Ultra-fast amplitude modulation of mid-IR free-space beams at room-temperature

TL;DR

This paper introduces a room-temperature, free-space amplitude modulator for mid-IR beams operating at GHz speeds, filling a critical gap in integrated mid-IR photonics technology.

Contribution

The authors developed a novel semiconductor hetero-structure modulator capable of ultra-fast amplitude modulation at room temperature, a significant advancement over existing mid-IR modulators.

Findings

Operates up to 1.5 GHz with -3dB cutoff at 750 MHz

Uses a semiconductor hetero-structure in a metal-metal resonator

Achieves modulation of mid-IR laser intensity via polaritonic state control

Abstract

Applications relying on mid-infrared radiation (Mid-IR, $\lambda\sim$ 3-30 $\mu$m) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs. Mid-IR cameras have propelled the field of thermal imaging. And the invention of the quantum cascade laser (QCL) has been a milestone, making compact, semiconductor-based mid-IR lasers available to a vast range of applications. All the recent breakthrough advances stemmed from the development of a transformative technology. In addition to the generation and detection of light, a key functionality for most photonics systems is the electrical control of the amplitude and/or phase of an optical beam at ultra-fast rates (GHz or more). However, standalone, broadband, integrated modulators are missing from the toolbox of present mid-IR photonics integrated circuits and systems developers. We have developed a free-space amplitude modulator for mid-IR radiation ($\lambda\sim$ 10 $\mu$m) that can operate up to at least 1.5 GHz (-3dB cut-off at $\sim$ 750 MHz) and at room-temperature. The device relies on a semiconductor hetero-structure enclosed in a judiciously designed metal-metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300K. By applying an appropriate bias, the device transitions to the weak coupling regime. The large change in reflectivity due to the disappearance of the polaritonic states is exploited to modulate the intensity of a mid-IR continuous-wave laser up to speeds of more than 1.5 GHz.