Research On Low-frequency Noise Measurement System For 450nm Blue Semiconductor Laser

Blue light has the advantages of short wavelength and small beam divergence,so the blue semiconductor laser has been widely used in many aspects such as high-density storage,color laser display,laser detection,and laser medicine.And studies have shown that low-frequency noise in semiconductor devices is related to device failures and internal defects,so the reliability of semiconductor devices can be characterized by low-frequency noise.In addition,as a temperature-sensitive device,semiconductor lasers can use the operating temperature as a control factor to study the low-frequency noise performance of the laser at different temperatures.In this paper,a low-frequency noise measurement system for 450nm blue semiconductor lasers was designed,which provides a measurement method and basis for the study of the correlation ship between low-frequency noise and device reliability.The measurement system was designed based on the research of the basic characteristics of blue semiconductor lasers,and it is composed of bias circuit,EMI filter circuit,preamplifier,laser temperature controller,data acquisition and shielding modules.Among them,the bias circuit can provide continuously variable bias current for the laser under test,and the temperature controller can change the working temperature of the laser.They keep the laser in different working conditions for measurement.The EMI filter is aimed to negated the electromagnetic interference signal from the power source and transmission line.It also filters out high-frequency signals.Thus,ensuring measurement accuracy.Since the low-frequency current noise can be as low as pA/√Hz,in order to achieve the dynamic range of the data acquisition module,the system needs to convert the current signal to voltage signal and amplify the signal by the preamplifier.Finally,data acquisition module transmits the low-frequency noise data to the PC via USB to complete the storage and spectrum estimation.The whole system is coordinated and controlled by the MCU.Based on the measurement system,an experiment was designed to verify the temperature control function of the system.Afterwards,the lasers was set to the operating temperatures of 20℃,25℃,30℃ to test,and obtained three groups of 1/f low-frequency noise power spectral density data.The comparison and analysis of the data and the spectral density curve shows that the low-frequency noise power spectral density increases significantly as the temperature increases,and the noise power spectral density increases by an order of magnitude after the temperature increases by 5℃ at 1 Hz.The system designed in this paper can accurately measure the 1/f low-frequency noise data of 450nm blue semiconductor lasers,it provides experimental support for further research on the relationship between low-frequency noise and the operating temperature and reliability of the semiconductor laser,it has certain practical value.