Device and method for measuring grating period and incident angle

Abstract

The invention discloses a device and a method for measuring a grating period and an incident angle. The device comprises a laser light source, a polaroid, a diaphragm, a high-precision turntable, an adjusting frame, a to-be-measured grating, a focusing lens and a detector. The laser light source is used for emitting laser beams. The polaroid is used for adjusting incident light polarization and light intensity. The diaphragm is used for limiting the size of light spots. The high-precision rotary table is used for rotating the grating to be measured and reading the rotation angle. The adjusting frame is used for adjusting the attitude of the to-be-measured grating. The focusing lens is used for focusing light spots. The detector is used for displaying and reading the position of the laser beam focused on the detector. According to the device and method for measuring the grating period and the incident angle, auto-collimation alignment with incident light is not needed, synchronous measurement of the double detectors and simultaneous equation solving are achieved, dependence on known parameters is directly eliminated, the operation process is remarkably simplified, and precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of grating period measurement, in particular to a device and method for measuring grating period by utilizing grating diffraction light. Technical Background

[0002] As an important dispersive element, diffraction grating is widely used in high-energy lasers, spectral analysis, integrated circuits, optical communications, optical precision measurement and other fields. One of the most basic and important indicators of a grating is the period value, which is often called the grating constant. Nowadays, people have higher and higher performance requirements for precision instruments, and thus the requirements for the error of the grating period are becoming more and more stringent. Therefore, inventing a device and method for measuring the grating period and the incident angle is of great significance to the realization of high-performance gratings.

[0003] At present, the method of measuring the grating period using grating self-collimation angle at home and abroad generally encounters the problem of difficulty in judging whether the self-collimated diffracted light and the incident light completely overlap. This leads to a large error in the measured grating period. The commonly used method to reduce the measurement error is to increase the propagation distance of the measurement beam, but this not only makes the measurement system too long, but also causes the light spot to diverge too large and difficult to align. Summary of the invention

[0004] In order to accurately measure the grating period, the present invention provides a device and method for measuring the grating period and the incident angle.

[0005] The technical solution of the present invention is as follows: A device for measuring grating period and incident angle, characterized in that it comprises: A laser light source, used for providing monochromatic coherent light with a wavelength of λ as incident light; The first polarizer, the second polarizer and the aperture are sequentially arranged along the optical path, and are used to adjust the polarization state and light intensity of the incident light and limit the beam diameter; The grating to be measured is fixed on a five-dimensional adjustment frame, which is installed on a high-precision turntable and is used to adjust the pitch, rotation and translation of the grating to be measured; A first focusing lens and a first detector are arranged in the first reflection light path of the grating to be measured, and are used to receive the 0th order reflection light and the mth order diffraction light; A second focusing lens and a second detector are arranged in the second reflection light path of the grating to be measured, and are used to receive the 0th order reflection light and the nth order diffraction light; The high-precision turntable is configured to change the angle of the light beam incident on the grating to be measured by rotating, and make the diffracted light of different orders incident on the first detector and the second detector respectively. Furthermore, the five-dimensional adjustment frame can realize pitch angle, rotation angle and translation adjustment along the X / Y / Z axis directions to ensure that the plane of the grating to be measured is aligned with the rotation axis of the high-precision turntable. Furthermore, the first detector and the second detector are industrial cameras or sensors with a light spot position detection function, which are used to record the coordinate position of the focused light spot. Furthermore, the polarization directions of the first polarizer and the second polarizer are adjustable, so as to optimize the intensity and polarization state of the light incident on the grating to be measured. The method for measuring the grating period and the incident angle using the above-mentioned device for measuring the grating period and the incident angle is characterized in that the method comprises the following steps: ① Adjust the five-dimensional adjustment frame so that during the rotation of the high-precision turntable, the reflected or diffracted light beam of the grating to be measured can pass through the first focusing lens and the second focusing lens to be incident on the first detector and the second detector respectively; ② Rotate the high-precision turntable so that the 0-level reflected light beam passing through the grating to be measured is incident on the first detector through the first focusing lens, and record the high-precision turntable angle θ at this time. 1 and the position of the focused light spot incident on the first detector (x 0 ,y 0 ); ③ Rotate the high-precision turntable so that the m-th order diffracted beam passing through the grating to be measured is incident on the same position (x) on the first detector through the first focusing lens. 0 ,y 0 ), record the high-precision turntable angle θ at this time 2 ; ④Rotate the high-precision turntable so that the 0-level reflected light beam passing through the grating to be measured is incident on the second detector through the second focusing lens, and record the high-precision turntable angle θ at this time 3 and the position of the focused light spot incident on the second detector (x 1 ,y 1 ); ⑤ Rotate the high-precision turntable so that the nth order diffracted beam passing through the grating to be measured is incident on the same position (x) on the second detector through the second focusing lens. 1 ,y 1 ), record the high-precision turntable angle θ at this time 4 ; ⑥Calculate the grating period d and the incident angle α 0 , the formula is as follows: Where: λ is the wavelength of the laser light source output light beam, m and n are the non-zero integer diffraction orders of the grating to be measured.

[0022] The present invention has the following advantages and outstanding effects:

[0023] Compared with the method of measuring the grating period by using the grating self-collimation angle, the present invention does not need to perform self-collimation alignment of the incident light, and can measure the period and incident angle of the grating by using only two detectors with known angles. The problem of difficulty in aligning the self-collimation line density is effectively avoided. In addition, the accuracy of period measurement is further improved by using a focusing lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of an embodiment of a device for measuring grating period and incident angle of the present invention.

[0025] Figure 2 Schematic diagram of the diffraction light of the grating to be measured when the first diffraction order is adopted in Example 1.

[0026] In the figure:

[0027] 1-laser light source, 21-first polarizer, 22-second polarizer, 3-aperture, 4-grating to be measured, 5-adjustment frame, 6-high-precision turntable, 71-first focusing lens, 72-second focusing lens, 81-first detector, 82-second detector. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention shall not be limited thereto.

[0029] Embodiment 1:

[0030] See also Figure 1 , Figure 1 It is a schematic diagram of an embodiment of a device for measuring a grating period and an incident angle of the present invention. As shown in the figure, a device for measuring a grating period and an incident angle includes a laser light source, a first polarizer, a second polarizer, an aperture, a grating to be measured, an adjustment frame, a high-precision turntable, a first focusing lens, a second focusing lens, a first detector and a second detector.

[0031] The laser light source adopts 532nm semiconductor laser. The first polarizer and the second polarizer adopt thin film linear polarizer with working wavelength of 400nm-700nm. Continuously adjustable aperture. The adjustment frame adopts a five-dimensional adjustment frame composed of a two-dimensional manual pitch stage and a three-dimensional manual translation stage. The high-precision turntable adopts a turntable with a minimum resolution of 5″. The first focusing lens and the second focusing lens adopt a plano-convex lens with a focal length of 500mm. The first detector and the second detector adopt an industrial camera with a minimum pixel size of 4μm.

[0032] The semiconductor laser emits a 532nm wavelength laser. The laser beam passes through the first polarizer, the second polarizer and the aperture and is incident on the grating to be measured. The first polarizer and the second polarizer are adjusted to reduce the laser beam power to 20μW. The aperture is adjusted to 1mm. The high-precision turntable is rotated counterclockwise to make the reflected laser beam passing through the grating to be measured deviate from the incident beam. The first focusing lens and the first detector are placed along the reflected laser beam. The position of the first detector is adjusted to the focal position of the first focusing lens. The high-precision turntable is rotated counterclockwise again. The second focusing lens and the second detector are placed along the rotated reflected laser beam. The position of the second detector is adjusted to the focal position of the second focusing lens.

[0033] Assume that the grating to be measured is a plane grating with a period of 1000nm (1000L / mm), the incident angle of the laser beam incident on the grating to be measured is 7°, and the angle between the two optical paths of the first focusing lens, the first detector and the second focusing lens, the second detector is 10°.

[0034] A method for measuring grating period and incident angle comprises the following steps:

[0035] ① Adjust the adjustment frame so that during the rotation of the high-precision turntable, the reflected or diffracted light beam of the grating to be measured can pass through the first focusing lens and the second focusing lens to be incident on the first detector and the second detector respectively;

[0036] ② Rotate the high-precision turntable so that the 0-level reflected light beam passing through the grating to be measured passes through the first focusing lens and is incident on the center position (0,0) of the cross mark on the first detector. Record the high-precision turntable angle reading θ at this time. 1 It is 4°32′22″, where 4°32′22″ is the high-precision turntable angle assumed to be read;

[0037] ③Rotate the high-precision turntable so that the first-order diffracted beam passing through the grating to be measured passes through the first focusing lens and is incident on the same cross mark center position (0,0) on the first detector. Record the high-precision turntable angle θ at this time. 2 =θ 1 +15°32′42″=20°5′4″, where 15°32′42″ is calculated by substituting the assumed grating period and incident angle into the grating equation;

[0038] ④Rotate the high-precision turntable so that the 0-level reflected light beam passing through the grating to be measured passes through the second focusing lens and is incident on the center position (0,0) of the cross mark on the second detector. Record the high-precision turntable angle θ at this time. 3 =θ 1 +5°=9°32′22″, where 5° is half of the assumed 10° angle between the two light paths;

[0039] ⑤Rotate the high-precision turntable so that the first-order diffracted beam passing through the grating to be measured passes through the second focusing lens and is incident on the same position (0,0) on the second detector. Record the high-precision turntable angle θ at this time. 4 =θ 3 +15°46′47″=25°19′9″, where 15°46′47″ is calculated by substituting the assumed grating period and incident angle into the grating equation;

[0040] ⑥ Use the following formula to calculate the grating period d and the incident angle α 0 :

[0041]

[0042] Where: λ is the wavelength of the laser light source, 532nm, m and n are the diffraction orders of the grating to be measured, m = n = 1, θ 1 and θ 2 The high-precision turntable angles recorded for step ② and step ③ are 4°32′22″ and 20°5′4″, respectively. 3 and θ 4 The high-precision turntable angles recorded for step ④ and step ⑤ are 9°32′22″ and 25°19′9″ respectively.

[0043] Using the formula in step ⑥, we can calculate the grating period d to be 1000.0073nm and the incident angle α 0 It is 6.99908°.

[0044] Example 2:

[0045] This embodiment 2 uses the same elements and steps as embodiment 1, with the only difference being that it is assumed that the period of the grating to be measured is 2000nm (500l / mm), the incident angle of the laser beam incident on the grating to be measured is 4°, and the angle between the two optical paths of the first focusing lens, the first detector and the second focusing lens, the second detector is -15°.

[0046] The same as in Example 1, the only difference is that steps ③ and ⑤ use m=n=3 order diffracted light incident, and read the angle θ of the high-precision turntable respectively. 1 =5°10′12″,θ 2 =θ 1 +23°34′35″=28°44′47″,θ 3 =θ 1 -7.5°=-2°19′48″, θ 4 =θ 3+23°33′44″=21°13′56″, where 5°10′12″ is the assumed high-precision turntable angle for reading, 23°34′35″ and 23°33′44″ are calculated by substituting the assumed grating period and incident angle into the grating equation, and -7.5° is half of the assumed angle of -15° between the two optical paths.

[0047] Using the formula in step ⑥, we can calculate the grating period d to be 2000.0091nm and the incident angle α 0 It is 3.99773°.

[0048] The present invention sets up two independent optical paths and records the spot positions and turntable angles of different diffraction orders at the same time, thus avoiding the error introduced by repeated adjustment of a single detector. By combining a five-dimensional adjustment frame (pitch, rotation, translation) with a high-precision turntable, the grating plane is ensured to be strictly aligned with the rotation axis, eliminating the influence of installation deviation on angle measurement. Based on two independent measurements (m-order and n-order diffraction), the grating equation is used to solve the grating period and the incident angle simultaneously, breaking through the traditional method's reliance on known parameters.

[0049] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for measuring grating period and incident angle, characterized in that: include: A laser light source, used for providing monochromatic coherent light with a wavelength of λ as incident light; The first polarizer, the second polarizer and the aperture are sequentially arranged along the optical path, and are used to adjust the polarization state and light intensity of the incident light and limit the beam diameter; The grating to be measured is fixed on a five-dimensional adjustment frame, which is installed on a high-precision turntable and is used to adjust the pitch, rotation and translation of the grating to be measured; A first focusing lens and a first detector are arranged in the first reflection light path of the grating to be measured, and are used to receive the 0th order reflection light and the mth order diffraction light; A second focusing lens and a second detector are arranged in the second reflection light path of the grating to be measured, and are used to receive the 0th order reflection light and the nth order diffraction light; The high-precision turntable is configured to change the angle of the light beam incident on the grating to be measured by rotating, and make the diffracted light of different orders incident on the first detector and the second detector respectively.

2. A device for measuring grating period and incident angle according to claim 1, characterized in that: The five-dimensional adjustment frame can realize the adjustment of the pitch angle, the rotation angle and the translation along the X / Y / Z axis directions to ensure that the plane of the grating to be measured is aligned with the rotation axis of the high-precision turntable.

3. The device for measuring grating period and incident angle according to claim 1, characterized in that: The first detector and the second detector are industrial cameras or sensors with a light spot position detection function, and are used to record the coordinate position of the focused light spot.

4. The device for measuring grating period and incident angle according to claim 1, characterized in that: The polarization directions of the first polarizer and the second polarizer are adjustable, and are used to optimize the intensity and polarization state of light incident on the grating to be measured.

5. A method for measuring grating period and incident angle using a device for measuring grating period and incident angle according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: ① Adjust the five-dimensional adjustment frame so that during the rotation of the high-precision turntable, the reflected or diffracted light beam of the grating to be measured can pass through the first focusing lens and the second focusing lens to be incident on the first detector and the second detector respectively; ② Rotate the high-precision turntable so that the 0-level reflected light beam passing through the grating to be measured is incident on the first detector through the first focusing lens, and record the high-precision turntable angle θ1 and the position of the focused light spot incident on the first detector (x0, y0); ③ Rotate the high-precision turntable so that the m-th order diffracted light beam passing through the grating to be measured passes through the first focusing lens and is incident on the same position (x0, y0) on the first detector, and record the high-precision turntable angle θ2 at this time; ④ Rotate the high-precision turntable so that the 0-order reflected light beam passing through the grating to be measured is incident on the second detector through the second focusing lens, and record the high-precision turntable angle θ3 and the position of the focused light spot incident on the second detector (x1, y1); ⑤Rotate the high-precision turntable so that the n-th order diffracted light beam passing through the grating to be measured passes through the second focusing lens and is incident on the same position (x1, y1) on the second detector, and record the high-precision turntable angle θ4 at this time; ⑥ Calculate the grating period d and the incident angle α0, the formula is as follows: Where: λ is the wavelength of the laser light source output light beam, m and n are the non-zero integer diffraction orders of the grating to be measured.

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