Guillaume Maire

High efficiency silicon nitride surface grating couplers

High efficiency surface grating couplers for silicon nitride waveguides have been designed, fabricated, and characterized. Coupling efficiencies exceeding 60 % are reported at a wavelength of 1.31 mum, as well as angular and wavelength -3 dB tolerances of 4 degrees and 50 nm, respectively. When the wavelength is increased from 1310 nm to 1450 nm the coupling efficiency progressively decreases but remains above 20 % at 1450 nm. The influence of the duty ratio of the grating has also been investigated: maximum coupling efficiency was obtained at 50 % duty ratio.

Ultracompact tapers for light coupling into two-dimensional slab photonic-crystal waveguides in the slow light regime

Optical coupling from a strip waveguide to a two-dimensional photonic crystal (PC) slab waveguide in the slow light regime is investigated. Group-velocity mismatch between optical modes is responsible for large coupling loss. Typical devices based on a W1 PC waveguide, with strip input and output waveguides on each side, are studied using finite-difference time-domain and plane-wave expansion calculations. Compact tapers based on PC lattice parameter tuning are proposed to reduce the coupling loss. At 1.6 μm, for an optical mode with group velocity v g /c=0.054, the transmission can be enhanced from 18% without tapers to 95% with a 3.4-μm-long taper on each side of the PC.

A high efficiency silicon nitride grating coupler

The experimental demonstration of a high efficiency silicon nitride grating coupler is reported for wavelengths from lambda = 1.25 to 1.45 mum for TE polarization. At the resonant angle, a coupling efficiency higher than 60% has been measured.

Bloch wave decomposition for prediction of strong light coupling efficiency into extended planar photonic crystals

Influence of Bloch wave decomposition on light coupling into planar photonic crystals is investigated using plane-wave-method and finite-difference time domain calculations. The contribution of each plane wave to the global Bloch wave energy is calculated to understand the relative power weights of fields excited in the patterned medium. It is shown that high coupling efficiency is obtained when plane-wave components excited through a direct parallel wave vector, i.e., without an additional lattice-induced translated parallel wave vector, bring an important amount of the overall Bloch propagating wave power.

Design of photonic crystal directional couplers for electro-optical wavelength switching in Si technology

Electro-optical wavelength switch in Si technology operating around = 1.55 µm and based on a photonic crystal directional coupler configuration was studied using Plane Wave Method and Finite Difference Time Domain simulations. Owing to the exploitation of slow wave supermodes, ultra-compact active devices (~ 20 µm) exploiting free carrier plasma dispersion effect in Si can be designed. Injection of input/output strip access waveguides with the photonic core area is optimized using tapering stages to gradually reduce light group velocity. With carrier injection around 1018 cm-3, the coupler configuration can be used as an optical switch of individual wavelengths or a multiplexer/demultiplexer device with active routing of wavelengths.