2-micron base order ultrafast laser polarization detection device and method based on Poincare sphere

Abstract

The invention discloses a 2-micron base-order ultrafast laser polarization detection device and method based on a Poincare sphere. The device comprises a polarization regulation and control module, a power detection module and a polarization analysis module, the polarization regulation and control module comprises a quarter-wave plate, an electric rotary displacement table and a polarization beam splitter; the power detection module comprises a power detector; the polarization analysis module comprises a data processor; and the data processor is respectively connected with the electric rotary displacement table and the power detector. The method comprises the following steps: placing the electric rotary displacement table and the quarter-wave plate on an x-o-y plane; enabling the x direction and the y direction of the input laser to generate # imgabs0 # phase difference; adjusting the polarization beam splitter to enable the polarization state of the laser penetrating along the optical axis to be only in the vertical direction; and calculating Stokes parameters and polarization state data, outputting and storing the calculated data, and meanwhile, displaying the laser polarization state data and polarization state images. According to the device and the method, efficient, accurate and rapid detection operation of the 2-micron wave band ultrafast laser polarization state can be realized.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular is a 2-micron fundamental-order ultrafast laser polarization detection device and method based on a Poincare sphere. Background Art

[0002] The detection of laser polarization characteristics is an important aspect in the research and application of laser technology, and has important scientific research and practical application significance. Traditional laser polarization detection methods often rely on complex optical components and long detection paths, which are difficult to meet the requirements of high precision and fast response.

[0003] In ultrafast laser technology, the duration of laser pulses is usually in picoseconds (10 -12 seconds) or femtoseconds (10 -15 Polarization detection of ultrafast lasers faces more challenges, because the time resolution of ultrafast laser pulses is extremely high, and traditional detection methods are difficult to achieve accurate measurement of such short pulses.

[0004] The Poincare sphere is a mathematical tool for describing the polarization state of light. Through the Poincare sphere, any polarization state of light can be represented as a point on the sphere. This representation method has the advantages of being intuitive and concise in analyzing and studying the polarization characteristics of light. The polarization detection method based on the Poincare sphere can more intuitively reflect the changes in the polarization state of the laser, providing a new way for efficient and accurate laser polarization detection.

[0005] Most traditional polarization detection methods require complex optical adjustment processes. For ultrafast lasers (especially femtosecond lasers), this adjustment process is not only time-consuming and labor-intensive, but also easily introduces additional phase noise, reducing the measurement resolution. In addition, most existing detection equipment is bulky and difficult to achieve portable and online monitoring, which limits its application in some specific scenarios (such as field environment monitoring, biomedical imaging, etc.).

[0006] Therefore, there is an urgent need to provide a 2-3 micron mid-infrared fundamental-order ultrafast laser polarization detection device based on the Poincare sphere to achieve efficient, accurate and rapid detection of the polarization state of ultrafast laser in the 2 micron band. Summary of the invention

[0007] In view of the problems existing in the above-mentioned prior art, the present invention provides a 2-micron fundamental-order ultrafast laser polarization detection device and method based on the Poincare sphere. The device has a simple and compact structure, is easy to operate and control, and has a low manufacturing cost. It can detect fundamental-order linear polarization, elliptically polarized and circularly polarized 2-micron ultrafast lasers based on the Poincare sphere, and can realize the detection of the polarization state of the 2-micron ultrafast laser; the method has a simple implementation process, and can quickly and efficiently detect linearly polarized, elliptically polarized and circularly polarized 2-micron ultrafast lasers.

[0008] In order to achieve the above-mentioned object, the present invention provides a 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere, comprising a polarization control module, a power detection module and a polarization analysis module;

[0009] The polarization control module includes a quarter wave plate, an electric rotation stage and a polarization beam splitter; the quarter wave plate is used to generate a quarter period phase difference in an orthogonal direction; the electric rotation stage is used to fix and support the quarter wave plate, and at the same time, to drive the quarter wave plate to rotate around the optical axis at a fixed angle; the polarization beam splitter is arranged on the outgoing light path of the quarter wave plate, and is used to limit the polarization state of the passing light, and only allows the light perpendicular to the beam splitting surface to pass;

[0010] The power detection module includes a power detector, which is connected to the polarization beam splitter and is used to dynamically detect the real-time data of the light intensity after each dynamic adjustment by the quarter-wave plate and the polarization beam splitter;

[0011] The polarization analysis module includes a data processor, which is connected to the electric rotation stage and the power detector respectively, and is used to control the electric rotation stage, thereby changing the angle between the fast axis of the quarter-wave plate and the positive direction of the x-axis to change the polarization state of the incident light. At the same time, the data processor is used to receive the state parameters of the electric rotation stage and the real-time data of the light intensity detected by the power detector, and analyze the polarization state of the input ultrafast laser based on the received data, calculate the Stokes parameter and the Poincare sphere, and complete the 2-micron ultrafast laser polarization detection.

[0012] Preferably, the quarter wave plate is a wave plate in a 2 micron band that can be used to adjust phase delay, and its transmittance between 1900 and 2150 nm is >97%, and its transmittance between 2700 and 2950 nm is >90%.

[0013] As a preference, the initial position of the fast axis of the quarter wave plate includes an angle of 0° with the x-axis, and each rotation around the optical axis is performed at a fixed angle of Δθ=22.5°.

[0014] Furthermore, in order to achieve precise adjustment of the rotation angle of the quarter-wave plate, the electric rotary displacement stage includes a transmission unit, a power unit and a feedback unit, the action force unit includes a worm gear transmission mechanism, whose transmission ratio is 1:30, the modulus is 1, and the lead angle is 20.12°, wherein the center of the worm wheel is a hollow structure and is provided with a limit groove, the quarter-wave plate is installed at the center of the turbine and is fixed in position by the limit groove, and a manually adjustable differential cylinder is provided at the end of the worm; the power unit includes a 42 two-phase four-wire stepper motor, and the output shaft of the 42 two-phase four-wire stepper motor is coaxially connected to the worm; the feedback unit includes a Hall sensor, and the Hall sensor is connected to the 42 two-phase four-wire stepper motor for real-time acquisition of the rotation angle information of the 42 two-phase four-wire stepper motor.

[0015] Preferably, the polarization beam splitter is a polarization beam splitter of 2 micron band, the angle between its beam splitting plane and xoz is 45°, and it can split the incident light into two polarized lights with mutually perpendicular polarization states, and make the polarized light perpendicular to the beam splitting plane be output along the z-axis; at the same time, the optical axis of the polarization beam splitter is collinear with the optical axis of the quarter wave plate.

[0016] As a preference, the power detector is a pyroelectric detector, which is used to detect ns-level ultrafast lasers and can realize full-band ultrafast laser power detection.

[0017] Preferably, the data processor is a computer.

[0018] As a preferred embodiment, the data processor includes a drive control unit, a data processing unit, a polarization state calculation unit, a display unit and a data storage unit;

[0019] The driving control unit is used to drive the electric rotary translation stage to perform an action according to the received adjustment action signal, so as to drive the quarter wave plate to rotate around the optical axis at a fixed angle;

[0020] The data processing unit is used to receive the state parameters of the electric rotary translation stage and the real-time data of the light intensity detected by the power detector, analyze and process the data to obtain the processed data, and then send the processed data to the polarization state calculation unit; at the same time, it is used to receive the Stokes parameters and the polarization state data, and send an adjustment action signal to the drive control unit according to the Stokes parameters and the polarization state data, and at the same time, it is used to obtain the polarization state image according to the Stokes parameters and the polarization state data, and send the polarization state data and the polarization state image to the display unit and the data storage unit;

[0021] The polarization state calculation unit is used to calculate the Stokes parameters and polarization state data of the laser based on the processed data and the Poincare sphere model, and send them to the data processing unit;

[0022] The display unit is used to display polarization state data and polarization state images;

[0023] The data storage unit is used to record and store polarization state data and polarization state images.

[0024] The present invention aims to utilize the advantages of the Poincare sphere and combine it with intelligent control technology to achieve efficient, accurate and rapid detection of the polarization state of ultrafast lasers in the 2-micron band. The use of this device can significantly improve the sensitivity and resolution of laser polarization detection, provide strong technical support for research and application in related fields, and achieve efficient, accurate and rapid measurement of the polarization state of 2-micron ultrafast lasers. The device can achieve multi-wavelength measurement by replacing quarter-wave plates and polarization beam splitters of different bands, and has a wide range of applications. The use of an electric rotary translation stage and a data processor for control can achieve automated measurement, reduce human operation errors, and significantly improve measurement efficiency. The data processor can automatically process data, quickly calculate the Stokes parameters and draw the Poincare sphere, which is convenient for users to analyze and understand the laser polarization state in real time.

[0025] The device has a simple and compact structure and is easy to operate and control. It can detect linearly polarized, elliptically polarized and circularly polarized 2-micron ultrafast lasers, and can detect the polarization state of 2-micron ultrafast lasers at a low cost.

[0026] The present invention also provides a 2-micron fundamental-order ultrafast laser polarization detection method based on the Poincare sphere, using a 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere, specifically comprising the following steps:

[0027] Step 1: Place the electric rotation stage on the xoy plane and install the quarter wave plate on the electric rotation stage. At the same time, keep the angle between the fast axis of the quarter wave plate and the positive direction of the x-axis at 0°;

[0028] Step 2: Make the input laser collinear with the optical axis of the quarter wave plate after free space or fiber coupling. At the same time, use the data processor to adjust the electric rotary stage through the python platform to make the fast axis of the quarter wave plate coincide with the x-axis at the beginning, and then rotate 22.5° every 0.2s until the fast axis of the quarter wave plate is 157.5° with the positive direction of the x-axis after seven rotations. Then, rotate in the opposite direction to make the fast axis of the quarter wave plate 0° with the positive direction of the x-axis.

[0029] Step 3: Adjust the angle of the polarization beam splitter in the xoy plane so that the main axis is parallel to the z axis and the angle between the beam splitting surface and the xoy plane is 45°, so that the polarization state of the laser transmitted along the optical axis is only in the horizontal direction;

[0030] Step 4: After obtaining the corresponding polarized beam, the data processor controls the power detector to collect laser power through the Python platform. At the same time, when the quarter-wave plate starts to rotate, data is collected every 22.5°. After collecting eight times, the Stokes parameters and polarization state data are calculated through the Python platform and the calculated data are output and stored. At the same time, the laser polarization state data and polarization state image are displayed;

[0031] The calculation process of Stokes parameters and polarization state data is as follows:

[0032] S41: combining the information collected by the power detector (4), using formula (1) to calculate ABCD by Fourier analysis method;

[0033]

[0034] S42: Solving all the Stokes parameters of the output laser according to formula (2);

[0035]

[0036] S43: Using the Python platform to draw the Poincare sphere representing the laser polarization state with mutually orthogonal S1, S2 and S3 as axes;

[0037] S44: Using formula (3), the polarization degree is calculated using the Python platform according to the Stokes parameter, the major axis of the ellipse is calculated using formula (4), the minor axis of the ellipse is calculated using formula (5), and the azimuth of the ellipse is calculated using formula (6).

[0038] and draw the polarization ellipse;

[0039]

[0040] ε=0.5*arctan(S1*S2) (6).

[0041] As a preferred embodiment, a data storage unit is integrated in the python platform, and the data storage unit is used to record and store polarization state data.

[0042] The present invention aims to provide a 2-micron ultrafast laser polarization detection method based on the Poincare sphere, which utilizes the birefringence effect of quartz crystal, photothermal detection technology and automatic control technology to quickly detect linearly polarized, elliptically polarized and circularly polarized 2-micron ultrafast lasers, and realizes the detection of the polarization state of the 2-micron ultrafast laser, and is simple to operate; compared with the prior art, it has the following advantages:

[0043] 1. Effectiveness of the method: It can directly detect the polarization state of 2-micron fundamental ultrafast laser, intuitively reflect the polarization state of laser, and take into account automatic control, and can realize automatic zero correction, data collection and polarization state analysis process;

[0044] 2. Low cost of the method: the device is simple, without additional polarization modulation devices, and easy to mass produce;

[0045] 3. Easy operation of the method: Users can use computers and Python software programming to control the electric translation stage, collect, process and store data, and display the polarization state and Poincare sphere. The operation is simple and intuitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a structural schematic diagram of the detection device in the present invention;

[0047] Figure 2 It is a schematic diagram of the process of the electric rotary translation stage driving the quarter wave plate to rotate in the present invention;

[0048] Figure 3 This is a schematic diagram of polarization characteristics of 2 micron 45° linear polarization measured by the present invention;

[0049] Wherein, (a) is a schematic diagram of the polarization ellipse of the light beam to be measured, and (b) is a schematic diagram of the polarization Poincare sphere of the light beam to be measured;

[0050] Figure 4 This is a schematic diagram of the polarization characteristics of 2 micron right-handed circularly polarized light measured by the present invention;

[0051] Wherein, (a) is a schematic diagram of the polarization ellipse of the light beam to be measured, and (b) is a schematic diagram of the polarization Poincare sphere of the light beam to be measured;

[0052] Figure 5 This is a schematic diagram of polarization characteristics of 2 micron circularly polarized light measured by the present invention;

[0053] Wherein, (a) is a schematic diagram of the polarization ellipse of the light beam to be measured, and (b) is a schematic diagram of the polarization Poincare sphere of the light beam to be measured;

[0054] Figure 6 The polarization characteristic diagram of 2 micron elliptically polarized light measured for the present invention;

[0055] Among them, (a) is the polarization ellipse diagram of the light beam to be measured, and (b) is the polarization Poincare sphere diagram of the light beam to be measured.

[0056] In the figure: 1. quarter wave plate, 2. electric rotation stage, 3. polarization beam splitter, 4. power detector, 5. data processor. DETAILED DESCRIPTION

[0057] like Figure 1As shown, the present invention provides a 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere, including a polarization control module, a power detection module and a polarization analysis module;

[0058] The polarization control module includes a quarter wave plate 1, an electric rotation stage 2 and a polarization beam splitter 3; the quarter wave plate 1 is used to generate a quarter period phase difference in an orthogonal direction; the electric rotation stage 2 is used to fix and support the quarter wave plate 1, and at the same time, to drive the quarter wave plate 1 to rotate around the optical axis at a fixed angle, and as a preferred embodiment, the fixed angle is 22.5°; as a preferred embodiment, the state parameters (rotation angle information) of the electric rotation stage 2 can be transmitted to the data processor 5 via a TTL serial port or Wifi;

[0059] The polarization beam splitter 3 is arranged on the outgoing light path of the quarter wave plate 1, and is used to limit the polarization state of the passing light, and only allows the light perpendicular to the beam splitting surface to pass, and the specific polarization state is vertical linear polarization;

[0060] The power detection module includes a power detector 4, which is connected to the polarization beam splitter 3 and is used to dynamically detect the real-time data of the light intensity after it passes through the quarter-wave plate 1 and the polarization beam splitter 3 each time after dynamic adjustment;

[0061] The polarization analysis module includes a data processor 5, which is connected to the electric rotation stage 2 and the power detector 4 respectively, and is used to control the electric rotation stage 2, thereby changing the angle between the fast axis of the quarter wave plate 1 and the positive direction of the x-axis to change the polarization state of the incident light. At the same time, it is used to receive the state parameters of the electric rotation stage 2 and the real-time data of the light intensity detected by the power detector 4, and analyze the polarization state of the input ultrafast laser based on the received data, calculate the Stokes parameter and the Poincare sphere, and complete the 2-micron ultrafast laser polarization detection. Preferably, the data processor 5 can control the electric rotation stage 2 and receive and process the data through a python platform.

[0062] As a preference, the quarter wave plate 1 is a wave plate in a 2 micron band that can be used to adjust phase delay, and its transmittance between 1900 and 2150 nm is >97%, and its transmittance between 2700 and 2950 nm is >90%.

[0063] As a preferred embodiment, Figure 2 As shown, the initial position of the fast axis of the quarter wave plate 1 is at an angle of 0° with the x-axis, and each rotation around the optical axis is at a fixed angle of Δθ=22.5°. At the same time, each rotation angle information can be transmitted to the data processor 5 in real time.

[0064] In order to achieve precise adjustment of the rotation angle of the quarter wave plate 1, the electric rotary displacement stage 2 includes a transmission unit, a power unit and a feedback unit. The action force unit includes a worm gear transmission mechanism, whose transmission ratio is 1:30, the modulus is 1, and the lead angle is 20.12°, wherein the center of the worm wheel is a hollow structure and a limit groove is provided. The quarter wave plate 1 is installed at the center of the turbine and fixed in position by the limit groove. The end of the worm is provided with a manually adjustable differential cylinder; the power unit includes a 42 two-phase four-wire stepper motor, and the output shaft of the 42 two-phase four-wire stepper motor is coaxially connected to the worm; the feedback unit includes a Hall sensor, and the Hall sensor is connected to the 42 two-phase four-wire stepper motor for real-time acquisition of the rotation angle information of the 42 two-phase four-wire stepper motor. As a preferred embodiment, the Hall sensor and the 42 two-phase four-wire stepper motor transmit the rotation angle data back through wifi, Bluetooth or TTL serial port, and the reporting frequency is 30Hz. As a further preference, the transmission unit and the power unit can be controlled by using a python platform built on the ESP32 development board, and at the same time, the information sent back by the feedback unit can be received.

[0065] As a preference, the polarization beam splitter 3 is a polarization beam splitter of 2 micron band, the angle between its beam splitting plane and xoz is 45°, which can split the incident light into two polarized lights with mutually perpendicular polarization states, and make the polarized light perpendicular to the beam splitting plane be output along the z-axis; at the same time, the optical axis of the polarization beam splitter 3 is collinear with the optical axis of the quarter wave plate 1.

[0066] As a preference, the power detector 4 is a pyroelectric detector, which is used to detect ns-level ultrafast lasers and can realize full-band ultrafast laser power detection. At the same time, the power data detected by the pyroelectric detector can be transmitted to the data processor 5 in real time.

[0067] As a preferred embodiment, the data processor 5 is a computer. In this way, the computer can realize the action of the electric rotary translation stage 2, as well as the data collection, processing and storage process through the Python platform, and at the same time, can display the polarization state and the Poincare sphere.

[0068] As a preferred embodiment, the data processor 5 includes a drive control unit, a data processing unit, a polarization state calculation unit, a display unit and a data storage unit;

[0069] The driving control unit is used to drive the electric rotary stage 2 to move according to the received adjustment action signal, so as to drive the quarter wave plate 1 to rotate around the optical axis at a fixed angle;

[0070] The data processing unit is used to receive the state parameters of the electric rotary translation stage 2 and the real-time data of the light intensity detected by the power detector 4, and analyze and process them to obtain processed data, and then send the processed data to the polarization state calculation unit; at the same time, it is used to receive Stokes parameters and polarization state data, and send an adjustment action signal to the drive control unit according to the Stokes parameters and polarization state data, and at the same time, it is used to obtain a polarization state image according to the Stokes parameters and polarization state data, and transmit the polarization state data and the polarization state image to the display unit and the data storage unit;

[0071] The polarization state calculation unit is used to calculate the Stokes parameters and polarization state data of the laser based on the processed data and the Poincare sphere model, and send them to the data processing unit;

[0072] The display unit is used to display polarization state data and polarization state images;

[0073] Preferably, the data storage unit is used to record and store polarization state data and polarization state images.

[0074] The present invention also provides a 2-micron fundamental-order ultrafast laser polarization detection method based on the Poincare sphere, using a 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere, specifically comprising the following steps:

[0075] Step 1: Place the electric rotation stage 2 on the xoy plane, and install the quarter wave plate 1 on the electric rotation stage 2. At the same time, keep the angle between the fast axis of the quarter wave plate 1 and the positive direction of the x-axis at 0°;

[0076] Step 2: Make the input laser collinear with the optical axis of the quarter wave plate 2 after free space or fiber coupling. At the same time, use the data processor 5 to adjust the electric rotary stage 2 through the python platform to drive the fast axis of the quarter wave plate 1 to coincide with the x-axis at the beginning, and then rotate 22.5° every 0.2s until after seven rotations, when the angle between the fast axis of the quarter wave plate 1 and the positive direction of the x-axis is 157.5°, and then rotate in the opposite direction so that the angle between the fast axis of the quarter wave plate 1 and the positive direction of the x-axis is 0°;

[0077] Among them, the python platform is built on the ESP32 development board to facilitate the control of the hollow rotary stage to step a fixed angle;

[0078] Step 3: Adjust the angle of the polarization beam splitter 3 in the xoy plane so that the main axis is parallel to the z axis and the angle between the beam splitting surface and the xoy plane is 45°, so that the polarization state of the laser transmitted along the optical axis is only in the horizontal direction;

[0079] Step 4: After obtaining the corresponding polarized light beam, the data processor 5 controls the power detector 4 through the Python platform to collect the laser power. At the same time, when the quarter wave plate 1 starts to rotate, data is collected every 22.5° rotation. After collecting eight times, the Stokes parameters and polarization state data are calculated through the Python platform and the calculated data are output and stored. At the same time, the laser polarization state data and polarization state image are displayed;

[0080] The calculation process of Stokes parameters and polarization state data is as follows:

[0081] S41: combining the information collected by the power detector (4), using formula (1) to calculate ABCD by Fourier analysis method;

[0082]

[0083] S42: Solving all the Stokes parameters of the output laser according to formula (2);

[0084]

[0085] S43: Using the Python platform to draw the Poincare sphere representing the laser polarization state with mutually orthogonal S1, S2 and S3 as axes;

[0086] S44: using formula (3), using the Python platform to calculate the degree of polarization according to the Stokes parameter, using formula (4) to calculate the major axis of the ellipse, using formula (5) to calculate the minor axis of the ellipse, using formula (6) to calculate the azimuth of the ellipse, and drawing the polarization ellipse;

[0087]

[0088]

[0089] ε=0.5*arctan(S1*S2) (6).

[0090] As a preferred embodiment, a data storage unit is integrated in the python platform, and the data storage unit is used to record and store polarization state data.

[0091] The present invention will be further described below in conjunction with embodiments:

[0092] Embodiment 1:

[0093] like Figure 1 As shown, the specific implementation process of the method of the present invention is as follows:

[0094] S1: Set the incident light. The incident light beam uses a 2-micron ultrafast laser with an arbitrary polarization direction. The light beam enters the 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere through free space coupling or multimode fiber coupling. In the experiment, 45° linear polarization, circular polarization and elliptically polarized light of the 2-micron thulium (Tm) system are selected for measurement and verification;

[0095] S2: Adjust the electric rotation stage 2 and the quarter wave plate 1. The electric rotation stage 2 drives the fixed quarter wave plate to rotate around its optical axis ( Figure 1 The optical beam is rotated along the z-axis in the optical stage 2 to make the optical beam pass through the quarter wave plate 1 vertically, and the center of the optical beam coincides with the center of the quarter wave plate 1. The initial angle of the fast axis of the quarter wave plate 1 is transmitted back to the data processor 5 through the Hall sensor, and the data processor 5 automatically adjusts the fast axis of the quarter wave plate 1 carried by the electric rotary stage 2 to the horizontal direction. The quarter wave plate 1 used in the experiment is suitable for the 2-micron band and is coated with a two-micron anti-reflection film.

[0096] S3: Adjust polarization beam splitter 3. Polarization beam splitter 3 uses a cubic PBS, the angle between its splitting surface and the xoy axis is 45°, and the distance between the optical axis and the z axis is no more than 2 mm, which is used to make the light passing through it be divided into two polarizations perpendicular to each other (P polarized light and S polarized light), and make the light beam with polarization direction parallel to the y axis continue to propagate along the z axis. The PBS selected in the experiment is a 2 micron band, which is consistent with the applicable band of the quarter wave plate 1.

[0097] S4: Regulate the power detector 4 to record the beam power. The probe of the power detector 4 is a pyroelectric detector, which is suitable for full-band laser power detection. The probe of the power detector 4 is made to coincide with the z-axis, and the light is vertically irradiated to the probe absorption array; the data of the power detector 4 is transmitted back to the data processor 5 through the data line for processing.

[0098] S5: Adjust the data processor 5 to control the electric rotation stage 2 to process and visualize the data. Use the python platform to control the electric rotation stage 2 to rotate 22.5° every 0.2s and collect data (such as Figure 2 As shown), after eight acquisitions, the data of the power detector are obtained (11.6, 14.0, 10.1, 6.0, 9.8, 14.5, 11.5, 7.5).

[0099] Furthermore, the data processor 5 uses the python platform in combination with the information collected by the power detector 4 to calculate ABCD by Fourier analysis method as follows: (21.25, -1.4071, -0.1, 7.5).

[0100] Furthermore, all the Stokes parameters of the laser can be solved After normalization, we get

[0101] Furthermore, the Poincare sphere representing the polarization state of the laser is drawn using the python platform with mutually orthogonal S1, S2 and S3 as axes.

[0102] Furthermore, the polarization degree is calculated using the Python platform according to the Stokes parameters: P = 0.706, and then the normalized ellipse major axis: a = 1, the ellipse minor axis: b = 0.001, and the ellipse azimuth: ε = 45.4° are calculated in turn, and the polarization ellipse and polarization Poincare sphere are plotted, as shown in Figure 6 shown.

[0103] Furthermore, the total polarization degree is 0.706, the linear polarization degree is 0.703, the circular polarization degree is 0.066, the light beam composition is 29.4% natural light + 70.6% left-handed elliptically polarized light (the angle between the major axis of the ellipse and the positive direction of the x-axis is 45.4 degrees), and the detection time is 0.334301 seconds.

[0104] Through the above embodiments combined Figures 3 to 6 It can be effectively proved that the present invention can measure the polarization state of 2 micron ultrafast laser efficiently, accurately and quickly. The device has a simple structure and is easy to operate and control. By replacing the quarter-wave plate and PBS, multi-wavelength measurement can be achieved, and the application range is wide. The use of an electric rotary translation stage and computer control can realize automated measurement, reduce human operation errors, and improve measurement efficiency. The computer automatically processes data through the python platform, and can quickly calculate the Stokes parameter and draw the Poincare sphere, which is convenient for users to analyze and understand the laser polarization state in real time.

[0105] Although the specific implementation methods of the present invention are described above, those skilled in the art should understand that these are merely examples, and that various changes or modifications may be made to these implementations (for example, replacing PBS with a polarizer or other polarizing optical element, replacing a pyroelectric detector with other types of power detectors, etc.) without departing from the principles and implementations of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.

Claims

1. A 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere, characterized in that: It includes a polarization control module, a power detection module and a polarization analysis module; The polarization control module comprises a quarter wave plate (1), an electric rotation displacement stage (2) and a polarization beam splitter (3); the quarter wave plate (1) is used to generate a quarter period phase difference in an orthogonal direction; the electric rotation displacement stage (2) is used to fix and support the quarter wave plate (1), and at the same time, is used to drive the quarter wave plate (1) to rotate around the optical axis at a fixed angle; the polarization beam splitter (3) is arranged on the output light path of the quarter wave plate (1), and is used to limit the polarization state of the passing light, and only allows the light perpendicular to the beam splitting surface to pass; The power detection module comprises a power detector (4), which is connected to the polarization beam splitter (3) and is used to dynamically detect real-time data of light intensity after being dynamically adjusted by the quarter-wave plate (1) and the polarization beam splitter (3) each time; The polarization analysis module comprises a data processor (5), which is connected to the electric rotary displacement stage (2) and the power detector (4) respectively, and is used to control the electric rotary displacement stage (2), thereby changing the angle between the fast axis of the quarter-wave plate (1) and the positive direction of the x-axis to change the polarization state of the incident light. At the same time, the data processor (5) is used to receive the state parameters of the electric rotary displacement stage (2) and the real-time data of the light intensity detected by the power detector (4), and analyze the polarization state of the input ultrafast laser based on the received data, deduce the Stokes parameter and the Poincare sphere, and complete the polarization detection of the 2-micron ultrafast laser.

2. The 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 1, characterized in that: The quarter wave plate (1) is a wave plate in the 2 micron band that can be used to adjust phase delay, and its transmittance between 1900 and 2150 nm is >97%, and its transmittance between 2700 and 2950 nm is >90%.

3. A 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 1 or 2, characterized in that: The initial position of the fast axis of the quarter wave plate (1) has an angle of 0° with the x-axis, and each rotation around the optical axis has a fixed angle of Δθ=22.5°.

4. The 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 3, characterized in that: The electric rotary displacement stage (2) comprises a transmission unit, a power unit and a feedback unit, wherein the action force unit comprises a worm gear transmission mechanism, wherein the transmission ratio is 1:30, the modulus is 1, and the lead angle is 20.12°, wherein the center of the worm wheel is a hollow structure and is provided with a limit groove, wherein the quarter wave plate (1) is installed at the center of the turbine and is fixed in position by the limit groove, and a manually adjustable differential cylinder is provided at the end of the worm; the power unit comprises a 42 two-phase four-wire stepping motor, wherein the output shaft of the 42 two-phase four-wire stepping motor is coaxially connected to the worm; and the feedback unit comprises a Hall sensor, wherein the Hall sensor is connected to the 42 two-phase four-wire stepping motor and is used for real-time acquisition of rotation angle information of the 42 two-phase four-wire stepping motor.

5. The 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 4, characterized in that: The polarization beam splitter (3) is a polarization beam splitter in the 2 micron band, and the angle between its beam splitting surface and xoz is 45°. It can split the incident light into two polarized lights with mutually perpendicular polarization states, and output the polarized light perpendicular to the beam splitting surface along the z axis; at the same time, the optical axis of the polarization beam splitter (3) is colinear with the optical axis of the quarter wave plate (1).

6. The 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 5, characterized in that: The power detector (4) is a pyroelectric detector, which is used to detect nanosecond-level ultrafast lasers and can detect ultrafast laser power in the entire wavelength band.

7. The 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 6, characterized in that: The data processor (5) is a computer.

8. The 2-micron fundamental-order ultrafast laser polarization detection device based on the Poincare sphere according to claim 7, characterized in that: The data processor (5) comprises a drive control unit, a data processing unit, a polarization state calculation unit, a display unit and a data storage unit; The driving control unit is used to drive the electric rotary displacement stage (2) to move according to the received adjustment action signal, so as to drive the quarter wave plate (1) to rotate around the optical axis at a fixed angle; The data processing unit is used to receive the state parameters of the electric rotary displacement stage (2) and the real-time data of the light intensity detected by the power detector (4), and to analyze and process the data to obtain processed data, and then send the processed data to the polarization state calculation unit; at the same time, it is used to receive Stokes parameters and polarization state data, and send an adjustment action signal to the drive control unit according to the Stokes parameters and polarization state data, and at the same time, it is used to obtain a polarization state image according to the Stokes parameters and polarization state data, and send the polarization state data and the polarization state image to the display unit and the data storage unit; The polarization state calculation unit is used to calculate the Stokes parameters and polarization state data of the laser based on the processed data and the Poincare sphere model, and send them to the data processing unit; The display unit is used to display polarization state data and polarization state images; The data storage unit is used to record and store polarization state data and polarization state images.

9. A 2-micron fundamental-order ultrafast laser polarization detection method based on Poincare sphere, using a 2-micron fundamental-order ultrafast laser polarization detection device based on Poincare sphere as claimed in any one of claims 1 to 8, characterized in that: The specific steps include: Step 1: Place the electric rotation stage (2) on the xoy plane, and install the quarter wave plate (1) on the electric rotation stage (2), while keeping the angle between the fast axis of the quarter wave plate (1) and the positive direction of the x-axis at 0°; Step 2: Make the input laser collinear with the optical axis of the quarter wave plate (2) after free space or fiber coupling. At the same time, use the data processor (5) to adjust the electric rotary stage (2) through the python platform to drive the fast axis of the quarter wave plate (1) to coincide with the x-axis at the beginning, and then rotate 22.5° every 0.2s until after seven rotations, when the angle between the fast axis of the quarter wave plate (1) and the positive direction of the x-axis is 157.5°, and then rotate in the opposite direction so that the angle between the fast axis of the quarter wave plate (1) and the positive direction of the x-axis is 0°; Step 3: Adjust the angle of the polarization beam splitter (3) in the xoy plane so that the main axis is parallel to the z axis and the angle between the beam splitting surface and the xoy plane is 45°, so that the polarization state of the laser transmitted along the optical axis is only in the horizontal direction; Step 4: After obtaining the corresponding polarized light beam, the data processor (5) controls the power detector (4) through the Python platform to collect laser power. At the same time, when the quarter wave plate (1) starts to rotate, data is collected every 22.5°. After collecting eight times, the Stokes parameters and polarization state data are calculated through the Python platform and the calculated data are output and stored. At the same time, the laser polarization state data and polarization state image are displayed; The calculation process of Stokes parameters and polarization state data is as follows: S41: combining the information collected by the power detector (4), using formula (1) to calculate ABCD by Fourier analysis method; S42: Solving all the Stokes parameters of the output laser according to formula (2); S43: Using the Python platform to draw the Poincare sphere representing the laser polarization state with mutually orthogonal S1, S2 and S3 as axes; S44: using formula (3), using the Python platform to calculate the degree of polarization according to the Stokes parameter, using formula (4) to calculate the major axis of the ellipse, using formula (5) to calculate the minor axis of the ellipse, using formula (6) to calculate the azimuth of the ellipse, and drawing the polarization ellipse; ε=0.5*arctan(S1*S2) (6).

10. The 2-micron fundamental-order ultrafast laser polarization detection method based on the Poincare sphere according to claim 9, characterized in that: The python platform is integrated with a data storage unit, which is used to record and store polarization state data.

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