CN115266039A - Device and method for measuring phase delay and fast axis azimuth angle - Google Patents
Device and method for measuring phase delay and fast axis azimuth angle Download PDFInfo
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Abstract
The application relates to a device and a method for measuring phase delay and a fast axis azimuth angle. The phase delay amount and fast axis azimuth angle measuring device comprises: a laser for outputting laser light; the collimating lens is used for collimating the laser output by the laser; the first half-wave plate is arranged on a laser light path of the laser; the attenuation sheet is arranged on a laser light path of the laser; the acousto-optic frequency shift unit is used for shifting the frequency of the light passing through the first half-wave plate and the attenuation plate; the second half-wave plate is arranged between the acousto-optic frequency shift unit and the sample to be detected; the reflector is used for reflecting the light passing through the sample to be detected to form reflected light, and enabling the reflected light to return to a laser cavity of the laser through the second half-wave plate, the acousto-optic frequency shift unit, the attenuation plate, the first half-wave plate and the collimating lens to generate self-mixing interference with the laser in the laser cavity; and the signal demodulation processor is used for demodulating the light after the mixed interference so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
Description
Technical Field
The present disclosure relates to the field of optical measurement technologies, and in particular, to a device and a method for measuring phase retardation and fast axis azimuth.
Background
Two important optical parameters of birefringent samples (samples with birefringent properties) are the amount of phase retardation and the fast axis azimuth. The birefringent sample needs to know the two parameters in many application scenarios, and therefore, it is particularly important to accurately measure the phase retardation and the fast axis azimuth angle.
The laser feedback phenomenon refers to a phenomenon that after output light of a laser is reflected or scattered by an external object, part of light is fed back into the laser to be mixed with light in a cavity, and then output change of the laser is caused. Laser feedback is widely concerned by scholars at home and abroad by virtue of the advantages of high sensitivity, auto-collimation, simple structure and the like. At present, two methods for measuring birefringence by laser feedback are known, namely a laser feedback polarization jump method and a laser feedback orthogonal light intensity modulation phase difference method. The two methods have the advantages of birefringence amplification, large measurement range, no need of knowing the main shaft direction of the element to be measured and the like. However, both methods require the sample to rotate in the outer cavity during measurement, which increases the complexity of measurement and measurement errors due to the non-uniform birefringence of the sample to be measured. And researches show that the output of the laser feedback system is not only influenced by the external cavity birefringence, but also influenced by the internal cavity birefringence and the nonlinearity of the piezoelectric ceramics. This shows that the two methods need to strictly control the birefringence of the laser cavity and also need to be calibrated to obtain a reliable measurement result. This means that the light source needs special processing before the system is built, and the system needs calibration after the system is built, which further increases the complexity of the system building.
Disclosure of Invention
In view of the above, there is a need to provide a phase delay amount and fast axis azimuth angle measuring apparatus and method for solving the problem of high complexity of the measuring system.
An embodiment of a first aspect of the present application provides a device for measuring a phase delay amount and a fast axis azimuth angle, including:
a laser for outputting laser light;
the collimating lens is used for collimating the laser output by the laser;
the first half-wave plate is arranged on a laser light path of the laser;
the attenuation sheet is arranged on a laser light path of the laser;
the acousto-optic frequency shift unit is used for shifting the frequency of the light passing through the first half wave plate and the attenuation plate;
the second half-wave plate is arranged between the acousto-optic frequency shift unit and the sample to be detected in a mode of rotating around the axis of the second half-wave plate;
the reflector is used for reflecting the light passing through the sample to be detected to form reflected light, and enabling the reflected light to pass through the second half-wave plate, the acousto-optic frequency shift unit, the attenuation plate, the first half-wave plate and the collimating lens to return to a laser cavity of the laser and generate self-mixing interference with the laser light in the laser cavity;
and the signal demodulation processor is used for demodulating the light after the mixed interference so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
In one embodiment, the signal demodulation processor comprises:
the photoelectric detector is used for detecting the optical signal of the light after the mixed interference and converting the optical signal into an electric signal;
and the signal processing unit is electrically connected with the photoelectric detector and is used for demodulating the electric signal so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
In one embodiment, the measuring apparatus further includes a beam splitter disposed on the laser light path of the laser, the beam splitter being configured to split the laser light output by the laser to form a second laser light path, and the photodetector is disposed on the second laser light path.
In one embodiment, the laser has an output end for emitting the laser light and a tail end far away from the output end, a detection hole communicated with the laser cavity is arranged at the tail end, and the photoelectric detector is arranged at the tail end and configured to detect an optical signal of the mixed and interfered light in the laser cavity through the detection hole.
In one embodiment, the acousto-optic audio unit comprises a first acousto-optic frequency shifter and a second acousto-optic frequency shifter, and the first acousto-optic frequency shifter and the second acousto-optic frequency shifter are sequentially arranged on a transmission light path of the attenuation sheet.
In one embodiment, the measuring apparatus further includes a rotating table, the second half-wave plate is disposed on the rotating table, the rotating table is configured to rotate the second half-wave plate, and a through hole for transmitting light is disposed on the rotating table.
Embodiments of the second aspect of the present application provide a method for measuring a phase delay amount and a fast axis azimuth angle, including:
outputting laser by a laser;
utilizing a collimating lens to collimate laser output by the laser;
enabling the collimated laser to enter an acousto-optic frequency shift unit for frequency shift after passing through a first half-wave plate and an attenuation plate;
the frequency-shifted light passes through a second half-wave plate which is arranged in a rotatable mode and then passes through a sample to be detected;
reflecting the light passing through the sample to be detected by using a reflector to form reflected light, returning the reflected light to a laser cavity of the laser through the second half-wave plate, the acousto-optic frequency shift unit, the attenuation plate, the first half-wave plate and the collimating lens, and performing self-mixing interference with the laser light in the laser cavity;
and demodulating the light after the mixed interference by using a signal demodulation processor so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
In one embodiment, the light intensity of the emitted light after mixed interference satisfies the following relation:
wherein Δ I represents a variation in intensity of laser light output from the laser, I s The output light intensity of the laser when the laser is stable is shown, G is a feedback gain coefficient and is related to relaxation oscillation frequency and frequency shift quantity of the laser, t is time, omega is the difference frequency shift quantity of an acousto-optic frequency shift unit, kappa is an external cavity equivalent reflection coefficient, R is an amplitude modulation coefficient,
expressing the phase modulation coefficient, phi the phase of the isotropic part of the external cavity, phi s Representing the fixed phase, theta the azimuth angle of the fast axis of the second half-wave plate, theta p Representing the azimuth angle of the fast axis of the sample to be detected, and delta representing the phase delay of the sample to be detected;
wherein, the first and the second end of the pipe are connected with each other,
and demodulating by the relational expression to obtain the phase delay amount and the fast axis azimuth angle.
In one embodiment, the phase delay amount and the fast axis azimuth angle are obtained through demodulation by a characteristic value method, and the specific process is as follows:
collecting the frequency shift amplitude signal I of the second half-wave plate rotating for one circle am (theta) and frequency-shifted phase signal I ph (θ)；
The phase delay amount is calculated by the following formula:
the fast axis azimuth is calculated by the following formula:
in one embodiment, the phase delay amount and the fast axis azimuth angle are obtained through fourier transform demodulation, and the specific process is as follows:
the rotation angular frequency of the second half-wave plate is X r/s, the modulation coefficient is satisfied as
Collecting frequency shift amplitude signal I of half-wave plate rotating for one circle am (t) sum frequency-shifted phase signal I ph (t) for the frequency-shifted amplitude signal I am (t) squaring and Fourier transforming to obtain amplitude spectrum signal F am (ω) to the frequency-shifted phase signal I ph (t) Fourier transform to obtain a phase spectrum signal F ph (ω)；
The phase delay amount is calculated by the following equation:
wherein the content of the first and second substances,
abs () is a function that extracts complex amplitudes;
the fast axis azimuth is calculated as follows:
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max And is and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min 、angle[F am (8X)]>0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min 、angle[F am (8X)]<0, and
when the temperature of the water is higher than the set temperature,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min And is and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max 、angle[F am (8X)]>0, and
when the temperature of the water is higher than the set temperature,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max 、angle[F am (8X)]<0, and
when the temperature of the water is higher than the set temperature,
wherein, tvalue min And tvalue max Respectively, the angle () is a function that extracts the complex phase angle.
The device and the method for measuring the phase retardation and the fast axis azimuth angle can be used for measuring the phase retardation and the fast axis azimuth angle of the birefringent sample. When the measuring device works, the laser outputs laser, the output laser is collimated by the collimating lens, passes through the first half-wave plate and the attenuation plate, and then enters the acousto-optic frequency shift unit for frequency shift. And the frequency-shifted light after frequency shift is reflected by the reflector after passing through the second half-wave plate and the sample to be detected to form reflected light. The reflected light returns to the laser cavity of the laser through the second half-wave plate, the acousto-optic frequency shift unit, the attenuator, the first half-wave plate and the collimating lens, and self-mixing interference is generated between the reflected light and laser in the laser cavity. And the signal demodulation processor demodulates the mixed and interfered light to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected. In the process, the collimating lens collimates the output laser, the first half wave plate is used for enabling the polarization direction of the laser to be parallel to any main shaft with single acousto-optic frequency shift so as to eliminate the birefringence characteristic of the acousto-optic frequency shift unit, and the attenuation sheet is used for attenuating the energy of the laser so as to enable the measuring device to be in a weak feedback level. The measuring device that this application embodiment provided, light path structure is simple relatively, and it is little to build the degree of difficulty to need not to carry out special treatment to the laser instrument, also need not to rotate the sample, consequently compare with the measurement system among the correlation technique, the measuring device's of this application embodiment complexity is lower. In addition, the measuring device also has the characteristic of double refraction amplification, and double refraction of the sample to be measured is amplified by adopting a reflection type structure, so that the phase delay amount and the fast axis azimuth angle of the sample can be accurately measured.
Drawings
FIG. 1 is a schematic structural diagram of a device for measuring phase retardation and fast axis azimuth in an embodiment of the present application;
fig. 2 is a schematic flow chart of a method for measuring a phase delay amount and a fast axis azimuth in the embodiment of the present application.
Description of reference numerals:
1-a laser; 2-a collimating lens; 3-a first half wave plate; 4-an attenuation sheet; 5-acousto-optic frequency shift unit; 51-a first acousto-optic frequency shifter; 52-a second acousto-optic frequency shifter; 6-a second half-wave plate; 7-a mirror; 8-a signal demodulation processor; 81-a photodetector; 82-a signal processing unit; 9-a rotating table; 10-a sample to be tested; 11-spectroscope.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, embodiments accompanying the present application are described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. This application is capable of embodiments in many different forms than those described herein and that modifications may be made by one skilled in the art without departing from the spirit and scope of the application and it is therefore not intended to be limited to the specific embodiments disclosed below.
In the description of the present application, it is to be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present application and for simplicity in description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the present application.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless explicitly specified otherwise.
In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and encompass, for example, both fixed and removable connections or integral parts thereof; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be interconnected within two elements or in a relationship where two elements interact with each other unless otherwise specifically limited. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as the case may be.
In this application, unless expressly stated or limited otherwise, a first feature is "on" or "under" a second feature such that the first and second features are in direct contact, or the first and second features are in indirect contact via an intermediary. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature "under," "beneath," and "under" a second feature may be directly under or obliquely under the second feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like as used herein are for illustrative purposes only and do not denote a unique embodiment.
As shown in fig. 1, the embodiment of the first aspect of the present application proposes a phase delay amount and fast axis azimuth angle measurement apparatus. Specifically, the measuring device comprises a laser 1, a collimating lens 2, a first half-wave plate 3, an attenuation plate 4, an acousto-optic frequency shift unit 5, a second half-wave plate 6, a reflecting mirror 7 and a signal demodulation processor 8. The laser device 1 is used for outputting laser, the collimating lens 2 is used for collimating the laser output by the laser device 1, the first half-wave plate 3 is arranged on a laser light path of the laser device 1, the attenuation plate 4 is arranged on the laser light path of the laser device 1, and the acousto-optic frequency shift unit 5 is used for shifting the frequency of the light passing through the first half-wave plate 3 and the attenuation plate 4. The second half-wave plate 6 is arranged between the acousto-optic frequency shift unit 5 and the sample 10 to be measured in a manner of rotating around the axis of the second half-wave plate. The reflector 7 is used for reflecting the light passing through the sample 10 to be detected to form reflected light, and the reflected light returns to the laser cavity of the laser 1 through the second half-wave plate 6, the acousto-optic frequency shift unit 5, the attenuation plate 4, the first half-wave plate 3 and the collimating lens 2 to generate self-mixing interference with the laser in the laser cavity. The signal demodulation processor 8 is configured to demodulate the mixed and interfered light to detect the phase retardation and the fast axis azimuth of the sample 10 to be detected.
The device for measuring the phase retardation and the fast axis azimuth angle can be used for measuring the phase retardation and the fast axis azimuth angle of the birefringent sample. When the measuring device works, the laser 1 outputs laser, the output laser is collimated by the collimating lens 2, passes through the first half-wave plate 3 and the attenuation plate 4, and then enters the acousto-optic frequency shift unit 5 for frequency shift. The frequency-shifted light after frequency shift is reflected by a reflecting mirror 7 after passing through a second half-wave plate 6 and a sample 10 to be measured to form reflected light. The reflected light returns to the laser cavity of the laser 1 through the second half-wave plate 6, the acousto-optic frequency shift unit 5, the attenuation plate 4, the first half-wave plate 3 and the collimating lens 2, and self-mixing interference is generated between the reflected light and laser in the laser cavity. The signal demodulation processor 8 demodulates the mixed and interfered light to detect the phase delay amount and the fast axis azimuth angle of the sample 10 to be detected. In the process, the collimating lens 2 collimates the output laser, the first half wave plate 3 is used for enabling the polarization direction of the laser to be parallel to any main shaft with single acousto-optic frequency shift so as to eliminate the birefringence characteristic of the acousto-optic frequency shift unit 5, and the attenuation sheet 4 is used for attenuating the energy of the laser and enabling the measuring device to be in a weak feedback level.
The measuring device that this application embodiment provided, light path structure is simple relatively, and it is little to build the degree of difficulty to need not to carry out special treatment to laser instrument 1, also need not to rotate the sample, consequently compare with the measurement system among the correlation technique, the measuring device's of this application embodiment complexity is lower. In addition, the measuring device also has the characteristic of double refraction amplification, and the double refraction of the sample 10 to be measured is amplified by two times by adopting a reflection type structure, so that the phase delay amount and the fast axis azimuth angle of the sample can be accurately measured.
Further, the attenuation plate 4 may be disposed on a side of the first half-wave plate 3 away from the collimator lens 2, or may be disposed between the first half-wave plate 3 and the collimator lens 2. When the attenuation plate 4 is arranged on one side of the first half-wave plate 3 far away from the collimating lens 2, the collimated laser firstly passes through the first half-wave plate 3 and then passes through the attenuation plate 4. When the attenuation plate 4 is arranged between the first half-wave plate 3 and the collimating lens 2, the collimated laser firstly passes through the attenuation plate 4 and then passes through the first half-wave plate 3. Further, the laser light output by the laser 1 may be linearly polarized light, and the mode is a fundamental transverse mode and a single longitudinal mode. The laser 1 may be a solid-state laser 1, a fiber laser 1, or a semiconductor laser 1. The solid-state laser 1 is a laser 1 using a solid-state laser material as a working substance. The semiconductor laser 1 is also called a laser diode, and is a laser 1 using a semiconductor material as a working substance. The Fiber Laser 1 (Fiber Laser) is a Laser 1 which is formed by taking an optical Fiber as a base, taking a doped optical Fiber doped with various rare earth element ions as a working substance and utilizing the nonlinear self-phase modulation effect of the optical Fiber.
In one embodiment, the signal demodulation processor 8 includes a photodetector 81 and a signal processing unit 82. The photodetector 81 is configured to detect an optical signal of the light after the mixed interference, and convert the optical signal into an electrical signal, and the signal processing unit 82 is electrically connected to the photodetector 81 and configured to demodulate the electrical signal to detect a phase delay amount and a fast axis azimuth of the sample 10 to be detected.
In one embodiment, the measuring apparatus further includes a beam splitter 11, the beam splitter 11 is disposed on the laser light path of the laser 1, the beam splitter 11 is configured to split the laser light output by the laser 1 to form a second laser light path, and the photodetector 81 is disposed on the second laser light path. With such an arrangement, the mixed and interfered light can reach the photodetector 81 under the light splitting effect of the spectroscope 11, so that the photodetector 81 can detect the optical signal of the mixed and interfered light.
Specifically, the beam splitter 11 may be disposed between the collimating lens 2 and the first half-wave plate 3 or the attenuation plate 4, or may be disposed between the first half-wave plate 3 and the attenuation plate 4. In the former case, the collimated laser light passes through the beam splitter 11, the first half-wave plate 3 and the attenuation plate 4. In the latter case, the collimated laser light first passes through one of the first half-wave plate 3 and the attenuation plate 4 (which passes through the collimating lens 2 first), then passes through the beam splitter 11, and then passes through the other of the first half-wave plate 3 and the attenuation plate 4.
In another embodiment, the laser 1 has an output end for emitting laser light and a tail end away from the output end, a detection hole is disposed at the tail end and communicated with the laser cavity, and the photodetector 81 is disposed at the tail end, and the photodetector 81 is configured to detect an optical signal of the mixed and interfered light in the laser cavity through the detection hole.
In one embodiment, the acousto-optic audio unit includes a first acousto-optic frequency shifter 51 and a second acousto-optic frequency shifter 52, and the first acousto-optic frequency shifter 51 and the second acousto-optic frequency shifter 52 are sequentially disposed on the transmission light path of the attenuator 4, and are used for performing differential frequency shift on the attenuated laser. When laser is diffracted by the ultrasonic grating through the acousto-optic medium, the propagation direction and the frequency of the laser are changed. The frequency of the diffracted light superimposes an ultrasonic frequency on the original input laser frequency, which is the acousto-optic shift frequency. The amount of change in the optical frequency is equal to the frequency of the applied rf power signal. When the output light is differential diffraction light (including two conditions, 1, the first acousto-optic frequency shifter 51 takes the positive pole, and the second acousto-optic frequency shifter 52 takes the negative first order, and 2, the first acousto-optic frequency shifter 51 takes the negative first pole, and the second acousto-optic frequency shifter 52 takes the positive first order), the frequency of the output light is the frequency of the original laser frequency power-up signal. By changing the frequency of the input electrical signal, the amount of frequency shift of the output light can be controlled. Since the acousto-optic frequency shifter requires the output light power as high as possible in practical use, the acousto-optic frequency shifter generally operates in a bragg diffraction mode.
In one embodiment, the measuring apparatus further includes a rotating platform 9, the second half-wave plate 6 is disposed on the rotating platform 9, the rotating platform 9 is used for driving the second half-wave plate 6 to rotate, and a through hole for transmitting light is disposed on the rotating platform 9. When the signal demodulation processor 8 performs demodulation, it is necessary to use a frequency shift amplitude signal and a frequency shift phase signal for one rotation of the second half-wave plate 6, and therefore the turntable 9 is provided and the second half-wave plate 6 is provided on the turntable 9. So that the second half-wave plate 6 is driven to rotate by one circle through the rotating platform 9, thereby acquiring signals required by demodulation.
As shown in fig. 2, an embodiment of the first aspect of the present application provides a method for measuring a phase delay amount and a fast axis azimuth angle, including:
s10: outputting laser by using a laser 1;
s20: utilizing a collimating lens 2 to collimate the laser output by the laser 1;
s30: after passing through the first half-wave plate 3 and the attenuation plate 4, the collimated laser enters the acousto-optic frequency shift unit 5 for frequency shift;
s40: the frequency-shifted light passes through a second half-wave plate 6 which is arranged in a rotatable mode and then passes through a sample 10 to be measured;
s50: the light passing through the sample 10 to be detected is reflected by the reflector 7 to form reflected light, and the reflected light returns to the laser cavity of the laser 1 through the second half-wave plate 6, the acousto-optic frequency shift unit 5, the attenuation plate 4, the first half-wave plate 3 and the collimating lens 2 to generate self-mixing interference with the laser in the laser cavity;
s60: the mixed and interfered light is demodulated by the signal demodulation processor 8 to detect the phase delay amount and the fast axis azimuth angle of the sample 10 to be detected.
The method for measuring the phase retardation and the fast axis azimuth angle can be used for measuring the phase retardation and the fast axis azimuth angle of a birefringent sample. In the implementation process of the method, the laser 1 outputs laser, the output laser is collimated by the collimating lens 2, passes through the first half-wave plate 3 and the attenuation plate 4, and then enters the acousto-optic frequency shift unit 5 for frequency shift. The frequency-shifted light after frequency shift is reflected by a reflecting mirror 7 after passing through a second half-wave plate 6 and a sample 10 to be measured to form reflected light. The reflected light returns to the laser cavity of the laser 1 through the second half-wave plate 6, the acousto-optic frequency shift unit 5, the attenuation plate 4, the first half-wave plate 3 and the collimating lens 2, and self-mixing interference is generated between the reflected light and laser in the laser cavity. The signal demodulation processor 8 demodulates the mixed and interfered light to detect the phase delay amount and the fast axis azimuth of the sample 10 to be detected. In the process, the collimating lens 2 collimates the output laser, the first half-wave plate 3 is used for enabling the polarization direction of the laser to be parallel to any main shaft with single acousto-optic frequency shift so as to eliminate the birefringence characteristic of the acousto-optic frequency shift unit 5, and the attenuation sheet 4 is used for attenuating the energy of the laser so as to enable the measuring device to be in a weak feedback level.
According to the measuring method provided by the embodiment of the application, the constructed light path structure is relatively simple, the construction difficulty is small, special treatment on the laser 1 is not needed, and a sample does not need to be rotated, so that the complexity of the constructed measuring system is low.
In one embodiment, the intensity of the emergent light of the mixed and interfered light satisfies the following relation:
wherein Δ I represents a light intensity variation value of the laser light output from the laser 1, I s The output light intensity when the laser 1 is stable is shown, G is a feedback gain coefficient and is related to relaxation oscillation frequency and frequency shift quantity of the laser 1, t is time, omega is differential frequency shift quantity of the acousto-optic frequency shift unit 5, kappa is an external cavity equivalent reflection coefficient, R is an amplitude modulation coefficient,
expressing the phase modulation coefficient, phi the phase of the isotropic part of the external cavity, phi s Representing the fixed phase, theta the azimuth of the fast axis of the second half-wave plate 6, theta p Indicating the azimuth angle of the fast axis of the sample 10 to be detected, and delta indicating the phase delay of the sample 10 to be detected;
wherein, the first and the second end of the pipe are connected with each other,
and demodulating by the relational expression to obtain the phase delay amount and the fast axis azimuth angle.
In a specific embodiment, the phase delay amount and the fast axis azimuth angle are obtained by demodulation through a characteristic value method, and the process is as follows:
collecting a frequency shift amplitude signal I of the second half-wave plate 6 rotating for one circle am (theta) and frequency-shifted phase signal I ph (θ)；
The phase delay amount is calculated by the following formula:
the fast axis azimuth is calculated by the following formula:
in another specific embodiment, the phase delay and the fast axis azimuth are obtained by fourier transform demodulation, as follows:
the second half-wave plate 6 has a rotation angular frequency of X r/s, and the modulation factor is satisfied as
Collecting frequency shift amplitude signal I of half-wave plate rotating for one circle am (t) sum frequency-shifted phase signal I ph (t) for the frequency-shifted amplitude signal I am (t) squaring and Fourier transforming to obtain amplitude spectrum signal F am (omega) for the frequency-shifted phase signal I ph (t) Fourier transform to obtain a phase spectrum signal F ph (ω)；
The phase delay amount is calculated by the following equation:
wherein, the first and the second end of the pipe are connected with each other,
abs () is a function that extracts complex amplitudes;
the fast axis azimuth is calculated as follows:
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max And is made of
When the temperature of the water is higher than the set temperature,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min 、angle[F am (8X)]>0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min 、angle[F am (8X)]<0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min And is made of
When the temperature of the water is higher than the set temperature,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max 、angle[F am (8X)]>0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max 、angle[F am (8X)]<0, and
when the utility model is used, the water is discharged,
wherein, tvalue min And tvalue max Respectively, the angle () is a function that extracts the complex phase angle.
All possible combinations of the technical features in the above embodiments may not be described for the sake of brevity, but should be considered as being within the scope of the present disclosure as long as there is no contradiction between the combinations of the technical features.
The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the claims. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.
Claims (10)
1. A phase delay amount and fast axis azimuth angle measuring apparatus, comprising:
a laser for outputting laser light;
the collimating lens is used for collimating the laser output by the laser;
the first half-wave plate is arranged on a laser light path of the laser;
the attenuation sheet is arranged on a laser light path of the laser;
the acousto-optic frequency shift unit is used for shifting the frequency of the light passing through the first half wave plate and the attenuation plate;
the second half-wave plate is arranged between the acousto-optic frequency shift unit and the sample to be detected in a mode of rotating around the axis of the second half-wave plate;
the reflector is used for reflecting the light passing through the sample to be detected to form reflected light, and enabling the reflected light to pass through the second half-wave plate, the acousto-optic frequency shift unit, the attenuation plate, the first half-wave plate and the collimating lens to return to a laser cavity of the laser and generate self-mixing interference with the laser light in the laser cavity;
and the signal demodulation processor is used for demodulating the light after the mixed interference so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
2. The apparatus for measuring phase delay and fast axis azimuth according to claim 1, wherein the signal demodulation processor comprises:
the photoelectric detector is used for detecting the optical signal of the light after the mixed interference and converting the optical signal into an electric signal;
and the signal processing unit is electrically connected with the photoelectric detector and is used for demodulating the electric signal so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
3. The apparatus of claim 2, further comprising a beam splitter disposed on the laser path of the laser, the beam splitter configured to split the laser output from the laser to form a second laser path, and the photodetector disposed on the second laser path.
4. The apparatus of claim 2, wherein the laser has an output end for emitting the laser light and a tail end away from the output end, a detection hole is disposed at the tail end and is in communication with the laser cavity, and the photodetector is disposed at the tail end and is configured to detect an optical signal of the mixed and interfered light in the laser cavity through the detection hole.
5. The apparatus of claim 1, wherein the acousto-optic audio unit comprises a first acousto-optic frequency shifter and a second acousto-optic frequency shifter, and the first acousto-optic frequency shifter and the second acousto-optic frequency shifter are sequentially disposed on a transmission light path of the attenuator plate.
6. The apparatus for measuring phase retardation and fast axis azimuth angle according to claim 1, further comprising a rotating stage, wherein the second half-wave plate is disposed on the rotating stage, the rotating stage is configured to rotate the second half-wave plate, and a through hole is disposed on the rotating stage for transmitting light.
7. A method for measuring phase delay and fast axis azimuth angle, comprising:
outputting laser by a laser;
utilizing a collimating lens to collimate laser output by the laser;
enabling the collimated laser to enter an acousto-optic frequency shift unit for frequency shift after passing through a first half-wave plate and an attenuation plate;
the frequency-shifted light passes through a second half-wave plate which is arranged in a rotatable mode and then passes through a sample to be detected;
reflecting the light passing through the sample to be detected by using a reflector to form reflected light, returning the reflected light to a laser cavity of the laser through the second half-wave plate, the acousto-optic frequency shift unit, the attenuation plate, the first half-wave plate and the collimating lens, and performing self-mixing interference with the laser light in the laser cavity;
and demodulating the light after the mixed interference by using a signal demodulation processor so as to detect the phase delay amount and the fast axis azimuth angle of the sample to be detected.
8. The method of claim 7, wherein the intensity of the emitted light after the mixed interference satisfies the following relation:
wherein Δ I represents a variation in intensity of laser light output from the laser, I s The output light intensity of the laser when the laser is stable is shown, G is a feedback gain coefficient and is related to relaxation oscillation frequency and frequency shift quantity of the laser, t is time, omega is the differential frequency shift quantity of an acousto-optic frequency shift unit, kappa is an external cavity equivalent reflection coefficient, R is an amplitude modulation coefficient,
denotes the phase modulation coefficient, phi denotes the phase of the isotropic part of the external cavity, and phi s Representing the fixed phase, theta representing the azimuth angle of the fast axis of the second half-wave plate, theta p Representing the azimuth angle of the fast axis of the sample to be detected, and delta representing the phase delay of the sample to be detected;
wherein the content of the first and second substances,
and demodulating by the relational expression to obtain the phase delay amount and the fast axis azimuth angle.
9. The method for measuring phase retardation and fast axis azimuth according to claim 8, wherein the phase retardation and the fast axis azimuth are obtained by demodulation using a eigenvalue method, and the specific process is as follows:
collecting a frequency shift amplitude signal I of the second half-wave plate rotating for one circle am (theta) and frequency-shifted phase signal I ph (θ)；
The phase delay amount is calculated by the following formula:
the fast axis azimuth is calculated by the following formula:
10. the method for measuring the phase delay and the fast axis azimuth angle according to claim 8, wherein the phase delay and the fast axis azimuth angle are obtained by demodulation through a fourier transform method, which comprises the following steps:
the second half-wave plate has a rotation angular frequency of X r/s, and the modulation factor is satisfied as
Collecting frequency shift amplitude signal I of half-wave plate rotating for one circle am (t) and frequency-shifted phase signal I ph (t) for the frequency-shifted amplitude signal I am (t) squaring and Fourier transforming to obtain amplitude spectrum signal F am (omega) for the frequency-shifted phase signal I ph (t) Fourier transform to obtain a phase spectrum signal F ph (ω)；
The phase delay amount is calculated by the following equation:
wherein the content of the first and second substances,
abs () is a function that extracts complex amplitudes;
the fast axis azimuth is calculated as follows:
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max And is and
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min 、angle[F am (8X)]>0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min 、angle[F am (8X)]<0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|<tvalue min And is and
when the temperature of the water is higher than the set temperature,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max 、angle[F am (8X)]>0, and
when the utility model is used, the water is discharged,
when | angle [ F am (8X)]-2·angle[F ph (4X)]|>tvalue max 、angle[F am (8X)]<0, and
when the temperature of the water is higher than the set temperature,
wherein, tvalue min And tvalue max Respectively, the angle () is a function that extracts the complex phase angle.
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