Abstract
Tunable oscillators are a key component of almost all electronic and photonic systems. Yet, a technology capable of operating in the terahertz (THz)-frequency range and fully suitable for widescale implementation is still lacking. This issue is significantly limiting potential THz applications in gas sensing, high-resolution spectroscopy, hyper-spectral imaging, and optical communications. The THz quantum cascade laser is arguably the most promising solution in terms of output power and spectral purity. In order to achieve reliable, repeatable, and broad tunability, here we exploit the strong coupling between two different cavity mode concepts: a distributed feedback one-dimensional photonic resonator (providing gain) and a mechanically actuated wavelength-size microcavity (providing tuning). The result is a continuously tunable, single-mode emitter covering a 162 GHz spectral range, centered on 3.2 THz. Our source has a few tens of MHz resolution, extremely high differential efficiency, and unprecedented compact and simple design architecture. By unveiling the large potential that lies in this technique, our results provide a robust platform for radically different THz systems exploiting broadly tunable semiconductor lasers.
Highlights
Tunable semiconductor lasers and, in particular, quantum cascade lasers (QCLs)1 are ideal devices for such applications, owing to their small size, stability, and their inherently high spectral purity.2 To address the operating requirements of high-resolution spectroscopy, solutions include arrays of thermally tunable QCLs,3,4 or externalcavity approaches where the frequency of a single broadband device is set by frequency-selective external feedback.5 In the THz region of the electromagnetic spectrum, QCLs are the only single-mode source capable of providing mW power levels in the 2–5 THz band
By unveiling the large potential that lies in this technique, our results provide a robust platform for radically different THz systems exploiting broadly tunable semiconductor lasers
Broadband tunable single-frequency THz QCLs would be an important technology for gas sensing and spectroscopy
Summary
In order to achieve reliable, repeatable, and broad tunability, here we exploit the strong coupling between two different cavity mode concepts: a distributed feedback onedimensional photonic resonator (providing gain) and a mechanically actuated wavelength-size microcavity (providing tuning). DFB lasers can be tuned by changing the effective refractive index of the waveguide dielectric through varying the temperature,10 by accessing the evanescent field through metallic plungers,11–13 by reversible material condensation,14 or by electrical modulation.15 Alternative solutions exploit sampled grating16,17 or difference frequency generation approaches.18,19 a)Author to whom correspondence should be addressed.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
