A turntable type coherent laser communication system and a polarization compensation method

Abstract

The application discloses a turntable type coherent laser communication system with polarization compensation and a compensation method. The device is composed of a laser light source, a collimating mirror, a polarization beam splitter, a rear optical path, a half-wave plate, a quarter-wave plate, a through-axis optical path and a telescope system. The light emitted by the laser light source is collimated by the collimating mirror and is polarized into horizontal polarized light by the polarization beam splitter. The horizontal polarized light passes through the rear optical path, is modulated by the half-wave plate and the quarter-wave plate, passes through the through-axis optical path and is emitted by the telescope system. The half-wave plate and the quarter-wave plate modulate the horizontal polarized light generated by the polarization beam splitter into right circular polarized light and compensate for the additional phase delay and the rotation of the polarization base of each optical path. The phase delay of the rear optical path, the through-axis optical path and the telescope system is measured before loading, and the rotation of the polarization base is obtained in real time according to the attitudes of the azimuth axis and the pitch axis. The compensation angle of the half-wave plate and the quarter-wave plate is calculated and obtained based on the matrix corresponding to the above parameters and through the Mueller-Stokes algorithm.

Description

Technical Field

[0001] This invention relates to a turntable-type coherent laser communication system and a compensation method with polarization compensation, specifically to real-time compensation of dynamic polarization degradation in a turntable-type optical system for space coherent laser communication, which can be applied to polarization-maintaining design of space coherent laser communication optical systems and optical system design for space quantum communication. Background Technology

[0002] Laser communication refers to a communication method that uses light waves as the carrier to transmit information. Compared with traditional wireless communication, it has many advantages such as wide bandwidth, large channel capacity, low power consumption, small size, and strong anti-interference ability, making it a promising approach for future high-data-volume information transmission. Depending on the transmission medium, it can be divided into space optical communication and fiber optic communication. Space optical communication is an effective solution for long-distance transmission.

[0003] Coherent laser communication typically transmits right-handed circularly polarized light and receives left-handed circularly polarized light. Optical components, such as mirrors, which are part of the optical path, introduce additional phase delays to the arriving light, causing degradation of the circularly polarized light transmitted and received by the system.

[0004] Polarization preservation technology is a method of controlling the polarization state of a system using polarization devices. Commonly used polarization devices include extruded optical fibers and waveplates. Waveplates, due to their good stability and high compensation accuracy, are frequently used in optical system compensation for space laser communication. In engineering applications, waveplates are typically made of materials with birefringence, such as quartz crystals, mica, or electro-optic crystals.

[0005] A turntable optical system is a pointing and tracking mechanism that changes the direction of the optical system by rotating a mechanical axis. Compared to a mirror-type mechanism, it has a larger rotation range and is easier to implement with large apertures, often used in long-distance communication. However, during system operation, the axis of the turntable optical system is constantly rotating, causing the polarization basis vectors to change dynamically. This leads to dynamic degradation of the circularly polarized light transmitted and received by the system, thus requiring dynamic polarization maintenance.

[0006] This invention is based on the Mueller-Stokes algorithm in polarization optics. It relies on the measurement of parameters of each subsystem of the optical system before loading and the real-time attitude acquisition of the rotation axis, and achieves real-time compensation for polarization degradation through a rotating waveplate. This method can also be applied to the design of polarization-coded space quantum communication optical systems, showing broad application prospects. Summary of the Invention

[0007] Specifically, it involves real-time compensation for polarization dynamic degradation caused by turntable optical systems in spatial coherent laser communication, which can be applied to the optical design of polarization-coded optical communication.

[0008] The purpose of this invention is to provide a turntable-type coherent laser communication system and compensation method with polarization compensation. Based on the measurement of system parameters and the real-time attitude acquisition of the rotating shaft before loading, the polarization state modulation and real-time compensation for dynamic polarization degradation are achieved by rotating the angle of the waveplate.

[0009] The apparatus of the present invention is as follows Figure 1 As shown, it includes a laser source 1, a collimator 2, a polarizing beam splitter 3, a rear optical path 4, a half-wave plate 5, a quarter-wave plate 6, a through-axis optical path 7, and a telescope system 8. The collimator 2 operates at a wavelength compatible with the laser source 1, and its focal length and numerical aperture match the dimensions of the polarizing beam splitter 3. The polarizing beam splitter 3 operates at a wavelength compatible with the laser source 1, transmitting horizontally polarized light and reflecting vertically polarized light, with a polarization extinction ratio of not less than 3000:1. The half-wave plate 5 and the quarter-wave plate 6 operate at wavelengths compatible with the laser source 1, with a transmittance of not less than 98% and a delay error of not less than λ / 300. The polarized beam first rotates through the azimuth axis ①, then passes through the through-axis optical path 7; the polarized beam first rotates through the pitch axis ②, then passes through the telescope system 8.

[0010] The polarization preservation method of the present invention includes the following steps:

[0011] 1) Measure the phase delay of optical path 4 before loading. Its transfer matrix can be represented by a 4x4 Mueller matrix as follows:

[0012]

[0013] 2) Measure the phase delay of the through-axis optical path 7 before loading. Its transmission matrix is:

[0014]

[0015] 3) Measure the phase delay of telescope system 8 before loading. Its transmission matrix is:

[0016]

[0017] 4) Obtain the rotation angle of the azimuth axis before communication. Its transmission matrix is:

[0018]

[0019] 5) Obtain the pitch axis rotation angle before communication. Its transmission matrix is:

[0020]

[0021] 6) Rotate the half-wave plate to the compensation angle 5. Quarter-wave plate with 6 to compensation angle The horizontally polarized light generated by polarization beam splitter 3 Converted into circularly polarized light .

[0022] Half-wave plate at 5 angles The corresponding transfer matrix is:

[0023]

[0024] Quarter wave plate 6 angle The corresponding transfer matrix is:

[0025]

[0026] Horizontal polarized light Circularly polarized light The corresponding Stokes parameter can be expressed as , Therefore, the overall process of the Mueller-Stokes algorithm system can be expressed as:

[0027]

[0028] =

[0029] When the azimuth and elevation angles are known = Given a quantity, the waveplate compensation angle satisfies the following condition:

[0030] 7) Calculate the compensation angle of the half-wave plate 5 according to the following formula. Quarter-wave plate with 6 compensation angle :

[0031]

[0032] 8) Rotate the half-wave plate to the compensation angle 5. Quarter-wave plate with 6 to compensation angle Compensation is achieved. The angle of the rotating half-wave plate is calculated based on the dynamic changes in azimuth and elevation angles. Quarter-wave plate at 6 angles The real-time updated value enables dynamic polarization maintenance.

[0033] This method provides a turntable-type coherent laser communication system with polarization compensation and a compensation method. Its advantages are: 1) The compensation device of the present invention has a simple structure; 2) The method of the present invention can compensate for the dynamic degradation of polarization state caused by systems such as turntable-type systems in real time; 3) Compared with the extruded fiber compensation method, the compensation accuracy of the present invention is higher. Attached Figure Description

[0034] Figure 1 A turntable-type coherent laser communication system with polarization compensation Detailed Implementation

[0035] The following describes in detail, with reference to the accompanying drawings, examples of implementation of the method of the present invention.

[0036] The main devices and systems used in the embodiments of this invention are described as follows:

[0037] It consists of a laser source, collimator, polarization beam splitter, rear optical path, half-wave plate, quarter-wave plate, through-axis optical path, and telescope system.

[0038] 1) Laser source 1: Laser source used for specific tasks, such as a 1550nm fiber-coupled laser;

[0039] 2) Collimator 2: The collimator is a Thorlabs product, model F810FC-1550, with the following main performance parameters: operating wavelength 1550nm, focal length 37.13mm, numerical aperture 0.24, fiber coupling via FC / PC port, and exit pupil 24.0mm.

[0040] 3) Polarization beam splitter 3: The polarization beam splitter adopts Ibtek's product, model MPBS24-1550, with the following main performance parameters: working wavelength 1550nm, polarization extinction ratio greater than 3000:1, and dimensions of 25.4mm×25.4mm×25.4mm.

[0041] 4) Rear optical path 4: The rear optical path of the laser communication optical system designed for a specific mission;

[0042] 5) Half-wave plate 5: The half-wave plate is an Ibtek product, model HWP10-1550B, with a working wavelength of 1550nm, a delay accuracy of λ / 300, a diameter of 25.4mm, and a transmittance of 99%;

[0043] 6) Quarter-wave plate 6: The quarter-wave plate is an Ibtek product, model QWP10-1550B, with a working wavelength of 1550nm, a delay accuracy of λ / 300, a diameter of 25.4mm, and a transmittance of 99%;

[0044] 7) Through-axis optical path 7: The through-axis optical path is the optical path between the azimuth and pitch axes;

[0045] 8) Telescope System 8: The telescope system is the optical system at the forefront of the optical system used for laser transmission and reception;

[0046] The schematic diagram of the main optical path of the method of the present invention is attached. Figure 1 As shown, the specific situation is described below:

[0047] The phase delay of optical path 4 at 1550nm was measured before loading. 21°, phase retardation of the transaxial optical path 7 at 1550nm 189°, the phase extension of the telescope system 8 at 1550nm 164°. The azimuth axis rotation angle at a certain moment. Pitch angle ; Calculate the compensation angle of the half-wave plate 5 according to the following formula. Quarter-wave plate with 6 compensation angle :

[0048]

[0049] The rotation angle of the half-wave plate can be obtained. , or Or rotate the angle or The half-wave plate 5 and the quarter-wave plate 6 are rotated to the compensation angle, and the angles of the half-wave plate 5 and the quarter-wave plate 6 are adjusted according to the rotation of the azimuth axis and the rotation of the pitch axis to achieve dynamic compensation.

Claims

1. A polarization compensation method for a turntable-type coherent laser communication system, characterized in that... The system consists of a laser source (1), a collimator (2), a polarization beam splitter (3), a rear optical path (4), a half-wave plate (5), a quarter-wave plate (6), a through-axis optical path (7), and a telescope system (8). The rotary table coherent laser communication system adds a half-wave plate (5) between the rear optical path (4) and the quarter-wave plate (6) of the conventional rotary table coherent laser communication system, which consists of a laser source (1), collimator (2), polarization beam splitter (3), rear optical path (4), quarter-wave plate (6), through-axis optical path (7) and telescope system (8). At the same time, the wave plate group needs to move with the rotation axis to ensure the circular deflection of the output light. The light emitted by the laser source (1) is collimated by the collimator (2) and then polarized into horizontally polarized light by the polarization beam splitter (3). The horizontally polarized light passes through the rear optical path (4), is modulated by the half-wave plate (5) and the quarter-wave plate (6), and is emitted by the telescope system (8) through the through-axis optical path (7). The half-wave plate (5) and the quarter-wave plate (6) are rotated to the calculated angle to modulate the horizontally polarized light generated by the polarization beam splitter (3) into right-hand circularly polarized light, and to compensate for the phase generated by the rear optical path (4), the through-axis optical path (7), and the telescope system (8), while also compensating for the basis angle deviation caused by the rotation of the azimuth axis and the rotation of the pitch axis. The polarization compensation method includes the following steps: 1) Measure the phase delay of the optical path (4) before loading Its transfer matrix can be represented by a 4x4 Mueller matrix as follows: 2) Measure the phase delay of the through-axis optical path (7) before loading. Its transmission matrix is: 3) Measure the phase delay of the telescope system (8) before loading. Its transmission matrix is: 4) Obtain the rotation angle of the azimuth axis before communication. Its transmission matrix is: 5) Obtain the pitch axis rotation angle before communication. Its transmission matrix is: 6) Rotate the half-wave plate (5) to the compensation angle. Quarter-wave plate (6) to compensation angle The horizontally polarized light generated by the polarization beam splitter (3) Converted into circularly polarized light ; Half-wave plate (5) angle The corresponding transfer matrix is: Quarter-wave plate (6) angle The corresponding transfer matrix is: Horizontal polarized light Circularly polarized light The corresponding Stokes parameter can be expressed as , The overall process of the Mueller-Stokes algorithm system can then be expressed as: = When the azimuth and elevation angles are known = Given a quantity, the waveplate compensation angle satisfies the following condition: 7) Calculate the compensation angle of the half-wave plate (5) according to the following formula. Quarter-wave plate (6) compensation angle : 8) Rotate the half-wave plate (5) to the compensation angle. Quarter-wave plate (6) to compensation angle To achieve compensation, the angle of the rotating half-wave plate (5) is calculated based on the dynamic changes in azimuth and elevation angles. , quarter-wave plate (6) angle The real-time updated value enables dynamic polarization maintenance.

2. The polarization compensation method for a turntable-type coherent laser communication system according to claim 1, characterized in that: The collimator (2) operates at a wavelength that is compatible with the operating wavelength of the laser source (1), and its focal length and numerical aperture are matched with the size of the polarization beam splitter (3).

3. The polarization compensation method for a turntable-type coherent laser communication system according to claim 1, characterized in that: The polarization beam splitter (3) operates at a wavelength that matches the wavelength of the laser source (1), transmits horizontally polarized light, reflects vertically polarized light, and has a polarization extinction ratio of not less than 3000:

1.

4. The polarization compensation method for a turntable-type coherent laser communication system according to claim 1, characterized in that: The half-wave plate (5) and quarter-wave plate (6) have working wavelengths that match the wavelength of the laser source (1), with a transmittance of not less than 98% and a delay error of not less than λ / 300.

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