Millimeter-wave and Terahertz Devices Group
Professor Qing Hu

Tunable THz wire lasers

http://www.rle.mit.edu/thz/Tunablewirelasers.htm

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 (l_o ~ 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 w<<l. 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.

Selected publications:

• E. E. Orlova, J. N. Hovenier, T. O. Klaassen, I. Kasalynas, A. J. L. Adam, A. Baryshev, J. R. Gao, T. M. Klapwijk, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, "Antenna Model for Wire Lasers," Phys. Rev. Lett. 96, 173904 (2006). [PDF]
• Q. Qin, B. S. Williams, S. Kumar, J. L. Reno, and Q. Hu, “Tuning a Terahertz Wire Laser,” Nature Photonics, 3, 732-737 (2009). [PDF]
• C. Gmachl, “A wrench of wavelength”, news & views, Nature Photonics, 3, 683 (2009). [PDF]
• A. W. M. Lee, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Tunable Terahertz Quantum Cascade Lasers with External Gratings,” Opt. Lett. 35, 910 (2010). [PDF]
• Qi Qin, John L. Reno, and Qing Hu, “MEMS-based tunable terahertz wire-laser over 330 GHz,” Opt. Lett. 36, 692 (2011). [PDF]
• Qi Qin and Qing Hu, “MEMS-plunger platform for tunable terahertz wire-laser at ~ 5 K,” J. Micromechanics and Microengineering, 21, 075004 (2011). [PDF]