Fabry-Perot Cavity design with DBRs, Sub-wavelength gratings, and Photonic crystal slabs.
We are designing a Vertical-Cavity Surface-Emitting Laser (VCSEL) structure, containing a Sub-Wavelength Grating (SWG) and a Photonic Crystal (Phc) slab, either of which might replace one of the Distributed Bragg Reflectors (DBRs), using Finite-Difference Time-Domain (FDTD) and a transfer matrix method.
We have studied a phase methodology to measure the phase of a single DBR, SWG, and Phc slab to be used as one of the mirrors in the VCSEL, and have estimated resonant wavelengths for the three different VCSEL structures. The maximum discrepancy between the FDTD phase and reflectance measurement was found to be less than 1.5nm throughout the simulations, indicating that our phase analysis is effective in accurately predicting resonances.We demonstrate that lithographical resonance tuning can be achieved up to a range of 60nm (SWG VCSEL) and 87nm (Phc VCSEL), while maintaining relatively high cavity Q values (>1,000). Phase and reflectivity peak are coincident for a broad range of FP wavelengths, resulting in a high cavity Q over a broad tuning range. This is a major improvement compared to the previous work FP cavities in SWG. We believe that varying lithographically defined parameters, in particular, α (SWG) and r (Phc slab), will provide resonance tunability superior to micromechanical tuning methods. Fabrications and reflectivity measurements for the air-suspended SWGs and Phc slabs are currently in progress.