Ultra-High-Capacity Optical Communications and Networking: Ultra-Broadband Gain Materials

University Of Maryland Baltimore County, Baltimore MD

Investigators

Abstract

This proposal was submitted in response to the solicitation NSF 01-65 on "Ultra-High Capacity Optical Communications and Networking." In this proposed research project, we study methods to achieve ultra-broadband gain materials for broadband optical communications and networking. Broadband materials with a gain profile of more than 500 nm wide are possible to be achieved in a single thin-film waveguide device. The materials include the Esaki-junction type of multi-band multi-quantum well gain material and the selective-area-growth (SAG) type broadband gain material. With the proposed methods, a multiple-quantum-well (MQW) material with a very broad and smooth gain profile of more than 250 nm has been obtained. Using the fabricated material, semiconductor lasers with a very wide tuning range of more than 200 nm and wavelength converters that can convert signals across 250 nm wavelength range, from 1550 nm to 1300 nm, have been demonstrated. In this research work, we will try to understand the limitations of these proposed methods and explore techniques to overcome them. It is highly possible to extend the full operational wavelength range from 1150 nm to 1700 nm. More than 500 nm bandwidth all optical operations of amplifying, switching, and wavelength conversions are targeted to be accomplished. The issues of using semiconductor optical amplifiers (SOAs) as an amplifying material have been their fast gain recovery time. The fast gain recovery time, caused by the short carrier lifetime, produces problems like high channel-crosstalk in a WDM system and high amplified-spontaneous-emission (ASE) noise. In the proposed research work we will study methods to increase carrier lifetime in a broadband SOA. In our previous work, we have grown quasi-indirect bandgap superlattice materials and observed materials changing from direct to indirect bandgaps when the superlattice period is varying. It is highly possible to change the carrier lifetime from the nanosecond scale to the microsecond scale with the quasi-indirect bandgap material. We have also grown the 1550 nm InGaAsP type II delta-doping gain material. We expect such a material will have a longer carrier lifetime due to the spatial separation of electrons and holes in the material. By combining the broadband gain material and the long carrier lifetime material techniques, it is highly possible we can obtain an ideal gain material with noise and crosstalk performance similar to the Er doped fiber amplifier (EDFA) but with an extremely broad wavelength-operation range of larger than 500 nm. Such a material can also be integrated with other thin-film waveguide optical components to obtain multiple-function integrated photonic devices. We believe this work will have a significant impact to the ultra-broadband optical communications.