Semiconductor Optical Buffers Using Grating Slow-Wave Devices

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Optical buffering is essential to optical packet switch implementations which have been proposed worldwide to overcome future problems with large electronic packet switches. We propose to design and fabricate semiconductor-based optical buffers by using sampled gratings, Moir gratings, and chirped Moir gratings. These gratings will be fabricated using a new method to obtain a photonic bandgap-engineered material that has a large index contrast, which is essential for group velocity reduction in our proposed gratings. Optical fiber delay lines have been commonly used in recent years in the design of optical buffers, typically through a fiber loop with standard components such as optical isolators, 3-dB couplers, and semiconductor laser amplifiers for the gating, interconnection, and signal amplification. The fundamental difficulty facing the design of an optical buffer is that variable-length buffers must be implemented with delay lines; however, by their nature, fiber loop optical delay lines are of fixed length. Our proposed optical buffer, unlike fiber loop delay lines, is variable by using current injection. Another significant advantage is that other semiconductor optoelectronic and optical devices can be integrated with our proposed variable optical buffers since they are based on the same semiconductor III-V compounds. Our proposed tasks include the design and fabrication of sampled gratings, Moir gratings, and chirped Moir gratings as slow-wave devices. The wavelength range for our proposed devices will be centered at 1.5-1.6 micron wavelength. Sampled gratings and Moir gratings can be shown to have a large group delay factor when a large contrast in the refractive index is introduced. This large refractive index contrast will be achieved using our proposed semiconductor and oxide materials. This contrast is at least two orders of magnitude larger than that of the fiber gratings. A chirped Moir grating allows for a broader bandwidth for the pass band. A novel photonic bandgap structure will be fabricated using periodic buried AlOx channels with growth on a patterned substrate. The advantages of this structure include tight optical and electrical confinement with very low defect densities. One or multiple current sources can be applied to the gratings via the doped AlGaAs layer to change the refractive index in the slow-wave structures for controlling the buffer delay. Our research will lead to the realization of a new class of semiconductor optical buffers, which can be immediately integrated with many optoelectronic devices.