Conventional grating out-couplers in III-V waveguides typically require lengths of several hundreds of microns to outcouple 50 to 90% of the incident optical power. Enhanced coupling strength (ECS) gratings, which reduce the out-coupler grating length to tens of microns, have a large relative permittivity difference between the materials on either side of the grating boundary along with a high index cover layer. With appropriately chosen permittivity and layer thicknesses, the addition of a cover layer “pulls” the peak of the optical mode towards the grating region, resulting in a significant increase in the grating confinement factor. The resulting ECS out-coupler is short, highly efficient, and can be integrated with other III-V optical components, including horizontal cavity lasers and modulators.
The theoretical dependence of the magnitude and spectral width of the out-coupled power as a function of cover layer thickness, low index material thickness, grating depth, and duty cycle is shown using a Floquet-Bloch analysis for two different ECS grating geometries. The design of a high-speed datacom transmitter with ECS grating reflectors and an ECS grating out-coupler is discussed. The proposed laser with an integrated electro-absorption modulator (Laser-EAM) theoretically provides Pulse Amplitude Modulation 2-Level (PAM-2) data rates in excess of 100Gbps with lower latency, less power consumption, and lower cost than existing commercial devices.
Electrical and Computer Engineering
Gary A. Evans
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Dezfuli, Maryam, "Second-Order Enhanced Coupling Strength Grating Out-Couplers for a Monolithic Laser-Electro-Absorption Modulator" (2022). Electrical Engineering Theses and Dissertations. 49.