A large-range high-precision differential wavefront sensing measurement device

Abstract

The application provides a wide-range high-precision differential wavefront sensing measurement device. A reference light beam is reflected by a first beam splitter group and then combined with a measurement light beam to enter a differential wavefront sensing unit. The beam splitter in the first beam splitter group forms a certain angle with the horizontal plane. The angle between the reference light beams is adjusted by adjusting the angle of each beam splitter in the first beam splitter group with the horizontal direction. Multi-frequency mixing is used to ensure high precision and realize wide-angle range measurement. The device has the characteristics of reasonable and simple structure, high measurement precision, wide range and high stability.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, and particularly relates to a large-range, high-precision differential wavefront sensing measurement device. Background Technology

[0002] Differential wavefront sensing measurement is an angle measurement technique based on heterodyne laser interferometry. The basic principle is that two laser beams with a stable difference frequency are simultaneously incident on a four-quadrant detector and meet the coherence condition, which will generate four beat frequency signals. The four beat frequency signals record the coherent light information received in the corresponding quadrant. Through signal processing, the phase information of the four beat frequency signals can be obtained. Combined with the phase angle conversion coefficient, the angle measurement of the two laser beams can be realized.

[0003] Differential wavefront sensing boasts advantages such as high measurement accuracy, strong anti-interference capability, and low coupling, making it widely used in high-precision laser interferometry applications. This technology can achieve measurement accuracy on the order of nrad. However, due to the periodic nonlinear error inherent in heterodyne laser interferometry, when the offset angle between the signal light and the local oscillator light increases to a certain extent, a single differential wavefront sensing device will experience phase ambiguity when the photodetector calculates the phase difference, rendering measurement impossible. Consequently, the angle measurement range is limited to the order of mrad. Therefore, how to increase the measurement range of differential wavefront sensing while maintaining high accuracy is a problem that needs to be solved. Summary of the Invention

[0004] Based on this, the present invention proposes a large-range, high-precision differential wavefront sensing measurement device, which achieves large-angle range measurement while ensuring high precision, and has high measurement accuracy.

[0005] This invention provides a large-range, high-precision differential wavefront sensing measurement device, comprising:

[0006] Laser source, first beam splitter group, differential wavefront sensing unit and measurement module;

[0007] A laser source generates a reference beam that is directed toward the first beam splitter group. The reference beam is reflected by the first beam splitter group and combined with the measurement beam, then 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 calculate the angle between the measurement beam and the reference beam based on the beat frequency signal.

[0010] The number of beam splitters in the first beam splitter group is the same as the number of reference beams, so that each reference beam is reflected by an independent beam splitter.

[0011] Adjust the angle between each beam splitter in the first beam splitter group and the horizontal direction so that the angle between two adjacent reference beams is within a preset range, thereby expanding the angle measurement range.

[0012] Furthermore, the preset range is that the angle between two adjacent reference beams is greater than half of the larger value of the measurement range corresponding to each of the two reference beams, and less than half of the sum of the measurement ranges corresponding to the two adjacent reference beams.

[0013] 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.

[0014] Furthermore, the measurement module includes at least:

[0015] Photoelectric conversion unit, AD sampling unit, digital phase meter and angle calculation unit;

[0016] The photoelectric conversion unit is configured to convert the beat frequency signal into an electrical signal;

[0017] The AD sampling unit is configured to convert the electrical signal output by the photoelectric conversion unit into a digital signal;

[0018] A digital phase meter, configured to calculate phase information of a reference beam and a measurement beam based on digital signals;

[0019] The angle calculation unit is configured to calculate the angle between the measurement beam and the reference beam based on the phase information.

[0020] Furthermore, the measurement module also includes:

[0021] An adjustable gain control unit and an anti-aliasing filter unit are located between the photoelectric conversion unit and the digital phase meter.

[0022] Furthermore, the above-mentioned device also includes a collimation module disposed between the laser source and the first beam splitter group, used to collimate the reference beam incident on the first beam splitter group.

[0023] 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 before entering the first beam splitter group.

[0024] Furthermore, the aforementioned device also includes an acousto-optic frequency shifter, positioned between the laser source and the collimation module.

[0025] Furthermore, the aforementioned device also includes a second beam splitter group, disposed after the laser source, configured to split the laser emitted by the laser source into at least two reference beams of equal intensity.

[0026] Furthermore, the measurement beam is formed by the reflection of laser light emitted from the laser source by the second beam splitter group.

[0027] The aforementioned large-range, high-precision differential wavefront sensing measurement device has the following beneficial effects:

[0028] This invention proposes a large-range, high-precision differential wavefront sensing measurement device. A reference beam is reflected by a first beam splitter group and then combined with the measurement beam before entering the differential wavefront sensing unit. The beam splitters in the first beam splitter group form a certain angle with the horizontal plane. By adjusting the angles between each beam splitter and the horizontal direction, the angles between the reference beams are set. Utilizing multi-frequency mixing, a large-angle range measurement is achieved while maintaining high precision. The device features a reasonable and simple structural design, high measurement accuracy, a large range, and high stability. The beat frequency signal passes through the same calculation module, exhibiting good noise common-mode suppression capability, 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 This is a schematic diagram of the structure of the large-range, high-precision differential wavefront sensing measurement device provided in Embodiment 1 of the present invention.

[0031] Figure 2 To utilize Figure 1 The schematic diagram illustrates the principle of expanding the measurement range when the device is used for angle measurement.

[0032] Figure 3 This is a schematic diagram of the structure of the large-range, high-precision differential wavefront sensing measurement device provided in Embodiment 2 of the present invention;

[0033] Figure 4 To utilize Figure 3 The schematic diagram illustrates the principle of expanding the measurement range when the device is used for angle measurement.

[0034] Figure 5 This is a schematic diagram of the structure of the large-range, high-precision differential wavefront sensing measurement device provided in Embodiment 3 of the present invention;

[0035] Figure 6 This is a schematic diagram of the structure of the large-range, high-precision differential wavefront sensing measurement device provided in Embodiment 4 of the present invention.

[0036] Figure 7This is a schematic diagram of the structure of the large-range, high-precision differential wavefront sensing measurement device provided in Embodiment 5 of the present invention;

[0037] Figure 8 This is a schematic diagram of the structure of the large-range, high-precision differential wavefront sensing measurement device provided in Embodiment Six of the present invention. Detailed Implementation

[0038] 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.

[0039] Example 1

[0040] like Figure 1 The diagram shows a structural schematic of a large-range, high-precision differential wavefront sensing and measurement device provided in this embodiment, which includes two unpolarized reference beams. Along the direction of light propagation, the following components are arranged sequentially: a frequency-stabilized laser (1), a beam splitter BS1 (2), a first acousto-optic frequency shifter AOM1 (3), a first polarization-maintaining fiber (4), a first collimating lens (5), a beam splitter BS2 (6), a second acousto-optic frequency shifter AOM2 (7), a second polarization-maintaining fiber (8), a second collimating lens (9), a beam splitter BS3 (10), a beam splitter BS4 (11), a beam splitter BS5 (12), a four-quadrant photoelectric detection circuit (13), a photoelectric conversion unit (14), an adjustable gain control unit (15), an anti-aliasing filter unit (16), an AD sampling unit (17), a digital phase meter (18), a two-dimensional angle calculation unit (19), and a two-dimensional angle result output unit (20).

[0041] The frequency-stabilized laser (1) generates a laser beam with frequency f. After passing through the beam splitter BS1 (2), it is split into a transmitted beam and a reflected beam. The transmitted beam enters the first acousto-optic frequency shifter AOM1 (3) to obtain a reference beam with frequency f1 and is coupled into the first polarization-maintaining fiber (4). It exits from the first collimating lens (5), is reflected by the beam splitter BS4 (11), and is transmitted through the beam splitter BS5 (12) to strike the photosensitive surface of the four-quadrant photodetector circuit (13). The reflected beam obtained by the beam splitter BS1 (2) is reflected by the beam splitter BS2 (6) to enter the second acousto-optic frequency shifter AOM2 (7) to obtain a reference beam with frequency f2 and is coupled into the second polarization-maintaining fiber (8). It exits from the second collimating lens (9), is reflected by the beam splitter BS3 (10), and is transmitted through the beam splitters BS4 (11) and BS5 (12) to strike the photosensitive surface of the four-quadrant photodetector circuit (13). Reference beams with frequencies f1 and f2 and measurement beams with frequency f0 are both incident on the photosensitive surface of the four-quadrant photoelectric detection circuit (113), resulting in heterodyne interference and forming three interference signals with beat frequencies of |f1-f0|, |f2-f0|, and |f2-f1|.

[0042] The three different frequency beat signals output by the four-quadrant photoelectric detection circuit (13) are respectively processed by the photoelectric conversion unit (14), the adjustable gain control unit (15), the anti-aliasing filter unit (16), the AD sampling unit (17), and the digital phase meter (18). Based on the different frequencies of the beat signals, the phase information of the measurement beam and each reference beam is obtained. After being processed by the two-dimensional angle calculation unit (19), the result is output by the two-dimensional angle result output unit (20).

[0043] Beam splitters BS4(11) and BS3(10) form angles α1 and α2 with the horizontal direction, respectively. Therefore, the two reference beams reflected by them have a fixed angle θ = α2 - α1. The angle between the reference beams should be greater than half the measurement range of each reference beam and less than half the sum of the measurement ranges of the two reference beams. Figure 1 In the scenario shown, the included angle θ must be greater than the range of each of the frequency f1 reference beam and the frequency f2 reference beam. Half the larger value, and less than the sum of the ranges of both. Half of it.

[0044] It should be understood that the measurement range mentioned above refers to the measurable range of angle measurement results for the measurement light when it interferes with a reference light. For example, the measurement range of a reference beam with frequency f1 refers to the measurable range of angle measurement results for the measurement light when the reference beam interferes with the measurement beam. The physical value of the angle measurement result is still the angle between the reference beam and the measurement beam. Therefore, the angle measurement result reflects the angular change of the measurement light relative to its initial position. The term "measurement range" mentioned below in this specification refers to this definition.

[0045] When the angle between the measurement beam and a reference beam increases to a certain extent, it can cause phase ambiguity when the photodetector calculates the phase difference, making measurement impossible. Therefore, it's crucial to keep the fixed angle within a set range. Figure 2 As shown, when the angle between the measuring beam and the reference beam at frequency f1 exceeds its range... At that time, it can enter the range of the reference beam at frequency f2. This allows the actual measurement range of the device to be extended to the sum of the measurement ranges of the differential wavefront sensing of the two reference beams. Effectively increases the range of differential wavefront sensing.

[0046] It is easy to understand that different reference beams can be generated by independent frequency-stabilized lasers or by the same laser source.

[0047] In a further embodiment, if the beat frequency does not exceed the bandwidth range of the four-quadrant photoelectric detection circuit, the number of reference beams with different angles and frequencies can be appropriately increased or decreased, and the range of the differential wavefront sensing measurement device can be expanded or reduced to achieve large-range, high-precision two-dimensional angle measurement.

[0048] In addition, the acousto-optic frequency shifter can be replaced by other instruments that can also adjust the laser frequency, such as the electro-optic frequency shifter.

[0049] Example 2

[0050] like Figure 3The diagram shown is a structural schematic of a large-range, high-precision differential wavefront sensing measurement device provided in this embodiment. The difference from Embodiment 1 is that this embodiment uses three unpolarized reference beams. Correspondingly, it adds a beam splitter BS6 (21), a third acousto-optic frequency shifter AOM3 (22), a third polarization-maintaining fiber (23), a third collimating lens (24), and a beam splitter BS7 (25). The laser generated by the frequency-stabilized laser (1) is reflected by beam splitter BS1 (2) and transmitted through beam splitter BS2 (6), entering the third acousto-optic frequency shifter AOM3 (22) to obtain a frequency of... The reference beam f3 is coupled into the third polarization-maintaining fiber (23), exits from the third collimating lens (24), is reflected by the beam splitter BS7 (25), and is transmitted through the beam splitter BS3 (10), beam splitter BS4 (11) and beam splitter BS5 (12), and strikes the photosensitive surface of the four-quadrant photodetector circuit (13), where it undergoes heterodyne interference with the measurement beam and the other two reference beams, forming six interference signals with beat frequencies of |f1-f0|, |f2-f0|, |f3-f0|, |f2-f1|, |f3-f1| and |f3-f2|.

[0051] Similarly, in this embodiment, which is similar to the first embodiment, the six different frequency beat signals output by the four-quadrant photoelectric detection circuit (13) are respectively processed by the photoelectric conversion unit (14), the adjustable gain control unit (15), the anti-aliasing filter unit (16), the AD sampling unit (17), and the digital phase meter (18). Based on the different frequencies of the beat signals, the phase information of the measurement beam and each reference beam is obtained. After being processed by the two-dimensional angle calculation unit (19), the result is output by the two-dimensional angle result output unit (20).

[0052] Beam splitters BS4(11), BS3(10), and BS7(25) form angles α1, α2, and α3 with the horizontal direction, respectively. Therefore, the reference beams of frequencies f1 and f2 reflected by beam splitters BS4(11), BS3(10), and BS7(25) have a fixed angle θ1 = α2 - α1, and the reference beams of frequencies f2 and f3 have a fixed angle θ2 = α3 - α2. The angle θ1 must be greater than the range of each reference beam at frequency f1 and frequency f2. Half the larger value, and less than the sum of the ranges of both. Half of the range, the included angle θ2 must be greater than the range of each of the frequency f2 reference beam and the frequency f3 reference beam. Half the larger value, and less than the sum of the ranges of both. Half of it.

[0053] When the angle between the measurement beam and a reference beam increases to a certain extent, it can cause phase ambiguity when the photodetector calculates the phase difference, making measurement impossible. Therefore, it's crucial to keep the fixed angle within a set range. Figure 4 As shown, when the angle between the measuring beam and the reference beam at frequency f1 exceeds its range... At that time, it can enter the range of the reference beam at frequency f2. Within this range, the angle between the measuring beam and the reference beam at frequency f2 exceeds its measurement range. At that time, it can enter the range of the reference beam at frequency f3. Within the device, the differential wavefront angle measurement range between the measurement beam and each reference beam can be continuously accumulated segment by segment. That is, the actual measurement range of the device can be extended to the sum of the measurement ranges of the differential wavefront sensing of the three reference beams. Effectively increases the range of differential wavefront sensing.

[0054] Example 3

[0055] like Figure 5 The diagram shown is a structural schematic of a large-range, high-precision differential wavefront sensing measurement device provided in this embodiment. The difference from the previous embodiment is that this embodiment sets up four unpolarized reference beams, and accordingly, adds a beam splitter BS8 (26), a fourth acousto-optic frequency shifter AOM4 (27), a fourth polarization-maintaining fiber (28), a fourth collimating lens (29), and a beam splitter BS9 (30).

[0056] The propagation of the reference beam, the processing of the optical signal, and the angle calculation are similar to those in the aforementioned embodiments, and will not be repeated here.

[0057] Example 4

[0058] like Figure 6 The diagram shown is a structural schematic of a large-range, high-precision differential wavefront sensing measurement device provided in this embodiment. The difference from Embodiment 2 is that this embodiment sets up three polarization reference beams. Correspondingly, the beam splitter BS5 (12) is replaced with a polarization beam splitter PBS (31), and an analyzer (32) is added. The propagation of the reference beams, the processing of the optical signal, and the angle calculation are similar to those in the previous embodiments, and will not be repeated here.

[0059] Example 5

[0060] like Figure 7 The diagram shown is a schematic of a large-range, high-precision differential wavefront sensing measurement device provided in this embodiment. Unlike the previous embodiments, the measurement beam in this embodiment originates from a distant satellite (33). 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.

[0061] Example 6

[0062] like Figure 8The diagram shown is a structural schematic of a large-range, high-precision differential wavefront sensing measurement device for laboratory precision angle measurement provided in this embodiment.

[0063] The difference from the previous embodiment is that the measurement beam in this embodiment is generated by a frequency-stabilized laser (1). Based on the second embodiment, the device in this embodiment also includes a reflector (34), a fifth acousto-optic frequency shifter AOM5 (35), a fifth polarization-maintaining fiber (36), a fifth collimating lens AOM5 (37), and a rotating mirror (38).

[0064] 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 high-precision, large-range, differential wavefront sensing measurement device, characterized in that, The device comprises a laser source, a first beam splitter group, a differential wavefront sensing unit and a calculation module. The laser source generates a reference beam which is reflected by the first beam splitter group and combined with a measurement beam to form an incident beam on the differential wavefront sensing unit. The differential wavefront sensing unit is configured to output a beat signal to the calculation module based on the incident beam. The calculation module is configured to calculate the included angle between the measurement beam and the reference beam according to the beat signal. The number of beam splitters in the first beam splitter group is the same as the number of reference beams, so that each reference beam is reflected by an independent beam splitter. The included angle between each beam splitter in the first beam splitter group and the horizontal direction is adjusted so that the included angle between two adjacent reference beams is greater than half of the larger value in the respective angle measurement range of the two reference beams and less than half of the sum of the angle measurement ranges of the two reference beams, thereby expanding the angle measurement range of the device for the measurement beam. The differential wavefront sensing unit comprises a four-quadrant photodetector circuit, and the reference beam and the measurement beam form a beat signal after being incident on the light-sensitive surface of the four-quadrant photodetector circuit.

2. The large range, high precision differential wavefront sensing measurement apparatus of claim 1, wherein, The calculation module comprises at least a photoelectric conversion unit, an AD sampling unit, a digital phase meter and an angle calculation unit.

3. The large range, high precision differential wavefront sensing measurement apparatus of claim 1, wherein, 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 based on the digital signal. The angle calculation unit is configured to calculate the included angle between the measurement beam and the reference beam based on the phase information. The calculation module further comprises an adjustable gain control unit and an anti-aliasing filter unit 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 first beam splitter group for collimating the reference beam incident on the first beam splitter group.

4. The large range, high precision differential wavefront sensing measurement apparatus of claim 3, 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 first beam splitter group. The device further comprises an acousto-optic frequency shifter arranged between the laser source and the collimation module.

5. The large range, high precision differential wavefront sensing measurement apparatus of claim 1, wherein, The device further comprises a second beam splitter group arranged after the laser source and configured to divide the laser emitted by the laser source into at least two reference beams with equal light intensity.

6. The large range, high precision differential wavefront sensing measurement apparatus of claim 5, wherein, The measurement beam is formed by reflecting the laser emitted by the laser source through the second beam splitter group.

7. The large range, high precision differential wavefront sensor measurement device of claim 5, wherein, ​ 8. The large range, high precision differential wavefront sensing measurement apparatus of claim 1, wherein, ​ 9. The large range, high precision differential wavefront sensing measurement apparatus of claim 1, wherein, ​

Images