A method for measuring the cavity surface temperature of a semiconductor laser

Abstract

The present invention belongs to the technical field of semiconductor lasers; in the study of traditional catastrophic optical damage of the cavity surface, the change in reflectivity is used to monitor the development of cavity surface damage and the detection of temperature changes. There is a lack of direct measurement of the change in reflectivity, and the temperature change cannot be accurately measured. The present invention provides a method for measuring the cavity surface temperature of a semiconductor laser, which introduces a polarization beam splitter, a differential detector, and a lock-in amplifier to achieve direct measurement of the change in reflectivity. The test beam is separated into a reference beam and a test beam. After reflection, the test beam and the reference beam are jointly focused on the differential detector through a second polarization beam splitter. The obtained differential signal is measured by the lock-in amplifier to measure the change in reflectivity and calculate the change value of the cavity surface temperature. The present invention uses a differential detector to avoid possible input saturation of the lock-in amplifier and eliminate experimental noise sources that may affect the reference and reflected beams, achieving higher measurement accuracy.

Description

Technical Field

[0001] The present invention relates to semiconductor lasers, and more particularly, to a method for measuring the cavity surface temperature of a semiconductor laser. Background Art

[0002] Most experimental methods for COD research rely on temperature measurement, especially the measurement of the cavity surface temperature when the laser is working, aiming to obtain the critical temperature of the cavity surface when damage occurs. In addition, in the research on measuring the recombination rate of surface states when the laser is working, data on the temperature change of the damaged area is also required. In conventional methods, Raman spectroscopy is used to measure the lattice temperature, and the phonon lines required for temperature measurement may not be extracted, resulting in errors in the measurement results. Thermal imaging technology, which detects Planck radiation and measures the temperature, has a relatively small applicable range. To solve the problems of complex and expensive instrument equipment and complicated algorithms, and to meet the research needs of high-speed laser chip cavity surface damage, it is necessary to develop a highly integrated and automated measuring instrument with comprehensive measurement, damage modeling, and damage prediction capabilities, providing measuring and analyzing instruments for theoretical research, system construction, and the development of related equipment in the field of high-speed optical communication. This patent designs a cavity surface temperature detection module, which measures the change in cavity surface reflectivity to achieve real-time and high-speed detection of the temperature change during the damage occurrence process. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for measuring the cavity surface temperature of a semiconductor laser. The technical problem to be solved by this invention is how to accurately measure the cavity surface temperature of the laser, so that the time resolution reaches 2 ns, and the high resolution can accurately simulate the development process of laser cavity surface damage.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A method for measuring the cavity surface temperature of a semiconductor laser, separating a test beam into a reference beam and a test beam by a polarization beam splitter, after reflection, the test beam and the reference beam are jointly focused on a differential detector by a second polarization beam splitter, measuring the obtained differential signal by a lock-in amplifier, measuring the change amount of the reflectivity, and calculating the change value of the cavity surface temperature, specifically including the following steps:

[0006] S1. A fiber-coupled laser diode provides a probe laser beam, which is transmitted through an optical fiber to the first port of a circulator, and the probe laser beam is output from the second port 2;

[0007] S2. After the probe laser beam is filtered by a filter, the first polarization beam splitter separates the probe laser beam into a reference beam and a test beam, and then the reference beam enters the differential detector;

[0008] S3. After being reflected by the chip, the test beam carrying the cavity surface temperature information is focused on the differential detector by the second polarization beam splitter. The test beam enters the second port of the circulator through the first bias beam splitter and the filter, and after being output from the third port of the circulator, enters the photodetector to measure the test beam current I2, and the current I2 is read by the oscilloscope.

[0009] S4. The differential detector measures the differential signal of the chip under test and inputs the differential signal into the lock-in amplifier to calculate the change amount ΔR of the reflectivity.

[0010] S5. According to the change amount ΔR of the reflectivity obtained in step S4, calculate the relative change ΔR / R of the reflectivity, where R is the sample mean reflectivity, and calculate the temperature change amount ΔT according to the functional relationship ΔR f / R = κΔT f , and calculate the temperature change amount ΔT.

[0011] Further, in step S4, the differential signal measured by the differential detector when there is no chip under test is I = I1 - I2R0, where I1 is the current of the reference beam, I2 is the test beam current, and R0 is the reflectivity of the laser cavity surface at room temperature; the differential signal measured by the differential detector when there is a chip under test is

[0012] Further, in step S4, the change amount ΔR of the reflectivity is calculated by the following formula:

[0013]

[0014] where ΔR0 is the change in the DC reflectivity caused by the DC dissipation power; ΔR f is the change in the reflectivity caused by the dissipation power at the frequency f; is the thermal phase shift at the frequency f, and the high-frequency term includes the change in the reflectivity caused by the power dissipation at high frequencies.

[0015] Further, in step S5, the relative change ΔR / R of the reflectivity is calculated by the following formula:

[0016]

[0017] where κ is the thermal reflection coefficient of the material and the wavelength of the probing light wave.

[0018] In summary, the invention has the following beneficial effects:

[0019] The present invention utilizes the functional relationship between the reflectivity of the laser cavity surface and the cavity surface temperature. By measuring the change in the cavity surface reflectivity, it realizes the real-time and high-speed detection of the temperature change during the damage occurrence process, providing a reliable basis and reference for scientific research such as the structural improvement and process improvement of high-speed laser chips. The test beam is separated into a reference beam and a test beam by a PBS. After reflection, the test beam and the reference beam are jointly focused on a differential detector through a second polarization beam splitter. The obtained differential signal is measured by a lock-in amplifier to measure the change in reflectivity, and then the change value of the cavity surface temperature is calculated. Compared with other cavity surface temperature measurement methods, the differential detector cited in the present invention can avoid possible input saturation of the lock-in amplifier and eliminate the experimental noise sources that may affect the reference and reflected beams, achieving higher measurement accuracy. Brief Description of the Drawings

[0020] Figure 1 is a flowchart of the present invention.

[0021] In the figure: 1 - the first port of the circulator, 2 - the second port of the circulator, 3 - the third port of the circulator. Detailed Embodiment

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] As Figure 1 shown, the present invention discloses a method for measuring the cavity surface temperature of a semiconductor laser. The test beam is separated into a reference beam and a test beam by a polarization beam splitter (PBS). After reflection, the test beam and the reference beam are jointly focused on a differential detector through a second polarization beam splitter. The obtained differential signal is measured by a lock-in amplifier to measure the change in reflectivity, and the change value of the cavity surface temperature is calculated. The specific steps are as follows:

[0024] S1. The fiber-coupled laser diode provides a probing laser beam, which is transmitted through the optical fiber to the first port of the circulator, and the probing laser beam is output from the second port 2.

[0025] S2. After the probing laser beam is filtered by a filter, the first polarization beam splitter separates the probing laser beam into a reference beam and a test beam, and then the reference beam enters the differential detector.

[0026] S3. After being reflected by the chip, the test beam carrying the cavity surface temperature information is focused on the differential detector through the second polarization beam splitter. The test beam enters the second port of the circulator through the first bias beam splitter and the filter, and after being output from the third port of the circulator, it enters the photodetector to measure the test beam current I2, and the current I2 is read by an oscilloscope.

[0027] S4. The differential detector measures the differential signal of the chip under test and inputs the differential signal into a lock-in amplifier to calculate the change in reflectivity ΔR; the overall reflectivity is denoted as R, then R = R0 + ΔR, where R0 is the reflectivity of the laser cavity surface at room temperature, and ΔR is the change in reflectivity caused by temperature change; the differential detector measures the differential signal without the chip under test as I = I1 - I2R0, where I1 is the current of the reference beam, I2 is the current of the test beam, and R0 is the reflectivity of the laser cavity surface at room temperature; the obtained differential signal when driven by a pulsed drive current is sent into a phase-locked loop, and by adjusting the phase-locked loop, such that we get I′ = I - I2ΔR f / 2, and then we can calculate ΔR f ; the differential detector measures the differential signal with the chip under test as

[0028] In step S4, the change in reflectivity ΔR is calculated by the following formula:

[0029]

[0030] where, ΔR0 is the change in DC reflectivity caused by DC dissipation power; ΔR f is the change in reflectivity caused by the dissipation power at frequency f; is the thermal phase shift at frequency f, and the high-frequency terms include the change in reflectivity caused by the power dissipation at high frequencies.

[0031] S5. According to the change in reflectivity ΔR obtained in step S4, calculate the relative change in reflectivity ΔR / R, where R is the sample mean reflectivity. According to the functional relationship ΔR f / R = κΔT f , calculate the temperature change ΔT.

[0032] A current source biases the diode and is connected to a voltage generator to modulate the drive current. The drive current has a duty cycle of 50% and its magnitude varies between 0.1 mA and I max . The adjustment range of I max is between 6 mA and 1 A. The change in the drive current causes a temperature change ΔT. Therefore, the relative change in reflectivity ΔR / R is calculated by the following formula:

[0033]

[0034] where, κ is the thermal reflection coefficient of the material and the wavelength of the probing light wave.

[0035] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. Any technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for measuring the cavity surface temperature of a semiconductor laser, characterized in that: The test beam is separated into a reference beam and a test beam by a polarization beam splitter. After reflection, the test beam and the reference beam are jointly focused on a differential detector through a second polarization beam splitter. The differential signal obtained is measured by a lock-in amplifier, the change amount of the reflectivity is measured, and the change value of the cavity surface temperature is calculated. The specific steps are as follows: S1. A fiber-coupled laser diode provides a probing laser beam, which is transmitted through an optical fiber to the first port of a circulator, and the probing laser beam is output from the second port. S2. After the probing laser beam is filtered by a filter, the first polarization beam splitter separates the probing laser beam into a reference beam and a test beam, and the reference beam enters the differential detector. After being reflected by the chip, the test beam carrying the cavity surface temperature information is focused on the differential detector through the second polarization beam splitter. The test beam enters the second port of the circulator through the first bias beam splitter and the filter, and after being output from the third port of the circulator, it enters a photodetector to measure the test beam current I2, and the current I2 is read by an oscilloscope. S4. The differential detector detects the differential signal of the chip under test and inputs the differential signal into a lock-in amplifier to calculate the change amount of the reflectivity ΔR. S5. Calculate the relative change in reflectivity ΔR / R based on the change in reflectivity ΔR obtained in step S4, where R is the sample mean reflectivity. According to the functional relationship ΔR f / R = κΔT f , calculate the temperature change ΔT. ΔR f is the change in reflectivity caused by the dissipated power at frequency f, and ΔT f is the temperature change at frequency f, and κ is the thermal reflectivity coefficient of the material and the probing light wave wavelength.

2. The method for measuring the cavity surface temperature of a semiconductor laser according to claim 1, characterized in that: In the step S4, the differential detector measures the differential signal without the chip under test as I = I1 - I2R0, where I1 is the current of the reference beam, I2 is the current of the test beam, and R0 is the reflectivity of the laser cavity surface at room temperature; the differential signal measured by the differential detector with the chip under test is △R0 is the change in the DC reflectivity caused by the DC dissipation power, and △R f is the change in the reflectivity caused by the dissipation power at the frequency f, and is the thermal phase shift at the frequency f.

3. The method for measuring the cavity surface temperature of a semiconductor laser according to claim 1, wherein: In step S4, the change amount of the reflectivity ΔR is calculated by the following formula: where ΔR is the change in reflectivity, ΔR0 is the change in DC reflectivity caused by DC dissipated power; ΔR f is the change in reflectivity caused by the dissipated power at frequency f; is the thermal phase shift at frequency f, and the higher frequency terms include the change in reflectivity caused by power dissipation at high frequencies.

4. The method for measuring the cavity surface temperature of a semiconductor laser according to claim 1, characterized in that: In step S5, the relative change of the reflectivity ΔR / R is calculated by the following formula: Where, ΔR is the change amount of the reflectivity, R is the sample mean reflectivity, ΔR / R is the relative change of the reflectivity, κ is the thermal reflection coefficient of the material and the wavelength of the probing light wave, and ΔT is the temperature change amount.

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