Quantum coherent saturable absorption for mid-infrared ultra-short pulses.

Muhammad Anisuzzaman Talukder,Curtis R. Menyuk

doi:10.1364/oe.22.015608

Abstract

We theoretically show that quantum coherent saturable absorption can be used to obtain ultra-short pulses from mid-infrared quantum cascade lasers (QCLs). In this proposal, quantum cascade structures are processed as two electrically isolated sections. The two sections will be biased with two different voltages so that one of the sections produces gain as is done in typical QCLs, while the other produces quantum coherent resonant absorption for the propagating waves. The quantum coherent absorbing section is saturable and favors the generation of ultra-short pulses. We find that stable ultra-short pulses on the order of ∼100 ps are created from a two-section QCL when the pumping in the gain and absorbing sections remains within critical limits. The intensity and the duration of the stable pulses can be significantly varied when the pumping in the gain and absorbing sections and the length of the gain and absorbing sections are varied.

Highlights

The realization of mid-infrared short pulses from compact semiconductor light sources, i.e., quantum cascade lasers (QCLs) has been a challenge for last one and a half decades
It has been shown that QCLs can be used to produce frequency combs using four-wave mixing or self frequency modulation [8,9,10,11]
It has been shown that the very fast gain recovery of QCLs favors the growth of continuous waves when the input current is above the threshold that is required for lasing [12]

Summary

Introduction

The realization of mid-infrared short pulses from compact semiconductor light sources, i.e., quantum cascade lasers (QCLs) has been a challenge for last one and a half decades. The key way in which SIT modelocking differs from standard modelocking is that it is no longer necessary to have a gain bandwidth that is equal to the inverse pulse duration [14] Structures with interleaved gain and absorbing periods can be used for active-SIT modelocking to increase the stability regime and self-start the laser [16]. The resonant absorbing section behaves like a saturable absorber; it absorbs continuous waves and suppresses the spatial hole-burning. We find that this scheme lets the laser self-start from random quantum noise and produces ultrashort stable pulses with durations that can be shorter than 100 fs.

Theoretical model

Maxwell-Bloch equations

Derivation of the critical pump parameters

Results

Conclusion