Narrow bandwidth and polarization independent design of hollow waveguide in-plane mirror with ultrawide tuning-range

A design of an integrated widely tunable in-plane micro-optical mirror based on a hollow waveguide (HWG) consisting of a high index contrast grating (HCG) and a dielectric multilayer distributed Bragg reflector (DBR) is proposed. The in-plane mirror is formed in a variable air-core HWG by loading a SiO(2) Bragg grating on the multilayer (DBR) mirror. Ultrawide tuning of 161 and 150 nm in Bragg wavelengths of TE and TM mode, respectively are reported in simulation with a simple tuning scheme and a single tuning parameter of variable air core. The presence of HCG in the proposed design causes a reduction from 88 nm (for DBR-DBR) to 48 nm (for HCG-DBR) in the 3 dB reflection-bandwidth of the proposed in-plane mirror. Also, a four-time reduction in the difference in the reflectivity of the Bragg wavelengths of TE and TM modes is reported because of the introduction of HCG into the hollow waveguide. The reflections of orthogonal polarizations and hence the polarization characteristics of the in-plane mirror are controlled by the combined effect of HCG and DBR.