An optical feedback tunable Fabry-Perot filter

Abstract

This invention belongs to the field of optical filter technology and discloses an optical feedback-type tunable Fabry-Perot filter, comprising: a support structure consisting of a fixed mirror tube and a load mirror tube connected by a tenon and mortise joint; a resonant cavity assembly including a first and second mirror that are parallel to each other; a tuning drive module including a piezoelectric ceramic, which adjusts the cavity length of the resonant cavity assembly by applying a voltage to the piezoelectric ceramic; and an optical feedback module for calculating the cavity length and cavity length deviation based on the diffraction pattern generated by the detection light through the diffraction slit between the first and second mirrors, thereby adjusting the driving voltage of the piezoelectric ceramic. This invention, by introducing an optical feedback mechanism based on the diffraction effect, monitors and compensates for changes in cavity length in real time, solving the problem of output peak drift caused by creep and hysteresis of the piezoelectric ceramic, while maintaining small size characteristics and high stability.

Description

Technical Field

[0001] This invention belongs to the field of optical filter technology, and particularly relates to an optical feedback tunable Fabry-Perot filter. Background Technology

[0002] Fabry-Perot filters, based on the principle of parallel-planar multi-beam interference, achieve selective transmission of specific wavelengths by adjusting the cavity length of the resonant cavity, offering advantages such as high spectral resolution and a wide free spectral range. However, traditional Fabry-Perot filters and existing improved schemes still have the following drawbacks:

[0003] Existing tunable Fabry-Perot filters rely on piezoelectric ceramics to drive and adjust the cavity length. However, piezoelectric ceramics have inherent creep and hysteresis, which can cause uncontrollable changes in the cavity length during long-term operation, leading to output wavelength drift and seriously affecting the stability of the filter. Although existing capacitive feedback schemes can achieve cavity length monitoring, the fabrication process of metal electrodes is complex and can easily introduce additional losses. Furthermore, the compatibility between the electrodes and the cavity mirror limits the integration of small-sized structures.

[0004] Therefore, there is an urgent need for a feedback regulation scheme that is adaptable to small-sized structures, can effectively suppress output drift caused by piezoelectric ceramic characteristics, and is easy to integrate, in order to improve the stability and reliability of tunable Fabry-Perot filters. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an optical feedback tunable Fabry-Perot filter. By introducing an optical feedback mechanism based on diffraction effects, it monitors and compensates for cavity length changes in real time, solving the output peak drift problem caused by piezoelectric ceramic creep and hysteresis, while maintaining small size characteristics and high stability. This invention provides the following technical solution:

[0006] An optical feedback tunable Fabry-Perot filter includes a support structure, a resonant cavity assembly, a tuning drive module, and an optical feedback module.

[0007] The support structure includes a fixed lens tube and a load-bearing lens tube, and the fixed lens tube and the load-bearing lens tube are connected by a mortise and tenon structure.

[0008] The resonant cavity assembly includes a first and a second mirror that are parallel to each other.

[0009] The tuning drive module includes a piezoelectric ceramic, and the cavity length of the resonant cavity assembly is adjusted by applying a voltage to the piezoelectric ceramic;

[0010] The optical feedback module is used to calculate the cavity length and cavity length deviation based on the diffraction pattern generated by the detection light in the diffraction slit between the first and second reflectors, thereby adjusting the driving voltage of the piezoelectric ceramic.

[0011] Preferably, both the first reflector and the second reflector are dielectric film reflectors.

[0012] Preferably, it also includes a first quartz gasket, a second quartz gasket, and a third quartz gasket;

[0013] The first quartz gasket is located between the first reflecting mirror and the fixed mirror tube;

[0014] The second quartz gasket is located between the second reflector and the piezoelectric ceramic.

[0015] The third quartz gasket is located between the piezoelectric ceramic and the load mirror barrel.

[0016] Preferably, the driving voltage range of the piezoelectric ceramic is 0-60V, and the displacement-voltage ratio is 0.055μm / V.

[0017] Preferably, the optical feedback module includes: a detection light source, a diffraction detection unit, a signal processing circuit, and a feedback control circuit;

[0018] The detection light source is used to emit detection light to illuminate the diffraction gap between the first reflector and the second reflector;

[0019] The diffraction detection unit is used to receive the diffraction fringe pattern generated by the diffraction slit.

[0020] The signal processing circuit is used to calculate the cavity length d and the cavity length deviation Δd based on the diffraction fringe pattern.

[0021] The feedback control circuit is used to adjust the driving voltage of the piezoelectric ceramic according to the change in cavity length.

[0022] Preferably, the detection light source is a helium-neon laser;

[0023] The laser emitted by the helium-neon laser is collimated into parallel light by a collimating lens with a focal length of 10 mm and then incident perpendicularly into the diffraction slit between the first and second reflecting mirrors.

[0024] Preferably, a narrow-band filter is provided in front of the diffraction detection unit to filter out ambient stray light.

[0025] Preferably, the signal processing circuit extracts the bright fringe centers in the diffraction fringe pattern using a threshold segmentation algorithm and an edge detection algorithm, calculates the spacing Δx between adjacent bright fringe centers, and calculates the cavity length d using the formula d=kλ0L / Δx, where k is the diffraction order, λ0 is the detection wavelength, and L is the distance from the diffraction slit to the detector.

[0026] Preferably, the feedback control circuit calculates the voltage compensation amount ΔV based on the cavity length deviation Δd and the displacement voltage ratio of the piezoelectric ceramic, and then drives the piezoelectric ceramic through a high-voltage operational amplifier.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention provides an optical feedback tunable Fabry-Perot filter. By introducing an optical feedback mechanism based on diffraction effect, it monitors and compensates for cavity length changes in real time, solving the problem of output peak drift caused by piezoelectric ceramic creep and hysteresis, while maintaining small size characteristics and high stability. Attached Figure Description

[0029] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a longitudinal sectional view of Embodiment 1 of the present invention;

[0031] Figure 2 This is a schematic block diagram illustrating the operation of the optical feedback system of the present invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Fixed lens tube; 2. First quartz gasket; 3. First reflecting mirror; 4. Second reflecting mirror; 5. Second quartz gasket; 6. Piezoelectric ceramic; 7. Injection hole; 8. Third quartz gasket; 9. Loading lens tube; 10. Diffraction slit; 11. Light passage. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] This invention provides an optical feedback tunable Fabry-Perot filter, comprising a support structure, a resonant cavity assembly, a tuning drive module, and an optical feedback module. The following describes the process in conjunction with... Figure 1 , Figure 2 As shown, the various components of the optical feedback tunable Fabry-Perot filter of the present invention are described in detail:

[0037] The supporting structure includes a fixed lens barrel 1 and a load-bearing lens barrel 9, which are connected by a mortise and tenon joint. Both are made of aluminum alloy, and both have a diameter of 20mm and a width of 10mm. The fixed lens barrel 1 has a protrusion at one end, and the load-bearing lens barrel 9 has a corresponding groove. During assembly, the protrusion is inserted into the groove for positioning, eliminating the need for additional fasteners, simplifying the structure and ensuring coaxiality.

[0038] The resonant cavity assembly includes a first reflector 3 and a second reflector 4 that are parallel to each other. Both reflectors are multilayer dielectric film reflectors with a diameter of 12 mm and a thickness of 5 mm, and a reflectivity of not less than 90% in the 1500-1600 nm wavelength range. The two reflectors are arranged in parallel to form a resonant cavity, and the cavity length is adjusted by a tuning drive module.

[0039] The tuning drive module uses piezoelectric ceramic 6 as the driving element. Piezoelectric ceramic 6 has an outer diameter of 12mm, an inner diameter of 6mm, and a thickness of 2mm. Applying a DC voltage to piezoelectric ceramic 6 generates a small deformation, thereby changing the cavity length of the resonant cavity assembly. The driving voltage range of piezoelectric ceramic 6 is 0-60V, with a displacement-voltage ratio of 0.055μm / V, enabling cavity length adjustment within the range of 0-3.3μm, meeting the requirements for wide-range wavelength tuning.

[0040] The filter also includes auxiliary structures, including a first quartz gasket 2, a second quartz gasket 5, and a third quartz gasket 8. The first quartz gasket 2 is located between the first reflector 3 and the fixed mirror tube 1, with an outer diameter of 12mm, an inner diameter of 6mm, and a thickness of 1mm. The second quartz gasket 5 is located between the second reflector 4 and the piezoelectric ceramic 6, with an outer diameter of 12mm, an inner diameter of 6mm, and a thickness of 1mm. The third quartz gasket 8 is located between the piezoelectric ceramic 6 and the load mirror tube 9, with an outer diameter of 16mm, an inner diameter of 6mm, and a thickness of 1mm. All quartz gaskets are made of quartz material and serve to isolate, distribute force evenly, and prevent contamination.

[0041] The optical feedback module is used to calculate the cavity length d and cavity length deviation Δd based on the diffraction pattern generated by the detection light through the diffraction slit 10 between the first reflector 3 and the second reflector 4, thereby adjusting the driving voltage of the piezoelectric ceramic 6. Specifically, the optical feedback module includes: a detection light source, a diffraction detection unit, a signal processing circuit, and a feedback control circuit.

[0042] The detection light source is a helium-neon laser with a wavelength of 632.8nm, a power of 5mW, and a spot diameter of ≤0.5mm. The laser emitted by the helium-neon laser is collimated into parallel light by a collimating lens with a focal length of 10mm and then incident perpendicularly into the micron-level diffraction slit 10 between the first reflecting mirror 3 and the second reflecting mirror 4.

[0043] The diffraction detection unit uses a 1280×960 pixel CMOS photodetector array, which is installed at a distance of about 100mm±5mm from the diffraction slit 10 to collect the diffraction fringe pattern generated by the diffraction slit 10. A narrow-band filter with a center wavelength of 632.8nm and a bandwidth of 10nm is provided in front of it to filter out ambient stray light.

[0044] The signal processing circuit, including a preamplifier, a 16-bit A / D converter, and an FPGA signal processing chip, is used to calculate the cavity length *d* and cavity length deviation *Δd* based on the diffraction fringe pattern. Specifically, it extracts the bright fringe centers from the diffraction fringe pattern using threshold segmentation and edge detection algorithms. The FPGA signal processing chip first controls the 16-bit A / D converter via an SPI interface to convert the analog diffraction light signal amplified by the preamplifier into a 16-bit digital signal. A FIFO buffer of 1280×960 pixel image data is used. First, a 5×5 Gaussian filter is applied to the diffraction fringe image acquired by the CMOS detector to reduce noise. Then, grayscale stretching maps the image grayscale range to 0-255 to improve the contrast between bright fringe and background. Subsequently, a statistical image grayscale histogram is used to solve for the optimal threshold, and the image is binarized to separate the bright fringe from the background. Next, an edge detection algorithm is used to calculate the image grayscale gradient and perform non-maximum suppression to refine the edges. A high threshold of 50 and a low threshold of 30 are used to filter strong edges and connected weak edges, extracting the left edge coordinates *X* of the bright fringe row by row. left and the right edge coordinate X right The center coordinates of a single bright fringe are calculated, and then the average of the effective center coordinates of the single bright fringe within the coverage area is taken to obtain the final center X of the corresponding diffraction order bright fringe. k The spacing Δx between adjacent bright fringes is calculated using the center coordinates of adjacent diffraction orders. The cavity length d is then calculated using the formula d = kλ0L / Δx, where k is the diffraction order, λ0 is the detection wavelength, and L is the distance from the diffraction slit 10 to the detector. Finally, the cavity length deviation Δd = d - d0 is calculated, where d0 is the target cavity length.

[0045] The feedback control circuit is used to adjust the driving voltage of the piezoelectric ceramic 6 according to the change in cavity length. Specifically, the feedback control circuit compares the real-time cavity length with the target value and outputs a voltage compensation signal to the piezoelectric ceramic driver that is matched with the piezoelectric ceramic 6, thereby driving the piezoelectric ceramic 6 and achieving cavity length stabilization. The feedback control circuit uses an STM32 microcontroller and a PID algorithm.

[0046] In the feedback control circuit, the STM32 microcontroller uses the cavity length deviation Δd transmitted from the FPGA as the input deviation e of the PID algorithm. It then calculates the proportional term using pre-tuned proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd. Integral terms Differential term The voltage compensation amount ΔV is obtained by superimposing the three factors. Combined with the displacement voltage ratio of the piezoelectric ceramic 6, the piezoelectric ceramic 6 is amplified by the high-voltage operational amplifier and driven to adjust the cavity length in real time with a period of 1ms, so that Δd≤±0.01μm. This PID algorithm is a mature technology. Stable control can be achieved by adjusting the parameters by trial and error.

[0047] The voltage compensation amount ΔV is calculated based on the ratio of cavity length deviation Δd to the displacement voltage of piezoelectric ceramic 6. Then, the piezoelectric ceramic 6 is driven by a high-voltage operational amplifier to make the cavity length deviation Δd ≤ ±0.01μm.

[0048] In this embodiment, AB adhesive (liquid A:liquid B = 1:2) is used to sequentially bond the first reflector 3, the second reflector 4, the first quartz gasket 2, the second quartz gasket 5, the third quartz gasket 8, and the piezoelectric ceramic 6. After applying adhesive to the non-coated side of the first reflector 3, it is bonded to the first quartz gasket 2. After applying adhesive to the non-coated side of the second reflector 4, it is bonded to the second quartz gasket 5, and a pressure of 0.1-0.3 MPa is applied. After applying adhesive to the other side of the second quartz gasket 5, it is bonded to the piezoelectric ceramic 6, ensuring that there is no residual adhesive on the sidewall of the piezoelectric ceramic 6. The bonded components are then placed in a 135°C oven for 2 hours or left to stand under pressure for 24 hours to complete the curing process.

[0049] The above-mentioned adhesive components are installed into the fixed lens barrel 1 and the load lens barrel 9. After being positioned by the tenon and mortise structure, the joint is initially fixed with α-cyanoacrylate adhesive. After standing for 1-2 hours, viscous AB glue is injected into the glue injection hole 7 in 3 times and applied to the joint gap. The joint is then cured a second time to enhance stability.

[0050] The filter is placed on a three-axis cage-type adjustment frame and a two-dimensional displacement stage. The laser image is projected onto the observation screen after passing through the light-transmitting hole 11. The parallelism of the reflector is coarsely adjusted by using a laser pointer until only one bright spot is displayed on the observation screen, thus completing the coarse adjustment of parallelism. Then, fine adjustment is performed by monitoring the output spectrum with a spectrometer.

[0051] Fix the helium-neon laser to the three-dimensional adjustment frame. After turning on the light source, fine-tune the laser direction through the adjustment frame so that the center of the laser beam coincides with the center of the diffraction slit 10 between the two mirrors. Place a piece of white paper behind the diffraction slit 10 and observe whether the light spot falls in the exact center of the diffraction slit 10. Then adjust the position of the collimating lens to ensure that the laser is incident as parallel light.

[0052] An initial voltage V0=10V is applied to the piezoelectric ceramic 6 to activate the CMOS detector and acquire the current diffraction fringe image. The center distance between the first-order bright fringe and the zero-order bright fringe is identified by the FPGA algorithm and recorded as the target fringe distance Δx. Different voltages are applied to the piezoelectric ceramic 6, and the fringe distance is repeatedly acquired to establish a calibration curve of "cavity length d-intervening distance Δx" to verify the accuracy of the formula d=kλ0L / Δx.

[0053] The target cavity length d0 = 1.65 μm was set, and the system automatically output an initial voltage of 10V. A small disturbance was applied manually (such as gently touching the load tube 9 with tweezers to simulate the cavity length change caused by vibration), and the response of the feedback system was observed: the detector collected the change in stripe spacing in real time, the FPGA calculated the cavity length deviation Δd within 10ms, the STM32 output a compensation voltage, and the piezoelectric ceramic 6 restored the cavity length to d0 ± 0.01 μm within 50ms. The system was continuously monitored for 24 hours, and the output peak drift was recorded by a spectrometer to ensure that the drift was stable within the range of ±0.1nm.

[0054] When the input optical signal is perpendicularly incident into the resonant cavity through the light-passing aperture 11, the light undergoes multiple reflections between the first reflecting mirror 3 and the second reflecting mirror 4, forming multi-beam interference. Only light that satisfies "2nd=kλ1" (where n is the refractive index of the cavity medium, d is the cavity length, k is the diffraction order, rounded to the nearest integer, and λ1 is the wavelength of the incident light) can be transmitted and output. If the cavity length of the piezoelectric ceramic 6 changes due to creep or hysteresis, the diffraction fringe spacing changes accordingly. The diffraction detection unit collects the change signal and transmits it to the signal processing circuit to calculate the cavity length deviation. The feedback control circuit outputs a voltage compensation amount to the piezoelectric ceramic 6 based on the deviation, adjusting its thickness to restore the cavity length to the target value. The filter has a spectral resolution ≤2nm and a free spectral range ≥33nm. After optical feedback adjustment, the output peak shift is controlled within ±0.1nm.

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An optically feedback tunable Fabry-Perot filter, characterized in that, The support structure, the resonant cavity assembly, the tuning driving module and the optical feedback module are included. The support structure includes a fixed mirror tube and a load mirror tube, and the fixed mirror tube is connected with the load mirror tube through a mortise and tenon structure. The resonant cavity assembly includes a first mirror and a second mirror which are parallel to each other. The tuning driving module includes a piezoelectric ceramic, and the cavity length of the resonant cavity assembly is adjusted by applying a voltage to the piezoelectric ceramic. The optical feedback module is used to calculate the cavity length and the cavity length deviation according to the diffraction pattern generated by the diffraction slit between the first mirror and the second mirror, so as to adjust the driving voltage of the piezoelectric ceramic. The optical feedback module includes a detection light source, a diffraction detection unit, a signal processing circuit and a feedback control circuit. The detection light source is used to emit detection light to irradiate the diffraction slit between the first mirror and the second mirror. The diffraction detection unit is used to receive the diffraction fringe pattern generated by the diffraction slit. The signal processing circuit is used to calculate the cavity length d and cavity length deviation Δd based on the diffraction fringe pattern; the signal processing circuit extracts the bright fringe centers in the diffraction fringe pattern using a threshold segmentation algorithm and an edge detection algorithm, calculates the spacing Δx between adjacent bright fringe centers using the coordinates of adjacent diffraction order fringe centers, and then calculates the spacing Δx using the formula... Calculate the cavity length d, where k is the diffraction order. To detect the wavelength of light, L is the distance from the diffraction slit to the detector, and the cavity length deviation is calculated. , Target cavity length; The feedback control circuit is used for adjusting the driving voltage of the piezoelectric ceramic according to the cavity length variation; the feedback control circuit calculates the voltage compensation amount AV according to the cavity length deviation Ad and the piezoelectric ceramic displacement voltage ratio, and then drives the piezoelectric ceramic through a high-voltage operational amplifier; wherein the cavity length deviation Ad is taken as the input deviation e of the PID algorithm, and the proportional term , the integral term , and the differential term are calculated through the pre-adjusted proportional coefficient Kp, integral coefficient Ki and differential coefficient Kd respectively, and the three are superimposed to obtain the voltage compensation amount AV.

2. The filter of claim 1, wherein, The first mirror and the second mirror are both dielectric film mirrors.

3. The filter of claim 1, wherein, A first quartz gasket, a second quartz gasket and a third quartz gasket are further included. The first quartz gasket is located between the first mirror and the fixed mirror tube. The second quartz gasket is located between the second mirror and the piezoelectric ceramic. The third quartz gasket is located between the piezoelectric ceramic and the load mirror tube.

4. The filter of claim 1, wherein, The driving voltage range of the piezoelectric ceramic is 0-60V, and the displacement voltage ratio is 0.055μm / V.

5. The filter of claim 1, wherein, The detection light source adopts a helium-neon laser. The laser emitted by the helium-neon laser is collimated into parallel light by a collimating lens with a focal length of 10mm, and then vertically incident to the diffraction slit between the first mirror and the second mirror.

6. The filter of claim 1, wherein, A narrow-band optical filter is arranged in front of the diffraction detection unit to filter ambient stray light.

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