Ultrahigh-precision small-angle measuring instrument and reference device based on optical frequency measurement

Abstract

The invention provides a small-angle measurement reference device based on light frequency measurement, which comprises a laser generating device, a narrow-band interference sheet (3), a reflector group and a beat frequency measurement module which are sequentially arranged on a light path, and is characterized in that the narrow-band interference sheet (3) is fixed on a high-precision horizontal rotating table (4); light output by the laser generating device passes through the narrow-band interference sheet (3) to obtain narrow-band light, and finally measured laser is output by the reflector group; measured laser is input to the beat frequency measurement module and is subjected to beat frequency comparison with comb teeth output by the optical comb system, and the rotation angle of the narrow-band interference sheet is obtained by measuring the beat frequency delta f. Due to the fact that the frequency fluctuation of the optical comb frequency is the Hz magnitude, and the frequency fluctuation of the free operation narrow-band interference sheet laser is dozens of kHz, the angle measurement limit can be converted into laser frequency measurement of dozens of kHz, and the corresponding angle measurement limit is about 0.0001 ''. The small-angle measurement reference device can meet the application requirements of high-precision equipment.

Description

Technical Field

[0001] The invention relates to a small angle measurement reference device, in particular to an ultra-high precision small angle measurement instrument and a reference device based on optical frequency measurement. Background Art

[0002] Improving the accuracy of small-angle measurement is crucial to many technical fields, involving multiple technical applications such as scientific research, engineering, manufacturing, navigation, etc. In scientific experiments and research, improving the accuracy of small-angle measurement can help scientists observe and measure tiny angle changes more accurately, thereby improving the reliability and accuracy of experiments.

[0003] In engineering fields, such as micromechanical systems (MEMS), precision instruments, and optical systems, improving the accuracy of small-angle measurement can improve the performance and stability of these systems. At present, the most commonly used angle measurements are based on the principle of laser interferometry (for example, the technical solutions disclosed in Chinese invention patents CN 104330054A, CN 1963384A, CN 102384730 B, and CN 102506768 B), that is, the change in angle is converted into the change in laser interference fringes. The small-angle measurement accuracy achieved by this type of method is relatively low and can no longer meet the demand for high-precision measurement. According to the records of the prior art, the highest accuracy that can be achieved by the currently implemented laser small-angle reference device is 0.001". However, with the development of science and technology, the requirements for high-precision measurement of small angles in application technologies such as lithography machines, laser radars, precision robots, and virtual reality are increasing, and further improving the accuracy of small-angle measurement has become a requirement for the application of these high-precision technologies. Summary of the invention

[0004] The purpose of the present invention is to further improve the accuracy of small angle measurement and to provide an ultra-high precision small angle measuring instrument and a reference device based on optical frequency measurement that convert angle measurement into frequency measurement.

[0005] The idea of ​​this invention is to use the ultra-high sensitivity of the laser frequency in the narrowband interference plate laser to the angle of the narrowband interference plate, attach the narrowband interference plate to the object to be measured, and detect the change of the narrowband interference plate laser output frequency in order to achieve ultra-high precision angle measurement of the device to be measured. -18 Compared with the measurement resolution that can be obtained by converting angles into laser wavelengths in the prior art, the present invention hopes to convert angle measurement into measurement of laser frequency. Since the resolution of frequency measurement is better than that of wavelength measurement, the resolution of small angle measurement will be greatly improved, so as to achieve precise measurement of 0.0001″ or even 0.00000001″.

[0006] To this end, the present invention provides a small angle measurement reference device based on optical frequency measurement, wherein the device comprises a laser generating device, a narrowband interference plate 3, a reflector group and a beat frequency measurement module which are sequentially arranged on an optical path, the narrowband interference plate 3 being fixed on a high-precision horizontal rotating table 4, the light output by the laser generating device is filtered out of the band after passing through the narrowband interference plate 3, and narrowband light is obtained; the narrowband light is returned to the laser diode after passing through the reflector group, and when the oscillation in the cavity reaches a threshold, the reflector group outputs the measured laser; the measured laser is input to the beat frequency measurement module, and the beat frequency measurement module beats the measured laser with the comb teeth output by the optical comb system to obtain the beat frequency, and when the high-precision horizontal rotating table (4) rotates to cause the measured laser frequency to change by Δf, the change in the beat frequency is equal to Δf.

[0007] Wherein, Δf=f0-f1, f0 is the measured laser frequency when the high-precision horizontal rotating stage is located at the initial position, and f1 is the measured laser frequency after the high-precision horizontal rotating stage rotates.

[0008] According to the formula f = cλ -1 , df=-cλ -2 cλ, where f is the operating frequency of the laser generator, c is the speed of light, and λ is the wavelength. The rotation angle of the narrowband interferometer plate has a linear relationship K (nm / °) with the measured laser wavelength λ. It is known that the relationship between the beat frequency change Δf and the rotation angle θ of the narrowband interferometer plate is:

[0009]

[0010] In the present invention, the laser generating device is a conventional setting in the art, and generally includes a laser diode 1 and a first collimating lens 2 which are sequentially arranged on the optical path. The working wavelength of the laser diode 1 can be any wavelength. Preferably, from the perspective of easy acquisition or economical saving, a 780nm wavelength laser diode can be used. Those skilled in the art can also select laser diodes with other working wavelengths, such as 420nm, 850nm, 1550nm laser diodes, etc.

[0011] In the present invention, a preferred embodiment is that the reflector group includes a partial reflector 7 arranged on the optical path. Preferably, a focusing lens 6 and a second collimating lens 8 can also be respectively arranged before and after the partial reflector 7. Those skilled in the art can also selectively increase / reduce optical elements according to the laser design principle.

[0012] In this way, the divergent light output by the laser diode 1 is collimated into parallel light by the first collimating lens 2. The parallel light is filtered out of the band light after passing through the narrow-band interference plate 3 to obtain narrow-band light; the narrow-band light reaches the partial reflector 7 after passing through the focusing lens 6, and the reflected light in the opposite direction of the narrow-band light is obtained after passing through the partial reflector 7; the reflected light returns to the laser diode 1 after passing through the narrow-band interference plate 3, and when the intracavity oscillation reaches the threshold, the partial reflector 7 outputs the laser, and the output laser to be measured is obtained after passing through the second collimating lens 8. The measured laser reaches the beat frequency measurement module after being reflected by the reflector 9, and the beat frequency is compared with the optical comb system. By measuring the change in the beat frequency Δf, it can be converted into the change in the rotation angle θ of the narrow-band interference plate.

[0013] In the present invention, the transmission peak center wavelength of the narrowband interference plate 3 matches the wavelength of the laser diode. For example, when a 780nm band laser diode is used, the transmission peak center wavelength of the narrowband interference plate 3 is 780nm. When the narrowband interference plate 3 is rotated clockwise / counterclockwise in one direction, the center frequency of the transmission wavelength of the narrowband interference plate changes with the rotation angle.

[0014] As a preferred embodiment, the beat frequency measurement module includes a first half-wave plate 10 arranged in the outgoing direction of the reflected light of the reflector 9, a polarization beam splitter prism 13, a broadband detector 14 and a frequency counter 15 arranged in the output light direction of the polarization beam splitter prism 13; the laser to be measured is completely reflected after being incident on the polarization beam splitter prism 13 through the first half-wave plate 10, the comb teeth emitted by the optical comb system are incident on the polarization beam splitter prism after passing through the second half-wave plate 12, the comb teeth are combined with the laser to be measured and arrive at the broadband detector 14, the broadband detector 14 is connected to the frequency counter 15, and the rotation angle of the narrow-band interference plate is obtained by measuring the change in the beat frequency.

[0015] In the present invention, the broadband detector, frequency counter and optical comb system are all existing devices in the art, for example, a 50 GHz broadband detector is used.

[0016] As an alternative technical solution, a prismatic super-strong grade reflective film 71 can be used to replace part of the reflector 7. When this technical solution is adopted, the narrow-band interference plate 3 can be bonded to the prismatic super-strong grade reflective film 71 to improve the mechanical robustness of the system, and there is no need to install the focusing lens 6 and the second collimating lens 8. Generally, the prismatic super-strong grade reflective film 71 with a high retroreflection coefficient can realize the technical solution of the present invention, such as the micro-prismatic reflective film disclosed in Chinese invention patent application CN 201410823342.3. The prismatic super-strong grade reflective film is set in a direction perpendicular to the incident light, and the incident light is returned along the original path within the rotation angle range of ±20°, and the intracavity oscillation output of the measured laser can be achieved. The high-precision horizontal rotation stage of the present invention is a commercially available product, such as the small rotation stage (PDR1C) sold by Thorlabs.

[0017] According to a preferred embodiment, the present invention further comprises an ultra-low expansion glass base 72, on which the laser diode 1, the first collimating lens 2, the narrowband interference plate 3, the high-precision horizontal rotating stage 4, the rotating stage fixing seat 5, the focusing lens 6 and the partial reflector 7 are fixed, which can be used to reduce the influence of the cavity length jitter on the frequency of the measured laser during free operation, and stabilize the laser frequency fluctuation to the Hz level. This setting can further improve the angle measurement resolution. Since the second collimating lens does not interfere with the frequency stability, the second collimating lens can be placed on the ultra-low expansion glass base.

[0018] In the present invention, the ultra-low expansion glass may be ultra-low expansion glass (ULE) sold by Corning Incorporated of the United States.

[0019] On the other hand, the present invention also provides a small angle measurement method based on a narrow-band interference plate laser, the method comprising the following steps:

[0020] (1) The laser light emitted by the laser diode is passed through a narrow-band interference plate to obtain narrow-band light; the narrow-band light is reflected by a partial reflector and then returns to the laser diode; when the oscillation in the cavity reaches a threshold, the partial reflector outputs the measured laser light; the initial wavelength of the measured laser light is λ0, and the real-time wavelength is λ;

[0021] (2) When the narrowband interference plate rotates, a curve of the rotation angle θ and λ is plotted. The expression of the narrowband interference plate rotation angle θ and the transmission wavelength λ is:

[0022]

[0023] λ0 is the transmission wavelength when the interference plate is perpendicular to the light beam, n eff is the refractive index of the narrowband interference plate;

[0024] From the expression of the narrowband interference plate rotation angle θ and λ, we get K, which is the slope of the curve:

[0025]

[0026] (3) The laser under test in step (1) is input to a beat frequency measurement module, and the beat frequency measurement module beats the laser under test with the comb teeth output by the optical comb system to obtain a beat frequency;

[0027] (4) Calculate the rotation angle θ (°) of the narrowband interference plate. The relationship between the change Δf of the beat frequency and the rotation angle θ of the narrowband interference plate is:

[0028]

[0029] In the present invention, K is the slope of the curve of the rotation angle θ and λ. When θ changes within a small range, K can be regarded as a constant. For example, when the initial wavelength of the laser is λ0=780nm, a small angle rotation occurs at θ=20°. When the narrowband interference plate changes at a small angle within this range, K is approximately 1nm / °. Substituting into the calculation, the relationship between the rotation angle θ of the narrowband interference plate and the frequency change Δf is 4.9×10 11 Hz / °.

[0030] The small angle measurement reference device of the present invention uses a narrowband interference plate to perform narrowband filtering, filters the broadband light emitted by the laser diode into a narrowband beam, and realizes the output of the measured laser whose laser frequency is extremely sensitive to the angle of the narrowband interference plate under the light feedback of the partial reflector. Subsequently, the beat frequency of the measured laser and the optical comb is measured by the beat frequency measurement module, so that the change of the small angle of the narrowband interference plate is reflected in the change of the beat frequency of the measured laser and the optical comb.

[0031] Since the stability of the optical comb frequency can reach the E-14 level and the frequency fluctuation is in the Hz level, while the frequency fluctuation of the free-running narrowband interference plate laser is in the order of tens of kHz, the angle measurement limit can be converted into a laser frequency measurement of tens of kHz, and the corresponding angle measurement limit is about 0.0001". When the frequency fluctuation of the free-running narrowband interference plate laser is further stabilized at the Hz level through an ultra-low expansion rate glass base, the corresponding angle measurement resolution can be achieved at the order of about 0.00000001", achieving a significant improvement in the resolution of ultra-high precision angle measurement for small angle metrology.

[0032] The present invention utilizes the structure and principle of a small angle measurement reference device based on a narrowband interference plate laser to realize an angle measuring instrument with an angle measurement limit of 0.0001″, which can be applied to MEMS, precision instruments and optical systems to meet the application requirements of such high-precision equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a structural schematic diagram of a small angle measurement reference device of Example 1;

[0034] Figure 2 This is a structural schematic diagram of a small angle measurement reference device of Example 3;

[0035] Figure 3 : is the relationship between the transmission wavelength of the narrow-band interference plate in Example 1 and the rotation angle of the narrow-band interference plate.

[0036] Among them, 1. laser diode, 2. first collimating lens, 3. narrow-band interference plate, 4. high-precision horizontal rotating stage, 5. rotating stage fixing seat, 6. focusing lens, 7. partial reflecting mirror, 71. prism-type super-strong reflective film, 72. ultra-low expansion rate glass base, 8. second collimating lens, 9. reflecting mirror, 10. first half-wave plate, 11. optical comb system, 12. second half-wave plate, 13. polarization beam splitter prism, 14. broadband detector, 15. frequency counter. DETAILED DESCRIPTION

[0037] The following examples are used to explain the technical solutions of the present invention in a non-limiting manner.

[0038] Example 1

[0039] like Figure 1 The small angle measurement reference device based on narrowband interference plate laser shown in the figure has an operating band of 780nm. The device mainly includes a laser diode 1, a first collimating lens 2, a narrowband interference plate 3, a focusing lens 6, a partial reflector 7, a second collimating lens 8 and a reflector 9 arranged in sequence on the optical path, an optical comb system 11 and a beat frequency measurement module are arranged in the reflected light output direction of the reflector 9, and a high-precision horizontal rotating table 4 is fixed on the rotating table fixing seat 5. Among them, the focusing lens 6 and the second collimating lens 8 are arranged before and after the partial reflector 7, which is conducive to improving the stability of the measured laser. Among them, the narrowband interference plate 3 is fixed on the high-precision horizontal rotating table 4, so the narrowband interference plate 3 can rotate in the horizontal direction to change the angle between the incident light and the narrowband interference plate. The beat frequency measurement module mainly includes a first half-wave plate 10, a second half-wave plate 12, a polarization beam splitter prism 13, a broadband detector 14 and a frequency counter 15.

[0040] The optical comb system 11 adopts Sanglok Lee et.al, Laser frequency stabilization in the10 -14 range via optimized modulation transfer spectroscopy on the 87 The 780nm ultra-stable laser system disclosed by the Rb D2 line (Opt. Lett. 48(4), 1020-1023(2023)) locks the comb frequency of the optical comb. The system uses modulation transfer spectroscopy (MTS) to achieve high-performance laser frequency stabilization on the Rb 87D2 transition line. The frequency stability of the two frequency-stabilized external cavity semiconductor lasers (ECDL) reaches Short-term stability, up to 10 5 s is only more than 2×10 -12 The structure consists of an MTS mounted on an optical table: a 87Wedge-shaped vapor cell for Rb (Thorlabs, GC19075-RB87). AMP, amplifier (Mini-Circuits, ZFL-500LN+); BE1 and BE2 are beam expanders; EOM is electro-optic modulator (Qubig, PM7-NIR_5); FC is fiber collimator; FG is signal generator; GT-P is Glan-Thompson polarizer; half-wave plate; LPF is low-pass filter (Mini-Circuit, SLP-1.9+, SLP-5+); mixer, phase detector (Mini-Circuits, ZRPD-1+); OS, oscilloscope; PBS is polarization beam splitter; PD is photodiode (Thorlabs, PDA10A2).

[0041] When working, the divergent light output by the 780nm laser diode 1 is collimated into parallel light by the first collimating lens 2. The parallel light passes through the narrowband interference plate 3 (transmission wavelength is near 780nm) and the out-of-band light is filtered out to obtain narrowband light within the range of 0.3nm. The narrowband light reaches the partial reflector 7 after passing through the focusing lens 6, and is reflected to obtain reflected light in the opposite direction of the narrowband light. The reflected light returns to the laser diode 1 through the narrowband interference plate 3. When the intracavity oscillation reaches the threshold, the partial reflector 7 outputs the laser, and the measured laser is obtained after passing through the second collimating lens 8.

[0042] The measured laser is reflected by the reflector 9 and reaches the beat frequency measurement module through the first half-wave plate 10. The beat frequency measurement module compares the measured laser with the comb teeth output by the optical comb system 11 to measure the beat frequency.

[0043] The first half-wave plate 10 and the second half-wave plate 12 in the beat frequency measurement module respectively adjust the polarization of the measured laser and the light comb to maximize the power after the beam is combined by the polarization beam splitter prism 13. The broadband detector 14 is used to measure the frequency difference between the measured laser and the light comb, and the change in the beat frequency Δf is read through the frequency counter 15.

[0044] In this embodiment, the transmission wavelength of the narrow-band interference plate 3 is around 780 nm, and the transmission wavelength changes accordingly with the change of the incident angle. Figure 3 It is the relationship between the transmission wavelength of the narrowband interference plate and the angle of the narrowband interference plate obtained by measurement. The horizontal axis is the incident angle (that is, the angle between the incident light and the normal of the narrowband interference plate), and the vertical axis represents the transmission center wavelength of the narrowband interference plate.

[0045] It can be seen that when the narrow-band interference plate rotates at an angle θ (i.e., the incident angle) of 10°, the slope K of the curve is about 0.55, that is, the relationship between the change in the angle θ of the interference plate and the change in the transmission wavelength can be regarded as 0.55nm / °, that is, when the laser and the interference plate have an incident angle of 10°, when the interference plate rotates at a small angle θ at this position, the angle modulation rate is about 0.55nm / °. Similarly, it can be concluded from the figure that when the incident angle between the laser and the interference plate is about 20°, the slope K of the curve is about 1, that is, when the narrow-band interference plate rotates at a small angle near this position, the relationship between the change in the rotation angle and the change in the transmission wavelength is 1nm / °, that is, the angle modulation rate is close to 1nm / ° (i.e., K is regarded as 1nm / °).

[0046] Therefore, according to

[0047]

[0048] The calculation shows that when the narrowband interference plate rotates at a small angle at θ = 20°, the relationship between the beat frequency change Δf and the rotation angle of the narrowband interference plate is 4.9×10 11 Hz / °(K=1nm / °).

[0049] Therefore, the small angle change θ of the narrow-band interference plate can be measured by measuring the change Δf of the beat frequency of the output laser.

[0050] Since the frequency stability of the optical comb is at the E-14 level, the frequency fluctuation range of the optical comb is about 1 Hz. Based on the mode selection principle of the narrow-band interferometer, the frequency fluctuation of the measured laser output by the free-running interferometer laser is about 30 kHz. That is, when the narrow-band interferometer does not rotate, the beat frequency change Δf has a frequency fluctuation of 30 kHz.

[0051] According to the above calculation, the relationship between Δf and the rotation angle of the narrowband interference plate is 4.9×10 11 Hz / ° (K is about 1nm / °), it can be known that when the beat frequency change Δf is 30kHz, the corresponding interference plate rotation angle is about 0.00022", that is, when the interference plate rotation angle is less than 0.00022", the interference plate angle change cannot be obtained by measuring Δf. When the interference plate rotation angle is greater than 0.00022", Δf is greater than 30kHz, the beat frequency change can be measured, and the angle change can be calculated. Therefore, the measuring device of this embodiment achieves a measurement accuracy of 0.0001".

[0052] Example 2

[0053] The difference from Example 1 is that the laser diode uses 852nm laser, and the rest of the structure remains unchanged.

[0054] Similarly, the transmission wavelength of the narrowband interference plate is around 852nm, and the transmission wavelength will change accordingly with the change of the incident angle. By plotting the curve of the rotation angle θ and λ and calculating the slope K of the curve, it can be seen that when the incident angle between the laser and the interference plate is about 20°, K is about 1, that is, when the narrowband interference plate rotates at a small angle near this position, the relationship between the rotation angle change and the transmission wavelength change is 1nm / °, that is, the angle modulation rate K = 1 (nm / °).

[0055] according to

[0056]

[0057] The relationship between the change in the beat frequency Δf and the rotation angle of the narrowband interference plate is 4.1×10 11 Hz / °, and the corresponding rotation angle is about 0.00026″ when the beat frequency change Δf is 30kHz. The small angle measurement with a measurement accuracy of 0.0001″ is also achieved.

[0058] Example 3

[0059] The difference from Example 1 is that part of the reflector 7 can be replaced by a prismatic super-strong reflective film 71, using the micro-prismatic reflective film disclosed in Chinese invention patent application CN 201410823342.3. Since the prismatic super-strong reflective film 71 is used, the focusing lens 6 and the second collimating lens 8 do not need to be installed.

[0060] The narrowband interference plate 3 is bonded to the prism-type super-strong reflective film 71 to reduce the laser frequency change caused by mechanical vibration, so that the angle measurement can be performed more accurately. In addition, the laser diode 1, the first collimating lens 2, the narrowband interference plate 3, the prism-type super-strong reflective film 71, the high-precision horizontal rotating table 4 and the rotating table fixing seat 5 are fixed on the base 72 made of ultra-low expansion rate glass, and the ultra-low expansion rate characteristics of the base are used to further overcome the interference caused by mechanical deformation.

[0061] During operation, the divergent light output by the laser diode 1 is collimated into parallel light by the first collimating lens 2. The parallel light passes through the narrow-band interference plate 3 and the out-of-band light is filtered out to obtain narrow-band light. At the same time, a part of the parallel light will be reflected by the narrow-band interference plate 3. After the narrow-band light reaches the prism-type super-strong reflective film 71, it is returned to the laser diode 1 by the original path. When the oscillation in the cavity reaches the threshold, the light reflected and output by the narrow-band interference plate 3 is used as the laser to be measured.

[0062] Same as in Example 1, Figure 3From the relationship between the transmission wavelength and the rotation angle of the medium and narrow-band interference plate, it can be seen that when the incident angle between the laser and the interference plate is 20°, K is approximately 1, that is, when the narrow-band interference plate rotates at a small angle near this position, the relationship between the change in rotation angle and the change in transmission wavelength is 1nm / °, that is, the angular modulation rate K=1(nm / °).

[0063] according to

[0064]

[0065] The relationship between the change in the beat frequency Δf and the rotation angle of the narrowband interference plate is 4.9×10 11 Hz / °, that is, the relationship between the change in beat frequency Δf and the change in wavelength is 4.9×10 11 Hz / nm.

[0066] The ultra-low expansion glass can stabilize the frequency fluctuation of the free-running narrow-band interference plate laser at the Hz level. Compared with the frequency fluctuation of about 30kHz when the measured laser is free-running in Example 1, this embodiment improves the stability of the frequency fluctuation of the measured laser when it is free-running to the Hz level, that is, it can be measured when the beat frequency change Δf is at the Hz level. Therefore, when the angular modulation rate K=1nm / ° and the beat frequency change Δf=1Hz, the corresponding rotation angle of the interference plate is about 0.0000000073", and the corresponding angle measurement resolution is at the 0.000000001" level. When the angular modulation rate K=0.55nm / ° and the beat frequency change Δf=1Hz, the corresponding rotation angle of the interference plate is about 0.000000013", and the corresponding angle measurement resolution is at the 0.00000001". Therefore, the measurement accuracy of this system can reach at least 0.00000001″ for small angle measurement, which means that the resolution of ultra-high precision angle measurement in small angle metrology can be greatly improved.

[0067] The ultra-high precision small angle measurement reference device of the present invention can realize a small angle measurement reference device based on a narrowband interference plate laser. Compared with the prior art, the present invention overcomes the limitations of the laser interferometer measurement method in measuring angle indicators, innovatively utilizes the principle of narrowband interference plate lasers, and uses the sensitivity of laser frequency to the rotation angle of the narrowband interference plate to convert the angle measurement into the laser frequency measurement, thereby realizing a small angle measurement reference device with the ability to measure tiny angles. The ultra-high precision small angle measurement reference device of the present invention can meet the application needs of aerospace laser gyroscopes, high-end equipment manufacturing, and precision optical devices.

Claims

1. A small angle measurement reference device based on optical frequency measurement, characterized in that The device comprises a laser generating device, a narrowband interference plate (3), a reflector group and a beat frequency measurement module which are arranged in sequence on an optical path. The narrowband interference plate (3) is fixed on a high-precision horizontal rotating table (4). The light output by the laser generating device passes through the narrowband interference plate (3) and out-of-band light is filtered out to obtain narrowband light. The narrowband light passes through the reflector group and returns to the laser generating device. When the oscillation in the cavity reaches a threshold, the reflector group outputs the measured laser. The measured laser is input to the beat frequency measurement module. The beat frequency measurement module beats the measured laser with the comb teeth output by the optical comb system to obtain a beat frequency. When the high-precision horizontal rotating table (4) rotates and causes the measured laser frequency to change by Δf, the change in the beat frequency is equal to Δf.

2. The small angle measurement reference device according to claim 1, characterized in that The laser generating device comprises a laser diode (1) and a first collimating lens (2) which are sequentially arranged on an optical path, and a reflector group comprises a focusing lens (6), a partial reflector (7) and a second collimating lens (8) which are sequentially arranged on the optical path.

3. The small angle measurement reference device according to claim 1, characterized in that The transmission peak center wavelength of the narrow-band interference plate (3) matches the wavelength of the laser diode (1).

4. The small angle measurement reference device according to claim 1, characterized in that The beat frequency measurement module comprises a reflector (9), a first half-wave plate (10) arranged in the emission direction of reflected light of the reflector (9), a polarization beam splitter prism (13), a broadband detector (14) arranged in the output light direction of the polarization beam splitter prism (13), and a frequency counter (15); the laser to be measured is incident on the polarization beam splitter prism (13) through the first half-wave plate (10) and then completely reflected; the comb teeth emitted by the optical comb system (11) are incident on the polarization beam splitter prism (13) after passing through the second half-wave plate (12); the comb teeth are combined with the laser to be measured and then arrive at the broadband detector (14); the broadband detector (14) is connected to the frequency counter (15); the frequency counter (15) measures the beat frequency between the comb teeth of the optical comb and the laser to be measured to obtain a variation Δf of the beat frequency.

5. The small angle measurement reference device according to claim 1, characterized in that A prism-type super-strong reflective film (71) is used to replace part of the reflector (7).

6. The small angle measurement reference device according to claim 1, characterized in that The device also includes an ultra-low expansion rate glass base, and the laser diode (1), the first collimating lens (2), the narrow-band interference plate (3), the high-precision horizontal rotating table (4), the rotating table fixing seat (5) and the prism-type super-strong reflective film (71) are fixed on the ultra-low expansion rate glass base (72).

7. The small angle measurement reference device according to claim 1, characterized in that The reflector assembly further comprises a second collimating lens (8) arranged between the partial reflector (7) and the reflector (9).

8. The small angle measurement reference device according to claim 1 or 4, characterized in that The narrowband interference plate rotation angle θ (°) is obtained by measuring the change Δf of the beat frequency. The relationship between the change Δf of the beat frequency and the rotation angle θ of the narrowband interference plate is: Where c is the speed of light, λ is the transmission wavelength, and K is the slope of the curve between the interference plate angle and the transmission wavelength, in nm / °.

9. A small angle measurement method based on a narrow-band interference plate laser, the method comprising the following steps: (1) The laser light emitted by the laser diode is passed through a narrow-band interference plate to obtain narrow-band light; the narrow-band light is reflected by a partial reflector and then returns to the laser diode; when the oscillation in the cavity reaches a threshold, the partial reflector outputs the measured laser light; the initial wavelength of the measured laser light is λ0, and the real-time wavelength is λ; (2) When the narrowband interference plate rotates, a curve of the rotation angle θ and λ is plotted. The expression of the narrowband interference plate rotation angle θ and the transmission wavelength λ is: λ0 is the transmission wavelength when the interference plate is perpendicular to the light beam, n eff is the refractive index of the narrowband interference plate; K is obtained from the expression of the narrow-band interference plate rotation angle θ and λ, where K is the slope of the curve: (3) The laser under test in step (1) is input to a beat frequency measurement module, and the beat frequency measurement module beats the laser under test with the comb teeth output by the optical comb system to obtain a beat frequency; (4) Calculate the rotation angle θ (°) of the narrowband interference plate. The relationship between the change Δf of the beat frequency and the rotation angle θ of the narrowband interference plate is:

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