Tunable THz Wire Lasers

Broadly tunable terahertz lasers are highly desired for applications in sensing/spectroscopy since many bio-chemical species have strong spectral fingerprints at terahertz frequencies. Conventionally, a laser’s frequency is tuned similarly to a stringed musical instrument such as the violin, whose pitch is varied by changing the string’s length (the longitudinal component of wave-vector) and/or its tension (the refractive index). However, such methods are difficult to implement for terahertz semiconductor lasers due to their poor out-coupling efficiencies because of the long wavelength at THz (~100 µm) relative to the cross section of the laser ridge (several 10 µm).

In this project, we demonstrate a novel tuning mechanism based on a unique “wire-laser” device whose transverse dimension is much smaller than the wavelength. Placing a movable object close to the wire-laser manipulates the large fraction of the waveguided mode propagating outside the cavity thereby tuning its resonant frequency. Continuous single-mode red-shift and blue-shift tuning is demonstrated from the same device by using either a dielectric or metallic movable object. Using a MEMS-based system, continuous tuning of ~330 GHz (~8.6% of the center frequency) is demonstrated from a single laser device at ~3.8 THz.