Ted Letsou - Research

My research focuses on expanding integrated photonics into the mid-infrared range using InP semiconductor platforms.

We design semiconductor photonics circuits, which combine sources, ring resonators, waveguides, and detectors on a single chip. These photonic circuits are used as frequency combs, pulse generators, optical filters, and tunable lasers to probe the rich chemical ecosystem that exists in the mid-infrared.

You can read some background on my research themes below, with related publications found on my Google Scholar or my Publications section.

We are developing active nonlinear integrated photonics in the mid-IR by leveraging quantum cascade lasers (QCLs) as both light sources and waveguides. This novel platform eliminates the need for hybrid integration of sources and passive waveguides, instead uniting light generation, manipulation, and guiding within a single, monolithic architecture. By combining QCLs laser cores with racetrack resonators, directional couplers, and other photonic building blocks, we aim to create tunable lasers, broadband frequency combs, and picosecond pulse generators entirely on-chip. Imaged above is a "Vernier tunable" laser using nine different QCL sections, which can each be individually-addressed using electrical bias.

QCLs are especially intriguing because they can emit multiple colors simultaneously, and sometimes these colors spontaneously synchronize, producing what is known as a frequency comb. Frequency combs have wide-ranging applications, from precise measurements and chemical detection to environmental monitoring and next-generation communication technologies. Much of our work revolved around optimizing the performance of QCL combs: increasing their output powers, reducing their sensitivity to optical feedback, and expanding their optical bandwidths.

We recently demonstrated a pair of QCL rings spontaneously generates a unique frequency comb with numerous interacting, phase-locked tones, leading to simultaneous circulation of bright and dark picosecond light pulses (solitons) exiting the cavity together—a phenomenon impossible in a standalone laser. Inspired by these results, our current research explores novel states of light emerging from multi-resonator QCL systems, aiming to manipulate light in even more sophisticated ways. We are also expanding our focus to include matrices of coupled lasers, paving the way for large-scale, integrated photonic networks with unprecedented capabilities.

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