A device for detecting the backscattered stray light of a laser transceiver common aperture telescope

Abstract

The present invention discloses a device for detecting backward stray light of a laser transceiver co-aperture telescope. The device is composed of a laser light source, a polarization beam splitter, a half-wave plate, a quarter-wave plate, an optical trap, an absorbing cone, an optical coupler, and a single-photon detector. The backward stray light generated by the laser light source irradiating the telescope is transmitted through the polarization beam splitter and enters the single-photon detector to achieve the detection of stray light. The polarization beam splitter is used to separate the optical path of the laser light source from the stray light optical path, and to combine the stray light optical path with the attenuated light optical path of the local light source. Placing or removing the optical trap in the attenuated light optical path of the local light source can achieve the switching of different detection tasks or detection requirements. The detection field of view is changed by a fast steering mirror in the optical path of the laser light source, and the stray light of the device itself is suppressed by the absorbing cone. The device has high detection accuracy and can perform real-time dynamic detection, and can be applied to the detection and evaluation of the suppression design of backward scattered stray light of a laser transceiver co-aperture telescope.

Description

Technical Field

[0001] The present invention relates to the performance detection of a laser transceiver co-aperture telescope, and specifically relates to a device for detecting the backscattered stray light of a laser transceiver co-aperture telescope. It is applicable to the design of a laser transceiver co-aperture telescope, the detection of weak stray light, and is particularly applicable to the design of stray light suppression for a space gravitational wave telescope. Background Art

[0002] Laser transceiver co-aperture telescopes are commonly used in lidar detection, space gravitational wave detection, and free space quantum communication. In order to obtain higher sensitivity detection, it is necessary to suppress background stray light. The backscattered stray light from the telescope is the main component of the background stray light. Especially for space gravitational wave detection, due to the high energy of the emitted laser light source and the weak received signal, the telescope is required to have a higher stray light suppression ratio.

[0003] Space gravitational wave detection is a technology that detects the optical path changes induced by gravitational wave-induced space distortion through an interference link composed of three satellites to obtain information such as the gravitational wave frequency. Since gravitational waves were detected by the ground-based gravitational wave detection system LIGO, detecting medium and low frequency gravitational waves through a space system has become an international hot topic. Currently, many national organizations are researching its key technologies, such as LISA of the European Space Agency, Tianqin and Taiji in China.

[0004] As one of the key technologies for space gravitational wave detection, the development and evaluation of a telescope that forms an interference link with the transmitted and received laser beams. In order to obtain high detection accuracy and reduce the impact on the interference system, the telescope is required to have a high backscattered stray light suppression ratio. For example, the Chinese space gravitational wave detection mission requires that the backscattered stray light of the telescope is less than one-tenth of the emitted laser power. 10 Therefore, it is necessary to design a set of stray light detection systems to evaluate the stray light suppression design of such telescopes. Summary of the Invention

[0005] The present invention provides a device for detecting the backscattered stray light of a laser transceiver co-aperture telescope, and sets up a detection system for stray light and an evaluation system for the stray light suppression effect. This stray light detection device has high detection accuracy, can achieve real-time dynamic detection, and can also evaluate the impact of stray light, and can be extended to the evaluation of other laser transceiver telescope systems.

[0006] The schematic diagram of the present invention is as shown in the appendix Figure 1As shown, the laser generated by the laser light source 10 is split into two orthogonally polarized light beams by the third polarization beam splitter 9. The vertically polarized light is reflected by the fast steering mirror 8 and then modulated into horizontally polarized light by the half-wave plate 7. The horizontally polarized light is reflected by the third polarization beam splitter 9, and the reflected light is modulated by the quarter-wave plate 2 to generate a test light source. The test light source is used to detect the backscattered stray light generated by the telescope 1 to be measured. After the backscattered stray light passes through the quarter-wave plate 2, it is transmitted by the first polarization beam splitter 3 and the second polarization beam splitter 5. The transmitted light and the horizontally polarized light reflected by the second polarization beam splitter 5 are coupled into the single-photon detector 13 by the optical coupler 12. When the optical trap 11 is placed in the optical path, it absorbs the polarized light reflected by the third polarization beam splitter 9, and the single-photon detector 13 detects the backscattered stray light generated by the telescope 1 to be measured. When the optical trap 11 is removed from the optical path, the single-photon detector 13 detects the backscattered stray light and the local light generated by the telescope 1 to be measured. At this time, the stray light effect of the interferometric telescope can be evaluated. The stray light in different fields of view can be measured by adjusting the fast steering mirror 8. The depolarization of the stray light can be measured by adjusting the angle of the quarter-wave plate 2. The first light absorption cone 4 and the second light absorption cone 6 respectively absorb the stray light transmitted by the first polarization beam splitter 3 and the second polarization beam splitter 5.

[0007] The wavelength of the laser light source 10 matches the designed wavelength of the telescope 1 to be measured. The laser is a pulsed laser, and its energy is lower than the energy thresholds of each device. 10% of the energy -10 Within the dynamic range of the single-photon detector 13, the repetition frequency is not higher than the operating frequency of the single-photon detector. The polarization extinction ratio of the first polarization beam splitter 3, the second light absorption cone 6, and the third polarization beam splitter 9 is better than 100,000:1 at a specific wavelength, transmitting horizontally polarized light and reflecting vertically polarized light. The absorption efficiency of the optical trap 11 is better than 10 -5 ; The absorption efficiencies of the first light absorption cone 4 and the second light absorption cone 6 are better than 10 -5 , and the width and height of the optical trap and the light absorption cone are greater than or equal to those of the first polarization beam splitter 3, the second light absorption cone 6, and the third polarization beam splitter 9. The sensitivity of the single-photon detector 13 at a specific wavelength is higher than 10% of the energy of the laser light source -10 ; The dynamic range of the fast steering mirror 8 should match the field of view of the telescope 1. The coupling efficiency of the optical coupler 12 at a specific wavelength is higher than 50%. The optical axis of the half-wave plate 7 should be rotated to +45°. When the optical axis of the quarter-wave plate 2 is rotated to different angles, the depolarization of the telescope to be measured is detected.

[0008] The advantages of this invention patent are as follows: 1. By detecting stray light with a single-photon detector, the sensitivity is high, and stray light under a high suppression ratio can be detected; 2. The devices can be electrically controlled, and real-time detection and evaluation of stray light in the entire field of view can be achieved through the fast steering mirror. Description of the Drawings

[0009] Figure 1 Schematic diagram of the backscattered stray light detection device for a laser transceiver co-aperture telescope. Detailed implementation mode

[0010] Taking the stray light detection of the space gravitational wave telescope as an example, the device mainly includes the following parts:

[0011] 1) Laser light source: In this implementation, it includes the laser light source 10, whose main function is to generate detection laser. A narrow linewidth frequency-stabilized laser is used, with a wavelength of 1064 nm and a power of 10 watts, which is consistent with the gravitational wave mission;

[0012] 2) Polarizing beam splitter: In this implementation, it includes the first polarizing beam splitter 3, the second polarizing beam splitter 5, and the third polarizing beam splitter 9. Its main function is to split light. The transmission extinction ratio is 100000:1 (1064 nm), the transmission efficiency is greater than 99%, with a size of 15 mm × 15 mm × 15 mm, and the loss threshold is 50 watts / cm;

[0013] 3) The quarter-wave plate 2 is a zero-order quartz wave plate, with a reflectivity of 0.1% at a specific wavelength; with a diameter of 15.0 mm and a thickness of 2 mm, and a reflectivity less than 0.1% (1064 nm);

[0014] 4) The half-wave plate 7 is a zero-order quartz wave plate, with a reflectivity of 0.1% at a specific wavelength; with a diameter of 15.0 mm and a thickness of 2 mm, and a reflectivity of 0.1% (1064 nm);

[0015] 5) The fast steering mirror 8 is a voice coil fast steering mirror, with a lens diameter of 20 mm, a resolution less than or equal to 0.5 μrad, a range of 3° (greater than the telescope field of view), and a phase delay of 0.5° for the lens to polarized light; the reflectivity is greater than 99.9% (1064 nm);

[0016] 6) The material of the light trap 11 is absorptive neutral density glass, with a maximum power density of 15 watts per square centimeter, and a backscattering of 10 -5 (1064 nm), and the entrance aperture is 11 mm;

[0017] 7) The materials of the first light absorption cone 4 and the second light absorption cone 6 are absorptive neutral density glass, with a maximum power density of 15 watts per square centimeter, and a backscattering of 10 -5 (1064 nm), and the entrance size is 11 mm × 11 mm × 11 mm;

[0018] 8) The single photon detector 13 is a silicon avalanche photodetector, with a counting rate of 20 MHz (maximum gain), a dark count rate less than 1500 Hz (maximum gain), a detection efficiency of 50% (1064 nm), and is fiber-optically connected;

[0019] 9) The optical coupler 12 is FC / PC collimated package, with a numerical aperture of 0.25, a focal length of 36.6 mm, and a coupling efficiency of 50%.

[0020] The following describes the specific working process of the stray light detection device, as Figure 1 shown: The laser generated by the laser light source 10 is split into two optical paths by the third polarization beam splitter 9. The transmitted light is vertically polarized light, and the reflected light is horizontally polarized light. The energy ratio of the two is 100,000:1. After the vertically polarized light is reflected by the fast steering mirror 8, it is modulated into horizontally polarized light by the half-wave plate 7 whose optical axis is rotated to 45°. The horizontally polarized light is reflected by the third polarization beam splitter 9 and is modulated by the quarter-wave plate 2 to generate the light source of the detection telescope system. After the light transmitted by the third polarization beam splitter 9 is absorbed by the light absorption cone, its energy is lower than 10 of the laser light source -10 . When the light hits the telescope system, most of the backward stray light generated is modulated into vertically polarized light after passing through the quarter-wave plate 2, and enters the stray light detection optical path through the first polarization beam splitter 3. This light is transmitted by the second polarization beam splitter 5 and is coupled into the single-photon detector 13 by the optical coupler 12 together with the horizontally polarized light reflected by the second polarization beam splitter 5; after being reflected twice by the third polarization beam splitter 9 and the second polarization beam splitter 5, the light in this path is attenuated to 10 of the light source energy -10 , so it can be used to evaluate the stray light after being coupled with the stray light. The stray light from the third polarization beam splitter 9 transmitted by the second polarization beam splitter 5 will be absorbed by the second light absorption cone 6. When the light trap 11 is placed in the optical path, it absorbs the polarized light reflected by the third polarization beam splitter 9, and the single-photon detector 13 detects the backward scattered stray light generated by the telescope under test 1; when the light trap 11 is removed from the optical path, the single-photon detector 13 detects the backward scattered stray light and the local light generated by the telescope under test 1 to evaluate the stray light effect; different field-of-view stray lights are measured by adjusting the fast steering mirror 8; the depolarization condition of the stray light is measured by adjusting the angle of the quarter-wave plate 2.

Claims

1. A device for detecting the backscattered stray light of a laser transceiver common-aperture telescope, comprising a telescope under test (1), a quarter-wave plate (2), a polarization beam splitter, an absorbing cone, a half-wave plate (7), a fast steering mirror (8), a laser light source (10), a light trap (11), an optical coupler (12) and a single-photon detector (13), characterized in that: The laser generated by the laser light source (10) is split into two orthogonally polarized light beams by a third polarization beam splitter (9). After the vertically polarized light is reflected by the fast steering mirror (8), it is modulated into horizontally polarized light by the half-wave plate (7), and after being reflected by the first polarization beam splitter (3), a test light source is generated by modulation of the quarter-wave plate (2). After the test light source enters the telescope under test (1), backscattered stray light is generated. After the backscattered stray light passes through the quarter-wave plate (2), it is transmitted by the first polarization beam splitter (3) and the second polarization beam splitter (5). The transmitted light and the horizontally polarized light reflected by the second polarization beam splitter (5) are coupled into the single-photon detector (13) by the optical coupler (12); when the light trap (11) is placed in the optical path, it absorbs the polarized light reflected by the third polarization beam splitter (9), and the single-photon detector (13) detects the backscattered stray light generated by the telescope under test (1); when the light trap (11) is removed from the optical path, the single-photon detector (13) detects the backscattered stray light and the local light generated by the telescope under test (1), and the stray light effect of the interferometric telescope can be evaluated; the stray light in different fields of view is measured by adjusting the fast steering mirror (8); when the optical axis of the quarter-wave plate (2) is rotated to different angles, the depolarization condition of the stray light is detected; the first absorbing cone (4) and the second absorbing cone (6) respectively absorb the stray light transmitted by the first polarization beam splitter (3) and the second polarization beam splitter (5); The working wavelengths of the first polarization beam splitter (3), the second absorbing cone (6) and the third polarization beam splitter (9) are matched with the laser light source; The width and height of the light trap and the absorbing cone are greater than or equal to the width and height of the first polarization beam splitter (3), the second absorbing cone (6) and the third polarization beam splitter (9); The dynamic range of the fast steering mirror (8) is matched with the field of view of the telescope under test (1); The wavelength of the optical coupler (12) is matched with the wavelength of the laser light source (10), and the coupling efficiency is higher than 50%; 2. The backscattered stray light detection device for a laser transceiver co-aperture telescope according to claim 1, characterized in that, The laser light source (10) uses a pulsed laser, whose wavelength matches the designed wavelength of the telescope under test (1), and the energy is lower than the energy thresholds of each device. 10% of the energy -10 is within the dynamic range of the single-photon detector (13), and the repetition frequency is not higher than the operating frequency of the single-photon detector.

3. The backscattered stray light detection device for a laser transceiver co-aperture telescope according to claim 1, characterized in that, Within the field of view of the telescope, the polarization extinction ratio is better than 100000:1, transmitting horizontally polarized light and reflecting vertically polarized light.

4. A backscattered stray light detection device for a laser transceiver common aperture telescope according to claim 1, characterized in that The light trap (11) has an absorption efficiency better than 10 at the wavelength of the laser light source -5 , and the first light absorption cone (4) and the second light absorption cone (6) have an absorption efficiency better than 10 -5 .

5. A device for detecting the backscattered stray light of a laser transceiver co-aperture telescope according to claim 1, characterized in that, The sensitivity of the single-photon detector (13) is higher than 10 of the energy of the laser light source -10 , and the central wavelength is matched with the laser light source (10).

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