Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis

Applied Physics Letters

et al. 2015

Terahertz-frequency quantum cascade lasers (THz QCLs) based on bound-to-continuum active regions are difficult to model owing to their large number of quantum states. We present a computationally efficient reduced rate equation (RE) model that reproduces the experimentally observed variation of THz power with respect to drive current and heat-sink temperature. We also present dynamic (time-domain) simulations under a range of drive currents and predict an increase in modulation bandwidth as the current approaches the peak of the light–current curve, as observed experimentally in mid-infrared QCLs. We account for temperature and bias dependence of the carrier lifetimes, gain, and injection efficiency, calculated from a full rate equation model. The temperature dependence of the simulated threshold current, emitted power, and cut-off current are thus all reproduced accurately with only one fitting parameter, the interface roughness, in the full REs. We propose that the model could therefore be used for rapid dynamical simulation of QCL designs.

“…15. The device was processed into a 140 lm Â 1.78 mm semi-insulating plasmon ridge, and the single-mode emission frequency, measured at threshold, is 2.59 THz.…”

mentioning

confidence: 99%

Efficient prediction of terahertz quantum cascade laser dynamics from steady-state simulations

Agnew

Grier

Applied Physics Letters

et al. 2015

“…This demonstrates the potential for imaging spatial (lateral) variations in refractive index or absorption of a target in the MIR range of the spectrum, following the procedure described in Ref. 19.…”

mentioning

confidence: 86%

“…21 The total amplitude change of the laser terminal voltage (3 lV peak-to-peak) as the target is displaced is an order of magnitude smaller than the typical signal obtained for in-plane diode lasers or vertical-cavity surface-emmiting lasers (which are both in the tens of microvolts 22,23 ) and several orders smaller than the terminal voltage change observed in terahertz QCLs (millivolts). 19,24 The experimental self-mixing waveform obtained in this way can be modelled through the use of the excess phase equation (that is, the steady-state solution to the Lang-Kobayashi rate equation model for a laser under optical feedback), when the stimulus is simply displacement linear in time. 7,25 The broken line in Fig.…”

mentioning

confidence: 99%

Demonstration of the self-mixing effect in interband cascade lasers

Bertling

Lim

Applied Physics Letters

et al. 2013

“…More information about the structure of the device can be found in [7], and the full set of rate and thermal equations for our model is detailed in [8]. The rate equation parameters comprising gain, carrier lifetimes, and injection efficiencies, were calculated specifically for our exemplar QCL using the structure of the device as input to a S-P solver for the full rate equations.…”

Section: Exemplar Device Modelmentioning

confidence: 99%

Terahertz quantum cascade laser bandwidth prediction

Agnew

Grier

2015 International Topical Meeting on Microwave Photonics (MWP)

et al. 2015

Self Cite

Abstract-Recent research shows that terahertz quantum cascade lasers are well-suited to high speed free space communication. The results of both theoretical and laboratory work indicate the devices are able to deliver bandwidths in the gigahertz to tens of gigahertz range without the burden of relaxation oscillations found in diode lasers. Using a novel rate equation model we explore the frequency response characteristics of a real device and report on the finding of a strongly peaked bias currentdependent response.Index Terms-Free space communication, terahertz quantum cascade laser, bandwidth