Wide and continuous wavelength tuning of microcavity devices for optoelectronic applications

Abstract

Ultra-widely tunable microcavity devices implemented by surface micromachining are studied. We model, fabricate, and characterize 1.55-μm vertical-resonator-based optical filters and vertical cavity surface emitting lasers (VCSELs) capable of wide, monotonic, and kink-free tuning by a single control parameter. Our devices are comprised of single or multiple horizontal air gaps in the dielectric and InP-based material system. Distributed Bragg mirrors with multiple air gaps are implemented. Due to the high refractive index contrast between air (n = 1) and InP (n = 3.17), only three periods are sufficient to guarantee a reflectivity exceeding 99.8% and offer an enormous stop-band width exceeding 500 nm. Unlike InGaAsP/InP or dielectric mirrors, they ensure short penetration depth of the optical intensity field in the mirrors and low absorption values. Stress control of the suspended membrane layers is of utmost importance for the fabrication of these devices. By controlling the stress, we are able to fabricate InP membranes that are extremely thin (357 nm thick) and at the same time flat (radius of curvature above 5 mm). Micromechanical single parametric actuation is achieved by both thermal and electrostatic actuation. Filter devices with a record tuning more than 142 nm with 3.2 V are presented.