University of Illinois team aim for terahertz modulation speeds
Milton Feng, a professor of Electrical and Computer Engineering at the University of Illinois, has recently received a $657,000 grant from the US Air Force Office of Scientific Research (AFOSR).
The aim is to enhance the modulation speed performance of the transistor laser (a novel 3-terminal device that he and ECE colleague Nick Holonyak Jr. invented in 2004) to terahertz speeds.
The transistor laser offers the potential for much faster broadband communications, both for long-haul telecommunications networks and for short-haul connections between and within chips for photonic integrated circuits (PICs).
Feng's group has demonstrated a transistor laser with a fast (30ps) recombination lifetime and modulated optical output with a 22Gb/s error-free transmission. By incorporating multiple quantum wells and reflectors and even coupling them with quantum dot regions, Feng is optimistic about reducing the recombination lifetime to 5ps.
An expert in high-frequency devices, Feng owns the world record for fastest (800 GHz) heterojunction bipolar transistors (HBTs). He aims to leverage this expertise with advanced processing techniques to produce this ultra-low-threshold, high-speed transistor laser.
Over the course of the three-year grant, Feng and his students are investigating ways to reduce the average recombination lifetime (light generation) and push the laser's modulation speed into the terahertz range.
"In the first year, we'll establish the theoretical framework for pushing the modulation speed of the transistor laser into the terahertz and beyond," said Feng, who is also affilated with MNTL. "In the second year, we'll pursue the epitaxial design for optimising the quantum wells necessary to reduce recombination lifetime below 10ps. In our final year, we'll demonstrate a transistor laser made of quantum dots and quantum wells with a lifetime below 5ps and modulation of 0.3THz."
Feng and Holonyak have received more than 20 US patents covering the transistor laser for optical interconnects, photonic integrated circuit signal mixing, and feedback control of the laser and collector outputs.
Since 2013, Feng and his students have also produced record-setting research on 850nm oxide vertical cavity surface emitting lasers (VCSELs) with low relative intensity noise and 40Gb/s error-free data transmission. Widely used by the datacom industry for short-distance (< 300 meters) applications, VCSELs have limited modulated bandwidth below 30GHz due to a relatively slow recombination lifetime of ~0.5ns.
Based on the picosecond recombination lifetime of a THz transistor, the transistor laser modulates very quickly, making it a good candidate to compete with oxide VCSELs in a variety of optical interconnect applications.
