Photonic bandstructure engineering of THz quantum-cascade lasers

Abstract

We present the design and realization of active photonic crystal (PhC) terahertz (THz) lasers operating in higher photonic bands. The structure consists of an array of isolated pillars fabricated from a THz quantum-cascade laser and embedded in a double-metal waveguide. The PhC geometry is adopted to achieve lasing in the first and second photonic bands. Thereby, the optical mode is pushed from the active pillars into the surrounding. The sensitivity of local sensors can be increased by almost one order of magnitude compared to designs operating in the lowest photonic band.

Photonic Engineering Technology for the Development of Terahertz Quantum Cascade Lasers

“…Consequently, most of the THz PhC lasers based on perforated top metallic contact operate on several modes of which the wavevectors correspond to high-symmetry points in the momentum space, [62][63][64] as indicated in Figure 3c. [72][73][74][75][76] Apart from the wavelength-selection mechanisms based on DFB and PhC geometries, other photonic structures also turn out effective in frequency engineering and single-mode operation. It is feasible to drill the air holes through the active region, [69,70] but complete PBG can only be achieved with a very high filling factor of air holes in the PhC structure.…”

“…[74] In this scheme, the refractive index contrast is more pronounced and thus, results in large PBG where the gain spectral range of THz QCLs can be aligned to one of the strong band-edge resonances for robust single-mode operation. [72][73][74][75][76] Apart from the wavelength-selection mechanisms based on DFB and PhC geometries, other photonic structures also turn out effective in frequency engineering and single-mode operation. For example, a circular resonant cavity with wavelengthcomparable size has a series of whisper-gallery modes with a large free spectral range.…”