Ultra-High-Capacity Optical Communications and Networking: III-nitride Wide Bandgap Semiconductors for Optical Communications

University Of Kansas Center For Research Inc, Lawrence KS

Investigators

Abstract

This proposal was submitted in response to the solicitation NSF 01-65 on "Ultra-High Capacity Optical Communications and Networking." III-nitride optoelectronic devices offer benefits including UV/blue emission, the ability to operate at very high temperatures and power levels. Large band offsets of GaN/AlGaN or InGaN/AlGaN heterostructures allowing novel quantum well devices, and high emission efficiencies. But the research in III-nitrides has been so far focused on their applications in the blue/UV optoelectronic devices. We propose a combined effort to develop novel photonic components and photonic integrated circuits based on III-nitride wide band gap semiconductors for fiber-optical communications. High-speed optical switches and wavelength routers are indispensable in future all-optical networks. Presently opto-mechnical switches and thermal tuning of silica-based array waveguide gratings (AWG) are not fast enough to perform optical packet switching. On the other hand, InP--based AWGs have high optical loss and temperature sensitivity due to high refractive index of the material and small waveguide size. The refractive index of GaN is about 2.2 in infrared, which is much better matched to the index of optical fiber (1.5) than InP (3.2). The index-controllable nature of Al Ga N and In Ga N alloys makes them an ideal candidate for optical waveguide devices. These together may allow the creation of photonic devices with unprecedented properties and functions. Since Il1-nitrides are semiconductor materials, carrier injection can be used to modulate the refractive index and change the phase delay of the waveguide. Another objective of this research is to make electrically pumped waveguide optical amplifiers in the optical communication windows. Currently, InGaAsP-based semiconductor optical amplifiers have sub-nanosecond carrier lifetime and they are not suitable for WDM optical systems because of the fast cross-gain saturation. Er-doped fiber amplifiers (EDFA) are suitable for WDM applications; however, optoelectronic integration is not possible with EDFAs because of the fiber length. III-nitride semiconductors appear to be able to host erbium ions. Electrical pumping on InGaN/GaN heterostructures generates photons at the wavelength of approximately 400 nm, which can be used to optically excite the erbium ions. Since erbium has much higher absorption efficiency in the short wavelengths than the currently used pumping wavelengths of either 980 nm or 1480 nm, the amplifier may potentially be made very short.