A 2-micron fundamental-order ultrafast laser polarization detection device and method based on a Poincaré sphere

Abstract

A polarization detection device and method for 2-micron fundamental-order ultrafast lasers based on a Poincaré sphere are disclosed. The device includes a polarization control module, a power detection module, and a polarization analysis module. The polarization control module comprises a quarter-wave plate, an electrically driven rotary stage, and a polarization beam splitter. The power detection module includes a power detector. The polarization analysis module includes a data processor, which is connected to both the electrically driven rotary stage and the power detector. The method involves placing the electrically driven rotary stage and the quarter-wave plate in the x-o-y plane; adjusting the phase difference between the x and y directions of the input laser; adjusting the polarization beam splitter to ensure that the polarization state of the laser transmitted along the optical axis is only in the vertical direction; calculating Stokes parameters and polarization state data, outputting and storing the calculated data, and simultaneously displaying the laser polarization state data and polarization state image. This device and method enable efficient, accurate, and rapid detection of the polarization state of 2-micron ultrafast lasers.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically a 2-micron fundamental-order ultrafast laser polarization detection device and method based on a Poincaré sphere. Background Technology

[0002] The detection of laser polarization characteristics is an important aspect of laser technology research and application, with significant scientific research and practical implications. Traditional laser polarization detection methods often rely on complex optical components and long detection paths, making it difficult to meet the demands for high precision and rapid response.

[0003] In ultrafast laser technology, the duration of the laser pulse is typically in the picosecond range (10^6). -12 (seconds) or femtoseconds (10) -15 The polarization detection of ultrafast lasers faces even greater challenges because the time resolution requirements of ultrafast laser pulses are extremely high, and traditional detection methods struggle to achieve accurate measurements of such short pulses.

[0004] A Poincaré sphere is a mathematical tool for describing the polarization state of light. Using a Poincaré sphere, any polarization state of light can be represented as a point on the sphere's surface. This representation is intuitive and concise in analyzing and studying the polarization characteristics of light. Polarization detection methods based on Poincaré spheres can more intuitively reflect changes in the polarization state of lasers, providing a new approach for efficient and accurate laser polarization detection.

[0005] Traditional polarization detection methods mostly 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 measurement resolution. In addition, most existing detection devices are bulky, making it difficult to achieve portable and online monitoring, which limits their application in certain specific scenarios (such as field environmental monitoring and biomedical imaging).

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

[0007] To address the problems existing in the prior art, this invention provides a 2-micron fundamental-order ultrafast laser polarization detection device and method based on a Poincaré sphere. The device has a simple and compact structure, is easy to operate and control, and has low manufacturing cost. It can detect 2-micron ultrafast lasers with fundamental-order linear polarization, elliptic polarization, and circular polarization based on a Poincaré sphere, and can realize the detection of the polarization state of 2-micron ultrafast lasers. The method is simple to implement and can quickly and efficiently detect 2-micron ultrafast lasers with linear polarization, elliptic polarization, and circular polarization.

[0008] To achieve the above objectives, the present invention provides a 2-micron fundamental-order ultrafast laser polarization detection device based on a Poincaré 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 electrically driven rotary displacement stage, and a polarization beam splitter. The quarter-wave plate is used to generate a quarter-cycle phase difference in the orthogonal direction. The electrically driven rotary displacement stage is used to fix and support the quarter-wave plate, and at the same time, it is used to drive the quarter-wave plate to rotate around the optical axis at a fixed angle. The polarization beam splitter is set in the output light path of the quarter-wave plate to limit the polarization state of the transmitted light, allowing only light with polarization perpendicular to the beam splitting plane to pass through.

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

[0011] The polarization analysis module includes a data processor connected to an electric rotary stage and a power detector. The data processor controls the electric rotary stage to change the angle between the fast axis of the quarter-wave plate and the positive x-axis, thereby changing the polarization state of the incident light. Simultaneously, it receives the state parameters of the electric rotary stage and the real-time light intensity data detected by the power detector. Based on the received data, it analyzes the polarization state of the input ultrafast laser, calculates the Stokes parameter and the Poincaré sphere, and completes the polarization detection of the 2-micron ultrafast laser.

[0012] As a preferred embodiment, the quarter-wave plate is a 2-micron band waveplate that can be used to adjust the phase delay, with a transmittance of >97% between 1900 and 2150 nm and a transmittance of >90% between 2700 and 2950 nm.

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

[0014] Furthermore, to achieve precise adjustment of the quarter-wave plate's rotation angle, the electric rotary displacement stage includes a transmission unit, a power unit, and a feedback unit. The power unit includes a worm gear transmission mechanism with a transmission ratio of 1:30, a module of 1, and a lead angle of 20.12°. The worm gear has a hollow center with a limiting groove. The quarter-wave plate is mounted at the center of the worm gear and its position is fixed by the limiting groove. The end of the worm gear has a manually adjustable differential cylinder. The power unit includes a 42-phase four-wire stepper motor, the output shaft of which is coaxially connected to the worm gear. The feedback unit includes a Hall sensor connected to the 42-phase four-wire stepper motor to collect the rotation angle information of the motor in real time.

[0015] As a preferred embodiment, the polarization beam splitter is a 2-micron band polarization beam splitter with a beam splitting surface at an angle of 45° to xoz, which can split the incident light into two beams of polarized light with mutually perpendicular polarization states, and make the polarized light perpendicular to the beam splitting surface 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 preferred embodiment, the power detector is a thermoelectric detector, used to detect nanosecond-level ultrafast lasers and to achieve ultrafast laser power detection across the entire wavelength range.

[0017] As a preferred embodiment, 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 drive control unit is used to drive the electric rotary displacement stage to perform actions 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 displacement stage and the real-time light intensity data detected by the power detector, 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 adjustment action signals 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 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 Poincaré sphere model, and then 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] This invention aims to leverage the advantages of the Poincaré 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. This device significantly improves the sensitivity and resolution of laser polarization detection, providing strong technical support for research and applications in related fields, and enabling efficient, accurate, and rapid measurement of the polarization state of 2-micron ultrafast lasers. By changing the quarter-wave plate and polarization beam splitter for different wavelengths, the device can achieve multi-wavelength measurements, making it widely applicable. The use of an electric rotary displacement stage and a data processor for control enables automated measurement, reducing human error and significantly improving measurement efficiency. The data processor can automatically process data, quickly calculate Stokes parameters, and plot the Poincaré sphere, facilitating real-time analysis and understanding of the laser polarization state.

[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 achieve the detection of the polarization state of 2-micron ultrafast lasers at a low cost.

[0026] This invention also provides a 2-micron fundamental-order ultrafast laser polarization detection method based on a Poincaré sphere, employing a 2-micron fundamental-order ultrafast laser polarization detection device based on a Poincaré sphere, specifically including the following steps:

[0027] Step 1: Place an electric rotary displacement stage on the xoy plane and mount a quarter-wave plate on the electric rotary displacement stage, while keeping the angle between the fast axis of the quarter-wave plate and the positive x-axis at 0°.

[0028] Step 2: After the input laser passes through free space or is coupled with an optical fiber, it is aligned with the optical axis of the quarter-wave plate. At the same time, the data processor is used to adjust the electric rotary displacement stage through the Python platform to drive the fast axis of the quarter-wave plate to coincide with the x-axis initially. Then, it rotates 22.5° every 0.2s until it rotates seven times. When the angle between the fast axis of the quarter-wave plate and the positive x-axis is 157.5°, it is rotated in the opposite direction to make the angle between the fast axis of the quarter-wave plate and the positive x-axis 0°.

[0029] Step 3: Adjust the angle of the polarization beam splitter in the xoy plane so that the principal 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 the 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 every eight collections, the Stokes parameters and polarization state data are calculated through the Python platform, and the calculated data is output and stored. At the same time, the laser polarization state data and polarization state image are displayed.

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

[0032] S41: Combining the information collected by the power detector (4), ABCD is calculated using the Fourier analysis method through formula (1);

[0033]

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

[0035]

[0036] S43: Using the mutually orthogonal axes S1, S2 and S3, draw a Poincaré sphere representing the laser polarization state through the Python platform;

[0037] S44: Using formula (3), the degree of polarization is calculated using the Python platform based on the Stokes parameters. The major axis of the ellipse is calculated using formula (4). The minor axis of the ellipse is calculated using formula (5). The azimuth angle 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, the Python platform integrates a data storage unit for recording and storing polarization state data.

[0042] This invention aims to provide a method for detecting the polarization of 2-micron ultrafast lasers based on a Poincaré sphere. Utilizing the birefringence effect of quartz crystals, photothermal detection technology, and automated control technology, it can rapidly detect linearly polarized, elliptically polarized, and circularly polarized 2-micron ultrafast lasers, achieving the detection of the polarization state of 2-micron ultrafast lasers. The method is simple to operate and has the following advantages compared to existing technologies:

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

[0044] 2. Low cost of the method: The device is simple, there are no additional polarization modulation devices, and it is easy to mass-produce;

[0045] 3. Easy to operate: Users can use computer and Python software to program and control the electric displacement stage, collect, process and store data, and display the polarization state and Poincaré sphere. The operation is simple and intuitive. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the detection device in this invention;

[0047] Figure 2 This is a schematic diagram of the process by which the electric rotary displacement stage drives the quarter-wave plate to rotate in this invention.

[0048] Figure 3 This is a schematic diagram of the polarization characteristics of 2-micrometer 45° linearly polarized light measured in this invention;

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

[0050] Figure 4 This is a schematic diagram showing the polarization characteristics of 2-micrometer right-handed circularly polarized light measured in this invention.

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

[0052] Figure 5 This is a schematic diagram illustrating the polarization characteristics of 2-micrometer circularly polarized light measured according to the present invention.

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

[0054] Figure 6 The polarization characteristic diagram of 2-micrometer elliptically polarized light obtained by this invention;

[0055] Among them, (a) is the polarization ellipse diagram of the beam under test, and (b) is the polarization Poincaré sphere diagram of the beam under test.

[0056] In the diagram: 1. Quarter-wave plate, 2. Electric rotary displacement stage, 3. Polarization beam splitter, 4. Power detector, 5. Data processor. Detailed Implementation

[0057] like Figure 1As shown, the present invention provides a 2-micron fundamental-order ultrafast laser polarization detection device based on a Poincaré 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 rotary displacement stage 2, and a polarization beam splitter 3. The quarter-wave plate 1 is used to generate a quarter-cycle phase difference in the orthogonal direction. The electric rotary displacement stage 2 is used to fix and support the quarter-wave plate 1, and at the same time, it is used to drive the quarter-wave plate 1 to rotate around the optical axis at a fixed angle, preferably 22.5°. Preferably, the status parameters (rotation angle information) of the electric rotary displacement stage 2 can be transmitted to the data processor 5 via TTL serial port or Wi-Fi.

[0059] The polarization beam splitter 3 is disposed in the outgoing light path of the quarter-wave plate 1 to limit the polarization state of the transmitted light, allowing only light perpendicular to the beam splitting surface to pass through, specifically vertically polarized light.

[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 light intensity after each dynamic adjustment through the quarter-wave plate 1 and the polarization beam splitter 3.

[0061] The polarization analysis module includes a data processor 5, which is connected to the electric rotary stage 2 and the power detector 4. The data processor 5 is used to control the electric rotary stage 2, thereby changing the angle between the fast axis of the quarter-wave plate 1 and the positive 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 rotary stage 2 and the real-time light intensity data 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 Poincaré sphere, and complete the polarization detection of the 2-micron ultrafast laser. Preferably, the control of the electric rotary stage 2 and the reception and processing of data by the data processor 5 can be performed through the Python platform.

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

[0063] As a preferred option, such as 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 its rotation around the optical axis is fixed at an angle of Δθ = 22.5° each time. At the same time, the rotation angle information can be transmitted to the data processor 5 in real time.

[0064] 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 power unit includes a worm gear transmission mechanism with a transmission ratio of 1:30, a module of 1, and a lead angle of 20.12°. The worm gear has a hollow center and a limiting groove. The quarter-wave plate 1 is mounted at the center of the worm gear and its position is fixed by the limiting groove. A manually adjustable differential cylinder is provided at the end of the worm. The power unit includes a 42-phase four-wire stepper motor, the output shaft of which is coaxially connected to the worm. The feedback unit includes a Hall sensor connected to the 42-phase four-wire stepper motor to collect the rotation angle information of the motor in real time. Preferably, the Hall sensor and the 42-phase four-wire stepper motor transmit rotation angle data back via Wi-Fi, Bluetooth, or a TTL serial port at a reporting frequency of 30Hz. As a further preferred option, the Python platform built on the ESP32 development board can be used to control the transmission unit and the power unit, while receiving information from the feedback unit.

[0065] As a preferred embodiment, the polarization beam splitter 3 is a 2-micron band polarization beam splitter with a beam splitting surface at an angle of 45° to xoz, which can split the incident light into two beams of polarized light with mutually perpendicular polarization states, and make the polarized light perpendicular to the beam splitting surface 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 preferred embodiment, the power detector 4 is a thermoelectric detector, which is used to detect nanosecond-level ultrafast lasers and can realize ultrafast laser power detection across the entire wavelength range. At the same time, the power data detected by the thermoelectric detector can be transmitted to the data processor 5 in real time.

[0067] Preferably, the data processor 5 is a computer. In this way, the computer can use the Python platform to implement the movement of the electric rotary stage 2, as well as the data collection, processing, and storage processes. Simultaneously, it can display the polarization state and the Poincaré 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 drive control unit is used to drive the electric rotary displacement stage 2 to perform actions 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 displacement stage 2 and the real-time light intensity data detected by the power detector 4, 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 adjustment action signals 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 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 Poincaré sphere model, and then send them to the data processing unit.

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

[0073] As a preferred embodiment, the data storage unit is used to record and store polarization state data and polarization state images.

[0074] This invention also provides a 2-micron fundamental-order ultrafast laser polarization detection method based on a Poincaré sphere, employing a 2-micron fundamental-order ultrafast laser polarization detection device based on a Poincaré sphere, specifically including the following steps:

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

[0076] Step 2: After the input laser passes through free space or is coupled with an optical fiber, it is collinear with the optical axis of the quarter-wave plate 2. At the same time, the data processor 5 is used to adjust the electric rotary displacement stage 2 through the Python platform to drive the fast axis of the quarter-wave plate 1 to coincide with the x-axis initially. Then, it rotates 22.5° every 0.2s until it rotates seven times. When the angle between the fast axis of the quarter-wave plate 1 and the positive x-axis is 157.5°, it is rotated in the opposite direction so that the angle between the fast axis of the quarter-wave plate 1 and the positive x-axis is 0°.

[0077] The Python platform is built on the ESP32 development board to facilitate the control of the hollow rotary displacement stage to step and fix the angle.

[0078] Step 3: Adjust the angle of 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 beam, the data processor 5 controls the power detector 4 to collect the laser power through the Python platform. At the same time, when the quarter-wave plate 1 starts to rotate, data is collected every 22.5°. After every eight collections, the Stokes parameters and polarization state data are calculated through the Python platform and the calculated data is output and stored. At the same time, the laser polarization state data and polarization state image are displayed.

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

[0081] S41: Combining the information collected by the power detector (4), ABCD is calculated using the Fourier analysis method through formula (1);

[0082]

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

[0084]

[0085] S43: Using the mutually orthogonal axes S1, S2 and S3, draw a Poincaré sphere representing the laser polarization state through the Python platform;

[0086] S44: Using formula (3), the degree of polarization is calculated using the Python platform based on the Stokes parameters. The major axis of the ellipse is calculated using formula (4). The minor axis of the ellipse is calculated using formula (5). The azimuth of the ellipse is calculated using formula (6). The polarization ellipse is then drawn.

[0087]

[0088]

[0089] ε=0.5*arctan(S1*S2) (6).

[0090] As a preferred embodiment, the Python platform integrates a data storage unit for recording and storing polarization state data.

[0091] The present invention will be further described below with reference to embodiments:

[0092] Example 1:

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

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

[0095] S2: Adjust the electric rotary displacement stage 2 and the quarter-wave plate 1. The electric rotary displacement stage 2 drives the fixed quarter-wave plate to rotate around its optical axis. Figure 1 The beam is rotated along the z-axis to pass perpendicularly through the quarter-wave plate 1, with the center of the beam coinciding 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 via a Hall sensor. The data processor 5 automatically adjusts the fast axis of the quarter-wave plate 1 mounted on the electric rotary displacement stage 2 to a horizontal position. The quarter-wave plate 1 used in the experiment is suitable for the 2-micron wavelength band and is coated with a 2-micron antireflection film.

[0096] S3: Adjusting the polarization beam splitter 3. The polarization beam splitter 3 uses a cubic PBS, with its splitting surface at a 45° angle to the xoy axis and the distance between the optical axis and the z-axis not exceeding 2 mm. It is used to split the light passing through it into two mutually perpendicular polarized beams (P-polarized light and S-polarized light), and to allow the beam with its polarization direction parallel to the y-axis to continue propagating along the z-axis. The PBS selected in the experiment is in the 2-micron band, consistent with the applicable band of the quarter-wave plate 1.

[0097] S4: Adjust power detector 4 to record beam power. The probe of power detector 4 is a thermoelectric detector, suitable for full-band laser power detection. Align the probe of power detector 4 with the z-axis, and let the light shine perpendicularly onto the probe absorption array; the data from power detector 4 is transmitted back to data processor 5 for processing via data line.

[0098] S5: Adjust data processor 5 to control the electric rotary stage 2, process and visualize data. Utilize the Python platform to control the electric rotary stage 2, rotating 22.5° every 0.2 seconds and collecting data once (e.g., ...). Figure 2 As shown), the power detector data was obtained after every eight acquisitions (11.6, 14.0, 10.1, 6.0, 9.8, 14.5, 11.5, 7.5).

[0099] Furthermore, the data processor 5, using the Python platform and the information collected by the power detector 4, can calculate ABCD as follows using Fourier analysis: (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, a Poincaré sphere representing the laser polarization state is drawn using the Python platform with mutually orthogonal axes S1, S2, and S3.

[0102] Furthermore, based on the Stokes parameters, the degree of polarization was calculated using the Python platform: P = 0.706. Then, the normalized major axis of the ellipse: a = 1, the minor axis: b = 0.001, and the azimuth angle of the ellipse: ε = 45.4° were calculated sequentially. The polarization ellipse and the polarization Poincaré sphere were then plotted, as shown below. Figure 6 As shown.

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

[0104] Combining the above embodiments Figures 3 to 6 This invention effectively demonstrates its efficient, accurate, and rapid measurement of the polarization state of 2-micron ultrafast lasers. The device is simple in structure and easy to operate and control. By changing the quarter-wave plate and PBS, multi-wavelength measurements can be achieved, making it widely applicable. The use of an electric rotary displacement stage and computer control enables automated measurement, reducing human error and improving measurement efficiency. The computer automatically processes data through the Python platform, quickly calculating Stokes parameters and plotting the Poincaré sphere, facilitating real-time analysis and understanding of the laser polarization state.

[0105] While the specific implementation methods of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples. Various changes or modifications can be made to these implementation methods without departing from the principles and implementation of the present invention (e.g., replacing the PBS with a polarizer or other polarizing optical element, replacing the thermoelectric detector with another type of power detector, etc.). Therefore, the scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for polarization detection of a 2-micron fundamental ultrafast laser based on a Poincaré sphere, employing a 2-micron fundamental ultrafast laser polarization detection device based on a Poincaré sphere. This device includes a polarization control module, a power detection module, and a polarization analysis module. The polarization control module includes a quarter-wave plate (1), an electrically driven rotary stage (2), and a polarization beam splitter (3). The quarter-wave plate (1) generates a quarter-cycle phase difference in the orthogonal direction. The electrically driven rotary stage (2) is used to fix and support the quarter-wave plate (1) and simultaneously drive the quarter-wave plate (1) to rotate around the optical axis at a fixed angle. The polarization beam splitter (3) is positioned on the outgoing light path of the quarter-wave plate (1) to restrict the polarization state of the transmitted light, allowing only those polarization states perpendicular to the beam splitter. The beam passes through the beam surface; the power detection module includes a power detector (4), which is connected to a polarization beam splitter (3) and is used to dynamically detect the real-time data of the light intensity after each pass through the quarter-wave plate (1) and the polarization beam splitter (3) after dynamic adjustment; the polarization analysis module includes a data processor (5), which is connected to an electric rotary displacement stage (2) and a power detector (4) respectively, and is used to control the electric rotary displacement stage (2) to change the angle between the fast axis of the quarter-wave plate (1) and the positive 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 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, calculate the Stokes parameter and the Poincaré sphere, and complete the polarization detection of the 2-micron ultrafast laser; Its features are, Specifically, the steps include the following: Step 1: Place an electric rotary displacement stage (2) on the xoy plane and install a quarter-wave plate (1) on the electric rotary displacement stage (2). At the same time, keep the angle between the fast axis of the quarter-wave plate (1) and the positive x-axis at 0°. Step 2: After the input laser passes through free space or is coupled with an optical fiber, it is collinear with the optical axis of the quarter-wave plate (2). At the same time, the data processor (5) is used to adjust the electric rotary displacement 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. Then, it rotates 22.5° every 0.2s until it rotates seven times. When the angle between the fast axis of the quarter-wave plate (1) and the positive x-axis is 157.5°, it is rotated in the opposite direction so that the angle between the fast axis of the quarter-wave plate (1) and the positive 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 splitter 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 beam, the data processor (5) controls the power detector (4) to collect the laser power through the Python platform. At the same time, when the quarter-wave plate (1) starts to rotate, data is collected once every 22.5° rotation. After every eight collections, the Stokes parameters and polarization state data are calculated through the Python platform and the calculated data is output and stored. At the same time, the laser polarization state data and polarization state image are displayed. The calculation process for the Stokes parameters and polarization state data is as follows: S41: Combining the information collected by the power detector (4), ABCD is calculated using the formula (1) and Fourier analysis. （1）； S42: Solve for all the Stokes parameters of the output laser according to formula (2); （2）； S43: Using the mutually orthogonal axes S1, S2 and S3, draw a Poincaré sphere representing the laser polarization state through the Python platform; S44: Using formula (3), the degree of polarization is calculated using the Python platform based on the Stokes parameters. The major axis of the ellipse is calculated using formula (4), the minor axis of the ellipse is calculated using formula (5), the azimuth angle of the ellipse is calculated using formula (6), and the polarization ellipse is drawn. （3）； （4）； （5）； （6）。 2. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 1, characterized in that, The Python platform integrates a data storage unit, which is used to record and store polarization state data.

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

4. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 3, characterized in that, The initial position of the fast axis of the quarter-wave plate (1) and x The included angle of the axis is Its rotation around the optical axis is a fixed angle each time. Spend.

5. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 4, characterized in that, The electric rotary displacement stage (2) includes a transmission unit, a power unit, and a feedback unit. The power unit includes a worm gear transmission mechanism with a transmission ratio of 1:30, a module of 1, and a lead angle of 20.12°. The worm gear has a hollow center and is provided with a limiting groove. The quarter-wave plate (1) is installed at the center of the worm gear and is fixed in position by the limiting groove. The end of the worm gear 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 gear. The feedback unit includes a Hall sensor, which is connected to the 42 two-phase four-wire stepper motor and is used to collect the rotation angle information of the 42 two-phase four-wire stepper motor in real time.

6. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 5, characterized in that, The polarization beam splitter (3) is a 2-micrometer band polarization beam splitter, and its splitting plane is parallel to... xoz With an angle of 45°, the incident light can be split into two beams of polarized light with mutually perpendicular polarization states, and the polarized light perpendicular to the beam splitting surface is 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).

7. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 6, characterized in that, The power detector (4) is a thermoelectric detector used to detect nanosecond-level ultrafast lasers and to detect ultrafast laser power across the entire wavelength range.

8. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 7, characterized in that, The data processor (5) is a computer.

9. The method for detecting the polarization of a 2-micron fundamental-order ultrafast laser based on a Poincaré sphere according to claim 8, characterized in that, 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; The drive control unit is used to drive the electric rotary displacement stage (2) to perform actions 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 light intensity data detected by the power detector (4), analyze and process them 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 Stokes parameters and polarization state data, and send adjustment action signals to the drive control unit according to the Stokes parameters and polarization state data; at the same time, it is used to obtain the polarization state image according to the Stokes parameters and polarization state data, and send the polarization state data and 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 Poincaré sphere model, and then 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.

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