A differential wavefront angle measurement device based on an optical wedge

Abstract

This application proposes a differential wavefront angle measurement device based on an optical wedge. A reference beam is reflected by a wedge-shaped mirror and combined with the measurement beam. Beam interference generates a beat frequency signal. The beat frequency signal is processed using differential wavefront sensing technology to obtain phase information. The phase difference-angle conversion coefficient is calibrated in real time based on the wedge angle value of the wedge-shaped mirror. The angle between the measurement beam and the reference beam is calculated using the real-time calibrated phase difference-angle conversion coefficient. This invention uses the wedge angle value of the wedge-shaped mirror as a traceable angle reference standard, ensuring the reliability of the coefficient calibration and improving the accuracy and stability of angle measurement.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, and particularly relates to a differential wavefront angle measurement device based on an optical wedge. Background Technology

[0002] Differential wavefront angle measurement technology is an angle measurement technique based on heterodyne interferometry. Its basic principle is that two laser beams with a stable difference frequency are simultaneously incident on a four-quadrant detector, satisfying the coherence condition. This generates four beat frequency signals, each recording the coherent light information received in its corresponding quadrant. Signal processing yields the phase information of these four beat frequency signals. Combined with the phase-angle conversion coefficient, the angle between the two laser beams can be measured. Differential wavefront angle measurement technology offers advantages such as high measurement accuracy, strong anti-interference capability, and low coupling, and is widely used in high-precision laser interferometry applications.

[0003] When using the differential wavefront method to measure beam angle, it is first necessary to calibrate the phase difference-angle conversion coefficient of the differential wavefront sensor. Only by obtaining this coefficient can the measured phase difference value be converted into a beam angle value. However, the instrument is unstable during the experiment due to environmental factors, temperature, and other influences. The phase difference-angle coefficient calibrated before the experiment changes with environmental factors and experimental conditions, leading to unreliable beam angle measurement results. How to achieve a highly stable, traceable, and reliable angle reference standard, and calibrate the phase difference-angle coefficient in real time to improve the accuracy of beam angle measurement, is a problem that needs to be solved. Summary of the Invention

[0004] Based on this, the present invention proposes a differential wavefront angle measurement device based on an optical wedge, which can calibrate the phase difference-angle conversion coefficient in real time and has high stability, traceability and high reliability.

[0005] This invention discloses a differential wavefront angle measurement device based on an optical wedge, comprising:

[0006] Laser source, wedge reflector, differential wavefront sensing unit and measurement module;

[0007] The laser source generates a reference beam that is directed toward a wedge-shaped mirror. After being reflected by the wedge-shaped mirror, the reference beam is combined with the measurement beam and incident on the differential wavefront sensing unit.

[0008] The differential wavefront sensing unit is configured to output a beat frequency signal to the measurement module based on the incident beam.

[0009] The measurement module is configured to calibrate the phase difference-angle conversion coefficient in real time based on the wedge angle value of the wedge reflector, and use the real-time calibrated phase difference-angle conversion coefficient to calculate the angle between the measurement beam and the reference beam.

[0010] Furthermore, the differential wavefront sensing unit includes a four-quadrant photoelectric detection circuit. After the reference beam and the measurement beam are combined, they are incident on the photosensitive surface of the four-quadrant photoelectric detection circuit to form a beat frequency signal.

[0011] Furthermore, the measurement module includes at least:

[0012] Photoelectric conversion unit, AD sampling unit, digital phase meter and angle calculation unit;

[0013] The photoelectric conversion unit is configured to convert the beat frequency signal into an electrical signal;

[0014] The AD sampling unit is configured to convert the electrical signal output by the photoelectric conversion unit into a digital signal;

[0015] A digital phase meter, configured to calculate phase information of a reference beam and a measurement beam based on digital signals;

[0016] The angle calculation unit is configured to calibrate the phase difference-angle conversion coefficient based on the phase information and the wedge angle value of the wedge reflector, and use this coefficient to calculate the angle between the measurement beam and the reference beam.

[0017] Furthermore, the measurement module also includes:

[0018] An adjustable gain control unit and an anti-aliasing filter unit are located between the photoelectric conversion unit and the digital phase meter.

[0019] Furthermore, the aforementioned device also includes a collimation module disposed between the laser and the wedge mirror for collimating the reference beam incident on the wedge mirror.

[0020] Furthermore, the collimation module includes a polarization-maintaining fiber and a collimating lens. Along the direction of light propagation, the reference beam first passes through the polarization-maintaining fiber and then through the collimating lens to enter the wedge-shaped mirror.

[0021] Furthermore, the aforementioned device also includes an acousto-optic frequency shifter, positioned between the laser source and the collimation module.

[0022] Furthermore, when there are multiple reference beams, the above-mentioned device also includes a coupler disposed between the acousto-optic frequency shifter and the collimation module.

[0023] Furthermore, the aforementioned device also includes a beam splitter, disposed after the laser source, configured to split the laser emitted by the laser source into at least two reference beams of equal intensity.

[0024] Furthermore, the beam splitter includes a first beam splitter and a second beam splitter. The laser emitted by the laser source is split into a first reference beam and a second beam by the first beam splitter.

[0025] The second beam is split into a second reference beam and a measurement beam by the second beam splitter.

[0026] Furthermore, the first surface of the wedge-shaped mirror is coated with a first high-reflectivity film, and the second surface is coated with a second high-reflectivity film, for reflecting the first reference beam and the second reference beam.

[0027] The aforementioned differential wavefront angle measurement device based on optical wedges has the following advantages:

[0028] This invention proposes a differential wavefront angle measurement device based on an optical wedge. It uses a fixed wedge angle of a wedge-shaped reflector to provide a high-precision angle reference, making the device highly stable and traceable during measurement. Simultaneously, the interference between the measurement reference beam and the measurement beam generates beat frequency signals of different frequencies, enabling real-time calibration of the phase difference-angle conversion coefficient and ensuring the reliability of the coefficient calibration. The beat frequency signals, processed by the same calculation module, exhibit excellent noise common-mode suppression capabilities, effectively improving the measurement accuracy of the differential wavefront angle. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 A schematic diagram of a differential wavefront angle measurement device based on an optical wedge provided in an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the structure of a highly stable and traceable differential wavefront angle measuring device based on an optical wedge for laboratory precision angle measurement provided in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of a differential wavefront angle measurement device based on an optical wedge for high-precision measurement and real-time on-orbit calibration of inter-satellite laser pointing, provided in an embodiment of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1The diagram shows a structural schematic of a differential wavefront angle measurement device based on an optical wedge provided in this embodiment. Along the direction of light propagation, the device is arranged in sequence as follows: a frequency-stabilized laser (1), a polarizing beam splitter (2), a right-angle mirror (3), a first acousto-optic frequency shifter AOM1 (4), a second acousto-optic frequency shifter AOM2 (5), a coupler (16), a polarization-maintaining fiber (7), a collimating lens (8), a wedge mirror (9), a beam splitter prism (10), a polarizer (11), a four-quadrant photoelectric detection circuit (12), a photoelectric conversion unit (13), an adjustable gain control unit (14), an anti-aliasing filter unit (15), an AD sampling unit (16), a digital phase meter (17), a two-dimensional angle calculation unit (18), and a two-dimensional angle result output unit (19).

[0036] A frequency-stabilized laser (1) generates orthogonally linearly polarized light with a frequency of f0. This light is split into two orthogonally linearly polarized beams, p-beam and s-beam, with frequencies of f0, by a polarization beam splitter (2). The p-beam's frequency changes to f3 after passing through a first acousto-optic frequency shifter (4). The s-beam's frequency changes to f2 after being reflected by a right-angle mirror (3) and then by a second acousto-optic frequency shifter (4). The p-beam with frequency f3 and the s-beam with frequency f2 are coupled into a polarization-maintaining fiber (7) by a coupler (6), and then incident on a wedge-shaped mirror (9) through a collimating lens (8). The incident surface of the wedge-shaped mirror (9) is coated with... The S-ray high-reflection film is coated with a P-ray high-reflection film on its back surface, which reflects the S-ray and P-ray respectively. The reflected S-ray and P-ray have a fixed angle determined by the wedge angle of the wedge-shaped reflector (9), which serves as two reference beams and passes through the beam splitter (10). The measurement beam with frequency f1 is reflected by the beam splitter (10) and then combined with the two reference beams. After passing through the analyzer (11), it is incident on the photosensitive surface of the four-quadrant photoelectric detection circuit (12) to form three interference signals with beat frequencies of |f1-f2|, |f1-f3| and |f2-f3| respectively.

[0037] The four-quadrant photoelectric detection circuit outputs three beat frequency signals of different frequencies, which are respectively processed by the photoelectric conversion unit (13), the adjustable gain control unit (14), the anti-aliasing filter unit (15), the AD sampling unit (16), and the digital phase meter (17) to obtain the phase information of the three beat frequency signals. The phase information is further processed by the differential wavefront sensing method. The phase difference-angle conversion coefficient of the differential wavefront is calibrated in real time by using the known fixed angle value of the two reference beams. Then, the differential wavefront phase difference value after interference between the measurement beam and any reference beam is converted into the angle value between the two beams in real time, realizing the real-time high-precision measurement of the angle change of the measurement beam. Moreover, the measured value can be traced back to the wedge angle value of the wedge reflector (9).

[0038] In a further embodiment, the number of reference beams can be increased. Since the wedge angle of the wedge reflector is fixed, the angle of the reference beams is also fixed. This allows the phase difference-angle conversion coefficient to be calibrated in real time during each measurement, resulting in higher and more stable calibration accuracy.

[0039] Example 2

[0040] like Figure 2 The diagram shown is a structural schematic of a highly stable and traceable differential wavefront angle measuring device based on an optical wedge for precision angle measurement in the laboratory, provided in this embodiment.

[0041] The difference from Embodiment 1 is that the measurement beam in this embodiment is generated by a frequency-stabilized laser (1). In addition to the components mentioned in Embodiment 1, the device in this embodiment also includes a second beam splitter (20), a second right-angle mirror (21), a third acousto-optic frequency shifter AOM3 (22), a second polarization-maintaining fiber (23), a second collimating lens (24), and a rotating mirror (25).

[0042] The frequency-stabilized laser (1) generates orthogonally linearly polarized light with a frequency of f0. After passing through the polarizing beam splitter (2), it is split into two orthogonally linearly polarized light p-beam and s-beam with a frequency of f0. After passing through the first acousto-optic frequency shifter (4), the frequency of the p-beam becomes f3. After being reflected by the right-angle mirror (3), the frequency of the s-beam becomes f2 after passing through the second acousto-optic frequency shifter (4). After being transmitted through the second beam splitter (20), the s-beam is reflected by the second right-angle mirror (21) and enters the third acousto-optic frequency shifter (22) with a frequency of f1 as the measurement beam. The p-beam with frequency f3 and the s-beam with frequency f2 are coupled into the polarization-maintaining fiber (7) by the coupler (6), and then directed to the wedge mirror (9) through the collimating lens (8). The incident surface of the wedge mirror (9) is coated with a high-reflectivity film for s-beams, and the rear surface is coated with a high-reflectivity film for p-beams, which reflect the s-beams and p-beams respectively. The reflected s-beams and p-beams have a fixed angle determined by the wedge angle of the wedge mirror (9), which serves as two reference beams and passes through the beam splitter (10). The measurement beam with frequency f1 is emitted through the second polarization-maintaining fiber (23) and the second collimating lens (24), and is reflected by the reflective surface of the rotating mirror (25). It is then combined with the two reference beams through the beam splitter (10), and after passing through the analyzer (11), it is incident on the photosensitive surface of the four-quadrant photoelectric detection circuit (12), forming three interference signals with beat frequencies of |f1-f2|, |f1-f3|, and |f2-f3|.

[0043] Similarly, this embodiment is similar to Embodiment 1, utilizing a photoelectric conversion unit (13), an adjustable gain control unit (14), an anti-aliasing filter unit (15), an AD sampling unit (16), and a digital phase meter (17) to obtain the phase information of the three beat frequency signals. Further, a differential wavefront sensing method is used to process the phase information, and using the known fixed angle between the two reference beams, the differential wavefront phase difference-angle conversion coefficient is calibrated in real time. Then, using this coefficient, the differential wavefront phase difference value after interference between the measurement beam and any reference beam is converted in real time into the angle value between the two beams, achieving real-time high-precision measurement of the angle change of the measurement beam, and this measurement value can be traced back to the wedge angle value of the wedge reflector (9).

[0044] Those skilled in the art should understand that the rotating mirror (25) in this embodiment is used to control the deflection angle of the light beam. In other implementations, it can be replaced by, for example, a reflecting mirror or other optical devices that have the same function of deflecting the light beam. The example in this embodiment is not to be regarded as a limitation of the present invention.

[0045] Example 3

[0046] like Figure 3 As shown, this embodiment provides a differential wavefront angle measurement device based on an optical wedge for high-precision inter-satellite laser pointing measurement and real-time on-orbit calibration. Unlike the previous embodiments, the measurement beam in this embodiment originates from a distant satellite (26). The propagation of the reference beam, the processing of the optical signal, and the angle calculation are similar to those in the previous embodiments, and will not be repeated here.

[0047] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0048] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wedge-based differential wavefront angle measurement device, comprising: The device comprises a laser source, a first beam splitter, a second beam splitter, a wedge-shaped mirror, a differential wavefront sensing unit and a calculation module. The laser source emits light which is split into a first reference beam and a second beam by the first beam splitter, and the second beam is split into a second reference beam and a measurement beam by the second beam splitter, and the first reference beam and the second reference beam are incident on the wedge-shaped mirror. The first surface of the wedge-shaped mirror is coated with a first high-reflection film, and the second surface is coated with a second high-reflection film, for reflecting the first reference beam and the second reference beam. The differential wavefront sensing unit comprises a four-quadrant photodetector circuit, and the first reference beam and the second reference beam are reflected by the wedge-shaped mirror and then combined with the measurement beam to form a beat signal on the light-sensitive surface of the four-quadrant photodetector circuit, and the beat signal is output to the calculation module. The calculation module is configured to calibrate a phase difference-angle conversion coefficient in real time according to the wedge angle of the wedge-shaped mirror, and calculate the included angle between the measurement beam and the reference beam using the real-time calibrated phase difference-angle conversion coefficient. The calculation module comprises at least:

2. The optical wedge-based differential wavefront angle measurement device of claim 1, wherein, a photoelectric conversion unit, an AD sampling unit, a digital phase meter and an angle calculation unit. The photoelectric conversion unit is configured to convert the beat signal into an electrical signal. The AD sampling unit is configured to convert the electrical signal output by the photoelectric conversion unit into a digital signal. The digital phase meter is configured to calculate the phase information of the reference beam and the measurement beam according to the digital signal. The angle calculation unit is configured to calibrate a phase difference-angle conversion coefficient according to the phase information and the wedge angle of the wedge-shaped mirror, and calculate the included angle between the measurement beam and the reference beam using the coefficient. The calculation module further comprises:

3. The optical wedge-based differential wavefront angle measurement device of claim 2, wherein, an adjustable gain control unit and an anti-aliasing filter unit, which are arranged between the photoelectric conversion unit and the digital phase meter. The device further comprises a collimation module arranged between the laser source and the wedge-shaped mirror, for collimating the reference beam incident on the wedge-shaped mirror.

4. The optical wedge-based differential wavefront angle measurement device of claim 1, wherein, The collimation module comprises a polarization maintaining optical fiber and a collimation lens, and the reference beam passes through the polarization maintaining optical fiber and then the collimation lens to be incident on the wedge-shaped mirror.

5. The optical wedge-based differential wavefront angle measurement device of claim 4, wherein, The device further comprises an acousto-optic frequency shifter arranged between the laser source and the collimation module.

6. The optical wedge-based differential wavefront angle measurement device of claim 4, wherein, ​

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