Grating-waveguide structures give very narrow spectral bandwidths

Investigations of resonance anomalies in grating-waveguide structures (GWSs) by researchers at the Weizmann Institute of Science (Rehovot, Israel) have led to very narrow spectral-resonance bandwidths of 0.12 nm at FWHM in the 1.55-µm range, ideal for spectral filters and modulation applications. The multilayer configuration of the GWSs was changed so that the grating layer is separated from the waveguide layer by a buffer layer that serves also as a stop layer of the etching process. By separating the waveguide and grating layers, the thickness of the layers are controlled to atomic accuracy, lowering inherent losses. The optical and geometrical parameters were predicted based on the exact eigenfunction using Maxwell's equations. To achieve the configuration, a waveguide layer of indium gallium arsenide phosphide (InGaAsP) was grown on a substrate of indium phosphide (InP) by metal-organic chemical-vapor deposition. Then a buffer layer of InP and a layer of InGaAsP were grown. A grating was formed in the upper InGaAsP layer and a cladding of InP deposited, smoothing the surface roughness at the grating/buffer interface. The resulting finesse was 13,000, and the peak reflected intensity was 86%. Improvements in fabrication may further reduce losses. Contact Guy Levy-Yurista at[email protected].