CN114739432B - Dual-wavelength quadrature phase bias locking interferometry method based on geometric phase shifter - Google Patents

Abstract

The invention discloses a dual-wavelength quadrature phase bias locking interferometry method based on a geometric phase shifter, which is characterized in that two beams of light with wavelengths of lambda ₁ and lambda ₂ are respectively incident into an optical path of an amplitude-division interferometer with quadrature phase bias in a linear polarization state, phase detection is realized by taking a light beam with the wavelength of lambda ₁ as a detection light beam, whether the optical path phase bias of the amplitude-division interferometer is orthogonal or not is monitored by taking a light beam with the wavelength of lambda ₂ as a feedback light beam, real-time locking of the quadrature phase bias of the interferometer is realized, phase shift errors caused by chromatic aberration between the two beams of light are corrected through the geometric phase shifter consisting of a 1/2 wave plate and a 1/4 wave plate, so that the influence of a noise source on the quadrature phase bias of the interferometer is avoided, and the interferometer always maintains good phase detection linearity and sensitivity.

Description

Dual-wavelength orthogonal phase bias-locked interferometry based on geometric phase shifter

Technical Field

The invention relates to interference measurement, and more specifically to a dual-wavelength orthogonal phase bias locking interference measurement method based on a geometric phase shifter, which is used for realizing high-sensitivity phase measurement.

Background technique

An optical interferometer is an optical instrument that uses the principle of light interference to obtain the phase information of light by measuring the optical path difference, thereby obtaining the physical quantities required for the experiment. Because the movement of interference fringes is caused by the change in the difference in the geometric paths of two coherent lights, changes in the optical path or the refractive index of the medium through which a beam of coherent light passes will cause changes in the optical path difference. Therefore, the phase change can be measured based on the movement of the interference fringes, thereby measuring other related physical quantities. For every fringe spacing that the interference fringes move, the optical path difference changes by one wavelength, so the interferometer measures the phase in units of the wavelength of the light wave, and its measurement accuracy is significantly better than other measurement methods.

According to the source of interference light, interferometers can be divided into two types: wavefront division type and amplitude division type. Typical amplitude division interferometers include Mach-Zehnder interferometer, Sagnac interferometer, Michelson interferometer, etc. Such interferometers are widely used in length measurement, refractive index measurement, optical component quality inspection and other fields. When they are used to measure small phase changes, in order to ensure the best phase detection sensitivity and linearity, the phase bias of the interferometer optical path needs to be maintained at ±π/2. However, in practical applications, due to the influence of environmental disturbances, mechanical vibrations, and beam drift, it is impossible to ensure that the phase bias of the interferometer optical path always remains in an orthogonal state. For this reason, it is necessary to monitor the phase of the system optical path in real time, and when the phase bias changes, it should be corrected in time. Due to the change in phase This can be achieved by changing the optical path difference ΔL, that is: Δφ＝(2π·ΔL)/λ, so the conventional method is to change the optical path difference by moving the reflector in the interferometer optical path, thereby achieving the purpose of phase shifting. However, as a high-precision optical detection system, changing the position of the optical element in the optical path will inevitably change the performance parameters of the entire measurement system. In order to ensure the reliability of the measurement results, the system needs to be recalibrated, which makes the measurement work more cumbersome.

Summary of the invention

The present invention is to avoid the shortcomings of the above-mentioned prior art and provide a dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter. For the amplitude-dividing interferometer, the phase shift is realized without moving the reflector and ensuring the stability of the performance parameters of the measurement system, so that the phase bias of the system optical path is maintained at ±π/2, so as to ensure the optimal phase detection sensitivity and linearity of the measurement system.

The present invention adopts the following technical solutions to achieve the purpose of the invention:

The dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter of the present invention is characterized in that two light beams with wavelengths of _λ1 and _λ2 are incident in a linear polarization state into an optical path of an amplitude-dividing interferometer with an orthogonal phase bias, a light beam with a wavelength of _λ1 is used as a detection light beam to realize phase detection, a light beam with a wavelength of _λ2 is used as a feedback light beam to monitor whether the phase bias of the optical path of the amplitude-dividing interferometer is orthogonal, and real-time locking of the orthogonal phase bias of the interferometer is realized, a phase shift error caused by the chromatic aberration between the two light beams is corrected by a geometric phase shifter composed of a 1/2 wave plate and a 1/4 wave plate, and the influence of a noise source on the orthogonal phase bias of the interferometer is avoided, so that the interferometer always maintains good phase detection linearity and sensitivity.

The dual-wavelength orthogonal phase bias locking interferometry measurement method based on geometric phase shifter of the present invention is also characterized in that:

The detection beam is divided into two beams of linear polarized detection light with equal light intensity by the first beam splitter, and enters the reference arm and the measuring arm of the amplitude division interferometer respectively; the linear polarized detection light in the reference arm passes through the geometric phase shifter and is then divided into two beams of reference arm linear polarized detection light with equal light intensity by the second beam splitter; the linear polarized light in the measuring arm is transmitted to the measured object by the second dichroic mirror A, refracted by the measured object, and then divided into two measuring arm linear polarized detection light with equal light intensity by the second beam splitter after passing through the second dichroic mirror B, and forms a detection beam interference signal corresponding to the two reference arm linear polarized detection lights one by one, and the detection beam interference signal is transmitted into the first signal acquisition and processing channel by the fourth dichroic mirror A and the fourth dichroic mirror B respectively, and the detection beam phase change caused by the measured object is obtained through signal processing in the first signal acquisition and processing channel;

The feedback light beam is divided into two beams of linear polarized feedback light with equal light intensity by the first beam splitter, and enters the reference arm and the measuring arm of the amplitude division interferometer respectively; the linear polarized feedback light in the reference arm passes through the geometric phase shifter, and is then divided into two beams of reference arm linear polarized feedback light with equal light intensity by the second beam splitter; the linear polarized feedback light in the measuring arm is reflected to the second beam splitter by the second dichroic mirror A, and is divided into two beams of measuring arm linear polarized feedback light with equal light intensity by the second beam splitter, and forms a feedback light beam interference signal corresponding to the two reference arm linear polarized feedback lights one by one, the feedback light beam interference signal is reflected by the fourth dichroic mirror A and the fourth dichroic mirror B and enters the second signal acquisition and processing channel, and outputs a feedback signal after signal processing by the second signal acquisition and processing channel, and the feedback signal is used to control the geometric phase shifter to shift the phase, so that the phase offset quadrature of the measuring light path is locked.

The dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter of the present invention is also characterized in that: the geometric phase shifter arranged in the reference arm of the amplitude division interferometer is composed of two 1/4 wave plates and one 1/2 wave plate, the angle between the fast axis of the two 1/4 wave plates and the x-axis is 45°, and one 1/2 wave plate is located between the two 1/4 wave plates and is installed on an electric rotating mirror frame. The rotation of the electric rotating mirror frame is controlled according to the feedback signal output by the second signal acquisition and processing channel, so as to adjust the angle between the fast axis of the 1/2 wave plate and the x-axis, so that the phase bias of the measuring optical path is locked at ±π/2.

The dual-wavelength orthogonal phase bias-locked interferometry measurement method based on a geometric phase shifter of the present invention is also characterized in that: a polarizer is set, the detection light beam is transmitted through a first dichroic mirror, and then emitted through the polarizer in a linear polarization state, forming a detection light beam in a linear polarization state; the feedback light beam is reflected by the first dichroic mirror, and then emitted through the polarizer in a linear polarization state, forming a feedback light beam in a linear polarization state.

The dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter of the present invention is also characterized in that: the object to be measured is an object that can change the optical path difference of the detection light beam.

The dual-wavelength orthogonal phase bias locking interferometry measurement method based on the geometric phase shifter of the present invention is also characterized in that: the detection beam refers to a beam with a wavelength of λ ₁ and can be transmitted by a dichroic mirror; the feedback beam refers to a beam with a wavelength of λ ₂ and can be reflected by a dichroic mirror; and the wavelengths λ ₁ and λ ₂ are symmetrical about the central wavelength λ of the geometric phase shifter, so that the phase delays generated by the detection beam and the feedback beam after passing through the geometric phase shifter are equal.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1. The present invention sets a feedback light beam for real-time monitoring of the phase of the amplitude-division interferometer optical path. When the phase changes, a feedback signal is provided for phase correction. The monitoring process is timely, stable and reliable.

2. The present invention realizes phase shifting without moving the reflector and ensuring the stability of the performance parameters of the measurement system, so that the phase offset of the system optical path is locked at ±π/2, thereby ensuring the optimal phase detection sensitivity and linearity of the measurement system.

3. The present invention adds a geometric phase shifter to the amplitude division interferometer to achieve correction of the phase shift error caused by chromatic aberration of light beams of different wavelengths.

4. The present invention has good universality and is applicable to most amplitude division interferometers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a dual-wavelength phase bias locking interferometry measurement method based on a geometric phase shifter according to the present invention;

FIG2 is a schematic diagram of the structure of the present invention applied to a Mach-Zehnder interferometer;

FIG3 is a phase delay characteristic curve of a 588nm zero-order quartz 1/2 wave plate;

FIG4 is a phase delay characteristic curve of a 588nm zero-order quartz quarter wave plate;

FIG5 is a phase delay characteristic curve of a geometric phase shifter composed of 588 nm wave plates;

FIG. 6 is a phase delay characteristic curve of the phase shifting scheme by changing the optical path difference.

Numbers in the figure: 1 detection beam, 2 feedback beam, 3 first dichroic mirror, 4 polarizer, 5 first beam splitter, 6a second dichroic mirror A, 6b second dichroic mirror B, 7 geometric phase shifter, 8 object to be measured, 9 second beam splitter, 10a third dichroic mirror A, 10b third dichroic mirror B, 11 first signal acquisition and processing channel, 12 second signal acquisition and processing channel, 13 first reflector, 14 second reflector, 15 third reflector.

Detailed ways

Referring to Figures 1 and 2, the dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter in this embodiment is to inject two light beams with wavelengths of λ ₁ and λ ₂ into the optical path of an amplitude-dividing interferometer with an orthogonal phase bias in a linear polarization state, and use the light beam with a wavelength of λ ₁ as a detection light beam 1 to realize phase detection, and use the light beam with a wavelength of λ ₂ as a feedback light beam 2 to monitor whether the phase bias of the optical path of the amplitude-dividing interferometer is orthogonal, thereby realizing real-time locking of the orthogonal phase bias of the interferometer, and the phase shift error caused by the chromatic aberration between the two light beams is corrected by a geometric phase shifter composed of a 1/2 wave plate and a 1/4 wave plate, thereby avoiding the influence of noise sources on the orthogonal phase bias of the interferometer, so that the interferometer always maintains good phase detection linearity and sensitivity.

The corresponding technical measures in this embodiment include:

As shown in Figures 1 and 2, the detection beam 1 is divided into two beams of linearly polarized detection light with equal light intensity by the first beam splitter 5, and enter the reference arm and the measuring arm of the amplitude division interferometer respectively; the linearly polarized detection light in the reference arm is reflected by the third reflector 15, and then passes through the geometric phase shifter 7, and is divided into two reference arm linearly polarized detection lights with equal light intensity by the second beam splitter 9; the linearly polarized light in the measuring arm is transmitted through the second dichroic mirror A6a, reflected by the first reflector 13 to the object to be measured 8, refracted by the object to be measured 8, and then transmitted through the second dichroic mirror B6b and then divided into two measuring arm linearly polarized detection lights with equal light intensity by the second beam splitter 9, and the detection beam interference signals are formed in one-to-one correspondence with the two reference arm linearly polarized detection lights, and the detection beam interference signals are transmitted through the fourth dichroic mirror A10a and the fourth dichroic mirror B10b respectively and enter the first signal acquisition and processing channel 11, and the phase change of the detection beam caused by the object to be measured is obtained through signal processing of the first signal acquisition and processing channel 11.

The feedback beam 2 is split into two beams of linearly polarized feedback light with equal intensity by the first beam splitter 5, and enters the reference arm and the measuring arm of the amplitude division interferometer respectively; the linearly polarized feedback light in the reference arm is reflected by the third reflector 15, and then passes through the geometric phase shifter 7, and is split into two reference arm linearly polarized feedback lights with equal intensity by the second beam splitter 9; the linearly polarized feedback light in the measuring arm is reflected by the second dichroic mirror A 6a, the second reflector 14, and the second dichroic mirror B 6b in sequence, and reaches the second beam splitter 9, and is split into two measuring arm linearly polarized feedback lights with equal intensity by the second beam splitter 9, and corresponds to the two reference arm linearly polarized feedback lights one by one to form a feedback beam interference signal, the feedback beam interference signal is reflected by the fourth dichroic mirror A10a and the fourth dichroic mirror B10b and enters the second signal acquisition and processing channel 12, and is output as a feedback signal after signal processing by the second signal acquisition and processing channel 12, and the geometric phase shifter 7 is controlled by the feedback signal to shift the phase, so that the phase offset quadrature of the measuring optical path is locked.

The geometric phase shifter 7 arranged in the reference arm of the amplitude division interferometer is composed of two 1/4 wave plates and one 1/2 wave plate. The angle between the fast axis direction of the two 1/4 wave plates and the x-axis direction is 45°. One 1/2 wave plate is located between the two 1/4 wave plates and is installed on the electric rotating mirror frame. The rotation of the electric rotating mirror frame is controlled according to the feedback signal output by the second signal acquisition and processing channel 12, so as to adjust the angle between the fast axis of the 1/2 wave plate and the x-axis, so that the phase bias of the measuring optical path is locked at ±π/2.

A polarizer 4 is provided, and the detection beam 1 is transmitted through the first dichroic mirror 3 and then emitted through the polarizer 4 in a linear polarization state, thereby forming a detection beam 1 in a linear polarization state; the feedback beam 2 is reflected by the first dichroic mirror 3 and then emitted through the polarizer 4 in a linear polarization state, thereby forming a feedback beam 2 in a linear polarization state.

FIG2 shows a dual-wavelength orthogonal phase bias-locked Mach-Zehnder interferometer based on a geometric phase shifter. In this embodiment, two photoelectric receivers and a differential amplifier circuit are selected to form a signal acquisition and processing channel. The detection beam passes through the object to be measured, causing the phase of the interference signal to change, which is received by the photoelectric receiver and output as a detection signal through the differential amplifier circuit to achieve the measurement of the physical quantity of the object to be measured. The feedback beam does not pass through the object to be measured. When the phase of the Mach-Zehnder interferometer optical path is no longer orthogonal, the interference signal of the feedback beam is received by the photoelectric receiver, and the differential signal is output through the differential circuit and fed back to the geometric phase shifter to change the phase delay and make the phase of the interferometer optical path orthogonal again.

In a specific implementation, the object to be measured 8 refers to an object that can change the optical path difference of the detection light beam 1 .

The detection beam 1 refers to a beam with a wavelength of λ ₁ that can be transmitted by the dichroic mirror; the feedback beam 2 refers to a beam with a wavelength of λ ₂ that can be reflected by the dichroic mirror; the wavelength λ ₁ and the wavelength λ ₂ are symmetrical about the central wavelength λ of the geometric phase shifter 7 so that the phase delays generated by the detection beam 1 and the feedback beam 2 after passing through the geometric phase shifter 7 are equal.

As shown in FIG5 , the phase delay characteristic curve of the geometric phase shifter composed of wave plates with a central wavelength of λ=588nm, light sources with a wavelength of λ ₁ =633nm and a wavelength of λ ₂ =532nm are selected as the detection beam and the feedback beam respectively. The large difference in wavelength makes it easier to separate, and the similar phase delay can reduce the phase shift error caused by chromatic aberration, so it can be used as an ideal input light source.

In this embodiment, the geometric phase shifter 7 is composed of three zero-order quartz wave plates with a wavelength of 588nm; first, the phase delay characteristics of the 1/2 wave plate and the 1/4 wave plate of 588nm are determined as shown in Figures 3 and 4. The phase delays of the first 1/4 wave plate and the second 1/4 wave plate are equal, that is, δ ₁ =δ ₂ , and the angle between the fast axis and the x-axis is 45°. The 1/2 wave plate is located between the two 1/4 wave plates, and the angle between the fast axis of the 1/2 wave plate and the x-axis is θ. The Jones matrices G ₁ and G ₃ of the two 1/4 wave plates, and the Jones matrix G ₂ of the one 1/2 wave plate are respectively:

Assume that the incident light is horizontally polarized light, and its Jones vector E _i is:

After the incident light passes through the geometric phase shifter, the Jones vector E _t of the outgoing light is obtained by using the Jones representation method:

E _t = G ₃ · G ₂ · G ₁ · E _i (1)

Using formula (1) and combining with MATLAB programming, the phase delay curve of the geometric phase shifter is fitted when θ = 22.5° as shown in Figure 5. At the central wavelength of 588nm, the geometric phase shifter can produce a phase delay of 45°, a phase delay of 44.30° at a wavelength of 633nm, and a phase delay of 43.65° at a wavelength of 532nm. Therefore, the geometric phase shifter has a good achromatic characteristic and can effectively reduce the phase shift error caused by chromatic aberration of the detection beam and the feedback beam. In actual measurement, the value of θ is adjusted in real time according to the feedback signal.

In this embodiment, a 588nm zero-order quartz wave plate is selected as the research object. In actual operation, wave plates of other materials or wavelengths can also be selected. The better the achromatic property of the wave plate itself, the better the achromatic property of the combined geometric phase shifter.

FIG6 shows the phase delay characteristic curve of the phase shifting scheme of changing the optical path difference, which means that when using the Mach-Zehnder interferometer for measurement, the optical path difference can also be changed by moving the position of the reflector in the optical path to achieve phase correction. When the central wavelength is 588nm, the phase delay characteristic curve of this phase shifting scheme is shown in Figure 6; by comparing the phase delay characteristic curve shown in Figure 6 with the phase delay curve of the geometric phase shifter in the present invention shown in Figure 5, it can be seen that the scheme shown in the curve in Figure 6 is highly dependent on the wavelength and cannot meet the requirements of the present invention.

Claims (5)

1. A dual-wavelength orthogonal phase bias locking interferometry measurement method based on geometric phase shifter, characterized in that: the wavelengths are and The two beams of light are incident on the optical path of the orthogonal phase biased amplitude-division interferometer in a linearly polarized state, with a wavelength of The light beam with wavelength of The light beam (2) is used as a feedback light beam to monitor whether the phase bias of the optical path of the amplitude division interferometer is orthogonal, so as to realize the real-time locking of the orthogonal phase bias of the interferometer. The phase shift error caused by the chromatic aberration between the two light beams is corrected by a geometric phase shifter composed of a 1/2 wave plate and a 1/4 wave plate, so as to avoid the influence of the noise source on the orthogonal phase bias of the interferometer, so that the interferometer always maintains good phase detection linearity and sensitivity; the detection light beam (1) is divided into two linearly polarized detection lights with equal light intensity by the first beam splitter (5), and enters the reference arm and the measurement arm of the amplitude division interferometer respectively; the detection light beam (1) in the reference arm ... The linearly polarized detection light passes through a geometric phase shifter (7) and is then split by a second beam splitter (9) into two reference arm linearly polarized detection lights of equal intensity. The linearly polarized light in the measuring arm is transmitted to the measured object (8) through a second dichroic mirror A (6a), refracted by the measured object (8), and then passed through a second dichroic mirror B (6b) and split by a second beam splitter (9) into two measuring arm linearly polarized detection lights of equal intensity. The detection light beam interference signals are formed in one-to-one correspondence with the two reference arm linearly polarized detection lights. The detection light beam interference signals are respectively transmitted by a fourth dichroic mirror A (10a) and a fourth dichroic mirror B (6b). The mirror B (10b) is transmitted into the first signal acquisition and processing channel (11), and the phase change of the detection light beam caused by the measured object is obtained through signal processing in the first signal acquisition and processing channel (11); the feedback light beam (2) is divided into two beams of linearly polarized feedback light with equal light intensity by the first beam splitter (5), and enters the reference arm and the measuring arm of the amplitude division interferometer respectively; the linearly polarized feedback light in the reference arm passes through the geometric phase shifter (7), and is then divided into two beams of reference arm linearly polarized feedback light with equal light intensity by the second beam splitter (9); the linearly polarized feedback light in the measuring arm passes through the second dichroic mirror A (6 a) is reflected to a second beam splitter (9), which is split by the second beam splitter (9) into two beams of measurement arm linear polarized feedback light with equal light intensity, and corresponds to the two beams of reference arm linear polarized feedback light in a one-to-one manner to form a feedback beam interference signal, the feedback beam interference signal is reflected by a fourth dichroic mirror A (10a) and a fourth dichroic mirror B (10b) and enters a second signal acquisition and processing channel (12), and a feedback signal is output after signal processing by the second signal acquisition and processing channel (12), and the feedback signal is used to control the geometric phase shifter (7) to perform phase shifting, so that the phase offset quadrature of the measurement light path is locked. 2. The dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter according to claim 1 is characterized in that: the geometric phase shifter (7) arranged in the reference arm of the amplitude division interferometer is composed of two 1/4 wave plates and one 1/2 wave plate, the fast axis of the two 1/4 wave plates and the x-axis have an angle of 45°, and the one 1/2 wave plate is located between the two 1/4 wave plates and is installed on an electric rotating mirror frame, and the rotation of the electric rotating mirror frame is controlled according to the feedback signal output by the second signal acquisition and processing channel (12), so as to adjust the angle between the fast axis of the 1/2 wave plate and the x-axis, so that the phase bias of the measurement light path is locked at . 3. The dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter according to claim 1 is characterized in that: a polarizer (4) is provided, the detection beam (1) is transmitted through a first dichroic mirror (3), and then emitted through the polarizer (4) in a linear polarization state, thereby forming a detection beam (1) in a linear polarization state; the feedback beam (2) is reflected through the first dichroic mirror (3), and then emitted through the polarizer (4) in a linear polarization state, thereby forming a feedback beam (2) in a linear polarization state. 4. The dual-wavelength orthogonal phase bias locking interferometry measurement method based on a geometric phase shifter according to claim 1, characterized in that: the object to be measured (8) is an object that can change the optical path difference of the detection light beam (1). 5. The dual-wavelength orthogonal phase bias locking interferometry measurement method based on geometric phase shifter according to claim 1 is characterized in that: the detection beam (1) is a wavelength of , and can be transmitted by the dichroic mirror; the feedback beam (2) refers to a light beam with a wavelength of and a light beam that can be reflected by a dichroic mirror; and a wavelength He Boru is about the central wavelength of the geometric phase shifter (7) The geometric phase shifter (7) is designed to be symmetrical so that the phase delays of the detection beam (1) and the feedback beam (2) after passing through the geometric phase shifter (7) are equal.