Flexible bandwidth tuning method and device for Lyot type liquid crystal filter

Abstract

The invention discloses a flexible bandwidth tuning method and device for a Lyot type liquid crystal filter. The method specifically comprises the following steps: a) setting initial structure parameters of the Lyot type liquid crystal filter; b) applying a driving voltage to the Nth-stage liquid crystal box in the N-stage Lyot basic structure, and adjusting the phase retardation of the Nth-stage liquid crystal box to gradually reduce the phase retardation of the Nth-stage liquid crystal box from an initial maximum value to 0; c) when the phase retardation of the last-stage liquid crystal box is reduced to 0, the Lyot basic structure of the stage enters an all-pass state, and at the moment, driving voltage is applied to the liquid crystal boxes of the (N-1)-stage Lyot basic structure, so that the phase retardation of the liquid crystal boxes is gradually reduced to 0, and the number of effective cascade layers is further reduced; d) repeating the step c) to sequentially apply the driving voltage to each level of liquid crystal box with the Lyot basic structure from back to front, and adjusting the phase retardation to 0 until a target filtering bandwidth is obtained; according to the method for flexibly tuning the bandwidth through electric control, the hardware structure does not need to be changed, and the bandwidth requirements of different application scenes can be met.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal filter technology, specifically to a method and apparatus for flexibly tuning the bandwidth of a Lyot-type liquid crystal tunable filter. Background Technology

[0002] Lyot-type liquid crystal filters (LCTFs), as optical filtering devices based on the anisotropy of liquid crystals, have been widely used in hyperspectral imaging, optical communication, and biomedical detection due to their advantages such as electronic tuning, compact structure, and fast response speed. However, the core limitation of traditional Lyot-type liquid crystal filters is that their filtering bandwidth is fixed by hardware structural parameters (such as the number of cascaded layers, liquid crystal cell thickness, and phase delay matching relationship), and once the device is manufactured, the bandwidth cannot be flexibly adjusted.

[0003] In practical applications, the bandwidth requirements for filtering vary significantly across different scenarios. For example, high-spectral-resolution detection requires narrowband filtering of 10-25 nm to achieve fine wavelength resolution, while scenarios such as efficient optical energy transmission and broadband imaging require broadband filtering of over 30 nm to ensure sufficient light flux. Traditional technologies require the design and manufacture of various filters with different structural parameters to meet these bandwidth demands, leading to high R&D costs, poor device versatility, and cumbersome replacement operations, severely limiting the application expansion of Lyot-type liquid crystal filters. Therefore, developing a method to achieve flexible bandwidth tuning solely through electronic control without altering the hardware structure has become a pressing technical challenge in this field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a bandwidth tuning method for a Lyot-type liquid crystal filter, addressing the shortcomings mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a bandwidth tuning method for a Lyot-type liquid crystal filter, wherein the Lyot-type liquid crystal filter comprises N cascaded Lyot basic structures, each Lyot basic structure consisting of a liquid crystal cell and polarizers symmetrically arranged on both sides of the liquid crystal cell, the optical axes of the polarizers being parallel to each other, and the optical axis direction of the liquid crystal cell forming a 45° angle with the transmission direction of the polarizers; the tuning method includes the following steps:

[0006] a) Set the operating band of the Lyot-type liquid crystal filter to 450-750nm and determine the target center wavelength λc;

[0007] b) Based on the birefringence effect of liquid crystal, a driving voltage is applied to the liquid crystal cell of the last stage in the N-stage Lyot basic structure to adjust its phase delay, so that the phase delay of the liquid crystal cell of this stage gradually decreases from the initial maximum value to 0, thereby realizing that the effective cascaded layer number of the filter decreases from N stages.

[0008] c) When the phase delay of the last stage liquid crystal cell decreases to 0, the Lyot basic structure of that stage enters the all-pass state. At this time, a driving voltage is applied to the liquid crystal cell of the penultimate Lyot basic structure to adjust its phase delay from the initial maximum value to 0, thereby further reducing the effective number of cascaded layers.

[0009] d) Repeat step c) sequentially apply driving voltages to the liquid crystal cells of each Lyot basic structure from back to front and adjust their phase delay to 0 until the target filtering bandwidth is obtained;

[0010] The phase retardation is determined by the ordinary refractive index n of the liquid crystal. o Unusual refractive index n e The thickness d of the liquid crystal cell and the wavelength λ of the incident light determine the relationship Δφ=2πΔnd / λ (Δn=n e -n o (where λ is the birefringence coefficient of the liquid crystal); the filter bandwidth is obtained by solving the full width at half maximum (FWHM) of the system's spectral transmittance curve, specifically, by calculating the transmittance at the center wavelength λc, T = 0.5T(λ). c The corresponding wavelengths λ1 and λ2 on both sides are calculated as follows:

[0011] .

[0012] N represents the number of liquid crystal cascade layers, corresponding to the initial phase retardation range of the liquid crystal cells in each Lyot basic structure (2). N-M-1 +1)λ-2 N-1 λ, where M is the number of cascaded layers with a phase delay of 0.

[0013] Furthermore, in steps b) and c), the application of the driving voltage causes the orientation angle θ of the liquid crystal molecules to be continuously adjusted from 0° (parallel to substrate orientation) to 90° (perpendicular to the electric field direction), by changing the unusual refractive index n. e Achieve continuous adjustment of the phase delay.

[0014] Furthermore, the tuning range of the filter bandwidth is 21.9nm-36.5nm, and the filter bandwidth is linearly positively correlated with the target center wavelength λc.

[0015] Furthermore, when N=5, adjusting the phase delay of the 5th liquid crystal cell within the range of 9λ-16λ can achieve narrowband tuning of 16.6nm-24.1nm;

[0016] After the 5th stage enters the all-pass state, adjusting the phase delay of the 4th stage liquid crystal cell within the range of 5λ-8λ can achieve broadband tuning of 33.3nm-45.8nm.

[0017] Furthermore, the system's filtering bandwidth is obtained based on the spectral transmittance curve of a multi-stage Lyot structure, fully considering the limiting effect of each stage of the liquid crystal cell on the spectral bandwidth.

[0018] Furthermore, during the tuning process, the optical hardware structure of the filter remains unchanged, and the effective number of cascaded layers is dynamically adjusted only through electronic control.

[0019] Furthermore, during the fabrication of the 5-layer cascaded structure experimental device, liquid crystal compensation layers are inserted into the 4th and 5th stages. The liquid crystal molecules in the compensation layer are orthogonal to the original liquid crystal cell, thereby compensating for the untunable quantities and achieving the purpose of zero phase delay tuning.

[0020] With the above structure, the present invention has the following advantages: no need to modify the hardware structure, convenient tuning: the present invention adjusts the phase delay of each liquid crystal cell through electronic control, without replacing the liquid crystal cell, adjusting the polarizer angle or changing the cascade structure, so as to realize the dynamic switching of the effective cascaded layer. The operation is simple, the response is fast, and the equipment maintenance cost is reduced.

[0021] Wide tuning range and strong adaptability: The filter bandwidth can be flexibly tuned in the range of 21.9nm-36.5nm, and supports precise tuning of narrowband (16.6nm-24.1nm) and wideband (33.3nm-45.8nm), which can meet the differentiated needs of different scenarios such as high spectral resolution, wide spectral imaging, and optical communication.

[0022] High tuning accuracy and good stability: Based on the continuous tuning characteristics of liquid crystal birefringence effect, the phase delay can be finely adjusted. Combined with the accurate calculation method of the full width at half maximum (FWHM) of the system spectral transmittance curve, the tuning accuracy of the filter bandwidth is ensured. At the same time, the bandwidth is linearly positively correlated with the center wavelength, and the filtering characteristics are stable and controllable.

[0023] Strong structural compatibility and wide range of applications: This invention is applicable to multi-cascaded Lyot-type liquid crystal filters, is compatible with the existing Lyot structure design framework, and can be directly applied to various optical systems such as hyperspectral imagers, optical sensors, and laser communication equipment, thus expanding the application boundaries of traditional Lyot-type liquid crystal filters. Attached Figure Description

[0024] Figure 1 A schematic diagram of optical wave transmission in a single-cascaded Lyot structure, which is a bandwidth tuning method for Lyot-type liquid crystal filters.

[0025] Figure 2 This is a schematic diagram of the bandwidth tuning structure of a Lyot-type liquid crystal filter bandwidth tuning method.

[0026] Figure 3 This is a schematic diagram showing the relationship between the full width at half maximum (FWHM) and phase delay of a Lyot-type liquid crystal filter bandwidth tuning method.

[0027] Figure 4 This is a schematic diagram showing the relationship between the full width at half maximum (FWHM) and the center wavelength of a Lyot-type liquid crystal filter bandwidth tuning method.

[0028] Figure 5 This is a diagram of an experimental setup for a Lyot-type liquid crystal filter bandwidth tuning method.

[0029] Figure 6 This is a transmittance curve of a Lyot-type liquid crystal filter bandwidth tuning method under different spectral bandwidths.

[0030] Figure 7 This is a comparison chart of experimental and theoretical data for a Lyot-type liquid crystal filter bandwidth tuning method. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings.

[0032] Combined with appendix Figure 1-7 A method for bandwidth tuning of a Lyot-type liquid crystal filter, wherein the Lyot-type liquid crystal filter comprises N cascaded Lyot basic structures, each Lyot basic structure consisting of a liquid crystal cell and polarizers symmetrically arranged on both sides of the liquid crystal cell, the optical axis of the liquid crystal cell forming a 45° angle with the transmission direction of the polarizer, and the tuning method comprising the following steps:

[0033] a) Set the operating wavelength of the Lyot-type liquid crystal filter to 450-750nm, and determine the target center wavelength λ. c ;

[0034] b) Based on the birefringence effect of liquid crystal, a driving voltage is applied to the liquid crystal cell of the last stage in the N-stage Lyot basic structure to adjust its phase delay, so that the phase delay of the liquid crystal cell of this stage gradually decreases from the initial maximum value to 0, thereby realizing that the effective cascaded layer number of the filter decreases from N stages.

[0035] c) When the phase delay of the last stage liquid crystal cell decreases to 0, the Lyot basic structure of that stage enters the all-pass state. At this time, a driving voltage is applied to the liquid crystal cell of the penultimate Lyot basic structure to adjust its phase delay from the initial maximum value to 0, thereby further reducing the effective number of cascaded layers.

[0036] d) Repeat step c) sequentially apply driving voltages to the liquid crystal cells of each Lyot basic structure from back to front and adjust their phase delay to 0 until the target filtering bandwidth is obtained;

[0037] The phase retardation is determined by the ordinary refractive index n of the liquid crystal. o Unusual refractive index n e The thickness d of the liquid crystal cell and the wavelength λ of the incident light determine the relationship Δφ=2πΔnd / λ (Δn=n e -n o (where λ is the birefringence coefficient of the liquid crystal); the filter bandwidth is obtained by solving the full width at half maximum (FWHM) of the system's spectral transmittance curve, specifically, by calculating the transmittance at the center wavelength λc, T = 0.5T(λ). c The corresponding wavelengths λ1 and λ2 on both sides are calculated as follows:

[0038] .

[0039] Introduction to Lyot-type filters:

[0040] The Lyot-type filter is an optical filter based on the anisotropy of liquid crystals. Its core structure consists of a pair of parallel polarizers P1 and P2 and a liquid crystal cell inserted in between. Figure 1 As shown in the diagram, in this filtering structure, the optical axis of the liquid crystal cell forms a 45° angle with the transmission direction of the polarizer. When the incident light wave passes through P1, it forms linearly polarized light and enters the liquid crystal layer. Due to the birefringence effect of the liquid crystal, this linearly polarized light is decomposed into two coherent linearly polarized beams—ordinary light (o-ray) and extraordinary light (e-ray). These two beams experience phase delay due to the difference in refractive index during propagation, and eventually interfere at P2, thus achieving wavelength-selective filtering. The relationship between the interference intensity and wavelength is as follows:

[0041]

[0042] Birefringence is the core physical mechanism of LCTF, and its macroscopic manifestation is the decomposition of incident light into o-rays and e-rays with orthogonal vibration directions. Therefore, the strength of the birefringence effect is characterized by Δn:

[0043]

[0044] Here n o and n eThese are the ordinary and unusual refractive indices of the liquid crystal, respectively. This parameter quantitatively describes the difference in refractive properties of the liquid crystal material for light waves with two orthogonal polarization directions. When a light beam with wavelength λ passes through a liquid crystal cell with thickness d, the following relationship holds:

[0045]

[0046] For positively dielectric anisotropic liquid crystals, when an external voltage is applied, the electric field changes the orientation angle θ of the liquid crystal molecules, thereby affecting the unusual refractive index n. e :

[0047]

[0048] Specifically, as the voltage increases, the liquid crystal molecules gradually shift from an orientation parallel to the substrate (θ=0°) to an orientation perpendicular to the electric field (θ=90°), resulting in n e It exhibits continuously adjustable characteristics. Therefore, as can be seen from equations (1) and (3), when a voltage is applied, the transmittance can be tuned, thereby obtaining peak transmittance at different wavelengths.

[0049] LCTF employs a multi-stage Lyot cascade design, when the filtering wavelength is λ. c When the transmittance of LCTF is such that:

[0050] (5)

[0051] Where N represents the number of cascaded filter layers. At this point, the liquid crystal in each stage satisfies the following relationship:

[0052]

[0053] The filtering characteristics of LCTF can be simulated and analyzed according to formula (5).

[0054] Methods for solving half-width at half-height (FWHM):

[0055] Spectral bandwidth, as a key parameter characterizing the spectral resolution of a filter, is determined by the full width at half maximum (FWHM) of the transmission spectrum at the center wavelength.

[0056] This invention employs a method for calculating the FWHM (Frequency Wide Width) using the system's spectral transmittance curve. First, the system's spectral transmittance curve is calculated using formula (5). Then, based on the definition of FWHM, the transmittance T = 0.5T(λ) is calculated on both sides of the center wavelength. c Given the corresponding wavelengths λ1 and λ2, calculate the filter bandwidth:

[0057]

[0058] Tuning method

[0059] For traditional Lyot-type filters, when the system structure parameters remain unchanged, the filtering bandwidth is also fixed, making it difficult to adapt to the differentiated requirements of spectral filtering characteristics in different application scenarios. Specifically, high spectral resolution requires optical systems to have narrowband filtering characteristics; while in other application scenarios, light energy transmission efficiency is more important, and the requirements for spectral bandwidth are relatively relaxed. This invention aims to achieve flexible tuning of the system bandwidth by flexibly controlling the liquid crystal device without changing the existing hardware structure, thereby meeting the differentiated requirements of spectral characteristics in different application scenarios. As a piezoelectric material, liquid crystal's molecular orientation rotates with changes in applied voltage, allowing for continuous adjustment of the phase retardation. Specifically, the phase retardation of the liquid crystal can be continuously adjusted between 0 and its maximum value. Utilizing the tuning characteristics of liquid crystal devices, this paper proposes... Figure 3 The liquid crystal tuning scheme shown achieves flexible tuning of the filter bandwidth. By applying the maximum driving voltage to the last cascaded layer sequentially, the phase retardation of the corresponding liquid crystal layer gradually decreases until it reaches 0, thereby achieving bandwidth tuning within a fixed number of cascaded layers and gradually reducing the effective filtering layers of the LCTF, ultimately achieving a gradual increase in bandwidth. Assuming the total number of cascaded layers of the LCTF is N and the number of cascaded layers with 0 phase retardation is M (M < N), then its bandwidth tuning range is:

[0060]

[0061] Under the premise of satisfying the phase delay matching condition, the bandwidth achievable within this tuning range exhibits a discrete distribution characteristic. To determine the achievable filter bandwidth, the phase matching condition in equation (6) needs to be restated as follows:

[0062]

[0063] Substituting formula (9) into formula (5) and then combining it with formula (7), the corresponding FWHM can be solved.

[0064] Based on the bandwidth tuning method described above, a simulation analysis is now performed using a five-layer cascaded structure as an example. The operating wavelength is set to 450-750nm, and the center wavelength λ... c =600nm, the obtained bandwidth tuning simulation results are as follows: Figure 4As shown, under all operating states of the five-layer cascaded structure, according to formula (9), it can be calculated that by adjusting the phase delay of the fifth cascade from 9λ to 16λ, a fine-tuned bandwidth of 16.6nm to 24.1nm can be achieved. When the maximum voltage is applied to the fifth cascade to make it enter the full-pass state, the system switches to the four-layer cascaded operating mode. At this time, by adjusting the phase delay of the fourth cascade from 5λ to 8λ, a wider bandwidth of 33.3nm to 45.8nm can be obtained. Therefore, for λc=600nm, by controlling the operating states of the fourth and fifth cascaded structures, the phase delay can be continuously tuned within the range of 5λ to 16λ, achieving bandwidth tuning from 16.6nm to 45.8nm, thereby realizing flexible tuning of the filter bandwidth.

[0065] Furthermore, to investigate the relationship between bandwidth characteristics and wavelength, this study selected multiple characteristic wavelength points at 25nm intervals for simulation, and the results are as follows. Figure 4 As shown, the results indicate that the spectral bandwidth and its tuning range are linearly positively correlated with the center wavelength. Within the 450-750 nm band, when the phase delay is continuously tuned from 5λ to 16λ, the FWHM exhibits a regular discrete variation characteristic, meaning the filter bandwidth can be flexibly tuned between these discrete values. Furthermore, within the 450-750 nm band, its bandwidth tuning range reaches 21.9-36.5 nm. This result demonstrates that continuous phase delay tuning can achieve discrete and flexible control of the filter bandwidth, providing a new approach for expanding the application scenarios of fixed-structure devices.

[0066] To verify the effectiveness of the method of this invention, the working wavelength range was 450-750nm. Nematic liquid crystal material with birefringence Δn of 0.305 (@589nm, 20℃) was selected for the experiment. The required liquid crystal cell thickness for each cascaded layer can be calculated based on the phase retardation. Accordingly, the thickness of each cascaded liquid crystal cell was set. In the actual fabrication process, a hierarchical optimization scheme was adopted. Specifically, the first to fourth layers used liquid crystal cells with cell thicknesses of 10μm, 12μm, 12μm and 15μm, respectively, and the fifth layer used two 20μm liquid crystal cells. It is worth noting that, in order to obtain zero phase delay in the experiment, liquid crystal compensation layers perpendicular to the original liquid crystal molecule orientation were inserted into the 4th and 5th cascades to compensate for the unmodulated phase delay of the liquid crystal cells. Based on the above design, the experimental optical path shown in Figure 7 was constructed. A halogen lamp white light source (Daheng Optoelectronics, model: LGY-B) with fiber optic output was used. The light beam was formed into a parallel beam through a collimating lens. After passing through the aperture stop, the beam passed through the five-layer cascade of LCTF in sequence and was finally focused by the converging lens onto the receiving end of the fiber optic spectrometer (Pusu Optoelectronics Technology Co., Ltd.) to realize real-time spectral detection. In terms of drive control, a self-developed multi-channel low-voltage drive board was used to drive each liquid crystal cell independently.

[0067] Experimental verification was conducted using the aforementioned optical path. A center wavelength of 600 nm was selected. For a 5-layer cascade, by independently adjusting the voltage applied to the fifth liquid crystal layer, two states with a phase delay of 9λ and 16λ were achieved. The filtering curves for these two states are shown below. Figure 6 As shown in the figure, after normalization, the transmittance curves reveal that the filter bandwidth corresponding to a phase retardation of 16λ is less than that of 9λ. To further verify the tunability of the bandwidth jump, the maximum voltage was applied to the fifth liquid crystal layer, while simultaneously controlling the phase retardation of its compensation layer to be equal to the inherent untunable value of that layer. This resulted in an effective phase retardation of 0 for the fifth cascade. In this case, the cascade does not contribute to the phase in the optical path, thus functionally it can be considered as "inactive." Similarly, different voltages were applied to the fourth liquid crystal layer, resulting in phase retardations of 5λ and 8λ, respectively. The experimental results are as follows: Figure 6 As shown, as the phase delay of the fourth layer increases, its bandwidth gradually narrows. Therefore, by adjusting the voltage of different liquid crystal layers, the bandwidth can be flexibly tuned.

[0068] Furthermore, to fully verify the effectiveness of bandwidth tuning, the aforementioned phase delay control method was used to quantitatively analyze the bandwidth tuning of the 5-layer cascaded filter structure. The results are as follows: Figure 7 As shown, simulation data was also included in the figure to compare and analyze the experimental and simulation results. In the experiment, only the 5th and 4th liquid crystal layers were flexibly adjusted. The phase delay of the 5th layer was controlled between 9λ and 16λ, and that of the 4th layer was controlled between 5λ and 8λ. The results show that the experimentally measured bandwidth is very close to the simulation results, with a maximum deviation of 2.9 nm and a minimum deviation of 0.1 nm. The maximum relative error is less than 3%. This result shows that the filter bandwidth can be flexibly tuned without changing the cascade structure by flexibly adjusting the phase delay of the liquid crystal layers.

[0069] The present invention and its embodiments have been described above. This description is not restrictive, and the actual structure is not limited thereto. In conclusion, if those skilled in the art, inspired by this description, design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the scope of protection of this invention.

Claims

1. A method for flexibly tuning the bandwidth of a Lyot-type liquid crystal filter, characterized in that: The Lyot-type liquid crystal filter includes N cascaded Lyot basic structures. Each Lyot basic structure consists of a liquid crystal cell and two parallel polarizers symmetrically arranged on both sides of the liquid crystal cell. The director of the liquid crystal cell forms a 45° angle with the transmission direction of the polarizers. The tuning method includes the following steps: a) Set the operating wavelength of the Lyot-type liquid crystal filter to 450-750nm, and determine the target center wavelength λ. c ; b) Based on the birefringence effect of liquid crystal, a driving voltage is applied to the liquid crystal cell of the last stage (Nth stage) in the N-stage Lyot basic structure to adjust its phase delay, so that the phase delay of the liquid crystal cell of this stage gradually decreases from the initial maximum value to 0, thereby realizing that the effective cascaded layer number of the filter decreases from the Nth stage. c) When the phase delay of the Nth stage liquid crystal cell decreases to 0, the Lyot basic structure of that stage enters the all-pass state. At this time, a driving voltage is applied to the liquid crystal cell of the N-1th stage Lyot basic structure to adjust its phase delay from the initial maximum value to 0, thereby further reducing the effective number of cascaded layers. d) Repeat step c) sequentially apply driving voltages to the liquid crystal cells of each Lyot basic structure from back to front and adjust their phase delay to 0 until the target filtering bandwidth is obtained; The phase retardation is determined by the ordinary refractive index n of the liquid crystal. o Unusual refractive index n e The thickness d of the liquid crystal cell and the wavelength λ of the incident light determine the relationship Δφ=2πΔnd / λ (Δn=n e -n o (where is the birefringence coefficient of the liquid crystal); the filter bandwidth is obtained by solving the full width at half maximum (FWHM) of the system's spectral transmittance curve. Specifically, the wavelengths λ1 and λ2 on both sides of the transmittance T = 0.5T(λc) at the center wavelength λc are calculated. The filter bandwidth is calculated as follows: 。 2. The bandwidth flexible tuning method for a Lyot-type liquid crystal filter according to claim 1, characterized in that: In steps b) and c), the application of the driving voltage causes the orientation angle θ of the liquid crystal molecules to be continuously adjusted from 0° (parallel to substrate orientation) to 90° (perpendicular to the electric field direction), by changing the unusual refractive index n. e Achieve continuous adjustment of the phase delay.

3. The bandwidth flexible tuning method for a Lyot-type liquid crystal filter according to claim 1, characterized in that: The tuning range of the filter bandwidth is 21.9nm-36.5nm, and the filter bandwidth is related to the target center wavelength λ. c They exhibit a linear positive correlation.

4. The bandwidth flexible tuning method for a Lyot-type liquid crystal filter according to claim 1, characterized in that: When N=5, adjusting the phase delay of the 5th liquid crystal cell within the range of 9λ-16λ can achieve narrowband tuning of 16.6nm-24.1nm. After the 5th stage enters the all-pass state, adjusting the phase delay of the 4th stage liquid crystal cell within the range of 5λ-8λ can achieve broadband tuning of 33.3nm-45.8nm.

5. The bandwidth flexible tuning method for a Lyot-type liquid crystal filter according to claim 1, characterized in that: The system's filtering bandwidth is obtained based on the spectral transmittance curve of a multi-stage Lyot structure, fully taking into account the limiting effect of each stage of the liquid crystal cell on the spectral bandwidth.

6. The bandwidth flexible tuning method for a Lyot-type liquid crystal filter according to claim 1, characterized in that: During the tuning process, the optical hardware structure of the filter remains unchanged, and the effective number of cascaded layers is dynamically adjusted only through electronic control.

7. The bandwidth flexible tuning method for a Lyot-type liquid crystal filter according to claim 1, characterized in that: During the fabrication of the 5-layer cascaded structure experimental device, liquid crystal compensation layers are inserted into the 4th and 5th stages. The liquid crystal molecules in the compensation layer are orthogonal to the original liquid crystal cell, thereby compensating for the untunable quantities and achieving the purpose of zero phase delay tuning.

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