Adjustable filter
By introducing modulation elements into the adjustable filter to change the incident angle of the light beam, the problems of poor high-speed filtering performance and poor fast response effect of the existing adjustable filter are solved, and the adjustable filter is ideal for high-speed filtering performance and good fast response effect are realized.
Patent Information
- Application Number
- CN202411997839.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-03-28
AI Technical Summary
The high-speed filtering performance of existing adjustable filters is not ideal and has poor fast response.
A fast response adjustable filter including Pigtail, modulation element, collimation element, dispersion element and reflective element is designed to change the eccentricity of the incident light channel by modulation element (such as an electronically controlled crystal or aligned liquid crystal) and control the incident angle of the light beam on the dispersion element, thereby achieving filtering of a specific wavelength.
It realizes an adjustable filter with ideal high-speed filtering performance and good fast response effect, and is suitable for high-speed optical communication filtering and modulation.
Smart Images
Figure CN119717146A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of filters, in particular to an adjustable filter. Background Art
[0002] A tunable filter is an electronic or optical device that can adjust its frequency response characteristics as needed to allow or block signals of a specific wavelength or frequency. Tunable filters are used in many fields, including communications, signal processing, and spectral analysis.
[0003] There are various types of tunable filters, among which waveguide tunable filters have large losses and high investment costs; the response time of filters with micro-electromechanical and planar grating structures is limited by the chip rate, and there will be polarization-related losses due to the influence of the polarization state of the incident light; the response time of filters composed of mechanical drive and filter is limited by the drive device; FP cavity filters use piezoelectric and mechanical drive methods to filter wavelengths and bandwidth. The high-speed filtering performance of these tunable filters is not ideal, and the fast response effect is poor. Summary of the invention
[0004] The embodiment of the present invention provides an adjustable filter to solve the problem that the adjustable filter in the prior art has unsatisfactory high-speed filtering performance and poor rapid response effect.
[0005] The invention discloses a fast-response adjustable filter, comprising: a Pigtail, a modulation element, a collimation element, a dispersion element and a reflection element; the Pigtail has a polarization-maintaining input channel and an output channel;
[0006] Pigtail, modulation element, collimation element, dispersion element and reflection element are arranged in sequence according to the direction of the incident light path;
[0007] The modulation element is an electrically controlled crystal or a nematic liquid crystal;
[0008] Among them, the incident light is incident through the polarization-maintaining input channel, and is sequentially modulated by the eccentric displacement of the modulation element, collimated by the collimation element, and dispersed by the dispersion element to obtain light beams of different wavelengths and emission angles. Each light beam is emitted to the reflection element, and the reflection element reflects the light beam along the original optical path. Among them, the light beam with a specific angle passes through the dispersion element, the collimation element and the modulation element in sequence and is received and emitted by the output channel.
[0009] Optionally, the Pigtail, the modulation element, and the collimation element are coaxially arranged.
[0010] Optionally, the dispersion element is tilted and forms an angle with the arrangement axis of the Pigtail, the modulation element and the collimation element, and the incident surface of the dispersion element faces the collimation element.
[0011] Optionally, the reflective element is located below the dispersive element.
[0012] Optionally, the collimating element is a collimating lens.
[0013] Optionally, the dispersive element is a planar grating.
[0014] Optionally, the reflective element is a mirror.
[0015] Optionally, the polarization-maintaining input channel is a polarization-maintaining optical fiber, and the output channel is a single-mode optical fiber; the slow axis direction of the polarization-maintaining optical fiber is parallel to the optical axis rotation plane of the electrically controlled crystal, and is perpendicular to the grid of the plane grating.
[0016] Optionally, the direction of a vertical line between the polarization-maintaining optical fiber and the single-mode optical fiber is perpendicular to a grating direction of the plane grating.
[0017] Optionally, the eccentric displacement controlled by the modulation element is D, the focal length of the collimating lens is f, and the ratio of the two is proportional to the incident angle α of the light incident on the plane grating, wherein:
[0018]
[0019] d ( sinα+sinβ ) =mλ
[0020] Where d, λ, and β are the grid width, central wavelength, and diffraction angle of the plane grating, respectively, and m corresponds to the order 1.
[0021] Compared with the prior art, the beneficial effect of the fast-response adjustable filter provided by the embodiment of the present invention is that: the adjustable filter of the present invention is provided with a modulation element in the optical path, and the modulation element is an electrically controlled crystal or a phase-nematic liquid crystal. The electrically controlled crystal or the phase-nematic liquid crystal changes the eccentricity between the incident light channel, i.e., the polarization-maintaining input channel and the axis of the collimation element, thereby controlling the incident angle on the dispersion element. When the light beam is incident on the dispersion element at different angles, different wavelengths of light at different angles will be separated. Light of a specific wavelength can be reflected by a reflector and received and emitted by the output channel after passing through the dispersion element, the collimation element and the modulation element in sequence. Light of non-required wavelengths cannot be received by reflecting back to the output channel, thereby realizing adjustable filtering. This implementation scheme has the advantages of a large modulation angle range and a fast response speed, and is suitable for high-speed optical communication filtering modulation. Therefore, the adjustable filter of the invention has ideal high-speed filtering performance and a good fast response effect. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, in which:
[0023] Figure 1 is a schematic diagram of the adjustable filter in the yz plane direction according to an embodiment of the present invention;
[0024] Figure 2 is a schematic diagram of the eccentric displacement of a light beam controlled by a modulation element according to an embodiment of the present invention;
[0025] Figure 3 is a schematic diagram of Pigtail in the xy plane direction according to an embodiment of the present invention;
[0026] Figure 4 It is a schematic diagram of the plane grating grid direction and the 7-direction rotation plane direction in the xy plane direction according to an embodiment of the present invention.
[0027] The reference numerals in the figures are:
[0028] 1. Pigtail; 11. Polarization-maintaining input channel; 12. Output channel; 2. Modulation element; 3. Collimation element; 4. Dispersion element; 5. Reflection element; 6. Plane grating grid direction; 7. Direction of the director rotation plane. DETAILED DESCRIPTION
[0029] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. Now, in conjunction with the accompanying drawings, a preferred embodiment of the present invention is described in detail.
[0030] The embodiment of the present invention provides a fast-response adjustable filter, such as Figure 1 As shown, the fast response tunable filter includes Pigtail 1, modulation element 2, collimation element 3, dispersion element 4 and reflection element 5; Pigtail 1 has a polarization-maintaining input channel 11 and an output channel 12. Pigtail 1, modulation element 2, collimation element 3, dispersion element 4 and reflection element 5 are arranged in sequence according to the direction of the incident light path. Modulation element 2 is an electrically controlled crystal or a nematic liquid crystal.
[0031] Among them, the incident light is incident through the polarization-maintaining input channel 11, and is sequentially modulated by the eccentric displacement of the modulation element 2, collimated by the collimation element 3, and dispersed by the dispersion element 4 to obtain light beams of different wavelengths and emission angles. Each light beam is emitted to the reflection element 5, and the reflection element 5 reflects the light beam along the original optical path. Among them, the light beam with a specific angle passes through the dispersion element 4, the collimation element 3 and the modulation element 2 in sequence and is received and emitted by the output channel 12.
[0032] The adjustable filter of the present invention is provided with a modulation element 2 in the optical path. The modulation element 2 is an electrically controlled crystal or a phase-nematic liquid crystal. The electrically controlled crystal or the phase-nematic liquid crystal changes the eccentricity of the incident light channel, i.e., the polarization-maintaining input channel 11, and the axis of the collimating element 3, thereby controlling the incident angle on the dispersion element 4. When the light beam is incident on the dispersion element 4 at different angles, different wavelengths of light at different angles will be separated. Light of a specific wavelength can be reflected by a reflector and sequentially passed through the dispersion element 4, the collimating element 3 and the modulation element 2, and then received and emitted by the output channel 12. Light of non-required wavelengths cannot be received by reflecting back to the output channel 12, thereby realizing adjustable filtering. This implementation scheme has the advantages of a large modulation angle range and a fast response speed, and is suitable for high-speed optical communication filtering modulation. Therefore, the adjustable filter of the invention has ideal high-speed filtering performance and a good rapid response effect.
[0033] Specifically, Pigtail 1 is a part of a fiber optic device (such as a laser, detector, fiber amplifier, etc.) that extends the optical fiber inside the device to connect to an external system. Pigtail 1 provides a flexible connection method that allows the fiber optic device to be moved or adjusted within a certain range without causing damage to the fiber itself.
[0034] Phase-Aligned Nematic Liquid Crystals and electrically controlled crystals (such as KDP uniaxial electrically controlled crystals) are both materials that can achieve electro-optic modulation. Electrically controlled crystals use the electro-optic effect (such as the Pockels effect or the Kerr effect). Under the action of an electric field, the refractive index of the crystal changes, thereby changing the phase or polarization state of the light wave passing through the crystal. The liquid crystal molecules of the phase-aligned liquid crystal will change their arrangement under the action of an electric field, causing the optical properties of the liquid crystal (such as the refractive index) to change, thereby affecting the light waves passing through the liquid crystal. That is, the phase-aligned liquid crystal has an electro-optic effect, that is, under the action of an external electric field, the arrangement of the liquid crystal molecules will change, causing the refractive index distribution of the liquid crystal to change accordingly. This change in refractive index can be used to modulate the light waves passing through the liquid crystal. Phase-aligned liquid crystals are encapsulated in practical applications.
[0035] The electrically controlled crystal has a fast response speed. Because it is a solid-state material, the response time of the electro-optical effect is usually in the microsecond level. The response speed of the phase-oriented liquid crystal is also fast, and the response time is in the sub-millisecond level. The electrically controlled crystal can provide high optical quality modulation and is suitable for applications that require high precision and high stability. The electrically controlled crystal can adopt KDP (potassium dihydrogen phosphate) uniaxial electrically controlled crystal. The phase-oriented liquid crystal modulation cost is low, it is easy to mass produce, and it is suitable for cost-sensitive applications.
[0036] The thickness of the electrically controlled crystal can control the modulation eccentric displacement, which is the offset of the center of the light beam relative to the center of the original light beam after the light wave is modulated by the electrically controlled crystal. By changing the thickness of the electrically controlled crystal or adjusting the voltage applied to the phase-coordinated liquid crystal, the eccentric displacement of the original light can be accurately controlled, thereby controlling the focal point or diffraction angle of the light wave. By controlling the eccentric displacement, the modulation element 2 can change the angle at which the light wave is incident on the dispersion element 4 (plane grating), thereby achieving modulation of a specific wavelength. This is because the diffraction efficiency of the grating depends on the angle and wavelength of the incident light. By adjusting the incident angle, light of a specific wavelength can be selectively diffracted.
[0037] The polarization-maintaining input channel 11 can keep the polarization state of light unchanged, so that the light can be correctly incident on the conditional element. Specifically, the polarization-maintaining input channel 11 is a polarization-maintaining optical fiber, and a panda-type polarization-maintaining optical fiber with a diameter of 9um, 125um or 250um can be selected. The polarization-maintaining optical fiber can keep the polarization state of light unchanged, and the tunable filter of the present application can maintain the polarization characteristics of light within a wider bandwidth.
[0038] Specifically, the polarization direction of the polarized light (i.e., the vibration direction of the electric field of the light wave) and the director of the electrically controlled crystal (i.e., the vector used to control the polarization direction of the light inside the electrically controlled crystal) are located in the same plane, ensuring that the electrically controlled crystal can effectively modulate the polarized light passing through it. By precisely controlling the direction of the polarized light, the angle at which the light passes through subsequent optical elements (such as the dispersion element 4) can be adjusted, thereby achieving modulation and filtering of specific wavelengths.
[0039] Specifically, the output channel 12 is a single-mode optical fiber, and SM28e single-mode optical fiber can be selected as the output channel 12 .
[0040] The modulation element 2 (electrically controlled crystal or phase-aligned liquid crystal) modulates the polarization direction of the incident light by changing the applied electric field, i.e., polarization modulation. The modulation element 2 can change the phase of the light wave, and this phase change can be used to adjust the interference and diffraction characteristics of the light wave, thereby affecting the propagation path of the light wave, i.e., phase modulation. By modulating the polarization and phase of the light wave, the modulation element 2 indirectly controls the angle at which the light wave is incident on the dispersion element 4 (plane grating), thereby achieving selective transmission of light waves of specific wavelengths. The modulation element 2 in the present invention can respond quickly to changes in the electric field, and can provide a wide range of modulation angles and a fast response speed to achieve rapid modulation of the wavelength of the light wave, which is particularly important for high-speed optical communication systems.
[0041] Dispersion refers to the phenomenon that after light passes through a grating, light of different wavelengths is dispersed. In the present invention, the function of the dispersive element 4 is to separate the incident light waves according to wavelength, so that light waves of different wavelengths undergo different degrees of diffraction when passing through, thereby separating them in space. Light waves of shorter wavelengths are diffracted at different angles compared to light waves of longer wavelengths. By adjusting the angle of the incident light or the parameters of the grating, light waves of specific wavelengths can be selectively allowed to pass through, while light waves of other wavelengths can be blocked or reduced, thereby achieving filtering or selection of specific wavelengths. In the present invention, the tunable filter can change the angle at which the light wave is incident on the dispersive element 4 (plane grating) by changing the modulation of the light wave by the modulating element 2 (such as an electrically controlled crystal or a phase-oriented liquid crystal), thereby achieving screening of light waves of different wavelengths, that is, achieving a tunable filtering function. The number of line pairs of the dispersive element 4 (plane grating) (i.e., the number of line pairs per millimeter) determines the fineness of the dispersion. A grating with a high number of line pairs can provide a higher spectral resolution. Different line pairs are required according to the filtering bandwidth requirements. The number of line pairs of the dispersion element 4 of the present invention is selected to be 800 to 1200 line pairs.
[0042] Specifically, the dispersion element 4 is a plane grating, which separates light waves of different wavelengths through the diffraction effect, so that the light of different wavelengths is dispersed in space, so that light of a specific wavelength can be selectively filtered out. By adjusting the angle at which the light wave is incident on the plane grating, light waves of a specific wavelength can be selectively allowed to pass, while light waves of other wavelengths can be blocked or reduced.
[0043] The collimating element 3 shapes the light beam emitted from the light source or the previous optical element into a parallel light beam for subsequent optical processing. Through collimation, the divergence and aberration in the light beam can be reduced, and the uniformity and quality of the light beam can be improved. Specifically for the present invention, the dispersive element 4 such as the plane grating requires a parallel light beam to effectively diffract and disperse. The collimating element 3 ensures that the light beam meets the incident condition of the grating, thereby achieving the best color separation effect, while improving the transmission efficiency of light and reducing the loss of light during transmission. In addition, the use of the collimating element 3 can make the optical path design simpler and more flexible, because it can ensure that the light beam remains parallel after long-distance transmission. Specifically, the collimating element 3 is a collimating lens.
[0044] The reflective element 5 is a reflector. The reflective surface of the reflector is provided with a 0-degree reflective film with an emissivity greater than 99.25%. The 0-degree reflective film has a very high reflectivity (R>99.25%) for light in a specific wavelength range at an incident angle of 0 degrees, which enables the reflector to reflect almost all incident light back to the original optical path without significant light loss.
[0045] For example, the incident light is light with a wavelength bandwidth of 1528-1568nm, and the required light beam is a specific wavelength light beam with a wavelength bandwidth of 1550nm. The electrically controlled crystal is applied with a corresponding specific voltage, and the light beam with a wavelength bandwidth of 1528nm-1568nm modulates the propagation path of the light wave through the electrically controlled crystal, generating an eccentric displacement D (such as Figure 2 ), the plane grating separates light beams of different wavelengths at the current light beam incident angle. At this time, the specific wavelength light beam with a wavelength bandwidth of 1550nm can be reflected by the reflector to the output channel 12, and the light beams with other wavelength bandwidths cannot be reflected to the output channel 12, thereby obtaining a specific wavelength light beam with a wavelength bandwidth of 1550nm, thereby achieving the filtering purpose. If a specific wavelength light beam with other wavelength bandwidths is required, the voltage applied to the electrically controlled crystal is changed, so that the propagation path of the light wave is modulated by the electrically controlled crystal to generate a corresponding eccentric displacement D, and the plane grating separates light beams of different wavelengths at the incident angle of the light beam. At this time, the specific wavelength light beam can be reflected by the reflector to the output channel 12.
[0046] Furthermore, Pigtail 1, modulation element 2, and collimation element 3 are arranged coaxially. Dispersion element 4 is arranged at an angle and forms an angle with the arrangement axis of Pigtail 1, modulation element 2, and collimation element 3, and the incident surface of dispersion element 4 faces collimation element 3. The coaxial arrangement of Pigtail 1, modulation element 2, and collimation element 3 helps to maintain the alignment and stability of the optical path, because the light beam is transmitted along the same axis, reducing alignment errors and optical path deviations. The coaxial arrangement simplifies the optical path design, allowing the light beam to be transmitted directly from one element to the next without complex optical path adjustments. The tilted setting of dispersion element 4 allows precise control of the angle of the incident light, which is crucial for adjusting the angle of the diffracted light and achieving screening of specific wavelengths.
[0047] The reflective element 5 is located below the dispersive element 4. Placing the reflective element 5 below the dispersive element 4 can achieve a more compact optical path design and save space. Specifically, the dispersive element 4 is a transmission type plane grating, which can reduce the spatial layout.
[0048] The slow axis of the polarization-maintaining fiber is parallel to the plane of rotation of the optical axis of the electrically controlled crystal and perpendicular to the grid of the plane grating. The slow axis of the polarization-maintaining fiber is the direction in which the polarized light propagates slower in the fiber, and this direction is parallel to the plane of rotation of the optical axis of the electrically controlled crystal. The optical axis of the electrically controlled crystal is the vector inside the crystal that determines the direction of polarization of light, and when an electric field is applied, this optical axis can rotate, thereby changing the polarization state of light passing through the crystal. The configuration of the slow axis of the polarization-maintaining fiber parallel to the plane of rotation of the optical axis of the electrically controlled crystal helps ensure that the polarization state of the light wave can be effectively modulated by the electrically controlled crystal. The grid of the plane grating is the arrangement of the lines on the grating, which are used to diffract the light wave. The configuration of the slow axis of the polarization-maintaining fiber perpendicular to the grid of the plane grating helps ensure that the light wave can be incident on the grating at the correct angle after being modulated by the electrically controlled crystal, thereby achieving effective diffraction and wavelength selection. By making the slow axis of the polarization-maintaining fiber parallel to the plane of rotation of the optical axis of the electrically controlled crystal, it can be ensured that the electrically controlled crystal can effectively modulate the polarization state of the light wave. The configuration of the slow axis of the polarization-maintaining fiber perpendicular to the plane grating grid helps ensure that the light wave is incident on the grating at the correct angle. The specific directional configuration of this solution helps optimize the entire optical path design, ensuring that the light wave can be processed by the filter in the correct way after modulation, collimation, dispersion and reflection, which helps improve the performance of the tunable filter, including modulation efficiency, wavelength selection accuracy and system response speed.
[0049] The vertical connection line between the polarization-maintaining fiber and the single-mode fiber is perpendicular to the plane grating grid direction 6. By ensuring that the vertical connection line of the fiber connection is perpendicular to the grating grid direction, the diffraction efficiency of the grating can be maximized, especially for light waves of a specific wavelength, which helps to improve the selectivity for light waves of a specific wavelength because it allows more precise control of the diffraction angle of the light wave.
[0050] Furthermore, the eccentric displacement controlled by the modulation element 2 is D, the focal length of the collimating lens is f, and the ratio of the two is proportional to the incident angle α of the light incident on the plane grating, and the diffraction angle of the plane grating is β, where:
[0051]
[0052] d ( sinα+sinβ ) =mλ
[0053] Where d and λ are the grid width and central wavelength of the plane grating, respectively, and m corresponds to the order 1.
[0054] By changing the eccentric displacement D of the modulation element 2, the angle at which the light is incident on the plane grating can be adjusted. By adjusting the incident angle α and the diffraction angle β, the selection of a specific wavelength λ can be achieved. By changing the eccentric displacement D, the incident angle α can be adjusted, thereby changing the diffraction conditions and achieving the selection of light waves of different wavelengths. This is because the change in the incident angle α will affect the value of sinα, which in turn affects the value of sinβ, and ultimately affects the wavelength λ of the diffracted light wave. Since the modulation element 2 (such as an electrically controlled crystal or a phase-oriented liquid crystal) can respond quickly to changes in the electric field, the eccentric displacement D can be quickly adjusted, thereby quickly changing the incident angle α of the grating and achieving rapid modulation of the wavelength of the light wave.
[0055] Further, the conclusion Figure 3 As shown, in the xy plane, the polarization-maintaining input channel 11 of the Pigtail 1 uses a Panda-type polarization-maintaining fiber. The polarization-maintaining fiber is used to keep the polarization state of light unchanged.
[0056] The cat's eye direction and the direction of the director of the electrically controlled crystal are in the same plane. The "cat's eye direction" refers to the characteristic direction used to maintain the polarization direction of light in the panda-type polarization-maintaining fiber, similar to the position of a panda's eyes. This direction and the direction of the director of the electrically controlled crystal need to be in the same plane to ensure that the polarized light can be correctly modulated by the electrically controlled crystal.
[0057] like Figure 4 As shown, during the process of electrically driving the electrically controlled crystal, the direction 7 of the rotation plane of the pointing vector coincides with the polarization direction of the incident light channel, and synchronization requires that the grid direction 6 of the plane grating be perpendicular to the above-mentioned direction 7 of the rotation plane of the pointing vector and the polarization direction. When an electric field is applied to the electrically controlled crystal, the pointing vector (the vector that determines the direction of polarized light) inside the electrically controlled crystal will rotate accordingly. This rotation plane needs to coincide with the polarization direction of the incident light channel so that the electrically controlled crystal can effectively modulate the polarization state of the incident light. In order to achieve effective light wavelength selection, the grid direction of the plane grating needs to be perpendicular to the rotation plane and polarization direction of the electrically controlled crystal. This ensures that the grating can correctly diffract the polarized light modulated by the electrically controlled crystal, thereby achieving screening of specific wavelengths.
[0058] like Figure 2As shown, based on the eccentric displacement modulation of extraordinary light by KDP (potassium dihydrogen phosphate) uniaxial electrically controlled crystal, the purpose of modulating the eccentricity D is achieved by changing the pointing vector of the optical axis, wherein the eccentricity is relative to the axis of the electrically controlled crystal, thereby achieving a change in the incident angle of the grating, that is, achieving the purpose of modulating the wavelength. KDP (potassium dihydrogen phosphate) uniaxial electrically controlled crystal is used to modulate extraordinary light (i.e., light whose polarization direction is not parallel to the optical axis of the crystal), and eccentric displacement modulation is achieved by changing the propagation path of the light wave in the crystal. The direction of the optical axis of the KDP (potassium dihydrogen phosphate) uniaxial electrically controlled crystal can be changed by applying an electric field, and this change affects the propagation path of the light wave in the crystal, thereby changing the eccentricity D of the light wave. The eccentricity D refers to the degree to which the light wave deviates from its central axis after being modulated by the crystal. By changing the eccentricity D, the angle at which the light wave is incident on the plane grating can be changed. Because the diffraction characteristics of the plane grating are related to the incident angle, different wavelengths can be selected by changing the incident angle while keeping the diffraction angle unchanged. That is, a specific wavelength can be selected or filtered by adjusting the incident angle of the light wave to the grating.
[0059] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents; and all these modifications and replacements should fall within the scope of protection of the claims attached to the present invention.
Claims
1. A fast-response adjustable filter, characterized in that: include: Pigtail, modulation element, collimation element, dispersion element and reflection element; the Pigtail has a polarization-maintaining input channel and an output channel; The Pigtail, modulation element, collimation element, dispersion element and reflection element are arranged in sequence according to the direction of the incident light path; The modulation element is an electrically controlled crystal or a nematic liquid crystal; Among them, the incident light is incident through the polarization-maintaining input channel, and is sequentially modulated by the eccentric displacement of the modulation element, collimated by the collimation element, and dispersed by the dispersion element to obtain light beams of different wavelengths and emission angles. Each light beam is emitted to the reflection element, and the reflection element reflects the light beam along the original optical path. Among them, the specific angle light beam is received and emitted by the output channel after sequentially passing through the dispersion element, the collimation element and the modulation element.
2. The tunable filter according to claim 1, characterized in that: The Pigtail, the modulation element and the collimation element are coaxially arranged.
3. The tunable filter according to claim 2, characterized in that: The dispersion element is tilted and forms an angle with the arrangement axes of the Pigtail, the modulation element and the collimation element, and the incident surface of the dispersion element faces the collimation element.
4. The tunable filter according to claim 3, characterized in that: The reflective element is located below the dispersive element.
5. The tunable filter according to any one of claims 1 to 4, characterized in that: The collimating element is a collimating lens.
6. The tunable filter according to claim 5, characterized in that: The dispersive element is a plane grating.
7. The tunable filter according to claim 6, characterized in that: The reflective element is a reflector.
8. The tunable filter according to claim 6, characterized in that: The polarization-maintaining input channel is a polarization-maintaining optical fiber, and the output channel is a single-mode optical fiber; the slow axis direction of the polarization-maintaining optical fiber is parallel to the optical axis rotation plane of the electrically controlled crystal, and is perpendicular to the grid of the plane grating.
9. The tunable filter according to claim 8, characterized in that: The vertical connection direction of the polarization-maintaining optical fiber and the single-mode optical fiber is perpendicular to the grid direction of the plane grating.
10. The tunable filter according to claim 6, characterized in that: The eccentric displacement controlled by the modulation element is D, the focal length of the collimating lens is f, and the ratio of the two is proportional to the incident angle α of the light incident on the plane grating, where: d ( sinα+sinβ ) =mλ Where d, λ, and β are the grid width, central wavelength, and diffraction angle of the plane grating, respectively, and m corresponds to the order 1.