CN116131095A - Linear frequency modulation continuous wave laser, calibration method and algorithm processing flow in calibration process - Google Patents

Linear frequency modulation continuous wave laser, calibration method and algorithm processing flow in calibration process Download PDF

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CN116131095A
CN116131095A CN202310040053.5A CN202310040053A CN116131095A CN 116131095 A CN116131095 A CN 116131095A CN 202310040053 A CN202310040053 A CN 202310040053A CN 116131095 A CN116131095 A CN 116131095A
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continuous wave
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frequency modulation
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李磊
张晓波
方舟
史弘康
陈泽
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Xifeng Photoelectric Technology Nanjing Co ltd
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Xifeng Photoelectric Technology Nanjing Co ltd
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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
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • 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
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0085—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for modulating the output, i.e. the laser beam is modulated outside the laser cavity

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Abstract

The invention discloses a linear frequency modulation continuous wave laser integrated with a calibration device on a chip, which comprises a gain chip and a silicon photon external cavity chip, wherein the calibration device is integrated on the silicon photon external cavity chip, an edge coupler, a first direct coupler, a phase control region, a beam splitter, a micro-ring filter and a second direct coupler are sequentially arranged on the silicon photon external cavity chip, and the edge coupler, the first direct coupler, the phase control region, the beam splitter, the micro-ring filter and the second direct coupler are all waveguide structures on the silicon photon external cavity chip and are connected by silicon waveguides. The invention also discloses a method for calibrating the linear frequency modulation continuous wave laser and an algorithm processing flow in the process of calibrating the linear frequency modulation continuous wave laser. The advantages are that: the calibration device is integrated on the silicon photon external cavity chip, and external arrangement is not needed, so that the integration level of the device is improved, and the cost is reduced.

Description

Linear frequency modulation continuous wave laser, calibration method and algorithm processing flow in calibration process
Technical Field
The invention relates to the technical field of frequency modulation interference sensing and measurement of semiconductor lasers, in particular to a linear frequency modulation continuous wave laser, a calibration method and an algorithm processing flow in the calibration process.
Background
The frequency modulation continuous wave signal transmitter is an indispensable device for transmitting the linear frequency modulation continuous wave radar, and the electric signal generating device generates an electric signal to modulate the linear frequency modulation continuous wave signal. The frequency modulation linearity of the frequency modulation continuous wave signal transmitter determines the signal quality of the linear frequency modulation continuous wave radar and also determines the ranging accuracy and range of the linear frequency modulation continuous wave radar. The greater the frequency modulation linearity, the lower the signal quality of the linear frequency modulation continuous wave radar, the lower the ranging accuracy of the linear frequency modulation continuous wave radar, and the shorter the range. The frequency modulation linearity is brought about by a frequency modulation nonlinear term, which is mainly caused by the nonlinear response of the electrical signal of the drive circuit and the frequency modulated continuous wave signal. Accurate assessment and calculation of response parameters of frequency-modulated nonlinear terms is critical to achieving frequency-modulated continuous waves.
In a frequency modulated continuous wave interferometry system, signal nonlinearities are eliminated by directly correcting the output frequency. There are two main methods, one is an open loop correction method and one is a closed loop correction method. The basic approach of the open loop correction method is to find a specific form of nonlinear modulation driving electrical signal, so that the output frequency of the semiconductor laser changes in a linear form over time. By measuring the output frequencies under different electric signal input conditions, a database is built, and the driving electric signal waveform which linearizes the output frequency of the laser is fitted. The closed loop correction method is to establish a feedback loop by adopting a delay self-heterodyning photoelectric phase-locked loop, namely, an interferometer light path structure is used for converting a laser frequency modulation slope value into an interferometer beat frequency signal frequency, the frequency or the phase is used as a closed loop correction amount, the frequency difference of the beat frequency signal is compensated in a negative feedback mode, and the stabilization of the modulation slope of a laser output signal is realized by stabilizing the beat frequency signal frequency of the interferometer, namely, the linearization correction of the laser output frequency modulation signal is realized. The open loop correction method has simple hardware system structure and easy implementation, but has the problem of low linear frequency modulation precision. The closed loop correction method can realize high-precision nonlinear correction, but the system is complex, and the linear frequency modulation range is greatly limited because the locking range of the photoelectric phase-locked loop is limited. The method belongs to the pre-correction method, and the method is characterized in that a correction light path is additionally used in both the open-loop correction method and the closed-loop correction method, and linearization of the output frequency modulation of the semiconductor laser is realized in advance through adjustment of the driving current of the semiconductor laser, so that the purpose of correcting nonlinearity of the frequency modulation interference signal is achieved.
Disclosure of Invention
The invention aims to provide a linear frequency modulation continuous wave laser of an on-chip integrated calibration device, solves the nonlinear problem of the linear frequency modulation continuous wave laser under low-cost application, can realize monolithic integration, does not need an external calibration light path, and has simple structure and convenient operation.
The technical scheme adopted is as follows:
a linear frequency modulation continuous wave laser of an on-chip integrated calibration device comprises a gain chip and a silicon photon external cavity chip, wherein the calibration device is integrated on the silicon photon external cavity chip and is used for evaluating and calculating response parameters of a frequency modulation nonlinear term to realize linear output; the silicon photon external cavity chip is sequentially provided with an edge coupler, a first direct coupler, a phase control area, a beam splitter, a micro-ring filter and a second direct coupler, wherein the edge coupler, the first direct coupler, the phase control area, the beam splitter, the micro-ring filter and the second direct coupler are all waveguide structures on the silicon photon external cavity chip and are connected through silicon waveguides;
the gain chip and the silicon photon external cavity chip are coupled through an end face to form a laser, the edge coupler is coupled with the gain chip through the end face, light is transmitted to the first direct coupler through the silicon waveguide to be divided into two paths, one path of signal light firstly enters the phase control area along the silicon waveguide and then is divided into two paths by the beam splitter to enter the micro-ring filter, and then the two paths of signal light are recombined to return to the original path of the wave; the other path of signal light propagates to the second direct coupler along the other silicon waveguide and is divided into two paths of light, most of the signal light is output from the out end as an output signal, and a small part of the signal light is transmitted to the calibrating device through the silicon waveguide.
In a further preferred embodiment of the present invention, two ends of the gain chip are respectively coated with a high reflection film and an antireflection film, and the edge coupler is to be matched with the gain chip die spot for reducing end surface coupling loss.
In a further preferred embodiment of the present invention, the phase control region is formed by a silicon waveguide and a heating electrode above the silicon waveguide, and the refractive index of the waveguide is changed by electrode electrothermal, so as to change the phase of the signal light, and precise control of the wavelength is realized by phase tuning, that is, the phase tuning is used for realizing frequency sweep.
Further preferably, the micro-ring filter comprises a plurality of micro-rings and heating electrodes above the micro-rings, and filtering is realized based on vernier effect. The effective refractive index of the micro-ring waveguide is changed by electrifying the electrode, so that the resonance wavelength of the micro-ring is changed, and the center wavelength is controlled.
Further preferably, the first direct coupler has a 1x2 structure, so that the light emitting of the laser external cavity chip is realized. The second direct coupler split ratio is set to 9:1, most of the light is output from the out end as an output signal, and a small part of the light is transmitted to the calibration device as a calibration signal by the silicon waveguide.
The calibration device comprises a Mach-Zehnder interferometer, a delay line, a detector and a feedback control circuit, wherein the feedback control circuit comprises a DAC (digital-to-analog converter), an ADC (analog-to-digital converter) and a corresponding data processing algorithm, and a small part of signals enter the Mach-Zehnder interferometer with the delay line, and beat signals are generated at the tail end of the Mach-Zehnder interferometer and are received by the detector; the ADC in the feedback control circuit samples the detection signal and carries out software algorithm processing to obtain nonlinear frequency offset, and thus calculates an electric signal compensation value required by each sampling point, and then generates a new electric signal waveform through the DAC and the signal generator, and the electric signal is applied to the phase control area as a next group of periodic signals for iteration until the linearity of the output signal meets the expectations.
The invention aims to provide a calibration method of a linear frequency modulation continuous wave laser, which comprises the following steps:
s1, initializing a laser, and fixing the center wavelength of a sweep frequency signal to a micro-ring filter;
s2, applying an electric signal with one period to the phase control area, and outputting a frequency modulation continuous wave signal with one period;
s3, a small part of frequency modulation continuous wave signals enter a calibration device through a second direct coupler, beat frequency signals are generated after passing through an interferometer and a delay line, and the power spectrum of the beat frequency signals is measured by a detector;
s4, sampling the beat frequency signal by an ADC in the feedback control circuit, performing data processing on the sampled signal by a software algorithm to obtain a nonlinear frequency offset, calculating an electric signal to be compensated value of each sampling point, enabling uk+1 (t) =uk (t) +p (t) & e (t), and generating a new electric signal waveform through a DAC and a signal generator;
s5, repeating the steps S2-S4 until the linearity of the iterative frequency modulation continuous wave reaches the expected value.
The invention aims to provide an algorithm processing flow in the calibration process of a linear frequency modulation continuous wave laser, wherein the iteration process is more stable, the waveform of an electric signal is smoother, and the waveform is closer to a theoretical value; better linearity and larger effective coverage area. The technical scheme adopted is as follows:
an algorithm processing flow in the process of calibrating a linear frequency modulation continuous wave laser comprises the following steps:
setting the output frequency of a desired linear frequency modulation continuous wave in one period as vd (T), wherein 0< = T, and T is the period; in a steady state, the voltage required by the frequency change delta G is delta V, wherein delta G is the maximum sweep frequency range;
step 1, applying a periodic triangular wave electric signal u (t) to a phase control area so as to generate a group of sweep frequency output signals v (t);
step 2, after the sweep frequency signal passes through the MZI with the delay line, generating a beat frequency signal at the tail end, wherein the frequency is fb (t) =ν (t+τ) - ν (t), and τ is delay time; the beat frequency signal power spectrum is measured by a detector and fed back to a control circuit;
step 3, the ADC samples the measured power spectrum and performs Hilbert transform processing on the sampled power spectrumThe instantaneous phase of each sampling point can be obtained
Figure BDA0004050582540000031
The instantaneous frequency v (t) of each sampling point can be calculated;
step 4, comparing the instantaneous frequency with the expected frequency to obtain a frequency difference rms (t), thereby obtaining a voltage compensation value e (t) of each sampling point;
step 5, deriving the obtained instantaneous frequency v (t), obtaining the slope k (t) of each point, and respectively extracting the maximum values k1 and k2 of the slopes of the rising edge and the falling edge; normalization processing is carried out on K (t), the rising edge part makes K (t) =k (t)/K1, and the falling edge part K (t) =k (t)/K2, so that a normalized iteration coefficient p (t) =1-K (t) in the whole period is obtained;
step 6, let u k+1 (t)＝u k (t)+p(t)·e(t)；
And 7, repeating the steps 1 to 6 until the linearity meets the expectations.
Further preferably, the algorithm processing flow in the calibration process of the linear frequency modulation continuous wave laser of the invention is that the linearity evaluation function is: 1-r 2 ＝SS res /SS tot I.e. linear regression coefficients, where r is linearity, SS res ＝∑ t (v(t)-v d (t)) 2 ，
Figure BDA0004050582540000041
Figure BDA0004050582540000042
Is v (t) average value.
In summary, the beneficial effects of the invention are as follows:
1. the calibration device is integrated on the silicon photon external cavity chip, and external arrangement is not needed, so that the integration level of the device is improved, and the cost is reduced.
2. The algorithm processing flow in the calibration process is a self-adaptive coefficient iterative algorithm, and the jump of the electric signal caused by endpoints and inflection points is reduced to a great extent, so that abnormal values in the iterative process are well avoided, the iterative process is more stable, the iterated electric signal is smoother, and the iterated electric signal is closer to a theoretical value; the linearity is better, the effective coverage area is larger, and meanwhile, the self-adaptive iteration coefficient can improve the iteration efficiency and avoid the waste of calculation resources.
3. The calibration device and the algorithm are simple and convenient, no external devices such as a phase-locked loop and the like are needed, and the practicability is high; and the algorithm is a self-adaptive algorithm, so that the waste of computing resources can be well avoided, and quick iteration is realized.
Drawings
FIG. 1 is a schematic diagram of a frequency modulated continuous wave laser with an on-chip integrated calibration device according to an embodiment of the present invention;
FIG. 2 is a flow chart of the algorithm processing flow in the calibration process in an embodiment of the invention;
FIG. 3 is a simulation result of 1 iteration of an electrical signal initialized to a symmetric triangular wave in an embodiment of the present invention;
FIG. 4 is a simulation result after 150 iterations of initializing a symmetric triangle wave electrical signal in an embodiment of the present invention;
FIG. 5 is a graph of linear regression coefficients versus iteration number in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings 1 to 5 and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
As shown in fig. 1, the present embodiment is a chirped continuous wave laser with an on-chip integrated calibration device, which includes a gain chip 1 and a silicon photon external cavity chip 2, wherein the calibration device is integrated on the silicon photon external cavity chip 2, and is used for evaluating and calculating response parameters of a frequency modulation nonlinear term to realize linear output; the silicon photon external cavity chip 2 is provided with the following components in sequence: the gain chip comprises an edge coupler 3, a first direct coupler 4, a phase control region 5, a heating electrode thereof, a 3dB beam splitter 6, a micro-ring filter 7, a heating electrode thereof and a second direct coupler 8, wherein the left end and the right end of the gain chip 1 are respectively plated with a high reflection film and an antireflection film, and are used as a broad spectrum light source to be coupled with the end face of a silicon photon external cavity chip; the silicon photon external cavity chip 2 is used as a laser resonant cavity, a plurality of micro-rings are used as filters to realize center wavelength selection based on vernier effect, and the effective refractive index of the waveguide is changed by heating the electrode to realize wavelength selection by utilizing the thermo-optical effect of silicon materials. The phase control area 5 is also based on the thermo-optic effect of the silicon material and is used for precisely controlling the wavelength, namely, the frequency modulation continuous wave signal output is realized by applying an electric signal to the phase control area; in addition, a calibration device is integrated on the silicon photon chip, and the calibration device comprises a Mach-Zehnder interferometer 9, a delay line 10, a detector 11 and a feedback control circuit 12, wherein the Mach-Zehnder interferometer and the delay line with the delay time tau are positioned on one arm of the interferometer. The calibration principle is as follows: a signal is applied to the gain chip 1 to cause it to spontaneously radiate broad spectrum signal light into the silicon photonic external cavity chip 2 through the edge coupler 3. The signal light sequentially passes through the first direct coupler 4, the phase control area 5 and the 3dB beam splitter 6 to enter the micro-ring filter 7, and the effective refractive index of the waveguide is changed by applying power to the heating electrode above the micro-ring by utilizing the vernier effect and the silicon-based thermo-optical effect, so that the signal in the target wavelength and the small range thereof can only pass through the Drop end primary return value gain chip 1 of the micro-ring and be reflected back through the high-reflection film to form resonance, thereby determining the center wavelength. A periodic voltage signal is applied to the phase control region 5, which generates a set of small-range sweep signals that are transmitted through the direct coupler 1 to the direct coupler 2, mostly as output signals, and a small fraction into the calibration device. A small portion of the signal is passed through a Mach-Zehnder interferometer with a delay line, where a beat signal is generated at the end of the interferometer and received by a detector. The ADC in the feedback control circuit 12 samples the detected signal and performs a software algorithm to obtain a nonlinear frequency offset, and thus calculates an electrical signal compensation value required for each sampling point, and then generates a new electrical signal waveform through the DAC and the signal generator, where the electrical signal is applied as a next set of periodic signals to the phased region for iteration until the linearity of the output signal meets the expectations.
A calibration method of a linear frequency modulation continuous wave laser comprises the following steps:
s1, initializing a laser, and fixing the center wavelength of a sweep frequency signal to a micro-ring filter;
s2, applying an electric signal with one period to the phase control area, and outputting a frequency modulation continuous wave signal with one period;
s3, a small part of frequency modulation continuous wave signals enter a calibration device through a second direct coupler, beat frequency signals are generated after passing through an interferometer and a delay line, and the power spectrum of the beat frequency signals is measured by a detector;
s4, sampling the beat frequency signal by an ADC in the feedback control circuit, performing data processing on the sampled signal by a software algorithm to obtain a nonlinear frequency offset, calculating an electric signal to be compensated value of each sampling point, enabling uk+1 (t) =uk (t) +p (t) & e (t), and generating a new electric signal waveform through a DAC and a signal generator;
s5, repeating the steps S2-S4 until the linearity of the iterative frequency modulation continuous wave reaches the expected value.
As shown in fig. 2, the algorithm processing flow in the calibration process of the chirped continuous wave laser comprises the following steps:
setting the output frequency of a desired linear frequency modulation continuous wave in one period as vd (T), wherein 0< = T, and T is the period; in steady state, the voltage required for the frequency change Δg is Δv, where Δg is the maximum sweep range.
Step 1, applying a periodic triangular wave electric signal u (t) to a phase control area so as to generate a group of sweep frequency output signals v (t);
step 2, after the sweep frequency signal passes through the MZI with the delay line, generating a beat frequency signal at the tail end, wherein the frequency is fb (t) =ν (t+τ) - ν (t), and τ is delay time; the beat frequency signal power spectrum is measured by a detector and fed back to a control circuit;
step 3, the ADC samples the measured power spectrum and performs Hilbert transform processing on the sampled power spectrum to obtain the instantaneous phase of each sampling point
Figure BDA0004050582540000061
The instantaneous frequency v (t) of each sampling point can be calculated;
step 4, comparing the instantaneous frequency with the expected frequency to obtain a frequency difference rms (t), thereby obtaining a voltage compensation value e (t) of each sampling point;
step 5, deriving the obtained instantaneous frequency v (t), obtaining the slope k (t) of each point, and respectively extracting the maximum values k1 and k2 of the slopes of the rising edge and the falling edge; normalization processing is carried out on K (t), the rising edge part makes K (t) =k (t)/K1, and the falling edge part K (t) =k (t)/K2, so that a normalized iteration coefficient p (t) =1-K (t) in the whole period is obtained;
step 6, let u k+1 (t)＝u k (t)+p(t)·e(t)；
And 7, repeating the steps 1 to 6 until the linearity meets the expectations.
The linearity evaluation function is: 1-r 2 ＝SS res /SS tot I.e. linear regression coefficients, where r is linearity, SS res ＝∑ t (ν(t)-v d (t)) 2 ，
Figure BDA0004050582540000062
Figure BDA0004050582540000063
Is the average value of v (t). Where the linearity estimation function is also known as a linear regression coefficient.
As shown in fig. 5, we generally evaluate the linearity of the swept laser with a linear regression coefficient, and fig. 5 shows the linear regression coefficient of the output frequency after different iterations. FIG. 3 shows the results of an iterative one-time simulation with a linear regression coefficient much greater than 10 -4 The linear regression coefficient gradually decreases with increasing iteration number, and after the iteration number reaches 150 times, the curve tends to saturate, and the linear regression coefficient reaches the minimum value, namely is close to 10 -8 I.e. the simulation results corresponding to fig. 4.
It is known that nonlinearity mainly derives from the corresponding delay in the temperature of the phase control region, and the differential equation expression of the temperature response of the phase control region is dT (T) =c×q (T) +d×d (T) -T0), where C is the thermal coefficient, Q (T) is the power consumption, d= -c×1/R/Δt, Δt is the temperature change caused by the voltage of 1V, and T0 is the initial temperature. According to the response differential equation, a temperature response curve of the phase control region can be obtained, so that the temperature variation of each moment is obtained, the voltage variation which is actually applied to the phase control region is obtained, the frequency variation is in direct proportion to the square of the voltage, and the response relation of the output frequency can be obtained. Based on the measured data, we selected C to be 70000 (time unit us), t0=25 ℃, r=365, Δt=14.8 ℃, and the frequency was changed by 3GHz when the square of the voltage was changed by 1.428.
When a linear symmetric triangle wave voltage signal with the initial input frequency of 4K is input, the actual output frequency curve is shown in fig. 3, the difference between the actual frequency and the expected frequency of each sampling point can be obtained, the frequency is in direct proportion to the square of the voltage, the voltage difference of each sampling point can be obtained, and the voltage difference is complemented according to an iterative algorithm to be used as a group of periodic voltage signals. Fig. 4 shows the output frequency of the result of fig. 3 after 150 iterations of the adaptive algorithm, and it can be seen that the actual output frequency curve substantially completely coincides with the expected output frequency after 150 iterations.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.

Claims (9)

1. A linear frequency modulation continuous wave laser of an on-chip integrated calibration device is characterized in that: the device comprises a gain chip (1) and a silicon photon external cavity chip (2), wherein a calibration device is integrated on the silicon photon external cavity chip (2) and is used for evaluating and calculating response parameters of a frequency modulation nonlinear term so as to realize linear output; the silicon photon external cavity chip (2) is sequentially provided with an edge coupler (3), a first direct coupler (4), a phase control region (5), a beam splitter (6), a micro-ring filter (7) and a second direct coupler (8), wherein the edge coupler (3), the first direct coupler (4), the phase control region (5), the beam splitter (6), the micro-ring filter (7) and the second direct coupler (8) are all waveguide structures on the silicon photon external cavity chip (2) and are connected through silicon waveguides;
the gain chip (1) and the silicon photon external cavity chip (2) form a laser through end face coupling, the edge coupler (3) is connected with the gain chip (1) through end face coupling, light is transmitted to the first direct coupler (4) through a silicon waveguide and is divided into two paths, one path of signal light enters the phase control area (5) along the silicon waveguide first, and then is divided into two paths by the beam splitter (6) to enter the micro-ring filter (7) and then returns in a wave combining original path; the other path of signal light propagates to the second direct coupler (8) along the other silicon waveguide and is divided into two paths of light, most of the signal light is output from the out end as an output signal, and the small part of the signal light is transmitted to the calibrating device through the silicon waveguide.
2. The on-chip integrated calibration device chirped continuous wave laser of claim 1 wherein: the two ends of the gain chip (1) are respectively plated with a high-reflection film and an antireflection film.
3. The on-chip integrated calibration device chirped continuous wave laser of claim 1 wherein: the phase control region (5) is composed of a silicon waveguide and a heating electrode above the silicon waveguide.
4. The on-chip integrated calibration device chirped continuous wave laser of claim 1 wherein: the micro-ring filter (7) consists of a plurality of micro-rings and heating electrodes above the micro-rings.
5. The on-chip integrated calibration device chirped continuous wave laser of claim 1 wherein: the first direct coupler (4) is of a 1x2 structure, the split ratio of the second direct coupler (8) is set to be 9:1, most of light is output from an out end as an output signal, and the small part of light is transmitted to the calibration device as a calibration signal through a silicon waveguide.
6. The on-chip integrated calibration device chirped continuous wave laser of claim 1 wherein: the calibration device comprises a Mach-Zehnder interferometer (9), a delay line (10), a detector (11) and a feedback control circuit (12), wherein the feedback control circuit (12) comprises a DAC (digital-to-analog converter), an ADC (analog-to-digital converter) and a corresponding data processing algorithm, and a small part of signals enter the Mach-Zehnder interferometer (9) with the delay line (10), and beat signals are generated at the tail end of the Mach-Zehnder interferometer (9) and are received by the detector (11); the ADC in the feedback control circuit (12) samples the detection signal and carries out software algorithm processing to obtain nonlinear frequency offset, and thus calculates an electric signal compensation value required by each sampling point, and then generates a new electric signal waveform through the DAC and the signal generator, and the electric signal is applied to a phase control area as a next group of periodic signals for iteration until the linearity of the output signal meets the expectations.
7. The method for calibrating a chirped continuous wave laser according to any of claims 1-6, wherein: the method comprises the following steps:
s1, initializing a laser, and fixing the center wavelength of a sweep frequency signal to a micro-ring filter;
s2, applying an electric signal with one period to the phase control area, and outputting a frequency modulation continuous wave signal with one period;
s3, a small part of frequency modulation continuous wave signals enter a calibration device through a second direct coupler, beat frequency signals are generated after passing through an interferometer and a delay line, and the power spectrum of the beat frequency signals is measured by a detector;
s4, sampling the beat frequency signal by an ADC in the feedback control circuit, performing data processing on the sampled signal by a software algorithm to obtain a nonlinear frequency offset, calculating an electric signal to be compensated value of each sampling point, enabling uk+1 (t) =uk (t) +p (t) & e (t), and generating a new electric signal waveform through a DAC and a signal generator;
s5, repeating the steps S2-S4 until the linearity of the iterative frequency modulation continuous wave reaches the expected value.
8. The algorithm process flow in the chirped continuous wave laser calibration process according to any one of claims 1-6, wherein: the method comprises the following steps:
setting the output frequency of a desired linear frequency modulation continuous wave in one period as vd (T), wherein 0< = T, and T is the period; in a steady state, the voltage required by the frequency change delta G is delta V, wherein delta G is the maximum sweep frequency range;
step 1, applying a periodic triangular wave electric signal u (t) to a phase control area so as to generate a group of sweep frequency output signals v (t);
step 2, after the sweep frequency signal passes through the MZI with the delay line, generating a beat frequency signal at the tail end, wherein the frequency is fb (t) =ν (t+τ) - ν (t), and τ is delay time; the beat frequency signal power spectrum is measured by a detector and fed back to a control circuit;
step 3, the ADC samples the measured power spectrum and performs Hilbert transform processing on the sampled power spectrum to obtain the instantaneous phase of each sampling point
Figure FDA0004050582530000021
The instantaneous frequency v (t) of each sampling point can be calculated;
step 4, comparing the instantaneous frequency with the expected frequency to obtain a frequency difference rms (t), thereby obtaining a voltage compensation value e (t) of each sampling point;
step 5, deriving the obtained instantaneous frequency v (t), obtaining the slope k (t) of each point, and respectively extracting the maximum values k1 and k2 of the slopes of the rising edge and the falling edge; normalization processing is carried out on K (t), the rising edge part makes K (t) =k (t)/K1, and the falling edge part K (t) =k (t)/K2, so that a normalized iteration coefficient p (t) =1-K (t) in the whole period is obtained;
step 6, let u k+1 (t)＝u k (t)+p(t)·e(t)；
And 7, repeating the steps 1 to 6 until the linearity meets the expectations.
9. The algorithm process flow in the chirped continuous wave laser calibration process according to claim 8, wherein: the linearity evaluation function is: 1-r 2 ＝SS res /SS tot Wherein r is linearity, SS res ＝∑ t (ν(t)-v d (t)) 2 ，
Figure FDA0004050582530000031
Figure FDA0004050582530000032
Is v (t) average value. />
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CN116706677A (en) * 2023-07-19 2023-09-05 希烽光电科技(南京)有限公司 Silicon-based external cavity tunable laser and mode locking method thereof

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116706677A (en) * 2023-07-19 2023-09-05 希烽光电科技(南京)有限公司 Silicon-based external cavity tunable laser and mode locking method thereof

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