Fast amplitude modulation up to 1.5 GHz of mid-IR free-space beams at room-temperature

Stefano Pirotta,Giorgio Biasiol,Ngoc-Linh Tran,Jean-Michel Manceau,Raffaele Colombelli,Adel Bousseksou,Paul Crozat,Arnaud Jollivet

doi:10.1038/s41467-020-20710-2

Abstract

Applications relying on mid-infrared radiation (λ ~ 3-30 μm) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs like mid-infrared cameras and quantum cascade lasers. On the other side, standalone and broadband devices allowing control of the beam amplitude and/or phase at ultra-fast rates (GHz or more) are still missing. Here we show a free-space amplitude modulator for mid-infrared radiation (λ ~ 10 μm) that can operate at room temperature up to at least 1.5 GHz (−3dB cutoff at ~750 MHz). The device relies on a semiconductor heterostructure enclosed in a judiciously designed metal–metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300 K. By applying an appropriate bias, the device transitions towards the weak-coupling regime. The large change in reflectance is exploited to modulate the intensity of a mid-infrared continuous-wave laser up to 1.5 GHz.

Highlights

Applications relying on mid-infrared radiation (λ ~ 3-30 μm) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs like midinfrared cameras and quantum cascade lasers
Our approach is to operate the device in the strong lightmatter coupling regime, and introduce the fast modulation by— ideally— switching the system in and out of strong coupling with the application of a bias voltage
The system, designed to operate in reflectance, is conveniently optimized so that the ISB transition is strongly coupled to the TM03 photonic mode of the resonator, whose electric-field distribution is shown in Fig. 1(b): the notation convention TM0i is defined in the caption

Summary

Introduction

Applications relying on mid-infrared radiation (λ ~ 3-30 μm) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs like midinfrared cameras and quantum cascade lasers. The first attempts based on the Stark shift were followed by a number of works exploiting coupled QWs9,10 In both cases, the application of an external bias depletes or populates the ground state of the QW at cryogenic temperatures (from 4 K up to 130 K) inducing a modulation of the ISB absorption[11]. Different approaches have been proposed to actively tune the reflectance/transmission of mid-IR and/or THz beams: phase transition in materials like VO2, liquid crystals orientation, carrier density control in metal–insulator-semiconductor junctions[13]. These devices operate on the principle that, at a given wavelength, a change in absorption translates in a modulation of the transmitted power.

Methods

Results

Conclusion