Pseudorandom dynamics of frequency combs in free-running quantum cascade lasers

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.

[1]  Mattias Beck,et al.  Octave-spanning semiconductor laser , 2014, Nature Photonics.

[2]  Carlo Sirtori,et al.  Distributed feedback quantum cascade lasers , 1997 .

[3]  Albert Schliesser,et al.  Mid-infrared frequency combs , 2012, Nature Photonics.

[4]  S. Diddams,et al.  Octave-spanning Ti:sapphire laser with a repetition rate >1 ghz for optical frequency measurements and comparisons. , 2006, Optics letters.

[5]  David A. Ritchie,et al.  Frequency-Comb-Assisted Terahertz Quantum Cascade Laser Spectroscopy , 2014 .

[6]  Yang Yang,et al.  Evaluating the coherence and time-domain profile of quantum cascade laser frequency combs. , 2015, Optics express.

[7]  Federico Capasso,et al.  Ultra-broadband semiconductor laser , 2002, Nature.

[8]  Simone Borri,et al.  Frequency stability characterization of a quantum cascade laser frequency comb , 2016 .

[9]  T. Kippenberg,et al.  Microresonator based optical frequency combs , 2012, 2012 Conference on Lasers and Electro-Optics (CLEO).

[10]  Federico Capasso,et al.  Mode-locked pulses from mid-infrared quantum cascade lasers. , 2009, Optics express.

[11]  Yamac Dikmelik,et al.  Coherent frequency combs produced by self frequency modulation in quantum cascade lasers , 2014 .

[12]  Qing Hu,et al.  186 K Operation of Terahertz Quantum-Cascade Lasers Based on a Diagonal Design , 2009 .

[13]  T. Hänsch,et al.  Optical frequency metrology , 2002, Nature.

[14]  Naota Akikusa,et al.  Absolute frequency measurements of CO2 transitions at 4.3 μm with a comb-referenced quantum cascade laser , 2013 .

[15]  J. Faist,et al.  Quantum Cascade Laser , 1994, Science.

[16]  Carlo Sirtori,et al.  High power frequency comb based on mid-infrared quantum cascade laser at λ ∼ 9 μm , 2015 .

[17]  Carlo Sirtori,et al.  Coherent sampling of active mode-locked terahertz quantum cascade lasers and frequency synthesis , 2011 .

[18]  B. Greene,et al.  Generation of optical pulses shorter than 0.1 psec by colliding pulse mode-locking , 1981, IEEE Journal of Quantum Electronics.

[19]  B. Williams.  Terahertz quantum cascade lasers , 2007, 2008 Asia Optical Fiber Communication & Optoelectronic Exposition & Conference.

[20]  D. Revin,et al.  Active mode locking of quantum cascade lasers in an external ring cavity , 2015, Nature communications.

[21]  Qing Hu,et al.  A terahertz pulse emitter monolithically integrated with a quantum cascade laser , 2011 .

[22]  S. Corzine,et al.  Coherent instabilities in a semiconductor laser with fast gain recovery , 2007 .

[23]  D. Burghoff,et al.  Gain measurements of scattering-assisted terahertz quantum cascade lasers , 2012 .

[24]  Aiting Jiang,et al.  Broadly tunable terahertz generation in mid-infrared quantum cascade lasers , 2013, Nature Communications.

[25]  Qing Hu,et al.  Terahertz laser frequency combs , 2014 .

[26]  Jérôme Faist,et al.  Dual-comb spectroscopy based on quantum cascade laser frequency combs , 2015, CLEO 2015.

[27]  Mattias Beck,et al.  Broadband external cavity tuning in the 3-4 μm window , 2013 .

[28]  J. Faist,et al.  Mid-infrared frequency comb based on a quantum cascade laser , 2012, Nature.

[29]  L. F. Tiemeijer,et al.  Passive FM locking in InGaAsP semiconductor lasers , 1989 .

[30]  Qing Hu,et al.  Terahertz multiheterodyne spectroscopy using laser frequency combs , 2016, 1604.01048.

[31]  T. Kippenberg,et al.  Microresonator-Based Optical Frequency Combs , 2011, Science.

[32]  Federico Capasso,et al.  Stable mode-locked pulses from mid-infrared semiconductor lasers , 2009, 0903.4385.

[33]  Nathan R Newbury,et al.  Phase-locked, erbium-fiber-laser-based frequency comb in the near infrared. , 2004, Optics letters.