Abstract-Optical side-band generation in THz Fabry-Perot laser cavities

Owen P. Marshall, Md. Khairuzzaman, Harvey E. Beere, David A. Ritchie,  Subhasish Chakrabort,

http://aip.scitation.org/doi/abs/10.1063/1.5001334

Optical nonlinearities in semiconductor laser cavities can be exploited to characterize the properties of laser radiation or perform high speed frequency conversion operations. For example, nonlinear up-conversion inside the cavity of quantum cascade lasers allows the use of near infrared optical components to measure high-speed terahertz or mid-infrared optical effects. This letter investigates two aspects of cavity up-conversion which control both the bandwidth and up-converted power: waveguide dispersion and cavity feedback. Specifically, we up-convert multi-mode Fabry Perot terahertz laser emission and detect each THz mode as a sideband signal on an optical carrier in the near infrared. Analysis of these results shows that a single frequency near infrared laser can up-convert terahertz modes spanning a bandwidth of approximately 220 GHz, limited by the group index mismatch between the near infrared and terahertz waves. Second, transfer matrix techniques are used to study strong cavity feedback on all three waves, which produces etalon-like resonances in the sideband power. This can significantly enhance the efficiency of the conversion process, in agreement with experiments. It is thus possible to achieve high up-conversion efficiency in quantum cascade lasers for both characterizing broadband laser sources and performing frequency conversion in the near infrared.

Abstract-Electronically tunable aperiodic distributed feedback terahertz lasers

O. P. Marshall¹, S. Chakraborty¹, Md. Khairuzzaman¹, T. Folland¹, A. Gholinia², H. E. Beere³, and D. A. Ritchie³

¹School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, United Kingdom
²School of Materials, University of Manchester, Manchester M1 7HS, United Kingdom
³Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom 

http://jap.aip.org/resource/1/japiau/v113/i20/p203103_s1?isAuthorized=no

Focussed ion beam milling can be used to introduce aperiodic distributed feedback (ADFB) gratings into fully packaged, operational terahertz (THZ) quantum cascade lasers to achieve electronically controlled, discretely tunable laser emission. These aperiodic gratings—designed using computer-generated hologram techniques—consist of multiple slits in the surface plasmon waveguide, distributed along the length of the laser cavity. Tuning behaviour and output power in ADFB lasers operating around 2.9 THz are investigated with a variety of slit dimensions and grating scales. Mode selectivity and grating losses are found to be strongly dependent on milling depth into the upper waveguide layers, dramatically increasing as the metallic layers are penetrated, then rising more slowly with deeper milling into the laser active region. Grating scale and placement along the laser cavity length are also shown to influence mode selection.http://jap.aip.org/resource/1/japiau/v113/i20/p203103_s1?isAuthorized=no

Abstract-Reversible mode switching in Y-coupled terahertz lasers

Owen P. Marshall¹, Subhasish Chakraborty¹, Md Khairuzzaman¹, Harvey E. Beere², and David A. Ritchie²

¹School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, United Kingdom
²Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom 

http://apl.aip.org/resource/1/applab/v102/i11/p111105_s1?isAuthorized=no 

Electrically independent terahertz (THz) quantum cascade lasers (QCLs) are optically coupled in a Y configuration. Dual frequency, electronically switchable emission is achieved in one QCL using an aperiodic grating, designed using computer-generated hologram techniques, and incorporated directly into the QCL waveguide by focussed ion beam milling. Multi-moded emission around 2.9 THz is inhibited, lasing instead occurring at switchable grating-selected frequencies of 2.88 and 2.92 THz. This photonic control and switching behaviour is selectively and reversibly transferred to the second, unmodified QCL via evanescent mode coupling, without the transfer of the inherent grating losses.

© 2013 American Institute of Physics

Abstract-Y coupled terahertz quantum cascade lasers

http://arxiv.org/abs/1206.0972

Owen P. Marshall, Subhasish Chakraborty, Md. Khairuzzaman, Harvey E. Beere, David A. Ritchie

(Submitted on 5 Jun 2012)

Abstract: Here we demonstrate a Y coupled terahertz (THz) quantum cascade laser (QCL) system. The two THz QCLs working around 2.85 THz are driven by independent electrical pulsers. Total peak THz output power of the Y system, with both arms being driven synchronously, is found to be more than the linear sum of the peak powers from the individual arms; 10.4 mW compared with 9.6 mW (4.7 mW + 4.9 mW). Furthermore, we demonstrate that the emission spectra of this coupled system are significantly different to that of either arm alone, or to the linear combination of their individual spectra.

Comments:	9 pages, 3 figures
Subjects:	Optics (physics.optics); Other Condensed Matter (cond-mat.other)
Cite as:	arXiv:1206.0972v1 [physics.optics]

Submission history

From: Subhasish Chakraborty [view email]
[v1] Tue, 5 Jun 2012 15:53:34 GMT (1026kb