A frequency modulated continuous wave laser radar chip

Abstract

The present invention proposes a frequency modulated continuous wave laser radar chip, which relates to the field of laser radar technology. The frequency modulated continuous wave laser radar chip includes: a tunable laser, a transmitting optical phased array, a receiving optical phased array and a balanced photodetector; the tunable laser is used to output a detection laser signal and realize wavelength tuning, the transmitting optical phased array is used to transmit laser signals outward, the receiving optical phased array is used to collect light from the outer space into an optical waveguide as signal light, and the balanced photodetector is used to receive local light and signal light, and convert the optical signal into an electrical signal with distance information and speed information of the object to realize ranging. The present invention uses a tunable laser to achieve more precise control of the wavelength tuning of the laser radar chip, realize wavelength tunability, and improve the ranging accuracy of the laser radar; the tunable laser uses a multi-path semi-reflective array waveguide to improve the stability of the laser radar chip ranging.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and more specifically, to a frequency modulated continuous wave laser radar chip. Background Art

[0002] LiDAR is the core technology for autonomous vehicles and unmanned vehicles to obtain three-dimensional spatial information and realize space remote sensing. LiDAR needs to have precise beam control capabilities. Currently, LiDAR is mainly mechanical or semi-mechanical. Due to the presence of mechanical moving parts, its life and stability are serious problems. The all-solid-state LiDAR with optoelectronic integrated chips as the core has the characteristics of small size, low energy consumption and low cost. Since there are no mechanical moving parts and it is purely electric scanning, it has good stability and fast scanning speed. In particular, the frequency modulated continuous wave LiDAR integrated on the chip can directly obtain the distance, angle, speed and other information of the target. It has the advantages of integration, miniaturization and chipization, and is a LiDAR with great application prospects.

[0003] The laser radar chips currently on the market emit laser signals through tunable lasers. The external cavity laser integrated with the chip is generally a double micro-ring structure with a high Q value, frequent mode hopping, and poor ranging stability. In addition, the end of the tunable laser uses total reflection and is not integrated with the optical phased array, so it cannot achieve optical path adjustment and has low ranging efficiency. Summary of the invention

[0004] In view of the problems in the background technology, the present invention provides a frequency modulated continuous wave laser radar chip to solve the defects of the laser radar device in the prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A frequency modulated continuous wave laser radar chip, comprising:

[0007] Tunable lasers, transmitting optical phased arrays, receiving optical phased arrays, and balanced photodetectors;

[0008] The tunable laser is used to output M-1 laser signals and one local light, and the tunable laser is also used to adjust the reflection center wavelength of the reflection spectrum to achieve wavelength tuning; wherein M is a positive integer greater than 2;

[0009] The transmitting optical phased array is used to transmit the M-1 laser signals outwardly;

[0010] The receiving optical phased array is used to collect light from the outer space into an optical waveguide as signal light;

[0011] The balanced photoelectric detector is used to receive the local light and the signal light, and convert the optical signal into an electrical signal. The electrical signal includes a direct current signal and an alternating current signal. The alternating current signal carries the distance and speed information of the object.

[0012] The tunable laser comprises a reflective optical amplifier, a phase modulator, a 1×M optical beam splitter and M semi-reflective array waveguides which are optically connected in sequence; the light emitted by the reflective optical amplifier passes through the phase modulator and then enters the 1×M optical beam splitter, the 1×M optical beam splitter outputs M paths of light which respectively enter the M semi-reflective array waveguides, wherein M-1 semi-reflective array waveguides output M-1 paths of light which enter the transmitting optical phased array, and another semi-reflective array waveguide outputs one path of light which enters the balanced photodetector as local light; the light reflected back by the M semi-reflective array waveguides passes through the 1×M optical beam splitter and the phase modulator in sequence and then returns to the reflective optical amplifier to form a laser resonant cavity.

[0013] The M semi-reflection array waveguides include: a phase modulator array, a first delay line array, a semi-reflector array, and a second delay line array; the 1×M optical beam splitter outputs M paths of light that pass through the phase modulator array, the first delay line array, the semi-reflector array, and the second delay line array in sequence; the phase modulator array, the first delay line array, and the second delay line array are equidistantly distributed, and the sum of the delay line lengths passed by each of the M paths of light entering the M semi-reflection array waveguides is the same; the reflection center wavelength is adjusted by adjusting the tolerance of the phase modulator array, and the relationship between the tolerance of the phase modulator array and the reflection center wavelength is:

[0014] ,

[0015] in, is the tolerance of the phase modulator array; is the tolerance of the first delay line array; is the vacuum wave vector; is the reflection center wavelength; is the group refractive index of the optical waveguide of the first delay line array.

[0016] The beneficial effects of the present invention are:

[0017] (1) Tunable lasers are obtained by adjusting the tolerance of the M-channel phase modulator array. The size of M can adjust the reflection center wavelength; at the same time, the larger the value of M, the narrower the width of the reflection spectrum, and the easier it is to achieve single-wavelength and narrow-linewidth laser emission; by adjusting the parameters of the tunable laser, the wavelength tuning of the lidar chip can be more finely controlled, which can improve the ranging accuracy of the lidar chip;

[0018] (2) The end of the tunable laser adopts a semi-reflector array structure. The light reflected by the semi-reflector array passes through the optical beam splitter and phase modulator in sequence and then returns to the reflective optical amplifier to form a laser resonant cavity, thereby realizing the amplification of light energy. The multi-path light output by the semi-reflector array is emitted outward through the transmitting optical phased array, avoiding the waste of light energy, and being able to realize the optical path adjustment more flexibly, thereby improving the efficiency and performance of the lidar ranging system.

[0019] (3) A multi-channel semi-reflective array waveguide is used with multiple outputs, which can become part of the optical phased array beam splitting, making the structure more compact; the semi-reflector array, the first delay line array, and the phase modulator array form a tunable reflector; compared with the traditional high-Q value double micro-ring external cavity tuned laser, the tunable reflector has the advantage of avoiding the instability caused by the self-heating effect caused by the high-Q value micro-ring and the disadvantage of a small free spectrum range, thereby improving the stability of the laser radar chip ranging;

[0020] (4) The phase modulator array, the first delay line array, and the second delay line array are equidistantly distributed, and the total length of the delay line passed by each of the M light paths entering the M semi-reflective array waveguides is the same. In practical applications, only one wavelength needs to be calibrated to achieve "wavelength independence". The appropriate wavelength is selected to reduce reflection interference and broaden the detection range of the lidar. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the present invention more easily understood, the present invention will be described in more detail by referring to the specific embodiments shown in the accompanying drawings. These drawings only depict typical embodiments of the present invention and should not be considered as limiting the scope of protection of the present invention.

[0022] Figure 1 is a schematic diagram of the structure of a frequency modulated continuous wave laser radar chip provided in an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of the structure of M semi-reflective array waveguides provided in an embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of the structure of a transmitting optical phased array provided by an embodiment of the present invention;

[0025] Figure 4 is a schematic structural diagram of a receiving optical phased array provided by an embodiment of the present invention;

[0026] Figure 5 is another structural schematic diagram of a laser radar chip provided by another embodiment of the present invention;

[0027] Figure 6is another structural schematic diagram of a laser radar chip provided by another embodiment of the present invention;

[0028] Figure 7 is another structural schematic diagram of a laser radar chip provided by another embodiment of the present invention;

[0029] Figure 8 This is another structural schematic diagram of a laser radar chip provided by another embodiment of the present invention.

[0030] Reference numerals:

[0031] 100-reflective optical amplifier, 200-phase modulator, 300-1×M optical beam splitter, 400-M semi-reflective array waveguides, 500-transmitting optical phased array, 600-receiving optical phased array, 700-balanced photodetector, 410-phase modulator array, 420-first delay line array, 430-semi-reflector array, 440-second delay line array, 510-optical beam splitter array, 520-phase modulator array, 530-photonic antenna array, 610-optical beam splitter, 620-phase modulator, 630-photonic antenna, 301-1×(M+1) optical beam splitter, 302-1×(M+2) optical beam splitter, 800-P×M optical hybrid beam splitter. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention with reference to the accompanying drawings so that those skilled in the art can better understand the present invention and implement it, but the enumerated embodiments are not intended to limit the present invention. In the absence of conflict, the following embodiments and the technical features in the embodiments can be combined with each other, wherein the same components are represented by the same reference numerals. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] Please refer to Figure 1 , Figure 2 , Figure 3 as well as Figure 4 , Figure 1 A schematic diagram of the structure of a frequency modulated continuous wave laser radar chip provided by an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the structure of M semi-reflective array waveguides; Figure 3 for Figure 1 Schematic diagram of the structure of the medium-launch optical phased array; Figure 4 for Figure 1 Schematic diagram of the structure of the receiving optical phased array.

[0034] See also Figure 1In an embodiment of the present invention, a frequency modulated continuous wave laser radar chip includes: a reflective optical amplifier 100, a phase modulator 200, a 1×M optical beam splitter 300, M semi-reflective array waveguides 400, a transmitting optical phased array 500, a receiving optical phased array 600 and a balanced photodetector 700; wherein, a tunable laser includes a reflective optical amplifier 100, a phase modulator 200, a 1×M optical beam splitter 300, and M semi-reflective array waveguides 400; the tunable laser is used to output M-1 laser signals and one local light, and the tunable laser can change the reflection center wavelength of the reflection spectrum by adjusting the phase to achieve wavelength tuning; wherein, M is a positive integer greater than 2.

[0035] The transmitting optical phased array 500 is configured to receive multiple laser signals output from a tunable laser and transmit the multiple laser signals into space, so that the laser signals can be transmitted to a target object; the receiving optical phased array 600 is configured to receive laser signals reflected by a target object after being transmitted by the transmitting optical phased array 500, and the receiving optical phased array 600 is used to collect light from external space into an optical waveguide as signal light.

[0036] The balanced photodetector 700 is used to receive local light and signal light, and convert the optical signal into an electrical signal, which includes a DC signal and an AC signal. The AC signal carries the distance and speed information of the object. Among them, the local light is the reference signal, and the signal light is the detection signal. The laser radar chip transmits a frequency modulated continuous wave to the target object to be measured, and then mixes the detection signal with the reference signal, and uses the beat frequency signal generated by laser interference to solve the distance and speed information of the target object. The signal processing process of the laser radar ranging belongs to the prior art and will not be repeated here.

[0037] The tunable laser includes a reflective optical amplifier 100, a phase modulator 200, a 1×M optical beam splitter 300 and M semi-reflective array waveguides 400 which are optically connected in sequence; the light emitted by the reflective optical amplifier 100 passes through the phase modulator 200 and then enters the 1×M optical beam splitter 300, the 1×M optical beam splitter 300 outputs M paths of light which respectively enter the M semi-reflective array waveguides 400, wherein M-1 semi-reflective array waveguides output M-1 paths of light which enter the transmitting optical phased array 500, and another semi-reflective array waveguide outputs one path of light which enters the balanced photodetector 700 as local light; the light reflected back by the M semi-reflective array waveguides 400 passes through the 1×M optical beam splitter 300 and the phase modulator 200 in sequence and then returns to the reflective optical amplifier 100 to form a laser resonant cavity. Among them, the phase modulator 200, 1×M optical beam splitter 300, M semi-reflective array waveguides 400, transmitting optical phased array 500, receiving optical phased array 600 and balanced photodetector 700 are integrated on a silicon-based chip, and the reflective optical amplifier chip and the silicon-based chip are hybrid integrated to realize the integrated integration of the laser radar chip. One side of the reflective optical amplifier 100 is full reflection and the other side is full transmission. The light emitted by the reflective optical amplifier 100 passes through the phase modulator 200 and enters the 1×M optical beam splitter 300, which divides the light into M parts and enters the M semi-reflective array waveguides 400 respectively; the multi-channel semi-reflective array waveguide has multiple outputs and can become a part of the optical phased array beam splitting, making the structure more compact.

[0038] See also Figure 2 , M semi-reflection array waveguides 400 include: a phase modulator array 410, a first delay line array 420, a semi-reflector array 430, and a second delay line array 440. The phase modulator array 410 can modulate the phase by thermo-optical effect, electro-optical effect, or plasma dispersion effect; the first delay line array 420 and the second delay line array 440 can be distributed in equal lengths, but the sum of the lengths of each delay line is the same, that is, the sum of the lengths of the delay lines passed by each of the M light beams entering the M semi-reflection array waveguides is the same; the semi-reflector array 430 can be a waveguide grating or a Sagnac waveguide structure. The light reflected back by the semi-reflector array 430 passes through the 1×M optical beam splitter 300 and the phase modulator 200 and returns to the reflective optical amplifier 100 to form a laser resonant cavity. The semi-reflector array 430, the first delay line array 420, and the phase modulator array 410 form a tunable reflector.

[0039] It is worth noting that the reflective optical amplifier, the phase modulator, the 1×M optical beam splitter, the phase modulator array, the first delay line array, the semi-reflector array and the second delay line array constitute a tunable laser structure. The end of the tunable laser adopts a semi-reflector array structure. The light reflected by the semi-reflector array passes through the optical beam splitter and the phase modulator in sequence and then returns to the reflective optical amplifier to form a laser resonant cavity, thereby realizing the amplification of light energy. The multi-path light output by the semi-reflector array is emitted outward through the transmitting optical phased array, thereby avoiding the waste of light energy, being able to realize the optical path adjustment more flexibly, and improving the efficiency and performance of the laser radar ranging system. The multi-path semi-reflector array waveguide is adopted, which has multi-path output and can become a part of the optical phased array beam splitting, making the structure more compact. The semi-reflector array, the first delay line array, and the phase modulator array form a tunable reflector, which can change the reflection center wavelength of the reflection spectrum by adjusting the phase. Compared with the traditional high-Q value double micro-ring external cavity tunable laser, its advantage is that it avoids the instability caused by the self-heating effect caused by the high-Q value micro-ring and the disadvantage of small free spectrum range, thereby improving the stability of the laser radar chip ranging.

[0040] The working principle of the tunable reflector is as follows: Taking the M-channel first delay line array 420 and the M-channel phase modulator array 410 as an example, after the M-channel light is combined into one beam, it can be expressed as the following formula (1):

[0041] (1),

[0042] Wherein, M is the number of light paths, m is the mth light path; i is the imaginary unit; is the tolerance of the M-channel phase modulator array 410; is the tolerance of the M-way first delay line array 420; is the effective refractive index of the optical waveguide of the first delay line array 420; is the vacuum wave vector; is the diffraction factor.

[0043] (2),

[0044] (3),

[0045] (4),

[0046] The reflection coefficient is shown in formula (2), where is the reflection coefficient, is the diffraction factor; It is expressed by formula (3); reflection coefficient Maximum value determines the tolerance of the phase modulator array 410 and reflection center wavelength The relationship between is formula (4), where is the group refractive index of the optical waveguide of the first delay line array 420, and is adjusted by adjusting the tolerance of the M-channel phase modulator array 410 The size of the reflection center wavelength can be adjusted, and by adjusting , which can make this adjustment ability stronger. The larger the value of M, the narrower the width of the reflection spectrum, and the easier it is to achieve single-wavelength and narrow-linewidth laser emission. The phase modulator 200 can realize the frequency sweeping function based on the original laser, that is, to achieve frequency-modulated continuous wave laser output; by adjusting multiple parameters of the tunable laser: the tolerance of the M-way phase modulator array 410 , the tolerance of the M-way first delay line array 420 The wavelength adjustment can be realized, making the wavelength adjustment more precise.

[0047] It is worth noting that the tunable laser is obtained by adjusting the tolerance of the M-channel phase modulator array. The size of the reflection center wavelength of the reflection spectrum can be adjusted, and single-wavelength and narrow-linewidth laser emission can be easily realized; the wavelength tuning of the laser radar chip can be more finely controlled by the tunable laser, and the wavelength can be tunable, which improves the ranging accuracy of the laser radar chip. The phase modulator array, the first delay line array, and the second delay line array adopt an arithmetic distribution, and the sum of the delay line lengths passed by each of the M paths of light entering the M semi-reflection array waveguides is the same, so that in practical applications, only one wavelength needs to be calibrated to achieve "wavelength independence", and the appropriate wavelength is selected to reduce reflection interference, improve the resolution and signal-to-noise ratio of the laser radar chip, and broaden the detection range of the laser radar.

[0048] See also Figure 3 The transmitting optical phased array 500 has M-1 input optical waveguides. In order to increase the number of optical phased arrays, each optical waveguide can be further split by an optical beam splitter array 510, and then pass through a phase modulator array 520 and enter a photon antenna array 530. Preferably, the photon antenna is a waveguide grating structure.

[0049] See also Figure 4 The receiving optical phased array 600 is similar to the transmitting optical phased array 500, including an optical beam splitter 610, a phase modulator 620 and a photon antenna 630, but has only one output optical waveguide. Its photon antenna 630 is similar to the photon antenna array 530 of the transmitting optical phased array. If a waveguide grating structure is used, it needs to be the same as the waveguide grating of the transmitting optical phased array.

[0050] exist Figure 1 Based on Figure 5 , Figure 6 , Figure 7 ,as well as Figure 8 , Figures 5 to 8 Each of them is another structural schematic diagram of a laser radar chip provided by another embodiment of the present invention.

[0051] See also Figure 5 , the parallel scanning function is increased by increasing the categories of transmitting optical phased array and receiving optical phased array. Figure 5 Taking Category 2 as an example, the transmitting optical phased array is divided into 2 categories, and the grating of each category is different. The receiving optical phased array is also divided into 2 categories, and the grating of each category is the same as the grating of the transmitting optical phased array.

[0052] The M semi-reflective array waveguides 400 output 2 paths of light which enter the balanced photodetector 700 respectively, and the M semi-reflective array waveguides 400 output M-2 paths of light which enter the transmitting optical phased array 500 respectively.

[0053] The advantages of this structure are: it can scan multiple different longitudinal angles at the same time, that is, each grating corresponds to a longitudinal angle, which improves the scanning speed and enhances the ranging efficiency of the lidar chip.

[0054] See also Figure 6 The local light comes directly from the beam splitter, which is a 1×(M+1) beam splitter 301 . The 1×(M+1) beam splitter 301 outputs M paths of light into M semi-reflective array waveguides 400 , and outputs another path of light into a balanced photodetector 700 .

[0055] See also Figure 7 ,exist Figure 6 The parallel scanning function is added on the basis of the structure, and a 1×(M+2) optical beam splitter 302 is adopted. The 1×(M+2) optical beam splitter 302 outputs two paths of light that directly enter the balanced photodetector 700 as local light. Figure 1 , Figure 5 and Figure 6 The relevant descriptions of the corresponding embodiments will not be repeated one by one.

[0056] See also Figure 8 In order to increase the optical power, Figure 1 On the basis of the invention, multiple (P) reflective optical amplifiers and multiple (P) phase modulators are used, and the original 1×M optical beam splitter is replaced with a P×M optical hybrid beam splitter 800 to mix and split the P incident lights. The P×M optical hybrid beam splitter 800 can be a star coupler with P input ends and M output ends, or a combination of an optical coupler and an optical beam splitter.

[0057] The advantages of this structure are: the power is further improved, which enhances the detection distance and resolution of the LiDAR chip; the higher the power of the laser pulse emitted by the LiDAR chip, the longer the detection distance, and it can penetrate more obstacles and detect farther distances; in addition, the increase in optical power can also improve the resolution and signal-to-noise ratio of the LiDAR chip, reduce noise interference, and make the ranging results more accurate.

[0058] The various embodiments of the present invention are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0059] The embodiments described above are only preferred specific implementations of the present invention. This specification uses the phrases "in one embodiment", "in another embodiment", "in yet another embodiment" or "in other embodiments", which may refer to one or more of the same or different embodiments according to the present disclosure. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A frequency modulated continuous wave laser radar chip, characterized in that: include: Tunable lasers, transmitting optical phased arrays, receiving optical phased arrays, and balanced photodetectors; The tunable laser is used to output M-1 laser signals and one local light, and the tunable laser is also used to adjust the reflection center wavelength of the reflection spectrum to achieve wavelength tuning; wherein M is a positive integer greater than 2; The transmitting optical phased array is used to transmit the M-1 laser signals outwardly; The receiving optical phased array is used to collect light from the outer space into an optical waveguide as signal light; The balanced photodetector is used to receive the local light and the signal light, and convert the optical signal into an electrical signal, wherein the electrical signal includes a DC signal and an AC signal, and the AC signal carries the distance and speed information of the object; The tunable laser comprises a reflective optical amplifier, a phase modulator, a 1×M optical beam splitter and M semi-reflective array waveguides which are optically connected in sequence; the light emitted by the reflective optical amplifier enters the 1×M optical beam splitter after passing through the phase modulator, and the 1×M optical beam splitter outputs M paths of light which respectively enter the M semi-reflective array waveguides, wherein M-1 semi-reflective array waveguides output M-1 paths of light which enter the transmitting optical phased array, and another semi-reflective array waveguide outputs one path of light as local light which enters the balanced photodetector; the light reflected back by the M semi-reflective array waveguides passes through the 1×M optical beam splitter and the phase modulator in sequence and then returns to the reflective optical amplifier to form a laser resonant cavity; The M semi-reflection array waveguides include: a phase modulator array, a first delay line array, a semi-reflector array, and a second delay line array; the 1×M optical beam splitter outputs M paths of light that pass through the phase modulator array, the first delay line array, the semi-reflector array, and the second delay line array in sequence; the phase modulator array, the first delay line array, and the second delay line array are equidistantly distributed, and the sum of the delay line lengths passed by each of the M paths of light entering the M semi-reflection array waveguides is the same; the reflection center wavelength is adjusted by adjusting the tolerance of the phase modulator array, and the relationship between the tolerance of the phase modulator array and the reflection center wavelength is: ， in, is the tolerance of the phase modulator array; is the tolerance of the first delay line array; is the vacuum wave vector; is the reflection center wavelength; is the group refractive index of the optical waveguide of the first delay line array.

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