Interference displacement measuring device based on Sagnac structure

Abstract

The invention discloses an interference displacement measuring device based on a Sagnac structure, and solves the problems that in the prior art, the displacement measurement error of a right-angle prism is large, and the interference displacement measuring device cannot be applied to displacement measurement of a plane mirror and the right-angle prism at the same time. The influence of original reflection of multi-order ghost reflection light is avoided, under the condition that quadruple optical subdivision is obtained, compared with laser interferometers visible in the current market and reported in literatures, a to-be-measured right-angle prism is utilized to form a Sagnac structure, a phase decoupling form formed by a measurement structure and a reference structure is utilized, and the measurement accuracy is improved. The periodic nonlinear error of the measurement system is reduced by using the measurement basis of the to-be-measured rectangular prism, and the measurement error in the phase shift of the to-be-measured rectangular prism is weakened by using the phase coupling of reference and measurement, so that the displacement measurement precision is improved.

Description

Technical Field

[0001] The invention relates to a displacement measuring device, in particular to an interference displacement measuring device based on a Sagnac structure. Background Art

[0002] In high-precision step displacement measurement, heterodyne laser interferometry devices often introduce multi-level nonlinear errors with graded changes due to the influence of periodic nonlinear errors, resulting in large stray light in nanometer-level step measurements. Numerous studies have shown that periodic nonlinear errors mainly include two parts: one is the periodic nonlinear error introduced by the laser cross-aliasing of the dual-frequency laser itself for dual-frequency lasers; the other is the periodic nonlinear error of multi-level virtual reflection beams generated by the optical interface of the optical elements in the measurement structure; and using a right-angle prism as a measurement substrate instead of a plane reflector can greatly reduce the impact of nonlinear errors.

[0003] In the development of photolithography machines today, the overlay error between the mask stage and the workpiece stage of the photolithography machine is reduced so that the circuit line width of the silicon wafer reaches the limit of 1nm. The displacement measurement accuracy of the right-angle prism needs to be 1nm, or even sub-picometer level. However, the displacement measurement error of the right-angle prism with the existing technology is still large, and it cannot be applied to the displacement measurement of both plane mirrors and right-angle prisms at the same time. Summary of the invention

[0004] The purpose of the present invention is to provide an interference displacement measurement device based on a Sagnac structure to solve the technical problems that the prior art has a large displacement measurement error for a right-angle prism and cannot be applied to the displacement measurement of a plane reflector and a right-angle prism at the same time.

[0005] The present invention replaces the plane reflector with a right-angle prism to avoid the influence of the original reflection of the multi-order virtual reflection light, and improves the measurement accuracy under the condition of obtaining four times optical subdivision.

[0006] In order to achieve the above purpose and complete the above invention concept, the present invention adopts the following technical solutions:

[0007] An interference displacement measuring device based on a Sagnac structure is used to measure the displacement of a right-angle prism to be measured and a plane reflector to be measured. The device is special in that it includes a dual-frequency laser, a first polarization beam splitter, a reflector and a first optical fiber coupler;

[0008] The first polarization beam splitter prism comprises four sides, wherein the first side is opposite to the third side, and the second side is opposite to the fourth side;

[0009] The first side is provided with the dual-frequency laser and the first optical fiber coupler in sequence along the length direction thereof, the dual-frequency laser is used to emit the measuring light and the reference light to the first polarization beam splitter prism; the first optical fiber coupler is used to receive the measuring light and the reference light after the measurement, obtain the corresponding Doppler frequency shift information, and realize the displacement measurement;

[0010] The reflector is arranged on the second side, and is used to reflect the light emitted from the first polarization beam splitter prism to the right-angle prism to be measured;

[0011] The third side is used to set a right-angle prism to be measured, a part of the bottom edge of the right-angle prism to be measured is opposite to the third side, and the other part corresponds to the reflector, which is used to receive the light reflected by the reflector and reflect it to the first polarization beam splitter prism;

[0012] The fourth side is used to set a plane reflector to be measured, and the plane reflector to be measured can reflect the light emitted from the first polarization beam splitter prism back to the first polarization beam splitter prism.

[0013] Further, it also includes a first quarter wave plate, a second quarter wave plate and a third quarter wave plate;

[0014] The first quarter wave plate is arranged on the optical path between the plane reflector to be measured and the first polarization beam splitter prism;

[0015] The second quarter wave plate is arranged on a portion of the optical path between the first polarization beam splitter prism and the right-angle prism to be measured, and the portion of the optical path corresponds to the first optical fiber coupler;

[0016] The third quarter wave plate is arranged on a portion of the optical path between the first polarization beam splitter prism and the first reflector, and the portion of the optical path is close to the right-angle prism to be measured.

[0017] Further, the first optical fiber coupler and the second quarter wave plate are arranged close to the fourth side of the first polarization beam splitter prism;

[0018] The dual-frequency laser is disposed close to the second side of the first polarization beam splitter prism.

[0019] Furthermore, the polarization angles of the first quarter wave plate, the second quarter wave plate and the third quarter wave plate are all 45°.

[0020] Further, it also includes a second polarization beam splitter prism and a beam splitter prism;

[0021] The second polarization beam splitter prism is arranged on the optical path between the dual-frequency laser and the first polarization beam splitter prism; the beam splitting surface of the second polarization beam splitter prism is perpendicular to the beam splitting surface of the first polarization beam splitter prism;

[0022] The beam splitter prism is arranged on the optical path between the first optical fiber coupler and the first polarization beam splitter prism; the beam splitting surface of the beam splitter prism is parallel to the beam splitting surface of the first polarization beam splitter prism.

[0023] Furthermore, it also includes a beam splitter prism, a second polarization beam splitter prism and a second optical fiber coupler;

[0024] The beam splitter prism is arranged on the optical path between the dual-frequency laser and the first polarization beam splitter prism; the beam splitting surface of the beam splitter prism is perpendicular to the beam splitting surface of the first polarization beam splitter prism;

[0025] The second polarization beam splitter prism is arranged on the optical path between the first optical fiber coupler and the first polarization beam splitter prism; the beam splitting plane of the second polarization beam splitter prism is parallel to the beam splitting plane of the first polarization beam splitter prism;

[0026] The second optical fiber coupler is arranged on the side of the second polarization beam splitter prism close to the second side of the first polarization beam splitter prism and away from the beam splitter prism, so that the first optical fiber coupler receives part of the measurement light and reference light after participating in the measurement to achieve rough displacement measurement, and the second optical fiber coupler receives another part of the measurement light and reference light after participating in the measurement to achieve fine displacement measurement.

[0027] An interferometric displacement measurement method based on a Sagnac structure, using the above-mentioned interferometric displacement measurement device based on a Sagnac structure, which is special in that it includes displacement measurement of a right-angle prism to be measured and displacement measurement of a plane reflector to be measured;

[0028] The displacement measurement of the right-angle prism to be measured includes the following steps:

[0029] Step A1, the plane reflector to be measured is fixed, and the dual-frequency laser emits a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0030] Step A2, the measuring light and the reference light enter the first optical fiber coupler after being acted upon by corresponding optical devices respectively;

[0031] Step A3: the first optical fiber coupler obtains the Doppler frequency shift amount;

[0032] Step A4, calculating the displacement of the right-angle prism to be measured by using the Doppler frequency shift obtained in step A3, and completing the displacement measurement of the right-angle prism to be measured;

[0033] The displacement measurement of the plane reflector to be measured includes the following steps:

[0034] Step B1, the right-angle prism to be measured is fixed, and the dual-frequency laser has a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0035] Step B2, the measuring light and the reference light enter the first optical fiber coupler after being acted upon by corresponding optical devices respectively;

[0036] Step B3, the first optical fiber coupler receives the acted measurement light and reference light to obtain the Doppler frequency shift;

[0037] Step B4: Calculate the displacement of the plane reflector to be measured by using the Doppler frequency shift obtained in step B3, and complete the displacement measurement of the plane reflector to be measured.

[0038] Further, step A2 is specifically as follows: the measurement light with a frequency of f1 is transmitted through the first polarization beam splitter prism to become horizontal linear polarized light, and then is reflected twice by the right-angle prism to be measured, reflected by the reflector, transmitted through the first polarization beam splitter prism, and transmitted through the first quarter wave plate in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then is reflected by the plane reflector to be measured, and transmitted through the first quarter wave plate in sequence, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then is reflected by the first polarization beam splitter prism, and transmitted through the second quarter wave plate in sequence, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light. Then, it is reflected twice by the right-angle prism to be measured, reflected by the reflector, and transmitted through the third quarter-wave plate, and the polarization state changes from right-handed elliptical polarized light to horizontal polarized light. Then, it is transmitted through the first polarization beam splitter prism and the first quarter-wave plate, and the polarization state changes from horizontal polarized light to left-handed elliptical polarized light. Then, it is reflected by the plane reflector to be measured, and transmitted through the first quarter-wave plate, and the polarization state changes from left-handed elliptical polarized light to vertical polarized light. Then, it is reflected by the first polarization beam splitter prism, reflected twice by the right-angle prism to be measured, reflected by the reflector, and reflected by the first polarization beam splitter prism, and finally incident on the first optical fiber coupler;

[0039] The reference light with a frequency of f2 is reflected by the first polarization beam splitter prism to become vertical linear polarized light, then transmitted through the third quarter wave plate, the polarization state changes from vertical polarized light to left-handed elliptically polarized light, then sequentially reflected by the reflector, reflected twice by the right-angle prism to be measured, transmitted through the second quarter wave plate, the polarization state changes from left-handed elliptically polarized light to horizontal polarized light, then transmitted through the first polarization beam splitter prism, and finally incident on the first optical fiber coupler;

[0040] Step A3 specifically includes: the first optical fiber coupler obtains the Doppler frequency shift Δf1;

[0041] Step A4 specifically includes calculating the displacement S1 of the right-angle prism to be measured by using the Doppler frequency shift Δf1 obtained in step A3:

[0042]

[0043] Where c is the speed of light, The total phase delay measured for the laser round trip;

[0044] Complete the displacement measurement of the right-angle prism to be measured;

[0045] Step B2 is specifically as follows: the measuring light with a frequency of f1 is transmitted through the first polarization beam splitter prism to become horizontal linear polarized light, and then is reflected twice by the right-angle prism to be measured, reflected by the reflector, transmitted through the first polarization beam splitter prism, and transmitted through the first quarter wave plate in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then is reflected by the plane reflector to be measured, and transmitted through the first quarter wave plate in sequence, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then is reflected by the first polarization beam splitter prism, and transmitted through the second quarter wave plate in sequence, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then is sequentially After being reflected twice by the right-angle prism to be measured and reflected by the reflector, it is transmitted through the third quarter-wave plate, and the polarization state changes from right-handed elliptical polarized light to horizontal polarized light. Then, it is transmitted through the first polarization beam splitter prism and the first quarter-wave plate in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptical polarized light. Then, it is reflected through the plane reflector to be measured and transmitted through the first quarter-wave plate in sequence, and the polarization state changes from left-handed elliptical polarized light to vertical polarized light. Then, it is reflected through the first polarization beam splitter prism, reflected twice by the right-angle prism to be measured, reflected by the reflector, and reflected by the first polarization beam splitter prism in sequence, and finally incident on the first optical fiber coupler;

[0046] The reference light with a frequency of f2 is reflected by the first polarization beam splitter prism to become vertical linear polarized light, then transmitted through the third quarter wave plate, the polarization state changes from vertical polarized light to left-handed elliptically polarized light, then sequentially reflected by the reflector, reflected twice by the right-angle prism to be measured, transmitted through the second quarter wave plate, the polarization state changes from left-handed elliptically polarized light to horizontal polarized light, then transmitted through the first polarization beam splitter prism, and finally incident on the first optical fiber coupler;

[0047] Step B3 specifically includes: the first optical fiber coupler receives the acted measurement light and the reference light to obtain the Doppler frequency shift Δf2;

[0048] Step B4 specifically includes calculating the displacement S2 of the plane reflector to be measured by using the Doppler frequency shift Δf2 obtained in step B3:

[0049]

[0050] Complete the displacement measurement of the plane reflector to be measured.

[0051] Further, step A2 is specifically as follows: the measurement light with a frequency of f1 is transmitted through the second polarization beam splitter prism to become horizontal linear polarized light, and then sequentially transmitted through the first polarization beam splitter prism, reflected twice by the right-angle prism to be measured, reflected by the reflector, transmitted through the first polarization beam splitter prism, and transmitted through the first quarter wave plate, and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light, and then sequentially reflected by the plane reflector to be measured, and transmitted through the first quarter wave plate, and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light, and then sequentially reflected through the first polarization beam splitter prism, and transmitted through the second quarter wave plate, and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light. The light is then reflected twice by the right-angle prism to be measured, reflected by the reflector, and transmitted by the third quarter-wave plate, and the polarization state is changed from right-handed elliptically polarized light to horizontal polarized light. It is then transmitted by the first polarization beam splitter prism and the first quarter-wave plate, and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light. It is then reflected by the plane reflector to be measured, and transmitted by the first quarter-wave plate, and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light. It is then reflected by the first polarization beam splitter prism, reflected twice by the right-angle prism to be measured, reflected by the reflector, reflected by the first polarization beam splitter prism, and transmitted by the beam splitter prism, and finally incident on the first optical fiber coupler;

[0052] The reference light with a frequency of f2 is reflected by the second polarization beam splitter prism into vertically polarized light, then reflected by the beam splitter prism, and finally incident on the first optical fiber coupler;

[0053] Step A3 specifically includes: the first optical fiber coupler obtains the Doppler frequency shift Δf1;

[0054] Step A4 specifically includes calculating the displacement S1 of the right-angle prism to be measured by using the Doppler frequency shift Δf1 obtained in step A3:

[0055]

[0056] Complete the displacement measurement of the right-angle prism to be measured;

[0057] Step B2 is specifically as follows: the measurement light with a frequency of f1 is transmitted through the second polarization beam splitter prism to become horizontal linear polarized light, and then sequentially transmitted through the first polarization beam splitter prism, reflected twice by the right-angle prism to be measured, reflected by the reflector, transmitted through the first polarization beam splitter prism, and transmitted through the first quarter wave plate, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then sequentially reflected by the plane reflector to be measured, and transmitted through the first quarter wave plate, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then sequentially reflected through the first polarization beam splitter prism, and transmitted through the second quarter wave plate, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then It passes through the right-angle prism to be measured, is reflected twice, is reflected by the reflector, and is transmitted through the third quarter-wave plate, and the polarization state changes from right-handed elliptical polarization to horizontal polarization. It then passes through the first polarization beam splitter prism and the first quarter-wave plate, and the polarization state changes from horizontal polarization to left-handed elliptical polarization. It then passes through the plane reflector to be measured, and is transmitted through the first quarter-wave plate, and the polarization state changes from left-handed elliptical polarization to vertical polarization. It then passes through the first polarization beam splitter prism, is reflected twice by the right-angle prism to be measured, is reflected by the reflector, is reflected by the first polarization beam splitter prism, is transmitted through the beam splitter prism, and finally enters the first optical fiber coupler.

[0058] The reference light with a frequency of f2 is reflected by the second polarization beam splitter prism into vertically polarized light, then reflected by the beam splitter prism, and finally incident on the first optical fiber coupler;

[0059] Step B3 specifically includes: the first optical fiber coupler receives the acted measurement light and the reference light to obtain the Doppler frequency shift Δf2;

[0060] Step B4 specifically includes calculating the displacement S2 of the plane reflector to be measured by using the Doppler frequency shift Δf2 obtained in step B3:

[0061]

[0062] Complete the displacement measurement of the plane reflector to be measured.

[0063] Furthermore, step A2 is specifically as follows: the measuring light and the reference light enter a beam splitter prism together, and are split by the beam splitter prism according to energy to form reflected light and transmitted light;

[0064] The reflected light is transmitted through the second polarization beam splitter prism to form horizontal linear polarized light a1 with a frequency of f1, and is reflected to form vertical linear polarized light a2 with a frequency of f2;

[0065] The horizontal linear polarized light a1 is incident on the second optical fiber coupler;

[0066] The vertical linear polarized light a2 is incident on the first optical fiber coupler;

[0067] The transmitted light is transmitted through the first polarization beam splitter prism to form horizontal linear polarized light b1 with a frequency of f1, and is reflected to form vertical polarized light b2 with a frequency of f2;

[0068] The horizontal linear polarized light b1 is reflected twice by the right-angle prism to be measured, reflected by the reflector, transmitted by the first polarization beam splitter prism, and transmitted by the first quarter wave plate in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light. It is then reflected by the plane reflector to be measured, transmitted by the first quarter wave plate in sequence, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light. It is then reflected by the first polarization beam splitter prism, transmitted by the second quarter wave plate in sequence, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light. It is then reflected twice by the right-angle prism to be measured, reflected by the reflector, and transmitted by the first quarter wave plate in sequence. The light is transmitted through the first quarter wave plate, and the polarization state changes from right-handed elliptically polarized light to horizontal polarized light. The light is then transmitted through the first polarization beam splitter prism and the first quarter wave plate, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light. The light is then reflected through the plane reflector to be measured, and the first quarter wave plate is transmitted, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light. The light is then reflected through the first polarization beam splitter prism, reflected twice by the right-angle prism to be measured, reflected by the reflector, reflected by the first polarization beam splitter prism, and reflected by the second polarization beam splitter prism, and finally incident on the second optical fiber coupler.

[0069] The vertically polarized light b2 is transmitted through the third quarter wave plate, and its polarization state changes from vertically polarized light to left-handed elliptically polarized light. The light is then reflected by the reflector, reflected twice by the right-angle prism to be measured, and transmitted through the second quarter wave plate. The polarization state changes from left-handed elliptically polarized light to horizontally polarized light. The light is then transmitted through the first polarization beam splitter prism, the second polarization beam splitter prism, and finally incident on the first optical fiber coupler.

[0070] Step A3 specifically includes: the first optical fiber coupler simultaneously receives two beams of orthogonal linear polarized light, and obtains the Doppler frequency shift Δf1 of the interference signal after the phase decoupling of the two beams of orthogonal linear polarized light;

[0071] The second optical fiber coupler simultaneously receives two beams of orthogonal linear polarized light to obtain a Doppler frequency shift 3Δf1 of an interference signal after phase decoupling of the two beams of orthogonal linear polarized light;

[0072] Step A4 specifically includes calculating the displacement S1 of the right-angle prism to be measured by using the Doppler frequency shifts Δf1 and 3Δf1 obtained in step A3:

[0073] When phase coupling is subtracted, the total phase delay is phase 1, then

[0074] When phase coupling is added, the total phase delay is phase 2, then

[0075] Complete the displacement measurement of the right-angle prism to be measured;

[0076] Step B2 specifically includes: the measuring light and the reference light enter a beam splitter prism together, and are split by the beam splitter prism according to energy to form reflected light and transmitted light;

[0077] The reflected light is transmitted through the second polarization beam splitter prism to form horizontal linear polarized light a1 with a frequency of f1, and is reflected to form vertical linear polarized light a2 with a frequency of f2;

[0078] The horizontal linear polarized light a1 is incident on the second optical fiber coupler;

[0079] The vertical linear polarized light a2 is incident on the first optical fiber coupler;

[0080] The transmitted light is transmitted through the first polarization beam splitter prism to form horizontal linear polarized light b1 with a frequency of f1, and is reflected to form vertical polarized light b2 with a frequency of f2;

[0081] The horizontal linear polarized light b1 is reflected twice by the right-angle prism to be measured, reflected by the reflector, transmitted by the first polarization beam splitter prism, and transmitted by the first quarter wave plate in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light. It is then reflected by the plane reflector to be measured, transmitted by the first quarter wave plate, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light. It is then reflected by the first polarization beam splitter prism, transmitted by the second quarter wave plate, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light. It is then reflected twice by the right-angle prism to be measured, reflected by the reflector, and transmitted by the third quarter wave plate in sequence. The light source is transmitted through a quarter wave plate, and its polarization state changes from right-handed elliptically polarized light to horizontal polarized light. The light source is then sequentially transmitted through a first polarization beam splitter prism and a first quarter wave plate, and its polarization state changes from horizontal polarized light to left-handed elliptically polarized light. The light source is then sequentially reflected through a plane reflector to be measured and transmitted through the first quarter wave plate, and its polarization state changes from left-handed elliptically polarized light to vertical polarized light. The light source is then sequentially reflected through a first polarization beam splitter prism, reflected twice by a right-angle prism to be measured, reflected by a reflector, reflected by a first polarization beam splitter prism, and reflected by a second polarization beam splitter prism, and finally incident on a second optical fiber coupler.

[0082] The vertically polarized light b2 is transmitted through the third quarter wave plate, and its polarization state changes from vertically polarized light to left-handed elliptically polarized light. The light b2 is then reflected by the reflector, reflected twice by the right-angle prism to be measured, and transmitted through the second quarter wave plate. The polarization state changes from left-handed elliptically polarized light to horizontally polarized light. The light b2 is then transmitted through the first polarization beam splitter prism, and transmitted through the second polarization beam splitter prism. The light b2 is finally incident on the first optical fiber coupler.

[0083] Step B3 specifically includes: the first optical fiber coupler simultaneously receives two beams of orthogonal linear polarized light, and obtains a Doppler frequency shift of an interference signal after phase decoupling of the two beams of orthogonal linear polarized light, which is 0;

[0084] The second optical fiber coupler simultaneously receives two beams of orthogonal linear polarized light to obtain a Doppler frequency shift 2Δf2 of an interference signal after phase decoupling of the two beams of orthogonal linear polarized light;

[0085] Step B4 specifically includes calculating the displacement S2 of the plane reflector to be measured by phase decoupling based on the Doppler frequency shift 0 and 2Δf2 obtained in step B3:

[0086]

[0087] Complete the displacement measurement of the plane reflector to be measured.

[0088] Beneficial effects of the present invention:

[0089] 1. Compared with the laser interferometers currently available on the market and reported in the literature, the present invention utilizes the right-angle prism to be measured to form a Sagnac structure, and uses the phase decoupling form formed by the measurement structure and the reference structure. It not only utilizes the measurement reference of the right-angle prism to be measured to reduce the periodic nonlinear error of the measurement system, but also utilizes the phase coupling of the reference and the measurement to weaken the measurement error in the phase shift of the right-angle prism to be measured, thereby improving the displacement measurement accuracy.

[0090] 2. The right-angle prism to be measured in the present invention is used as a measurement reference to achieve 4 times optical subdivision. At the same time, a polarization beam splitter prism is also used to separate the dual-frequency laser of the dual-frequency laser twice, further improving the displacement measurement accuracy.

[0091] 3. The present invention can perform two-dimensional synchronous measurement, one way is to measure displacement based on a plane reflector as a reference, and the other way is to measure displacement based on a right-angle prism to be measured. In actual engineering applications, it can be applied to plane processing of CNC machine tools, workpiece table and displacement table control. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 It is a structural schematic diagram of a first embodiment of an interference displacement measurement device based on a Sagnac structure of the present invention;

[0093] Figure 2 It is a structural schematic diagram of a second embodiment of an interference displacement measurement device based on a Sagnac structure of the present invention;

[0094] Figure 3 It is a structural schematic diagram of a third embodiment of an interference displacement measurement device based on a Sagnac structure of the present invention.

[0095] Figure Number:

[0096] 1-dual frequency laser, 201-first polarization beam splitter prism, 202-second polarization beam splitter prism, 3-right angle prism to be measured, 401-reflector, 402-plane reflector to be measured, 501-first quarter wave plate, 502-second quarter wave plate, 503-third quarter wave plate, 601-first fiber coupler, 602-second fiber coupler, 7-beam splitter prism. DETAILED DESCRIPTION

[0097] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0098] Embodiment 1:

[0099] An interferometric displacement measuring device based on a Sagnac structure is used for measuring a right angle prism 3 and a plane reflector 402, such as Figure 1 As shown, the displacement measuring device includes a dual-frequency laser 1 , a first polarization beam splitter prism 201 , a reflector 401 , a first fiber coupler 601 , a first quarter wave plate 501 , a second quarter wave plate 502 and a third quarter wave plate 503 .

[0100] The first polarization beam splitter prism 201 includes four sides, wherein the first side is opposite to the third side, and the second side is opposite to the fourth side; the first side is sequentially provided with a dual-frequency laser 1 and a first optical fiber coupler 601 along the length direction thereof, and the dual-frequency laser 1 is used to emit measurement light and reference light to the first polarization beam splitter prism 201; the first optical fiber coupler 601 is used to receive the measurement light and reference light after the measurement, obtain the corresponding Doppler frequency shift information, and realize the displacement measurement; the second side is provided with a reflector 401, and the reflector 401 is used to transmit the measurement light and reference light from the first polarization beam splitter prism 201 ... The light emitted from the polarization beam splitter prism 201 is reflected to the right-angle prism 3 to be measured; the third side is used to set the right-angle prism 3 to be measured, a part of the bottom edge of the right-angle prism 3 to be measured is opposite to the third side, and the other part corresponds to the reflector 401, which is used to receive the light reflected by the reflector 401 and reflect it to the first polarization beam splitter prism 201; the fourth side is used to set the plane reflector 402 to be measured, and the plane reflector 402 to be measured can reflect the light emitted from the first polarization beam splitter prism 201 back to the first polarization beam splitter prism 201. The first quarter wave plate 501 is arranged on the optical path between the plane reflector 402 to be measured and the first polarization beam splitter prism 201; the second quarter wave plate 502 is arranged on the partial optical path between the first polarization beam splitter prism 201 and the right angle prism 3 to be measured, and the partial optical path corresponds to the first fiber coupler 601; the third quarter wave plate 503 is arranged on the partial optical path between the first polarization beam splitter prism 201 and the first reflector 401, and the partial optical path is close to the right angle prism 3 to be measured. The polarization angles of the first quarter wave plate 501, the second quarter wave plate 502 and the third quarter wave plate 503 are all 45°. The first fiber coupler 601 and the second quarter wave plate 502 are arranged close to the fourth side of the first polarization beam splitter prism 201; the dual-frequency laser 1 is arranged close to the second side of the first polarization beam splitter prism 201.

[0101] The displacement measurement device of the first embodiment is used to measure the displacement of the right-angle prism 3 to be measured, and the steps include:

[0102] Step A1, the plane reflector 402 to be measured is fixed, and the dual-frequency laser 1 emits a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0103] Step A2, the measuring light with a frequency of f1 is transmitted through the first polarization beam splitter prism 201 to become horizontal linear polarized light, and then is reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, transmitted through the first polarization beam splitter prism 201, and transmitted through the first quarter wave plate 501 in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then is reflected by the plane reflector 402 to be measured, and transmitted through the first quarter wave plate 501 in sequence, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then is reflected by the first polarization beam splitter prism 201 in sequence, and transmitted through the second quarter wave plate 502 in sequence, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then is reflected by the right-angle prism 3 to be measured in sequence. The light is reflected by the mirror 3 twice, reflected by the reflector 401, transmitted by the third quarter wave plate 503, and the polarization state is changed from right-handed elliptical polarization light to horizontal polarization light. The light is then sequentially transmitted by the first polarization beam splitter prism 201 and the first quarter wave plate 501, and the polarization state is changed from horizontal polarization light to left-handed elliptical polarization light. The light is then sequentially reflected by the plane reflector 402 to be measured, and transmitted by the first quarter wave plate 501, and the polarization state is changed from left-handed elliptical polarization light to vertical polarization light. The light is then sequentially reflected by the first polarization beam splitter prism 201, reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, and reflected by the first polarization beam splitter prism 201, and finally incident on the first optical fiber coupler 601.

[0104] The reference light with a frequency of f2 is reflected by the first polarization beam splitter prism 201 to become vertical linear polarized light, and then transmitted through the third quarter wave plate 503, and the polarization state is changed from vertical polarized light to left-handed elliptically polarized light, and then sequentially reflected by the reflector 401, reflected twice by the right angle prism 3 to be measured, and transmitted through the second quarter wave plate 502, and the polarization state is changed from left-handed elliptically polarized light to horizontal polarized light, and then transmitted through the first polarization beam splitter prism 201, and finally incident on the first fiber coupler 601;

[0105] Step A3: the first optical fiber coupler 601 obtains the Doppler frequency shift Δf1;

[0106] Step A4, record the Doppler frequency shift information of the measuring light as f1-3Δf1; record the Doppler frequency shift information of the reference light as f2-Δf1; record the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere as f1-f2-2Δf1;

[0107] The displacement S1 of the right-angle prism 3 to be measured is calculated based on the Doppler frequency shift information f1-3Δf1, f2-Δf1, f1-f2-2Δf1 and the laser's own reference frequency information f1-f2:

[0108]

[0109] Where c is the speed of light, The total phase delay measured for the laser round trip;

[0110] Complete the displacement measurement of the right-angle prism 3 to be measured;

[0111] The displacement measurement device of the first embodiment is used to measure the displacement of the plane reflector 402 to be measured, and the steps include:

[0112] Step B1, the right angle prism 3 to be measured is fixed, and the dual frequency laser 1 has a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0113] Step B2, the measuring light with a frequency of f1 is transmitted through the first polarization beam splitter prism 201 to become horizontal linear polarized light, and then is reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, transmitted through the first polarization beam splitter prism 201, and transmitted through the first quarter wave plate 501 in sequence, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then is reflected by the plane reflector 402 to be measured, and transmitted through the first quarter wave plate 501 in sequence, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then is reflected by the first polarization beam splitter prism 201 in sequence, and transmitted through the second quarter wave plate 502 in sequence, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then is reflected by the right-angle prism 3 to be measured in sequence. The light is reflected by the mirror 3 twice, reflected by the reflector 401, transmitted by the third quarter wave plate 503, and the polarization state is changed from right-handed elliptical polarization light to horizontal polarization light. The light is then sequentially transmitted by the first polarization beam splitter prism 201 and the first quarter wave plate 501, and the polarization state is changed from horizontal polarization light to left-handed elliptical polarization light. The light is then sequentially reflected by the plane reflector 402 to be measured, and transmitted by the first quarter wave plate 501, and the polarization state is changed from left-handed elliptical polarization light to vertical polarization light. The light is then sequentially reflected by the first polarization beam splitter prism 201, reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, and reflected by the first polarization beam splitter prism 201, and finally incident on the first optical fiber coupler 601.

[0114] The reference light with a frequency of f2 is reflected by the first polarization beam splitter prism 201 to become vertical linear polarized light, and then transmitted through the third quarter wave plate 503, and the polarization state is changed from vertical polarized light to left-handed elliptically polarized light, and then sequentially reflected by the reflector 401, reflected twice by the right angle prism 3 to be measured, and transmitted through the second quarter wave plate 502, and the polarization state is changed from left-handed elliptically polarized light to horizontal polarized light, and then transmitted through the first polarization beam splitter prism 201, and finally incident on the first fiber coupler 601;

[0115] Step B3: the first optical fiber coupler 601 receives the acted measurement light and reference light to obtain a Doppler frequency shift Δf;

[0116] Step B4, record the Doppler frequency shift information of the measuring light as f1-2Δf2; record the Doppler frequency shift information of the reference light as f2; record the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere as f1-f2-2Δf2;

[0117] The displacement S2 of the plane reflector 402 to be measured is calculated based on the Doppler frequency shift information f1-2Δf2, f2, f1-f2-2Δf2 and the reference frequency information f1-f2 of the laser itself:

[0118]

[0119] The displacement measurement of the plane reflective mirror 402 to be measured is completed.

[0120] Embodiment 2:

[0121] like Figure 2 As shown, the displacement measuring device of this embodiment is basically the same as the displacement measuring device of the first embodiment, except that the displacement measuring device of this embodiment further includes a second polarization beam splitter prism 202 and a beam splitter prism 7; the second polarization beam splitter prism 202 is arranged on the optical path between the dual-frequency laser 1 and the first polarization beam splitter prism 201; the beam splitter plane of the second polarization beam splitter prism 202 is perpendicular to the beam splitter plane of the first polarization beam splitter prism 201; the beam splitter prism 7 is arranged on the optical path between the first optical fiber coupler 601 and the first polarization beam splitter prism 201; the beam splitter plane of the beam splitter prism 7 is parallel to the beam splitter plane of the first polarization beam splitter prism 201.

[0122] The displacement measurement device of the second embodiment is used to measure the displacement of the right-angle prism 3 to be measured, and specifically comprises the following steps:

[0123] Step A1, the plane reflector 402 to be measured is fixed, and the dual-frequency laser 1 emits a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0124] Step A2, the measuring light with a frequency of f1 is transmitted through the second polarization beam splitter prism 202 to become horizontal linear polarized light, and then sequentially transmitted through the first polarization beam splitter prism 201, reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, transmitted through the first polarization beam splitter prism 201, and transmitted through the first quarter wave plate 501, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then sequentially reflected by the plane reflector 402 to be measured, and transmitted through the first quarter wave plate 501, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then sequentially reflected by the first polarization beam splitter prism 201, and transmitted through the second quarter wave plate 502, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then sequentially transmitted through ... transmitted through the plane reflector 402 to be measured, and transmitted through the first quarter wave plate 501, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then sequentially transmitted through the plane reflector 402 to be measured, and transmitted through the first quarter wave plate 501, and the polarization state The light is reflected through the right-angle prism 3, twice, reflected through the reflector 401, and transmitted through the third quarter-wave plate 503, and the polarization state changes from right-handed elliptical polarized light to horizontal polarized light. The light is then sequentially transmitted through the first polarization beam splitter prism 201 and the first quarter-wave plate 501, and the polarization state changes from horizontal polarized light to left-handed elliptical polarized light. The light is then sequentially reflected through the plane reflector 402 to be measured, and transmitted through the first quarter-wave plate 501, and the polarization state changes from left-handed elliptical polarized light to vertical polarized light. The light is then sequentially reflected through the first polarization beam splitter prism 201, twice reflected through the right-angle prism 3 to be measured, reflected through the reflector 401, reflected through the first polarization beam splitter prism 201, and transmitted through the beam splitter prism 7, and finally incident on the first optical fiber coupler 601.

[0125] The reference light with a frequency of f2 is reflected by the second polarization beam splitter prism 202 to become vertically polarized light, then reflected by the beam splitter prism 7, and finally incident on the first fiber coupler 601;

[0126] Step A3: the first optical fiber coupler 601 obtains the Doppler frequency shift Δf1;

[0127] Step A4, record the Doppler frequency shift information of the measuring light as f1-3Δf1; record the Doppler frequency shift information of the reference light as f2; record the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere as f1-f2-3Δf1;

[0128] The displacement S1 of the right-angle prism 3 to be measured is calculated based on the Doppler frequency shift information f1-3Δf1, f2, f1-f2-3Δf1 and the laser's own reference frequency information f1-f2:

[0129]

[0130] Complete the displacement measurement of the right-angle prism 3 to be measured;

[0131] The displacement measurement device of the second embodiment is used to measure the displacement of the plane reflector 402 to be measured, and specifically includes the following steps:

[0132] Step B1, the right angle prism 3 to be measured is fixed, and the dual frequency laser 1 has a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0133] Step B2 is specifically as follows: the measuring light with a frequency of f1 is transmitted through the second polarization beam splitter prism 202 to become horizontal linear polarized light, and then sequentially transmitted through the first polarization beam splitter prism 201, reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, transmitted through the first polarization beam splitter prism 201, and transmitted through the first quarter-wave plate 501, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light, and then sequentially reflected by the plane reflector 402 to be measured, and transmitted through the first quarter-wave plate 501, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light, and then sequentially reflected by the first polarization beam splitter prism 201, transmitted through the second quarter-wave plate 502, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light, and then sequentially transmitted through the plane reflector 402 to be measured, and transmitted through the first quarter-wave plate 501, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light. The light is reflected by the right-angle prism 3, twice, reflected by the reflector 401, and transmitted by the third quarter-wave plate 503, and the polarization state changes from right-handed elliptical polarized light to horizontal polarized light, and then sequentially transmitted through the first polarization beam splitter prism 201 and the first quarter-wave plate 501, and the polarization state changes from horizontal polarized light to left-handed elliptical polarized light, and then sequentially reflected by the plane reflector 402 to be measured, and transmitted through the first quarter-wave plate 501, and the polarization state changes from left-handed elliptical polarized light to vertical polarized light, and then sequentially reflected by the first polarization beam splitter prism 201, twice reflected by the right-angle prism 3 to be measured, reflected by the reflector 401, reflected by the first polarization beam splitter prism 201, and transmitted by the beam splitter prism 7, and finally incident on the first optical fiber coupler 601;

[0134] The reference light with a frequency of f2 is reflected by the second polarization beam splitter prism 202 to become vertically polarized light, then reflected by the beam splitter prism 7, and finally incident on the first fiber coupler 601;

[0135] Step B3: the first optical fiber coupler 601 receives the acted measurement light and reference light to obtain a Doppler frequency shift Δf2;

[0136] Step B4 specifically includes recording the Doppler frequency shift information of the measuring light as f1-2Δf2; recording the Doppler frequency shift information of the reference light as f2; recording the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere as f1-f2-2Δf2;

[0137] The displacement S2 of the plane reflector 402 to be measured is calculated based on the Doppler frequency shift information f1-2Δf2, f2, f1-f2-2Δf2 and the reference frequency information f1-f2 of the laser itself:

[0138]

[0139] The displacement measurement of the plane reflective mirror 402 to be measured is completed.

[0140] Embodiment three:

[0141] like Figure 3 As shown, the displacement measuring device of this embodiment is basically the same as the displacement measuring device of the first embodiment, except that the displacement measuring device of this embodiment further includes a beam splitter prism 7, a second polarization beam splitter prism 202 and a second fiber coupler 602; the beam splitter prism 7 is arranged on the optical path between the dual-frequency laser 1 and the first polarization beam splitter prism 201; the beam splitting surface of the beam splitter prism 7 is perpendicular to the beam splitting surface of the first polarization beam splitter prism 201; the second polarization beam splitter prism 202 is arranged on the optical path between the first fiber coupler 601 and the first polarization beam splitter prism 201; the beam splitting surface of the second polarization beam splitter prism 202 is parallel to the beam splitting surface of the first polarization beam splitter prism 201; the second fiber coupler 602 is arranged on the side of the second polarization beam splitter prism 202 close to the second side of the first polarization beam splitter prism 201, so that the first fiber coupler 601 receives part of the measurement light and reference light after participating in the measurement to achieve rough displacement measurement, and the second fiber coupler 602 receives another part of the measurement light and reference light after participating in the measurement to achieve fine displacement measurement.

[0142] The displacement measurement device of the third embodiment is used to measure the displacement of the right-angle prism 3 to be measured, and specifically includes the following steps:

[0143] Step A1, the plane reflector 402 to be measured is fixed, and the dual-frequency laser 1 emits a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0144] Step A2, the measuring light and the reference light enter the beam splitter prism 7 together, and are split according to energy by the beam splitter prism 7 to form reflected light and transmitted light;

[0145] The reflected light is transmitted through the second polarization beam splitter prism 202 to form horizontal linear polarized light a1 with a frequency of f1, and is reflected to form vertical linear polarized light a2 with a frequency of f2;

[0146] Horizontally polarized light a1 is incident on the second optical fiber coupler 602;

[0147] The vertical linear polarized light a2 is incident on the first optical fiber coupler 601;

[0148] The transmitted light is transmitted through the first polarization beam splitter prism 201 to form horizontal linear polarized light b1 with a frequency of f1, and is reflected to form vertical polarized light b2 with a frequency of f2;

[0149] The horizontal linear polarized light b1 is sequentially reflected twice by the right angle prism 3 to be measured, reflected by the reflector 401, transmitted by the first polarization beam splitter prism 201, and transmitted by the first quarter wave plate 501, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light. Then, it is sequentially reflected by the plane reflector 402 to be measured, and transmitted by the first quarter wave plate 501, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light. Then, it is sequentially reflected by the first polarization beam splitter prism 201, and transmitted by the second quarter wave plate 502, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light. Then, it is sequentially reflected twice by the right angle prism 3 to be measured, reflected by the reflector 401, and transmitted by the third quarter wave plate 501. The light is transmitted through the first wave plate 503, and the polarization state changes from right-handed elliptical polarization to horizontal polarization. The light is then transmitted through the first polarization beam splitter prism 201 and the first quarter wave plate 501, and the polarization state changes from horizontal polarization to left-handed elliptical polarization. The light is then reflected through the plane reflector 402 to be measured and transmitted through the first quarter wave plate 501, and the polarization state changes from left-handed elliptical polarization to vertical polarization. The light is then reflected through the first polarization beam splitter prism 201, reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, reflected by the first polarization beam splitter prism 201, and reflected by the second polarization beam splitter prism 202, and finally incident on the second optical fiber coupler 602.

[0150] The vertically polarized light b2 is transmitted through the third quarter wave plate 503, and its polarization state changes from vertically polarized light to left-handed elliptically polarized light. The light b2 is then reflected by the reflector 401, reflected twice by the right angle prism 3 to be measured, and transmitted through the second quarter wave plate 502, and its polarization state changes from left-handed elliptically polarized light to horizontally polarized light. The light b2 is then transmitted through the first polarization beam splitter prism 201, and transmitted through the second polarization beam splitter prism 202, and finally incident on the first optical fiber coupler 601.

[0151] Step A3, the first optical fiber coupler 601 simultaneously receives two beams of orthogonal linear polarized light, and the Doppler frequency shift information of the reference light is recorded as f2; the Doppler frequency shift information of the measuring light is recorded as f2-Δf1; the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere is recorded as Δf1;

[0152] The second optical fiber coupler 602 receives two orthogonal linear polarized lights at the same time, and the Doppler frequency shift information of the reference light is recorded as f1; the Doppler frequency shift information of the measuring light is recorded as f1-3Δf1; and the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere is recorded as 3Δf1;

[0153] Step A4: Through phase decoupling, when the interference signal of the first optical fiber coupler 601 and the interference signal of the second optical fiber coupler 602 are added, the Doppler frequency shift is 4Δf1; when the two are subtracted, the Doppler frequency shift is 2Δf1, and the displacement S1 of the right-angle prism 3 to be measured is calculated:

[0154] When phase coupling is subtracted, the total phase delay is phase 1, then

[0155] When phase coupling is added, the total phase delay is phase 2, then

[0156] The displacement measurement device of the third embodiment is used to measure the displacement of the plane reflector 402 to be measured, and specifically includes the following steps:

[0157] Step B1, the right angle prism 3 to be measured is fixed, and the dual frequency laser 1 has a measuring light with a frequency of f1 and a reference light with a frequency of f2;

[0158] Step B2 specifically includes: the measuring light and the reference light enter the beam splitter prism 7 together, and are split according to energy by the beam splitter prism 7 to form reflected light and transmitted light;

[0159] The reflected light is transmitted through the second polarization beam splitter prism 202 to form horizontal linear polarized light a1 with a frequency of f1, and is reflected to form vertical linear polarized light a2 with a frequency of f2;

[0160] Horizontally polarized light a1 is incident on the second optical fiber coupler 602;

[0161] The vertical linear polarized light a2 is incident on the first optical fiber coupler 601;

[0162] The transmitted light is transmitted through the first polarization beam splitter prism 201 to form horizontal linear polarized light b1 with a frequency of f1, and is reflected to form vertical polarized light b2 with a frequency of f2;

[0163] The horizontal linear polarized light b1 is sequentially reflected twice by the right angle prism 3 to be measured, reflected by the reflector 401, transmitted by the first polarization beam splitter prism 201, and transmitted by the first quarter wave plate 501, and the polarization state changes from horizontal polarized light to left-handed elliptically polarized light. Then, it is sequentially reflected by the plane reflector 402 to be measured, and transmitted by the first quarter wave plate 501, and the polarization state changes from left-handed elliptically polarized light to vertical polarized light. Then, it is sequentially reflected by the first polarization beam splitter prism 201, and transmitted by the second quarter wave plate 502, and the polarization state changes from vertical polarized light to right-handed elliptically polarized light. Then, it is sequentially reflected twice by the right angle prism 3 to be measured, reflected by the reflector 401, and transmitted by the third quarter wave plate 501. The light is transmitted through the first wave plate 503, and the polarization state changes from right-handed elliptical polarization to horizontal polarization. The light is then transmitted through the first polarization beam splitter prism 201 and the first quarter wave plate 501, and the polarization state changes from horizontal polarization to left-handed elliptical polarization. The light is then reflected through the plane reflector 402 to be measured and transmitted through the first quarter wave plate 501, and the polarization state changes from left-handed elliptical polarization to vertical polarization. The light is then reflected through the first polarization beam splitter prism 201, reflected twice by the right-angle prism 3 to be measured, reflected by the reflector 401, reflected by the first polarization beam splitter prism 201, and reflected by the second polarization beam splitter prism 202, and finally incident on the second optical fiber coupler 602.

[0164] The vertically polarized light b2 is transmitted through the third quarter wave plate 503, and its polarization state changes from vertically polarized light to left-handed elliptically polarized light. The light b2 is then reflected by the reflector 401, reflected twice by the right angle prism 3 to be measured, and transmitted through the second quarter wave plate 502, and its polarization state changes from left-handed elliptically polarized light to horizontally polarized light. The light b2 is then transmitted through the first polarization beam splitter prism 201, and transmitted through the second polarization beam splitter prism 202, and finally incident on the first optical fiber coupler 601.

[0165] Step B3, the first optical fiber coupler 601 simultaneously receives two beams of orthogonal linear polarized light, obtains interference signals after phase decoupling of the two beams of orthogonal linear polarized light; the Doppler frequency shift information of the reference light is recorded as f2; the Doppler frequency shift information of the measuring light is recorded as f2; the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere is recorded as 0;

[0166] The second optical fiber coupler 602 simultaneously receives two orthogonal linear polarized lights, and the Doppler frequency shift information of the reference light is recorded as f1; the Doppler frequency shift information of the measuring light is recorded as f1-2Δf2; and the Doppler frequency shift information of the interference signal when the measuring light and the reference light interfere is recorded as 2Δf2;

[0167] Step B4: Based on the Doppler frequency shift 0 and 2Δf2, the displacement S2 of the plane reflector 402 to be measured is calculated by phase decoupling:

[0168]

[0169] The displacement measurement of the plane reflective mirror 402 to be measured is completed.

[0170] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An interferometric displacement measuring device based on a Sagnac structure, used for measuring the displacement of a right-angle prism (3) to be measured and a plane reflector (402) to be measured, characterized in that: It comprises a dual-frequency laser (1), a first polarization beam splitter prism (201), a reflector (401) and a first optical fiber coupler (601); The first polarization beam splitting prism (201) comprises four sides, wherein the first side is opposite to the third side, and the second side is opposite to the fourth side; The first side is provided with the dual-frequency laser (1) and the first optical fiber coupler (601) in sequence along the length direction thereof, the dual-frequency laser (1) being used to emit measurement light and reference light to the first polarization beam splitter prism (201); the first optical fiber coupler (601) being used to receive the measurement light and reference light after measurement, obtain corresponding Doppler frequency shift information, and realize displacement measurement; The reflector (401) is disposed on the second side, and the reflector (401) is used to reflect the light emitted from the first polarization beam splitting prism (201) to the right-angle prism (3) to be measured; The third side is used to set a right-angle prism (3) to be measured, a part of the bottom edge of the right-angle prism (3) to be measured is opposite to the third side, and the other part corresponds to the reflector (401), and is used to receive the light reflected by the reflector (401) and reflect it to the first polarization beam splitting prism (201); The fourth side is used to set a plane reflector (402) to be measured, and the plane reflector (402) to be measured can reflect light emitted from the first polarization beam splitter prism (201) back to the first polarization beam splitter prism (201).

2. The interferometric displacement measuring device based on the Sagnac structure according to claim 1, characterized in that: Also includes a first quarter wave plate (501), a second quarter wave plate (502) and a third quarter wave plate (503); The first quarter-wave plate (501) is arranged on the optical path between the plane reflector (402) to be measured and the first polarization beam splitting prism (201); The second quarter-wave plate (502) is arranged on a portion of the optical path between the first polarization beam splitter prism (201) and the right-angle prism (3) to be measured, and the portion of the optical path corresponds to the first optical fiber coupler (601); The third quarter-wave plate (503) is arranged on a portion of the optical path between the first polarization beam splitter prism (201) and the first reflector (401), and the portion of the optical path is close to the right-angle prism (3) to be measured.

3. The interferometric displacement measuring device based on the Sagnac structure according to claim 2, characterized in that: The first optical fiber coupler (601) and the second quarter wave plate (502) are arranged close to the fourth side of the first polarization beam splitter prism (201); The dual-frequency laser (1) is arranged close to the second side of the first polarization beam splitting prism (201).

4. The interferometric displacement measuring device based on the Sagnac structure according to claim 2 or 3, characterized in that: The polarization angles of the first quarter wave plate (501), the second quarter wave plate (502) and the third quarter wave plate (503) are all 45°.

5. The interferometric displacement measuring device based on the Sagnac structure according to claim 4, characterized in that: It also includes a second polarization beam splitter prism (202) and a beam splitter prism (7); The second polarization beam splitter prism (202) is arranged on the optical path between the dual-frequency laser (1) and the first polarization beam splitter prism (201); the beam splitting surface of the second polarization beam splitter prism (202) is perpendicular to the beam splitting surface of the first polarization beam splitter prism (201); The beam splitter prism (7) is arranged on the optical path between the first optical fiber coupler (601) and the first polarization beam splitter prism (201); the beam splitting surface of the beam splitter prism (7) is parallel to the beam splitting surface of the first polarization beam splitter prism (201).

6. The interferometric displacement measuring device based on the Sagnac structure according to claim 4, characterized in that: It also includes a beam splitter prism (7), a second polarization beam splitter prism (202) and a second optical fiber coupler (602); The beam splitter prism (7) is arranged on the optical path between the dual-frequency laser (1) and the first polarization beam splitter prism (201); the beam splitter surface of the beam splitter prism (7) is perpendicular to the beam splitter surface of the first polarization beam splitter prism (201); The second polarization beam splitter prism (202) is arranged on the optical path between the first optical fiber coupler (601) and the first polarization beam splitter prism (201); the beam splitting surface of the second polarization beam splitter prism (202) is parallel to the beam splitting surface of the first polarization beam splitter prism (201); The second optical fiber coupler (602) is arranged on the side of the second polarization beam splitter (202) close to the second side of the first polarization beam splitter (201) and away from the beam splitter (7), so that the first optical fiber coupler (601) receives part of the measurement light and reference light after participating in the measurement, thereby realizing coarse displacement measurement, and the second optical fiber coupler (602) receives another part of the measurement light and reference light after participating in the measurement, thereby realizing fine displacement measurement.

7. An interferometric displacement measurement method based on a Sagnac structure, using the interferometric displacement measurement device based on a Sagnac structure according to claim 1, characterized in that: The method comprises the following steps: measuring the displacement of a right-angle prism (3) to be measured and measuring the displacement of a plane reflector (402) to be measured; The displacement measurement of the right-angle prism (3) to be measured comprises the following steps: Step A1, the plane reflector (402) to be measured is fixed, and the dual-frequency laser (1) emits a measuring light with a frequency of f1 and a reference light with a frequency of f2; Step A2, the measuring light and the reference light enter the first optical fiber coupler (601) after being acted upon by corresponding optical devices respectively; Step A3: the first optical fiber coupler (601) obtains the Doppler frequency shift amount; Step A4, calculating the displacement of the right-angle prism (3) to be measured by using the Doppler frequency shift obtained in step A3, and completing the displacement measurement of the right-angle prism (3) to be measured; The displacement measurement of the plane reflector (402) to be measured comprises the following steps: Step B1, the right angle prism (3) to be measured is fixed, and the dual frequency laser (1) emits a measuring light with a frequency of f1 and a reference light with a frequency of f2; Step B2, the measuring light and the reference light enter the first optical fiber coupler (601) after being acted upon by corresponding optical devices respectively; Step B3, the first optical fiber coupler (601) receives the acted measurement light and reference light to obtain the Doppler frequency shift; Step B4, calculating the displacement of the plane reflector (402) to be measured by using the Doppler frequency shift obtained in step B3, and completing the displacement measurement of the plane reflector (402) to be measured.

8. The interferometric displacement measurement method based on the Sagnac structure according to claim 7, characterized in that: Step A2 specifically comprises the following steps: the measuring light with a frequency of f1 is transmitted through the first polarization beam splitter prism (201) to become horizontal linear polarized light; the measuring light is then reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), transmitted through the first polarization beam splitter prism (201), and transmitted through the first quarter wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light; the measuring light is then reflected by the plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light; the measuring light is then reflected by the first polarization beam splitter prism (201), and transmitted through the second quarter wave plate (502), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then reflected by the plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state is changed from vertical polarized light to right-handed elliptically ... plane reflector (402) to be measured, and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light. The light is reflected twice by the mirror (3), reflected by the reflector (401), transmitted by the third quarter wave plate (503), and the polarization state is changed from right-handed elliptically polarized light to horizontally polarized light. The light is then sequentially transmitted by the first polarization beam splitter prism (201) and the first quarter wave plate (501), and the polarization state is changed from horizontally polarized light to left-handed elliptically polarized light. The light is then sequentially reflected by the plane reflector (402) to be measured, and transmitted by the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertically polarized light. The light is then sequentially reflected by the first polarization beam splitter prism (201), reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), and reflected by the first polarization beam splitter prism (201), and finally incident on the first optical fiber coupler (601). The reference light with a frequency of f2 is reflected by the first polarization beam splitter prism (201) to become vertical linear polarized light, then transmitted through the third quarter wave plate (503), the polarization state of which changes from vertical polarized light to left-handed elliptically polarized light, then sequentially reflected by the reflector (401), reflected twice by the right angle prism (3) to be measured, transmitted through the second quarter wave plate (502), the polarization state of which changes from left-handed elliptically polarized light to horizontal polarized light, then transmitted through the first polarization beam splitter prism (201), and finally incident on the first optical fiber coupler (601); Step A3 specifically includes: the first optical fiber coupler (601) obtains the Doppler frequency shift Δf1; Step A4 specifically comprises calculating the displacement S1 of the right-angle prism (3) to be measured by using the Doppler frequency shift Δf1 obtained in step A3: Where c is the speed of light, The total phase delay measured for the laser round trip; Complete the displacement measurement of the right-angle prism (3) to be measured; Step B2 specifically comprises the following steps: the measuring light with a frequency of f1 is transmitted through the first polarization beam splitter prism (201) to become horizontal linear polarized light; the measuring light is then reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), transmitted through the first polarization beam splitter prism (201), and transmitted through the first quarter wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light; the measuring light is then reflected by the plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light; the measuring light is then reflected by the first polarization beam splitter prism (201), and transmitted through the second quarter wave plate (502), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then reflected by the plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state is changed from vertical polarized light to right-handed elliptically ... plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then reflected by the plane reflector (402) to be measured, and the polarization state is changed from The light is reflected twice by the mirror (3), reflected by the reflector (401), transmitted by the third quarter wave plate (503), and the polarization state is changed from right-handed elliptically polarized light to horizontally polarized light. The light is then sequentially transmitted by the first polarization beam splitter prism (201) and the first quarter wave plate (501), and the polarization state is changed from horizontally polarized light to left-handed elliptically polarized light. The light is then sequentially reflected by the plane reflector (402) to be measured, and transmitted by the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertically polarized light. The light is then sequentially reflected by the first polarization beam splitter prism (201), reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), and reflected by the first polarization beam splitter prism (201), and finally incident on the first optical fiber coupler (601). The reference light with a frequency of f2 is reflected by the first polarization beam splitter prism (201) to become vertical linear polarized light, then transmitted through the third quarter wave plate (503), the polarization state of which changes from vertical polarized light to left-handed elliptically polarized light, then sequentially reflected by the reflector (401), reflected twice by the right angle prism (3) to be measured, transmitted through the second quarter wave plate (502), the polarization state of which changes from left-handed elliptically polarized light to horizontal polarized light, then transmitted through the first polarization beam splitter prism (201), and finally incident on the first optical fiber coupler (601); Step B3 specifically includes: the first optical fiber coupler (601) receives the acted measurement light and reference light to obtain the Doppler frequency shift Δf2; Step B4 specifically includes calculating the displacement S2 of the plane reflector (402) to be measured by using the Doppler frequency shift Δf2 obtained in step B3: The displacement measurement of the plane reflector (402) to be measured is completed.

9. The interferometric displacement measurement method based on the Sagnac structure according to claim 7, characterized in that: Step A2 specifically comprises the following steps: the measuring light with a frequency of f1 is transmitted through the second polarization beam splitter prism (202) to become horizontal linear polarized light; the measuring light is then sequentially transmitted through the first polarization beam splitter prism (201), reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), transmitted through the first polarization beam splitter prism (201), and transmitted through the first quarter wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light; the measuring light is then sequentially reflected through the plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light; the measuring light is then sequentially reflected through the first polarization beam splitter prism (201), and transmitted through the second quarter wave plate (502), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then sequentially transmitted through the first polarization beam splitter prism (201), and transmitted through the second quarter wave plate (502), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then sequentially transmitted through the plane reflector (402) to be measured, and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light. The light is reflected twice by the right-angle prism (3), reflected by the reflector (401), and transmitted by the third quarter-wave plate (503), and the polarization state is changed from right-handed elliptical polarized light to horizontal polarized light. The light is then sequentially transmitted through the first polarization beam splitter prism (201) and the first quarter-wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptical polarized light. The light is then sequentially reflected by the plane reflector (402) to be measured, and transmitted through the first quarter-wave plate (501), and the polarization state is changed from left-handed elliptical polarized light to vertical polarized light. The light is then sequentially reflected by the first polarization beam splitter prism (201), reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), reflected by the first polarization beam splitter prism (201), and transmitted by the beam splitter prism (7), and finally incident on the first optical fiber coupler (601); The reference light with a frequency of f2 is reflected by the second polarization beam splitter prism (202) to become vertically polarized light, then reflected by the beam splitter prism (7), and finally incident on the first optical fiber coupler (601); Step A3 specifically includes: the first optical fiber coupler (601) obtains the Doppler frequency shift Δf1; Step A4 specifically comprises calculating the displacement S1 of the right-angle prism (3) to be measured by using the Doppler frequency shift Δf1 obtained in step A3: Complete the displacement measurement of the right-angle prism (3) to be measured; Step B2 specifically comprises the following steps: the measuring light with a frequency of f1 is transmitted through the second polarization beam splitter prism (202) to become horizontal linear polarized light; the measuring light is then sequentially transmitted through the first polarization beam splitter prism (201), reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), transmitted through the first polarization beam splitter prism (201), and transmitted through the first quarter-wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light; the measuring light is then sequentially reflected through the plane reflector (402) to be measured, and transmitted through the first quarter-wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light; the measuring light is then sequentially reflected through the first polarization beam splitter prism (201), and transmitted through the second quarter-wave plate (502), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then sequentially transmitted through the right-angle prism (3) to be measured, and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then sequentially transmitted through the plane reflector (402) to be measured, and transmitted through the first quarter-wave plate (501), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light; the measuring light is then sequentially transmitted through the right-angle prism (3) to be measured, and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light. The light is then reflected by a right-angle prism (3), reflected twice, reflected by a reflector (401), and transmitted by a third quarter-wave plate (503), and the polarization state is changed from right-handed elliptically polarized light to horizontally polarized light. The light is then sequentially transmitted by a first polarization beam splitter prism (201) and a first quarter-wave plate (501), and the polarization state is changed from horizontally polarized light to left-handed elliptically polarized light. The light is then sequentially reflected by a plane reflector (402) to be measured, and transmitted by a first quarter-wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertically polarized light. The light is then sequentially reflected by a first polarization beam splitter prism (201), reflected twice by a right-angle prism (3) to be measured, reflected by a reflector (401), reflected by a first polarization beam splitter prism (201), and transmitted by a beam splitter prism (7), and finally incident on a first optical fiber coupler (601); The reference light with a frequency of f2 is reflected by the second polarization beam splitter prism (202) to become vertically polarized light, then reflected by the beam splitter prism (7), and finally incident on the first optical fiber coupler (601); Step B3 specifically includes: the first optical fiber coupler (601) receives the acted measurement light and reference light to obtain the Doppler frequency shift Δf2; Step B4 specifically includes calculating the displacement S2 of the plane reflector (402) to be measured by using the Doppler frequency shift Δf2 obtained in step B3: The displacement measurement of the plane reflector (402) to be measured is completed.

10. The interferometric displacement measurement method based on Sagnac structure according to claim 7, characterized in that: Step A2 specifically comprises: the measuring light and the reference light enter a beam splitter prism (7) together, and are split according to energy by the beam splitter prism (7) to form reflected light and transmitted light; The reflected light is transmitted through a second polarization beam splitter prism (202) to form horizontal linear polarized light a1 with a frequency f1, and is reflected to form vertical linear polarized light a2 with a frequency f2; The horizontal linear polarized light a1 is incident on the second optical fiber coupler (602); The vertical linear polarized light a2 is incident on the first optical fiber coupler (601); The transmitted light is transmitted through a first polarization beam splitting prism (201) to form horizontal linear polarized light b1 with a frequency of f1, and is reflected to form vertical polarized light b2 with a frequency of f2; The horizontal linear polarized light b1 is reflected twice by the right angle prism (3) to be measured, reflected by the reflector (401), transmitted by the first polarization beam splitter prism (201), and transmitted by the first quarter wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light. The horizontal linear polarized light b1 is then reflected twice by the right angle prism (3) to be measured, reflected by the reflector (401), transmitted by the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light. The horizontal linear polarized light b1 is then reflected twice by the right angle prism (3) to be measured, reflected by the reflector (401), and transmitted by the third quarter wave plate (501), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light. The light is transmitted through a first wave plate (503), and the polarization state changes from right-handed elliptically polarized light to horizontally polarized light. The light is then transmitted through a first polarization beam splitter prism (201) and a first quarter wave plate (501), and the polarization state changes from horizontally polarized light to left-handed elliptically polarized light. The light is then reflected through a plane reflector (402) to be measured, and transmitted through the first quarter wave plate (501), and the polarization state changes from left-handed elliptically polarized light to vertically polarized light. The light is then reflected through a first polarization beam splitter prism (201), reflected twice by a right-angle prism (3) to be measured, reflected by a reflector (401), reflected by the first polarization beam splitter prism (201), and reflected by a second polarization beam splitter prism (202), and finally incident on a second optical fiber coupler (602). The vertically polarized light b2 is transmitted through the third quarter wave plate (503), and its polarization state changes from vertically polarized light to left-handed elliptically polarized light. The light is then sequentially reflected through the reflector (401), reflected twice through the right angle prism (3) to be measured, and transmitted through the second quarter wave plate (502), and its polarization state changes from left-handed elliptically polarized light to horizontally polarized light. The light is then transmitted through the first polarization beam splitter prism (201), and then through the second polarization beam splitter prism (202), and finally incident on the first optical fiber coupler (601). Step A3 specifically comprises: the first optical fiber coupler (601) simultaneously receives two beams of orthogonal linear polarized light, and obtains the Doppler frequency shift Δf1 of the interference signal after the phase decoupling of the two beams of orthogonal linear polarized light; The second optical fiber coupler (602) simultaneously receives two beams of orthogonal linear polarized light to obtain a Doppler frequency shift 3Δf1 of an interference signal after phase decoupling of the two beams of orthogonal linear polarized light; Step A4 specifically comprises calculating the displacement S1 of the right-angle prism (3) to be measured by using the Doppler frequency shift Δf1 and 3Δf1 obtained in step A3: When phase coupling is subtracted, the total phase delay is phase 1, then When phase coupling is added, the total phase delay is phase 2, then Complete the displacement measurement of the right-angle prism (3) to be measured; Specifically, step B2 comprises: the measuring light and the reference light enter a beam splitter prism (7) together, and are split according to energy by the beam splitter prism (7) to form reflected light and transmitted light; The reflected light is transmitted through a second polarization beam splitter prism (202) to form horizontal linear polarized light a1 with a frequency f1, and is reflected to form vertical linear polarized light a2 with a frequency f2; The horizontal linear polarized light a1 is incident on the second optical fiber coupler (602); The vertical linear polarized light a2 is incident on the first optical fiber coupler (601); The transmitted light is transmitted through a first polarization beam splitting prism (201) to form horizontal linear polarized light b1 with a frequency of f1, and is reflected to form vertical polarized light b2 with a frequency of f2; The horizontal linear polarized light b1 is reflected twice by the right angle prism (3) to be measured, reflected by the reflector (401), transmitted by the first polarization beam splitter prism (201), and transmitted by the first quarter wave plate (501), and the polarization state is changed from horizontal polarized light to left-handed elliptically polarized light. The horizontal linear polarized light b1 is then reflected twice by the right angle prism (3) to be measured, reflected by the reflector (401), transmitted by the first quarter wave plate (501), and the polarization state is changed from left-handed elliptically polarized light to vertical polarized light. The horizontal linear polarized light b1 is then reflected twice by the right angle prism (3) to be measured, reflected by the reflector (401), and transmitted by the third quarter wave plate (501), and the polarization state is changed from vertical polarized light to right-handed elliptically polarized light. The light is transmitted through the wave plate (503), and the polarization state changes from right-handed elliptically polarized light to horizontally polarized light. The light is then transmitted through the first polarization beam splitter prism (201) and the first quarter wave plate (501), and the polarization state changes from horizontally polarized light to left-handed elliptically polarized light. The light is then reflected through the plane reflector (402) to be measured, and the first quarter wave plate (501) to be measured, and the polarization state changes from left-handed elliptically polarized light to vertically polarized light. The light is then reflected through the first polarization beam splitter prism (201), reflected twice by the right-angle prism (3) to be measured, reflected by the reflector (401), reflected by the first polarization beam splitter prism (201), and reflected by the second polarization beam splitter prism (202), and finally incident on the second optical fiber coupler (602). The vertically polarized light b2 is transmitted through the third quarter wave plate (503), and its polarization state changes from vertically polarized light to left-handed elliptically polarized light. The light is then sequentially reflected through the reflector (401), reflected twice through the right angle prism (3) to be measured, and transmitted through the second quarter wave plate (502), and its polarization state changes from left-handed elliptically polarized light to horizontally polarized light. The light is then transmitted through the first polarization beam splitter prism (201), and then through the second polarization beam splitter prism (202), and finally incident on the first optical fiber coupler (601). Step B3 specifically comprises: the first optical fiber coupler (601) simultaneously receives two beams of orthogonal linear polarized light, and obtains a Doppler frequency shift of an interference signal after phase decoupling of the two beams of orthogonal linear polarized light, which is 0; The second optical fiber coupler (602) simultaneously receives two beams of orthogonal linear polarized light to obtain a Doppler frequency shift 2Δf2 of an interference signal after phase decoupling of the two beams of orthogonal linear polarized light; Step B4 specifically includes calculating the displacement S2 of the plane reflector (402) to be measured by phase decoupling based on the Doppler frequency shift 0 and 2Δf2 obtained in step B3: The displacement measurement of the plane reflector (402) to be measured is completed.

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