Thin-film wavelength demultiplexer based on photonic crystal and group velocity effects

Abstract

We experimentally observe the superprism effect in a periodic thin-film structure acting as a one-dimensional photonic crystal. The design of non-periodic structures exhibiting a linear shift with wavelength in the EDFA C-band is discussed. 2002 Optical Society of America OCIS codes: (260.2030) Dispersion; (060.4230) Multiplexing; (230.4170) Multilayers WDM systems create a strong need for compact wavelength splitting devices that can be easily manufactured. Here we demonstrate the capability of group velocity effects in multilayer dielectric structures to provide wavelength splitting. In contrast to typical dielectric interference filters, in this approach, one multilayer structure can separate multiple beams of different wavelengths. We demonstrate beam shifts with wavelength in a periodic multilayer stack; such a structure can also be viewed as a one- dimensional photonic crystal. We also extend the analysis to design non-periodic structures with superior wavelength splitting properties. One-dimensional (1,2), two-dimensional (1), and three-dimensional (3) photonic crystals exhibit strong dispersion at wavelengths close to the stop band (i.e., the reflection band in such a structure when used as a mirror). This superprism effect can be used to spatially separate beams of different wavelength. We focus on one-dimensional structures, as they are easy to fabricate with well-known technology allowing for compact, cost-effective WDM devices. Fig. 1 shows a schematic of our periodic thin-film device. Light is incident onto the dielectric stack from the substrate side. Close to the stop band, different wavelengths propagate at different angles within the periodic stack. Thus, beams of different wavelength are spatially separated along the x-direction. In order to achieve a higher separation, multiple bounces can be performed in the stack.