A plane grating full parameter test system and a measuring method

Abstract

The application discloses a plane grating full-parameter testing system and a measuring method. The system comprises a light source system, a double-layer rotating motion system, a phase-locked system, a monitoring system and a measurement and control system. The light source system comprises an adjustable monochromatic light source module and a frequency-stabilized narrow-line-width laser module. The adjustable monochromatic light source is used for diffraction efficiency measurement, and the frequency-stabilized narrow-line-width laser is used for stray light and period measurement. The double-layer rotating motion system is used for separately controlling a to-be-measured grating and a detector, and is used for angle and translation adjustment. The phase-locked system is used for weak signal measurement. The monitoring system is used for accurately positioning a grating rotation angle. The measurement and control system is used for completing light source control, motion control, signal acquisition, parameter calculation and result output. The application can realize integrated measurement of plane grating diffraction efficiency, stray light and period parameters.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and more specifically, to a planar grating full-parameter testing system and measurement method that takes into account grating diffraction efficiency, grating stray light and grating period measurement. Background Technology

[0002] Planar gratings, as important spectroscopic elements, are widely used in spectral analysis, imaging, metrology, and related optical measurement technologies. Parameters such as grating diffraction efficiency, stray light, and grating period directly affect the spectroscopic capability, signal-to-noise ratio, and measurement accuracy of an optical system; therefore, it is necessary to accurately measure these grating parameters.

[0003] Existing methods for measuring grating parameters mainly focus on single-parameter measurements. For example, the detection of grating diffraction efficiency typically employs either the "single-line method" or the "continuous spectroscopy method." While the "single-line method" offers high wavelength accuracy, it can only measure diffraction efficiency values ​​corresponding to a limited number of standard spectral lines, making it difficult to reflect the efficiency variation trend of the grating under test across the entire wavelength range. The "continuous spectroscopy method," on the other hand, can obtain a continuous diffraction efficiency curve, but its overall structure is complex, the instrument is bulky, and assembly and adjustment are challenging.

[0004] For measuring stray light from gratings, existing methods characterize it by scanning the light intensity between adjacent diffraction orders and combining it with energy integration. This method can reflect the magnitude difference between diffracted and stray light, but it usually places high demands on the accuracy of angle scanning control, the ability to detect weak signals, and the ability to suppress environmental noise.

[0005] For measuring the grating period, existing methods are based on the principle of diffraction. They record the angle of diffracted light of a specific order, the self-collimation position, or the diffraction interference signal, and then calculate the grating period or grating pitch by combining this with the grating equation. However, the measurement accuracy is often directly affected by factors such as the accuracy of angle measurement, the accuracy of the turntable, and the length of the measuring arm.

[0006] In existing technologies, multi-parameter measurement of gratings can be achieved, such as patent application CN202010738785.8, "An Automatic Measurement System for Grating Diffraction Angle Spectrum." This patent can measure the diffraction angle spectrum at different incident angles, measure the diffraction efficiency of each order and the stray light situation between orders, and calculate parameters such as the number of grating lines based on the diffraction angle spectrum curve. However, this patent mainly focuses on diffraction angle spectrum measurement and has not yet constructed an integrated measurement system for diffraction efficiency, stray light, and grating period, nor has it solved problems such as wide-band adaptation, high-precision extraction of weak signals, and high-precision period measurement integration. Therefore, it is difficult to meet the needs of full-parameter testing of planar gratings. Therefore, it is necessary to provide a planar grating full-parameter testing system and measurement method to achieve integrated measurement of grating diffraction efficiency, stray light, and period parameters. Summary of the Invention

[0007] The purpose of this invention is to provide a planar grating full-parameter testing system and measurement method to solve the problems of scattered measurement functions for grating diffraction efficiency, stray light and period in the prior art, system complexity, insufficient measurement capability for weak signals and weak wide-band adaptability, as well as the problem of detector arrangement difficulties caused by the incident light coinciding or approximately coinciding with the target order diffraction light under self-collimation or Littrow measurement conditions.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A planar grating full-parameter testing system includes:

[0010] The light source system includes an adjustable monochromatic light source module and a frequency-stabilized narrow-linewidth laser module;

[0011] A dual-layer rotary motion system is used to separately carry and independently rotate and adjust the grating under test and the optical signal detector;

[0012] A phase-locked system is used to perform phase-locked amplification measurement of the diffraction light and stray light signals generated by the grating under test;

[0013] A monitoring system is used to monitor and locate the position of the grating under test in autocollimation mode;

[0014] The measurement and control system is connected to the light source system, the double-layer rotary motion system, the phase-locked system and the monitoring system respectively, and is used to perform light source switching control, motion control, signal acquisition, parameter calculation and result output;

[0015] The dual-layer rotational motion system is configured such that, under self-collimation or Littrow measurement conditions, when the target order diffracted light of the grating under test coincides or approximately coincides with the direction of the incident light, the grating under test is controlled to generate an out-of-plane deflection angle γ, so that the target order diffracted light and the incident light are spatially separated in a direction perpendicular to the incident plane, and the optical signal detector is driven to move to the receiving position of the separated diffracted light.

[0016] Furthermore, the monitoring system includes a beam splitter and a monitoring CCD. In the period measurement mode, the diffracted light in the self-collimated state forms a returning spot on the monitoring CCD after passing through the beam splitter. The measurement and control system determines the reference centroid position by extracting the centroid coordinates of the returning spot, and adjusts the rotation angle of the grating under test so that the centroid coordinates of the returning spot in the dispersion direction in different self-collimated states coincide with or deviate from the reference centroid position by less than a preset threshold, thereby obtaining the self-collimated rectangular position of the grating under test, and then calculating the grating period.

[0017] Furthermore, the optical signal detector includes a PMT detector and a photodiode detector; the measurement and control system automatically switches the detector type according to the measurement mode and measurement wavelength: a PMT detector is used when measuring stray light; when measuring diffraction efficiency, a photodiode detector is used under strong light conditions and a PMT detector is used under weak light conditions.

[0018] Furthermore, the adjustable monochromatic light source module includes an LDLS white light source and a monochromator, used to output continuously adjustable monochromatic collimated light in the wavelength range of 200nm to 2000nm in the diffraction efficiency measurement mode; the frequency-stabilized narrow-linewidth laser module includes a He-Ne frequency-stabilized laser and a collimation and beam expansion assembly, used to output a narrow-linewidth laser beam in stray light measurement mode and period measurement mode.

[0019] Furthermore, the dual-layer rotary motion system includes an upper turntable, a lower turntable, a straight guide rail, and a displacement adjustment assembly; the upper turntable is used to install and adjust the rotation angle of the grating under test; the lower turntable is used to support the straight guide rail on which the optical signal detector is installed, and can drive the detector to rotate around the center of the grating under test; the displacement adjustment assembly includes a dual-layer angle stage, a displacement stage, and a lifting stage, the dual-layer angle stage being used to adjust the off-plane sway angle γ.

[0020] A method for measuring the full parameters of a planar grating based on the above system includes the following steps:

[0021] In the diffraction efficiency measurement mode, the monochromatic collimated light of the target wavelength output by the adjustable monochromatic light source module is incident on the grating under test. The optical signal detector is adjusted to the direction of the target order diffraction light to obtain the diffraction light energy. Then, the grating under test is moved out of the optical path and the optical signal detector is moved to the incident light path to obtain the incident reference light energy. The diffraction efficiency measurement value is obtained according to the ratio of the diffraction light energy to the incident reference light energy.

[0022] In stray light measurement mode, the laser beam output by the frequency-stabilized narrow-linewidth laser module is modulated by the chopper of the phase-locked system and then incident on the grating under test. The optical signal detector is controlled to scan within a preset angle range, and the effective signal corresponding to the stray light is extracted by the phase-locked system to calculate the stray light coefficient.

[0023] In the period measurement mode, the laser beam output by the frequency-stabilized narrow linewidth laser module is incident on the grating under test after passing through the beam splitting element of the monitoring system. The rotation angle of the grating under test is adjusted to obtain the self-collimation position corresponding to different diffraction orders. The angle parameters are recorded by the monitoring CCD of the monitoring system, and the period measurement value is calculated according to the grating diffraction equation.

[0024] Specifically, when the target order diffracted light coincides or nearly coincides with the incident light under self-collimation or Littrow measurement conditions, in the diffraction efficiency measurement mode or stray light measurement mode, the grating under test is controlled to generate an out-of-plane deflection angle γ, so that the target order diffracted light and the incident light are spatially separated in a direction perpendicular to the incident plane, and the optical signal detector is driven to move to the separated diffracted light receiving position to collect the signal.

[0025] Furthermore, the value range of the out-of-plane deflection angle γ is 0.5° to 5°; the spatial separation angle between the incident light and the target order diffracted light is 2γ.

[0026] Furthermore, in the periodic measurement mode, the reference centroid position is determined by extracting the centroid coordinates of the self-collimated return spot, and the centroid coordinates of the return spots corresponding to different diffraction orders in the dispersion direction coincide with or deviate from the reference centroid position by less than a preset threshold, so as to obtain the self-collimated rectangular position.

[0027] Furthermore, in the diffraction efficiency measurement, stray light measurement, and grating period measurement modes, the grating under test can be moved along the horizontal and vertical directions by the displacement stage and the lifting stage, so that the incident light acts on multiple preset sampling positions within the effective aperture of the grating under test in sequence, and the measurement results at each position are measured and the average value is taken as the final measurement result.

[0028] Furthermore, the grating under test includes a transmission grating and a reflection grating; when the grating under test is a transmission grating, the optical signal detector is located on the side of the transmission diffraction light, and the measurement and control system switches to the transmission measurement mode to adjust the scanning angle range of the detector.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] First, the entire system takes into account the detection functions of grating diffraction efficiency, grating stray light and grating period, realizing the combination of system multifunctionality and high detection precision.

[0031] Secondly, by combining a wide-band LDLS light source with a monochromator, a wide-band monochromatic adjustable output of 200-2000nm is achieved. At the same time, a monochromatic light source with a narrower linewidth is also realized, overcoming the system complexity under traditional filter structure filtering and the lack of near-ultraviolet light sources such as xenon lamps and tungsten lamps.

[0032] Third, a phase-locked system combining a chopper and a lock-in amplifier is used to achieve precise measurement of weak signals, overcome the influence of ambient stray light on the accuracy of the detection system, and improve the signal-to-noise ratio.

[0033] Fourth, the spatial separation of incident light and target order diffracted light under self-collimation or Littrow measurement conditions is achieved by using the out-of-plane deflection angle γ. This, combined with the lower turntable and straight guide rail, completes the detector receiving position adjustment, thereby completing the diffraction efficiency and stray light measurement without the detector blocking the incident light. This improves the applicability of the system to grating measurement scenarios such as echelle gratings and reflective blazed gratings. Attached Figure Description

[0034] To illustrate the present invention more clearly, the accompanying drawings will be described and explained below.

[0035] Figure 1 This is a schematic diagram of the overall scheme of the planar grating full parameter testing system of the present invention;

[0036] Figure 2 This is a structural diagram of the double-layer rotary motion turntable of the present invention;

[0037] Figure 3 This is a schematic diagram of the phase-locked loop detection of weak signals according to the present invention;

[0038] Figure 4 This is a schematic diagram of the grating diffraction efficiency testing scheme of the present invention;

[0039] Figure 5 This is a schematic diagram of the grating stray light testing scheme of the present invention;

[0040] Figure 6 This is a schematic diagram of the grating period testing scheme of the present invention;

[0041] Figure 7 This is a schematic diagram showing the 9-point sampling measurement positions and movement directions of the present invention;

[0042] Figure 8 This is a schematic diagram illustrating the principle of grating period measurement order recognition under the self-collimation structure of the present invention;

[0043] Figure 9 The diagram shows the diffraction optical path under the non-self-collimation structure and the self-collimation or Littrow structure of the present invention; wherein, (a) is the diffraction optical path under the non-self-collimation structure, and (b) is the diffraction optical path under the self-collimation or Littrow structure.

[0044] Figure 10 This is a schematic diagram of the real-time self-collimation positioning principle based on the coincidence of the centroid of the light spot in this invention. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or modifications made by those skilled in the art without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0046] like Figure 1 As shown, the present invention provides a planar grating full parameter testing system, which mainly includes an LDLS white light source 01, a monochromator 02, a He-Ne frequency-stabilized laser 03, a collimating beam expander 04, an attenuator 05, a chopper 06, a monitoring CCD 07, ​​a beam splitter 08, a detector 09, a double-layer rotation motion system 10, and a grating under test 11.

[0047] The detector 09 is used to receive incident reference light, target order diffracted light, or inter-order stray light signals. The detector 09 includes a PMT detector and a photodiode detector. The photodiode detector is preferably used for measuring the energy of incident reference light and target order diffracted light with high intensity in diffraction efficiency measurements; the PMT detector is preferably used for stray light measurement, weak diffraction light measurement, and diffraction efficiency measurement under low light intensity conditions. Since a single detector cannot cover the wide-band energy detection requirements from near-ultraviolet to near-infrared, the detector 09 adopts a band-segmented configuration. By setting PMT detectors or photodiode detectors with different response bands, it can receive light signals in different bands from 200nm to 2000nm. In actual measurements, the measurement and control system can switch the corresponding type or band of detector according to the test wavelength, measurement mode, and intensity of the light signal to be measured, thereby achieving matching and conversion of the detection capabilities of the detection system.

[0048] The measurement and control system is used to coordinate with the overall measurement system to achieve unified control, data acquisition, parameter processing, and result output of various functional modules. The system is mainly used to complete the acquisition of PMT or photodiode detection signals, motion drive control of the dual-layer rotary motion system, wavelength selection control of the monochromator, and display and output of measurement results. The system has a software interface where all system data parameters are collected and displayed. Instrument parameter settings are decomposed into corresponding control commands and transmitted to each functional module via the system. The host computer software includes an input interface for the basic parameters of the grating under test. The system drives the corresponding components to complete the detection process according to the input parameters and detection mode, processes and calculates the acquired signals, and finally outputs the measurement results of the grating under test. Preferably, the system switches the detector 09 according to the measurement mode and wavelength: a PMT detector is used for stray light measurement; a photodiode detector is used under strong light conditions and a PMT detector is used under weak light conditions for diffraction efficiency measurement. After selecting the detector type, the system further switches to the corresponding band detector according to the measurement wavelength and performs self-calibration.

[0049] The grating 11 under test includes a transmission grating and a reflection grating. The system described in this invention is applicable to both types of gratings. When the grating 11 under test is a transmission grating, the detector 09 is located on the side of the transmitted diffraction light; when the grating 11 under test is a reflection grating, the detector 09 is located on the side of the reflected diffraction light. The following embodiments involving optical path arrangement mainly illustrate the measurement of reflection gratings. When measuring transmission gratings, the position and scanning range of the detector 09 can be adjusted according to the direction of the transmitted diffraction light, and the measurement principle is the same.

[0050] Preferably, when the grating 11 under test is a transmission grating, the detector 09 is arranged on the emission side of the grating 11 to receive the transmitted diffracted light. In this case, the lower turntable in the dual-layer rotation system 10 drives the detector 09 to perform angular scanning within the half-space containing the transmitted diffracted light, while the upper turntable adjusts the incident angle of the grating 11 under test. Compared to reflection grating measurement, it is only necessary to move the detector 09 along the optical path to the other side of the grating 11 under test and switch to transmission measurement mode in the measurement and control system to adjust the scanning angle range of the detector 09.

[0051] The LDLS white light source 01 is connected to the monochromator 02 and is used to output continuously adjustable monochromatic light to meet the light source requirements for grating diffraction efficiency measurement. The He-Ne frequency-stabilized laser 03 is used to output stable laser light to meet the light source requirements for stray light measurement and period measurement. Specifically, the LDLS white light source 01 generates broadband light, which is introduced into the monochromator 02 through a light source coupler. The monochromator 02 splits the broadband light and outputs monochromatic light of the target wavelength. The monochromatic light is collimated by an exit collimator to form parallel light entering the test optical path. The collimation and beam expansion assembly 04 is set on the output path of the He-Ne frequency-stabilized laser 03 and is used to collimate and expand the laser beam. The attenuator 05 is used to adjust the beam intensity. The chopper 06 is used to modulate the continuous light into modulated light of a specific frequency.

[0052] The beam splitter 08 and the monitoring CCD 07 work together to form a monitoring optical path, used for beam splitting and position monitoring of the returned light spot during grating period measurement. The beam splitter 08 and the monitoring CCD 07 together constitute a self-collimation test structure. Diffracted light in the self-collimation state forms a light spot on the monitoring CCD after passing through the beam splitter. The measurement and control system determines the reference centroid position by extracting the centroid coordinates of the returned light spot, and adjusts the rotation angle of the grating under test so that the centroid coordinates of the returned light spot in the dispersion direction coincide with or deviate from the reference centroid position by less than a preset threshold under different self-collimation states, thereby obtaining the self-collimation rectangular position of the grating under test, and then calculating the grating period. The dual-layer rotation motion system 10 carries the grating under test 11 and the detector 09, and realizes the attitude adjustment and incident angle adjustment of the grating under test 11, as well as the angle scanning and detection distance adjustment of the detector 09, thus meeting the angle and position adjustment requirements under different test modes.

[0053] like Figure 2 As shown, the dual-layer rotary motion system 10 includes a grating fixture 12, a dual-layer angle stage 13, a displacement stage 14, an upper turntable 15, a lifting stage 16, a lower turntable 17, and a straight guide rail 18. The grating fixture 12 is mounted above the dual-layer angle stage 13 to fix the grating 11 under test; the dual-layer angle stage 13 is used to adjust the pitch angle of the grating 11 under test; the displacement stage 14 is used to adjust the horizontal position of the grating 11 under test; the upper turntable 15 is used to drive the grating 11 under test to rotate, thereby changing the grating incident angle; the lifting stage 16 is used to adjust the height position of the grating 11 under test; the lower turntable 17 is used to drive the straight guide rail 18 to rotate around the center of the grating 11 under test; the straight guide rail 18 is mounted on the lower turntable 17 to support the detector 09 (PMT or photodiode detector), and the detector 09 can move radially along the straight guide rail 18 to adjust the detection distance. Both the upper and lower turntables have a rotation range of 360°, and the straight guide rail is either a telescopic guide rail or a fixed guide rail.

[0054] like Figure 7 As shown, the measurement system also has an effective aperture multi-point sampling function. Figure 7In the illustrated embodiment, there are nine preset sampling positions, preferably distributed in a 3×3 array within the effective aperture range of the grating 11 under test. Specifically, the grating 11 under test is moved in two directions by the displacement stage 14 and the lifting stage 16, so that the incident light sequentially acts on the nine preset sampling positions within the effective aperture of the grating 11 under test. The multi-point sampling function of the effective aperture can be applied to one or more measurement modes, including diffraction efficiency measurement, stray light measurement, and grating period measurement. The measurement and control system can control the grating 11 under test to move sequentially to each sampling position, and complete the acquisition and calculation of the corresponding measurement parameters at the corresponding sampling positions. Then, the measurement results of the nine sampling positions are averaged or statistically analyzed to obtain the average measurement result of the grating 11 under test within the effective aperture range. This reduces the influence of single-point measurement errors and factors such as local surface shape and local unevenness of the scribing on the measurement results, improving the accuracy and reliability of the measurement results.

[0055] like Figure 3 As shown, the core of the phase-locked loop system includes a chopper 06, a detector 09, a preamplifier 19, and a lock-in amplifier 20, and works in conjunction with a He-Ne frequency-stabilized laser 03, a dual-layer rotation system 10, and a host computer and software 21 to complete stray light measurement. The chopper 06 modulates continuous light into modulated light of a specific frequency. The PMT or photodiode detector receives the diffracted light or stray light generated by the grating under test and converts it into an electrical signal. The lock-in amplifier 20 extracts the effective signal component with the same frequency as the modulation frequency. During testing, the laser beam emitted by the He-Ne frequency-stabilized laser 03 is frequency-modulated by chopper 06, and the frequency is simultaneously input into lock-in amplifier 20. Alternatively, the laser source can be simulated by using a custom output frequency of lock-in amplifier 20, thereby enabling the source to obtain a modulation signal. This modulated source is incident on the dual-layer rotating motion system 10. By adjusting the upper and lower turntables, signals of diffracted light and stray light of different orders can be tested. The light intensity signal is received by detector 09 and amplified. The intensity signal is converted into an electrical signal and input into lock-in amplifier 20. Lock-in amplifier 20 performs signal processing and calculation to obtain a test signal with the same frequency as the modulation frequency. The diffraction efficiency or stray light intensity is obtained through the host computer and software 21, realizing the function of grating parameter measurement.

[0056] Based on the above system, the present invention can realize the measurement of grating diffraction efficiency, grating stray light and grating period respectively, as follows.

[0057] Example 1: Example of Diffraction Efficiency Measurement Based on the System of the Invention

[0058] like Figure 4As shown, in this embodiment, an LDLS white light source 01 and a monochromator 02 are combined as the test light source. The broadband light emitted by the LDLS white light source 01 is selected by the monochromator 02 and output as monochromatic light of the target wavelength. The monochromatic light is incident on the grating 11 to be tested, which is installed on the double-layer rotating motion system 10, along a predetermined optical path.

[0059] During testing, the dual-layer rotation system 10 adjusts the attitude and incident angle of the grating 11 under test, ensuring that incident light illuminates the surface of the grating 11 at a set angle. The grating 11 then generates diffracted light of different orders. The dual-layer rotation system 10 rotates the detector 09 to the direction of the target order diffracted light, and the detection distance of the detector 09 is adjusted along the straight guide rail 18 as needed to receive the target order diffracted light signal.

[0060] In a preferred embodiment, detector 09 scans within the angular range (θ1-θ2) of the target-order diffracted light to obtain the energy distribution of the target-order diffracted light; when the effective receiving surface of detector 09 covers the energy range of the target diffracted light, the energy of the target-order diffracted light can also be directly measured. After completing the measurement of the target-order diffracted light energy, the grating 11 under test is moved out of the optical path, and detector 09 is moved to the incident light propagation position to measure the incident reference light energy. The measurement and control system calculates the diffraction efficiency of the grating 11 under test at the corresponding wavelength and corresponding order based on the target-order diffracted light energy and the incident reference light energy.

[0061] Preferably, diffraction efficiency It can be represented as:

[0062]

[0063] in, The energy of the target-order diffracted light. The energy of the incident reference light.

[0064] Preferably, such as Figure 9 As shown in (b), for the grating 11 under test (e.g., an echelle grating or a reflective blazed grating) that needs to be measured for diffraction efficiency under self-collimation or Littrow conditions, when the incident light direction coincides with or is approximately coincident with the target order diffraction light direction, this embodiment adopts an out-of-plane deflection angle γ measurement strategy, which includes the following steps:

[0065] (1) The measurement and control system controls the adjustable monochromatic light source module to output monochromatic light of the target wavelength, and adjusts the rotation angle of the grating 11 to be measured through the upper turntable 15 so that it meets the autocollimation or Littrow measurement geometry of the target level;

[0066] (2) On the basis of maintaining the above geometric relationship, the measurement and control system controls the double-layer angular stage 13 in the double-layer rotation motion system 10 to adjust the attitude of the grating 11 to be measured, and introduces a preset off-plane deflection angle γ so that the target order diffracted light is spatially separated from the incident light in a direction perpendicular to the main diffraction plane.

[0067] When the grating under test is under self-collimation or Littrow measurement conditions, and the incident light coincides with or nearly coincides with the target order diffracted light, the dual-layer rotation motion system controls the grating under test to generate a predetermined out-of-plane deflection angle γ, so that the target order diffracted light is spatially separated from the incident light in a direction perpendicular to the original incident diffraction plane. The measurement and control system, based on the out-of-plane deflection angle γ, incident wavelength, diffraction order, and detection distance, controls the lower turntable and straight guide rail to move the detector to the receiving position of the separated target order diffracted light, thereby completing the diffraction efficiency signal acquisition under self-collimation or Littrow measurement conditions. The spatial separation angle between the incident light and the target order diffracted light is approximately 2γ.

[0068] The out-of-plane deflection angle γ is determined based on the detector's receiving aperture, the movement range of the lower turntable, and the adjustment distance of the straight guide rail. Under the premise of ensuring that the detector can receive the target order diffracted light without blocking the incident light propagation path, the out-of-plane deflection angle γ should be taken as small as possible to reduce the impact of the out-of-plane deflection on the original autocollimation or Littrow measurement geometry and the diffracted light energy distribution.

[0069] (3) The measurement and control system controls the lower turntable 17 and the straight guide rail 18 to drive the detector 09 to move to the target order diffraction light receiving position after separation, and collects the target order diffraction light energy.

[0070] (4) The measurement and control system controls the displacement stage 14 or the lifting stage 16 to move the grating 11 under test out of the incident light path, and controls the lower turntable 17 and the straight guide rail 18 to move the detector 09 to the incident light propagation position to collect the incident reference light energy.

[0071] (5) The measurement and control system calculates the diffraction efficiency based on the target order diffraction light energy and the incident reference light energy, and outputs the diffraction efficiency measurement results.

[0072] By controlling the monochromator 02 to scan point by point within a preset wavelength range and simultaneously adjusting the positions of the dual-layer rotating motion system 10 and the detector 09, the diffraction efficiency curves of the grating 11 under test can be obtained under different wavelengths, different incident angles, and different diffraction orders.

[0073] Example 2: Stray Light Measurement Example Based on the System of the Invention

[0074] like Figure 5As shown, in this embodiment, a He-Ne frequency-stabilized laser 03 is used as the test light source. The laser beam emitted by the He-Ne frequency-stabilized laser 03 passes through the collimation and beam expansion assembly 04, the attenuator 05 and the chopper 06 in sequence to form a test beam with a set light intensity and is modulated, and then incident on the grating 11 under test installed on the double-layer rotation motion system 10.

[0075] During testing, the mounting posture and incident angle of the grating 11 under test are adjusted by the dual-layer rotation system 10 to bring the grating 11 into a predetermined test state. After being illuminated by incident light, the grating 11 under test generates strong diffraction light in the main diffraction order direction, while generating weak stray light signals on both sides of the main diffraction peak and between adjacent orders. The dual-layer rotation system 10 drives the detector 09 to scan within a preset angle range (θ0-θ3) to obtain the light intensity distribution at different angular positions.

[0076] Since stray light signals are typically weak, this embodiment employs a phase-locked loop system to measure and process the electrical signal output by detector 09, in order to extract the effective signal components corresponding to the stray light, suppress ambient light and background noise interference, and improve the sensitivity and signal-to-noise ratio of weak signal measurements. The processed measurement signal is transmitted to the host computer and software 21, which then completes data acquisition, processing, and display.

[0077] In a preferred embodiment, detector 09 scans the angular range near the main diffraction peak and between adjacent orders, and then processes the received optical signal according to the principle of energy integration.

[0078] Preferably, the specific calculation of m-order stray light can be expressed as the integral of the light intensity energy of the irregular distribution between adjacent diffraction orders. Integral of intensity and energy of m-order diffraction The ratio:

[0079]

[0080] in, Grating stray light coefficient, wavelength of incident light The luminous flux between the m-th order diffracted light and its adjacent orders of diffracted light. wavelength of incident light The intensity of the m-th order diffracted light, where θ0, θ1, θ2, and θ3 are the positions of the minimum values ​​between the m-th order diffracted light and the two adjacent diffraction orders.

[0081] Preferably, the positions of the main diffraction peak and adjacent minima can be determined based on the multi-slit Fraunhofer diffraction theory.

[0082] Preferably, such as Figure 9As shown in (b), for the grating under test (e.g., a middle echelle grating or a reflective blazed grating) that requires stray light measurement under self-collimation or Littrow conditions, when the incident light direction coincides with or is approximately coincident with the target order diffracted light direction, this embodiment adopts an out-of-plane deflection angle γ measurement strategy, which includes the following steps:

[0083] (1) The measurement and control system controls the output of the test laser by the frequency-stabilized narrow linewidth laser module and modulates the test laser by the chopper 06. At the same time, it controls the upper turntable 15 to adjust the rotation angle of the grating 11 under test so that it meets the autocollimation or Littrow measurement geometry of the target level.

[0084] (2) On the basis of maintaining the above geometric relationship, the measurement and control system controls the double-layer angular stage 13 in the double-layer rotation motion system 10 to adjust the attitude of the grating 11 to be measured, and introduces a preset out-of-plane deflection angle γ so that the target order diffracted light is spatially separated from the incident light.

[0085] When the grating under test is under self-collimation or Littrow measurement conditions, and the incident light coincides with or nearly coincides with the target order diffracted light, the dual-layer rotation system controls the grating under test to generate a predetermined out-of-plane deflection angle γ, causing the target order diffracted light to spatially separate from the incident light in a direction perpendicular to the original incident diffraction plane. The measurement and control system, based on the out-of-plane deflection angle γ, incident wavelength, diffraction order, and detection distance, controls the lower turntable and straight guide rail to move the detector to the receiving position of the separated target order diffracted light, thus completing the acquisition of stray light signals under self-collimation or Littrow measurement conditions. The spatial separation angle between the incident light and the target order diffracted light is approximately 2γ.

[0086] The out-of-plane deflection angle γ is determined based on the detector's receiving aperture, the movement range of the lower turntable, and the adjustment distance of the straight guide rail. Under the premise of ensuring that the detector can receive the target order diffracted light without blocking the incident light propagation path, the out-of-plane deflection angle γ should be taken as small as possible to reduce the impact of the out-of-plane deflection on the original autocollimation or Littrow measurement geometry and the diffracted light energy distribution.

[0087] (3) The measurement and control system controls the lower turntable 17 to drive the detector 09 to scan within a preset angle range, and adjusts the detection distance of the detector 09 through the straight guide rail 18 so that the detector 09 can receive the separated target order diffraction light and the inter-order stray light signal in the adjacent angle range.

[0088] (4) The measurement and control system calls the lock-in amplifier 20 to extract the detection signal at the same frequency, obtain the effective signal of stray light, and output the stray light distribution curve or stray light measurement result.

[0089] Through the above method, this embodiment can realize the measurement of stray light distribution of the grating 11 under test, which is suitable for the measurement and analysis of weak stray light signals.

[0090] Example 3: Example of grating period measurement based on the system of the present invention

[0091] like Figure 6 As shown, in this embodiment, a He-Ne frequency-stabilized laser 03 is used as the test light source, and a self-collimating monitoring optical path is formed by combining a beam splitter 08 and a monitoring CCD 07. The laser beam emitted by the He-Ne frequency-stabilized laser 03 is incident on the beam splitter 08 after passing through the collimation and beam expander 04 and the attenuator 05. The beam splitter 08 then guides the test light to the grating 11 under test installed on the double-layer rotating motion system 10.

[0092] Preferably, to improve the accuracy of grating period measurement, the monitoring CCD07 is used to detect the centroid coordinates of the returning spot in the self-collimated state and assist in completing the rotation angle positioning of the grating 11 under test.

[0093] In one implementation, the monitoring CCD07 undergoes angle calibration and reference establishment before use. The specific calibration process is as follows: A plane mirror is installed on the upper turntable 15, and the mirror's attitude is adjusted to be approximately perpendicular to the incident light path; the frequency-stabilized narrow-linewidth laser module is activated, and the laser light, after passing through the beam splitter 08, is incident on the mirror. The reflected light returns and is imaged onto the monitoring CCD07 by the beam splitter 08. The measurement and control system records the centroid coordinates of the currently returned light spot as the initial reference centroid position; the upper turntable 15 is controlled to rotate sequentially by multiple known angles. (i=1,2,…,n), after each rotation, the returned light spot is acquired by monitoring the CCD07, and the centroid coordinates of the light spot are calculated using the gray-scale weighted centroid method to obtain the pixel displacement. The measurement and control system calculates the corresponding values ​​for each point based on multiple sets of data. The average value is taken as the angle calibration coefficient. After calibration is completed, in subsequent measurements, the measurement and control system can calculate the change in rotation angle of the grating 11 under test by multiplying the actual pixel displacement of the returned light spot on the monitoring CCD07 by the calibration coefficient k.

[0094] In another embodiment, such as Figure 10 As shown, monitoring the CCD07 does not require pre-establishing a calibration relationship between pixel position and rotation angle; instead, it employs a real-time self-collimation positioning method based on the coincidence of the spot centroid positions. Specifically, as... Figure 10As shown in (a), when the diffracted light under the self-collimation structure forms a returning light spot on the monitoring CCD 07 after passing through the beam splitter 08, the measurement and control system performs image acquisition and processing on the returning light spot, and uses the centroid extraction algorithm to obtain the centroid coordinates of the returning light spot, which is used as the reference centroid position; at the same time, the measurement and control system can display the reference centroid coordinates on the monitoring interface.

[0095] like Figure 10 As shown in (b), during subsequent measurements, the measurement and control system controls the rotation of the grating 11 under test, so that the self-collimated return spots corresponding to different diffraction orders are sequentially imaged onto the monitoring CCD07, and the centroid coordinates of the current return spot are calculated in real time. Preferably, the centroid position coincidence mainly refers to the judgment of the centroid coordinates in the dispersion direction, that is, judging whether the component of the current centroid coordinate in the dispersion direction coincides with the reference centroid position, or whether the deviation between the two is less than a preset threshold; the position deviation in the non-dispersion direction can be compensated by adjusting the installation position or attitude of the grating 11 under test.

[0096] When the centroid coordinates of the self-collimated returning spot in the dispersion direction corresponding to different diffraction orders coincide with or deviate from the reference centroid position by less than a preset threshold, the measurement and control system determines this state as the self-collimated rectangular position of the corresponding diffraction order. After obtaining the self-collimated rectangular positions corresponding to different diffraction orders, the measurement and control system records the corresponding turntable angle parameters and calculates the grating period of the grating 11 under test based on the diffraction order, laser wavelength, and grating equation. This method eliminates the need for complex pixel-angle calibration and can directly utilize the coincidence relationship of the spot centroid positions to determine the self-collimated rectangular position, thereby improving the real-time performance and system adaptability of the grating period measurement process.

[0097] In a preferred embodiment, by adjusting the rotation angle of the grating 11 under test, the autocollimation positions corresponding to different diffraction orders can be obtained, and the corresponding angle parameters can be recorded.

[0098] Preferably, for the grating 11 under test with a low scribe line density, since it can correspond to multiple diffraction orders under a self-collimation structure, the diffraction orders can be identified by measuring the grating rotation angle under multiple self-collimation states. For example... Figure 8 As shown, under the self-collimation structure, different diffraction orders correspond to different grating rotation angles, and the rotation angle interval between adjacent orders gradually increases with the order, with the smallest rotation angle interval between the 0th and 1st orders. Based on this rule, the self-collimation positions corresponding to the 0th and 1st orders can be identified among multiple self-collimation rotation angles, thereby determining the diffraction order, and the grating period of the grating 11 under test can be calculated according to the grating equation.

[0099] Preferably, for the grating 11 under test with a large scribe line density, the positions of its 0th and 1st order diffraction angles are more distinct. The diffraction order can be directly determined based on the autocollimation rotation angles corresponding to the 0th and 1st orders, and the grating period of the grating 11 under test can be calculated by combining the incident laser wavelength and the grating equation.

[0100] It should be noted that the aforementioned diffraction order identification method is a method for determining the angular positions corresponding to different diffraction orders under self-collimation measurement conditions, and is mainly used in the grating period measurement process. In diffraction efficiency measurement and stray light measurement, when using self-collimation to pre-position or confirm the target diffraction order, the order identification results and corresponding angular relationships obtained by this method can also be used to help determine the estimated direction of the target order diffracted light, the detector receiving direction, and the stray light scanning angle range.

[0101] Preferably, in the reflective self-collimating measurement structure used in this embodiment, the grating diffraction equation can be expressed as:

[0102]

[0103] in, For the grating period, Angle of incidence The diffraction angle, For diffraction orders, Let be the incident laser wavelength. Under self-collimation measurement conditions, the incident light and the target-order diffracted light satisfy the self-collimation return relationship, and the incident angle and the diffraction angle are equal, i.e. When determining the autocollimation rotation angle corresponding to the first-order diffraction, take... Then the grating period can be expressed as:

[0104]

[0105] in, This is the grating rotation angle corresponding to the first-order autocollimation state.

[0106] Therefore, this embodiment can realize the measurement of the period of the grating 11 under test.

[0107] Example 4: Full-parameter automatic measurement embodiment based on the system of the present invention

[0108] When a user selects the "full parameter measurement" mode in the measurement and control system, the system automatically executes the following steps according to a preset procedure:

[0109] (1) Initialization and Reset: Control the double-layer rotary motion system 10 to reset to the reference zero position, and complete the self-test of the light source, detector 09 and lock-in amplifier 20, and complete the light source switching, detector selection and motion system initial position configuration according to the input measurement mode;

[0110] (2) Diffraction efficiency measurement: Control the adjustable monochromatic light source module to output monochromatic light of preset wavelength, and complete the acquisition of target order diffraction light energy and incident reference light energy, and calculate the diffraction efficiency; Preferably, when it is necessary to measure under self-collimation or Littrow conditions and the incident light and the target order diffraction light direction coincide or approximately coincide, the measurement and control system controls the double-layer angular stage 13 in the double-layer rotation motion system 10 to adjust the attitude of the grating 11 to be measured, introduces a preset off-plane deflection angle γ, so that the target order diffraction light and the incident light form spatial separation, and controls the lower turntable 17 and the straight guide rail 18 to drive the detector 09 to move to the receiving position after separation to complete energy acquisition;

[0111] (3) Stray light measurement: Switch to the frequency-stabilized narrow-linewidth laser module, turn on the chopper 06 and set the modulation frequency, control the detector 09 to scan within the preset angle range, extract the stray light signal through the lock-in amplifier 20 and generate the stray light distribution curve; if the incident light coincides or nearly coincides with the target order diffracted light under self-collimation or Littrow conditions during the measurement process, the measurement and control system controls the double-layer angular stage 13 in the double-layer rotation motion system 10 to adjust the attitude of the grating 11 under test, introduce a preset out-of-plane deflection angle γ, so that the target The diffracted light of the first order is spatially separated from the incident light, and the detector 09 is controlled to scan within the separated diffracted light and inter-order stray light regions. The out-of-plane deflection angle γ is determined based on the detector's receiving aperture, the movement range of the lower turntable, and the adjustment distance of the straight guide rail. Under the premise of ensuring that the detector can receive the target order diffracted light without blocking the propagation path of the incident light, the out-of-plane deflection angle γ is taken to be as small as possible to reduce the impact of the out-of-plane deflection on the original autocollimation or Littrow measurement geometry and the energy distribution of the diffracted light.

[0112] (4) Period measurement: Switch to the self-collimation positioning mode of monitoring CCD07, adjust the rotation angle of the grating 11 under test to obtain the self-collimation angle corresponding to different diffraction orders, and calculate the grating period according to the grating equation.

[0113] (5) Results output: The measurement and control system stores and displays the three types of measurement results; when the effective aperture multi-point sampling function is enabled, the measurement results of multiple sampling positions are averaged or statistically analyzed; finally, the diffraction efficiency, stray light measurement results and grating period parameters of the grating 11 under test are output.

[0114] In summary, this invention provides a planar grating full-parameter testing system and measurement method. The system includes a light source system, a dual-layer rotational motion system, a phase-locked loop system, a monitoring system, and a measurement and control system. The light source system includes an adjustable monochromatic light source module and a frequency-stabilized narrow-linewidth laser module. The adjustable monochromatic light source is used for diffraction efficiency measurement, and the frequency-stabilized narrow-linewidth laser is used for stray light and period measurement. The dual-layer rotational motion system is used for separate control of the grating under test and the detector, while also allowing for angle and translation adjustments. The phase-locked loop system is used for weak signal measurement. The monitoring system is used for precise positioning of the grating rotation angle. The measurement and control system is used to complete light source control, motion control, signal acquisition, parameter calculation, and result output. This invention can achieve integrated measurement of planar grating diffraction efficiency, stray light, and period parameters.

[0115] The above embodiments are merely typical implementations of the present invention and are not intended to limit the present invention. Any equivalent substitutions or improvements made within the scope of the claims of the present invention are within the protection scope of the present invention.

Claims

1. A planar grating full-parameter testing system, characterized in that, include: The light source system includes an adjustable monochromatic light source module and a frequency-stabilized narrow-linewidth laser module; A dual-layer rotary motion system is used to separately carry and independently rotate and adjust the grating under test and the optical signal detector; A phase-locked system is used to perform phase-locked amplification measurement of the diffraction light and stray light signals generated by the grating under test; A monitoring system is used to monitor and locate the position of the grating under test in autocollimation mode; The measurement and control system is connected to the light source system, the double-layer rotary motion system, the phase-locked system and the monitoring system respectively, and is used to perform light source switching control, motion control, signal acquisition, parameter calculation and result output; The dual-layer rotational motion system is configured such that, under self-collimation or Littrow measurement conditions, when the target order diffracted light of the grating under test coincides or approximately coincides with the direction of the incident light, the grating under test is controlled to generate an out-of-plane deflection angle γ, so that the target order diffracted light and the incident light are spatially separated in a direction perpendicular to the incident plane, and the optical signal detector is driven to move to the receiving position of the separated diffracted light.

2. The system according to claim 1, characterized in that, The monitoring system includes a beam splitter and a monitoring CCD. In period measurement mode, the diffracted light in the self-collimated state forms a returning spot on the monitoring CCD after passing through the beam splitter. The measurement and control system determines the reference centroid position by extracting the centroid coordinates of the returning spot, and adjusts the rotation angle of the grating under test so that the centroid coordinates of the returning spot in the dispersion direction in different self-collimated states coincide with or deviate from the reference centroid position by less than a preset threshold, thereby obtaining the self-collimated rectangular position of the grating under test, and then calculating the grating period.

3. The system according to claim 1, characterized in that, The optical signal detector includes a PMT detector and a photodiode detector; the measurement and control system automatically switches the detector type according to the measurement mode and measurement wavelength: a PMT detector is used when measuring stray light; when measuring diffraction efficiency, a photodiode detector is used under strong light conditions and a PMT detector is used under weak light conditions.

4. The system according to claim 1, characterized in that, The adjustable monochromatic light source module includes an LDLS white light source and a monochromator, used to output continuously adjustable monochromatic collimated light in the wavelength range of 200nm to 2000nm in diffraction efficiency measurement mode; the frequency-stabilized narrow-linewidth laser module includes a He-Ne frequency-stabilized laser and a collimation and beam expansion assembly, used to output a narrow-linewidth laser beam in stray light measurement mode and period measurement mode.

5. The system according to claim 1, characterized in that, The dual-layer rotary motion system includes an upper turntable, a lower turntable, a straight guide rail, and a displacement adjustment assembly. The upper turntable is used to install and adjust the rotation angle of the grating under test. The lower turntable is used to support the straight guide rail on which the optical signal detector is installed, and can drive the detector to rotate around the center of the grating under test. The displacement adjustment assembly includes a dual-layer angle stage, a displacement stage, and a lifting stage. The dual-layer angle stage is used to adjust the out-of-plane deflection angle γ.

6. A method for measuring the full parameters of a planar grating based on the system described in any one of claims 1 to 5, characterized in that, Includes the following steps: In the diffraction efficiency measurement mode, the monochromatic collimated light of the target wavelength output by the adjustable monochromatic light source module is incident on the grating under test. The optical signal detector is adjusted to the direction of the target order diffraction light to obtain the diffraction light energy. Then, the grating under test is moved out of the optical path and the optical signal detector is moved to the incident light path to obtain the incident reference light energy. The diffraction efficiency measurement value is obtained according to the ratio of the diffraction light energy to the incident reference light energy. In stray light measurement mode, the laser beam output by the frequency-stabilized narrow-linewidth laser module is modulated by the chopper of the phase-locked system and then incident on the grating under test. The optical signal detector is controlled to scan within a preset angle range, and the effective signal corresponding to the stray light is extracted by the phase-locked system to calculate the stray light coefficient. In the period measurement mode, the laser beam output by the frequency-stabilized narrow linewidth laser module is incident on the grating under test after passing through the beam splitting element of the monitoring system. The rotation angle of the grating under test is adjusted to obtain the self-collimation position corresponding to different diffraction orders. The angle parameters are recorded by the monitoring CCD of the monitoring system, and the period measurement value is calculated according to the grating diffraction equation. Specifically, when the target order diffracted light coincides or nearly coincides with the incident light under self-collimation or Littrow measurement conditions, in the diffraction efficiency measurement mode or stray light measurement mode, the grating under test is controlled to generate an out-of-plane deflection angle γ, so that the target order diffracted light and the incident light are spatially separated in a direction perpendicular to the incident plane, and the optical signal detector is driven to move to the separated diffracted light receiving position to collect the signal.

7. The measurement method according to claim 6, characterized in that, The value range of the out-of-plane deflection angle γ is 0.5° to 5°; the spatial separation angle between the incident light and the target order diffracted light is 2γ.

8. The measurement method according to claim 6, characterized in that, In periodic measurement mode, the reference centroid position is determined by extracting the centroid coordinates of the self-collimated return spot, and the centroid coordinates of the return spots corresponding to different diffraction orders in the dispersion direction coincide with or deviate from the reference centroid position by less than a preset threshold, so as to obtain the self-collimated rectangular position.

9. The measurement method according to claim 6, characterized in that, In the diffraction efficiency measurement, stray light measurement, and grating period measurement modes, the grating under test can be moved along the horizontal and vertical directions by the displacement stage and the lifting stage, so that the incident light acts on multiple preset sampling positions within the effective aperture of the grating under test in sequence, and the measurement results at each position are measured and the average value is taken as the final measurement result.

10. The measurement method according to claim 6, characterized in that, The grating under test includes a transmission grating and a reflection grating; when the grating under test is a transmission grating, the optical signal detector is located on the side of the transmission diffraction light, and the measurement and control system switches to the transmission measurement mode to adjust the scanning angle range of the detector.

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