Dynamics of ultra-broadband terahertz quantum cascade lasers for comb operation

Abstract

We present an experimental investigation of the multimode dynamics and the coherence of terahertz quantum cascade lasers emitting over a spectral bandwidth of ~1THz. The devices are studied in free-running and under direct RF modulation. Depending on the pump current we observe different regimes of operation, where RF spectra displaying single and multiple narrow beat-note signals alternate with spectra showing a single beat-note characterized by an intense phase-noise, extending over a bandwidth up to a few GHz. We investigate the relation between this phase-noise and the dynamics of the THz modes through the electro-optic sampling of the laser emission. We find that when the phase-noise is large, the laser operates in an unstable regime where the lasing modes are incoherent. Under RF modulation of the laser current such instability can be suppressed and the modes coherence recovered, while, simultaneously, generating a strong broadening of the THz emission spectrum.

Dynamics of a broad-band quantum cascade laser: from chaos to coherent dynamics and mode-locking

“…In this case a "rule of thumb" can be obtained to gauge the laser operating regimes towards irregular (spatio-temporal chaos) or coherently locked emission, the latter leading to regular oscillations of the output field. In Section 3 our simulations show that increasing the bias current leads to the destabilization of the lowest threshold TW and drives the laser through a sequence of alternating irregular regimes and regular, mode-locked, regimes in agreement with recent experiments results on the multimode dynamics of an ultra-broad-gain THz-QCL [8,34]. Also, we find that a larger LEF (more typical of a Mid-IR QCL [1]) favors the TW destabilization towards multimode regimes.…”

“…This feature can thus explain the disappearance of the fundamental BN observed in Fig. 4.a and in certain dynamical regimes reported in [34] (see for example Fig.4 of [34] in the region between 400 and 420 mA). We could a posteriori verify that this traveling structure is also present in the field profile just above threshold (µ = 1.002µ th ) where, of course, the low absolute emission For an easier comparison with experimental data, the frequency in physical units is drawn on the upper horizontal scale.…”

“…3.a and Fig. 3.b we report µ th as a function of k, considered as a continuous variable, for different values of α and l. We set Γ = 1.1 that corresponds to a gain linewidth of 1.75T Hz which is close to that of the broad-band QCL studied in [8,34]. Clearly, an increment of α or l lowers the lasing threshold for an increasing number of TWs.…”

Энергетический Спектр И Тепловые Свойства Терагерцового Квантово-Каскадного Лазера На Основе Резонансно-Фононного Дизайна

“…На основе микроэлектромеханической системы была достигнута перестройка частоты на 330 ГГц у ТГц ККЛ с центральной частотой 3.85 ТГц [4]. В работах [5,6] продемонстрированы ТГц ККЛ в режиме частотной гребенки со спектральной полосой более 1 ТГц, что позволяет разрабатывать ТГц спектрометры с большим отношением сигнал/шум. Таким образом, продемонстри-рованные параметры и режимы работы AlGaAs/GaAs ТГц ККЛ показывают перспективность данного компакт-ного твердотельного ТГц источника по сравнению с твердотельными электронными приборами и оптической генерацией ТГц-излучения [7,8].…”

Beat note analysis and spectral modulation of terahertz quantum cascade lasers with radio frequency injection

“…It has already been verified that QCLs emitting in mid-infrared and terahertz wavelength ranges can be modulated and injection locked up to dozens of gigahertz [12][13][14][15] . The injection locking technique plays an important role in the phase locking [16,17] and broadband frequency comb operation [18,19] of terahertz QCLs.…”