A laser transceiver co-boresight structure

Abstract

The application discloses a laser transceiving common-aperture structure and belongs to the technical field of beam deflection. The structure comprises a laser light source, a polarization beam splitter, a Faraday optical rotator, a first quarter-wave plate, a laser beam expander, a liquid crystal beam deflector, a second quarter-wave plate and a detector. The laser beam expander is arranged between the Faraday optical rotator and the liquid crystal beam deflector, so that the laser emitted from the Faraday optical rotator can be expanded by several times, and the aperture of the final emitted light beam is relatively large. In addition, the first quarter-wave plate and the second quarter-wave plate of the application can be common wave plates such as quartz wave plates and polymer wave plates, so that the energy loss is low, and the energy utilization rate is higher.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of light beam deflection technology, and in particular to a laser transceiver common-aperture structure. BACKGROUND

[0002] The light beam deflector is the core part of many optoelectronic information fields such as laser radar, laser guidance, laser imaging and remote sensing, target detection and attack, and the liquid crystal light beam deflector based on liquid crystal polarization grating is a new type of non-mechanical light beam deflection technology. This technology can simultaneously consider large aperture and large angle as two core indicators in the light beam deflection process, and can realize electrically controlled agile control, and is currently widely concerned at home and abroad.

[0003] The common-aperture structure is widely concerned due to its high aperture utilization rate, high transceiver consistency, small volume and light weight, and it is crucial to maintain its large aperture, high efficiency and high reliability on the basis of realizing laser transceiver common-aperture of the liquid crystal light beam deflector.

[0004] Patent No. CN106656325A discloses a high-speed single-light-source bidirectional free-space laser communication system. The base station downlink signal is modulated by an electro-optical modulator, coupled into free space by a first space-fiber coupling device, and then emitted by a first optical antenna. After the second optical antenna of the terminal receives the base station signal, it is coupled into the optical coupler by a second space-fiber coupling device. A part of the optical signal is detected and received by the second receiving module of the terminal to obtain the downlink signal data. Another part of the optical signal is incident into the reflective semiconductor optical amplifier, and then is erased and modulated, amplified and reflected back to the optical coupler by the reflective semiconductor optical amplifier. The reflected optical signal is received by the first receiving module of the base station to obtain the uplink signal data. Although this invention can greatly improve the transmission rate of the bidirectional free-space laser communication system and reduce the complexity of the communication equipment, it uses an optical circulator to separate the transmitted laser and the received laser, and has the problem of poor transceiver isolation.

[0005] The patent with the publication number CN108574533B discloses a common-aperture laser communication optical terminal based on a phased array, which comprises a communication laser source, a beam expander, a polarization beam splitter, a Faraday rotator, a polarization beam splitter prism, a lambda / 4 wave plate, a fine phased array scanning device, a liquid crystal adjustable wave plate one, a coarse scanning device, a liquid crystal adjustable wave plate two, a narrow-band filter, a polariscope, an objective lens, and a detector. Although the invention uses a Faraday rotator and combines a polarization beam splitter prism and a polariscope to realize the separation of transmitting laser and receiving laser, the aperture of the Faraday rotator, the aperture of the fine phased array scanning device, and the position of the beam expander greatly limit the actual working aperture of the invention. Moreover, due to the working mode of the fine phased array scanning device and the current technology of the liquid crystal adjustable wave plate, the invention still has problems such as low energy utilization. SUMMARY

[0006] The purpose of the present application is to solve the problems of small available aperture and large energy loss of the current laser transceiver common-aperture liquid crystal beam deflector by providing a laser transceiver common-aperture structure.

[0007] To achieve the above-mentioned purpose, the present application provides a laser transceiver common-aperture structure, which comprises a laser source, a polarization beam splitter, a Faraday rotator, a first quarter wave plate, a laser beam expander, a liquid crystal beam deflector, a second quarter wave plate, and a detector.

[0008] When transmitting communication laser, the laser source generates transmitting laser, which is incident to the polarization beam splitter, reflected inside the polarization beam splitter, and then passes through the Faraday rotator. After passing through the Faraday rotator, the polarization direction is rotated °. Then the transmitting laser is incident to the first quarter wave plate, and the polarization state of the transmitting laser changes from linearly polarized light to circularly polarized light after passing through the first quarter wave plate. Then the transmitting laser is incident to the liquid crystal beam deflector through the laser beam expander, and the direction of the transmitting laser beam is deflected in the liquid crystal beam deflector, while the polarization state remains circularly polarized light. Then the transmitting laser is incident to the second quarter wave plate, and the polarization state of the transmitting laser changes from circularly polarized light to linearly polarized light after passing through the second quarter wave plate. Finally, the transmitting laser is transmitted to the target.

[0009] When receiving the communication laser, the emitted incident laser first passes through the second quarter-wave plate, which changes the polarization state of the incident laser from linearly polarized light to circularly polarized light, and then the incident laser is incident into the liquid crystal beam deflector, in which the deflection of the emitted laser beam direction is realized, and the polarization state remains circularly polarized light, then the incident laser is incident on the first quarter-wave plate through the laser beam expander, and after passing through the first quarter-wave plate, the polarization state changes from circularly polarized light to linearly polarized light, then the incident laser passes through the Faraday rotator, and after passing through the Faraday rotator, the polarization direction continues to rotate by 45°, and finally the incident laser is incident into the polarization beam splitter, and after reflection in the polarization beam splitter, the incident probe is obtained.

[0010] The laser beam expander is used to realize the expansion of the laser emission beam and the contraction of the incident laser beam, so that the aperture of the Faraday rotator matches the aperture of the liquid crystal beam deflector.

[0011] Further, the laser source emits linearly polarized light, which includes but is not limited to ultraviolet light, visible light or infrared light.

[0012] Further, the polarization beam splitter is a beam splitting device for two orthogonal linearly polarized lights, which couples the emission laser source into the structure and couples the incident laser beam out of the structure to the probe.

[0013] Further, the liquid crystal beam deflector is a cascade combination of a liquid crystal wave plate and a liquid crystal polarization grating, the liquid crystal wave plate realizes switching or maintaining of left-handed circular polarization state and right-handed circular polarization state, and the liquid crystal polarization grating realizes beam deflection, and the combination of the two realizes large-angle, non-continuous one-dimensional or two-dimensional beam deflection and scanning.

[0014] Further, the angle between the linear polarization direction of the laser emitted from the Faraday rotator and the fast axis direction of the first quarter-wave plate is 45° or 135°, and the fast axis of the second quarter-wave plate can be directed to any direction on the exit plane of the liquid crystal beam deflector.

[0015] Further, the first quarter-wave plate and the second quarter-wave plate include but are not limited to quartz wave plates, polymer wave plates or liquid crystal wave plates.

[0016] Advantages of the present application

[0017] Compared with the prior art, firstly, the application realizes the expansion of the laser emission beam and the contraction of the incident laser beam by using a laser expander, matches the aperture of the Faraday rotator with the aperture of the liquid crystal beam deflector, and places the laser expander between the Faraday rotator and the liquid crystal beam deflector, so that the laser emitted from the Faraday rotator can be expanded by several times (for example, 10 times), and finally the aperture of the emitted beam is relatively large; secondly, the first quarter wave plate and the second quarter wave plate of the application can be common wave plates such as quartz wave plates and polymer wave plates, the energy loss is low, and the energy utilization rate can be very high. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 A laser transceiving common aperture structure provided by the application is shown in the figure;

[0019] Fig. 2 A structure schematic diagram of the liquid crystal beam deflector provided by the application is shown in the figure;

[0020] In the figure,

[0021] 1, laser source; 2, polarization beam splitter; 3, Faraday rotator; 4, first quarter wave plate; 5, laser expander; 6, liquid crystal beam deflector; 7, second quarter wave plate; 8, detector; 9, target;

[0022] 61, liquid crystal wave plate; 62, liquid crystal polarization grating; 63, circuit driving board. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions of the application, the application will be further described in detail below with reference to the drawings.

[0024] Referring to Figs. 1-2 the figure;

[0025] A laser transceiving common aperture structure, the structure comprising: a laser source 1, a polarization beam splitter 2, a Faraday rotator 3, a first quarter wave plate 4, a laser expander 5, a liquid crystal beam deflector 6, a second quarter wave plate 7, a detector 8;

[0026] When transmitting communication laser, the laser source 1 generates transmitting laser, which is incident to the polarization beam splitter 2, reflected inside the polarization beam splitter 2, passes through the Faraday rotator 3, and then is incident to the first quarter-wave plate 4. After the transmitting laser passes through the first quarter-wave plate 4, the polarization state changes from linear polarization to circular polarization. Then the transmitting laser passes through the laser expander 5 and is incident to the liquid crystal beam deflector 6, in which the direction of the transmitting laser beam is deflected, and the polarization state remains circular polarization. Then the transmitting laser is incident to the second quarter-wave plate 7, and after passing through the second quarter-wave plate 7, the polarization state changes from circular polarization to linear polarization. Finally, the transmitting laser is incident to the target 9.

[0027] When receiving communication laser, the incident laser first passes through the second quarter-wave plate 7, which changes the polarization state of the incident laser from linear polarization to circular polarization. Then the incident laser is incident to the liquid crystal beam deflector 6, in which the direction of the transmitting laser beam is deflected, and the polarization state remains circular polarization. Subsequently, the incident laser passes through the laser expander 5 and is incident to the first quarter-wave plate 4. After passing through the first quarter-wave plate 4, the polarization state changes from circular polarization to linear polarization. Then the incident laser passes through the Faraday rotator 3, and after passing through the Faraday rotator 3, the polarization direction is rotated by 45°. Finally, the incident laser is incident to the polarization beam splitter 2 and is reflected inside the polarization beam splitter 2 to the detector 8.

[0028] The laser expander 5 is used to expand the transmitting laser beam and shrink the incident laser beam, so that the aperture of the Faraday rotator 3 matches the aperture of the liquid crystal beam deflector 6.

[0029] Further, the laser source 1 emits linearly polarized laser, which includes but is not limited to ultraviolet light, visible light, or infrared light.

[0030] Further, the polarization beam splitter 2 is a beam splitting device for two orthogonal linearly polarized lights, which couples the transmitting laser source in and couples the incident laser beam out to the detector 8.

[0031] Further, the liquid crystal beam deflector 6 is a cascade combination of a liquid crystal wave plate and a liquid crystal polarization grating. The liquid crystal wave plate switches or maintains the left-handed circular polarization state and the right-handed circular polarization state, and the liquid crystal polarization grating deflects the light beam. The combination of the two achieves large-angle, non-continuous one-dimensional or two-dimensional light beam deflection and scanning.

[0032] Further, the angle between the linear polarization direction of the laser emitted from the Faraday rotator 3 and the fast axis direction of the first quarter-wave plate 4 is 45° or 135°, and the fast axis of the second quarter-wave plate 7 can be directed to any direction on the exit plane of the liquid crystal beam deflector 6.

[0033] Furthermore, the first quarter-wave plate 4 and the second quarter-wave plate 7 include, but are not limited to, quartz wave plates, polymer wave plates, or liquid crystal wave plates.

[0034] Example 1

[0035] like Fig. 2 As shown, this embodiment provides a schematic diagram of a liquid crystal beam deflector 6 composed of four cascaded liquid crystal waveplates 61 and four liquid crystal polarization gratings 62. In this embodiment, the liquid crystal polarization grating 62 is characterized by its optical axis continuously changing within one period, satisfying the following relationship:

[0036]

[0037] In the formula, Λ is the period of the liquid crystal polarization grating. The most important characteristic of the liquid crystal polarization grating 62 is that it can completely deflect a beam of circularly polarized light to the +1st or -1st order with 100% theoretical diffraction efficiency. The direction of deflection is controlled by its incident polarization state. Each liquid crystal polarization grating 62 can be regarded as a binary (±1st order, passive liquid crystal polarization grating) or ternary (0th order and ±1st order, active liquid crystal polarization grating) beam deflection device. In this embodiment, the liquid crystal waveplate 61 is a nematic liquid crystal waveplate with an antiparallel alignment liquid crystal cell structure. The birefringence difference Δn = 0.12 and the thickness of the liquid crystal waveplate exceeds the half-wave condition d = λ / (2*Δn) = 4.4 μm, with a measured value of 5.3 μm. Under the control of AC voltage, it can switch or maintain the left-hand circular polarization state and the right-hand circular polarization state, thus realizing four forms of polarization state conversion: switching from left-hand circular polarization light to right-hand circular polarization light, maintaining left-hand circular polarization light to left-hand circular polarization light, switching right-hand circular polarization light to left-hand circular polarization light, and maintaining right-hand circular polarization light to right-hand circular polarization light.

[0038] In this embodiment, the emitted laser beam is 1064nm circularly polarized light. The four liquid crystal waveplates 61 have the same structure, and the periods of the four liquid crystal polarization gratings 62 are 190.5μm, 95.3μm, 47.6μm, and 23.8μm, respectively, to achieve beam deflection and scanning in a one-dimensional horizontal direction within a range of ±4.9° and ±0.64°.

[0039] In this embodiment, the Faraday rotator 3 has an aperture of Φ3mm, the liquid crystal polarization grating 62 has an aperture of 60mm*52mm, and the emitted laser beam has an aperture of Φ30mm.

[0040] In this embodiment, the Faraday rotator 3 has a transmittance of 98%, the first quarter-wave plate 4 and the second quarter-wave plate 7 have a transmittance of 99.5%, the liquid crystal wave plate 61 has an energy transmittance of 95.2%, the liquid crystal polarization grating 62 has an intrinsic diffraction efficiency of 99.80%, the liquid crystal polarization grating 62 has an energy transmittance of 99.47%, and the overall energy utilization efficiency of the liquid crystal beam deflector 6 is about 80%.

[0041] The above description is merely that of the preferred embodiments of the present application and is not intended to limit the present application. The present application can be variously changed and modified by those skilled in the art without departing from the spirit and scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. A laser transceiver common aperture structure, characterized in that, The structure includes: a laser source (1), a polarization beam splitter (2), a Faraday rotator (3), a first quarter-wave plate (4), a laser beam expander (5), a liquid crystal beam deflector (6), a second quarter-wave plate (7), and a detector (8). When emitting laser, the laser source (1) generates the emitted laser. The emitted laser is incident on the polarization beam splitter (2). After being reflected inside the polarization beam splitter (2), it passes through the Faraday rotator (3). After passing through the Faraday rotator (3), the polarization direction is rotated by 45°. Then the emitted laser is incident on the first quarter-wave plate (4). After passing through the first quarter-wave plate (4), the polarization state of the emitted laser changes from linearly polarized light to circularly polarized light. Then the emitted laser is incident on the liquid crystal beam deflector (6) through the laser beam expander (5). The direction of the emitted laser beam is deflected in the liquid crystal beam deflector (6), while the polarization state remains circularly polarized light. Then the emitted laser is incident on the second quarter-wave plate (7). After passing through the second quarter-wave plate (7), the polarization state of the emitted laser changes from circularly polarized light to linearly polarized light. Finally, it is emitted towards the target (9). When receiving laser light, the emitted incident laser light first passes through the second quarter-wave plate (7), which changes the polarization state of the incident laser light from linearly polarized light to circularly polarized light. Then the incident laser light is incident into the liquid crystal beam deflector (6), where the direction of the emitted laser beam is deflected, while the polarization state remains circularly polarized. Subsequently, the incident laser light passes through the laser beam expander (5) and is incident onto the first quarter-wave plate (4). After passing through the first quarter-wave plate (4), the polarization state changes from circularly polarized light to linearly polarized light. Then the incident laser light passes through the Faraday rotator (3), and the polarization direction continues to rotate by 45° after passing through the Faraday rotator (3). Finally, it is incident onto the polarization beam splitter (2), and after being reflected inside the polarization beam splitter (2), it is incident onto the detector (8). The laser beam expander (5) is used to expand the laser emitted beam and shrink the incident laser beam, so that the aperture of the Faraday rotator (3) matches the aperture of the liquid crystal beam deflector (6).

2. The laser transceiver common aperture structure according to claim 1, characterized in that, The laser source (1) emits linearly polarized light, which is ultraviolet light, visible light or infrared light.

3. The laser transceiver common aperture structure according to claim 1, characterized in that, The polarization beam splitter (2) is a beam splitting device for two orthogonally linearly polarized lights. It couples the emitted laser light source into the structure and couples the incident laser beam out of the structure to the detector (8).

4. The laser transceiver common aperture structure according to claim 1, characterized in that, The liquid crystal beam deflector (6) is a cascaded combination of a liquid crystal waveplate and a liquid crystal polarization grating. The liquid crystal waveplate realizes the switching or maintenance of the left-hand circular polarization state and the right-hand circular polarization state, and the liquid crystal polarization grating realizes the beam deflection. The combination of the two realizes large-angle, discontinuous one-dimensional or two-dimensional beam deflection and scanning.

5. The laser transceiver common aperture structure according to claim 1, characterized in that, The linear polarization direction of the laser emitted from the Faraday rotator (3) is at an angle of 45° or 135° to the fast axis of the first quarter-wave plate (4), and the fast axis of the second quarter-wave plate (7) can be directed toward any direction of the emission plane of the liquid crystal beam deflector (6).

6. The laser transceiver common aperture structure according to claim 1, characterized in that, The first quarter-wave plate (4) and the second quarter-wave plate (7) are: quartz wave plates, polymer wave plates or liquid crystal wave plates.

Images