A device and method for improving the optical efficiency of a Doppler simulator using a wave plate set

Abstract

The present invention discloses a device and method for improving the optical efficiency of a Doppler simulator using a wave plate group. The simulator consists of a laser collimation transmitter, a polarization beam splitter prism, a 1 / 2 and 1 / 4 wave plate group, a multiple reflection angle cone group, and a laser convergence receiver. The laser transmitted from the laser collimation transmitter to the laser convergence receiver is reflected multiple times by n fixed small angle cone prisms and a movable large hollow angle cone in the multiple reflection angle cone group. The optical path change speed is 4n times the movement speed of the large hollow angle cone, thereby simulating the Doppler effect caused by the relative motion between the satellite and the ground. A single 1 / 4 wave plate cannot completely compensate for the polarization phase of the angle cone group in the system. The return light beam is only partially received, resulting in low system efficiency. The present invention uses a hollow angle cone to achieve optical path return to avoid the depolarization effect, and uses a wave plate group to compensate for the additional phase, thereby improving the optical transmission efficiency of the Doppler simulator. This method is suitable for fields such as high-precision time-frequency transmission between satellites and the ground, and Doppler frequency shift compensation.

Description

Technical Field

[0001] The present invention relates to a ground Doppler simulation system, and more particularly to a device and method for improving the optical efficiency of a Doppler simulator using a wave plate set. The device is applicable to fields involving Doppler compensation, such as ground time-frequency transmission and satellite-to-ground optical communications. Background Art

[0002] Satellite-based high-precision time and frequency transmission technology is of great significance for fields such as precise timing, precision measurement, gravitational wave detection, and quantum relay. To achieve satellite-to-ground time and frequency transmission with an ultimate accuracy of 10-18, numerous challenges must be addressed, including long-range atmospheric influences, Doppler effect compensation, and the development of highly reliable optical frequency sources.

[0003] The Doppler effect caused by satellite motion degrades time-frequency alignment accuracy. This effect shifts the frequency of the carrier transmitted from the ground to the satellite, and also shifts the carrier received by the satellite. The Doppler effect caused by satellite motion results in a time-frequency alignment error of approximately 10⁻⁶ to 10⁻⁵. For a 200MHz repetition rate optical comb, the Doppler shift is in the hundreds to kilohertz range, comparable to the difference frequency of a linear sampling system, impacting the overall operation of the linear sampling system. High-precision time-frequency alignment requires accuracy on the order of 10⁻⁶. To achieve this, accurate measurement and compensation of the Doppler effect are required. Satellite Doppler noise compensation technology combines coarse time calibration with laser ranging to compensate for Doppler frequency errors in real time.

[0004] To accurately measure and compensate for the Doppler effect, it must be simulated on the ground. The National Institute of Standards and Technology (NIST) in the United States has developed a method that uses multiple reflections of a light beam to produce a Doppler shift by varying the optical path at a relative velocity equal to the velocity of relative motion between the satellite and the Earth. This relative velocity is 4n times the actual orbital velocity (n is the number of small cones). This method is difficult to calibrate, suffers from poor stability, and suffers from low overall optical efficiency.

[0005] From the perspective of improving the performance of a Doppler simulator, the present invention proposes a device and method for improving the optical efficiency of a Doppler simulator by using a wave plate group. In the Doppler simulator, a 1 / 2 wave plate and a 1 / 4 wave plate group are used to control the polarization state of the laser, thereby improving the optical efficiency of the entire system. Summary of the Invention

[0006] The purpose of the present invention is to provide a device and method for improving the optical efficiency of a Doppler simulator by using a wave plate group, mainly for improving the performance of a ground Doppler simulator.

[0007] The method of the present invention is as follows Figure 1 As shown, it includes a laser collimation transmitter 1, a polarization beam splitter prism 2, a 1 / 4 wave plate 3 with a rotating structure, a 1 / 2 wave plate 4 with a rotating structure, a multiple reflection angle cone group 5 and a laser convergence receiver 6, wherein the laser collimation transmitter 1 is composed of a polarization-maintaining fiber laser 1-1 and a transmitting collimator 1-2; the multiple reflection angle cone group 5 is composed of a large hollow angle cone 5-1, a first solid angle cone 5-2, a second solid angle cone 5-3, a third solid angle cone 5-4 and a hollow angle cone 5-5; the laser convergence receiver 6 is composed of a reflector 6-1, a receiving collimator 6-2 with a polarization-maintaining fiber and a detector 6-3. The outgoing laser of the polarization-maintaining fiber laser 1-1 is collimated by the emitting collimator 1-2 and then emits horizontally polarized light. The horizontally polarized light is transmitted through the polarization beam splitter prism 2 and then passes through the 1 / 4 wave plate 3 with a rotating structure and the 1 / 2 wave plate 4 with a rotating structure in sequence, and then enters the multiple reflection angle cone group 5. After multiple reflections by the large hollow angle cone 5-1, the first solid angle cone 5-2, the second solid angle cone 5-3, and the third solid angle cone 5-4, it passes through the center of the hollow angle cone 5-5 and returns along the original path, and then passes through the 1 / 2 wave plate 4 with a rotating structure and the 1 / 4 wave plate 3 with a rotating structure in sequence. The polarized light after compensation by the wave plate group is vertically polarized light. The vertically polarized light is reflected by the polarization beam splitter prism 2 and then enters the laser convergence receiver 6. The returned polarized light passes through the reflector 6-1 and the receiving collimator 6-2 with polarization-maintaining fiber and is detected by the detector 6-3.

[0008] By adjusting the rotation angles θ1 and θ2 of the quarter wave plate 3 with a rotating structure and the half wave plate 4 with a rotating structure, the optical power of the laser light finally received by the detector 6 - 3 reaches a maximum value.

[0009] The optical fiber end face of the polarization-maintaining fiber laser 1-1 needs to be located at the focal plane of the emitting collimator 1-2, and the operating wavelength range of the emitting collimator 1-2 needs to cover the wavelength of the polarization-maintaining fiber laser 1-1; the operating wavelength ranges of the polarization beam splitter 2, the 1 / 4 wave plate 3 with a rotating structure, and the 1 / 2 wave plate 4 with a rotating structure need to cover the laser wavelength corresponding to the polarization-maintaining fiber laser 1-1; the large hollow angle cone 5-1 has the ability to move at high speed, and the movement direction of the large hollow angle cone 5-1 needs to be parallel to the output laser optical axis of the laser collimation transmitter 1. When the laser enters the first solid angle cone 5-2, the second solid angle cone 5-3, and the third solid angle cone 5-4, the light spot can only be within one sector of the angle cone prism, as shown in the attached figure. Figure 2As shown, the position of the laser when entering the hollow angle cone 5-5 needs to coincide with the intersection of the three sectors of the hollow angle cone; the wavelength range of all angle cones used in the multiple reflection angle cone group 5 needs to cover the laser wavelength corresponding to the polarization-maintaining fiber laser 1-1, and the reflectivity of the laser in this band needs to reach more than 94%; the wavelength range of the reflector 6-1, the receiving collimator 6-2 with polarization-maintaining fiber and the detector 6-3 needs to cover the laser wavelength corresponding to the polarization-maintaining fiber laser 1-1.

[0010] The present invention provides a device and method for improving the optical efficiency of a Doppler simulator by using a wave plate set. The specific implementation steps and basic principles are as follows:

[0011] 1) The outgoing laser of the polarization-maintaining fiber laser 1-1 is collimated by the emission collimator 1-2 and then emits horizontal polarized light. The horizontal polarized light is transmitted through the polarization beam splitter prism 2. At this time, the transmitted light maintains the horizontal polarization state. The polarized light is recorded as S H ,

[0012] S H =[1 1 0 0] T

[0013] 2) The light transmitted by the polarization beam splitter prism 2 passes through the quarter wave plate 3 with a rotating structure and the half wave plate 4 with a rotating structure in sequence. After compensation, the angle between the long axis direction of the quarter wave plate 3 with a rotating structure and the horizontal direction is θ1, and the angle between the long axis direction of the half wave plate 4 with a rotating structure and the horizontal direction is θ2. At this time, the transmission matrix of the quarter wave plate 3 with a rotating structure and the half wave plate 4 with a rotating structure is Can be expressed as:

[0014]

[0015] 3) The polarized light beam then enters the multi-reflection cone group 5, and after multiple reflections from the large hollow cone 5-1, the first solid cone 5-2, the second solid cone 5-3, and the third solid cone 5-4, it passes through the center of the hollow cone 5-5 and returns along the original path. The multi-reflection cone group 5 can be regarded as a phase delay system, and the transmission matrix of the multi-reflection cone group 5 can be recorded as M δ,0 , which satisfies:

[0016]

[0017] 4) After multiple reflections, the polarized light passes through the 1 / 2 wave plate 4 with a rotating structure and the 1 / 4 wave plate 3 with a rotating structure again. When observed along the direction of the incident light, the angles between the 1 / 2 wave plate 4 with a rotating structure and the 1 / 4 wave plate 3 with a rotating structure and the horizontal direction are -θ2 and -θ1 respectively. The transmission matrix Can be expressed as:

[0018]

[0019] After the polarization state of the returning light is adjusted by the wave plate group, it needs to evolve into vertically polarized light, and its Stokes vector S V It can be expressed as:

[0020] S V =[0 0 1 1] T

[0021] 5) The compensation angle of the wave plate group needs to satisfy the following relationship:

[0022]

[0023] After calculation, we can get:

[0024]

[0025] 6) The polarized light after compensation by the wave plate group is vertically polarized light. After being reflected by the polarization splitter prism 2, the polarized light enters the laser convergence receiver 6, which can ensure the highest system efficiency. The returned polarized light passes through the reflector 6-1 and the receiving collimator 6-2 with polarization-maintaining fiber, and is detected by the detector 6-3.

[0026] The 1 / 4 wave plate 3 with a rotating structure and the 1 / 2 wave plate 4 with a rotating structure are rotated to specific angles θ1 and θ2 to ensure that the efficiency of the system can be maximized; when only the 1 / 4 wave plate 3 with a rotating structure is used, the return light cannot be compensated to the vertical linear polarization state, resulting in part of the energy being transmitted through the polarization splitter prism 2, thereby reducing the optical efficiency of the system.

[0027] The present invention provides a device and method for improving the optical efficiency of a Doppler simulator by using a wave plate group. The advantage of this method is that a wave plate group composed of a quarter wave plate and a half wave plate can achieve relatively perfect polarization state adjustment, thereby improving the overall optical transmission efficiency of the entire Doppler simulator. The effect comparison curve of using only a single quarter wave plate for compensation is shown in the attached figure. Figure 3 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Device for improving the optical efficiency of Doppler simulator

[0029] Figure 2 Schematic diagram of the sector where the solid cone incident light spot is located

[0030] Figure 3 The comparison curve of the optical efficiency measured by the Doppler simulator in the embodiment DETAILED DESCRIPTION

[0031] The following is combined with Figure 1 The implementation examples of the method of the present invention are described in detail.

[0032] The main components used in the present invention are described as follows:

[0033] 1) Laser collimation transmitter 1: The laser collimation transmitter 1 consists of a polarization-maintaining fiber laser 1-1 and an emission collimator 1-2. In this embodiment, the polarization-maintaining fiber laser 1-1 adopts a polarization-maintaining fiber-coupled laser light source from Thorlabs, a polarization-maintaining fiber output light source model S5FC1005P, an output laser wavelength of 1550nm, a polarization-maintaining fiber output, and an output power greater than 22mw; the emission collimator 1-2 adopts a reflective collimator from Thorlabs, model RC12FC-P01, which has an operating wavelength range of 450nm-20000nm, a focal length of 50.8mm, and an output light aperture of 22mm;

[0034] 2) Polarization beam splitter prism 2: In this embodiment, the polarization beam splitter prism 2 adopts a 25.4 mm polarization beam splitter cube from Thorlabs, model PBS254, which has an operating wavelength range of 1200-1600 nm and Tp / Ts>1000:1;

[0035] 3) Quarter-wave plate 3 with rotating structure: In this embodiment, the rotating structure of the quarter-wave plate 3 with rotating structure adopts a 1-inch rotating structure from Thorlabs, model RSP1X15, with a reading accuracy of 0.5°; the quarter-wave plate adopts a zero-order wave plate model WPQ05M-1550 from Thorlabs, with a wave plate delay accuracy of <λ / 300;

[0036] 4) 1 / 2 wave plate 4 with rotating structure: In this embodiment, the rotating structure of the 1 / 2 wave plate 4 with rotating structure adopts a 1-inch rotating structure of Thorlabs, model RSP1X15, with a reading accuracy of 0.5°; the 1 / 2 wave plate adopts a zero-order wave plate model WPH05M-1550 of Thorlabs, with a wave plate delay accuracy of <λ / 300;

[0037] 5) Multiple reflection cone group 5: Multiple reflection cone group 5 consists of a large hollow cone 5-1, a first solid cone 5-2, a second solid cone 5-3, a third solid cone 5-4 and a hollow cone 5-5. In this embodiment, the large hollow cone 5-1 is a customized hollow retroreflector with a light aperture of 150 mm. The rotation accuracy of the cone is required to be better than 5", and the reflective surface of the cone is silver-coated. The first solid cone 5-2, the second solid cone 5-3, the third solid cone 5-4 and the hollow cone 5-5 are all made of a quartz crystal. Corner cone 5-4 is a custom product. To increase internal reflection efficiency, the corner cone is made of high-refractive-index material SF55, with an anti-reflection coating on the surface. The wavelength range is 1050-1700nm, the optical aperture is 30.8mm, and the rotation accuracy is required to be better than 5". The hollow corner cone 5-5 uses a hollow retroreflector from Thorlabs, model HRR203-P01 with silver coating, with a optical aperture of 30.8mm and a rotation accuracy of better than 5".

[0038] 6) Laser convergence receiver 6: The laser convergence receiver 6 consists of a reflector 6-1, a receiving collimator 6-2 with polarization-maintaining fiber, and a detector 6-3. In this embodiment, the reflector 6-1 adopts the Thorlabs model PF07-03-P01 reflector, and the reflector surface is silver-coated; the receiving collimator 6-2 with polarization-maintaining fiber adopts the Thorlabs reflective collimator and the Thorlabs polarization-maintaining fiber jumper. The reflective collimator model is RC12FC-P01, and its operating wavelength range is 450nm-20000nm, its focal length is 50.8mm, and its diameter is 22mm; the polarization-maintaining fiber jumper model is P1-1550PM-FC-1, and its length is 1m; the detector 6-3 adopts a 1550nm power probe.

[0039] The main optical path diagram of the method of the present invention is shown in the attached figure. Figure 1 The specific situation is described as follows:

[0040] 1) According to the attached Figure 1 Fix the laser collimation transmitter 1. The linearly polarized light emitted by the polarization-maintaining fiber laser 1-1 is collimated by the emission collimator 1-2, generating horizontally polarized parallel light. This parallel light is transmitted through the polarization beam splitter 2 and then sequentially passes through the 1 / 4 wave plate 3 with a rotating structure and the 1 / 2 wave plate 4 with a rotating structure, and finally enters the multi-reflection angle cone group 5. First, by adjusting the azimuth and pitch angles of the laser collimation transmitter 1, the laser optical axis is parallel to the movement direction of the large hollow angle cone 5-1, ensuring that the position of the laser incident on the large hollow angle cone 5-1 does not change during the movement.

[0041] 2) Adjust the positions of the first solid angle cone 5-2, the second solid angle cone 5-3, and the third solid angle cone 5-4 so that the laser spot can only be within one sector of the corner cone prism when it enters the first solid angle cone 5-2, the second solid angle cone 5-3, and the third solid angle cone 5-4, as shown in the attached figure. Figure 2 The positions of the solid cones are adjusted sequentially so that the light beam can be reflected back and forth, eventually reaching the position of the hollow cone 5-5. The position of the hollow cone 5-5 is finely adjusted so that the position of the laser entering the hollow cone 5-5 coincides with the intersection of the three sectors of the hollow cone, ensuring that the light returns along the original optical path.

[0042] 3) The laser is reflected multiple times by the cone group and returns to the wave plate group. After passing through the 1 / 2 wave plate 4 with a rotating structure and the 1 / 4 wave plate 3 with a rotating structure, it enters the laser convergence receiver 6. By adjusting the direction and pitch angle of the reflector 6-1 in the laser convergence receiver 6, the return light is adjusted to the optical fiber of the receiving collimator 6-2 with polarization-maintaining optical fiber.

[0043] 4) By adjusting the angles of the quarter-wave plate 3 and the half-wave plate 4 with a rotating structure in the wave plate set, the laser power incident on the optical fiber is maximized, completing the system adjustment. The principle of adjusting the angle of the wave plate set is as follows:

[0044] The horizontal polarized light generated by the laser collimation transmitter 1 remains in a horizontal polarization state after passing through the polarization beam splitter prism 2. This polarized light is recorded as S H ,

[0045] S H =[1 1 0 0] T

[0046] The light transmitted by the polarization beam splitter prism 2 passes through the quarter wave plate 3 with a rotation structure whose long axis and the horizontal direction have an angle of θ1, and the half wave plate 4 with a rotation structure whose long axis and the horizontal direction have an angle of θ2. At this time, the transmission matrix of the quarter wave plate 3 with a rotation structure and the half wave plate 4 with a rotation structure is Can be expressed as:

[0047]

[0048] The polarized light beam then enters the multi-reflection cone group 5 and returns along the original path. The multi-reflection cone group 5 can be regarded as a phase delay system, and the transmission matrix of the multi-reflection cone group 5 can be recorded as M δ,0 , which satisfies:

[0049]

[0050] After multiple reflections, the polarized light passes through the 1 / 2 wave plate 4 with a rotating structure and the 1 / 4 wave plate 3 with a rotating structure again. When observed along the direction of the incident light, the angles between the 1 / 2 wave plate 4 with a rotating structure and the 1 / 4 wave plate 3 with a rotating structure and the horizontal direction are -θ2 and -θ1 respectively. The transmission matrix Can be expressed as:

[0051]

[0052] After the polarization state of the returning light is adjusted by the wave plate group, it needs to evolve into vertically polarized light, and its Stokes vector S V It can be expressed as: S V =[0 0 1 1] T , the compensation angle of the wave plate group needs to satisfy the following relationship:

[0053]

[0054] After calculation, we can get:

[0055]

[0056] By adjusting the angles of the 1 / 4 wave plate 3 with a rotating structure and the 1 / 2 wave plate 4 with a rotating structure to one of the above angles, the optical power received by the laser convergence receiver 6 can be maximized, thereby achieving maximum efficiency of the Doppler simulator.

[0057] 6) In actual experimental tests, we conducted an experimental comparison. When a wave plate group consisting of a 1 / 4 wave plate 3 with a rotating structure and a 1 / 2 wave plate 4 with a rotating structure is used, the overall optical efficiency of the Doppler simulator is greatly improved compared to when only the 1 / 4 wave plate 3 with a rotating structure is used for polarization adjustment. Figure 3 shown.

Claims

1. A device for improving the optical efficiency of a Doppler simulator by using a wave plate group, comprising a laser collimating transmitter (1), a polarization beam splitter prism (2), a quarter wave plate with a rotating structure (3), a half wave plate with a rotating structure (4), a multi-reflection angle cone group (5) and a laser converging receiver (6), characterized in that: The laser collimation transmitter (1) is composed of a polarization-maintaining fiber laser (1-1) and a transmitting collimator (1-2); The multiple reflection angle cone group (5) consists of a large hollow angle cone (5-1), a first solid angle cone (5-2), a second solid angle cone (5-3), a third solid angle cone (5-4) and a hollow angle cone (5-5); The laser convergence receiver (6) is composed of a reflector (6-1), a receiving collimator (6-2) with a polarization-maintaining optical fiber, and a detector (6-3); The laser light emitted by the polarization-maintaining fiber laser (1-1) is collimated by the emission collimator (1-2) and then emits horizontally polarized light. The horizontally polarized light is transmitted through the polarization beam splitter (2) and then sequentially passes through a quarter wave plate (3) with a rotating structure and a half wave plate (4) with a rotating structure, and then enters a multi-reflection angle cone group (5), and then passes through a large hollow angle cone (5-1), a first solid angle cone (5-2), a second solid angle cone (5-3), and a third solid angle cone (5-4). After reflection, the light passes through the center of the hollow cone (5-5) and returns along the original path, and then passes through the 1 / 2 wave plate (4) with a rotating structure and the 1 / 4 wave plate (3) with a rotating structure in sequence. The polarized light compensated by the wave plate group is modulated into vertical polarized light. The vertical polarized light is reflected by the polarization splitting prism (2) and enters the laser convergence receiver (6). The returned polarized light passes through the reflector (6-1) and the receiving collimator (6-2) with polarization-maintaining optical fiber and is detected by the detector (6-3).

2. The device for improving the optical efficiency of a Doppler simulator using a wave plate assembly according to claim 1, characterized in that: The fiber end face of the polarization-maintaining fiber laser (1-1) in the laser collimation transmitter (1) needs to be located at the focal plane of the emission collimator (1-2), and the operating wavelength range of the emission collimator (1-2) covers the wavelength of the polarization-maintaining fiber laser (1-1).

3. The device for improving the optical efficiency of a Doppler simulator using a wave plate assembly according to claim 1, characterized in that: The large hollow angle cone (5-1) in the multiple reflection angle cone group (5) has the ability to move at high speed, and the movement direction of the large hollow angle cone (5-1) remains parallel to the output laser optical axis of the laser collimation transmitter (1); when the laser enters the first solid angle cone (5-2), the second solid angle cone (5-3) and the third solid angle cone (5-4), the light spot can only be in one sector of the angle cone prism, and the position of the laser when entering the hollow angle cone (5-5) needs to coincide with the intersection of the three sectors of the hollow angle cone; the wavelength range of all angle cones used in the multiple reflection angle cone group (5) needs to cover the laser wavelength corresponding to the polarization-maintaining fiber laser (1-1), and the reflectivity for the laser wavelength in this band reaches more than 94%.

4. The device for improving the optical efficiency of a Doppler simulator using a wave plate assembly according to claim 1, characterized in that: The operating wavelength ranges of the reflector (6-1), the receiving collimator (6-2) with polarization-maintaining optical fiber, and the detector (6-3) in the laser convergence receiver (6) need to cover the laser wavelength corresponding to the polarization-maintaining optical fiber laser (1-1).

5. A method for improving the optical efficiency of a Doppler simulator using a wave plate set, characterized by comprising the following steps: 1) The output laser of the polarization-maintaining fiber laser (1-1) is collimated by the emission collimator (1-2) and then emits horizontal polarized light. The horizontal polarized light is transmitted through the polarization beam splitter prism (2). At this time, the transmitted light maintains the horizontal polarization state. The polarized light is recorded as S H , S H ＝[1 1 0 0] T ； 2) The light transmitted through the polarization beam splitter (2) passes through the quarter wave plate (3) with a rotating structure and the half wave plate (4) with a rotating structure in sequence. The angle between the long axis direction of the quarter wave plate (3) with a rotating structure and the horizontal direction is θ1, and the angle between the long axis direction of the half wave plate (4) with a rotating structure and the horizontal direction is θ2. At this time, the transmission matrix of the quarter wave plate (3) with a rotating structure and the half wave plate (4) with a rotating structure is Respectively expressed as: 3) The polarized light beam then enters the multi-reflection cone group (5), and after multiple reflections from the large hollow cone (5-1), the first solid cone (5-2), the second solid cone (5-3), and the third solid cone (5-4), it passes through the center of the hollow cone (5-5) and returns along the original path. The multi-reflection cone group (5) is regarded as a phase delay system, and the transmission matrix of the multi-reflection cone group (5) is denoted as M δ,0 , which satisfies: Where: δ is the sum of phase delays in the phase delay system; 4) After multiple reflections, the polarized light passes through the 1 / 2 wave plate (4) with a rotating structure and the 1 / 4 wave plate (3) with a rotating structure again. When observed along the direction of the incident light, the angles between the long axis direction of the 1 / 2 wave plate (4) with a rotating structure and the 1 / 4 wave plate (3) with a rotating structure and the horizontal direction are -θ2 and -θ1 respectively. The transmission matrix Respectively expressed as: After the polarization state of the returning light is adjusted by the wave plate group, it needs to evolve into vertically polarized light, and its Stokes vector S V Expressed as: S V ＝[0 0 1 1] T ； 5) The compensation angle of the wave plate group needs to meet the following requirements: After calculation, we get: 6) The polarized light compensated by the wave plate group is vertically polarized light. After being reflected by the polarization splitting prism (2), the polarized light enters the laser convergence receiver (6). The returned polarized light passes through the reflector (6-1) and the receiving collimator (6-2) with polarization-maintaining optical fiber, and is detected by the detector (6-3).

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