Method and system for measuring chirp factor of semiconductor laser

Abstract

The application provides a method and system for measuring the chirp factor of a semiconductor laser, and relates to the technical field of semiconductor lasers. The method comprises: obtaining a spectral broadening amount of first output light generated by first laser incident on a first periodically poled lithium niobate crystal, and obtaining a rate of change of phase with time obtained by autocorrelation processing of second output light generated by second laser incident on a second periodically poled lithium niobate crystal, the first laser and the second laser being two lasers generated by splitting the outgoing light of the semiconductor laser to be measured; calculating a frequency domain chirp representation factor according to the spectral broadening amount; calculating a time domain chirp representation factor according to the rate of change of phase with time; and calculating the chirp factor of the semiconductor laser to be measured according to the frequency domain chirp representation factor and the time domain chirp representation factor. The application can realize real-time measurement of the chirp factor of a semiconductor laser.

Description

Technical Field

[0001] This application relates to the field of semiconductor laser technology, and more specifically, to a method and system for measuring the chirp factor of a semiconductor laser. Background Technology

[0002] Directly modulated semiconductor lasers generate frequency chirp in high-speed communication, which is a momentary frequency shift that affects signal transmission quality. It is necessary to measure the frequency chirp of the semiconductor laser in order to calibrate the communication signal.

[0003] Existing methods for measuring frequency chirp are divided into interferometry and spectral analysis. Interferometry requires precise optical path adjustment, has poor vibration resistance, cannot be detected online, and has high detection costs. Spectral analysis is limited by the resolution of the spectrometer and cannot separate chirp from intensity noise.

[0004] Therefore, there is an urgent need to provide a solution for measuring the chirp factor of semiconductor lasers. Summary of the Invention

[0005] The purpose of this application is to address the shortcomings of the prior art by providing a method and system for measuring the chirp factor of a semiconductor laser, so as to achieve real-time measurement of the chirp factor of the semiconductor laser.

[0006] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows:

[0007] In a first aspect, embodiments of this application provide a method for measuring the chirp factor of a semiconductor laser, the method comprising:

[0008] The spectral broadening of the first output light generated after the first laser of the semiconductor laser under test is incident on the first periodically polarized lithium niobate crystal is obtained, and the phase change rate over time is obtained by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal. The first laser and the second laser are two lasers generated after the output light of the semiconductor laser under test is split.

[0009] Calculate the frequency domain chirp characterization factor based on the spectral broadening amount;

[0010] The time-domain chirp characterization factor is calculated based on the rate of change of the phase over time;

[0011] The chirp factor of the semiconductor laser under test is calculated based on the frequency domain chirp characterization factor and the time domain chirp characterization factor.

[0012] Optionally, the phase-time rate of change obtained by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal includes:

[0013] Acquire the low-frequency electrical modulation signal of the second output light after autocorrelation processing;

[0014] Phase extraction is performed on the low-frequency electrical modulation signal to determine the chirp information phase term;

[0015] Calculate the first derivative of the chirped information phase term with respect to the optical path delay time to determine the rate of change of the phase over time.

[0016] Optionally, calculating the chirp factor of the semiconductor laser under test based on the frequency domain chirp characterization factor and the time domain chirp characterization factor includes:

[0017] The frequency domain chirp characterization factor and the time domain chirp characterization factor are weighted according to a preset weighting factor to calculate the chirp factor.

[0018] Optionally, the method further includes:

[0019] The preset weighting factor is determined based on the frequency domain signal-to-noise ratio of the first output light and the time domain signal-to-noise ratio of the second output light.

[0020] Optionally, the method further includes:

[0021] Based on the first refractive index of the first periodically polarized lithium niobate crystal, the first wave vector mismatch between the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser is determined.

[0022] Based on the first wave vector mismatch, the temperature of the first periodically polarized lithium niobate crystal is adjusted to change the first refractive index, so that the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser satisfy a preset phase matching condition.

[0023] Optionally, the method further includes:

[0024] Based on the second refractive index of the second periodically polarized lithium niobate crystal, the second wave vector mismatch of the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser is determined.

[0025] Based on the second wave vector mismatch, the temperature of the second periodically polarized lithium niobate crystal is adjusted to change the second refractive index, so that the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser satisfy the preset phase mismatch condition.

[0026] Secondly, embodiments of this application also provide a chirp factor measurement system for a semiconductor laser, the chirp factor measurement system comprising: a first beam splitter, a first periodically polarized lithium niobate crystal, a second periodically polarized lithium niobate crystal, a spectrometer, and an autocorrelator;

[0027] The light-emitting surface of the semiconductor laser under test faces the light-incident surface of the first beam splitter, so that the first beam splitter splits the emitted light of the semiconductor laser under test into a first laser and a second laser.

[0028] The two light-emitting surfaces of the first beam splitter are respectively directed toward the light-incident surfaces of the first periodically polarized lithium niobate crystal and the second periodically polarized lithium niobate crystal, so that the first laser beam and the second laser beam are respectively incident on the first periodically polarized lithium niobate crystal and the second periodically polarized lithium niobate crystal.

[0029] The light-emitting surface of the first periodically polarized lithium niobate crystal faces the spectrometer;

[0030] The light-emitting surface of the second periodically polarized lithium niobate crystal faces the autocorrelator;

[0031] The chirp factor measurement system is used to employ the chirp factor measurement method as described in any of the first aspects.

[0032] Optionally, the autocorrelator includes: a Michelson interferometer, a photodetector, and a programmable logic device;

[0033] The light-emitting surface of the second periodically polarized lithium niobate crystal faces the light-incident surface of the Michelson interferometer, and the light-emitting surface of the Michelson interferometer faces the photodetector.

[0034] The photodetector is connected to the programmable logic device.

[0035] Optionally, the chirp factor measurement system further includes: a DC bias and a signal generator;

[0036] The DC biaser is connected to the semiconductor laser under test and is used to provide bias current to the semiconductor laser under test;

[0037] The signal generator is connected to the semiconductor laser under test and is used to provide a modulation signal for the semiconductor laser under test.

[0038] Optionally, the chirp factor measurement system further includes: two temperature controllers and two heaters;

[0039] Each heater is arranged in surface contact with the corresponding periodically polarized lithium niobate crystal, and each temperature controller is connected to each heater to control the temperature of the corresponding periodically polarized lithium niobate crystal through each heater.

[0040] Thirdly, embodiments of this application also provide a chirp factor measurement device for a semiconductor laser, the device comprising:

[0041] The information acquisition module is used to acquire the spectral broadening of the first output light generated after the first laser of the semiconductor laser under test is incident on the first periodically polarized lithium niobate crystal, and to acquire the phase change rate over time obtained by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal. The first laser and the second laser are two lasers generated after the output light of the semiconductor laser under test is split.

[0042] The chirp factor calculation module is used to calculate the frequency domain chirp characterization factor based on the spectral broadening amount;

[0043] The chirp factor calculation module is also used to calculate the time-domain chirp characterization factor based on the phase change rate over time.

[0044] The chirp factor calculation module is further configured to calculate the chirp factor of the semiconductor laser under test based on the frequency domain chirp characterization factor and the time domain chirp characterization factor.

[0045] Optionally, the information acquisition module is specifically used to acquire the low-frequency electrical modulation signal after the second output light has undergone autocorrelation processing; to extract the phase of the low-frequency electrical modulation signal to determine the chirp information phase term; and to calculate the first derivative of the chirp information phase term with optical path delay time to determine the phase change rate with time.

[0046] Optionally, the chirp factor calculation module is specifically used to calculate the chirp factor by weighting the frequency domain chirp characterization factor and the time domain chirp characterization factor according to a preset weighting factor.

[0047] Optionally, the device further includes:

[0048] The weighting factor calculation module is used to determine the preset weighting factor based on the frequency domain signal-to-noise ratio of the first output light and the time domain signal-to-noise ratio of the second output light.

[0049] Optionally, the device further includes:

[0050] The temperature adjustment module is specifically used to determine the first wave vector mismatch between the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser based on the first refractive index of the first periodically polarized lithium niobate crystal; and to adjust the temperature of the first periodically polarized lithium niobate crystal based on the first wave vector mismatch to change the first refractive index, so that the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser satisfy a preset phase matching condition.

[0051] Optionally, the temperature adjustment module is further configured to determine the second wave vector mismatch between the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser based on the second refractive index of the second periodically polarized lithium niobate crystal; and adjust the temperature of the second periodically polarized lithium niobate crystal based on the second wave vector mismatch to change the second refractive index, so that the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser satisfy a preset phase mismatch condition.

[0052] Fourthly, the present invention provides an electronic device, comprising: a processor and a storage medium, the storage medium storing machine-readable instructions executable by the processor, wherein when the electronic device is running, the processor communicates with the storage medium, and the processor executes the machine-readable instructions to perform the steps of the chirp factor measurement method as described in any of the foregoing embodiments.

[0053] Fifthly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of the chirp factor measurement method as described in any of the foregoing embodiments.

[0054] The beneficial effects of this application are:

[0055] The chirp factor measurement method and system for semiconductor lasers provided in this application are based on the optical nonlinear effect of periodically polarized lithium niobate crystals. Employing a dual-path second harmonic design, a chirp-noise mixed signal is captured at a quasi-phase-matching point of the first periodically polarized lithium niobate crystal, and a pure noise baseline is extracted at a specific phase mismatch point of the second periodically polarized lithium niobate crystal. This allows for the calculation of the frequency-domain chirp characterization factor based on the chirp-noise mixed signal and the time-domain chirp characterization factor based on the pure noise baseline. Finally, a dual-domain fusion calculation is performed to obtain the final chirp factor. This method solves the problem of separating chirp and noise in existing technologies, significantly improving the performance of semiconductor lasers. The improved chirp factor measurement accuracy enhances the resistance of semiconductor lasers to environmental vibrations, eliminating the need to mount them on high-vibration-resistant platforms. By calculating the chirp factor using time-domain chirp characterization, real-time detection of transient chirps is achieved with extremely high speed, achieving a single measurement time of <10ms. Furthermore, by employing autocorrelation down-conversion technology to reduce the frequency of the second output light, the GHz chirp signal is compressed to kHz, eliminating the need for expensive high-speed photodetectors, high-speed oscilloscopes, and other instruments in the measurement system, thus reducing the system's cost. This solution can be widely integrated and applied in optical module production lines. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 An architectural diagram of a chirp factor measurement system provided for embodiments of this application;

[0058] Figure 2 An architectural diagram of another chirp factor measurement system provided for embodiments of this application;

[0059] Figure 3 An architectural diagram of another chirp factor measurement system provided in this application embodiment;

[0060] Figure 4 A flowchart illustrating a chirp factor measurement method provided in an embodiment of this application;

[0061] Figure 5 A flowchart illustrating another method for measuring the chirp factor provided in this application embodiment;

[0062] Figure 6 A schematic diagram of the structure of the chirp factor measuring device provided in the embodiments of this application;

[0063] Figure 7 A schematic diagram of an electronic device provided in an embodiment of this application. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0065] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0066] In the description of this application, it should be noted that if the terms "upper", "lower", etc. appear to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the product of this application is usually placed in, it is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0067] Furthermore, the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Additionally, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0068] It should be noted that, where there is no conflict, the features in the embodiments of this application can be combined with each other.

[0069] Spectral analysis directly measures the broadening of the modulated laser spectrum using a spectrometer to estimate the chirp factor of a semiconductor laser. However, its limitation lies in the insufficient resolution of the spectrometer, which prevents the separation of chirp and intensity noise.

[0070] The Mach-Zehnder Interferometer (MZI) converts the optical path difference between the two arms into a phase difference to inversely calculate the chirp factor. Its limitations include poor anti-interference ability and susceptibility to environmental factors such as mechanical vibration, temperature drift, and airflow disturbance. The test accuracy is affected by the visibility of the interference; when the visibility of the interference decreases, the test error increases significantly.

[0071] In view of this, embodiments of this application provide a method and system for measuring the chirp factor of a semiconductor laser. The method employs a dual-path second harmonic design, capturing a chirp-noise mixed signal at a quasi-phase-matching point of a first periodically polarized lithium niobate crystal, and extracting a pure noise baseline at a specific phase mismatch point of a second periodically polarized lithium niobate crystal. This allows for the calculation of the frequency-domain chirp characterization factor based on the chirp-noise mixed signal, and the calculation of the time-domain chirp characterization factor based on the pure noise baseline. Finally, a dual-domain fusion calculation is performed to obtain the final chirp factor. This solves the problem of separating chirp and noise in existing technologies, enabling real-time measurement of the chirp factor of semiconductor lasers with high accuracy and efficiency. It can be widely integrated and applied in optical module production lines.

[0072] The following describes the specific implementation of the chirp factor measurement system for semiconductor lasers provided in this application, with reference to the embodiments.

[0073] Figure 1 An architecture diagram of a chirp factor measurement system provided in this application embodiment is shown below. Figure 1 As shown, the chirp factor measurement system may include: a first beam splitter 101, a first periodically polarized lithium niobate crystal 102, a second periodically polarized lithium niobate crystal 103, a spectrometer 104, and an autocorrelator 105.

[0074] The emitting surface of the semiconductor laser under test faces the incident surface of the first beam splitter 101, causing the first beam splitter 101 to split the emitted light from the semiconductor laser under test into a first laser beam and a second laser beam. The two emitting surfaces of the first beam splitter 101 face the incident surfaces of the first periodically polarized lithium niobate crystal 102 and the second periodically polarized lithium niobate crystal 103, respectively, so that the first laser beam and the second laser beam are incident on the first periodically polarized lithium niobate crystal 102 and the second periodically polarized lithium niobate crystal 103, respectively. The emitting surface of the first periodically polarized lithium niobate crystal 102 faces the spectrometer 104; the emitting surface of the second periodically polarized lithium niobate crystal 103 faces the autocorrelator 105.

[0075] In this embodiment, preferably, the semiconductor laser under test is a high-speed semiconductor laser. The semiconductor laser under test generates outgoing light, and a first beam splitter 101 is set in the optical path output direction of the semiconductor laser under test. The first beam splitter 101 splits the outgoing light into two spatially separated laser beams, a first laser beam and a second laser beam, according to a preset beam splitting ratio.

[0076] Preferably, the preset splitting ratio of the first laser beam and the second laser beam can be 50:50.

[0077] Periodically polarized lithium niobate (PPLN) is a highly efficient nonlinear optical crystal. It achieves efficient laser wavelength conversion by optimizing the crystal structure of lithium niobate (LiNbO3) through periodic polarization technology.

[0078] The first laser beam, acting as the fundamental frequency light, is incident on the first periodically polarized lithium niobate crystal 102, defined as the main path. The first periodically polarized lithium niobate crystal 102 operates at a phase-matching point to maximize the Second Harmonic Generation (SHG) efficiency. Based on second-order nonlinear optical effects, the SHG process converts two fundamental frequency photons into one output photon, which is then output as the first output light through the first periodically polarized lithium niobate crystal 102. Since the output light of the semiconductor laser under test has a time-varying instantaneous frequency and phase, this dynamic phase fluctuation is significantly amplified and transferred to the output light spectrum during the SHG process, resulting in a characteristic broadening of the measured SHG spectral signal relative to the fundamental frequency light.

[0079] Spectrometer 104 is a high-speed spectrometer. It filters and detects the frequency-doubled light in the first output light emitted from the first periodically polarized lithium niobate crystal 102, separates and acquires the spectral map of the SHG component, and quantitatively calculates the spectral broadening of the frequency-doubled light by analyzing the full width at half maximum (FWHM) or specific energy percentage of the spectrum. The spectral broadening is directly related to the instantaneous rate of change of laser intensity and peak power, reflecting the nonlinear chirp characteristics of the semiconductor laser under high-speed modulation.

[0080] To eliminate the inherent defect of system noise being mixed with the real signal in single-path measurement, this application innovatively introduces a parallel auxiliary path, the purpose of which is to synchronously acquire a pure reference benchmark under completely consistent spatiotemporal conditions.

[0081] The second laser beam, as the fundamental frequency light, is incident on the second periodically polarized lithium niobate crystal 103 and is defined as the auxiliary path. The second periodically polarized lithium niobate crystal 103 operates at the phase mismatch point, actively suppressing the second-order nonlinear effect of the second path light, making the SHG conversion efficiency of this path less than 1% of its peak value. This effectively closes the SHG spectral signal conversion channel, outputting a second output light that does not contain effective SHG spectral characteristics. The spectral composition of the second output light is equivalent to the spectrum of the incident fundamental frequency light, without spectral broadening caused by nonlinear frequency conversion. The second output light completely preserves the intensity noise and system noise of the semiconductor laser under test, forming a dynamic reference noise.

[0082] The autocorrelator 105 performs autocorrelation beat frequency analysis on the fundamental frequency light of the second output light emitted from the second periodically polarized lithium niobate crystal 103, and determines the phase change rate of the fundamental frequency light of the second output light over time by phase demodulation and rate of change calculation.

[0083] The spectral broadening of the frequency-doubled light of the first output light and the phase change rate of the fundamental light of the second output light are time-aligned to correspond to the same modulation state of the semiconductor laser under test. The chirp factor is used to indicate the proportionality between the frequency chirp caused by nonlinear effects and the intensity change during the dynamic modulation of the semiconductor laser under test. The instantaneous angular frequency shift is determined based on the phase change rate of the fundamental light of the second output light, and the instantaneous intensity change is determined based on the spectral broadening of the frequency-doubled light of the first output light. The chirp factor of the semiconductor laser under test is calculated based on the instantaneous angular frequency shift and the instantaneous intensity change.

[0084] The chirp factor measurement system provided in the above embodiments captures the chirp-noise mixed signal through a first periodically polarized lithium niobate crystal and extracts the pure noise baseline through a second periodically polarized lithium niobate crystal, so as to calculate the chirp factor of the semiconductor laser under test. This solves the problem of separating chirp and noise in the prior art and realizes online detection of the chirp factor of semiconductor lasers.

[0085] In one possible implementation, Figure 2 An architectural diagram of another chirp factor measurement system provided in this application embodiment is shown below. Figure 2 As shown, the autocorrelator 105 may include: a Michelson interferometer 51, a photodetector 52, and a programmable logic device 53.

[0086] The light-emitting surface of the second periodically polarized lithium niobate crystal 103 faces the light-incident surface of the Michelson interferometer 51, and the light-emitting surface of the Michelson interferometer 51 faces the photodetector 52; the photodetector 52 is connected to the programmable logic device 53.

[0087] In this embodiment, as Figure 2 As shown, the Michelson interferometer 51 may include: an optical isolator 511, a second beam splitter 512, a fixed reflector 513, and a galvanometer 514.

[0088] The second output light from the second periodically polarized lithium niobate crystal 103 is split into two beams after passing through the optical isolator 511 and the second beam splitter 512. One reflected beam is reflected by the fixed reflector 513 and returns along the original optical path, while the other transmitted beam is reflected by the galvanometer 514 and also returns along the original path. The two reflected beams are recombined at the second beam splitter 512 to form laser interference and generate an autocorrelation beat frequency signal.

[0089] When the emitted light from the semiconductor laser under test has an instantaneous frequency chirp (GHz band), the transmitted light is subject to a time-varying delay due to the action of the galvanometer 514. When the two reflected beams are combined, a time-varying phase difference is generated. This interference process linearly maps the high-frequency phase adjustment information of the outgoing light onto the low-frequency envelope change of the interference light intensity, so that the frequency of the autocorrelation beat frequency signal is compressed to the kHz band related to the scanning frequency of the galvanometer 514.

[0090] The photodetector 52 receives the combined interference light and converts it into a corresponding time-domain electrical signal. From this signal, a low-frequency electrical modulation signal characterizing the original laser chirp is extracted. A programmable logic device 53 forms a real-time signal processing system based on a field-programmable gate array (FPGA). This system performs a real-time Hilbert transform on the low-frequency electrical modulation signal, extracting the chirp information phase term containing the laser chirp information. The chirp information phase term is then analyzed as a function of the optical path delay time. The first derivative is used to determine the rate of change of phase over time.

[0091] In some embodiments, such as Figure 2 As shown, the Michelson interferometer may further include: a galvanometer driver 515, which receives a control signal, typically an analog voltage signal, which precisely defines the rotation angle and speed of the galvanometer 514. Based on the control signal, the galvanometer driver 515 controls the galvanometer 514 to reciprocate at a fixed frequency to reflect the transmitted beam.

[0092] For example, galvanometer 514 can be a high-speed galvanometer.

[0093] The chirp factor measurement system provided in the above embodiments uses an autocorrelator composed of an interferometer, a photodetector, and a programmable logic device to down-frequency the high-frequency chirp information to a low-frequency band that is easy to detect. Only a low-frequency signal analyzer is needed, and there is no need to configure a high-speed photodetector and a high-speed oscilloscope, which reduces the system cost.

[0094] In one possible implementation, such as Figure 1 As shown, the chirp factor measurement system may also include a DC bias 106 and a signal generator 107.

[0095] DC bias 106 is connected to the semiconductor laser under test and is used to provide bias current to the semiconductor laser under test; signal generator 107 is connected to the semiconductor laser under test and is used to provide modulation signal to the semiconductor laser under test.

[0096] In this embodiment, the output terminal of the DC bias 106 is coupled to the driving terminal of the semiconductor laser under test, and is used to provide the semiconductor laser under test with a DC bias current higher than a preset threshold current, so that the semiconductor laser under test can work stably in the laser emission state.

[0097] The output of the signal generator 107 is coupled to the modulation end of the semiconductor laser under test, and is used to provide a high-frequency electrical modulation signal to the semiconductor laser under test to modulate the intensity of the emitted light of the semiconductor laser under test.

[0098] In one possible implementation, Figure 3 An architectural diagram of another chirp factor measurement system provided in this application embodiment is shown below. Figure 3 As shown, the chirp factor measurement system may also include two temperature controllers 108 and two heaters 109.

[0099] Each heater 109 is arranged in surface contact with the corresponding periodically polarized lithium niobate crystal 102 / 103, and each temperature controller 108 is connected to each heater 109 to control the temperature of the corresponding periodically polarized lithium niobate crystal 102 / 103 through each heater 109.

[0100] In this embodiment, the temperature of the heater 109 is adjusted by the temperature controller 108, so as to change the temperature of the periodically polarized lithium niobate crystals 102 / 103 through the heater 109, so that the first periodically polarized lithium niobate crystal 102 operates at the phase matching point and the second periodically polarized lithium niobate crystal 103 operates at the phase mismatch point.

[0101] The chirp factor measurement system provided in the above embodiments adjusts the temperature of the dual-path periodically polarized lithium niobate crystals through a temperature controller and a heater, so that the two periodically polarized lithium niobate crystals operate at the phase matching point and the phase mismatch point, respectively. This allows the system to capture the chirp-noise mixed signal and the pure noise baseline, enabling the calculation of the chirp factor of the semiconductor laser under test. This solves the problem of separating chirp and noise in the prior art, significantly improves the measurement accuracy of the chirp factor of semiconductor lasers, and enhances the resistance of semiconductor lasers to environmental vibration, eliminating the need to place the semiconductor laser on a high-vibration-resistant platform. By calculating the chirp factor through time-domain chirp characterization, real-time detection of transient chirp can be achieved with extremely fast detection speed, with a single measurement time of <10ms. By employing autocorrelation down-frequency reduction technology to autocorrelate the second output light, the GHz chirp signal is compressed to kHz, eliminating the need for expensive high-speed photodetectors, high-speed oscilloscopes, and other instruments in the measurement system, thus reducing the cost of the measurement system.

[0102] The following section describes the specific implementation of the chirp factor measurement method applied to the chirp factor measurement system described above.

[0103] Figure 4This is a flowchart illustrating a chirp factor measurement method provided in an embodiment of this application. The execution subject of this method can be an electronic device such as a computer, server, or processor. Figure 1 As shown, the method may include:

[0104] S201. Obtain the spectral broadening of the first output light generated after the first laser of the semiconductor laser under test is incident on the first periodically polarized lithium niobate crystal, and obtain the phase change rate over time obtained by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal. The first laser and the second laser are two lasers generated after the output light of the semiconductor laser under test is split.

[0105] In this embodiment, the emitted light from the semiconductor laser under test is split by a first beam splitter to generate a first laser and a second laser. The first laser undergoes SHG (Sequencing and Spectroscopy) through a first periodically polarized lithium niobate crystal operating at a phase-matching point to generate a first output light. The frequency-doubled light of the first output light is analyzed by a spectrometer to determine the spectral broadening. .

[0106] The second laser beam undergoes SHG suppression via a second periodically polarized lithium niobate crystal operating at a phase mismatch point, generating a second output beam. An autocorrelator is used to perform autocorrelation beat frequency processing, phase extraction, and differentiation on the fundamental frequency of the second output beam to determine the phase change rate over time. .

[0107] S202. Calculate the frequency domain chirp characterization factor based on the spectral broadening.

[0108] In this embodiment, the spectral broadening of the frequency-doubled light of the first output light is determined based on... The incident light power of the first laser beam The incident wavelength of the first laser beam The frequency domain chirp characterization factor is calculated based on the nonlinear coefficient C of the first periodically polarized lithium niobate crystal. The frequency domain chirp characterization factor is the average amount of chirp information of the semiconductor laser under test over a complete modulation cycle, reflecting the chirp energy level of the semiconductor laser under test during long-term operation.

[0109] Example, frequency domain chirp characterization factor The calculation formula can be expressed as:

[0110]

[0111] in, It is the speed of light in a vacuum.

[0112] S203. Calculate the time-domain chirp characterization factor based on the rate of change of phase over time.

[0113] In this embodiment, the phase change rate of the fundamental frequency light of the second output light over time is used as a basis. Incident wavelength of the second laser Calculate the time-domain chirp characterization factor The time-domain chirp characterization factor is the instantaneous quantity of chirp information of the semiconductor laser under test, reflecting the transient behavior in the dynamic response of the semiconductor laser under test.

[0114] Example, time-domain chirp characterization factor The calculation formula can be expressed as:

[0115]

[0116] S204. Calculate the chirp factor of the semiconductor laser under test based on the frequency domain chirp characterization factor and the time domain chirp characterization factor.

[0117] In this embodiment, the frequency domain chirp characterization factor and the time domain chirp characterization factor are fused in a dual-domain manner to obtain the chirp factor of the semiconductor laser under test.

[0118] In some embodiments, the frequency domain chirp characterization factor and the time domain chirp characterization factor are weighted and summed according to a predetermined first weight and second weight to obtain the chirp factor of the semiconductor laser under test.

[0119] Furthermore, the first and second weights are dynamically changing. When the semiconductor laser under test is running smoothly, the first weight of the frequency domain chirp characterization factor is higher to ensure that the calculated chirp factor is more stable. When the semiconductor laser under test experiences sudden disturbances, the second weight of the time domain chirp characterization factor is higher so that the transient chirp factor of the semiconductor laser under test can be captured.

[0120] The chirp factor measurement method provided in the above embodiments employs a dual-path second harmonic design. It captures a chirp-noise mixture signal at a quasi-phase-matching point in a first periodically polarized lithium niobate crystal, and extracts a pure noise baseline at a specific phase mismatch point in a second periodically polarized lithium niobate crystal. This allows for the calculation of the frequency-domain chirp characterization factor based on the chirp-noise mixture signal, and the calculation of the time-domain chirp characterization factor based on the pure noise baseline. Finally, a dual-domain fusion calculation is performed to obtain the final chirp factor. This method solves the problem of separating chirp and noise in existing technologies and significantly improves the measurement accuracy of the chirp factor in semiconductor lasers. This improves the resistance of semiconductor lasers to environmental vibration, eliminating the need to place them on a high-vibration-resistant platform. By calculating the chirp factor through time-domain chirp characterization, real-time detection of transient chirp can be achieved with extremely fast detection speed, with a single measurement time of <10ms. By employing autocorrelation down-frequency reduction technology to autocorrelate the second output light, the GHz chirp signal is compressed to kHz, eliminating the need for expensive high-speed photodetectors, high-speed oscilloscopes, and other instruments, thus reducing the cost of the measurement system. This solution can be widely integrated and applied in optical module production lines.

[0121] In one possible implementation, Figure 5 A flowchart illustrating another chirp factor measurement method provided in this application embodiment is shown below. Figure 5 As shown, the process of obtaining the phase change rate over time by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal in step S201 can include:

[0122] S301. Obtain the low-frequency electrical modulation signal after autocorrelation processing of the second output light.

[0123] S302. Perform phase extraction on the low-frequency electrical modulation signal to determine the chirp information phase term.

[0124] S303. Calculate the first derivative of the chirped information phase term with respect to the optical path delay time, and determine the rate of phase change with time.

[0125] In this embodiment, the second output light of the second periodically polarized lithium niobate crystal is split by the second beam splitter and reflected by the fixed mirror and the galvanometer before returning along the original path to form laser interference, generating an autocorrelation beat frequency signal. This interference process linearly maps the high-frequency phase adjustment information of the outgoing light onto the low-frequency envelope change of the interference light intensity, so that the frequency of the autocorrelation beat frequency signal is compressed from the GHz band to the kHz band related to the scanning frequency of the galvanometer.

[0126] The photodetector extracts the low-frequency envelope frequency from the autocorrelation beat frequency signal to obtain a low-frequency electrical modulation signal. A real-time signal processing system based on an FPGA is then constructed using programmable logic devices to perform a real-time Hilbert transform on the low-frequency electrical modulation signal, extracting the chirp information phase term containing laser chirp information. This chirp information phase term is then analyzed as a function of the optical path delay time. The first derivative determines the rate of change of phase with time. .

[0127] The chirp factor measurement method provided in the above embodiments obtains the intensity noise baseline through a second periodically polarized lithium niobate crystal operating at the phase mismatch point, and calculates the phase change rate of the low-frequency electrical modulation signal over time through autocorrelation beat frequency, so as to calculate the transient chirp information of the semiconductor laser under test, i.e., the time domain chirp characterization factor, thereby improving the online monitoring capability of the transient chirp of the semiconductor laser under test.

[0128] In one possible implementation, the process of calculating the chirp factor of the semiconductor laser under test based on the frequency domain chirp characterization factor and the time domain chirp characterization factor in S204 may include:

[0129] The frequency domain chirp characterization factor and the time domain chirp characterization factor are weighted according to the preset weighting factor to calculate the chirp factor.

[0130] In this embodiment, a preset weighting factor is used to represent the stability of the semiconductor laser under test. If the preset weighting factor is used... As a characterization factor of frequency domain chirp The weights are determined based on preset weight factors. The time-domain chirp characterization factor can be calculated. The weight, i.e., 1 - preset weight factor The higher the stability of the semiconductor laser under test, the higher the preset weighting factor. The larger the value, the lower the stability of the semiconductor laser under test. (Preset weighting factor) The smaller the value. Similarly, if a preset weighting factor is used... As a characterization factor of time-domain chirp The higher the weight of the semiconductor laser under test, the higher its stability. (Preset weighting factor) The smaller the value, the lower the stability of the semiconductor laser under test. (Preset weighting factor) The larger.

[0131] According to the preset weighting factor Characterization factor of frequency domain chirp and time-domain chirp characterization factor The chirp factor of the semiconductor laser under test is obtained by performing a weighted summation calculation. .

[0132] For example, with preset weighting factors As a characterization factor of frequency domain chirp The weight of the chirp factor is... The calculation formula can be expressed as:

[0133]

[0134] In some embodiments, the method may further include:

[0135] A preset weighting factor is calculated based on the frequency domain signal-to-noise ratio of the first output light and the time domain signal-to-noise ratio of the second output light.

[0136] In this embodiment, the frequency domain signal-to-noise ratio The ratio of the peak power (or integrated power) to the background noise power of the SHG spectrum of the first output light generated by the first periodically polarized lithium niobate crystal reflects the quality of spectral broadening and the time-domain signal-to-noise ratio. To determine the phase reliability of the autocorrelation beat frequency signal of the second output light generated by the second periodically polarized lithium niobate crystal, a preset weighting factor is used. As a characterization factor of frequency domain chirp The weights are determined based on the frequency domain signal-to-noise ratio. and time domain signal-to-noise ratio Calculate the preset weighting factor The calculation formula can be expressed as:

[0137]

[0138] The chirp factor measurement method provided in the above embodiments dynamically fuses the frequency domain chirp characterization factor and the time domain chirp characterization factor based on a preset weighting factor, ensuring the stability and instantaneity of the chirp factor calculation of the semiconductor laser under test.

[0139] In one possible implementation, the method may further include:

[0140] Based on the first refractive index of the first periodically polarized lithium niobate crystal, the first wave vector mismatch between the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser is determined; based on the first wave vector mismatch, the temperature of the first periodically polarized lithium niobate crystal is adjusted to change the first refractive index, so that the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser satisfy the preset phase matching condition.

[0141] In this embodiment, a heater is attached to the first periodically polarized lithium niobate crystal. The heater is driven by a temperature controller to obtain the first refractive index of the first periodically polarized lithium niobate crystal for the fundamental frequency light of the first laser at the current temperature. The first refractive index of frequency-doubled light Based on the first refractive index of the fundamental frequency light of the first laser beam and the wavelength of fundamental frequency light Calculate the wave vector of the first laser beam. Based on the first refractive index of the frequency-doubled light of the first laser beam and the wavelength of frequency-doubled light Calculate the wave vector of the frequency-doubled light of the first laser beam. According to the wave vector of the first laser beam The wave vector of the frequency-doubled light of the first laser beam Calculate the first wave of vector mismatch. .

[0142] Example, first wave of vector mismatch The calculation formula can be expressed as:

[0143]

[0144] in, This represents the polarization period of the first periodically polarized lithium niobate crystal.

[0145] Determine the first wave of vector mismatch Whether the preset phase matching condition is met; if not, the first wave vector mismatch can be used as a reference. The size of the temperature controller generates a temperature adjustment command, which adjusts the heater accordingly, thereby changing the first refractive index of the first periodically polarized lithium niobate crystal. and By continuously adjusting the temperature and recalculating the first wave of mismatch, So that the first wave of vector mismatch If the preset phase matching conditions are met, the first periodically polarized lithium niobate crystal is determined to be operating at the phase matching point.

[0146] In some embodiments, the phase matching condition can be Less than or equal to the first threshold, for example, the phase matching condition can be: .

[0147] In another possible implementation, the method may also include:

[0148] Based on the second refractive index of the second periodically polarized lithium niobate crystal, the second wave vector mismatch of the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser is determined; based on the second wave vector mismatch, the temperature of the second periodically polarized lithium niobate crystal is adjusted to change the second refractive index, so that the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser satisfy the preset phase mismatch condition.

[0149] In this embodiment, a heater is attached to the second periodically polarized lithium niobate crystal. The heater is driven by a temperature controller to obtain the second refractive index of the second periodically polarized lithium niobate crystal for the fundamental frequency light of the second laser at the current temperature. The second refractive index of frequency-doubled light According to the second refractive index of the fundamental frequency light of the second laser... and the wavelength of fundamental frequency light Calculate the wave vector of the second laser beam. According to the second refractive index of the frequency-doubled light of the second laser beam and the wavelength of frequency-doubled light Calculate the wave vector of the frequency-doubled light of the second laser beam. According to the wave vector of the second laser Wave vector of the frequency-doubled light of the second laser Calculate the second wave vector mismatch. .

[0150] Example, second-wave vector mismatch The calculation formula can be expressed as:

[0151]

[0152] in, This represents the polarization period of the second periodically polarized lithium niobate crystal.

[0153] Determine the second wave of vector mismatch Whether the preset phase mismatch condition is met; if not, the mismatch can be determined based on the second wave vector. The size of the temperature controller generates a temperature adjustment command, which adjusts the heater accordingly, thereby changing the second refractive index of the second periodically polarized lithium niobate crystal. and By continuously adjusting the temperature and recalculating the second-wave mismatch, So that the second wave of vector mismatch If the preset phase mismatch condition is met, the second periodically polarized lithium niobate crystal is determined to be operating at the phase mismatch point.

[0154] In some embodiments, the phase mismatch condition can be Less than or equal to the second threshold, for example, the phase mismatch condition can be: .

[0155] The chirp factor measurement method provided in the above embodiments changes the refractive index of the periodically polarized lithium niobate transistor by adjusting the temperature of the periodically polarized lithium niobate crystal, thereby determining whether the periodically polarized lithium niobate crystal is operating at a phase-matching point or a phase-mismatching point. The chirp-noise mixed signal is captured at the quasi-phase-matching point of the first periodically polarized lithium niobate crystal, and the pure noise baseline is extracted at a specific phase-mismatching point of the second periodically polarized lithium niobate crystal, thus solving the problem of separating chirp and noise in the prior art.

[0156] For example, the chirp factor measurement method of this application will be described using a 25G 1550nm directly modulated semiconductor laser (DML) as an example.

[0157] Specifically, a 50mA DC bias current is applied to DML, and a 25Gbps PRNS7 modulation signal is used for modulation.

[0158] The size of the first periodically polarized lithium niobate crystal is selected as 10×1×0.5 mm³, and the polarization period is... =16.5um, nonlinear coefficient C=1.2×10 -4 m 2 / W; the incident power of DML is P0 = 10 mW; the temperature of heater TEC1 is set to 35°C to ensure that the first periodically polarized lithium niobate crystal meets the phase matching condition. .

[0159] The SHG spectral broadening under the main path was measured using a spectrometer. =0.142nm, and the frequency domain chirp characterization factor is calculated to be =2.77, frequency domain signal-to-noise ratio =26.5dB.

[0160] The size of the second periodically polarized lithium niobate crystal was selected as 5×1×0.5 mm³, and the polarization period was... =16.5um, nonlinear coefficient C=1.2×10 -4 m 2 / W; The temperature of heater TEC2 is set to 39.3°C to ensure that the second periodically polarized lithium niobate crystal meets the phase mismatch condition. .

[0161] Using a photodetector and an FPGA-based real-time signal processing system composed of programmable logic devices, the low-frequency envelope frequency in the beat frequency signal is extracted, thereby resolving the time-domain chirp characterization factor. =2.85, time-domain signal-to-noise ratio =21.8dB.

[0162] Based on frequency domain signal-to-noise ratio and time domain signal-to-noise ratio The weighting factors are calculated. =0.75, then the chirp factor measure of DML is:

[0163]

[0164] The chirp factor measurement method provided in this application embodiment has a measurement accuracy of ±0.04, which is significantly improved compared to the measurement error of ±0.1 in the traditional scheme. The measurement accuracy of this application embodiment is ≤10ms for a single measurement, and the detection speed is extremely fast. It can be integrated into the high-speed optical module production line and is suitable for online quality inspection and performance evaluation of 25Gbps and above high-speed optical modules.

[0165] Based on the above method embodiments, this application also provides a device for measuring the chirp factor of a semiconductor laser. Figure 6 This is a schematic diagram of the structure of the chirp factor measuring device provided in the embodiments of this application, as shown below. Figure 6 As shown, the device may include:

[0166] The information acquisition module 402 is used to acquire the spectral broadening of the first output light generated after the first laser of the semiconductor laser under test is incident on the first periodically polarized lithium niobate crystal, and to acquire the phase change rate over time obtained by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal. The first laser and the second laser are two lasers generated after the output light of the semiconductor laser under test is split.

[0167] Chirp factor calculation module 404 is used to calculate the frequency domain chirp characterization factor based on the spectral broadening.

[0168] The chirp factor calculation module 404 is also used to calculate the time-domain chirp characterization factor based on the rate of change of phase over time;

[0169] The chirp factor calculation module 404 is also used to calculate the chirp factor of the semiconductor laser under test based on the frequency domain chirp characterization factor and the time domain chirp characterization factor.

[0170] Optionally, the information acquisition module 402 is specifically used to acquire the low-frequency electrical modulation signal after the second output light has undergone autocorrelation processing; to extract the phase of the low-frequency electrical modulation signal and determine the chirp information phase term; and to calculate the first derivative of the chirp information phase term with optical path delay time and determine the phase change rate with time.

[0171] Optionally, the chirp factor calculation module 404 is specifically used to calculate the chirp factor by weighting the frequency domain chirp characterization factor and the time domain chirp characterization factor according to a preset weighting factor.

[0172] Optionally, the device may further include:

[0173] The weighting factor calculation module 403 is used to determine a preset weighting factor based on the frequency domain signal-to-noise ratio of the first output light and the time domain signal-to-noise ratio of the second output light.

[0174] Optionally, the device may further include:

[0175] The temperature adjustment module 401 is specifically used to determine the first wave vector mismatch between the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser based on the first refractive index of the first periodically polarized lithium niobate crystal; and to adjust the temperature of the first periodically polarized lithium niobate crystal based on the first wave vector mismatch to change the first refractive index so that the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser satisfy the preset phase matching condition.

[0176] Optionally, the temperature adjustment module 401 is further configured to determine the second wave vector mismatch between the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser based on the second refractive index of the second periodically polarized lithium niobate crystal; and adjust the temperature of the second periodically polarized lithium niobate crystal based on the second wave vector mismatch to change the second refractive index, so that the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser satisfy the preset phase mismatch condition.

[0177] The above-described device is used to execute the method provided in the foregoing embodiments, and its implementation principle and technical effect are similar, so they will not be described again here.

[0178] These modules can be one or more integrated circuits configured to implement the above methods, such as one or more Application Specific Integrated Circuits (ASICs), one or more microprocessors, or one or more Field Programmable Gate Arrays (FPGAs). Alternatively, when a module is implemented using processing element scheduler code, the processing element can be a general-purpose processor, such as a Central Processing Unit (CPU) or other processor capable of calling program code. Furthermore, these modules can be integrated together as a system-on-a-chip (SOC).

[0179] Figure 7This is a schematic diagram of an electronic device provided in an embodiment of this application. The electronic device 500 may include a processor 501 and a storage medium 502. The storage medium 502 stores machine-readable instructions executable by the processor 501. When the electronic device 500 is running, the processor 501 communicates with the storage medium 502, and the processor 501 executes the machine-readable instructions to perform the above-described method embodiment. The specific implementation and technical effects are similar and will not be described in detail here.

[0180] Optionally, this application also provides a computer-readable storage medium storing a computer program, which is executed by a processor to perform the above-described method embodiments.

[0181] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0182] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0183] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in a combination of hardware and software functional units.

[0184] The integrated units implemented as software functional units described above can be stored in a computer-readable storage medium. These software functional units, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute some steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0185] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for measuring the chirp factor of a semiconductor laser, characterized in that, The method includes: The spectral broadening of the first output light generated after the first laser beam from the semiconductor laser under test is incident on the first periodically polarized lithium niobate crystal is obtained, and the phase change rate over time is obtained by autocorrelation processing of the second output light generated after the second laser beam is incident on the second periodically polarized lithium niobate crystal. The first laser beam and the second laser beam are two laser beams generated after the output light of the semiconductor laser under test is split. The first periodically polarized lithium niobate crystal operates at the phase-matching point, and the second periodically polarized lithium niobate crystal operates at the phase-mismatching point. The frequency domain chirp characterization factor is calculated based on the spectral broadening of the frequency-doubled light of the first output light, the incident light power of the first laser, the incident light wavelength of the first laser, and the nonlinear coefficient of the first periodically polarized lithium niobate crystal. The time-domain chirp characterization factor is calculated based on the phase change rate of the fundamental frequency light of the second output light and the incident wavelength of the second laser. The frequency domain chirp characterization factor and the time domain chirp characterization factor are weighted according to a preset weighting factor to calculate the chirp factor of the semiconductor laser under test.

2. The method as described in claim 1, characterized in that, The phase-time rate of change obtained by autocorrelation processing of the second output light generated after the second laser is incident on the second periodically polarized lithium niobate crystal includes: Acquire the low-frequency electrical modulation signal of the second output light after autocorrelation processing; Phase extraction is performed on the low-frequency electrical modulation signal to determine the chirp information phase term; Calculate the first derivative of the chirped information phase term with respect to the optical path delay time to determine the rate of change of the phase over time.

3. The method as described in claim 1, characterized in that, The method further includes: The preset weighting factor is determined based on the frequency domain signal-to-noise ratio of the first output light and the time domain signal-to-noise ratio of the second output light.

4. The method as described in claim 1, characterized in that, The method further includes: Based on the first refractive index of the first periodically polarized lithium niobate crystal, the first wave vector mismatch between the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser is determined. Based on the first wave vector mismatch, the temperature of the first periodically polarized lithium niobate crystal is adjusted to change the first refractive index, so that the wave vector of the first laser and the wave vector of the frequency-doubled light of the first laser satisfy a preset phase matching condition.

5. The method as described in claim 1, characterized in that, The method further includes: Based on the second refractive index of the second periodically polarized lithium niobate crystal, the second wave vector mismatch of the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser is determined. Based on the second wave vector mismatch, the temperature of the second periodically polarized lithium niobate crystal is adjusted to change the second refractive index, so that the wave vector of the second laser and the wave vector of the frequency-doubled light of the second laser satisfy the preset phase mismatch condition.

6. A chirp factor measurement system for a semiconductor laser, the chirp factor measurement system being used to perform the chirp factor measurement method as described in any one of claims 1 to 5, characterized in that, The chirp factor measurement system includes: a first beam splitter, a first periodically polarized lithium niobate crystal, a second periodically polarized lithium niobate crystal, a spectrometer, and an autocorrelator; The light-emitting surface of the semiconductor laser under test faces the light-incident surface of the first beam splitter, so that the first beam splitter splits the emitted light of the semiconductor laser under test into a first laser and a second laser. The two light-emitting surfaces of the first beam splitter are respectively directed toward the light-incident surfaces of the first periodically polarized lithium niobate crystal and the second periodically polarized lithium niobate crystal, so that the first laser beam and the second laser beam are respectively incident on the first periodically polarized lithium niobate crystal and the second periodically polarized lithium niobate crystal. The light-emitting surface of the first periodically polarized lithium niobate crystal faces the spectrometer; The light-emitting surface of the second periodically polarized lithium niobate crystal faces the autocorrelator.

7. The chirp factor measurement system as described in claim 6, characterized in that, The autocorrelator includes: a Michelson interferometer, a photodetector, and a programmable logic device; The light-emitting surface of the second periodically polarized lithium niobate crystal faces the light-incident surface of the Michelson interferometer, and the light-emitting surface of the Michelson interferometer faces the photodetector. The photodetector is connected to the programmable logic device.

8. The chirp factor measurement system as described in claim 6, characterized in that, The chirp factor measurement system also includes: a DC biaser and a signal generator; The DC biaser is connected to the semiconductor laser under test and is used to provide bias current to the semiconductor laser under test; The signal generator is connected to the semiconductor laser under test and is used to provide a modulation signal for the semiconductor laser under test.

9. The chirp factor measurement system as described in claim 6, characterized in that, The chirp factor measurement system also includes: two temperature controllers and two heaters; Each heater is arranged in surface contact with the corresponding periodically polarized lithium niobate crystal, and each temperature controller is connected to each heater to control the temperature of the corresponding periodically polarized lithium niobate crystal through each heater.

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