All in One-Chip, Electrolyte-Gated Graphene Amplitude Modulator, Saturable Absorber Mirror and Metrological Frequency-Tuner in the 2–5 THz Range

Abstract

Layered 2D materials display unique optical and electrical properties that can enable manipulation, propagation, and detection of electromagnetic waves over a broad spectral range, with a high level of control, offering the potential to activate different functionalities, by optical or electrical means, in a single chip. Here, a compact optoelectronic device behaving as an amplitude modulator, saturable absorber mirror (SA mirror), and frequency-tuner is conceived at terahertz (THz) frequencies. It comprises a gate-tunable single layer graphene (SLG), embedded in a quarter-wave cavity, operating in the 1–5 THz range. The use of electrolyte ionic liquid gate ensures 40% optical amplitude modulation depth. Z-scan self-mixing interferometry reveals 60% reflectivity modulation, with ≈4.5 W cm−2 saturation intensity. By integrating the modulator/SA mirror with a heterogeneous THz quantum cascade laser frequency comb, in an external cavity configuration, fine-tuning of the intermode beatnote frequency is also demonstrated. This opens intriguing perspectives for short pulse generation, phase-locking, frequency tuning/chirping, phase modulation, and metrological referencing, inter alia.