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Optical Engineering

Pseudorandom dynamics of frequency combs in free-running quantum cascade lasers
Author(s): Nathan Henry; David Burghoff; Yang Yang; Qing Hu; Jacob B. Khurgin
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Paper Abstract

Recent research has shown that free-running quantum cascade lasers are capable of producing frequency combs in midinfrared and THz regions of the spectrum. Unlike familiar frequency combs originating from mode-locked lasers, these do not require any additional optical elements inside the cavity and have temporal characteristics that are dramatically different from the periodic pulse train of conventional combs. Frequency combs from quantum cascade lasers are characterized by the absence of sharp pulses and strong frequency modulation, periodic with the cavity round trip time but lacking any periodicity within that period. To explicate for this seemingly perplexing behavior, we develop a model of the gain medium using optical Bloch equations that account for hole burning in spectral, spatial, and temporal domains. With this model, we confirm that the most efficient mode of operation of a free-running quantum cascade laser is indeed a pseudorandom frequency-modulated field with nearly constant intensity. We show that the optimum modulation period is commensurate with the gain recovery time of the laser medium and the optimum modulation amplitude is comparable to the gain bandwidth, behavior that has been observed in the experiments.

Paper Details

Date Published: 12 September 2017
PDF: 12 pages
Opt. Eng. 57(1) 011009 doi: 10.1117/1.OE.57.1.011009
Published in: Optical Engineering Volume 57, Issue 1
Show Author Affiliations
Nathan Henry, Johns Hopkins Univ. (United States)
David Burghoff, Massachusetts Institute of Technology (United States)
Yang Yang, Massachusetts Institute of Technology (United States)
Qing Hu, Massachusetts Institute of Technology (United States)
Jacob B. Khurgin, Johns Hopkins Univ. (United States)

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