Conventional first-order DBR gratings in III-V waveguides often require hundreds of microns to achieve near 100% reflected power and provide narrow spectral reflectivity width for a single wavelength, limiting temperature performance of devices. Narrow reflectivity spectral width is desired for spectroscopy and wavelength division multiplexing applications where device temperature is regulated. However, Enhanced Coupling Strength (ECS) gratings provide in-plane reflectors with significantly higher reflected power per unit length, broad spectral reflectivities, and reduced losses at the waveguide-grating interface in III-V waveguides. These properties of ECS gratings allow integration of optical components such as high-speed modulators with short horizontal cavity lasers that can operate without temperature control over wide temperature and wavelength ranges. ECS gratings improve the grating coupling coefficient, κ, through two mechanisms. First, the relative permittivity difference is increased on either side of the grating boundary with a layer of low index material (relative to the high index III-V material). By covering the low-index material with a high index cover layer, the fraction of the waveguide mode power interacting with the grating region is substantially increased. The result is the enhancement of the coupling coefficient. The theoretical dependence of the peak and spectral width of the reflected power as a function of cover layer thickness, grating depth, and duty cycle is investigated using Floquet-Bloch analysis for two different ECS grating geometries. Integration of ECS grating reflector structures within a novel high-speed Laser-Electro-Absorption-Modulator (Laser-EAM) Transmitters is discussed. The prospective Laser-EAM Transmitter is calculated to provide data speeds greater than 100 Gbps NRZ with lower cost, reduced latency, and lower power consumption than existing commercial devices.
Electrical and Computer Engineering
Dr. Gary A. Evans
Dr. Jerome K. Butler
Dr. Ping Gui
Dr. Ralph Johnson
Dr. Duncan MacFarlane
Dr. Preston Young
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Castillo II, Freddie, "First Order Enhanced Coupling Strength (ECS) Gratings for Laser-Electro Absorption Modulator (EAM) Transmitters" (2022). Electrical Engineering Theses and Dissertations. 47.