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Researchers Slow Down Laser Light, Deliver Control to Break Power and Speed Limits

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WASHINGTON, D.C., Nov. 20, 2020 — George Washington University (GWU) researchers have combined multiple transverse coupled cavities to develop a new vertical-cavity surface-emitting laser (VCSEL). The cavities in the laser system enhance the laser’s optical feedback capabilities, helping the laser demonstrate record-fast temporal bandwidth, the researchers reported.

VCSELs, a class of semiconductor laser diodes accompanying a monolithic resonator that emits light in a direction perpendicular to the surface of a chip, are comparatively energy-efficient and high-speed optical interconnects in data centers and supercomputers. VSCELs are compact and deliver high optoelectronic performance. As miniaturized lasers, VSCELs function as an optical source in high-speed, short-wavelength communications and optical data networks. They also support a combination of dense traffic and high-speed transmission in data communications, as well as in other applications, including those in automotive.

Traditionally, however, thermal effects, parasitic resistance, capacitance, and influence from nonlinear gain all limit the 3-dB bandwidth, regarded as the VSCEL “speed limit.” Nonlinear optical amplification effects, or gain relaxation oscillations, prevent direct VSCEL modulation from exceeding 30 GHz.

The researchers debuting the new design relied on a multifeedback approach, combining multiple, coupled cavities to fortify the system feedback known as “slow-light.” The use and design of the cavities extended the temporal laser bandwidth, or laser speed, beyond the known limit of the relaxation oscillation frequency.

Fast, powerful compact lasers: a novel VCSEL for next-generation datacenters and sensors. Courtesy of Volker Sorger/GWU.
Fast, powerful, compact lasers: a novel VCSEL for next-generation data centers and sensors. Courtesy of Volker Sorger/GWU.
To achieve functionality, the direct feedback from each cavity needed only to be of a moderate strength; further, users are able to precisely control and manipulate the feedback by way of the coupled cavities, delivering an extended range of design freedom. The research team said it anticipates achieving a modulation bandwidth in the 100-GHz range.

“This invention is timely since demand for data services is growing rapidly and moving toward next-generation communication networks such as 6G, but also in automotive as proximity sensor of smartphone’s face ID,” said Hamed Dalir, co-author of the paper describing the laser and inventor of the technology. “Furthermore, the coupled cavity system paves a way for emerging applications in quantum information processors such as coherent Iasing machines.”

The research was published in Nanophotonics (www.doi.org/10.1515/nanoph-2020-0437).

Photonics.com
Nov 2020
GLOSSARY
nanophotonics
The study of how light interacts with nanoscale objects and the technology of applying photons to the manipulation or sensing of nanoscale structures.
optoelectronics
A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.
chip
1. A localized fracture at the end of a cleaved optical fiber or on a glass surface. 2. An integrated circuit.
optical communications
The transmission and reception of information by optical devices and sensors.
nanophotonicsAmericasVolker Sorgerlaserslaser controlVCSELsemiconductor lasersoptical amplificationnovel optical amplification techniquesdiode lasersoptoelectronicschipchip arrayGeorge WashingtonGeorge Washington UniversityautomotiveCommunicationsoptical communications

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