Integrated Optics Using High Contrast Gratings

High contrast grating (HCG) is a new class of optical grating with many distinct features that are not found in conventional gratings [1–6]. These features include broadband ultrahigh reflectivity, broadband ultrahigh transmission, or very high quality factor resonance, for optical beam surface-normal or in oblique incidence to the direction of grating periodicity. Furthermore, these features can be designed with simple top–down guidelines. The extraordinary features originate from a special “near-wavelength” regime that HCG operates at and from a large index contrast between the grating and its surrounding media. The “near-wavelength” regime lays between the conventional diffraction regime [7] and the deep-subwavelength regime. It refers to a regime where the grating period is between the wavelength of the grating material and that of its surrounding media. With many extraordinary properties, HCG establishes a new platform for planar optics and integrated optics. A single-layer, ultrathin HCG with broadband high reflectivity for surface-normal incidence was first proposed with numerical simulation [3], followed by experimental demonstration of HCG having R > 98.5% over a wavelength span of Δλ∕λ > 35% [4]. TheHCG is subsequently incorporated as the topmirror in vertical-cavity surfaceemitting lasers (VCSELs) emitting at 850-nm, 980-nm, 1330-nm, and 1550-nmwavelength regimes, replacing traditional multilayer distributed Bragg reflectors (DBRs)