Wavelength tunable VCSELs based on voltage-dependent birefringence of liquid crystal

Abstract

For developing the tunable performance and stability, we present a widely tunable 850nm-range VCSEL structure based on the voltage-dependent birefringence of liquid crystal. An intracavity liquid crystal layer is imbedded between the top DBR (Distributed Bragg Reflector) and the Half VCSEL as an electro-optic index modulator. An Al0.98Ga0.02As oxidization layer was grown above the active region for current and optical confinement. By the calculation, we found tuning efficiency increased after thickening the liquid crystal layer. However, the optical loss in resonance cavity also increased simultaneously. For compromise, we got that 1837nm is the most suitable thickness. And the tuning efficiency is obviously larger than the electrostatic method. Then, we calculated the electric field intensity distribution, the gain characteristics of GaAs/Al0.3Ga0.7 As quantum wells and the threshold features when thickness of liquid crystal layer is 1837nm. By analyzing these results, tuning efficiency of 5.4nm/V and 15nm tuning range are obtained at last. Our study could provide insight into tunable VCSELs design and optimization.