Study Of Wavelength Tunable Vertical-cavity Surface-emitting Laters

Vertical-cavity surface-emitting laser (VCSEL) was first proposed in1977byProf. Kenichi Iga from Tokyo Institute of Technology, which has more than30years.It is a new type of semiconductor laser with some advantages such as laser beamperpendicular to the substrate, on-chip testing, low threshold current, high modulation,single longitude mode and easy-to-fiber coupling owing to circular beam profile,which have widely used on data transmission, optical interconnection, gas detectionand other applications. In1990s tunable VCSEL was widely studied. Due to ownstructural Superiority, tunable VCSEL not only have some advantages forconventional VCSEL but also can achieve continuous wavelength tuning in singlelongitude mode. There have huge potential for DWDM application, replacedsemiconductor laser array for different frequencies by single device, effect reducingapplication costs, increasing the flexibility and reliability of the network.Base on the obtained research foundation, in this dissertation, a wavelengthtunable VCSEL is investigated both on structure design and experiment. Multi-physics coupling software COMSOL based on FEM and rigorous couple-wave theoryis used to simulate the polarization characteristics of tunable spectrum and optimizegrating parameter for tunable VCSEL based on inner-cavity sub-wavelength grating.From the aspects of effective refractive index anisotropic, center wavelength, andwavelength tuning, TE mode and TM mode are separated and controlled effectively.In addition, an empirical model is used to analyze the relationship between variousphysics mechanisms induced dissipated power and injection current in device. Weobtain that carrier leakage in quantum wells induced self-heating is main reason forthermal rollover phenomenon in VCSELs. The via-hole of GaAs substrate by dryetching is studied in device fabrication.VCSEL and tunable VCSEL device arefabricated successfully and tested. The main research contents of this dissertation asfollows:1. A now type of inner-cavity sub-wavelength grating tunable VCSEL is used tocontrol polarization stability of tunable VCSEL. It composed two parts: one isnano-electro-mechanical systems (NEMS) containing distributed Bragg reflectors(DBR); another part is “half-VCSEL”, including sub-wavelength grating, multi-quantum wells active regime and bottom DBR. The effective refractive indexanisotropic of sub-wavelength grating is employed to achieve the separation oftwo polarization mode. From calculation, when the grating period is200nm, theduty cycle is0.35, the grating depth is130nm and the maximum separation of twopolarization mode of20.9nm is obtained. Different polarization modes have different threshold gain; thereby, controlling polarization can be achieved fortunable VCSEL.2. Multi-physics coupling software based on FEM is used to simulate the mechanicalcharacteristics of MEMS membrane for GaAs materials. The air gap is2um in ourdeign. When the radius of membrane is50μm, the length of lags is300μm and thewidth of lags is35μm, the pull-in voltage of13.6V and maximum displacement of689nm is obtained from the simulation.3. Combining with the empirical model for dissipated power of VCSEL andmeasurement data, temperature in resonance cavity is calculated in differentcurrent. The thermal resistance of VCSEL is measured using an indirect method.Various dissipated power mechanisms are analyzed with the injection current.Carrier leakage in quantum well induced dissipated power is the main factor forVCSEL thermal rollover behavior.4. VCSELs for different oxide apertures are fabricated, the L-I-V characteristics ofdevice is measured in different temperatures. Emission wavelength and thresholdcurrent of VCSEL are analyzed with the changes of temperatures. TunableVCSEL is successfully fabricated using two-chip method and then tested. In roomtemperature, tunable VCSEL with14μm achieve maximum optical power of4.56mW with the injection current of30mA. The threshold current is0.6mA.When tuning voltage change from0V to3V, wavelength blue shift from976.8nmto970.0nm. A6.8nm continuous wavelength tuning is realized.