planar holographic diffraction grating 3), and the extension direction of the rotation axis is the same as the extension direction of the grooves of the planar holographic diffraction grating 3.
Preferably, the wavelength range of the planar holographic diffraction grating 3 is 500nm to 2500 nm.
Preferably, the acousto-optic tunable filter 1 comprises a crystal and a transducer, the transducer is arranged on the crystal, the adjustable radio frequency source generates a radio frequency signal and converts the radio frequency signal into ultrasonic vibration through the transducer so as to penetrate through the crystal, and meanwhile, the transducer avoids reflected sound waves from causing interference to forward sound wavesThereby improving the stability of the performance. Further, the crystal of the acousto-optic tunable filter 1 has an acousto-optic structure capable of normal bragg diffraction, and an incident light beam entering the acousto-optic tunable filter 1 meets the condition of abnormal bragg diffraction. Further, the crystal is preferably TeO2Crystals (tellurium dioxide crystals) with excellent acousto-optic properties and easy access to larger sized intraocular lenses, light passing through TeO2When the crystal is crystallized, the principle of anomalous Bragg diffraction is satisfied.
Preferably, the first diffracted light beam and the fourth diffracted light beam are both + 1-order diffracted light beams emitted by the acousto-optic tunable filter 1; the second diffracted light beam and the third diffracted light beam are + 1-order diffracted light beams of the plane holographic diffraction grating 3. Specifically, after the incident light beam enters the acousto-optic tunable filter 1, acousto-optic interaction is carried out between the incident light beam and ultrasonic waves in a crystal of the acousto-optic tunable filter 1, bragg diffraction is carried out, the acousto-optic tunable filter 1 emits a zero-order light beam and two diffracted light beams in the same direction as the incident light beam, the two diffracted light beams are respectively a + 1-order diffracted light beam and a-1-order diffracted light beam, the two diffracted light beams are respectively positioned on two sides of the zero-order light beam and are monochromatic polarized light with the same central wavelength, and the polarization states of the two diffracted light beams are orthogonal to each other. It should be noted that, if the first diffracted beam, the second diffracted beam, the third diffracted beam, and the fourth diffracted beam are + 1-order diffracted beams, other zero-order beams and-1-order beams are absorbed by the optical trap of the preset value; in addition, the first diffracted beam may also be a-1 st order diffracted beam, but the optical path structure of the high-resolution optical system of the present invention needs to be adaptively adjusted, and will not be described herein.
Preferably, as shown in fig. 1, the first optical lens group includes a collimating and focusing lens group 2, and after the first diffracted light beam enters the collimating and focusing lens group 2, the collimating and focusing lens group 2 emits a parallel light beam, and the parallel light beam enters the planar holographic diffraction grating 3. Further, the collimating and focusing lens group 2 is composed of one or more optical lenses.
Preferably, as shown in fig. 1, the second set of optical lenses includes a mirror group 4 for collimating and focusing the second diffracted beam. Further, the mirror group 4 is composed of one or more mirrors, and has collimating and focusing functions.
Preferably, as shown in fig. 1, the third optical lens group includes a shaping focusing lens group 5 and a turning lens 6, and the third diffracted light beam passes through the shaping focusing lens group 5 and the turning lens 6 in sequence and exits a third exiting light beam from the turning lens 6. Further, the third diffracted light beam enters the focusing mirror group 5, the focusing mirror group 5 shapes the third diffracted light beam with a certain divergence angle into a parallel light beam, the parallel light beam enters the turning mirror 6, and the turning mirror 6 emits a third emergent light beam. It should be noted that the turning mirror 6 is usually composed of a single mirror, and mainly reflects the parallel light beams at a certain angle, but if the light spot is seriously deformed during the implementation process, a plurality of mirrors are used to realize the function of the turning mirror 6.
Preferably, referring to FIG. 1, the incident light beam has a polar angle θ with respect to the incident light of the acousto-optic tunable filter 1i0The polar angle of the diffracted light of the first diffracted light beam in the acousto-optic tunable filter 1 is thetad0The first diffracted light beam has a dielectric external diffraction angle beta relative to the acousto-optic tunable filter 10(ii) a Referring to FIG. 1, the polar angle of the incident light of the third emergent beam with respect to the acousto-optic tunable filter 1 is θi1The diffraction light polar angle of the fourth diffraction light beam in the acousto-optic tunable filter 1 is thetad1The fourth diffracted light beam has a dielectric external diffraction angle beta relative to the acousto-optic tunable filter 11. Further, θi0＝θi1，θd0＝θd1The center wavelength of the acousto-optic tunable filter 1 is conveniently and effectively controlled; beta is a0＝β1。
Preferably, as shown in fig. 1, the incident beam is perpendicularly incident on the crystal surface of the acousto-optic tunable filter 1 (in fig. 1, the vertical mark of the lower edge line of the incident beam and the acousto-optic tunable filter 1 indicates the perpendicular relationship between the incident beam and the crystal surface of the acousto-optic tunable filter 1), which facilitates the calculation process in the aspects of the optical path direction, the spectrum selection and the like, and of course, the incident beam may not be perpendicularly incident on the acousto-optic tunable filter 1, but the control method of the transducer may be complicated.
Preferably, as shown in fig. 1, in each light splitting process of the planar holographic diffraction grating 3, a light beam incident on the planar holographic diffraction grating 3 is recorded as a pre-diffraction light beam, a light beam emitted from the planar holographic diffraction grating 3 is recorded as a post-diffraction light beam, and the pre-diffraction light beam and the post-diffraction light beam satisfy the following grating equations:
dcosξ(sinα+sinφ)＝mλ
wherein d is a grating constant, ξ is an angle (i.e. solid angle) between a chief ray of the light beam before diffraction and a main cross section of the plane holographic diffraction grating 3, α is an angle between a projection of the chief ray of the light beam before diffraction on the main cross section of the plane holographic diffraction grating 3 and a grating normal of the plane holographic diffraction grating 3, m is a diffraction order of the light beam after diffraction, and λ is a central wavelength of the light beam after diffraction. After the light beam before diffraction is split by the plane holographic diffraction grating 3, the obtained light beam after diffraction has narrower spectral broadband, which is beneficial to improving the spectral resolution of the high-resolution optical system based on the acousto-optic tunable filter. Further, as shown in fig. 2, assuming that an included angle between projections of chief rays of the pre-diffracted beam and the post-diffracted beam on the main cross section of the planar holographic diffraction grating 3 is δ, when directions of the pre-diffracted beam and the post-diffracted beam are determined (that is, the included angle δ between chief rays of the pre-diffracted beam and the post-diffracted beam is a determined value), a grating equation satisfied by the pre-diffracted beam and the post-diffracted beam may be deformed as follows:
wherein ω is a rotation angle of the planar holographic diffraction grating 3 (which means an angle rotated by the planar holographic diffraction grating 3 relative to a predetermined position of the planar holographic diffraction grating 3, i.e. a 0 ° position of the planar holographic diffraction grating 3 after each rotation), a rotation center line of a rotation axis of the wavelength coupling unit is coplanar with a main plane of the planar holographic diffraction grating 3, and an extending direction of the rotation axis is the same as an extending direction of the grooves on the planar holographic diffraction grating 3So that; due to the fact that
The central wavelength λ of the diffracted beam is a constant, and therefore, the central wavelength λ of the diffracted beam is linearly related to sin ω, that is, when the frequency of the rf signal applied to the acousto-optic tunable filter 1 is continuously changed, the central wavelength λ of the output light (i.e., the first diffracted beam) selected by the acousto-optic tunable filter 1 can be determined by selecting the corresponding ω value.
For example, as shown in FIG. 2, Ao represents the chief ray of the pre-diffracted beam, Bo represents the chief ray of the post-diffracted beam, the origin o is located at the center of the plane holographic diffraction grating 3, the y-axis is parallel to the grooves of the plane holographic diffraction grating 3, the x-axis passes through the normal of the center of the plane holographic diffraction grating 3 (i.e., the x-axis is the grating normal of the plane holographic diffraction grating 3), yoz represents the plane coincident with the principal plane of the plane holographic diffraction grating 3, xoz represents the principal cross-section of the plane holographic diffraction grating 3, A1o is the projection of the chief ray of the pre-diffracted beam on the principal cross-section of the plane holographic diffraction grating 3, B1o is the projection of the chief ray of the post-diffracted beam on the principal cross-section of the plane holographic diffraction grating 3, and angle A1ox (i.e., α) is the angle between the projection of the chief ray of the pre-diffracted beam on the principal cross-section of the plane holographic diffraction grating 3 and the grating 3, an angle B1ox (namely phi) is an included angle between the projection of the chief ray of the diffracted light beam on the main section of the holographic planar diffraction grating 3 and the grating normal of the holographic planar diffraction grating 3, and an angle AoA1 (namely xi) is an included angle between the chief ray of the light beam before diffraction and the main section of the holographic planar diffraction grating 3.
Specifically, the method comprises the following steps:
as shown in fig. 1, the projection of the chief ray of the first emergent beam on the main cross section of the planar holographic diffraction grating 3 forms an angle α with the normal of the planar holographic diffraction grating 30The projection of the chief ray of the second diffracted light beam on the main section of the planar holographic diffraction grating 3 forms an included angle phi with the normal of the planar holographic diffraction grating 30The included angle between the chief ray of the first emergent beam and the main section of the plane holographic diffraction grating 3 is xi1The central wavelength of the second diffracted beam is lambda2。
As shown in fig. 1, the projection of the chief ray of the second outgoing beam on the main cross section of the planar holographic diffraction grating) and the normal of the planar holographic diffraction grating 3 form an angle phi1The projection of the chief ray of the third diffracted beam on the main section of the planar holographic diffraction grating 3 forms an angle alpha with the normal of the planar holographic diffraction grating 31The included angle between the principal ray of the second emergent beam and the main section of the plane holographic diffraction grating 3 is xi2The central wavelength of the third diffracted beam is lambda3(ii) a And satisfies the following conditions: alpha is alpha0＝φ1，λ2＝λ3＝λ。
The first outgoing beam and the second diffracted beam satisfy the following grating equation:
wherein phi is0Is the included angle between the projection of the chief ray of the second diffracted beam on the main section of the plane holographic diffraction grating 3 and the normal of the plane holographic diffraction grating 3, d is the grating constant, xi1Is the angle (i.e. solid angle) between the principal ray of the first exit beam and the principal cross-section of the planar holographic diffraction grating 30Is the included angle between the projection of the chief ray of the first emergent beam on the main section of the plane holographic diffraction grating 3 and the normal of the plane holographic diffraction grating 3, lambda is the central wavelength of the second diffracted beam, and omega is the rotation angle of the plane holographic diffraction grating 3;
the second emergent beam and the third diffracted beam satisfy the following grating equation:
wherein ξ2Is the angle (i.e. solid angle) between the principal ray of the second emergent beam and the principal cross-section of the planar holographic diffraction grating 31Main section of the holographic diffraction grating 3 in plane for the chief ray of the second emergent beamThe projection on the surface forms an included angle with the normal line of the plane holographic diffraction grating 3, and the central wavelength of the third diffracted light beam is the same as that of the second diffracted light beam.
The angle of the first emergent beam incident on the planar holographic diffraction grating 3 and the angle of the second emergent beam incident on the planar holographic diffraction grating 3 are in a symmetrical relation, namely alpha is shown in figure 10＝φ1On the one hand, it is advantageous to improve the convenience of controlling the rotation angle ω of the planar holographic diffraction grating 3, the equation of the quadratic grating
Sum grating equation
Can be obtained by simplified arrangement:
the dispersion ratio of the planar holographic diffraction grating 3
Wherein γ is the magnification; since both the first outgoing beam and the second outgoing beam are incident on the plane hologram diffraction grating 3, γ is1＝γ21, the dispersion ratio of the planar holographic diffraction grating 3 is thus
The spectral bandwidth of the third diffracted beam is
Where f is the focal length of the optical system and τ is the effective focal length of the mirror assembly 4.
The spectral bandwidths of the first and fourth diffracted beams may each be calculated by: Δ λ ═ 1.8 π λ0 2/brL, wherein
Derived by extrapolation, the fourth diffracted beam has a spectral bandwidth of
Wherein λ is0The central optical wavelength of the third exit beam.
For example: the utility model relates to a high-resolution optical system based on an acousto-optic tunable filter, which comprises the following components:
the acousto-optic tunable filter 1 selects an ultrasonic polar angle of 78 degrees, an incident beam of a crystal of the acousto-optic tunable filter 1 is a convergent beam with an aperture angle, and the incident polar angle of the incident beam is thetai024 °, acousto-optic interaction distance 4.2 mm; the effective focal length of the reflector group 4 is 100mm, and the central light wavelength of the incident light beam is 800 nm;
the spectral bandwidth of the first diffracted light beam is 2.4nm and the spectral bandwidth of the fourth diffracted light beam is 0.05nm through calculation, and therefore the comprehensive diffraction efficiency of the high-resolution optical system based on the acousto-optic tunable filter can be kept at about 68%.
The foregoing is a more detailed description of the utility model in connection with specific preferred embodiments and it is not intended that the utility model be limited to these specific details. For those skilled in the art to which the utility model pertains, several simple deductions or substitutions can be made without departing from the spirit of the utility model, and all shall be considered as belonging to the protection scope of the utility model.
Claims (13)
1. A high-resolution optical system based on an acousto-optic tunable filter is characterized in that: the optical fiber surface acoustic wave filter comprises a hybrid filter unit, wherein the hybrid filter unit comprises an acousto-optic tunable filter (1), a first optical lens group, a planar holographic diffraction grating (3), a second optical lens group and a third optical lens group; a first light path and a second light path which enable the acousto-optic tunable filter (1) and the plane holographic diffraction grating (3) to respectively diffract twice are formed in the hybrid filter unit;
the first light path is: an incident beam enters the acousto-optic tunable filter (1) and emits a first diffracted beam from the acousto-optic tunable filter (1), the first diffracted beam enters the first optical lens group and emits a first emergent beam from the first optical lens group, the first emergent beam enters the planar holographic diffraction grating (3) and emits a second diffracted beam from the planar holographic diffraction grating (3), and the second diffracted beam enters the second optical lens group and emits a second emergent beam from the second optical lens group;
the second light path is: the second emergent beam enters the plane holographic diffraction grating (3) and emits a third diffracted beam from the plane holographic diffraction grating (3), the third diffracted beam enters the third optical lens group and emits a third emergent beam from the third optical lens group, and the third emergent beam enters the acousto-optic tunable filter (1) and emits a fourth diffracted beam from the acousto-optic tunable filter (1).
2. The acousto-optic tunable filter based high resolution optical system of claim 1, wherein: the first optical lens group comprises a collimation focusing lens group (2), and the first emergent light beam is a parallel light beam.
3. The acousto-optic tunable filter based high resolution optical system of claim 1, wherein: the second optical lens group comprises a reflector group (4) for collimating and focusing the second diffracted light beam.
4. The acousto-optic tunable filter based high resolution optical system of claim 1, wherein: the third optical lens group comprises a shaping focusing lens group (5) and a turning lens (6), the third diffracted light beam sequentially passes through the shaping focusing lens group (5) and the turning lens (6) and is emitted into a third emergent light beam by the turning lens (6), and the third emergent light beam is incident into the acousto-optic tunable filter (1).
5. The acousto-optic tunable filter based high resolution optical system of claim 1, wherein: the first diffracted light beam and the fourth diffracted light beam are + 1-order diffracted light beams in diffracted light emitted by the acousto-optic tunable filter (1); the second diffracted light beam and the third diffracted light beam are + 1-order diffracted light beams in diffracted light emitted by the plane holographic diffraction grating (3).
6. The acousto-optic tunable filter based high resolution optical system of claim 1, wherein: the high-resolution optical system further comprises a wavelength coupling unit, the wavelength coupling unit comprises a rotating shaft linked with the plane holographic diffraction grating (3), and the plane holographic diffraction grating (3) rotates around the rotating shaft to enable the central wavelength of the third emergent beam to be equal to the central wavelength of the first emergent beam.
7. The acousto-optic tunable filter based high resolution optical system according to any one of claims 1-5, characterized in that:
the incident light beam has an incident light polar angle theta relative to the acousto-optic tunable filter (1)i0The polar angle of the diffracted light of the first diffracted light beam in the acousto-optic tunable filter (1) is thetad0The first diffracted light beam has a medium external diffraction angle beta relative to the acousto-optic tunable filter (1)0(ii) a The polar angle of the third emergent light beam relative to the incident light of the acousto-optic tunable filter (1) is thetai1The polar angle of the diffracted light of the fourth diffracted light beam in the acousto-optic tunable filter (1) is thetad1The medium external diffraction angle of the fourth diffracted light beam relative to the acousto-optic tunable filter (1) is beta1(ii) a And satisfies the following conditions: thetai0＝θi1，θd0＝θd1，β0＝β1。
8. The acousto-optic tunable filter based high resolution optical system according to any one of claims 1-5, characterized in that:
the projection of the chief ray of the first emergent beam on the main section of the plane holographic diffraction grating (3) and the normal of the plane holographic diffraction grating (3) form an included angle alpha0Chief ray of second diffracted rayThe included angle between the projection of the line on the main section of the plane holographic diffraction grating (3) and the normal of the plane holographic diffraction grating (3) is phi0The included angle between the principal ray of the first emergent beam and the principal section of the plane holographic diffraction grating (3) is xi1The central wavelength of the second diffracted beam is lambda2；
The projection of the chief ray of the second emergent beam on the main section of the plane holographic diffraction grating (3) and the normal of the plane holographic diffraction grating (3) form an included angle phi1The projection of the chief ray of the third diffracted beam on the main section of the plane holographic diffraction grating (3) and the normal of the plane holographic diffraction grating (3) form an included angle alpha1The included angle between the principal ray of the second emergent beam and the principal section of the plane holographic diffraction grating (3) is xi2The central wavelength of the third diffracted beam is lambda3(ii) a And satisfies the following conditions: alpha is alpha0＝φ1，λ2＝λ3＝λ。
9. The acousto-optic tunable filter based high resolution optical system of claim 7, wherein: the angle of the first emergent beam incident on the plane holographic diffraction grating (3) and the angle of the second emergent beam incident on the plane holographic diffraction grating (3) are in a symmetrical relation.
10. The acousto-optic tunable filter based high resolution optical system of claim 6, wherein: the rotation center line of the rotating shaft is coplanar with the main plane of the plane holographic diffraction grating (3), and the extending direction of the rotating shaft is the same as the extending direction of the grooves on the plane holographic diffraction grating (3).
11. The acousto-optic tunable filter based high resolution optical system of claim 1, wherein: the acousto-optic crystal of the acousto-optic tunable filter (1) has an acousto-optic structure capable of anomalous Bragg diffraction, and an incident beam emitted into the acousto-optic tunable filter (1) meets the condition of anomalous Bragg diffraction.
12. The acousto-optic tunable filter based high resolution optical system of claim 11, wherein: the acousto-optic structure comprises acousto-optic crystal adopting TeO2Crystal with ultrasonic polar angle of 78 deg. and corresponding incident light polar angle thetai024 degrees, and the acousto-optic interaction distance L is 4.2 mm.
13. The acousto-optic tunable filter based high resolution optical system according to claim 11 or 12, characterized in that: the condition that the incident light beam satisfies the abnormal Bragg diffraction comprises that the incident light beam is a convergent light beam with an aperture angle, and the incident light polar angle of a main light beam is thetai0，θi0Is 24 deg..
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