CN116990784A - Linearity correction system of double micro-ring resonant cavity type semiconductor laser - Google Patents
Linearity correction system of double micro-ring resonant cavity type semiconductor laser Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/497—Means for monitoring or calibrating
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
- H01S5/0608—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by light, e.g. optical switch
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/1071—Ring-lasers
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/14—External cavity lasers
- H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
- H01S5/5054—Amplifier structures not provided for in groups H01S5/02 - H01S5/30 in which the wavelength is transformed by non-linear properties of the active medium, e.g. four wave mixing
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Abstract
The invention discloses a linearity correction system of a double micro-ring resonant cavity type semiconductor laser, which belongs to the field of laser correction, and is characterized in that nonlinear frequency signals output by the double micro-ring resonant cavity type semiconductor laser driven by standard triangular wave modulation signals are corrected to obtain predistortion waveforms, the predistortion waveforms are amplified in proportion and then output three paths of driving signals to be applied to a double micro-ring modulator and a phase shifter integrated in the double micro-ring resonant cavity type semiconductor laser, the output nonlinear frequency signals are corrected, and the double micro-ring resonant cavity type semiconductor laser outputs frequency modulation linear continuous triangular wave frequency signals through multiple-round correction, so that the linearity correction of the double micro-ring resonant cavity type semiconductor laser is completed. The laser ranging device can be used for high-precision laser ranging, can effectively solve the problem of frequency modulation nonlinearity of the double micro-ring resonant cavity type semiconductor laser under the condition of large-range sweep frequency, and reduces the measurement error caused by the laser.
Description
Technical Field
The invention relates to the technical field of laser correction, in particular to a linearity correction system of a double micro-ring resonant cavity type semiconductor laser.
Background
The frequency modulation continuous wave (Frequency Modulated Continuous Wave, FMCW) laser radar adopts a mode of coherent detection rather than direct detection, and detects beat signals of emission and echo signals through laser frequency modulation in a time domain, so as to complete simultaneous detection of the distance and the speed of a target. Compared with the traditional time-of-flight (TOF) laser radar, the frequency modulation continuous wave laser radar has the advantages of stronger environment interference resistance, capability of realizing farther-distance detection and the like, and is widely paid attention to the industry and academia.
In the future, silicon-based integration of the laser radar is a necessary trend, so that the frequency modulation continuous wave laser in the laser radar light source is necessary to go forward in the direction of silicon light integration, and the integration miniaturization of the laser radar is necessarily less than that of an integrated micro laser. The double micro-ring resonant cavity type semiconductor laser is a laser manufactured by adopting a silicon optical integration technology, has the characteristics of small volume, large tunable range and the like, and the tuning mode is mainly controlled by a micro-ring modulator and a phase shifter. The double micro-ring resonant cavity type semiconductor laser manufactured by adopting the silicon optical integration technology is integrated with the whole FMCW frequency modulation continuous wave system, so that the cost and the volume of the existing laser radar system are greatly reduced. However, the chirp signal produced by a fm continuous wave lidar system is typically not perfectly linear, such that the nonlinear signal produced by the fm continuous wave can severely broaden the spectral band of the beat signal and affect the final ranging accuracy.
If the laser has nonlinear effect, the overall accuracy and resolution of the laser radar will be reduced, and the dual micro-ring resonant cavity type semiconductor laser applied in the field of FMCW laser radar is loaded with linear drive, and the output is not linear output but has nonlinear frequency output, so how to solve inherent nonlinearity of the dual micro-ring resonant cavity type semiconductor laser is the focus of research in the industry.
Disclosure of Invention
The invention provides a linearity correction system of a double micro-ring resonant cavity type semiconductor laser, which solves the problems that in the prior art, under the condition of wide-range frequency sweep of the double micro-ring resonant cavity type semiconductor laser, the frequency spectrum obtained by FMCW laser radar measurement is difficult to distinguish, the target position cannot be identified and the like due to the nonlinear problem of the laser.
The embodiment of the invention provides a linearity correction system of a double micro-ring resonant cavity type semiconductor laser, which comprises a first micro-ring resonator, a second micro-ring resonator and a phase shifter, wherein the linearity correction system comprises:
the temperature controller is connected with the double micro-ring resonant cavity type semiconductor laser and used for keeping the temperature of the double micro-ring resonant cavity type semiconductor laser constant so as to prevent the output wavelength of the double micro-ring resonant cavity type semiconductor laser from jumping from a mode;
the input end of the emission light path is connected with the double micro-ring resonant cavity type semiconductor laser and is used for generating two paths of optical signals, wherein the first path of optical signals are sent to a laser radar emission end, and the second path of optical signals are sent to an MZI (Mach-Zehnder Interferometer ) structure of a non-equal arm;
the MZI structure of the unequal arm is used for carrying out frequency mixing on the received optical signals after different time delays to generate optical signals after beat frequency;
the input end of the balance photoelectric detector is connected with the output end of the MZI structure of the unequal arm and is used for converting the optical signal after beat frequency into an electric signal after beat frequency;
the data processing module is used for calculating the frequency and the phase of the optical signal after beat frequency after analog-digital conversion of the electric signal after beat frequency, calculating the chirp frequency and the linearity of the output optical signal of the double micro-ring resonant cavity type semiconductor laser according to the frequency and the phase, further calculating the expected linear frequency straight line of continuous wave frequency modulation, calculating an error value between an ideal frequency modulation curve and an actual frequency modulation curve, and generating a predistortion waveform by overlapping the error value with the actual frequency modulation curve after scale conversion of the error value in a preset range proportion;
the input end of the proportional amplifying circuit is connected with the output end of the data processing module, the three output ends of the proportional amplifying circuit are respectively connected with the first micro-ring resonator, the second micro-ring resonator and the phase shifter of the double micro-ring resonant cavity type semiconductor laser, the proportional amplifying circuit is used for amplifying the predistortion waveform according to a set proportion to obtain three output voltages, the three output voltages are respectively applied to the first micro-ring resonator, the second micro-ring resonator and the phase shifter of the double micro-ring resonant cavity type semiconductor laser, the first micro-ring resonator and the second micro-ring resonator form a filter structure with vernier effect, and frequency modulation linear continuous triangular wave frequency signals are generated by adjusting the phase shifter, the first micro-ring resonator and the second micro-ring resonator to realize alignment with resonant wavelengths with vernier effect and performing mode selection.
In one embodiment of the invention, the emission light path includes:
the input end of the optical isolator is connected with the output end of the double micro-ring resonant cavity type semiconductor laser;
the input end of the first optical beam splitter is connected with the output end of the optical isolator, the first output end is a laser radar transmitting end, and the first optical beam splitter is used for splitting laser emitted by the double micro-ring resonant cavity type semiconductor laser.
In one embodiment of the invention, the MZI structure of the non-equal arm comprises:
the second optical beam splitter receives a second path of optical signals of the first optical beam splitter and is used for dividing the received optical signals into two paths of optical signals;
the input end of the first optical attenuator receives a first path of optical signals of the second optical beam splitter;
the input end of the delay line receives a second path of optical signals of the second optical beam splitter and is used for applying delay to the second path of optical signals;
the input end of the second optical attenuator is connected with the output end of the delay line and is used for receiving a delayed second path of optical signals;
the optical mixer comprises a first input end, a second input end and an output end, wherein the first input end of the optical mixer is connected with the output end of the first optical attenuator, the second input end of the optical mixer is connected with the output end of the second optical attenuator, the output end of the optical mixer is connected with the input end of the balance photoelectric detector, the light intensities of two paths of output light are matched by commonly adjusting the first optical attenuator and the second optical attenuator, and the two paths of optical signals are mixed to generate optical signals after beat frequency.
In one embodiment of the invention, the data processing module comprises:
the input end of the analog-to-digital converter is connected with the output end of the balance photoelectric detector and is used for converting the electric signal after beat frequency into a digital signal;
the input end of the data processing unit is connected with the output end of the analog-to-digital converter, the data processing unit is used for carrying out Hilbert transformation on a beat frequency digital signal to obtain a transformed complex signal, according to the characteristic that the Hilbert transformation has a 90-degree phase shift filter, a phase change curve of the beat frequency digital signal is obtained by utilizing the quotient of an imaginary part and a real part of the complex signal, a chirp frequency curve of the double micro-ring resonant cavity type semiconductor laser is obtained by utilizing the constant proportional relation between the phase change curve and an original chirp frequency curve of a frequency modulation continuous wave, a corresponding expected chirp frequency straight line is calculated according to the phase change curve, a frequency modulation nonlinearity of a transmission signal of the double micro-ring resonant cavity type semiconductor laser is obtained according to the relation between an obtained actual frequency modulation curve and an ideal linear frequency modulation continuous wave frequency, an error value between the ideal frequency modulation curve and the actual frequency modulation curve is obtained by calculation, and the predistortion waveform is generated after the scale transformation of the error value in a preset range and the actual frequency modulation curve phase is overlapped;
the input end of the digital-to-analog converter is connected with the output end of the data processing unit, and the output end of the digital-to-analog converter is connected with the input end of the proportional amplifying circuit and is used for converting the digital signal of the data processing unit into an electric signal and outputting the electric signal to the proportional amplifying circuit.
According to the linearity correction system of the double micro-ring resonant cavity type semiconductor laser, a double micro-ring modulator and a phase shifter are integrated in the double micro-ring resonant cavity type semiconductor laser, in an initial stage, the double micro-ring resonant cavity type semiconductor laser is driven through standard triangular wave modulation signals, nonlinear frequency signals are output by the double micro-ring resonant cavity type semiconductor laser in a nonlinear output mode, predistortion waveforms are obtained through correction of the nonlinear frequency signals output by the double micro-ring resonant cavity type semiconductor laser, the predistortion waveforms are amplified in proportion and then output three paths of driving signals to be applied to the double micro-ring modulator and the phase shifter integrated in the double micro-ring resonant cavity type semiconductor laser for driving, the nonlinear frequency signals output by the double micro-ring resonant cavity type semiconductor laser are corrected, and the frequency-modulated linear continuous triangular wave frequency signals are output by the double micro-ring resonant cavity type semiconductor laser through multiple-wheel correction, so that the linearity correction of the double micro-ring resonant cavity type semiconductor laser is completed. The laser ranging device can be used for high-precision laser ranging, can effectively solve the problem of frequency modulation nonlinearity of the double micro-ring resonant cavity type semiconductor laser under the condition of large-range sweep frequency, and reduces the measurement error caused by the laser.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:
fig. 1 is a schematic diagram of a basic principle of a frequency modulation linear continuous wave laser radar ranging according to an embodiment of the present invention;
FIG. 2 is a diagram showing a comparison of ranging of a frequency modulated nonlinear continuous wave laser radar according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a system for linearity correction of a dual micro-ring resonator type semiconductor laser according to an embodiment of the present invention;
FIG. 4 is a scaled up circuit diagram provided in accordance with an embodiment of the present invention;
FIG. 5 is a block diagram of a linearity correction system for a semiconductor laser, specifically a dual micro-ring resonator, according to an embodiment of the present invention;
fig. 6 is a flowchart of a nonlinear correction method according to an embodiment of the present invention.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
FIG. 1 (a) is a frequency modulated triangular waveform showing a standard time-dependent frequency-time relationship of triangular wave variation; fig. 1 (b) is a time domain amplitude plot of a frequency modulated signal, showing the amplitude of the frequency modulated signal as a function of time; and (c) of FIG. 1 is a frequency-modulated triangular waveform and corresponding beat signal before and after delayThe graph shows the frequency change relation with time before and after delay and the beat frequency signal change relation with time after self heterodyning. The local oscillation light and the echo signal interfere in the coupler and are converted into a beat frequency signal f after being converted into an electric signal by the balanced photoelectric detector beat The method comprises the following steps:
f beat (t)＝γτ
wherein, gamma is the modulation slope of the frequency modulation triangle wave, tau is the delay time of the echo signal, and is calculated by the optical path and the speed of the echo signal. It can be seen from fig. 1 that in the case of chirp, the output beat signal is a constant over a period of time, and the slope section of the beat signal is mainly caused by the abrupt turning of the chirp triangle wave around the extreme point.
As shown in fig. 2, a laser radar ranging contrast diagram of a nonlinear frequency modulation continuous wave is shown, where (a) in fig. 2 is a time-frequency relation diagram of a local signal and a delayed receiving signal, and (b) in fig. 2 is a time-frequency relation diagram of the local signal and the receiving signal after beat frequency, it can be seen that there is nonlinearity in a modulation slope, and as a result, an unstable and non-constant phenomenon of the beat frequency signal is caused, which has a significant influence on measurement accuracy. In order to solve the above problems, the present invention provides a linearity correction system for a dual micro-ring resonator type semiconductor laser.
Specifically, fig. 3 is a schematic structural diagram of a linearity correction system of a dual micro-ring resonator type semiconductor laser according to an embodiment of the present invention.
The dual micro-ring resonator type semiconductor laser 100 includes three thermal tuning modules, namely a first micro-ring resonator 101, a second micro-ring resonator 102 and a phase shifter 103, and when the dual micro-ring resonator type semiconductor laser 100 receives control of a driving voltage, the three internal thermal tuning modules are heated by electricity and generate optical signals according to the thermo-optical effect of materials. The two micro-ring resonators form a filter structure with vernier effect, a large-range tunable laser output can be obtained, the mode selection is realized by adjusting the phase shifter and the two micro-ring resonators to align with the resonance wavelength with vernier effect, and continuously adjustable output wavelength is generated, so that the common adjustment of optical signals is realized.
As shown in fig. 3, the linearity correction system 10 of the dual micro ring resonator type semiconductor laser includes: a temperature controller 200, an emission optical path 300, an unequal arm MZI structure 400, a balanced photodetector 500, a data processing module 600, and a proportional amplifying circuit 700.
And a temperature controller 200, the temperature controller 200 being connected to the dual micro-ring resonator type semiconductor laser 100 for maintaining the temperature of the dual micro-ring resonator type semiconductor laser 100 such that the output wavelength of the dual micro-ring resonator type semiconductor laser 100 does not jump to the mode.
Specifically, the temperature controller 200 may control the operating environment temperature of the dual micro-ring resonator type semiconductor laser 100 to stabilize the temperature variation of the laser. By changing the temperature of the temperature controller 200 integrated on the surface of the dual micro-ring resonator type semiconductor laser 100, the output wavelength of the laser can be effectively adjusted. The mode-jump phenomenon of the laser caused by the change of the internal temperature during the power-on tuning process can be effectively prevented by setting the constant temperature of the temperature controller 200.
The input end of the transmitting optical path 300 is connected with the double micro-ring resonant cavity type semiconductor laser 100 and is used for generating two paths of optical signals, wherein the first path of optical signals are sent to the laser radar transmitting end, and the second path of optical signals are sent to the MZI structure 400 of the unequal arm.
The MZI structure 400 of the unequal arm is configured to mix the received optical signals after different delays to generate the optical signals after beat frequency.
The input end of the balanced photoelectric detector 500 is connected with the output end of the MZI structure 400 of the non-equal arm, and is used for converting the optical signal after beat frequency into the electric signal after beat frequency.
The data processing module 600 is configured to calculate, after performing analog-to-digital conversion on the electric signal after the beat frequency, the frequency and the phase of the optical signal after the beat frequency, calculate the chirp frequency and the linearity of the output optical signal of the dual micro-ring resonant cavity semiconductor laser according to the frequency and the phase, further calculate the desired chirped continuous wave frequency straight line, calculate an error value between the ideal chirped frequency and the actual chirped frequency curve, and generate a predistortion waveform by overlapping the error value with the actual chirped frequency curve after the scale conversion of the error value in a preset range proportion.
The data processing module 600 includes a predistortion processing module, and can perform data arithmetic processing.
The input end of the proportional amplifying circuit 700 is connected with the output end of the data processing module 600, the three output ends are respectively connected with the first micro-ring resonator 101, the second micro-ring resonator 102 and the phase shifter 103 of the double micro-ring resonant cavity type semiconductor laser 100, and are used for amplifying predistortion waveforms according to a set proportion to obtain three output voltages, and the three output voltages are respectively applied to the first micro-ring resonator, the second micro-ring resonator and the phase shifter of the double micro-ring resonant cavity type semiconductor laser, so that the first micro-ring resonator 101 and the second micro-ring resonator 102 form a filter structure with vernier effect, and frequency modulation linear continuous triangular wave frequency signals are generated by adjusting the phase shifter 103, the first micro-ring resonator 101 and the second micro-ring resonator 102 to realize alignment with resonant wavelengths with vernier effect and performing mode selection.
The proportional amplifying circuit 700 includes a single-path analog voltage signal input from the data processing module 600, and three output signals with proportionally adjustable output voltages are output to the input end of the dual micro-ring resonator type semiconductor laser, namely two micro-ring resonators and a phase shifter of the dual micro-ring resonator type semiconductor laser. The proportional amplifying circuit sends driving voltage to three thermal tuning devices of the laser, and after the laser is controlled by external driving voltage, the output of optical signals is completed under the common tuning of the internal thermal tuning devices.
The tunable large-range wavelength output of the double micro-ring resonant cavity type semiconductor laser is mainly controlled by the internal integrated thermal tuning components, namely a first micro-ring resonator, a second micro-ring resonator and a phase shifter, and the first micro-ring resonator, the second micro-ring resonator and the phase shifter can independently or jointly realize tunable continuous output of the wavelength of the double micro-ring resonant cavity type semiconductor laser. The dual micro-ring resonator and the phase shifter driving the dual micro-ring resonant cavity type semiconductor laser have different power-on proportion voltage outputs through the design of the proportional amplifying circuit, and the wavelength output which has narrow line width and is tunable in a large range and has no mode-jump phenomenon is realized.
Further, as shown in fig. 4, a circuit diagram of the scaling circuit is shown. The proportional amplifying circuit can realize single-path voltage input and multi-path voltage output in proportion. The proportional amplifying circuit receives the voltage control signal of the upper stage, adjusts the size of the output adjustable resistor, controls the relation of the three output voltage ratios, and then loads the relation to the first micro-ring resonator, the second micro-ring resonator and the phase shifter of the laser respectively to drive the laser to generate optical signals. Further, the reason for adjusting the output adjustable resistance value and controlling the relation of the three output voltage ratios is to enable the thermal tuning devices inside the laser to jointly generate continuously tunable frequency modulation signals after being driven by voltage and not to generate a mode-jump phenomenon, and the voltage proportion relation of the thermal tuning devices can be obtained through testing in practical experiments.
According to the linearity correction system of the double micro-ring resonant cavity type semiconductor laser, the corrected predistortion waveform is amplified through the proportional amplifying circuit, three paths of driving signals are obtained, the three paths of driving signals are utilized for powering up the double micro-ring resonant cavity type semiconductor laser, and the laser outputs frequency-modulated linear continuous triangular wave frequency signals. Specifically, the temperature controller is used for stabilizing the output wavelength of the laser without mode jump, the output light is divided into two parts after passing through the transmitting light path, one light beam is used for the transmitting end of the laser radar, and the other light beam passes through the MZI structure of the unequal arm. The optical signals received by the second optical beam splitter of the MZI structure of the non-equal arm are subjected to different time delays and then mixed to generate optical signals with beat frequency, the optical signals with beat frequency are changed into electrical signals with beat frequency through the balance photoelectric detector, the electrical signals are output again after being processed by the data processing module, a predistortion waveform is generated and used for a proportional amplifying circuit, three paths of driving signals are obtained after the predistortion waveform is amplified through the proportional amplifying circuit, a double micro-ring resonator and a phase shifter of the double micro-ring resonant cavity type semiconductor laser are driven, the two micro-ring modulators form a filtering structure with vernier effect, a large-range tunable laser output can be obtained, the mode selection is realized by adjusting the phase shifter and the two micro-ring modulators and the resonant wavelength with vernier effect, frequency signals of frequency-modulated linear continuous triangular wave frequencies are generated, and nonlinear correction is realized.
As shown in fig. 5, in one embodiment of the present invention, the transmit optical path 300 includes:
an optical isolator 301, wherein an input end of the optical isolator 301 is connected with an output end of the dual micro-ring resonant cavity type semiconductor laser 200;
the input end of the first optical splitter 302 is connected with the output end of the optical isolator 301, the first output end is a laser radar transmitting end, and the first optical splitter 302 is used for splitting laser emitted by the double micro-ring resonant cavity type semiconductor laser 200.
As shown in fig. 5, in one embodiment of the present invention, a MZI structure 400 of an unequal arm comprises:
a second optical splitter 401, the second optical splitter 401 receiving a second optical signal of the first optical splitter 302 for splitting the received optical signal into two optical signals;
a first optical attenuator 402, an input end of the first optical attenuator 402 receives the first optical signal of the second optical splitter 401;
a delay line 403, where an input end of the delay line 403 receives the second optical signal of the second optical splitter 401, and is used to delay the second optical signal;
the input end of the second optical attenuator 404 is connected with the output end of the delay line 403, and is used for receiving the delayed second path of optical signals;
the first input end of the optical mixer 405 is connected with the output end of the first optical attenuator 402, the second input end of the optical mixer 405 is connected with the output end of the second optical attenuator 404, the output end of the optical mixer is connected with the input end of the balanced photoelectric detector 500, the light intensities of two paths of output light are matched by commonly adjusting the first optical attenuator 402 and the second optical attenuator 404, and the two paths of optical signals are mixed to generate optical signals after beat frequency.
Specifically, the MZI structure of the non-equal arm receives the optical signal emitted by the laser and generates a coherent optical signal. The second optical beam splitter splits the input light into two parts, one part of light is output through the first optical attenuator, the other part of light is output after passing through the delay line and the second optical attenuator, the output light intensities of the two parts of output light are matched by commonly adjusting the first attenuator and the second attenuator, and then the two parts of light are synthesized into one part of light output after passing through the optical frequency mixer to form beat frequency optical signals, and the beat frequency optical signals are sent to the balance photoelectric detector.
As shown in fig. 5, in one embodiment of the present invention, the data processing module 600 includes:
the input end of the analog-to-digital converter 601 is connected with the output end of the balance photoelectric detector 500 and is used for converting the electric signal after beat frequency into a digital signal;
the data processing unit 602, the input end of the data processing unit 602 is connected with the output end of the analog-to-digital converter 601, and is used for performing hilbert transformation on the beat frequency digital signal to obtain a transformed complex signal, according to the characteristic that the hilbert transformation has a 90-degree phase shift filter, the quotient of the imaginary part and the real part of the complex signal is utilized to obtain a phase change curve of the beat frequency digital signal, the constant proportional relation between the phase change curve and the original chirp frequency curve of the frequency modulation continuous wave is utilized, the chirp frequency curve of the double micro-ring resonant cavity type semiconductor laser is obtained according to the calculation of the phase change curve, the corresponding expected chirp frequency straight line is calculated through the chirp frequency curve, the frequency modulation nonlinearity of the transmission signal of the double micro-ring resonant cavity type semiconductor laser is obtained according to the calculation of the relation between the obtained actual frequency modulation curve and the ideal chirp continuous wave frequency, the error value between the ideal frequency modulation and the actual frequency modulation curve is obtained, and the error value between the actual frequency modulation curve is superimposed according to the scale transformation of the error value in a preset range proportion, and a predistortion waveform is generated;
the input end of the digital-to-analog converter 603 is connected with the output end of the data processing unit 602, and the output end is connected with the input end of the proportional amplifying circuit 700, and is used for converting the digital signal of the data processing unit 602 into an electric signal and outputting the electric signal to the proportional amplifying circuit 700.
As shown in fig. 6, a process flow of the data processing module according to an embodiment of the present invention is shown.
S100: performing Hilbert transformation on the obtained beat frequency signal according to the obtained beat frequency signal to obtain a transformed complex signal;
s101: the phase curve of the beat signal is calculated according to the complex signal, reflects the original frequency change of the laser, and has a certain proportionality constant. Calculating and selecting Hilbert transformation and phase curves of beat frequency signals in a partial complete period, and calculating frequency modulation linearity through the phase curves;
s102: calculating the expression form of the expected ideal linear frequency modulation continuous wave signal by taking the phase curve as a basis to obtain a time-varying curve of the output frequency of the actual linear frequency modulation continuous wave signal of the laser and a time-varying relation of the linear frequency modulation continuous wave frequency under the ideal condition, and calculating to obtain an error value of the output frequency of the actual linear frequency modulation continuous wave signal and the time-varying relation of the linear frequency modulation continuous wave frequency;
s103: judging whether to continue nonlinear correction according to the magnitude relation between the obtained frequency modulation nonlinearity and the envisaged threshold value, if the requirement of the set threshold value is not met, performing corresponding scale conversion on the error value, and then superposing the error value and an actual frequency modulation continuous wave driving signal to finish nonlinear correction compensation on an original driving signal, if the requirement of the set threshold value is met, finishing nonlinear correction on a laser;
s104: and repeating the steps S100 to S103 by using an iterative updating method until the predistortion driving waveform meeting the requirement of the set threshold value is obtained.
According to the linearity correction system of the double micro-ring resonant cavity type semiconductor laser, in an initial stage, the double micro-ring resonant cavity type semiconductor laser is driven by a standard triangular wave modulation signal, and as the nonlinear output nonlinear frequency signal of the double micro-ring resonant cavity type semiconductor laser is corrected, a predistortion waveform is obtained by correcting the nonlinear frequency signal output by the double micro-ring resonant cavity type semiconductor laser, the predistortion waveform is amplified in proportion and then three paths of driving signals are output and are applied to a double micro-ring modulator and a phase shifter integrated in the double micro-ring resonant cavity type semiconductor laser to drive, the nonlinear frequency signal output by the double micro-ring resonant cavity type semiconductor laser is corrected, and the frequency modulation linear continuous triangular wave frequency signal is output by the double micro-ring resonant cavity type semiconductor laser through multi-wheel correction, so that the linearity correction of the double micro-ring resonant cavity type semiconductor laser is completed. The invention can be used for high-precision laser ranging, can effectively solve the problem of frequency modulation nonlinearity of the double micro-ring resonant cavity type semiconductor laser under the condition of wide-range sweep frequency, and reduces the measurement error caused by the laser
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or N embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
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 at least one such feature. In the description of the present invention, "N" means at least two, for example, two, three, etc., unless specifically defined otherwise.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and additional implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order from that shown or discussed, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the embodiments of the present invention.
Claims (4)
1. A linearity correction system of a dual micro-ring resonator type semiconductor laser including a first micro-ring resonator, a second micro-ring resonator, a phase shifter, characterized by comprising:
the temperature controller is connected with the double micro-ring resonant cavity type semiconductor laser and used for keeping the temperature of the double micro-ring resonant cavity type semiconductor laser constant so as to prevent the output wavelength of the double micro-ring resonant cavity type semiconductor laser from jumping from a mode;
the input end of the transmitting light path is connected with the double micro-ring resonant cavity type semiconductor laser and is used for generating two paths of optical signals, wherein the first path of optical signals are sent to the laser radar transmitting end, and the second path of optical signals are sent to the MZI structure of the unequal arm;
the MZI structure of the unequal arm is used for carrying out frequency mixing on the received optical signals after different time delays to generate optical signals after beat frequency;
the input end of the balance photoelectric detector is connected with the output end of the MZI structure of the unequal arm and is used for converting the optical signal after beat frequency into an electric signal after beat frequency;
the data processing module is used for calculating the frequency and the phase of the optical signal after beat frequency after analog-digital conversion of the electric signal after beat frequency, calculating the chirp frequency and the linearity of the output optical signal of the double micro-ring resonant cavity type semiconductor laser according to the frequency and the phase, further calculating the expected linear frequency straight line of continuous wave frequency modulation, calculating an error value between an ideal frequency modulation curve and an actual frequency modulation curve, and generating a predistortion waveform by overlapping the error value with the actual frequency modulation curve after scale conversion of the error value in a preset range proportion;
the input end of the proportional amplifying circuit is connected with the output end of the data processing module, the three output ends of the proportional amplifying circuit are respectively connected with the first micro-ring resonator, the second micro-ring resonator and the phase shifter of the double micro-ring resonant cavity type semiconductor laser, the proportional amplifying circuit is used for amplifying the predistortion waveform according to a set proportion to obtain three output voltages, the three output voltages are respectively applied to the first micro-ring resonator, the second micro-ring resonator and the phase shifter of the double micro-ring resonant cavity type semiconductor laser, the first micro-ring resonator and the second micro-ring resonator form a filter structure with vernier effect, and frequency modulation linear continuous triangular wave frequency signals are generated by adjusting the phase shifter, the first micro-ring resonator and the second micro-ring resonator to realize alignment with resonant wavelengths with vernier effect and performing mode selection.
2. The system for linearity correction of a dual micro-ring resonator type semiconductor laser of claim 1, wherein said emission optical path includes:
the input end of the optical isolator is connected with the output end of the double micro-ring resonant cavity type semiconductor laser;
the input end of the first optical beam splitter is connected with the output end of the optical isolator, the first output end is a laser radar transmitting end, and the first optical beam splitter is used for splitting laser emitted by the double micro-ring resonant cavity type semiconductor laser.
3. The system for linearity correction of a dual micro-ring resonator type semiconductor laser of claim 2, wherein said MZI structure of the non-equal arm comprises:
the second optical beam splitter receives a second path of optical signals of the first optical beam splitter and is used for dividing the received optical signals into two paths of optical signals;
the input end of the first optical attenuator receives a first path of optical signals of the second optical beam splitter;
the input end of the delay line receives a second path of optical signals of the second optical beam splitter and is used for applying delay to the second path of optical signals;
the input end of the second optical attenuator is connected with the output end of the delay line and is used for receiving a delayed second path of optical signals;
the optical mixer comprises a first input end, a second input end and an output end, wherein the first input end of the optical mixer is connected with the output end of the first optical attenuator, the second input end of the optical mixer is connected with the output end of the second optical attenuator, the output end of the optical mixer is connected with the input end of the balance photoelectric detector, the light intensities of two paths of output light are matched by commonly adjusting the first optical attenuator and the second optical attenuator, and the two paths of optical signals are mixed to generate optical signals after beat frequency.
4. The system for linearity correction of a dual micro-ring resonator type semiconductor laser of claim 1, wherein said data processing module comprises:
the input end of the analog-to-digital converter is connected with the output end of the balance photoelectric detector and is used for converting the electric signal after beat frequency into a digital signal;
the input end of the data processing unit is connected with the output end of the analog-to-digital converter, the data processing unit is used for carrying out Hilbert transformation on a beat frequency digital signal to obtain a transformed complex signal, according to the characteristic that the Hilbert transformation has a 90-degree phase shift filter, a phase change curve of the beat frequency digital signal is obtained by utilizing the quotient of an imaginary part and a real part of the complex signal, a chirp frequency curve of the double micro-ring resonant cavity type semiconductor laser is obtained by utilizing the constant proportional relation between the phase change curve and an original chirp frequency curve of a frequency modulation continuous wave, a corresponding expected chirp frequency straight line is calculated according to the phase change curve, a frequency modulation nonlinearity of a transmission signal of the double micro-ring resonant cavity type semiconductor laser is obtained according to the relation between an obtained actual frequency modulation curve and an ideal linear frequency modulation continuous wave frequency, an error value between the ideal frequency modulation curve and the actual frequency modulation curve is obtained by calculation, and the predistortion waveform is generated after the scale transformation of the error value in a preset range and the actual frequency modulation curve phase is overlapped;
the input end of the digital-to-analog converter is connected with the output end of the data processing unit, and the output end of the digital-to-analog converter is connected with the input end of the proportional amplifying circuit and is used for converting the digital signal of the data processing unit into an electric signal and outputting the electric signal to the proportional amplifying circuit.
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