Optical circulator and coaxial laser radar

Abstract

The invention discloses an optical circulator and a coaxial laser radar, and belongs to the technical field of optical processing. The optical circulator comprises a first birefringent crystal, a second birefringent crystal, a third birefringent crystal, a Faraday rotating mirror and a half-wave plate, and the first birefringent crystal and the third birefringent crystal are arranged in parallel. The first birefringent crystal is used for receiving an optical signal input by the first optical input port and reflecting the optical signal to the second optical receiving port; the third birefringent crystal is used for receiving an optical signal input by the second optical input port and reflecting the optical signal to the first optical receiving port; and the third port is used for outputting the emitted light signal transmitted by the second birefringent crystal, receiving the reflected light signal and returning the reflected light signal to the second birefringent crystal. According to the invention, the isolation degree of the optical circulator is improved, and the overall performance of the coaxial laser radar is improved.

Description

Technical Field

[0001] The present application relates to the field of light processing technology, and in particular to an optical circulator and a coaxial laser radar. Background Art

[0002] Laser radar (LiDAR) detects the position, surface reflectivity and speed of a target object by emitting a laser beam to the target object and receiving the beam reflected from the target object. Coaxial LiDAR uses the same optical path for emitting and receiving beams, which can reduce costs and size. In addition, since only ambient light from a single angle can enter when receiving the beam, the signal-to-noise ratio of LiDAR is greatly improved.

[0003] Many coaxial laser radars use a semi-transmissive and semi-reflective lens design, that is, the laser emission signal reaches the scanning component through the lens, and the receiving signal reaches the photodetector through the reflector; or the laser emission signal reaches the scanning component through the reflector, and the receiving signal reaches the photodetector through the lens. In this method, the same lens takes into account both the reception and transmission of the coaxial laser radar, which has a great impact on the receiving efficiency; it is difficult to avoid crosstalk with such a single lens, that is, the transmitted light is directly reflected into the receiving light path, and the transmitted light and the received light have low directivity, thus causing system crosstalk. If absorbing ink is added to the edge, the process is cumbersome; a single lens cannot distinguish the polarization state of the return light, and is not suitable for frequency modulated continuous wave (FMCW); in addition, the receiving surface of such a lens often has certain size requirements, which is not suitable for future all-solid-state laser radars.

[0004] Many FMCW LiDARs use optical circulators to achieve coaxial effects. Optical circulators are non-reciprocal optical passive devices with multiple input and output ports. They are widely used in optical communication scenarios because they have functions such as optical circulation and optical isolation, and have low internal insertion loss. However, since the isolation requirements of LiDARs are much greater than those of optical communications (about 3 orders of magnitude or more), directly using current circulators often causes LiDAR misdetection and limits system performance.

[0005] Application Contents

[0006] To this end, the present application provides an optical circulator and a coaxial laser radar to improve the isolation of the optical circulator and improve the overall performance of the coaxial laser radar.

[0007] In order to achieve the above-mentioned object, the present application provides an optical circulator in a first aspect, comprising:

[0008] A first birefringent crystal, a second birefringent crystal, a third birefringent crystal, a Faraday rotator and a half-wave plate, wherein the first birefringent crystal is arranged in parallel with the third birefringent crystal and is arranged in sequence with the Faraday rotator, the half-wave plate and the second birefringent crystal:

[0009] The first birefringent crystal is used to receive the optical signal input from the first optical input port, and to reflect the optical signal to the second optical receiving port; the third birefringent crystal is used to receive the optical signal input from the second optical input port, and to reflect the optical signal to the first optical receiving port; the third port is used to output the emitted optical signal transmitted by the second birefringent crystal, and to receive the reflected optical signal and return it to the second birefringent crystal.

[0010] Optionally, the optical axis directions of the second birefringent crystal and the third birefringent crystal are the same; the optical axis directions of the first birefringent crystal and the third birefringent crystal are different;

[0011] The first birefringent crystal, the second birefringent crystal and the third birefringent crystal have the same thickness.

[0012] Optionally, the first optical input port is not adjacent to the first optical receiving port.

[0013] and used to carry optical signals having the same polarization state;

[0014] The second optical input port is not adjacent to the second optical receiving port, and is used to carry optical signals having the same polarization state.

[0015] Optionally, the first optical input port is adjacent to the second optical receiving port, or the second optical input port is adjacent to the first optical receiving port.

[0016] Optionally, the first optical input port, the second optical receiving port, the second optical input port and the first optical receiving port are four ports arranged on the same end face of the optical circulator, and a spacing between the four ports is greater than 250 microns.

[0017] A second aspect of the present application provides a coaxial laser radar, comprising a transmitting unit, an optical fiber array, the optical circulator according to any one of the first aspects, a first receiving unit and a second receiving unit;

[0018] A transmitting unit, configured to transmit a first transmitting optical signal and a second transmitting optical signal having different polarization states;

[0019] The optical fiber array is used to guide the first transmitted optical signal and the second transmitted optical signal to the optical circulator; and to guide the echo optical signal of the first transmitted optical signal transmitted back by the optical circulator to the first receiving unit, and guide the echo optical signal of the second transmitted optical signal to the second receiving unit.

[0020] Optionally, the optical fiber array includes a first input waveguide, a second input waveguide, a first receiving waveguide, and a second receiving waveguide;

[0021] The first input waveguide matches the first optical input port, the second input waveguide matches the second optical input port, the first receiving waveguide matches the first optical receiving port, and the second receiving waveguide matches the second optical receiving port.

[0022] Optionally, the transmitting unit includes a laser, an electro-optical modulator, a frequency modulation generator, a polarization beam splitter rotator, a first beam splitter and a second beam splitter;

[0023] The laser is used to output a continuous wave into the photoelectric modulator;

[0024] The electro-optical modulator is used to modulate the frequency of the continuous wave onto the optical signal under the action of the frequency modulation signal generated by the frequency modulation generator, and the adjusted optical signal is transmitted to the polarization beam splitter rotator;

[0025] The polarization beam splitter rotator is used to split the optical signal into a first transmission optical signal and a second transmission optical signal with different polarization states, output the first transmission optical signal through the first optical splitter, and output the second transmission optical signal through the second optical splitter.

[0026] Optionally, the first receiving unit includes a first beam combiner, a first photodetector and a first receiving circuit; the second receiving unit includes a second beam combiner, a second photodetector and a second receiving circuit;

[0027] The first beam combiner receives the echo optical signal of the first transmitted optical signal transmitted back by the optical circulator, and processes the echo optical signal through the first photodetector and the first receiving circuit;

[0028] The second beam combiner receives the echo optical signal of the second transmitted optical signal transmitted back by the optical circulator, and processes the echo optical signal via the second photodetector and the second receiving circuit.

[0029] Optionally, the first beam combiner, the second beam combiner, the first beam splitter and the second beam splitter are implemented using an integrated photonic chip.

[0030] This application has the following advantages:

[0031] Through the cooperation of the first birefringent crystal, the second birefringent crystal, the third birefringent crystal, the Faraday rotator and the half-wave plate set on the optical circulator, the positions of the light output and return light of the optical signals in different polarization states are changed, and the dual optical input port and the dual optical receiving port are realized, thereby improving the directivity of the optical circulator, that is, the isolation, and achieving the purpose of optical ring and optical isolation, so as to meet the isolation requirements of the laser radar. Moreover, after being applied to the laser radar, the overall performance of the laser radar can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present application, but do not constitute a limitation to the present application.

[0033] Figure 1 A schematic diagram of the structure of an optical circulator provided in an embodiment of the present application;

[0034] Figure 2 A schematic diagram of the working principle of an optical circulator when transmitting an optical signal provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of the working principle of an optical circulator when receiving an optical signal provided in an embodiment of the present application;

[0036] Figure 4 A port diagram of an optical circulator provided in an embodiment of the present application;

[0037] Figure 5 A schematic diagram of the structure of a coaxial laser radar provided in an embodiment of the present application;

[0038] Figure 6 A schematic diagram of the structure of an optical fiber array provided in an embodiment of the present application;

[0039] Figure 7 A schematic diagram of the structure of a transmitting unit provided in an embodiment of the present application;

[0040] Figure 8 A schematic diagram of the structure of a laser provided in an embodiment of the present application;

[0041] Fig. 9 A schematic diagram of the structure of a wavelength sensing module provided in an embodiment of the present application;

[0042] Fig.10 A schematic diagram of the structure of an optical filter provided in an embodiment of the present application;

[0043] Fig.11 A schematic diagram of an integrated structure of a wavelength sensing module and an optical filter provided in an embodiment of the present application;

[0044] Fig.12 A schematic diagram comparing the material properties of a birefringent crystal provided in an embodiment of the present application. DETAILED DESCRIPTION

[0045] The specific implementation of the present application is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present application, and is not used to limit the present application.

[0046] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0047] The terms used in this application are only used to describe specific embodiments and are not intended to limit the present application.As used in this application, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0048] When the terms “comprising” and / or “made of…” are used in this application, it specifies the existence of the stated features, integers, steps, operations, elements and / or components, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0049] Unless otherwise defined, all terms (including technical and scientific terms) used in this application have the same meaning as those commonly understood by those of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this application, and will not be interpreted as having an idealized or overly formal meaning unless explicitly defined in this application.

[0050] In a first aspect, an embodiment of the present application provides an optical circulator, which is a five-port optical circulator. Figure 1 As shown, the first birefringent crystal 10, the second birefringent crystal 11, the third birefringent crystal 12, the Faraday rotator (FR) 13 and the half-wave plate (λ / 2WP) 14, the first birefringent crystal 10 is parallel to the third birefringent crystal 12, and is arranged sequentially with the Faraday rotator 13, the half-wave plate 14 and the second birefringent crystal 11.

[0051] The first birefringent crystal 10 is used to receive the optical signal input from the first optical input port TX1, and reflect the optical signal to the second optical receiving port RX2; the third birefringent crystal 12 is used to receive the optical signal input from the second optical input port TX2, and reflect the optical signal to the first optical receiving port RX1; the third port 15 is used to output the emission optical signal transmitted by the second birefringent crystal 11, and receive the reflected optical signal and return it to the second birefringent crystal 11. The third port 15 serves as an optical emission outlet and an optical reflection interface to achieve a coaxial effect.

[0052] In some embodiments, the first birefringent crystal 10, the second birefringent crystal 11 and the third birefringent crystal 12 have the same thickness. The optical axis directions of the second birefringent crystal 11 and the third birefringent crystal 12 are the same; the optical axis directions of the first birefringent crystal 10 and the third birefringent crystal 12 are different. This ensures that the O light or the E light can return to the same horizontal axis after being deflected twice.

[0053] In some embodiments, the first optical input port TX1 is not adjacent to the first optical receiving port RX1, and is used to carry optical signals with the same polarization state; the second optical input port TX2 is not adjacent to the second optical receiving port RX2, and is used to carry optical signals with the same polarization state. The purpose of this is to make the physical interval of the transmission of optical signals with the same polarization state as large as possible, to prevent the light reflected from the crystal surface of the optical circulator from directly entering the optical input port from the optical receiving port, causing crosstalk. For example, avoid entering the first optical input port TX1 from the first optical receiving port RX1, or entering the second optical input port TX2 from the second optical receiving port RX2.

[0054] In some embodiments, the first optical input port TX1 is adjacent to the second optical receiving port RX2, or the second optical input port TX2 is adjacent to the first optical receiving port RX1. The first optical input port TX1 and the second optical receiving port RX2 carry optical signals with different polarization states. Even if an optical signal is transmitted from the second optical receiving port RX2 to the first optical input port TX1, it cannot be mixed subsequently and cannot cause crosstalk. Similarly, the second optical input port TX2 and the first optical receiving port RX1 will not cause crosstalk.

[0055] When transmitting an optical signal, the working principle of the optical circulator is as follows: Figure 2 As shown, light signals of different polarization states enter the optical circulator from different positions, wherein, when the light signal enters for the first time, the first birefringent crystal (BC1) 10 and the third birefringent crystal (BC3) 12 have different optical axis directions, ensuring that the light signals of two different polarization states are not refracted; the light signal passes through the Faraday rotator 13, and the deflection state changes by 45 degrees. Due to its own magnetic field characteristics, this deflection is independent of the incident direction of the light signal; then, the light signal passes through the half-wave plate 14, and the deflection state changes by 45 degrees, restoring to the original state at the time of incidence; after passing through the second birefringent crystal (BC2) 11, the light path is deflected due to the different refractive indices encountered by the light signal of the polarization state transmitted through the first birefringent crystal 10, and after converging at the end of the second birefringent crystal 11 with the light signal of the polarization state transmitted through the third birefringent crystal 12, they are output together and enter the collimator.

[0056] When receiving optical signals, the optical circulator works as follows: Figure 3As shown, the optical signal reflected from the target object is transmitted to the second birefringent crystal (BC2) 11 through the third port 15, and optical signals of different polarization states are deflected to different positions; after passing through the half-wave plate 14, the polarization state changes by 45 degrees; then after passing through the Faraday rotator 13, the polarization state changes by 45 degrees again; compared with the optical signal before entering the half-wave plate 14, the optical signal at this time has undergone a 90-degree polarization state change, and the two polarization states before and after the change are both E light (Extraordinary) for the first birefringent crystal (BC1) 10 and the third birefringent crystal (BC3) 12, and the optical signal deflected by the first birefringent crystal 10 enters the second optical signal receiving end RX2, and the optical signal deflected by the third birefringent crystal 12 enters the first optical signal receiving end RX1.

[0057] It should be noted that Figure 2 and Figure 3 The deflection conditions shown in are only examples, and the system can also work normally when all light polarization states are deflected by 90 degrees.

[0058] In some embodiments, the first optical input port TX1, the second optical receiving port RX2, the second optical input port TX2 and the first optical receiving port RX1 are four ports arranged on the same end face of the optical circulator, and the spacing between the four ports is greater than 250 microns. In an exemplary embodiment, the spacing between the four ports is greater than 250 microns and is an integer multiple of 125 microns. The circulator can be a device operating under optical fiber, waveguide or spatial light conditions. Under different working conditions, the structure of the circulator may be slightly different. For example, when it needs to be connected to an optical fiber array, there needs to be enough space to place the optical fiber, so the circulator port spacing must be greater than 250 microns. When working under a spatial light environment, this design point does not need to be considered.

[0059] The design of the optical circulator provided in the embodiment of the present application achieves the functions of optical circulation and optical isolation by modifying the existing circulator structure, and utilizes birefringent crystals to change the positions of light output and return light of light in different polarization states, thereby greatly improving the directionality of the circulator, that is, the isolation, so that the isolation requirements of the laser radar can be met.

[0060] Figure 4 The figure shows a port schematic diagram of the optical circulator provided in the embodiment of the present application. Compared with the traditional optical circulator, the difference is that the optical circulator provided in the embodiment of the present application has dual optical input ports (i.e., output 1 and output 2) and dual optical receiving ports (i.e., receiving 1 and receiving 2), and the same port is used for light output and light reception, so that it can be used with the coherent receiving chip of the frequency modulated continuous wave laser radar, because the polarization state of light must be consistent when performing coherent detection, and the role of using dual ports is to input or receive optical signals of different polarization states into or from different positions to avoid crosstalk.

[0061] In a second aspect, the present application embodiment provides a coaxial laser radar, such as Figure 5 The structure diagram of the coaxial laser radar is shown, which mainly includes a transmitting unit 501, an optical circulator 503, a first receiving unit 504 and a second receiving unit 505. The specific structure of the optical circulator 503 refers to the description of the optical circulator in the first aspect, which will not be repeated here.

[0062] The transmitting unit 501 is used to transmit a first transmitting optical signal and a second transmitting optical signal having different polarization states;

[0063] The optical circulator 503 is used to receive the first transmitted optical signal and the second transmitted optical signal, and guide the returned echo optical signal of the first transmitted optical signal to the first receiving unit 504 , and guide the echo optical signal of the second transmitted optical signal to the second receiving unit 505 .

[0064] In some embodiments, the coaxial laser radar further includes an optical fiber array 502, which is used to guide the first transmitted optical signal and the second transmitted optical signal to the optical circulator 503; and is used to guide the echo optical signal of the first transmitted optical signal transmitted back by the optical circulator 503 to the first receiving unit 504, and guide the echo optical signal of the second transmitted optical signal to the second receiving unit 505. The optical fiber array facilitates the coupling of the structures of the optical circulator, the transmitting unit, the first receiving unit, and the second receiving unit. When the structures of the optical circulator, the transmitting unit, the first receiving unit, and the second receiving unit can be directly coupled, the optical fiber array can be omitted.

[0065] Among them, the coaxial laser radar also includes a collimating lens 506. The optical signal output by the optical circulator 503 is emitted to the target object after passing through the collimating lens 506, and the echo optical signal reflected by the target object is also received by the optical circulator 503 after passing through the collimating lens 506.

[0066] In some embodiments, Figure 6 The figure is a schematic diagram of the structure of the optical fiber array 502, which includes a first input waveguide 601, a second input waveguide 602, a first receiving waveguide 603 and a second receiving waveguide 604; the first input waveguide 601 matches the first optical input port TX1, the second input waveguide 602 matches the second optical input port TX2, the first receiving waveguide 603 matches the first optical receiving port RX1, and the second receiving waveguide 604 matches the second optical receiving port RX2.

[0067] The first input waveguide 601 and the second input waveguide 602 in the middle of the optical fiber array 502 correspond to the TX1 and TX2 ports, carry output signals, but have different polarization states, and the first receiving waveguide 603 and the second receiving waveguide 604 on both sides correspond to the RX1 and RX2 ports respectively, and receive optical signals with different polarization states. Among them, the waveguide corresponding to TX1 is not adjacent to the waveguide corresponding to RX1, but can carry optical signals with the same polarization state, and the waveguide corresponding to TX2 is similar to the waveguide corresponding to RX2. The purpose of this design is to make the physical interval of the transmission of optical signals with the same polarization state as large as possible, to prevent the reflected light on the crystal surface of the optical circulator 503 from being directly transmitted from the output to the input, causing crosstalk. The waveguide corresponding to TX1 is adjacent to the waveguide corresponding to RX2, but the polarization states of the optical signals carried by the waveguides are different. Even if there is an optical signal returned from the end face, it cannot be mixed with the intrinsic signal in the second receiving unit 505, and cannot cause system crosstalk. The waveguide corresponding to TX2 is adjacent to the waveguide corresponding to RX1, which is similar.

[0068] In some embodiments, Figure 7 It is a schematic diagram of the structure of the transmitting unit. The transmitting unit 501 includes a laser 701, an electro-optical modulator 702, a frequency modulation generator 703, a polarization beam splitter rotator (PBSR) 704, a first beam splitter 705 and a second beam splitter 706.

[0069] Laser 701, used to output continuous wave into optoelectronic modulator 702;

[0070] The electro-optical modulator 702 is used to modulate the continuous wave frequency to the optical signal under the action of the frequency modulation signal generated by the frequency modulation generator 703, and the adjusted optical signal is transmitted to the polarization beam splitter rotator 704;

[0071] The polarization beam splitter rotator 704 is used to split the optical signal into a first transmission optical signal and a second transmission optical signal with different polarization states, output the first transmission optical signal through the first optical splitter 705 , and output the second transmission optical signal through the second optical splitter 706 .

[0072] In some embodiments, Figure 7 As shown, the first receiving unit 504 includes a first beam combiner 5041 , a first photodetector 5042 and a first receiving circuit 5043 ; the second receiving unit 505 includes a second beam combiner 5051 , a second photodetector 5052 and a second receiving circuit 5053 .

[0073] The first beam combiner 5041 receives the echo optical signal of the first transmitted optical signal transmitted back by the optical circulator 503, and processes the echo optical signal through the first photodetector 5042 and the first receiving circuit 5043; the second beam combiner 5051 receives the echo optical signal of the second transmitted optical signal transmitted back by the optical circulator 503, and processes the echo optical signal through the second photodetector 5052 and the second receiving circuit 5053.

[0074] In some embodiments, the first beam combiner, the second beam combiner, the first beam splitter, and the second beam splitter are implemented using an integrated photonic chip.

[0075] In an exemplary embodiment, Figure 8 It is a schematic diagram of the structure of a laser 701, which may include a continuous wave laser 802, a wavelength sensing module 804, and an optical filter 806. These three modules together can provide a high-quality continuous wave laser beam.

[0076] The continuous wave laser 802 outputs a continuous wave laser beam 801. The laser beam will be used to detect or scan a target object. The continuous wave laser 802 can be, for example, a solid-state laser (such as a vertical cavity surface emitting laser (VCSEL), an edge emitting laser (EEL) or an external cavity semiconductor laser (ECDL)), a laser diode, or a fiber laser. The operating wavelength of the continuous wave laser 802 can be 650nm to 1150nm, 800nm ​​to 1000nm, 850nm to 950nm or 1300nm to 1600nm. The operating wavelength of the continuous wave laser 802 can be fixed or tunable. In one or more embodiments, the continuous wave laser 802 can also include an optical component optically coupled to the continuous wave laser 802 for collimating or focusing the light beam emitted by the continuous wave laser 802.

[0077] The wavelength sensing module 804 is optically coupled to the continuous wave laser 802. The wavelength sensing module 804 is configured to receive a portion 801-1 of the continuous wave laser beam 801 output by the continuous wave laser 802, and output a sensing electrical signal 803 indicating the central wavelength of the continuous wave laser beam 801. That is, the wavelength sensing module 804 can realize the measurement of the central wavelength of the continuous wave laser beam 801, which includes the photoelectric conversion from the optical signal 801-1 to the electrical signal 803. The sensing electrical signal 803 indicates the central wavelength of the continuous wave laser beam 801, which means that the central wavelength of the continuous wave laser beam 801 can be uniquely determined from the size of the sensing electrical signal 803. The size of the sensing electrical signal 803 can be linearly related or nonlinearly related to the central wavelength of the continuous wave laser beam 801. The linear relationship means that if the central wavelength of the continuous wave laser beam 801 is changed, the size of the sensing electrical signal 803 is also changed accordingly, and the slope of the change in the size of the sensing electrical signal 803 relative to the change in the central wavelength is constant for different central wavelengths. The nonlinear relationship means that if the central wavelength of the continuous wave laser beam 801 is changed, the magnitude of the sensing electrical signal 803 also changes accordingly, and the slope of the magnitude change of the sensing electrical signal 803 relative to the magnitude change of the central wavelength is not constant for different central wavelengths. The wavelength sensing module 804 may include, but is not limited to, various known wavelength measurement technologies based on interferometers, gratings, prisms, etc.

[0078] In some embodiments, the magnitude of the sensing electrical signal 803 may be linearly related to the central wavelength of the continuous wave laser beam 801. A linear relationship is much simpler in terms of operation than a nonlinear relationship. In this way, since the mapping relationship from the central wavelength to the magnitude of the electrical signal is relatively simple, the subsequent signal processing of the sensing electrical signal 803 to determine the central wavelength of the continuous wave laser beam 801 can reduce the computational overhead required.

[0079] In some embodiments, in addition to realizing a linear relationship between the sensed electrical signal 803 and the central wavelength of the continuous wave laser beam 801, it is also desired that the wavelength sensing module 804 has the advantages of fast response speed and easy integration. Fig. 9 Specifically, the wavelength sensing module 804 may be implemented based on an optical add-drop ring resonator.

[0080] The optical filter 806 is also optically coupled to the continuous wave laser 802. The passband of the optical filter 806 has a central wavelength set according to the sensing electrical signal 803 output by the wavelength sensing module 804, and the central wavelength is set to match the central wavelength of the continuous wave laser beam 801. The optical filter 806 can be a passband filter, and the central wavelength of the passband filter is configurable. In some embodiments, the optical filter 806 can receive the sensing electrical signal 803 from the wavelength sensing module 804, and determine the central wavelength of the continuous wave laser beam 801 according to the sensing electrical signal 803, and be configured to match the central wavelength of its own passband with the central wavelength of the continuous wave laser beam 801, that is, substantially equal. In some embodiments, the measurement of the central wavelength of the continuous wave laser beam 801 by the wavelength sensing module 804 can be completed in real time (including near real time), that is, the wavelength sensing module 804 has a high response speed. This can be achieved by, for example, combining the following method. Fig. 9 The wavelength sensing module 804 described above is implemented. Further, in some embodiments, the setting of the center wavelength of the passband of the optical filter 806 based on the sensed electrical signal 803 can also be completed in real time (including near real time). This means that starting from receiving a portion 801-1 of the continuous wave laser beam, the setting of the passband center wavelength of the optical filter 806 can be completed relatively quickly (including, for example, femtoseconds, nanoseconds, milliseconds) without a large delay.

[0081] In some embodiments, in order to set the central wavelength of the passband of the optical filter 806 based on the sensing electrical signal 803, the laser 701 may further include a filter setting module (not shown in the figure). The filter setting module may be included inside or outside the optical filter 806. The filter setting module is configured to receive the sensing electrical signal 803, convert the sensing electrical signal 803 into a physical quantity that can set the central wavelength of the passband of the optical filter 806, and then provide the physical quantity to the optical filter 806. Thus, the optical filter 806 can set the central wavelength of its passband based on the physical quantity. The optical filter 806 can be implemented using various existing filter structures (such as gratings, resonant cavities, etc.), and for different filter structures, the corresponding physical quantities that can change the central wavelength of its passband are also different. In some embodiments, the physical quantity includes a filter structure size parameter related to the central wavelength of the passband. In other embodiments, as a non-limiting example, the physical quantity may include at least one of heat, sound waves, deformation, pressure, material refractive index and vibration. Such physical quantities can set the filter passband central wavelength by changing the effective refractive index of the optical transmission medium in the optical filter. Compared with structural size parameters, the latter type of physical quantities has the advantages of fast response speed and easy adjustment.

[0082] In some embodiments, the optical filter 806 includes a tunable optical filter, that is, the passband center wavelength of the optical filter 806 can be changed within a certain range. In this way, when the center wavelength of the continuous wave laser beam 801 changes with time, the sensing electrical signal 803 can include a one-dimensional matrix on a time series, each value in the matrix represents the center wavelength of the continuous wave laser beam 801 at a corresponding time point, and accordingly, the center wavelength of the passband of the optical filter 806 is set to change accordingly based on the sensing electrical signal. That is, when the continuous wave laser 802 is a tunable laser, the optical filter 806 can be a tunable optical filter. As described above, if the wavelength sensing module 804 and the optical filter 806 both have a faster response speed, the passband center wavelength of the optical filter 806 can change in real time with the change of the center wavelength of the continuous wave laser beam 801. This means that the tuning speed of the tunable optical filter can be of the same order of magnitude as the tuning speed of the tunable laser.

[0083] After or almost simultaneously with setting the passband center wavelength, the optical filter 806 receives another portion 801 - 2 of the continuous wave laser beam 801 , optically filters it, and outputs a filtered laser beam 805 . Figure 8 The midpoint A may represent a beam splitter for splitting the continuous wave laser beam 801 into a beam 801-1 and a beam 801-2. Since the beam 801-1 is only used for wavelength measurement, the beam 801-1 may only account for a small portion of the energy of the continuous wave laser beam 801 (e.g., 1%, 2%, 5%, 10% or other values ​​that meet the measurement accuracy requirements), and the remaining majority of the continuous wave laser beam 101 can be input into the optical filter 806 as the beam 801-2.

[0084] In some embodiments, in order to obtain a better beam quality improvement effect (e.g., a better sidelobe suppression ratio), the optical filter 806 may be a high Q value filter. The higher the Q value, the smaller the filter passband bandwidth is compared to its center frequency, that is, the better the filter selectivity is. In some embodiments, the optical filter 806 has a high Q value so that its passband width can suppress one or more side lobes in the input laser beam. In a further embodiment, the optical filter 806 has a Q value high enough to make the sidelobe closest to the main lobe in the input laser beam (often the sidelobe with the highest intensity) outside the passband of the optical filter 806. For example, when the center wavelength of the optical filter 806 is aligned with the center wavelength of the input laser beam, due to the high Q value of the microring resonator, the passband width (e.g., half-maximum full width) of the optical filter 806 can be greater than the line width of the main lobe to ensure that the main lobe is not suppressed, but the side lobes are suppressed.

[0085] The electro-optic modulator 808 receives the filtered laser beam 805, and modulates the frequency modulated electrical signal 807 onto the laser beam 805 to output a modulated optical signal 809. The electro-optic modulator 808 is a modulator based on the electro-optic effect of the electro-optic crystal material. When a voltage carrying a change in the electrical signal is applied to the electro-optic crystal material, the refractive index of the electro-optic crystal material changes, causing corresponding changes in the phase, amplitude, intensity and / or polarization state of the light wave passing through the crystal material, thereby the electrical signal is loaded onto the light to form an optical signal. The electro-optic crystal material includes but is not limited to lithium niobate (LiNbO3), gallium arsenide (GaAs) or lithium tantalate (LiTaO3). By adopting different structures, the electro-optic modulator 108 can be an intensity modulator, a phase modulator or an I / Q (in-phase / quadrature phase) modulator. Taking the intensity modulator as an example, the electro-optic modulator 808 can be a Mach-Zehnder modulator (MZM) based on the Mach-Zehnder interferometer structure. The MZM includes a radio frequency (RF) input port and a bias input port. The RF input port is used to receive an electrical signal, such as a frequency modulated electrical signal 807. The bias input port is used to receive a bias voltage. In order to maintain the linearity between the modulated optical signal and the frequency modulated electrical signal, the bias voltage can be set at a quadrature bias point (also called a half-wave voltage), where the applied voltage results in a 50% transmittance.

[0086] The frequency modulated electrical signal 807 is an electrical signal whose frequency varies with time, also known as a chirp signal. In some embodiments, the frequency modulated electrical signal 807 can be generated by directly or indirectly frequency or phase modulating an electrical carrier signal. In another embodiment, the frequency modulated electrical signal 807 can be generated by an arbitrary waveform generator. The frequency modulated electrical signal 807 may include a linear frequency modulated signal and a nonlinear frequency modulated signal. In laser radar applications, the use of a linear frequency modulated signal can simplify the processing of electrical signals after photoelectric detection of the echo light signal. As a linear frequency modulated signal, from the curve of the frequency variation with time, the frequency modulated electrical signal 807 may include a sawtooth wave signal, a triangle wave signal, a segmented linear frequency modulated signal, and the like.

[0087] Fig. 9 FIG. 8 is a schematic diagram showing a specific example of a wavelength sensing module 804 of a laser 701 according to an embodiment of the present disclosure. As a non-limiting example only, the wavelength sensing module 804 can be used to implement Figure 8The wavelength sensing module 804. The wavelength sensing module 804 mainly includes an optical plug-and-drop type ring resonator 902. The optical plug-and-drop type ring resonator 902 may include a ring waveguide 907 and straight waveguides 906 and 908 respectively coupled to the ring waveguide 907 on opposite sides. The number of ring waveguides 907 between the two straight waveguides 906 and 908 may be one or more. The ring waveguide 907 may include, but is not limited to, one or more of a microsphere, a microring, a microdisk, a microcolumn, and a microring core. The optical plug-and-drop type ring resonator 902 may include four ports: an input port 909, a through port 910 directly connected to the input port 909 through a straight waveguide, a drop port 911 on the same side as the input port 909 on another straight waveguide, and an insertion port 912 on the opposite side of the input port 909 on another straight waveguide. The optical plug-and-drop type ring resonator 902 may have symmetry. This means that the input port 909 of the optical plug-and-drop type ring resonator 902 may not be limited to Fig. 9 Instead of being the specific position shown in FIG. 1 , it can be any one of the four ports, and the positions of the other ports will also change accordingly.

[0088] The input laser beam 901 enters from the input port 909 of the ring resonator 902. The root mean square of the ratio of the optical power of the through port 910 and the drop port 911 of the ring resonator 902 is denoted as the amplitude comparison function (ACF), and the ACF can be approximately expressed as:

[0089]

[0090] Where Δλ represents the shift of the central wavelength of the input laser beam 901 relative to the resonant wavelength of the ring resonator 902, r and t are the self-coupling coefficient and the mutual coupling coefficient of the ring resonator 902, respectively, k is the ratio of the coupling loss of the through port 910 and the drop port 911, and FSR is the free spectral range. After the ring resonator 902 is manufactured, r, t, k and FSR are all values ​​related to the geometric dimensions of the micro-ring resonator, that is, they are constants, so ACF has a linear relationship with respect to Δλ.

[0091] In some embodiments, the linearity of ACF with respect to Δλ is associated with the loss experienced by the laser in the ring waveguide 907 of the ring resonator 902. Specifically, the smaller the loss experienced by the laser in one circle of the ring waveguide 907 of the ring resonator 902, the closer the relationship of ACF with respect to Δλ is to the linear relationship in formula (1). The loss experienced by the laser in one circle of the ring waveguide 907 can be determined by the power loss coefficient γ (unit: 1 / cm) of the ring waveguide material and the optical path length L of the ring waveguide 907 (i.e., the circumference of the ring waveguide 907). When the ring waveguide material is constant, i.e., the power loss coefficient γ is constant, the smaller the optical path length L is, the smaller the loss experienced by the laser in the ring waveguide 907 is. As a non-limiting example, the optical path length L can be on the order of tens of micrometers, hundreds of micrometers, or several millimeters. At this time, if the ring waveguide 907 is made of a typical silicon material (only as a non-limiting example), the loss experienced by the laser in the ring waveguide 907 can be extremely small, thereby effectively ensuring that the ACF and Δλ obey the linear relationship in formula (1). In other embodiments, the optical path length L can also be other lengths.

[0092] In some embodiments, in order to further improve the Q value, working stability and size of the ring resonator 902, the ring resonator 902 can be designed as a microcavity operating in the whispering gallery mode. This can be achieved by selecting the refractive index of the materials on both sides of the dielectric boundary of the ring waveguide 907 of the ring resonator 902. In some embodiments, the ring resonator 902 can be implemented on a silicon on insulator (SOI) wafer. At this time, a standard complementary metal oxide semiconductor (CMOS) manufacturing process can be used to facilitate integration with other optical paths and circuits. In other embodiments, the ring resonator 902 can be formed on other optical waveguide materials, including optical chip integration platforms such as silicon dioxide (SiO2) materials, organic polymer materials, silicon nitride (SiN) materials, indium phosphide (InP) materials and lithium niobate (LiNbO3) materials. Since the ring resonator 902 can be implemented on various different material integration platforms, the ring resonator 902 can sometimes be integrated with at least part of the laser that generates the laser beam to improve the overall integration.

[0093] In order to calculate the ACF, the wavelength sensing module 804 may include a power detection and post-processing circuit 913. The circuit 913 may include optical power measurement circuits 914 and 915 connected to the through port 910 and the drop port 911, respectively, and a post-processing circuit 916. The optical power measurement circuits 914 and 915 measure the optical power values ​​of the two ports, respectively, and the post-processing circuit 916 calculates the ratio of the two optical power values ​​and obtains the square root. As an example, the post-processing circuit 916 may include an analog-to-digital converter (ADC) and a digital signal processing circuit, so that the ratio and square root of the power can be obtained in the digital domain. Based on digital circuit integration technology, the post-processing circuit 916 can be better integrated with the optical power measurement circuits 914 and 915 (for example, based on III-V semiconductor material process integration) and the ring resonator 902 (applicable to various material integration platforms) to reduce the device size. Therefore, the sensing electrical signal 803 output by the wavelength sensing module 804 is or indicates the root mean square of the ratio of the optical power of the through port 910 and the drop port 911 of the ring resonator 902, that is, ACF. Fig. 9 The structure of the power detection and post-processing circuit 913 shown is only an example. In other embodiments, the power detection and post-processing circuit 913 may adopt other circuit structures. For example, in some embodiments, the power detection and post-processing circuit 913 may further include a digital-to-analog converter (DAC) in the post-processing circuit 916 to convert the obtained digital value into an analog current / voltage signal that can indicate the size of the central wavelength of the input laser beam 901, and output it as the sensing electrical signal 803. As will be described later, the analog electrical signal can be provided to the optical filter 806 to control the central wavelength of its passband.

[0094] Fig.10 FIG. 8 is a schematic diagram showing a specific example of an optical filter 806 of a laser radar device according to an embodiment of the present disclosure. Figure 8 The optical filter 806 is an example of an optical filter 806 in FIG. 1 , but not limited thereto. The optical filter 806 mainly includes an optical insertion-splitting ring resonator 1002, and Fig. 9The optical plug-and-drop type ring resonator 1002 is similar to the optical plug-and-drop type ring resonator 902. The optical plug-and-drop type ring resonator 1002 may include a ring waveguide 1007 and straight waveguides 1006 and 1008 respectively coupled to the ring waveguide 1007 on opposite sides thereof. The number of the ring waveguides 1007 between the two straight waveguides 1006 and 1008 may be one or more. The ring waveguide 1007 may include, but is not limited to, one or more of a microsphere, a microring, a microdisk, a microcolumn, and a microring core. The optical plug-and-drop type ring resonator 1002 may include four ports: an input port 1009, a through port 1010 directly connected to the input port 1009 through a straight waveguide, a drop port 1011 on the same side as the input port 1009 on another straight waveguide, and an insertion port 1012 on the opposite side of the input port 1009 on another straight waveguide. The optical plug-and-drop type ring resonator 1002 may have symmetry. For example, the optical plug-and-drop type ring resonator 1002 may be centrally symmetrical. This means that the input port 1009 of the optical add / drop ring resonator 1002 may not be limited to Fig.10 Instead of being the specific position shown in FIG. 1 , it can be any one of the four ports, and the positions of the other ports will also change accordingly.

[0095] Laser beam 1001 (e.g. Figure 8 The continuous wave laser beam 801-2) enters from the input port 1009 of the ring resonator 1002, and the laser beam 1005 after filtering is output from the output port 1011 of the ring resonator 1002. The ring resonator 1002 connected in this way constitutes a passband filter.

[0096] The ring resonator 1002 can set its passband center wavelength based on the sensed electrical signal 803. For example, the passband center wavelength of the ring resonator 1002 can be set based on the sensed electrical signal 803 by the filter setting module 1013. In some embodiments, the filter setting module 1013 can convert the sensed electrical signal 803 (for example, in the form of voltage or current) into one or more physical quantities such as heat, sound waves, deformation, pressure, material refractive index and vibration. Then, the physical quantity is provided to the ring resonator 1002 to set or adjust the filter passband center wavelength of the ring resonator 1002. For example, the physical quantity can be provided to the optical coupling region of the ring resonator 1002 to set or adjust the filter passband center wavelength of the ring resonator 1002 by changing the effective refractive index of the medium in the optical coupling region. Other features of the filter setting module have been described above and will not be repeated here.

[0097] The use of the optical filter 806 can not only achieve precise filtering, but also has the advantages of fast response speed, high Q value, small size and easy integration.

[0098] In some embodiments, in order to further improve the Q value, working stability and size of the ring resonator 1002, the ring resonator 1002 can be designed as a microcavity operating in the whispering gallery mode. This can be achieved by selecting the refractive index of the materials on both sides of the dielectric boundary of the ring waveguide 1007 of the ring resonator 1002. In some embodiments, the ring resonator 1002 can be implemented on an SOI wafer. In this case, a standard CMOS manufacturing process can be used to facilitate integration with other optical paths and circuits. In other embodiments, the ring resonator 1002 can be formed on other optical waveguide materials, including optical chip integration platforms such as SiO2 materials, organic polymer materials, SiN materials, InP materials and LiNbO3 materials. Since the ring resonator 1002 can be implemented on various material integration platforms, the ring resonator 1002 can sometimes be integrated with at least part of the laser that generates the laser beam to improve the overall integration.

[0099] In some embodiments, for ease of manufacture, the ring resonator 1002 can be Fig. 9 The ring resonator 902 is manufactured using the same integration process and the same size parameters; or, taking a step back, the ring resonator 1002 can be manufactured using the same integration process as the ring resonator 902 but with different size parameters.

[0100] Fig.11 Shows the Fig. 9 The wavelength sensing module and Fig.10 Schematic diagram of an example of integrating an optical filter. The input light is divided into two parts by the optical coupler 1102, a small part of which is transmitted to the ring resonator 1104 of the wavelength sensing module for wavelength sensing, and most of it is transmitted to the ring resonator 1110 of the optical filter for optical filtering. The through port and the drop port of the ring resonator 1104 are respectively connected to the photodetector PD, and each enters the post-processing circuit after analog-to-digital conversion (ADC) to obtain ACF. The obtained digital value is then converted into a voltage / current signal by digital-to-analog conversion (DAC). The voltage / current signal is provided to a micro heater set in the optical coupling area of ​​the ring resonator 1110 to generate a certain amount of heat, change the refractive index of the optical coupling area, so that the passband center wavelength of the ring resonator 1110 matches the center wavelength of the input light sensed by the ring resonator 1104, so as to achieve the purpose of precise filtering.

[0101] The coaxial laser radar provided in the embodiment of the present application optimizes the shared path of the coaxial laser radar, allowing as many optical devices as possible to share transmission and reception, reducing costs, and the coaxial design also reduces environmental noise. After integrating the optical circulator provided in the embodiment of the present application, it can be distinguished by polarization state, improve isolation, and reduce system crosstalk. In addition, by sharing optical devices, the coaxial laser radar is small in size and easy to integrate with integrated photonic chips, and can be used for integrated frequency modulated continuous wave laser radar.

[0102] In the above embodiments, the first birefringent crystal 10, the second birefringent crystal 11 and the third birefringent crystal 12 can be Fig.12 The invention is prepared by any one of the four materials shown, wherein the four materials include yttrium vanadate (YVO4), titanium dioxide (TiO2), calcium carbonate (CaCO3), and lithium niobate (LiNbO3).

[0103] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0104] Those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is meant to be within the scope of the present embodiment and to form different embodiments.

[0105] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present application, but the present application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of the present application, and these modifications and improvements are also considered to be within the scope of protection of the present application.

Claims

1. An optical circulator, characterized in that: include: A first birefringent crystal, a second birefringent crystal, a third birefringent crystal, a Faraday rotator and a half-wave plate, wherein the first birefringent crystal is arranged in parallel with the third birefringent crystal and is arranged in sequence with the Faraday rotator, the half-wave plate and the second birefringent crystal: The first birefringent crystal is used to receive the optical signal input from the first optical input port, and to reflect the optical signal to the second optical receiving port; the third birefringent crystal is used to receive the optical signal input from the second optical input port, and to reflect the optical signal to the first optical receiving port; the third port is used to output the emitted optical signal transmitted by the second birefringent crystal, and to receive the reflected optical signal and return it to the second birefringent crystal.

2. The optical circulator according to claim 1, characterized in that: The optical axes of the second birefringent crystal and the third birefringent crystal are in the same direction; the optical axes of the first birefringent crystal and the third birefringent crystal are in different directions; The first birefringent crystal, the second birefringent crystal and the third birefringent crystal have the same thickness.

3. The optical circulator according to claim 1 or 2, characterized in that: The first optical input port is not adjacent to the first optical receiving port and is used to carry optical signals having the same polarization state; The second optical input port is not adjacent to the second optical receiving port, and is used to carry optical signals having the same polarization state.

4. The optical circulator according to claim 3, characterized in that: The first optical input port is adjacent to the second optical receiving port, or the second optical input port is adjacent to the first optical receiving port.

5. The optical circulator according to claim 4, characterized in that: The first optical input port, the second optical receiving port, the second optical input port and the first optical receiving port are four ports arranged on the same end face of the optical circulator, and a spacing between the four ports is greater than 250 micrometers.

6. A coaxial laser radar, characterized in that: It comprises a transmitting unit, an optical circulator according to any one of claims 1 to 5, a first receiving unit and a second receiving unit; A transmitting unit, configured to transmit a first transmitting optical signal and a second transmitting optical signal having different polarization states; The optical circulator is used to receive the first transmitted optical signal and the second transmitted optical signal, and guide the returned echo optical signal of the first transmitted optical signal to the first receiving unit, and guide the echo optical signal of the second transmitted optical signal to the second receiving unit.

7. The coaxial laser radar according to claim 6, characterized in that: The coaxial laser radar also includes an optical fiber array; The optical fiber array is used to guide the first transmitted optical signal and the second transmitted optical signal to the optical circulator; and to guide the echo optical signal of the first transmitted optical signal transmitted back by the optical circulator to the first receiving unit, and guide the echo optical signal of the second transmitted optical signal to the second receiving unit.

8. The coaxial laser radar according to claim 7, characterized in that: The optical fiber array includes a first input waveguide, a second input waveguide, a first receiving waveguide, and a second receiving waveguide; The first input waveguide matches the first optical input port, the second input waveguide matches the second optical input port, the first receiving waveguide matches the first optical receiving port, and the second receiving waveguide matches the second optical receiving port.

9. The coaxial laser radar according to claim 8, characterized in that: The transmitting unit includes a laser, an electro-optical modulator, a frequency modulation generator, a polarization beam splitter rotator, a first beam splitter and a second beam splitter; The laser is used to output a continuous wave into the photoelectric modulator; The electro-optical modulator is used to modulate the frequency of the continuous wave onto the optical signal under the action of the frequency modulation signal generated by the frequency modulation generator, and the adjusted optical signal is transmitted to the polarization beam splitter rotator; The polarization beam splitter rotator is used to split the optical signal into a first transmission optical signal and a second transmission optical signal with different polarization states, output the first transmission optical signal through the first optical splitter, and output the second transmission optical signal through the second optical splitter.

10. The coaxial laser radar according to claim 9, characterized in that: The first receiving unit includes a first beam combiner, a first photodetector and a first receiving circuit; the second receiving unit includes a second beam combiner, a second photodetector and a second receiving circuit; The first beam combiner receives the echo optical signal of the first transmitted optical signal transmitted back by the optical circulator, and processes the echo optical signal through the first photodetector and the first receiving circuit; The second beam combiner receives the echo optical signal of the second transmitted optical signal transmitted back by the optical circulator, and processes the echo optical signal via the second photodetector and the second receiving circuit.

11. The coaxial laser radar according to claim 10, characterized in that: The first beam combiner, the second beam combiner, the first beam splitter and the second beam splitter are implemented using an integrated photonic chip.

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