Lateral Heterogeneous Integration of Quantum Cascade Lasers

Abstract

Broadband terahertz radiation potentially has extensive applications, ranging from personal health care to industrial quality control and security screening. While traditional methods for broadband terahertz generation rely on bulky and expensive mode-locked lasers, frequency combs based on quantum cascade lasers (QCLs) can provide an alternative compact, high power, wideband terahertz source. QCL frequency combs incorporating a heterogeneous gain medium design can obtain even greater spectral range by having multiple lasing transitions at different frequencies. However, despite their greater spectral coverage, the comparatively low gain from such gain media lowers the maximum operating temperature and power. Lateral heterogeneous integration offers the ability to cover an extensive spectral range while maintaining the competitive performance offered from each homogeneous gain media. Here, we present the first lateral heterogeneous design for broadband terahertz generation: by combining two different homogeneous gain media, we have achieved a two-color frequency comb spaced by 1.5 THz.

Terahertz hyperspectral imaging with dual chip-scale combs

“…(c) Reference spectroscopic data of α-D-glucose monohydrate (GMH) and α-D-lactose monohydrate (LMH) from Ref [32],. and L-histidine monohydrochloride monohydrate (LHHM) from Ref [33]. showing the frequency-dependent attenuation of the absorbers responsible for the different zone colors in (b).…”

“…The acquisition speed of the instrument is currently limited by the slow mechanical raster scan, but assessments of the short-term precision of the system indicate that percentage level fractional absorption could be obtained on the subsecond time-scale with faster scanning. Future developments of the THz combs are expected to further increase the optical power and address the current limitations in optical bandwidth [33]. Already, octavespanning multimode THz-QCLs have been demonstrated [34].…”

Coexisting frequency combs spaced by an octave in a monolithic quantum cascade laser

“…Only recently QCL FC formation in the dispersive regime at 4.6 THz has been reported by Y. Yang et al in Ref. [21].…”

“…In this paper we explore two coexisting FCs spaced by one octave and simultaneously operating in the same waveguide. Only recently, two comb lasing based on heterogeneous waveguide coupling has been reported [21]. Here we employ our 4-well active region [22] by rescaling and centering the two emission frequencies at 2.3 THz and 4.6 THz, in order to have high intensities and stable phase coherent operation independently at the octave spacing.…”

“…), the bulk group refractive index change over the bandwidth of the FC is estimated to be ∆n ≈ 0.08. Only recently QCL FC formation in the dispersive regime at 4.6 THz has been reported by Y. Yang et al in Ref [21]…”