Holographic interference fringe phase and period synchronous locking device and method

Abstract

According to the device and the method for synchronously locking the phase and the period of the holographic interference fringes, two sets of locking devices are adopted and are respectively arranged at two ends of a holographic interference exposure field in the same direction as the period of the interference fringes, one set is used for compensating the phase of the interference light field to lock the phase of the interference fringes, and the other set is used for locking the period of the interference fringes. And the other one is used for compensating the output laser frequency of the laser to lock the interference fringe period. According to the interference fringe phase and period synchronous locking method, the problem that the contrast ratio of interference fringes is degraded due to phase and period drift of the interference fringes in the exposure process of a large-aperture holographic grating is solved, and particularly an interference fringe period real-time locking module is used; the problem that the fringe contrast is gradually deteriorated in the periodic direction due to periodic change of interference fringes is effectively solved, and a reliable solution is provided for preparation of the meter-scale large-aperture, high-contrast and high-uniformity holographic grating.

Description

Technical Field

[0001] The present invention belongs to the field of large-aperture diffraction grating fabrication, and particularly relates to a device and method for synchronously locking the phase and period of holographic interference fringes.

[0002] , which is used to solve the problem of deteriorated fringe contrast caused by phase drift and period change of interference fringes during the fabrication of meter-scale ultra-large-aperture holographic gratings. It aims at the fringe locking technology for large-aperture interference exposure fields and solves the problem of high-contrast interference exposure lithography for large-aperture photoresist grating masks. Background Art

[0003] Meter-scale large-aperture diffraction gratings have important application values in the fields of ultra-intense and ultra-short laser technology, laser weapons, and high-precision displacement measurement. At present, the two-beam holographic interference exposure technology is the mainstream technical solution for fabricating large-aperture diffraction gratings. In this solution, two large-aperture ultraviolet parallel beams overlap in the photoresist film coated on the surface of the grating substrate, forming periodic interference fringes that are recorded inside the photoresist. Subsequently, a photoresist grating mask is prepared through wet development, and finally, the required diffraction grating element is fabricated through coating replication or etching transfer technology. During the holographic interference exposure process, factors such as the vibration of the external environment and the optical adjustment frame, air flow in the interference optical path, and temperature and humidity changes will cause the drift of the interference fringes, thereby reducing the contrast of the recorded fringes. In severe cases, the interference fringes cannot be recorded, resulting in the failure of grating fabrication.

[0004] In order to actively lock the interference fringe drift, the invention patent with the patent number 200610039967.6 and the invention title "Method and Device for Stabilizing Holographic Interference Fringes with a Control Device" discloses a linear array CCD fitting fringe locking method. This method uses a linear array CCD to collect reference Moiré fringes, finds the wave troughs of the fringes through the fitting method, and locks the phase of the fringes by controlling the piezoelectric ceramics. The invention patent with the patent number 2013106933281 and the invention title "Holographic Grating Exposure Method Using Heterodyne Interference Fringe Locking Control" discloses a heterodyne method fringe locking method. It uses a beam splitter to derive two sub-beams, receives signals with phase receivers respectively, and controls the frequency of the acousto-optic modulator through a human-computer interaction interface and software to lock the interference fringes in real time. The response speed of this method is higher than that of the linear array CCD method. The utility model patent with the patent number 201920855074.1 and the name "An Interference Fringe Locking Control Device" proposes to use two high-speed photodetectors to monitor the Moiré fringe intensity signal and the laser power fluctuation respectively, and make the input drive signal of the acousto-optic modulator more accurate by real-time correcting the reference signal of the PID, improving the high-frequency response speed and locking accuracy of the interference fringes. The existing fringe locking methods only sample and phase-lock a single point position in the entire interference field area. In fact, according to the holographic interference fringe period formula Λ = λ / 2 / sin(θ), it can be seen that when the interference exposure system changes due to the interference angle θ or the laser output wavelength λ, it will also cause the period of the interference fringes in the entire interference area to change, which means the drift of the interference fringes and the decrease of the contrast. Especially when the grating aperture exceeds the meter level, a change in the interference fringe period of picometer level may cause a change of micrometer level in the fringes at the edge position of the interference field, which will seriously affect the fringe contrast of the large-aperture grating. Taking the 1620mm×1070mm bidirectional meter-level grating (the grating sizes perpendicular and parallel to the grating bars both exceed the meter level, called bidirectional meter-level) being developed by the project team where the applicant of this invention is located as an example, assuming the grating line density is 1400 lines / mm (period 714nm), then there are 2.24×10 6 fringes within the 1600mm effective aperture. In the case of only performing single-point fringe locking at one end of the interference light field, if the fringe period changes by 1pm, the grating fringes at the 1600mm position in the horizontal direction of the grating will move 2.24×10 3 nm, and the fringe drift amount is linearly variable at different positions in the horizontal direction of the grating substrate. This means that for large gratings above the meter level, if only the phase of one position in the interference field is locked without locking the period, it will cause the fringe contrast to gradually deteriorate along the period direction, seriously affecting the groove type contrast and grating quality of the meter-level large grating.

[0005] Therefore, there is an urgent need for a technology that can synchronously lock the phase and period of interference fringes to solve the problem of contrast non-uniformity caused by period drift in the preparation of meter-scale gratings. Summary of the Invention

[0006] Aiming at the problem of contrast degradation caused by interference fringe phase drift and period change during the preparation of meter-scale large-aperture holographic gratings, the present invention proposes a device and method for synchronously locking the phase and period of holographic interference fringes. Through the collaborative control of two sets of independent locking devices, synchronous compensation for the phase of the interference field and the output frequency of the laser is achieved, suppressing the full-field period drift and phase shift, and significantly improving the contrast and uniformity of the grating mask.

[0007] The technical solution of the present invention is as follows:

[0008] A device and method for synchronously locking the phase and period of holographic interference fringes, characterized by two sets of devices for phase locking and period locking, which are respectively installed at both ends of the holographic interference exposure field along the period direction of the interference fringes. One set is used to compensate the phase of the interference light field to lock the phase of the interference fringes, and the other set is used to compensate the output laser frequency of the laser to lock the period of the interference fringes. The whole device includes:

[0009] A tunable laser, used to form a large-area interference fringe to expose the photoresist to form a photoresist grating. At the same time, the output laser frequency is adjustable to achieve compensation for the period of the interference field. The laser can be a fiber laser with an output wavelength in the range of 200nm - 450nm.

[0010] The first photoelectric sampling module and the second photoelectric sampling module, which are composed of a sampling grating, a ground glass, a CCD camera, and an adjustment frame, are respectively fixed at both ends of the grating substrate to be exposed. The surfaces of the sampling gratings in the first photoelectric sampling module and the second photoelectric sampling module are on the same plane as the front surface of the grating substrate, and are used to sample and amplify the interference field fringes, providing feedback information for the subsequent control module.

[0011] A frequency modulation module, used to adjust the output frequency of the tunable laser. It can directly regulate the output wavelength of the tunable laser using an acousto-optic frequency shifter, or regulate the wavelength of the seed light source of the tunable laser using a voltage / current regulation module, and achieve the regulation of the wavelength of the frequency-doubled output ultraviolet laser by changing the wavelength of the seed light source.

[0012] A phase compensation module, including a beam translation module composed of a piezoelectric ceramic and a mirror and a beam translation module controller, mainly uses the piezoelectric ceramic to translate the mirror to compensate the phase of the interference light field and stabilize the holographic interference fringes.

[0013] A method for fringe locking using the above holographic interference fringe phase and period synchronous locking device includes two steps: building a double-beam holographic interference exposure system, building a phase and period synchronous locking system, and locking control. Specifically:

[0014] Step 1) Building a double-beam holographic interference exposure system

[0015] Step 1.1) Place a first half-wave plate and a polarization beam splitter prism in sequence along the transmission direction of the laser beam output by the tunable frequency laser, and divide the laser beam into a transmitted beam and a reflected beam through the polarization beam splitter prism;

[0016] Step 1.2) Place a first mirror, a second half-wave plate, a second mirror, a first focusing objective lens, a first spatial filter, a third mirror, and a first collimating parabolic mirror in sequence along the transmission direction of the transmitted beam output by the polarization beam splitter prism, and expand and collimate the transmitted beam into a large-aperture parallel beam;

[0017] Step 1.3) Place a fourth mirror, a beam translation module, a second focusing objective lens, a second spatial filter, and a second collimating parabolic mirror in sequence along the transmission direction of the reflected beam output by the polarization beam splitter prism, and expand and collimate the reflected beam into another large-aperture parallel beam;

[0018] Step 1.4) Rotate and adjust the first half-wave plate and the second half-wave plate to make the intensities of the two large-aperture parallel beams the same and overlap on the front surface of the grating substrate to form an interference exposure field;

[0019] Step 1.5) Use a high-precision theodolite to measure the angle θ between the two large-aperture parallel beams, and calculate the period Λ of the interference exposure field using the formula Λ = λ / 2 / sin(θ / 2), where λ is the central wavelength output by the tunable frequency laser.

[0020] Step 2) Building a phase and period synchronous locking system and locking control

[0021] Step 2.1) Design and prepare a sampling grating with a period of 2Λ according to the grating period Λ of the double-beam holographic interference exposure system built in the above step 1), assemble the sampling grating at the front ends of the first photoelectric sampling module and the second photoelectric sampling module respectively, and fix the photoelectric sampling modules on the left and right sides of the grating substrate respectively to ensure that the two large-aperture parallel beams overlap on the surface of the sampling grating;

[0022] Step 2.2) Adjust the spatial orientation of the sampling grating so that the ±1st order diffracted lights of the large-aperture parallel beam can interfere to form a Moiré fringe pattern with appropriate thickness;

[0023] Step 2.3) Adjust the focal lengths of the CCD cameras in the first photoelectric sampling module and the second photoelectric sampling module so that the Moiré fringes in step 2.2 are clearly imaged on the CCD;

[0024] Step 2.4) Connect the beam translation module to the beam translation module controller and then to the computer. At the same time, connect the frequency modulation module to the frequency-adjustable laser and the computer respectively;

[0025] Step 2.5) Compile the control program, and according to the moiré fringe offset collected by the first photoelectric sampling module and the second photoelectric sampling module during the exposure process, feedback is respectively used to control the movement of the PZT in the beam translation module and the output voltage of the frequency modulation module, so as to achieve the change of the phase of the large-aperture parallel beam and the change of the grating period Λ formed by the interference of the large-aperture parallel beam, thereby achieving the synchronous locking of the phase and period of the interference fringe.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] 1. Compared with the traditional single-point phase locking scheme, the present invention realizes synchronous locking of the period and phase of the large-aperture holographic interference exposure field, solves the problem of gradual degradation of the contrast of the holographic interference fringes along the period direction due to the slight change (sub-picometer level) of the interference field period during single-point phase locking, greatly improves the fringes contrast of the holographic grating mask along the period direction, and provides a reliable solution for the manufacture of meter-level large-aperture, high-contrast holographic grating masks.

[0028] 2. The present invention controls the period of the holographic interference fringes by tuning the wavelength of the ultraviolet exposure light source, cleverly avoiding the phase crosstalk problem when the period locking and phase locking are synchronously executed in the period locking scheme by adjusting the interference beam angle. Because, if the grating period is locked by adjusting the double-beam interference angle, the phase of the interference light field will also change significantly when the position of one of the point light sources is feedback-controlled, that is, the interference fringes will shift and change periodically at the same time, which will produce phase crosstalk with the module that controls the translation of the fringes in another phase lock, resulting in the inability to lock the period and phase of the interference field. Moreover, by using the method of tuning the exposure light source wavelength to lock the period, the input voltage of the laser frequency modulation module is subdivided with high precision, and the period locking accuracy of the sub-picometer level can be achieved.

[0029] 3. The problem of the gradual deterioration of the fringe contrast along the periodic direction due to the periodic change of the interference fringes during the exposure process of the meter-scale ultra-large aperture grating is solved, and a reliable solution is provided for the preparation of meter-scale ultra-large aperture, high contrast, and high uniformity holographic grating. The present invention is applicable to any technical solution for preparing large-aperture, high-contrast holographic diffraction gratings using double-beam interference exposure technology, and has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1It is a schematic structural diagram of an embodiment of a device for synchronously locking the phase and period of holographic interference fringes according to the present invention

[0031] In the figure: 1 - tunable laser, 2 - first half-wave plate, 3 - polarization beam splitter prism, 4 - first mirror, 5 - second half-wave plate, 6 - second mirror, 7 - first focusing objective lens, 8 - first spatial filter, 9 - third mirror, 10 - first collimating parabolic mirror, 11 - large-aperture parallel light beam, 12 - first photoelectric sampling module, 13 - grating substrate, 14 - second photoelectric sampling module, 15 - large-aperture parallel light beam, 16 - second collimating parabolic mirror, 17 - second spatial filter, 18 - second focusing objective lens, 19 - fourth mirror, 20 - beam translation module, 21 - beam translation module controller, 22 - computer, 23 - frequency modulation module

[0032] Figure 2 It is a curve of the translation amount of the interference fringes at both ends of the 1620-mm grating substrate over time when the phase locking is turned on and the period locking is turned off

[0033] Figure 3 It is a curve of the translation amount of the interference fringes at both ends of the 1620-mm grating substrate over time when both the phase locking and the period locking are turned on Specific embodiments

[0034] The present invention will be further described below in conjunction with embodiments and the accompanying drawings, but the protection scope of the present invention should not be limited thereby

[0035] A device for synchronously locking the phase and period of holographic interference fringes includes two sets of locking devices, which are respectively installed at both ends of the holographic interference exposure field along the period direction of the interference fringes. One set is used to compensate the phase of the interference light field to lock the phase of the interference fringes, and the other set is used to compensate the output laser frequency of the laser to lock the period of the interference fringes. The entire device includes a tunable laser, a first photoelectric sampling module, a second photoelectric sampling module, a phase compensation module, a frequency modulation module and a computer

[0036] Figure 1 It is a schematic structural diagram of an embodiment of a device for synchronously locking the phase and period of holographic interference fringes according to the present invention. As shown in the figure, it mainly includes the following components

[0037] Frequency-tunable laser 1 , in this embodiment, an optical fiber laser with an output center wavelength of 390 nm and a wavelength tuning range of ~±1 pm is used to generate an ultraviolet interference light beam

[0038] Dual-beam interference exposure system, the laser beam from the tunable laser 1 sequentially passes through the first half-wave plate (2) and the polarization beam splitter prism (3) and is divided into a transmitted beam and a reflected beam; among them, the transmitted beam successively passes through the first mirror (4), the second half-wave plate (5), the second mirror (6), the first focusing objective lens (7), the first spatial filter (8), the third mirror (9) and the first collimating paraboloid mirror (10) to form a first parallel beam 11 with an aperture of 1650 mm; the reflected beam successively passes through the fourth mirror (19), the beam translation module (20), the second focusing objective lens (18), the second spatial filter (17) and the second collimating paraboloid mirror (16) to form a second parallel beam 15. By rotating the first half-wave plate 2 and the second half-wave plate 5, the intensities of the first parallel beam 11 and the second parallel beam 15 are made the same, and they overlap on the front surface of the grating substrate 13 to form an interference exposure field.

[0039] Use a high-precision autocollimation photoelectric theodolite to measure the angle θ between the first parallel beam 11 and the second parallel beam 15, and use the formula Λ = λ / 2 / sin(θ / 2) to calculate the period Λ of the interference exposure field, where λ is the central wavelength output by the tunable laser 1.

[0040] In this embodiment, the apertures of the first collimating paraboloid mirror 10 and the second collimating paraboloid mirror 16 used are 1650 mm × 1120 mm, that is, the lateral dimension of the interference field can reach 1650 mm, and the adjusted interference exposure period Λ is 714.28 nm (corresponding to a line density of 1400 lines / mm).

[0041] First optoelectronic sampling module 12 and second optoelectronic sampling module 14 , including:

[0042] - A sampling grating with an aperture of 12.7 mm (period 1.428 μm), installed at both ends of the grating substrate (13), and its surface is coplanar with the front surface of the grating substrate;

[0043] - A ground glass of 12.7 mm, used to homogenize the sampling beam and reduce speckle noise;

[0044] - A CCD camera, model MV-CA013-20GM of Hikvision Robotics, used to capture the Moiré fringe offset;

[0045] Phase compensation module , including:

[0046] - A piezoelectric positioning stage (model P66.X30S, Harbin Xinmingtian Technology Co., Ltd.);

[0047] - A piezoelectric controller (model E53.B, Harbin Xinmingtian Technology Co., Ltd.), which receives instructions from the computer (22) and drives the piezoelectric ceramic to achieve phase compensation.

[0048] Frequency modulation module 23, including an NI board (model SCB-68) for generating high-precision voltage signals to control the wavelength tuning of the laser seed source, and a low-pass filter (model EF114, THORLABS) for filtering out high-frequency noise to ensure the stability of the frequency modulation signal;

[0049] A method for synchronously locking the phase and period of holographic interference fringes includes the following steps:

[0050] Step 1) Construction of a double-beam holographic interference exposure system

[0051] Place a first half-wave plate 2 and a polarization beam splitter prism 3 in sequence along the transmission direction of the laser beam output by the tunable laser 1. The laser beam is split into a transmitted beam and a reflected beam by the polarization beam splitter prism 3. Place a first mirror 4, a second half-wave plate 5, a second mirror 6, a first focusing objective 7, a first spatial filter 8, a third mirror 9, and a first collimating parabolic mirror 10 in sequence along the transmission direction of the transmitted beam to expand and collimate the transmitted thin beam to form a large-aperture first parallel beam 11. Place a fourth mirror 19, a beam translation module 20, a second focusing objective 18, a second spatial filter 17, and a second collimating parabolic mirror 16 in sequence along the transmission direction of the reflected beam to expand and collimate the reflected thin beam to form a large-aperture second parallel beam 15. Among them, adjust the angle of the first half-wave plate (2) so that the intensities of the transmitted beam and the reflected beam output by the polarization beam splitter prism (3) are equal. The transmitted beam is expanded to a diameter of 1650 mm × 1120 mm by the first collimating parabolic mirror (10), and the reflected beam is synchronously expanded by the second collimating parabolic mirror (16). The two beams overlap on the front surface of the grating substrate (13) to form an interference field.

[0052] Use a high-precision autocollimation photoelectric theodolite to measure the included angle θ between the two beams and calculate the initial period Λ of the interference field. The formula is as follows:

[0053] Λ = λ / 2 / sin(θ / 2),

[0054] where λ is the central wavelength output by the tunable laser 1.

[0055] Step 2) Construction and control of the synchronous locking system

[0056] Step 2.1) Installation and calibration of the sampling grating:

[0057] Prepare a sampling grating with a period of 2Λ and install the sampling grating at both ends of the grating substrate (13) with its surface coplanar with the front surface of the grating substrate;

[0058] Fine-tune the pitch, deflection, and lateral position of the sampling grating through a six-axis adjustment frame to ensure that it is strictly parallel to the front surface of the grating substrate (13), so that both the first and second parallel beams 11 and 15 can irradiate on the surface of the sampling grating;

[0059] Step 2.2) Moiré fringe generation and optimization:

[0060] Adjust the spatial orientation of the sampling grating so that the ±1st order diffracted lights of the two parallel beams 11 and 15 can interfere to form a Moiré fringe pattern on the CCD target surface;

[0061] By observing the CCD image in real time, adjust the rotation angle of the sampling grating so that the Moiré fringe period is 5 - 10 pixel widths (moderate thickness), which is convenient for subsequent image processing.

[0062] Adjust the focal lengths of the CCD cameras in the first photoelectric sampling module 12 and the second photoelectric sampling module 14 so that the Moiré fringes are clearly imaged on the CCD;

[0063] After connecting the beam translation module 20 and the beam translation module controller 21, connect them to the computer 22. At the same time, connect the frequency modulation module 23 to the tunable laser 1 and the computer 22 respectively. Among them, the beam translation module realizes the nano-scale displacement of the beam path through the piezoelectric ceramic (PZT) drive, which is used to adjust the phase of the interference fringes. The frequency modulation module controls the spatial period of the interference fringes by changing the laser frequency Δf; the computer serves as the control center, responsible for sending control instructions and receiving feedback signals to achieve closed-loop control.

[0064] Step 2.3) Feedback control program writing:

[0065] According to the Moiré fringe offset collected by the first photoelectric sampling module 12 and the second photoelectric sampling module 14 during the exposure process, real-time feedback controls the movement of the PZT of the beam translation module 20 and the output voltage of the frequency modulation module 23, realizes the change of the phase of the large-aperture parallel beam 15 and the change of the grating period Λ formed by the interference of the large-aperture parallel beams 11 and 15, and further realizes the synchronous locking of the phase and period of the interference fringes.

[0066] The first photoelectric sampling module monitors the phase offset of the interference fringes (compensated by adjusting the PZT through the beam translation module). The second photoelectric sampling module monitors the period offset of the interference fringes (compensated by adjusting the laser frequency through the frequency modulation module).

[0067] When the system detects the phase offset of the interference fringes, the computer sends a signal to the beam translation module controller to drive the PZT to expand and contract to change the optical path difference and compensate the phase error in real time. When the period offset of the interference fringes is detected, the computer adjusts the output of the frequency modulation module to change the laser frequency (Δf), thereby dynamically correcting the period of the interference fringes.

[0068] Using the PID control algorithm, based on the real-time data of the Moiré fringe offset, calculate the required PZT displacement and frequency adjustment amount to achieve nanometer-level accuracy (<1nm) and megahertz-level frequency response (>10MHz).

[0069] Based on the above locking device and method, the fringe drift at both ends of the grating substrate under single-point phase locking and phase-period synchronous locking was experimentally tested. The size of the grating substrate used in the test was 1620mm (length) × 1070mm (height), and two sets of locking devices were installed at both ends along the 1620mm length direction of the substrate respectively. Figure 2 It is the change curve of the fringe drift amount at both ends recorded when the phase locking is on and the period locking is off. It can be seen from it that when the phase-locked end is in the open state, the fringe drift amount can be controlled at a level less than 0.1d (d is the fringe period of the interference field), while at the other end where the period locking is off, within the short exposure time of 300s, the interference fringe drift amount fluctuates violently with the exposure time, and the maximum fringe drift amount has reached ~1d, which will lead to a decrease in the contrast of the interference field, thus affecting the contrast of the groove pattern of the lithography grating mask.

[0070] Figure 3 It is the change curve of the interference fringe drift amount at both ends of the 1620mm grating substrate with time when both the phase and period locking are on. It can be seen from the figure that due to the locking of the period of the interference field, even within the long exposure time of 2000s, the fringe translation amount at both ends of the 1620mm substrate can basically be controlled at a level less than 0.05d (d is the fringe period of the interference field), which can meet the high-contrast exposure requirements.

Claims

1. A device for synchronously locking the phase and period of holographic interference fringes, characterized in that Comprising: A tunable frequency laser (1) for outputting ultraviolet laser, whose wavelength is tunable to control the interference fringe period; A double-beam interference system for splitting a laser beam into two large-aperture parallel beams (11, 15) and forming an interference exposure field on the surface of a grating substrate (13); A first photoelectric sampling module (12) and a second photoelectric sampling module (14), which are respectively fixed at both ends of the grating substrate (13) along the interference fringe period direction. Each module includes a sampling grating with a period of 2Λ, a ground glass, and a CCD camera for real-time monitoring of the interference field phase and period offset; wherein, the surface of the sampling grating is coplanar with the front surface of the grating substrate (13), and Λ is the interference exposure field period A phase compensation module, including a beam translation module (20) composed of a piezoelectric ceramic and a mirror and a beam translation module controller (21), for adjusting the beam phase according to the feedback of the first photoelectric sampling module (12) to compensate for the interference fringe phase offset; A frequency modulation module (23) for adjusting the seed light source current of the tunable frequency laser (1) according to the feedback signal of the second photoelectric sampling module (14) to realize wavelength tuning to lock the interference fringe period; A computer (22) is connected to the phase compensation module and the frequency modulation module (23), for real-time processing of the feedback data of the two photoelectric sampling modules, and driving the phase compensation and frequency modulation operations through an independent closed-loop control algorithm to realize the synchronous locking of the interference fringe phase and period.

2. The device for synchronously locking the phase and period of holographic interference fringes according to claim 1, characterized in that, The double-beam interference system is composed of a polarization beam splitting prism (3), a first mirror (4), a second mirror (6), a third mirror (9), a fourth mirror (19), a first focusing objective lens (7), a second focusing objective lens (18), a first spatial filter (8), a second spatial filter (17), a first collimating paraboloid mirror (10) and a second collimating paraboloid mirror (16). The apertures of the collimating paraboloid mirrors (10, 16) are ≥1650mm×1120mm, and the effective aperture of the grating substrate (13) covered by the generated interference field is ≥1600mm.

3. The device for synchronous locking of holographic interference fringe phase and period according to claim 1, characterized in that The tunable frequency laser (1) is a fiber laser with a doubled frequency output wavelength of 200nm - 450nm.

4. The device for synchronously locking the phase and period of holographic interference fringes according to claim 1, wherein The frequency modulation module (23) is used to directly regulate the output wavelength of the tunable frequency laser (1) by using an acousto-optic frequency shifter, or to regulate the seed light wavelength of the tunable frequency laser (1) by using a voltage / current regulation module.

5. A method for synchronously locking the phase and period of holographic interference fringes, which is implemented based on the device described in any one of claims 1-5, and is characterized in that, Including the following steps: Step 1) Construction of a double-beam holographic interference exposure system The laser beam output by the tunable frequency laser (1) is split into a transmitted beam and a reflected beam by the polarization beam splitting prism (3), and respectively forms two large-aperture parallel beams (11, 15) through beam expansion and collimation, and an interference field is generated by overlapping on the surface of the grating substrate (13); Using a high-precision autocollimation photoelectric theodolite to measure the included angle θ between the two large-aperture parallel beams (11, 15), and calculating the period Λ of the interference exposure field according to the formula Λ = λ / 2 / sin(θ / 2), where λ is the central wavelength output by the tunable frequency laser 1. Step 2) Construction and control of a synchronous locking system Install sampling gratings with a period of 2Λ at both ends of the grating substrate (13), and adjust their spatial orientation so that the ±1st order diffracted lights of two parallel light beams (11, 15) form Moiré fringes on the CCD target surface; Extract the offset Δx of the Moiré fringe center position in real time through the first optoelectronic sampling module (12), and generate a piezoelectric ceramic drive signal using the PID control algorithm to compensate for the phase offset of the light beam; Analyze the change ΔΛ of the Moiré fringe period in real time through the second optoelectronic sampling module (14), and inversely deduce the wavelength adjustment amount Δλ according to the formula Δλ = 2ΔΛ·sin(θ / 2), and adjust the output wavelength of the laser through the frequency modulation module (23); The computer (22) processes the feedback signals at both ends in real time, independently controls the phase compensation module and the frequency modulation module (23), and realizes the synchronous locking of the phase and the period.

6. The holographic interference fringe phase and period synchronous locking method according to claim 5, characterized in that The line density of the grating substrate (13) is ≥1400 lines / mm, the effective aperture is ≥1600 mm, and the interference exposure time is ≥2000 s.

7. The holographic interference fringe phase and period synchronous locking method according to claim 5, characterized in that During the synchronous locking process, the fluctuation of the interference fringe contrast is ≤5%, and the cumulative error of the edge position is <100 nm.

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