Heterodyne coherent detection of phase modulation in a mid-infrared unipolar device

TL;DR

This paper demonstrates phase modulation in a mid-infrared quantum Stark effect modulator using heterodyne detection, achieving measurable phase shifts and amplitude modulation, with results aligning with theoretical models.

Contribution

It introduces a novel mid-infrared phase modulator based on quantum Stark effect and demonstrates heterodyne detection of phase and amplitude modulation.

Findings

Phase shift exceeds 5 degrees

Intensity modulation of 5% observed

Experimental results match theoretical model

Abstract

Phase modulation is demonstrated in a quantum Stark effect modulator designed to operate in the mid-infrared at wavelength around 10 $\mu$m. Both phase and amplitude modulation are simultaneously resolved through the measurement of the heterodyne signal arising from the beating of a quantum cascade laser with a highly stabilized frequency comb. The highest measured phase shift is more than 5 degrees with an associated intensity modulation of 5%. The experimental results are in full agreement with our model in which the complex susceptibility is precisely described considering the linear voltage dependent Stark shift of the optical resonance.