CN117630884A

CN117630884A - Laser emitting device, frequency control method and laser radar

Info

Publication number: CN117630884A
Application number: CN202211000042.6A
Authority: CN
Inventors: 赵刚; 向少卿
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2022-08-19
Filing date: 2022-08-19
Publication date: 2024-03-01

Abstract

The present invention provides a laser emitting device including: a laser which emits a laser beam; a first coupler for receiving the laser beam and dividing the laser beam into a first laser beam and a second laser beam; a frequency-to-amplitude converter receiving the first laser beam from the first coupler, including a phase modulator; the phase control unit can control the phase modulator to set the phase modulation characteristic of the phase modulator according to a preset mode, the frequency-amplitude converter can generate an optical signal with amplitude variation according to the set phase modulation characteristic, and the optical signal with amplitude variation can represent the set phase modulation characteristic; the detection module is used for receiving the optical signal with amplitude variation and the second laser beam and generating a control signal representing the set phase modulation characteristic according to the optical signal with amplitude variation and the second laser beam; and a control device coupled to the detection module and the laser, for adjusting a driving signal of the laser according to the control signal to change the frequency of the laser beam.

Description

Laser emitting device, frequency control method and laser radar

Technical Field

The present invention relates generally to the field of optoelectronics, and more particularly to a laser emitting device, a laser radar including the same, and a method of controlling the frequency of a laser.

Background

For the laser, the linewidth of the laser is a key index affecting the measurement performance, and when the laser is used for measurement, the smaller the linewidth (the full width at half maximum of an emission spectrum) of the laser is, the better the distance measurement capability and the distance measurement precision can be realized. This is especially true for Frequency Modulated Continuous Wave (FMCW) radars. The sweep frequency laser has important application in a plurality of application scenes such as laser radar, optical frequency domain reflectometer, laser imaging, biosensing and the like. The sweep frequency speed of the sweep frequency laser determines the measurement speed, and the smaller the line width of the sweep frequency laser is, the better the sweep frequency linearity is, the better the distance measuring capability and the distance measuring precision can be realized by the laser radar. Therefore, the sweep frequency laser with the characteristics of high sweep frequency speed, narrow line width, high linearity and the like can realize high-precision, high-speed and long-distance laser detection. Fig. 1 shows a swept-frequency signal in the form of a triangular wave commonly used in fm continuous wave lidar, comprising two linear sweep intervals of different slope.

At present, the frequency sweep of the frequency modulation continuous wave laser radar is realized by two methods: 1) External modulation, namely, loading a radio frequency signal by a photoelectric modulator to realize frequency modulation; 2) And directly adjusting, namely changing the working current of the laser to enable the working wavelength of the laser to realize linear frequency modulation. The 1 st external adjustment mode has low integration level and high cost; for the 2 nd direct modulation mode, in the prior art, it is proposed to directly modulate the current of a distributed feedback laser (DFB) to realize frequency sweep and optimize the linearity of the frequency sweep through a photoelectric phase-locked loop, but the frequency noise is larger, thereby affecting the measurement accuracy. In the prior art, it is also proposed to lock the output wavelength of the DFB laser on the center wavelength of a Fiber Bragg Grating (FBG) filter, suppress the frequency noise of the laser by using the narrowband characteristic of the filter to achieve the effect of compressing the linewidth of the laser, and then change the frequency of the laser with the center wavelength of the filter by using the wavelength tunable characteristic of the filter, so as to realize frequency sweep, but because the wavelength tuning of the FBG filter depends on temperature, the speed is slow. Meanwhile, the FBG filter is required to realize high-precision grating inscription, the requirement on the process is very high, and the FBG cannot realize multiplexing of different laser frequencies in the multi-wavelength laser radar due to single passband frequency, cannot be suitable for different wavelengths and has a small working temperature range, so that the practical application requirement cannot be met.

The matters in the background section are only those known to the inventors and do not, of course, represent prior art in the field.

Disclosure of Invention

In view of one or more of the deficiencies in the prior art, the present invention provides a laser emitting apparatus comprising:

a laser configured to emit a laser beam;

a first coupler configured to receive the laser beam and split it into a first laser beam and a second laser beam;

a frequency-to-amplitude converter configured to receive the first laser beam from the first coupler, the frequency-to-amplitude converter comprising a phase modulator; and

a phase control unit, wherein the phase control unit is configured to control the phase modulator to set a phase modulation characteristic of the phase modulator in a preset mode, wherein the frequency-to-amplitude converter is configured to generate an optical signal having an amplitude variation according to the set phase modulation characteristic, the optical signal having an amplitude variation being characterizable of the set phase modulation characteristic;

a detection module configured to receive the optical signal having a change in amplitude and the second laser beam and to generate a control signal indicative of the set phase modulation characteristic based on the optical signal having a change in amplitude and the second laser beam; and

And a control device coupled to the detection module and the laser and configured to adjust a driving signal of the laser according to the control signal to change a frequency of a laser beam emitted by the laser.

According to one aspect of the invention, the frequency-to-amplitude converter is configured to generate the optical signal with amplitude variation in dependence on frequency jitter and a set phase modulation characteristic of the first laser beam, the optical signal with amplitude variation being indicative of frequency jitter and a set phase modulation characteristic of the first laser beam, the detection module is configured to generate a control signal indicative of frequency jitter and a set phase modulation characteristic of the first laser beam, the control device is configured to adjust a drive signal of the laser in dependence on the control signal to reduce frequency jitter of a laser beam emitted by the laser.

According to an aspect of the invention, the phase control unit is further configured to control the phase modulator according to the optical signal having the amplitude variation to stabilize the phase modulation characteristic of the phase modulator.

According to one aspect of the invention, the frequency-to-amplitude converter has a first transmission arm and a second transmission arm, and a second coupler and a third coupler connected across the first transmission arm and the second transmission arm, respectively, the second coupler being configured to divide the first laser beam into a first sub-beam and a second sub-beam, wherein the first sub-beam is coupled into the first transmission arm and the second sub-beam is coupled into the second transmission arm, the first sub-beam and the second sub-beam generating the optical signal with the amplitude variation after passing through the third coupler.

According to an aspect of the present invention, the phase modulator includes an optical path variable element connected in the first transmission arm and/or the second transmission arm, and the phase control unit is configured to control the laser linear sweep by setting a phase modulation characteristic of the phase modulator by changing an optical path of the optical path variable element in accordance with the preset pattern.

According to an aspect of the present invention, the optical path variable element includes an electro-optic crystal, and the phase control unit is configured to change the optical path thereof by changing a voltage applied to the electro-optic crystal.

According to one aspect of the invention, the phase control unit comprises a first detector, a filter and a first driving source, the third coupler is configured to split the optical signal with amplitude variation into a third sub-beam and a fourth sub-beam, wherein the first detector receives the third sub-beam, the detection module is configured to receive the fourth sub-beam, the filter is coupled between the first detector and the first driving source and is configured to filter an output signal of the first detector, and the first driving source is configured to control the first driving source according to the output signal of the filter so as to change a voltage applied to the electro-optic crystal.

According to one aspect of the invention, the phase control unit is configured to compare the intensity of the output signal of the filter with a preset value, and when the intensity of the output signal of the filter deviates from the preset value, the optical length of the first transmission arm and/or the second transmission arm is changed by changing the voltage of the electro-optical crystal so that the intensity of the output signal of the filter approaches the preset value to stabilize the phase modulation characteristic of the phase modulator.

According to one aspect of the invention, the detection module comprises a second detector configured to receive the optical signal having a change in amplitude and a third detector configured to receive the second laser beam, the control signal being determined by a difference in outputs of the second detector and the third detector.

According to an aspect of the present invention, the laser emitting device further includes an attenuator connected between the first coupler and the third detector to attenuate the second laser beam, wherein an attenuation amount of the attenuator is set according to an attenuation amount of the first laser beam in light intensity passing through the frequency-amplitude converter.

According to one aspect of the invention, the control device comprises an amplifier, a second control unit and a laser driving source which are connected in sequence between the detection module and the laser, wherein the amplifier is configured to amplify the control signal, and the second control unit is configured to control the laser driving source to adjust the driving current of the laser to change the frequency of the laser beam emitted by the laser and reduce the frequency jitter of the laser beam emitted by the laser according to the amplified control signal.

According to one aspect of the present invention, the laser emitting device includes a wavelength division multiplexer and a plurality of the lasers, wherein laser beams emitted by the plurality of lasers are time-division coupled into the first coupler through the wavelength division multiplexer.

According to an aspect of the present invention, the plurality of lasers have different center frequencies, the control means controls the plurality of lasers in a time-sharing manner, and the phase control unit sets the phase modulation characteristics of the phase modulator in accordance with the center frequencies of the plurality of lasers in a time-sharing manner.

According to one aspect of the present invention, the first transmission arm and the second transmission arm in the frequency-amplitude converter include optical fibers or planar waveguides of different lengths, and the optical fibers or planar waveguides of the same material as the first transmission arm and the second transmission arm are connected between the first coupler and the third detector, for transmitting the second laser beam.

The present invention also provides a method of controlling the frequency of a laser using a frequency-to-amplitude converter, wherein the frequency-to-amplitude converter comprises a phase modulator, the method comprising:

emitting a laser beam by a laser;

dividing the laser beam into a first laser beam and a second laser beam;

setting the phase modulation characteristic of the phase modulator according to a preset mode, and generating an optical signal with amplitude variation according to the set phase modulation characteristic through the frequency-amplitude converter, wherein the optical signal with amplitude variation can represent the set phase modulation characteristic;

generating a control signal characterizing the set phase modulation characteristic from the optical signal having amplitude variation and the second laser beam; and

and adjusting a driving signal of the laser according to the control signal so as to change the frequency of the laser beam emitted by the laser.

According to one aspect of the invention, the step of generating an optical signal having a change in amplitude comprises: generating, by the frequency-to-amplitude converter, the optical signal having the amplitude variation according to the frequency jitter of the first laser beam and the set phase modulation characteristic,

The step of generating a control signal characterizing the set phase modulation characteristic from the optical signal having amplitude variation and the second laser beam comprises: generating a control signal characterizing the frequency jitter and the set phase modulation characteristic of the first laser beam from the optical signal having the amplitude variation and the second laser beam,

the step of adjusting the driving signal of the laser according to the control signal comprises: and adjusting a driving signal of the laser according to the control signal so as to reduce frequency jitter of a laser beam emitted by the laser.

According to one aspect of the invention, the method further comprises: the phase modulator is driven and controlled according to the optical signal with amplitude variation so as to stabilize the phase modulation characteristic of the phase modulator.

According to one aspect of the invention, the frequency-to-amplitude converter has a first transmission arm and a second transmission arm, and the step of generating an optical signal having a change in amplitude comprises:

dividing the first laser beam into a first sub-beam and a second sub-beam;

coupling the first sub-beam into the first transmission arm for transmission;

coupling the second sub-beam into the second transmission arm for transmission; and

And synthesizing the first sub-beam and the second sub-beam into the optical signal with the amplitude variation.

According to one aspect of the invention, the phase modulator comprises an optical path variable element connected in the first and/or second transmission arm, the method further comprising:

and changing the optical path of the optical path variable element according to the preset mode to set the phase modulation characteristic of the phase modulator, so as to control the laser to linearly sweep.

According to an aspect of the present invention, the optical path variable element is an electro-optic crystal, the method further comprising:

splitting the optical signal with the amplitude variation into a third sub-beam and a fourth sub-beam;

filtering the third sub-beam;

comparing the intensity of the third sub-beam after filtering with a preset value, and changing the optical length of the first transmission arm and/or the second transmission arm by changing the voltage of the electro-optical crystal when the intensity of the third sub-beam deviates from the preset value, so that the intensity of the third sub-beam after filtering approaches the preset value to stabilize the phase modulation characteristic of the phase modulator.

According to one aspect of the invention, the step of generating the control signal comprises:

Receiving the optical signal with the amplitude variation through a second detector;

receiving the second laser beam by a third detector; and

the control signal is determined by the difference in the outputs of the second detector and the third detector.

According to an aspect of the present invention, the frequency control method further includes: and attenuating the second laser beam by an attenuator, wherein the attenuation amount of the attenuator is set according to the light intensity attenuation amount of the first laser beam passing through the frequency-amplitude converter.

According to one aspect of the invention, the step of adjusting the drive signal of the laser comprises:

amplifying the control signal;

and controlling a driving source of the laser to adjust a driving current of the laser according to the amplified control signal so as to change the frequency of the laser beam emitted by the laser and reduce the frequency jitter of the laser beam emitted by the laser.

The present invention also provides a laser radar including:

the laser emitting device as described above; wherein a part of the laser beam emitted by the laser of the laser emission device is emitted to the surrounding environment of the laser radar as detection light for detecting an obstacle;

A detection unit for receiving an echo of the detection light; and

and the processing unit is coupled with the detection unit and is used for calculating the distance and/or the speed of the obstacle at least according to the echo.

According to one aspect of the invention, the laser radar comprises a fourth coupler, a fifth coupler, a circulator, a collimating unit and a scanning mirror, wherein the fourth coupler is configured to divide a laser beam emitted by the laser into the detection light and the local oscillation light, the circulator is configured to receive the detection light at a first port and emit the detection light from a second port, the detection light is collimated by the collimating unit and reflected by the scanning mirror and is emitted to the environment surrounding the laser radar, the scanning mirror is configured to receive the echo and reflect the echo to the collimating unit, then enters a second port of the circulator and is output from a third port of the circulator, and the local oscillation light and the echo are mixed by the fifth coupler and are output to the detection unit.

The embodiment of the invention can output narrow linewidth laser, and can improve the distance measuring capability and the distance measuring precision when being applied to the frequency modulation continuous wave laser radar. High sweep frequency speed and high linearity can be realized through electric control phase modulation. In addition, the frequency-amplitude converter not only has a periodic multi-passband, but also can realize multi-wavelength multiplexing of the laser radar, and realize scanning in one-dimensional direction (for example, in the direction of vertical field of view) by utilizing the multi-wavelength characteristic so as to simplify the scanning structure of the radar (reduce the scanning structure from two dimensions to one dimension). Moreover, the frequency-amplitude converter can be integrated with the existing optical fiber or on-chip laser radar receiving and transmitting system, has low realization difficulty, and can meet the requirements of miniaturization and low cost of the FMCW laser radar.

Drawings

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate the invention and together with the embodiments of the invention, serve to explain the invention. In the drawings:

FIG. 1 shows a swept frequency signal in the form of a triangular wave commonly used by Frequency Modulated Continuous Wave (FMCW) lidar;

FIG. 2 illustrates a laser emitting device that may be used to implement a frequency sweep in accordance with one embodiment of the present invention;

fig. 3 shows a schematic diagram of the output signal of the detection module including components corresponding to the set phase modulation characteristics and components corresponding to frequency jitter characterizing the first laser beam;

FIG. 4 shows a laser emitting device according to a preferred embodiment of the present invention;

FIG. 5 illustrates a detection module according to a preferred embodiment of the present invention;

FIG. 6 shows a transmittance curve of a frequency-to-amplitude converter according to one embodiment of the invention;

fig. 7 is a graph illustrating a change in output intensity when the frequency of the laser beam is dithered, with one transmission peak in the transmittance curve of fig. 6 as an example;

FIG. 8A shows a plot of actual frequency of an outgoing laser beam of a laser over time;

FIG. 8B shows a plot of the intensity of the optical signal with amplitude jitter output from the frequency-to-amplitude converter versus time jitter;

FIG. 9 shows the operation of the laser emitting apparatus of the embodiment of FIG. 4 for sweeping a frequency;

FIG. 10 shows fluctuations in the transmittance curve of the frequency-to-amplitude converter when subjected to external disturbances;

FIG. 11 shows a specific structure of a multi-wavelength laser module according to another embodiment of the present invention;

FIG. 12 illustrates a method of controlling the frequency of a laser according to one embodiment of the invention;

FIG. 13 illustrates a lidar according to an embodiment of the invention; and

fig. 14 shows a specific structure of a lidar according to a preferred embodiment of the present invention.

Detailed Description

Hereinafter, only certain exemplary embodiments are briefly described. As will be recognized by those of skill in the pertinent art, the described embodiments may be modified in various different ways without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be fixedly connected, detachably connected, or integrally connected, and may be mechanically connected, electrically connected, or may communicate with each other, for example; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

In the present invention, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is less level than the second feature.

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. In order to simplify the present disclosure, components and arrangements of specific examples are described below. They are, of course, merely examples and are not intended to limit the invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, which are for the purpose of brevity and clarity, and which do not themselves indicate the relationship between the various embodiments and/or arrangements discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art will recognize the application of other processes and/or the use of other materials.

The preferred embodiments of the present invention will be described below with reference to the accompanying drawings, it being understood that the preferred embodiments described herein are for illustration and explanation of the present invention only, and are not intended to limit the present invention.

Fig. 2 illustrates a laser emitting device 10 that may be used to implement a frequency sweep in accordance with one embodiment of the present invention, as described in detail below with reference to fig. 2. As shown in fig. 2, the laser emitting device 10 includes a laser 11, a first coupler 12, a frequency-amplitude converter 13, a detection module 14, a control device 15, and a phase control unit 16. Wherein the laser 11 is configured to emit a laser beam L0, the laser 11 may be various types of lasers including, but not limited to, semiconductor lasers or fiber lasers. A first coupler 12 is provided downstream of the laser 11 and configured to receive the laser beam L0 and split the laser beam L0 into a first laser beam L1 and a second laser beam L2. The beam splitting ratio of the first coupler 12 may be set as needed, and it is preferable that the beam splitting ratio of the first laser beam L1 and the second laser beam L2 be 1:1. The first laser beam L1 and the second laser beam L2 each retain the frequency characteristic of the laser beam L0, and the respective light intensities are distributed in accordance with the beam splitting ratio of the first coupler 12. The frequency-amplitude converter 13 is configured to receive the first laser beam L1 from the first coupler 12, and the frequency-amplitude converter 13 includes a phase modulator 131. The phase modulator 131 has a certain phase modulation characteristic and can modulate the phase of the light beam incident thereto. In the present invention, the phase modulation characteristic of the phase modulator 131 is adjustable. The frequency-to-amplitude converter 13 is configured to generate an optical signal LA having an amplitude variation, which characterizes the set phase modulation characteristic, in accordance with the phase modulation characteristic of the set phase modulator 131. The frequency-amplitude converter 13 is a device that can convert a frequency variation of an incident light beam into an amplitude variation, and a specific structure of the frequency-amplitude converter 13 according to a preferred embodiment of the present invention will be described below.

The phase control unit 16 is configured to control the phase modulator 131 to set the phase modulation characteristic of the phase modulator 131 in a preset mode. The detection module 14 is configured to receive the optical signal LA with amplitude variation and the second laser beam L2 and to generate a control signal SF characterizing the set phase modulation characteristic from the optical signal LA with amplitude variation and the second laser beam L2. A control device 15 is coupled to the detection module 14 and the laser 11 and configured to adjust the driving signal of the laser 11 according to the control signal SF to change the frequency of the laser beam emitted by the laser 11.

The frequency-to-amplitude converter 13 has a transmittance curve, i.e. the transmittance of the light beam through the frequency-to-amplitude converter 13 may vary with the frequency of the light beam. The transmittance curve of the frequency-amplitude converter 13 is variable by the action of the phase modulator 131 provided thereon. By adjusting the phase modulator 131 by means of the phase control unit 16, an additional phase can be applied to the transmittance curve of the frequency-amplitude converter 13, so that the central wavelength of the transmission peak in the transmittance curve is changed, the change is reflected by the optical signal LA with amplitude change generated by the frequency-amplitude converter 13, a corresponding control signal SF is generated after passing through the detection module 14, and the control device 15 drives the laser according to the control signal SF, and locks the laser at the working frequency corresponding to the central wavelength, thereby realizing the linear sweep frequency as shown in fig. 1. The specific structure of the frequency-amplitude converter 13 will be described in detail below.

In the laser emitting device 10 shown in fig. 2, the phase modulation characteristic of the phase modulator 131 is set in a preset mode by the phase control unit 16, thereby changing the optical signal LA having an amplitude variation outputted from the frequency-amplitude converter 13, the detection module 14 receives the optical signal LA and simultaneously receives the second laser beam L2, generates a control signal SF representing the set phase modulation characteristic, and the control device 15 feedback-adjusts a driving signal of the laser 11, such as a current or a voltage applied to the laser 11, according to the control signal SF, thereby adjusting the frequency of the laser beam outputted from the laser 11, and realizing a linear sweep as shown in fig. 1.

Thus, as described above, by the phase control unit 16 and the phase modulator 131, the operating point of the laser 11, i.e. the operating frequency of the laser, can be determined.

Typically, during operation, the laser beam L0 emitted by the laser 11 is not always stable at the operating frequency, but is dithered over a range.

When there is a jitter in the frequency of the laser beam L0 emitted from the laser 11, the frequency variation of the emitted laser beam L0 cannot be directly detected with the detector. Such frequency dithering of the laser is disadvantageous for frequency modulated continuous wave lidars that require narrow linewidth to improve ranging capability and ranging accuracy. In the present invention, with the frequency-amplitude converter 13 shown in fig. 2, the frequency jitter of the laser can be converted into amplitude jitter by the frequency-amplitude converter 13, so that it can be detected by the detector. According to one embodiment of the present invention, the frequency-to-amplitude converter 13 is configured to generate the optical signal LA with amplitude variation according to the frequency jitter and the set phase modulation characteristic of the first laser beam L1, and the optical signal LA with amplitude variation may characterize the frequency jitter and the set phase modulation characteristic of the first laser beam L1. In this case, the optical signal LA includes both a component capable of characterizing the set phase modulation characteristic and a component capable of characterizing the frequency jitter of the first laser beam L1. The component characterizing the frequency jitter is due to the frequency jitter of the incident beam and may reflect the frequency jitter size and direction (e.g., larger or smaller). According to one embodiment of the present invention, the optical signal LA includes at least: the component LAL corresponding to the set phase modulation characteristic corresponds to the component LAH characterizing the frequency jitter of the first laser beam L1, and the reference light intensity LA0 is also included in the optical signal LA.

The detection module 14 is configured to receive the optical signal LA with the amplitude variation and the second laser beam L2 and to include in the generated control signal SF not only a component characterizing the set phase modulation characteristic but also a component characterizing the frequency jitter. The control device 15 is configured to adjust the driving signal of the laser 11 according to the control signal SF, so that the light emission frequency of the laser can be set, for example, to achieve a linear change with time frequency, and at the same time, the frequency jitter of the laser beam emitted by the laser 11 can be reduced.

Both the optical signal LA with amplitude variation and the second laser beam L2 come from the laser beam L0 emitted from the laser 11, wherein the optical signal LA with amplitude variation includes three components: the amplitude (intensity) LA0 (i.e., the reference light intensity described above) caused by the amplitude (intensity) L10 of the first laser beam L1 corresponds to the component LAL of the set phase modulation characteristic, corresponds to the component LAH characterizing the frequency jitter of the first laser beam L1, and all three of the components can be detected and converted into a current by the detection module 14. The second laser beam L2 includes two components: the amplitude (intensity) L20 of the second laser beam L2 corresponds to a component L2H characterizing the frequency jitter of said second laser beam L2, which two components can only be detected by the detection module 14 and converted into a current, since the detector cannot directly detect the frequency variation of the second laser beam L2. By flexibly setting the splitting ratio of the first coupler 12, or setting the attenuation of L2 such that L20 is equal to LA0, both cancel each other out, so that the output signal of the final detection module 14 only includes the component LAL corresponding to the set phase modulation characteristic and the current signal corresponding to the component LAH characterizing the frequency jitter of the first laser beam L1, as shown in fig. 3.

Therefore, in the present embodiment, the control device 15 can control the frequency of the laser beam emitted from the laser 11 to achieve a linear sweep according to the optical signal LA having the amplitude variation (the component characterizing the phase modulation characteristic), and at the same time, can reduce the frequency jitter of the laser beam emitted from the laser 11 by the component characterizing the frequency jitter of the first laser beam L1 in the optical signal LA having the amplitude variation, and stabilize it at the frequency determined by the component characterizing the phase modulation characteristic in the optical signal LA. The control device 15 is coupled to the detection module 14 and the laser 11 and configured to adjust the driving signal SD of the laser 11 according to the control signal SF to set or adjust the operating frequency of the laser while reducing the frequency jitter of the laser beam emitted by the laser 11.

Fig. 4 shows the laser emitting device 10 according to a preferred embodiment of the present invention, in which the specific structures of the frequency-amplitude converter 13, the detection unit 14, the control unit 15, and the phase control unit 16 are shown in detail. Described in detail below with reference to fig. 4.

As shown in fig. 4, the frequency-to-amplitude converter 13 has a first ARM1 and a second ARM2, and a second coupler 131 and a third coupler 132, the second coupler 131 and the third coupler 132 are respectively connected to two ends of the first transmission ARM1 and the second transmission ARM2, the second coupler 131 is configured to split the first laser beam L1 into a first sub-beam L11 and a second sub-beam L12, where the first sub-beam L11 is coupled to the first ARM1 for further transmission, and the second sub-beam L12 is coupled to the second ARM2 for further transmission. The first and second sub-beams L11 and L12 pass through the third coupler 132 to generate the optical signal LA having the amplitude variation.

According to an embodiment of the invention, the first ARM1 and the second ARM2 have different optical lengths, so that the first and second beamlets L11 and L12 propagate paths of different lengths in the first transport ARM1 and the second transport ARM2 respectively, when reaching the third coupler 132, the phase relationship with each other changes by an amount related to the optical path difference between the first ARM1 and the second ARM2 (the optical path difference is known) and also to the frequency fluctuation of the first light beam L1. Therefore, after the beam combination in the third coupler 132, the generated optical signal LA having the amplitude variation contains an amplitude jitter component caused by the frequency fluctuation of the first light beam L1. Typically, both the first ARM1 and the second ARM2 of the frequency-to-amplitude converter 13 may be made of a waveguide, which may be made of the same material as the through ARM waveguide between the first coupler 12 and the second detector 142, thereby facilitating the integration of the system. Specifically any of the following materials may be employed: (1) an optical fiber for integration in a fiber optic structural radar; (2) Planar optical waveguide, silicon or silicon nitride or silicon dioxide, the frequency-amplitude converter 13 and the through arm are manufactured on a silicon or silicon nitride chip through a CMOS compatible process for on-chip laser radar integration; (3) lithium niobate.

As shown in fig. 4, the detection module 14 includes a second detector 141 and a third detector 142, the second detector 141 being configured to receive the optical signal LA having a change in amplitude, the third detector 142 being configured to receive the second laser beam L2, and the control signal SF being determined by a difference between outputs of the second detector 141 and the third detector 142, i.e., as shown in fig. 3. According to one embodiment of the invention, the first ARM1 and the second ARM2 of the frequency-to-amplitude converter 13 comprise optical fibers or planar waveguides of different lengths, an optical fiber or a planar waveguide of the same material as the first transmission ARM1 and the second transmission ARM2 is connected between the first coupler 12 and the third detector 142, and is used for transmitting the second laser beam L2.

Fig. 5 shows a detection module 14 according to a preferred embodiment of the invention. As shown in fig. 5, the first detector 141 and the second detector 142 are photodiodes (other types of photodiodes are also possible to convert the optical signal into an electrical signal for output), where the first detector 141 generates a photocurrent I when receiving the optical signal LA with amplitude jitter ₁ The second detector 142 generates a photocurrent I when receiving the second laser beam L2 ₂ The positive electrode of the first detector 141 is connected to the negative electrode of the second detector 142, and the signal output terminal is located therebetween, so that the current outputted from the signal output terminal is Δi=i ₁ -I ₂ The electricity isThe stream signal is the signal characterizing the set phase modulation characteristic and frequency jitter.

According to an embodiment of the present invention, the laser emitting device 10 further includes an attenuator 17, the attenuator 17 being connected between the first coupler 12 and the third detector 142 to attenuate the second laser beam L2, wherein an attenuation amount of the attenuator 17 is set according to an attenuation amount of the first laser beam L1 passing through the frequency-amplitude converter 13. Preferably, when the splitting ratio of the first coupler 12 is 1:1, the attenuation amount of the attenuator 17 is the same as the light intensity attenuation amount of the first laser beam L1 passing through the frequency-amplitude converter 13.

By providing the attenuator 17, the component LA0 of the optical signal LA with the amplitude variation can be made equal to the component L20 of the second laser beam L2, and then the components are cancelled by the detection module 14 as shown in fig. 5, so that the current output by the signal output end only characterizes the set phase modulation characteristic and the frequency jitter signal. Of course, the present invention is not limited to necessarily providing an attenuator. When the attenuator is not provided, the light splitting ratio according to the first coupler 12 can be flexibly set.

According to a preferred embodiment of the present invention, as shown in fig. 4, the control device 15 includes an amplifier 151, a second control unit 152 and a laser driving source 153 sequentially connected between the detection module 14 and the laser 11, wherein the amplifier 151 is configured to amplify the control signal SF, and the second control unit 152 is configured to control the laser driving source 153 to adjust the driving current of the laser 11 according to the amplified control signal to change the frequency of the laser beam emitted from the laser 11 to achieve a linear sweep and to reduce the frequency jitter of the laser beam emitted from the laser.

The working principle of the embodiment of fig. 4 is described below.

Due to the interference effect of the first and second beamlets L11, L12 at the third coupler 132, a transmittance curve as shown in fig. 6 may be formed. The transmittance curve shown in fig. 6 has a certain periodicity, and the transmittance peaks correspond to different frequencies (wavelengths), and have the same frequency interval therebetween. As an example, for a single mode fiber, when the ARM length difference of the first transmission ARM1 and the second transmission ARM2 is 0.5m, the full width at half maximum corresponding to the transmission peak at 1550nm is 200MHz.

Since the frequency of the outgoing laser beam L0 of the laser 11 is dithered, the detector cannot directly detect the frequency variation of the outgoing laser, and the first beam L1 after the outgoing laser beam L0 is split is incident on the frequency-amplitude converter 13, the frequency dithering is converted into amplitude dithering, and the amplitude dithering is detected by the detector. Assuming that the ideal frequency (or center frequency) of the laser 11 is f0, the actual frequency will shake around f 0. Fig. 7 shows, for example, one transmission peak, that when the frequency of the outgoing laser beam L0 of the laser 11 is dithered (dithering is f1 or f2 over time), the intensity of the output differs due to the corresponding transmittance difference. When the outgoing laser beam L0 has a frequency f0, the corresponding transmittance is 1/2, and the corresponding intensity is LA0 (la0=1/2L 10), fig. 8A shows a plot of the actual frequency jitter of the outgoing laser beam L0 of the laser 11 over time, and fig. 8B shows a plot of the intensity of the component representing the frequency jitter of the first laser beam L1 over time in the optical signal LA having a change in amplitude outputted from the frequency-amplitude converter 13. As shown in fig. 8A and 8B, when the outgoing laser beam L0 has a stable ideal frequency f0, the intensity of the optical signal LA is LA0. When the frequency of the outgoing laser beam L0 is dithered around the ideal frequency f0, the intensity of the optical signal LA is dithered around LA0 as well. And when f0, f1, f2 are located in the linear section of the transmittance curve, the frequency jitter and the intensity jitter are in proportional relation. By the detection module 14 in fig. 2, the LA0 component of the intensity of the optical signal LA can be removed according to the intensity of the second laser beam L2, and only the intensity jitter component LAH due to frequency jitter remains. The laser driving module (shown as laser current source 153) is controlled in accordance with a control signal generated by the detection module 14 corresponding to a component LAH characterizing the frequency jitter of said first laser beam L1, for example such that the current supplied to the laser varies in opposite direction to the output signal. Specifically when the frequency dither signal indicates that the frequency becomes large, as in fig. 6, when f0 becomes f2 (i.e., the wavelength becomes smaller by λ2< λ0), the frequency is pulled back from f2 to f0 by increasing the laser drive current; similarly, when the frequency jitter signal indicates a decrease in frequency, as in fig. 6, from f0 to f1 (i.e., a wavelength increase λ1> λ0), the frequency is pulled back from f1 to f0 by decreasing the laser driving current, thereby suppressing the frequency jitter of the laser, i.e., decreasing the linewidth thereof. The control unit 152 may, for example, establish a relationship between the frequency jitter signal intensity and the variation of the laser driving current, and control the variation of the driving current of the laser by the laser current source according to the relationship.

Fig. 8A and 8B show the case where LA0 is a fixed value (the center frequency is a fixed value), but since the linear sweep is performed, the center frequency is time-varying, LA0 is a function of the center frequency, but since the intensity of the second laser beam L2 is also a function of the center frequency, LA0 and L20 can be canceled.

Fig. 9 shows the operation of the laser emitting device 10 of the embodiment of fig. 4 in a frequency sweep. It is assumed that the first ARM1 is provided with a phase modulator 133, the phase modulator 133 is an electro-optical crystal, the length of the electro-optical crystal is L, the refractive index of the electro-optical crystal is n, and the refractive index n varies with the voltage V of the driving source applied to the crystal, that is, the refractive index n is a function of the voltage V, so that the total optical length of the first ARM1 varies. As an additional phase is applied to the transmittance curve of the frequency-amplitude converter 13 by the first driving source 163, the center wavelength of the transmission peak is changed and the operating point is moved, thereby realizing the desired set linear sweep. According to the control signal generated by the detection module 14 and corresponding to the component LAL of the set phase modulation characteristic, the laser 11 is always locked at the operating point under the action of the control device 15, so that a linear frequency sweep is realized. Specifically, as shown in fig. 9. At a first time T1, the operating point corresponds to a first frequency (corresponding to a first wavelength, as shown by a solid line waveform), at a second time T2, the operating point corresponds to a second frequency (corresponding to a second wavelength, as shown by a dotted line waveform), and at a third time T3, the operating point corresponds to a third frequency (corresponding to a third wavelength, as shown by a dotted line waveform), a linear sweep as shown in fig. 1 is finally formed.

When an external disturbance occurs, for example, when the ambient temperature changes, the phase modulation characteristic of the phase modulator 131 may change or fluctuate accordingly. Such variations or fluctuations are detrimental to the control of the laser linear sweep. In view of external disturbances, according to a preferred embodiment of the invention, the phase control unit 16 is further configured to control the phase modulator 131 in dependence of the optical signal LA with amplitude variation to stabilize the phase modulation characteristics of the phase modulator 131, e.g. to ensure linearity. For example, when the phase modulation characteristic of the phase modulator 131 of the frequency-amplitude converter 13 fluctuates due to external disturbance (e.g., temperature change), the laser 11 may be caused to lose lock. The operating point can thus be stabilized by the optical signal LA with amplitude variation, so that the entire swept laser operates stably. Specific preferred embodiments will be described in detail below.

In the embodiment of fig. 4, the phase modulator 133 may comprise an optical path variable element connected in the first transmission ARM1, and the phase control unit 16 is configured to control the laser 11 to realize a linear sweep by setting the phase modulation characteristic of the phase modulator 133 by changing the optical path of the optical path variable element according to the preset pattern. According to a preferred embodiment of the invention, the optical path variable element comprises an electro-optic crystal, and the phase control unit is configured to change its optical path by changing a voltage applied to the electro-optic crystal. The optical path variable element is shown in fig. 4 as being connected in the first ARM1, to which the invention is not limited, the variable optical path element can also be connected in the second ARM2, or in both the first ARM1 and the second ARM 2. As shown in fig. 4, when the phase modulation characteristic of the phase modulator 131 fluctuates due to external disturbance and the laser 11 is caused to lose lock, a function of stabilizing the phase modulation characteristic of the phase modulator 131 can be achieved by the behavior control unit 16 with a feedback function. As shown in fig. 4, according to a preferred embodiment of the present invention, the phase control unit 16 includes a first detector 161, a filter 162, and a first driving source 163, wherein the first detector 161 is configured to detect the intensity of the optical signal LA having amplitude jitter. Specifically, after the third coupler 132 combines the first sub-beam L11 and the second sub-beam L12 into the optical signal LA with amplitude jitter, the optical signal LA with amplitude jitter may be further split, for example, a part of the optical signal (for example, a smaller proportion of 5%, 3%, 1% or a larger proportion of 50%) is transmitted to the first detector 161 (the third sub-beam) for making feedback adjustment for external interference, and another part of the optical signal LA is transmitted to the detection unit 14 (the fourth sub-beam). The first detector 161 converts a small portion of the optical signal from the optical signal LA having amplitude jitter into an electrical signal and filters it through the filter 162. The filter 162 is preferably a low pass filter. The change in the optical signal LA caused by external interference is typically a low frequency component. By using a low-pass filter, both the component LAL of LA corresponding to the set phase modulation characteristic and the component LAH corresponding to the frequency jitter characterizing the first laser beam L1 as described above can be filtered out, leaving only the low-frequency component, achieving the objective of making feedback adjustments for external disturbances.

The filter 162 is coupled between the first detector 161 and the first driving source 163, and is configured to filter an output signal of the first detector 161, and the first driving source 163 is configured to control the phase modulator 133, for example, to change a voltage applied to the electro-optical crystal to change an optical path thereof, according to an output signal of the filter 162.

According to one embodiment of the invention, the phase control unit 16 is configured to compare the intensity of the output signal of the filter 162 with a preset value, and when the intensity of the output signal of the filter 162 deviates from the preset value, the optical length of the first transmission ARM1 and/or the second transmission ARM2 is changed by changing the voltage of the electro-optical crystal, so that the intensity of the output signal of the filter 162 approaches the preset value to stabilize the phase modulation characteristic of the phase modulator 133. In addition to the electro-optic crystal, the phase modulator 133 may include a piezoelectric layer disposed on the first ARM ARM1 and/or the second ARM ARM 2. The refractive index of the first ARM1 and/or the second ARM2 may be changed by adjusting the voltage applied thereto using a piezoelectric layer. By changing the optical length of the first ARM1 and/or the second ARM2, the optical modulation characteristic of the frequency-to-amplitude converter 13 will be changed, and thus the intensity of the optical signal LA output from the third coupler 132 will be changed.

Fig. 10 shows fluctuations in the transmittance curve of the frequency-amplitude converter 13 when subjected to external disturbance (e.g., temperature change). When the temperature fluctuates, the curve affected by the temperature can be pulled back to the ideal curve by the phase control unit 16; fig. 10 shows an ideal transmittance curve and an actual transmittance curve at a certain point in time, and when the actual operating point deviates from the ideal operating point due to the influence of temperature (for example, the transmittance corresponding to the actual operating point is no longer 1/2), the output light intensity changes. When there is no external disturbance, the intensity of the output signal received by the first detector 161 after filtering is the expected value, that is, half of the input light intensity, and when the external disturbance occurs, the magnitude and the influence direction of the external disturbance can be calculated according to the variation of the detected intensity of the output signal relative to the expected value, so that the first driving source 163 is used to stabilize the phase modulation characteristic of the phase modulator 133 and adjust the transmittance curve of the frequency-converter 13.

Thus, even if the laser is out of lock due to the potential for the frequency-to-amplitude converter to be disturbed by the external environment, the signal obtained by the first detector 161 can be used to stabilize the operating point of the laser so that the entire laser sweep operates stably. As shown in fig. 10, the actual working point deviates from the ideal working point, at this time, the intensity of the output signal received by the first detector 161 and filtered deviates from the expected value, and the output signal is converted into the control signal of the first driving source according to the magnitude of the deviation from the expected value, so that the actual working point is pulled back to the ideal working point, and the linearity of the frequency sweep is ensured through real-time monitoring. Therefore, even if the temperature change is large, the normal operation of the laser is not affected.

In the above embodiments, the laser emitting devices 10 each include one laser. The present invention is not limited thereto and may include a plurality of lasers.

Fig. 11 shows a specific structure of a multi-wavelength laser module according to an embodiment of the present invention. As shown in fig. 11, the laser emitting device 10 includes a wavelength division multiplexer 18 and a plurality of the lasers 11, four lasers are schematically shown in fig. 11 as lasers 11-1, 11-2, 11-3 and 11-4, respectively. Wherein laser beams emitted from the plurality of lasers 11 are coupled into the first coupler 12 through the wavelength division multiplexer 18 and output from the first coupler 12 in a time-sharing manner. Lasers 11-1, 11-2, 11-3 and 11-4 have different center frequencies f00, f01, f02, f03, respectively, corresponding to the four transmission peaks in the transmission curve as in FIG. 6. The four lasers are time-division coupled into the same waveguide for transmission (laser beam L0) through the wavelength division multiplexing device 18, then time-division into the first coupler 12, and divided into two beams by the first coupler 12, respectively, a first laser beam L1 and a second laser beam L2, the first laser beam L1 enters the frequency-amplitude converter 13, the laser LA exiting from the frequency-amplitude converter 13 enters the detection module 14, detected by the first detector 141, the second laser beam L2 passes through the through waveguide directly into the detection module 14, detected by the second detector 142 (optionally after passing through the attenuator 16 shown in fig. 4, detected by the second detector 142), and in addition, the phase control unit 16 time-division sets the phase modulation characteristics of the phase modulator 133 according to the center frequencies of the plurality of lasers. The detection module 14 is configured to detect amplitude variations caused by frequency jitter and set phase modulation characteristics of the laser 11-1 at time t 1; at time t2, the detection module 14 is configured to detect … amplitude variations caused by frequency jitter and the set phase modulation characteristics of the laser 11-2, and so on. The control unit 152 controls the laser current sources 153 to supply the respective driving currents to the different lasers 11 in a time-sharing manner, thereby stabilizing the frequency compression linewidths of the plurality of lasers and enabling the plurality of lasers to realize linear sweep.

The frequency-amplitude converter 13 of the invention has a periodic passband, so that the frequency-amplitude converter can be integrated in a multi-wavelength frequency modulation continuous wave FMCW system, the temperature/current of lasers with different wavelengths can be adjusted, the frequency of each laser is positioned in the middle of the rising edge or the falling edge of a transmission peak (the jitter of the frequency is in a linear section, and the same frequency jitter brings about the same intensity jitter), and multiplexing of a multi-wavelength line width compression function can be realized by using a single frequency-amplitude conversion device, thereby effectively reducing the complexity and the cost of the system.

The present invention also provides a method 100 of controlling the frequency of a laser using a frequency-to-amplitude converter comprising a phase modulator 133. Described in detail below with reference to fig. 12, and fig. 1-10. As shown in fig. 12, the method 100 includes:

in step S101: emitting a laser beam L0 by a laser 11;

in step S102: dividing the laser beam into a first laser beam L1 and a second laser beam L2;

in step S103: setting the phase modulation characteristic of the phase modulator 133 in a preset mode, and generating an optical signal LA having an amplitude variation, which characterizes the set phase modulation characteristic, from the set phase modulation characteristic by the frequency-amplitude converter 13;

In step S104: generating a control signal SF characterizing the set phase modulation characteristic from the optical signal LA having the amplitude variation and the second laser beam L2; and

in step S105: the driving signal of the laser 11 is adjusted according to the control signal SF to change the frequency of the laser beam emitted by the laser.

According to one embodiment of the invention, the step of generating an optical signal having a change in amplitude comprises: generating the optical signal LA with amplitude variation according to the frequency jitter of the first laser beam L1 and the set phase modulation characteristic by the frequency-amplitude converter 13,

the step of adjusting the driving signal of the laser 11 according to the control signal SF includes: the driving signal of the laser 11 is adjusted according to the control signal SF to reduce frequency jitter of the laser beam emitted from the laser 11.

According to one embodiment of the invention, the method further comprises: the phase modulator 133 is drive-controlled according to the optical signal LA having the amplitude variation to stabilize the phase modulation characteristic of the phase modulator 133.

According to one embodiment of the invention, the frequency-to-amplitude converter 13 has a first ARM1 and a second ARM2, and the step of generating the optical signal LA with a variation in amplitude comprises:

dividing the first laser beam L1 into a first sub-beam L11 and a second sub-beam L12;

coupling the first sub-beam L11 into the first transmission ARM1 for transmission;

coupling the second sub-beam L12 into the second transmission ARM2 for transmission; and

the first and second sub-beams L11 and L12 are combined into the optical signal LA having the amplitude variation.

According to one embodiment of the invention, the phase modulator 13 comprises an optical path variable element connected in the first ARM1 and/or the second ARM2, the method further comprising:

the phase modulation characteristic of the phase modulator 133 is set by changing the optical path of the optical path variable element in accordance with the preset pattern, thereby controlling the linear sweep of the laser 11.

According to an embodiment of the invention, the optical path variable element is an electro-optic crystal, the method further comprising:

splitting the optical signal LA with the amplitude variation into a third sub-beam and a fourth sub-beam;

filtering the third sub-beam;

comparing the intensity of the filtered third sub-beam with a preset value, and changing the optical length of the first transmission ARM ARM1 and/or the second transmission ARM ARM2 by changing the voltage of the electro-optical crystal when the intensity of the third sub-beam deviates from the preset value, so that the intensity of the filtered third sub-beam approaches the preset value to stabilize the phase modulation characteristic of the phase modulator 133.

According to one embodiment of the invention, the step of generating the control signal SF comprises:

receiving the optical signal LA with the amplitude variation by the second detector 141;

receiving the second laser beam L2 by a third detector 142; and

the control signal SF is determined by a difference of outputs of the second detector 141 and the third detector 142.

According to one embodiment of the invention, the method further comprises: the second laser beam L2 is attenuated by an attenuator 17, wherein the attenuation amount of the attenuator 17 is set according to the light intensity attenuation amount of the first laser beam L1 through the frequency-amplitude converter 13.

According to one embodiment of the present invention, the step of adjusting the driving signal of the laser 11 includes:

amplifying the control signal SF;

according to the amplified control signal, the driving source of the laser 11 is controlled to adjust the driving current of the laser 11 to change the frequency of the laser beam emitted from the laser 11 and to reduce the frequency jitter of the laser beam emitted from the laser 11.

The present invention also relates to a lidar 200, as shown in fig. 13, described in detail below with reference to fig. 13. As shown in fig. 13, the lidar 200 includes: the laser emitting device 10, the detection unit 202, and the processing unit 203 as described above. Wherein a larger part L of the laser beam emitted by the laser of the laser emitting device 10 is emitted as detection light into the environment surrounding the lidar for detecting an obstacle. A smaller portion enters the first coupler 12 for linewidth compression and scanning frequency control (not shown), for example, by providing a proportional beam splitter upstream of the first coupler 12. The detection unit 202 is configured to receive the echo L 'of the detection light and convert the echo L' into an electrical signal. A processing unit 203 is coupled to the detection unit 202 for calculating the distance and/or velocity of the obstacle at least from the echoes.

Fig. 14 shows a specific structure of a lidar 200 according to a preferred embodiment of the present invention, wherein the lidar 200 is a frequency modulated continuous wave FMCW radar. As shown in fig. 14, in addition to the laser emitting device 10, the detecting unit 202 and the processing unit 203, the laser radar 200 further includes a fourth coupler 204, a fifth coupler 20, a circulator 206, a collimating unit 207 and a scanning mirror 208, wherein the fourth coupler 204 is configured to use a larger portion L of the laser beam emitted from the laser emitting device 10 for detection (a smaller portion is used for line width compression and scanning frequency control, not shown in the drawing), the portion for detection is divided into detection light and local oscillation light, the circulator 206 is configured to receive the detection light at the first port 1 and emit the detection light from the second port 2, and the detection light is collimated by the collimating unit 207 and reflected by the scanning mirror 208 and then emitted into the environment surrounding the laser radar. The scanning mirror 208 is configured to receive the echo and reflect it to the collimating unit 207, then enter the second port 2 of the circulator 206 and output from the third port 3 of the circulator 206, and the local oscillation light and the echo are mixed by the fifth coupler 205 and output to the detecting unit 202, and then information such as the distance of an obstacle is calculated via the processing unit 203.

Because the laser transmitting device 10 of the invention can output narrow linewidth laser, the distance measuring capability and the distance measuring precision can be improved when the laser transmitting device is applied to the frequency modulation continuous wave laser radar. High sweep frequency speed and high linearity can be realized through electric control phase modulation. In addition, the frequency-amplitude converter not only has a periodic multi-passband, but also can realize multi-wavelength multiplexing of the laser radar, and realize scanning in one-dimensional direction (for example, in the direction of vertical field of view) by utilizing the multi-wavelength characteristic so as to simplify the scanning structure of the radar (reduce the scanning structure from two dimensions to one dimension). Moreover, the frequency-amplitude converter can be integrated with the existing optical fiber or on-chip laser radar receiving and transmitting system, has low realization difficulty, and can meet the requirements of miniaturization and low cost of the FMCW laser radar.

Finally, it should be noted that: the foregoing description is only a preferred embodiment of the present invention, and the present invention is not limited thereto, but it is to be understood that modifications and equivalents of some of the technical features described in the foregoing embodiments may be made by those skilled in the art, although the present invention has been described in detail with reference to the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser emitting device comprising:

a laser configured to emit a laser beam;

2. The laser emitting device of claim 1, wherein the frequency-to-amplitude converter is configured to generate the optical signal having an amplitude variation in accordance with a frequency jitter and a set phase modulation characteristic of the first laser beam, the optical signal having an amplitude variation being indicative of the frequency jitter and the set phase modulation characteristic of the first laser beam, the detection module being configured to generate a control signal indicative of the frequency jitter and the set phase modulation characteristic of the first laser beam, the control device being configured to adjust a drive signal of the laser in accordance with the control signal to reduce the frequency jitter of the laser beam emitted by the laser.

3. The laser emitting device according to claim 1, wherein the phase control unit is further configured to control the phase modulator according to the optical signal having the amplitude variation to stabilize a phase modulation characteristic of the phase modulator.

4. The laser emitting device of claim 1, wherein the frequency-to-amplitude converter has first and second transmission arms, and second and third couplers connected at both ends of the first and second transmission arms, respectively, the second coupler configured to divide the first laser beam into first and second sub-beams, wherein the first sub-beam is coupled into the first transmission arm, the second sub-beam is coupled into the second transmission arm, and the first and second sub-beams generate the optical signal having the amplitude variation after passing through the third coupler.

5. The laser emitting device according to claim 4, wherein the phase modulator includes an optical path variable element connected in the first transmission arm and/or the second transmission arm, the phase control unit being configured to control the laser linear sweep by setting a phase modulation characteristic of the phase modulator by changing an optical path of the optical path variable element in accordance with the preset pattern.

6. The laser light emitting device according to claim 5, wherein the optical path variable element comprises an electro-optical crystal, and the phase control unit is configured to change an optical path thereof by changing a voltage applied to the electro-optical crystal.

7. The laser light emitting device according to claim 6, wherein the phase control unit includes a first detector, a filter, and a first driving source, a third coupler configured to split the optical signal having a change in amplitude into a third sub-beam and a fourth sub-beam, wherein the first detector receives the third sub-beam, the detection module is configured to receive the fourth sub-beam, the filter is coupled between the first detector and the first driving source, and is configured to filter an output signal of the first detector, and the first driving source is configured to control the first driving source according to an output signal of the filter to change a voltage applied to the electro-optical crystal.

8. The laser light emitting device according to claim 7, wherein the phase control unit is configured to compare the intensity of the output signal of the filter with a preset value, and when the intensity of the output signal of the filter deviates from the preset value, the optical length of the first transmission arm and/or the second transmission arm is changed by changing the voltage of the electro-optical crystal so that the intensity of the output signal of the filter approaches the preset value to stabilize the phase modulation characteristic of the phase modulator.

9. The laser emitting device of claim 4, wherein the detection module comprises a second detector configured to receive the optical signal having a change in amplitude and a third detector configured to receive the second laser beam, the control signal being determined by a difference in outputs of the second and third detectors.

10. The laser emitting device according to claim 9, further comprising an attenuator connected between the first coupler and the third detector to attenuate the second laser beam, wherein an attenuation amount of the attenuator is set according to an amount of light intensity attenuation of the first laser beam through the frequency-amplitude converter.

11. The laser emitting device according to claim 4, wherein the control device comprises an amplifier, a second control unit and a laser driving source connected in this order between the detection module and the laser, wherein the amplifier is configured to amplify the control signal, and the second control unit is configured to control the laser driving source to adjust a driving current of the laser to change a frequency of the laser beam emitted by the laser and to reduce frequency jitter of the laser beam emitted by the laser according to the amplified control signal.

12. The laser emitting device according to any one of claims 1-7, wherein the laser emitting device comprises a wavelength division multiplexer and a plurality of the lasers, wherein laser beams emitted by the plurality of lasers are time-division coupled into the first coupler by the wavelength division multiplexer.

13. The laser emitting apparatus according to claim 12, wherein a plurality of the lasers have different center frequencies, the control means controls the plurality of the lasers in a time-sharing manner, and the phase control unit sets the phase modulation characteristics of the phase modulator in accordance with the center frequencies of the plurality of lasers in a time-sharing manner.

14. The laser emitting device according to claim 9 or 10, wherein the first and second transmission arms in the frequency-amplitude converter comprise optical fibers or planar waveguides of different lengths, and an optical fiber or planar waveguide of the same material as the first and second transmission arms is connected between the first coupler and the third detector for transmitting the second laser beam.

15. A method of controlling a frequency of a laser using a frequency-to-amplitude converter, wherein the frequency-to-amplitude converter comprises a phase modulator, the method comprising:

emitting a laser beam by a laser;

dividing the laser beam into a first laser beam and a second laser beam;

16. The method of claim 15, wherein the step of generating an optical signal having a change in amplitude comprises: generating, by the frequency-to-amplitude converter, the optical signal having the amplitude variation according to the frequency jitter of the first laser beam and the set phase modulation characteristic;

17. The method of claim 15, further comprising: the phase modulator is driven and controlled according to the optical signal with amplitude variation so as to stabilize the phase modulation characteristic of the phase modulator.

18. The method of any of claims 15-17, wherein the frequency-to-amplitude converter has a first transmission arm and a second transmission arm, the step of generating an optical signal having a change in amplitude comprising:

Dividing the first laser beam into a first sub-beam and a second sub-beam;

coupling the first sub-beam into the first transmission arm for transmission;

19. The method of claim 18, wherein the phase modulator comprises an optical path variable element connected in the first and/or second transmission arm, the method further comprising:

20. The method of claim 19, wherein the optical path variable element is an electro-optic crystal, the method further comprising:

filtering the third sub-beam;

21. The method of claim 18, wherein generating the control signal comprises:

receiving the second laser beam by a third detector; and

22. The method of claim 21, further comprising: and attenuating the second laser beam by an attenuator, wherein the attenuation amount of the attenuator is set according to the light intensity attenuation amount of the first laser beam passing through the frequency-amplitude converter.

23. The method of claim 15, wherein the step of adjusting the drive signal of the laser comprises:

amplifying the control signal;

24. A lidar, comprising:

the laser emitting device of any one of claims 1-14; wherein a part of the laser beam emitted by the laser of the laser emission device is emitted to the surrounding environment of the laser radar as detection light for detecting an obstacle;

A detection unit for receiving an echo of the detection light; and

25. The lidar of claim 24, wherein the lidar comprises a fourth coupler configured to split a laser beam emitted by the laser into the probe light and a local oscillator light, a fifth coupler configured to receive the probe light at a first port and to emit the probe light from a second port, the probe light being collimated by the collimation unit and reflected by the scanning mirror and to emit the probe light into an environment surrounding the lidar, a circulator configured to receive the echo and reflect it to the collimation unit, and then to enter the second port of the circulator and to output from the third port of the circulator, the local oscillator light and the echo being mixed by the fifth coupler and output to the detection unit.