Monolithic high contrast grating on GaSb/AlAsSb based epitaxial structures for mid-infrared wavelength applications.

We demonstrate monolithic high contrast gratings (MHCG) based on GaSb/AlAs0.08Sb0.92 epitaxial structures with sub-wavelength gratings enabling high reflection of unpolarized mid-infrared radiation at the wavelength range from 2.5 to 5 µm. We study the reflectivity wavelength dependence of MHCGs with ridge widths ranging from 220 to 984 nm and fixed 2.6 µm grating period and demonstrate that peak reflectivity of above 0.7 can be shifted from 3.0 to 4.3 µm for ridge widths from 220 to 984 nm, respectively. Maximum reflectivity of up to 0.9 at 4 µm can be achieved. The experiments are in good agreement with numerical simulations, confirming high process flexibility in terms of peak reflectivity and wavelength selection. MHCGs have hitherto been regarded as mirrors enabling high reflection of selected light polarization. With this work, we show that thoughtfully designed MHCG yields high reflectivity for both orthogonal polarizations simultaneously. Our experiment demonstrates that MHCGs are promising candidates to replace conventional mirrors like distributed Bragg reflectors to realize resonator based optical and optoelectronic devices such as resonant cavity enhanced light emitting diodes and resonant cavity enhanced photodetectors in the mid-infrared spectral region, for which epitaxial growth of distributed Bragg reflectors is challenging.

Electrically injected VCSEL with a composite DBR and MHCG reflector.

We achieve the continuous-wave (CW) lasing of electrically-injected, first-of-their-kind vertical-cavity surface-emitting lasers (VCSELs) that use a subwavelength monolithic high-refractive-index-contrast grating (MHCG) mirror. The MHCG, unlike the well-known high-refractive-index-contrast grating (HCG) is neither a membrane suspended in the air nor a structure that requires a cladding layer. The MHCG is patterned in a semiconductor material atop the VCSEL cavity creating an all-semiconductor laser. Static measurements show CW operation of the VCSELs from room temperature up to 75 °C. The VCSEL with a 13.5 µm current oxide aperture diameter operates with quasi-single mode emission from threshold to rollover. Our results open a way to produce all-semiconductor surface emitting lasers emitting at wavelengths from the ultraviolet and the visible (GaN-based) to the infrared (InP- and GaSb-based) with a reduced vertical thickness and thus we believe the manufacturing costs potentially will be reduced by approximately up to about 90% in comparison to the typical DBR VCSELs. Our VCSELs have immediate and emerging applications in optical communication, illumination, sensing, and as light sources in photonic integrated circuits.

Monolithic high-index contrast grating: a material independent high-reflectance VCSEL mirror.

In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.