Planarized THz quantum cascade lasers for broadband coherent photonics

TL;DR

This paper introduces a planarized THz quantum cascade laser platform with integrated active and passive components, achieving broadband coherent emission, mode-locking, and low-loss waveguides for advanced THz photonics applications.

Contribution

It presents a novel integrated photonic platform with an extended top metallization for improved THz laser performance and on-chip integration of active and passive elements.

Findings

Achieved broadband THz emission spanning over 1.6 THz.

Produced mode-locked pulses as short as 4.4 ps.

Demonstrated low-loss passive waveguides enabling cavity tuning.

Abstract

Recently, there has been a growing interest in integrated THz photonics for various applications in communications, spectroscopy and sensing. We present a new integrated photonic platform based on active and passive elements integrated in a double-metal, high confinement waveguide layout planarized with a low-loss polymer. An extended top metallization results in low waveguide losses and improved dispersion, thermal and RF properties, as it enables to decouple the design of THz and microwave cavities. Free-running on-chip quantum cascade laser combs spanning 800 GHz, harmonic states over 1.1 THz and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed. With a strong external RF drive, actively mode-locked pulses as short as 4.4 ps can be produced, as measured by SWIFTS. We demonstrate as well passive waveguides with low insertion loss, enabling the tuning of the laser cavity boundary conditions and the co-integration of active and passive components on the same THz photonic chip.