Catastrophic Optical Damage (COD) Threshold Test Technology for Semiconductor Laser Devices

Abstract

The invention relates to the field of semiconductor laser device testing, and mainly to a catastrophic optical damage (COD) threshold test technology for semiconductor laser devices. A pulse current drives a semiconductor laser, and parameters such as pulse peak current, pulse width, repetition frequency, temperature, pulse number, stress, etc. are gradually changed from small to large. A photoelectric detector measures the pulse laser, responds to a sharp decline in peak power, and determines the occurrence of COD. The time interval of the laser pulse is a multiple of a sampling period, and the decimal part is a non-circular decimal within the effective number of bits, so that the sampling points collected from a series of pulse waveforms are scanned on the laser waveform, and the complete waveform of the laser pulse is obtained after reconstruction, thereby compensating for the influence of undersampling on the peak power measurement. The average value of the sampling point response is taken within a certain time domain near the peak point of the pulse waveform, thereby reducing the influence of noise on the peak power measurement result and optimizing the measurement uncertainty. The damage threshold is determined by adopting the sudden change of the pulse laser waveform, thereby reducing the test cost.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor laser device testing, and mainly to a catastrophic optical damage (COD) threshold test technology of a semiconductor laser device, and in particular to a threshold parameter measurement based on COD occurring under a pulse current driving condition of a semiconductor laser chip, wherein parameters such as pulse peak current, pulse width, repetition frequency, temperature, pulse number, stress, etc. are set to gradually change from small to large, and when a pulse power supply is driven, the semiconductor laser device outputs a pulse laser response peak value that sharply decays, and the COD occurrence is judged, and the COD threshold of the semiconductor laser device is measured. Background Art

[0002] Semiconductor lasers are currently the most efficient commercially engineered laser devices for electro-optical energy conversion. They are driven by pulsed currents, and photodetectors receive pulsed lasers and output the time-domain pulse waveforms of pulsed lasers. The response characteristics of semiconductor lasers are deduced by analyzing the changes in the pulse waveforms. COD threshold tests on semiconductor laser devices can more quickly and meticulously observe the evolution of the time-domain waveform of the laser output after COD occurs, which is beneficial for discovering defect characteristics of semiconductor lasers and providing a technical basis for improving designs.

[0003] At present, semiconductor lasers are usually driven by continuous current or microsecond pulse current to emit lasers. The laser output parameters are measured within a certain period of time for aging screening. After the device fails due to COD, it is sliced ​​and planed, and the evolution of COD is deduced from the microscopic image of the planed section. The original damage image obtained by this post-processing method is difficult to determine the initial condition of COD due to severe damage, and cannot provide technical support for subsequent product improvements.

[0004] Laser peak power is an important parameter for evaluating the COD threshold of semiconductor lasers. Usually, a repetitive nanosecond pulse current source is used to drive the semiconductor laser, and a photodetector + high-bandwidth oscilloscope is used to measure the laser output pulse waveform. The peak response voltage of the pulse waveform is extracted and converted to obtain the laser peak power density. The measurement uncertainty introduced by random noise in high-bandwidth signal measurement is difficult to overcome, and the cost of high-bandwidth oscilloscopes is high. The frequency stability of commercially available repetitive pulse laser current drive power supplies is insufficient, and it is difficult to meet the requirements of timing scanning to reconstruct the pulse waveform under undersampling conditions. Summary of the invention

[0005] The purpose of the present invention is to overcome the limitations of the current COD test of semiconductor laser devices and to provide a COD threshold measurement technology based on pulsed laser peak power under undersampling conditions.

[0006] The first technical problem to be solved by the present invention is to provide a COD threshold measurement device for a semiconductor laser device, comprising a repetitive pulse current driving power supply, a semiconductor laser carrier, a fast photodetector, a synchronous ultra-high-speed data acquisition card, a computer servo control and a data acquisition and processing system; the repetitive pulse current driving power supply is a peak current stable output pulse power supply and a temperature control power supply with adjustable repetition frequency, pulse width, pulse number and current; the semiconductor laser carrier is a carrier for carrying a semiconductor laser device with a built-in semiconductor refrigerator (TEC) and a temperature sensor; the rise time of the fast photodetector is much smaller than the rise time of the laser pulse, and is used to measure the time domain waveform of the pulsed laser at the far-field position output by the semiconductor laser; the synchronous ultra-high-speed data acquisition card is used to collect the pulsed laser response analog signal output by the photodetector into a digital signal sequence; the computer servo control and data acquisition and processing system are used to measure the COD threshold measurement device for a semiconductor laser device, and the COD threshold measurement device is ... The computer servo control and data acquisition and processing system includes repetitive pulse current driving power supply control software, temperature control software for providing a stable ambient temperature for the stage, and waveform reconstruction and peak power calculation software for pulse laser digital signals; the output end of the repetitive pulse current driving power supply is fixedly connected to the semiconductor laser stage, and the semiconductor laser is powered by needle pressure contact, the semiconductor laser outputs laser pulses, and the fast photoelectric detector samples and receives laser pulses in the far field, outputs the pulse laser time domain waveform of the analog signal, inputs the acquisition card, and the computer program controls the acquisition of the pulse laser time domain waveform and calculates the pulse laser peak power; the power supply and environmental assignment conditions of the semiconductor laser are gradually increased for measurement, the laser pulse peak power is monitored, the occurrence of COD is judged by the attenuation of the peak power, and the assignment conditions of the corresponding pulse current and environment before the occurrence of COD are given as the threshold of COD.

[0007] The second technical problem to be solved by the present invention is to provide a method for measuring the peak power of a pulsed laser under undersampling conditions, wherein the measuring steps are as follows:

[0008] ① Set the repetition frequency f of the repetitive pulse current driving power supply so that the time interval T of the laser output laser pulse is equal to δ, which is 1 / f divided by the sampling period T0 of the acquisition card. The decimal part of δ is a non-repeating decimal within the effective number of bits, ensuring that the sampling point scans on the pulse laser waveform;

[0009] ② The laser emits a pulse laser with a repetition frequency of f. The fast photodetector receives a series of laser pulses and outputs a series of pulse waveforms. The acquisition card collects a series of k pulse waveforms and extracts the response value and relative timing data of each pulse waveform sampling point.

[0010] ③ Find the response peaks and their timing positions of k pulse waveforms, and find the maximum value Vp of the response peaks;

[0011] ④ Find the k waveforms whose response value is within ±x% of Vp / 2 among the trailing edges of k waveforms.i The sampling points of the waveform M i , i = 1, 2, 3, ..., k i , and sort by response value, for sampling point M i Assign the time sequence M in reverse order of j with a=T0 / k multiples ij , j = 1, 2, 3, ..., k i ;

[0012] ⑤Find k i The remaining sampling points of the waveform are determined, and the timing positions of the other sampling points are determined according to the sampling timing of the pulse laser waveform. (i，nT0+ja) , n = ±1, ±2, ±3;

[0013] ⑥Find the solution to remove k i The sampling point B on the leading edge of the other k' pulse laser waveforms other than k i The response values ​​on the leading edge of the waveforms are compared, and the timing position B is determined by the proportional insertion method according to the response value. (k’，t) ;

[0014] ⑦ Determine the other sampling points B of k' waveforms (k’，nT0+t) , draw a waveform diagram based on the response values ​​and timing positions of all sampling points;

[0015] ⑧ Calculate the leading and trailing edge contour coverage areas A of k pulse waveforms, slightly adjust the timing positions of the sampling points on the contour lines to minimize the coverage area A, and obtain the pulse waveform reconstruction image;

[0016] ⑨ Calculate the average value V of the response values ​​of all sampling points within the time sequence of ±T0 / m near the corresponding point falling into the maximum value Vp in the pulse waveform reconstruction diagram, where m is an integer;

[0017] ⑩ Calculate the peak power P = CRV, where: C is the attenuation factor and R is the response sensitivity of the fast photodetector.

[0018] The third technical problem to be solved by the present invention is to provide a semiconductor laser COD testing method, wherein the measuring steps are as follows:

[0019] ① Estimate the threshold conditions for COD occurrence of the semiconductor laser chip under test, set the repetition frequency, pulse width, current range, current step, number of pulses, and temperature of the repetitive pulse current driving power supply so that the threshold conditions for COD occurrence are within the set range;

[0020] ②Set the trigger mode of acquisition card sampling;

[0021] ③ Start emitting a series of laser pulses from a small current, the photodetector receives the laser pulses, and the acquisition card synchronously collects and records the series of pulse laser waveforms;

[0022] ④ Reconstruct the pulse laser waveform as shown in the peak power measurement method, and calculate the peak power corresponding to the applied current;

[0023] ⑤ Increase the pulse laser current step by step and measure the response curve of pulse laser peak power-current;

[0024] ⑥Until the laser peak power decays sharply, i.e. COD occurs, the previous pulse laser current is output as the COD threshold under the corresponding conditions;

[0025] ⑦ And so on, COD threshold measurement of setting parameters such as repetition frequency, pulse width, number of pulses, temperature, etc.

[0026] The fourth technical problem to be solved by the present invention is to provide a spectral wavelength measurement method based on the pulse laser peak power-current response curve in order to further understand the response characteristics of the semiconductor laser, calculate the slope of the pulse laser peak power-current response, judge the change of the laser wavelength through the transition of the slope, and deduce the stress change of the gain medium region.

[0027] The fifth technical problem to be solved by the present invention is to provide a time-series shape mutation evolution process based on the pulsed laser waveform to determine the damage threshold, limit the damage threshold judgment condition of the semiconductor laser chip to a recoverable range, reduce damage to the semiconductor laser, and save testing costs.

[0028] The present invention has the following advantages:

[0029] The present invention uses the peak power of pulsed laser as the basis for determining the occurrence of COD, so that the evolution process of semiconductor laser chips can be carefully detected, providing a technical basis for locating the initial defects of semiconductor lasers and providing a technical basis for users to design the application scope of semiconductor lasers;

[0030] The present invention adopts the method that the decimal part of the time interval of the laser pulse is a multiple of the sampling period and the effective number of bits is a non-repeating decimal, so that when the series of pulse waveforms are input into the acquisition card, the collected sampling points are scanned on the laser waveform, and the complete waveform of the laser pulse is obtained after reconstruction, which makes up for the influence of undersampling on the peak power measurement;

[0031] The present invention adopts the method of taking the average value of the sampling point response in a certain time domain near the peak point of the pulse waveform, which effectively reduces the influence of random noise on the peak power measurement result and optimizes the measurement uncertainty;

[0032] The present invention adopts the response curve of pulse laser peak power-current, uses the slope change of the curve to judge the change of spectral wavelength, and then deduce the stress change of the laser chip, providing technical support for the rapid detection of the internal physical mechanism of the semiconductor laser.

[0033] The present invention adopts the time sequence mutation of the pulse reconstruction waveform to judge the damage occurrence threshold and avoid damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of semiconductor laser device catastrophic optical damage (COD) threshold test system

[0035] Figure 2 Waveform diagram of series laser pulse sampling

[0036] Figure 3 Pulse laser waveform reconstruction

[0037] Figure 4 Response curve of pulse laser peak power-current

[0038] Figure 5 Waveform diagram of front and rear two-stage laser pulse sampling DETAILED DESCRIPTION

[0039] Preferred embodiment 1 A semiconductor laser device optical catastrophic damage (COD) threshold test device, as shown in the schematic diagram Figure 1 As shown, it includes a repetitive pulse current drive power supply and temperature control power supply 1, a semiconductor laser carrier 2, a fast photodetector 3, a synchronous ultra-high-speed data acquisition card 4, and a computer servo control and data acquisition and processing system 5; the output end of the repetitive pulse current drive power supply and temperature control power supply 1 is fixedly connected to the semiconductor laser carrier, and the power supply is realized by acupressure contact with the semiconductor laser. The repetitive pulse current drive power supply and temperature control power supply 1 are set to a repetition frequency of 339Hz, a pulse width of 100ns, a pulse number of 40, a current from 1A-100A, a step interval of 1A, and a temperature of 23°C. The semiconductor laser outputs laser pulses. The semiconductor laser carrier 2 is a built-in semiconductor refrigerator (TEC) and a temperature sensor thermistor for stabilizing the ambient temperature of the semiconductor laser; the fast photodetector 3 is a silicon photodiode with a rise time of less than 3ns, which is used to measure the time domain waveform of the pulsed laser at the far-field position output by the semiconductor laser. The synchronous ultra-high-speed data acquisition card 4 has a sampling rate of 20MS / s and a sampling interval of 50ns, which is used to collect the pulse laser response analog signal output by the fast photodetector 3 into a digital signal sequence such as Figure 2 As shown, the waveform reconstruction and peak power calculation software of the pulsed laser digital signal of the computer servo control and data acquisition and processing system 5 processes and calculates the pulsed laser peak power; the power supply current of the semiconductor laser and the assigned conditions of the environment are gradually increased to measure, the laser pulse peak power is monitored, the occurrence of COD is judged by the attenuation of the peak power, and the assignment conditions of the pulse current and the environment before the occurrence of COD are given as the threshold of COD.

[0040] Preferred embodiment 2 provides a method for measuring the peak power of a pulsed laser under undersampling conditions, and the measuring steps are as follows:

[0041] ① Set the repetition frequency of the repetitive pulse current driving power supply 1 to 339Hz, so that the time interval T of the laser output laser pulse is (1 / 339)s divided by the acquisition card sampling period of 50ns is an irrational number, and ensure that the laser waveform of the sampling point is scanned upward when the repetitive pulse laser is input;

[0042] ② The laser emits a pulse laser with a repetition frequency of 339Hz. The fast photodetector 3 receives a series of laser pulses and outputs a series of pulse waveforms. The acquisition card 4 collects a series of 40 pulse waveforms. The series of laser pulse sampling waveforms is shown in the figure below. Figure 2 As shown;

[0043] ③ Extract the response value and relative timing data of each pulse waveform sampling point, find the response peak value and timing position of k pulse waveforms, and find the maximum value Vp of the response peak value;

[0044] ④ Find the k waveforms whose response value is within ±x% of Vp / 2 among the trailing edges of k waveforms. i The sampling points of the waveform M i , i = 1, 2, 3, ..., k i , and sort by response value, X is less than 10, for sampling point M i Assign the timing M in reverse order of multiples of a = 1.67ns ij , j = 1, 2, 3, ..., k i ;

[0045] ⑤Find k i The remaining sampling points of the waveform are determined, and the timing positions of the other sampling points are determined according to the sampling timing. (i，nT0+ja) , n = ±1, ±2, ±3;

[0046] ⑥Find the solution to remove k i The sampling points B on the leading edges of the other k' pulse waveforms other than the k pulse waveforms are i The response values ​​on the leading edge of the waveforms are compared, and the timing position B is determined by the proportional insertion method according to the response value. (k’，t) ;

[0047] ⑦ Determine the other sampling points B of k' waveforms (k’，nT0+t) , according to the response values ​​and timing positions of all sampling points, a waveform diagram is drawn to obtain the pulse waveform reconstruction diagram, such as Figure 3 As shown;

[0048] ⑧ Calculate the leading and trailing edge contour coverage area A of k pulse waveforms, and slightly adjust the timing position of the sampling points on the contour line to make the coverage area A take the minimum value;

[0049] ⑨ Calculate the average value V of the response values ​​of all sampling points within the time sequence of ±T0 / m near the corresponding point falling into the maximum value Vp in the pulse waveform reconstruction diagram, preferably m is 4;

[0050] ⑩ Calculate the peak power P = CRV, where: C is the attenuation multiple, and R is the response sensitivity of the fast photodetector.

[0051] Preferred embodiment 3, a semiconductor laser COD testing method, the measuring steps are as follows:

[0052] ① Estimate the threshold conditions for COD occurrence of the semiconductor laser chip under test, set the repetition frequency 339, pulse width 100, current range, current step, number of pulses, and temperature of the repetitive pulse current driving power supply 1 so that the threshold conditions for COD occurrence are within the set range;

[0053] ②Set the trigger mode of acquisition card sampling;

[0054] ③ A series of laser pulses are emitted from a small current, the photodetector 3 receives the laser pulses, and the acquisition card 4 synchronously acquires and records the series of pulse laser waveforms;

[0055] ④ Reconstruct the pulse laser waveform as in Example 2, and calculate and give the peak power of the corresponding power-on current;

[0056] ⑤Gradually increase the pulse laser current and measure the pulse laser peak power-current response curve as shown in Figure 4 As shown;

[0057] ⑥Until the laser peak power decays sharply, that is, COD occurs, the previous level pulse laser current is output as the COD threshold under the corresponding conditions. The waveforms of the two levels of laser pulse sampling are shown in Figure 5 As shown;

[0058] ⑦ And so on, COD threshold measurement of setting parameters such as repetition frequency, pulse width, number of pulses, temperature, etc.

[0059] ⑧ Calculate the response slope of the pulsed laser peak power-current, determine the change in laser wavelength through the jump in the slope, and deduce the stress change in the gain medium region.

[0060] ⑨ By increasing the pulse laser current step by step and observing the sudden change of the reconstructed pulse laser waveform, the damage threshold can be determined.

Claims

1. A method for measuring pulse laser peak power under undersampling conditions, characterized in that: ① Set the repetition frequency f of the repetitive pulse current driving power supply (1) so that the time interval T of the laser output laser pulses = 1 / f divided by the sampling period T0 of the acquisition card (4) is equal to δ, and the decimal part of δ is a non-repeating decimal within the effective number of bits, ensuring that the sampling point scans on the pulse laser waveform; ② The laser emits a pulse laser with a repetition frequency f, the fast photodetector (3) receives a series of laser pulses and outputs a series of pulse waveforms, and the acquisition card (4) acquires a series of k pulse waveforms and extracts the response value and relative timing data of each pulse waveform sampling point; ③ Find the response peaks and their timing positions of k pulse waveforms, and find the maximum value Vp of the response peaks; ④ Find the k waveforms whose response value is within ±x% of Vp / 2 among the trailing edges of k waveforms. i The sampling points of the waveform M i , i = 1, 2, 3, ..., k i , and sort by response value, for sampling point M i Assign the time sequence M in reverse order of j with a=T0 / k multiples ij , j = 1, 2, 3, ..., k i ; ⑤Find k i The remaining sampling points of the waveform are measured, and the timing positions of other sampling points are determined based on the relative positions of the measured sampling timing. (i,nT0+ja) , n = ±1, ±2, ±3; ⑥Find the solution to remove k i The sampling point B on the leading edge of the other waveform k' is different from k i The response values ​​on the leading edge of the waveforms are compared, and the timing position B is determined by the proportional insertion method according to the response value. (k’，t) ; ⑦ Determine the other sampling points B of k' waveforms (k',nT0+t) , draw a waveform diagram based on the response values ​​and timing positions of all sampling points; ⑧ Calculate the leading and trailing edge contour coverage areas A of k pulse waveforms, slightly adjust the timing positions of the sampling points on the contour lines to minimize the coverage area A, and obtain the pulse waveform reconstruction image; ⑨ Calculate the average value V of the response values ​​of all sampling points within the time sequence of ±T0 / m near the corresponding point falling into the maximum value Vp in the pulse waveform reconstruction diagram, where m is an integer; ⑩ Calculate the peak power P = CRV, where: C is the attenuation factor, and R is the response sensitivity of the fast photodetector (3).

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