Phase-shifting four-shearing interferometry system based on active liquid crystal chessboard grating
By using a phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating and employing a five-channel liquid crystal controller to achieve synchronous linkage control of the light beam, the problems of redundant optical paths and stability in traditional systems are solved, enabling high-speed, automated dynamic measurement and multi-wavelength adaptation.
Patent Information
- Application Number
- CN202521854643.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-29
- Publication Date
- 2026-08-25
- Estimated Expiration
- 2035-08-29
AI Technical Summary
Traditional phase-shifting four-shear interferometry systems have long optical paths, a large number of components, and are easily affected by mechanical vibrations, making them difficult to meet the requirements of high-speed and dynamic measurements, and they also have a low degree of automation.
A phase-shifting four-shearing interferometer system based on an active liquid crystal checkerboard grating is adopted. The synchronous linkage control of the beam is realized through a five-channel liquid crystal controller, including an active two-dimensional checkerboard liquid crystal grating and a four-segment active liquid crystal phase delayer, which supports microsecond-level electrically controlled phase shift and multi-wavelength adaptation.
It achieves high-speed dynamic measurement, simplifies the hardware structure, improves the control accuracy and automation level, supports real-time adaptive adjustment, and adapts to the rapid switching of various laser wavelengths.
Smart Images
Figure CN224682490U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of optical interference, and in particular to a phase-shifting four-shearing interference system based on an active liquid crystal checkerboard grating. Background Technology
[0002] Traditional transverse four-shear interferometry (two orthogonal directions, each with positive and negative shearing) typically requires multiple beam splitters, mirrors, or rotating diffraction gratings for multiple beam splitting and shearing direction controls. This results in a long optical path, numerous components, large system size, difficult assembly and adjustment, and stability susceptible to mechanical vibration and environmental influences. Phase-shifting interferometry (such as four-step phase shifting) is often achieved by mechanically moving a reference mirror (piezoelectric ceramic PZT), rotating a waveplate, or using acousto-optic / electro-optic modulators. Mechanical movement is slow, prone to backlash errors, and has limited reliability; rotating a waveplates require precise mechanical structures and are difficult to switch at high speeds; dedicated electro-optic / acousto-optic modulators are expensive and may introduce additional aberrations. These methods are difficult to meet the requirements of high-speed, dynamic measurements. In four-shear interferometry, it is necessary to simultaneously and independently introduce precisely controllable phase delays (e.g., 0°, 90°, 180°, 270°) into the beams in four different shearing directions (+x, -x, +y, -y) to achieve synchronous four-step phase shifting. Traditional methods struggle to physically separate and independently control the phases of the four beams, typically requiring highly complex optical path designs or multiple independent phase shifters, significantly increasing system complexity and cost. Since beam splitting, shearing control, and phase shifting all rely on discrete optomechanical components, the overall system integration is low, hindering miniaturization. Furthermore, the slow mechanical phase shifting speed limits its application in real-time, dynamic wavefront measurements (such as in vivo biological measurements, online detection, and adaptive optics closed-loop control). Changing the shearing amount or performing phase shift measurements often requires manual adjustment of the aperture, replacement of the grating, or manual operation of the phase shifting mechanism, a cumbersome process with low automation, hindering rapid and efficient measurements. Therefore, it is necessary to propose a fast and efficient phase-shifting four-shearing interferometry system. Utility Model Content
[0003] Purpose of the utility model: The purpose of this utility model is to provide a phase-shifting four-shearing interference system based on an active liquid crystal checkerboard grating.
[0004] Technical Solution: This utility model is a phase-shifting four-shearing interference system based on an active liquid crystal checkerboard grating, comprising a laser, a collimating lens, a linear polarizer, an active two-dimensional checkerboard liquid crystal grating, a first Fourier lens, a five-channel liquid crystal controller, a pinhole aperture, a second Fourier lens, a four-segment active liquid crystal phase delay unit, and a CCD camera. The laser emitted by the laser is collimated by the collimating lens, and the incident light is modulated into linearly polarized light in a specific direction by the linear polarizer. Then, different voltages are applied by the driving circuit through the active two-dimensional checkerboard liquid crystal grating to change the orientation of the liquid crystal molecules. After that, the light field of the active two-dimensional checkerboard liquid crystal grating is Fourier transformed to the back focal plane by the first Fourier lens, and high-frequency stray light is filtered out by the pinhole aperture. The filtered spectral light field is inversely transformed back to the spatial domain by the second Fourier lens. Finally, the phase delay adjustment in the range of 0-2π is achieved by the four-segment active liquid crystal phase delay unit to realize phase shift, generating interference fringes. The acquisition processor acquires the interference fringe image and converts the optical signal into a digital signal for transmission to the data processing unit.
[0005] Furthermore, the collimating lens is a cemented doublet achromatic collimating lens, which converts the divergent beam emitted by the laser into a parallel beam through refraction.
[0006] Furthermore, the active two-dimensional checkerboard liquid crystal grating is composed of two ITO glass sheets sandwiching a liquid crystal layer, with a two-dimensional checkerboard pattern laser-written on the surface.
[0007] Furthermore, both the first Fourier lens and the second Fourier lens are plano-convex lenses with a focal length of 100mm.
[0008] Furthermore, the aperture of the pinhole stop is 50 μm and is located at the back focal plane of the first Fourier lens, allowing only the zeroth and ±1st order diffracted light to pass through.
[0009] Furthermore, the four-zone active liquid crystal phase delay unit is divided into four independent control regions, each equipped with an independent driving electrode.
[0010] Furthermore, the CCD camera uses a high-resolution area array CCD with a pixel resolution of 2048×2048 and a frame rate of 30fps.
[0011] Beneficial effects: Compared with the prior art, this invention has the following advantages: It can achieve microsecond-level electrically controlled phase shift and support high-speed dynamic measurement; it achieves wavelength adaptation through electrically tunable diffraction efficiency; it breaks through the temporal limitation through spatial partitioning; it realizes the synchronous linkage of "wavelength-shearing-phase shift" parameters, improving the control accuracy; it simplifies the hardware structure and reduces the complexity of system integration; and it supports real-time adaptive adjustment in dynamic scenarios. Attached Figure Description
[0012] Figure 1This is a schematic diagram of the structure of this utility model;
[0013] Figure 2 This is an ITO design drawing for a four-zone active liquid crystal phase delay liquid crystal cell product. Detailed Implementation
[0014] The technical solution of this utility model will be further described below with reference to the accompanying drawings.
[0015] This invention relates to a phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating, comprising three main parts: a light source and initial modulation module, a beam processing module, and a phase-shifting and detection module. These modules work closely together to achieve transverse four-shearing interferometry and phase-shifting functions.
[0016] like Figure 1 The diagram illustrates the core working logic of the optical path. Laser 1 generates a coherent beam, which is collimated and polarized, then split and sheared by a liquid crystal grating. After Fourier transform and filtering, a phase shift is achieved using a liquid crystal phase delay unit, ultimately generating interference fringes which are then acquired and processed by CCD camera 10.
[0017] (a) The light source and initial modulation module includes a laser 1, a collimating lens 2, and a linear polarizer 3;
[0018] Laser 1: A highly coherent semiconductor laser is selected to output a laser beam with a stable wavelength, providing a basic light source for interferometric measurements. Its coherence length meets the requirements of multi-beam interference in the optical path, ensuring the stability and clarity of the interference fringes.
[0019] Collimating Lens 2: A cemented doublet achromatic collimating lens is used to convert the divergent beam emitted by the laser into a parallel beam through refraction, reducing the beam divergence angle to below 0.1 mrad, ensuring uniform transmission of the beam in the subsequent optical path, and reducing energy loss.
[0020] Linear polarizer 3: Using a high-performance polarizer, incident light can be modulated into linearly polarized light in a specific direction, laying the foundation for subsequent optical path control based on polarization characteristics.
[0021] (ii) The beam processing module includes an active two-dimensional checkerboard liquid crystal grating 4, a first Fourier lens 5, a pinhole aperture 7, and a second Fourier lens 8.
[0022] Active two-dimensional checkerboard liquid crystal grating 4: It consists of two ITO glass sheets sandwiching a liquid crystal layer, with a two-dimensional checkerboard pattern laser-written on the surface. By applying different voltages through an external driving circuit, the orientation of the liquid crystal molecules is changed, and the diffraction efficiency of the grating is dynamically adjusted.
[0023] First Fourier lens 5 and pinhole aperture 7:
[0024] The first Fourier lens 5 is a plano-convex lens with a focal length of 100mm, which performs Fourier transform on the light field distribution of the liquid crystal grating to the back focal plane.
[0025] The pinhole stop 7 has an aperture of 50μm and is set at the back focal plane of the Fourier lens 1. It only allows zero-order and ±1-order diffracted light to pass through, effectively filtering out high-frequency stray light and improving beam quality.
[0026] The second Fourier lens 8 uses the same parameters as the Fourier lens 1 to inversely transform the filtered spectral light field back into the spatial domain, preparing for subsequent phase shifting and interference.
[0027] (III) The phase shift and detection module includes a four-zone active liquid crystal phase delayer 9, a linear polarizer 3, and a CCD camera 10;
[0028] The four-segment active liquid crystal phase delay circuit 9: It divides the circuit into four independent control regions, each equipped with an independent driving electrode. Different voltages are applied to the four regions via a driving circuit to achieve phase delay adjustment within the range of 0-2π. For example, in four-shear phase-shift interference, the four regions are sequentially controlled to generate phase delays of 0, π / 2, π, and 3π / 2, obtaining four sets of interference fringes with different phases, such as... Figure 2 As shown.
[0029] Linear polarizer 3: Further optimizes the polarization state of light to ensure that the interference light enters the CCD camera 10 in the best state.
[0030] CCD Camera 10: Utilizes a high-resolution area array CCD with a pixel resolution of 2048×2048 and a frame rate of 30fps, enabling rapid acquisition of interference fringe images and conversion of optical signals into digital signals for transmission to the data processing unit.
[0031] I. Breakthrough in Grating Technology: "Active and Controllable Two-Dimensional Shearing + Multi-Wavelength Adaptation"
[0032] In traditional shearing interferometry, the diffraction efficiency and applicable wavelength of the grating are fixed (e.g., only suitable for 632.8nm helium-neon lasers). If the light source wavelength is changed (e.g., 532nm green light), the grating must be replaced, which is complex and costly. This invention's active two-dimensional checkerboard liquid crystal grating achieves dynamic adjustment of diffraction efficiency and multi-wavelength adaptation through voltage regulation.
[0033] Core principle: The birefringence of liquid crystal molecules changes with voltage. By outputting a gradient voltage through the liquid crystal controller, the equivalent refractive index periodic distribution of the grating can be changed, thereby adjusting the diffraction efficiency (0-90% continuously adjustable).
[0034] Multi-wavelength adaptation: When the light source wavelength is switched from 632.8nm to 532nm, the diffraction efficiency can be maintained above 80% simply by adjusting the voltage of the LCD controller, without the need to replace the grating element. The adapted wavelength range covers 400-1100nm (including visible light to near infrared).
[0035] This feature overcomes the limitation of traditional gratings being "single wavelength compatible", making the system compatible with a variety of lasers (such as helium-neon lasers, semiconductor lasers, and fiber lasers).
[0036] II. Integrated Optical Path and Dynamic Control Design of "Active Shearing + Four-Party Phase Shift"
[0037] Based on the existing integrated "shearing-phase shifting" technology, and combined with the multi-wavelength adaptation capability of the grating, a full-link dynamic control advantage is further formed: In addition to realizing the adjustment of shearing amount and shearing direction switching in the x and y directions (x alone, y alone, and two-dimensional simultaneously), the active two-dimensional checkerboard liquid crystal grating can meet the shearing requirements of different wavelength light sources. The four-segment active liquid crystal phase delay unit is adapted to multiple wavelength light sources: For linearly polarized light of different wavelengths, by adjusting the voltage of each segment, the phase shift accuracy (0.01π) remains unchanged, avoiding phase shift errors caused by wavelength changes.
[0038] The two work together to achieve coordinated control of "wavelength-shearing-phase shift", which can be adapted to multiple measurement scenarios (such as 632nm for lens detection and 808nm for infrared material detection) without adjusting the optical path structure.
[0039] Three- or four-part delayer spatial registration structure
[0040] This invention features a pioneering spatial matching design between a fan-shaped four-segment retarder and the spectral surface beam of a 4f system. The retarder segmentation angle is 90° × 4 segments. The beam spot-segment mapping effect achieves physical optical path separation of the four beams, enabling full-resolution parallel phase shifting.
[0041] Four- and five-channel LCD controllers coordinate to control the active raster and the four-zone LCD cell.
[0042] A four-step phase-shift hardware synchronous control process based on a five-channel LCD controller (cooperative control of active grating and delay unit).
[0043] By employing a five-channel LCD controller (one channel for the active two-dimensional checkerboard LCD grating, and four channels corresponding to the four zones of the four-zone active LCD phase delay unit) to simultaneously control the core components, the shortcomings of the traditional discrete control mode can be fundamentally solved. Specific advantages are as follows:
[0044] (1) Achieve synchronous linkage of "wavelength-shearing-phase shift" parameters to improve control accuracy.
[0045] There is a strong correlation between the parameters of the active two-dimensional checkerboard liquid crystal grating and the four-segment liquid crystal retarder. When the wavelength of the light source changes, the shearing amount of the grating (dependent on diffraction efficiency) and the phase shift of the retarder (dependent on birefringence effect) need to be adjusted synchronously to ensure the interference effect.
[0046] The five-channel LCD controller achieves centralized control through the same main control chip:
[0047] When switching wavelengths (e.g., from 632.8nm to 532nm), the controller first outputs a control voltage to the grating through the built-in wavelength-voltage mapping algorithm (pre-stores the optimal voltage parameters corresponding to wavelengths of 400-1100nm) to ensure diffraction efficiency ≥80%.
[0048] Simultaneously, synchronous voltages are output to the four zones of the four-zone delay unit (e.g., zone I increases from 1.25V to 1.5V), ensuring that the phase shift remains at a precise difference of 0, π / 2, π, and 3π / 2. This avoids the 10-20ms parameter mismatch time caused by "the grating has been adjusted but the delay unit has not responded" in traditional discrete control, effectively shortening the interference fringe stabilization time and controlling the phase shift accuracy fluctuation within ±0.005π.
[0049] (2) Simplify hardware structure and reduce system integration complexity.
[0050] In traditional solutions, gratings and delay units need to be equipped with independent controllers (at least two controllers), which leads to problems such as complex wiring, poor power supply compatibility (different controllers may have different power supply voltages), and high duty cycles.
[0051] The five-channel LCD controller adopts an integrated design:
[0052] Hardware level: It integrates a single-channel grating drive module and a four-channel partition delay drive module, sharing a 5V power supply and heat sink. Compared with discrete solutions, it reduces a large number of circuit components (such as reducing 3 power management chips and 8 sets of wiring terminals). The overall size of the optical path system is reduced to 1 / 3 of the traditional solution (it can be integrated into a compact control box).
[0053] At the software level: Parameter configuration is achieved through the same firmware program, eliminating the need for communication calibration between two controllers and reducing the difficulty of system debugging.
[0054] (3) Supports real-time adaptive adjustment in dynamic scenarios
[0055] When measuring dynamically changing objects (such as phase fluctuations caused by temperature gradients or optical path shifts under vibration), it is necessary to adjust the grating shearing and retarder phase shift in real time to compensate for interference.
[0056] The centralized architecture of the five-way controller provides rapid response capabilities:
[0057] When the contrast of the interference fringes acquired by the CCD decreases (e.g., from 0.8 to 0.4), the controller analyzes the fringe changes through a real-time feedback algorithm (sampling frequency 1kHz) and synchronously outputs a fine-tuning voltage to the grating (e.g., ±0.1V to adjust the shearing amount and optimize the beam overlap).
[0058] The compensation voltage is output to the delay unit section (e.g., 0.02V is added to a section to correct the phase shift deviation). The entire adjustment process is completed within 10ms. In contrast, traditional discrete control has an adjustment response time of more than 50ms due to the separation of the feedback link, and is prone to losing dynamic measurement data.
[0059] In summary, the core value of the five-channel LCD controller lies in its ability to upgrade the active grating and LCD delay unit from "independent operation" to "coordinated operation" through the synergistic effect of "synchronous control - structural simplification - adaptive response". It retains the innovative features of multi-wavelength adaptation, dynamic shearing and precise phase shifting in the solution, while solving the practical problems of parameter matching, system integration and scenario expansion at the hardware level, further improving the feasibility and practical value of the solution.
Claims
1. A phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating, characterized in that: The system includes a laser (1), a collimating lens (2), a linear polarizer (3), an active two-dimensional checkerboard liquid crystal grating (4), a first Fourier lens (5), a five-channel liquid crystal controller (6), a pinhole aperture (7), a second Fourier lens (8), a four-segment active liquid crystal phase delay unit (9), and a CCD camera (10). The laser emitted by the laser (1) is collimated by the collimating lens (2), and the incident light is modulated into linearly polarized light in a specific direction by the linear polarizer (3). Then, the light is driven by the active two-dimensional checkerboard liquid crystal grating (4) and different electrical currents are applied by the driving circuit. The light field of the active two-dimensional checkerboard liquid crystal grating (4) is transformed to the back focal plane by the first Fourier lens (5), and the high-frequency stray light is filtered out by the pinhole aperture (7). The filtered spectral light field is then inversely transformed back to the spatial domain by the second Fourier lens (8). Finally, the phase delay adjustment in the range of 0-2π is achieved by the four-segment active liquid crystal phase delay device (9) to achieve phase shift and generate interference fringes. The CCD camera (10) collects the interference fringe image and converts the light signal into a digital signal to be transmitted to the data processing unit.
2. The phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating according to claim 1, characterized in that: The collimating lens (2) is a cemented doublet achromatic collimating lens, which converts the divergent beam emitted by the laser into a parallel beam through refraction.
3. The phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating according to claim 1, characterized in that: The active two-dimensional checkerboard liquid crystal grating (4) is composed of two ITO glass plates sandwiching a liquid crystal layer, and the surface is laser-written with a two-dimensional checkerboard pattern.
4. The phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating according to claim 1, characterized in that: Both the first Fourier lens (5) and the second Fourier lens (8) are plano-convex lenses with a focal length of 100mm.
5. The phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating according to claim 1, characterized in that: The aperture of the pinhole stop (7) is 50 μm and is set at the back focal plane of the first Fourier lens (5), allowing only the zeroth and ±1st order diffracted light to pass through.
6. The phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating according to claim 1, characterized in that: The four-zone active liquid crystal phase delay unit (9) is divided into four independent control regions, each equipped with an independent driving electrode.
7. The phase-shifting four-shearing interferometry system based on an active liquid crystal checkerboard grating according to claim 1, characterized in that: A linear polarizer (3) is provided between the CCD camera (10) and the four-segment active liquid crystal phase delay unit (9).