Wide Tuning Range And Stable Polarization Control Of Semiconductor Laser

With the rapid development of modern information network technology,the requirements for high-speed information processing,high-speed information transmission,transmission data capacity are also constantly improved.Tunable VCSEL has become the most competitive ideal light source in this field because of its unique circular symmetrical spot,low power consumption,single longitudinal mode,continuous wavelength adjustment,easy 2-D array and low cost.However,due to the special circular symmetric waveguide resonator and the feedback DBR mirror without polarization selection function,the anisotropy between polarization modes is weak,resulting in the lack of stable single polarization mode output characteristics of tunable VCSEL.In order to achieve polarization stability and expand wavelength tunable range of VCSELs,we designed three kinds of tunable VCSELs with polarization stability and wide wavelength tuning range respectively,including intracavity subwavelength grating structure,top corrugated mirror structure and intracavity liquid crystal structure.In this paper,based on the key technology of device fabrication,we fabricated a tunable VCSEL with intracavity subwavelength grating structure by semiconductor micromachining technology,and tested the output of the device.The contents and conclusions of this paper are as follows:(1)Based on the research of tunable VCSEL structure with intracavity subwavelength grating,we used the birefringence and antireflection characteristics of subwavelength grating to control the output polarization mode and improve the wavelength tuning range.Through optimizing,the resonant wavelengths between polarization modes in the tunable VCSEL cavity can achieve the maximum wavelength separation in the material gain spectrum(17.5nm for TE mode and 28 nm for TM mode),so that it can maintain stable single polarization mode output in the process of wavelength tuning.The device test shows that the maximum output power is 1.6m W,the wavelength tuning range is 22.7nm and the OPSR is more than 20 d B at 20℃.(2)Based on the research of tunable VCSEL structure with a top wavy mirror,the output polarization mode is controlled by the reflection loss difference between the polarization modes.we studied the influence of structural parameters on polarization mode reflection characteristics.A micro optical structure with high reflectivity,large reflective bandwidth and high polarization selection ratio is designed.The results show that the threshold gain of TM mode is always greater than that of TE mode in the continuous wavelength tuning range of 84.5 nm,and the maximum increase is more than 10 times.(3)Based on the research of tunable VCSEL structure with intracavity liquid crystal,we designed a new type of liquid crystal tunable VCSEL structure with an internal coupling layer to enhance the free spectral range of the device.The results show that the wavelength tuning range of liquid crystal tunable VCSEL is extended from 27.4nm to 41.1 nm with the addition of coupling layer.In the study of polarization characteristics,we analyzed the relationship between resonant wavelength of polarization mode and threshold characteristics with the thickness of liquid crystal.The control mechanism of liquid crystal thickness on the output polarization mode in the process of wavelength tuning of tunable VCSEL is explained.