Graphene‐Coupled Terahertz Semiconductor Lasers for Enhanced Passive Frequency Comb Operation

Abstract

Optical frequency combs, consisting of well‐controlled equidistant frequency lines, have been widely used in precision spectroscopy and metrology. Terahertz combs have been realized in quantum cascade lasers (QCLs) by employing either an active mode‐locking or phase seeding technique, or a dispersion compensator mirror. However, it remains a challenge to achieve the passive comb formation in terahertz semiconductor lasers due to the insufficient nonlinearities of conventional saturable absorbers. Here, a passive terahertz frequency comb is demonstrated by coupling a multilayer graphene sample into a QCL compound cavity. The terahertz modes are self‐stabilized with intermode beat note linewidths down to a record of 700 Hz and the comb operation of graphene‐coupled QCLs is validated by on‐chip dual‐comb measurements. Furthermore, the optical pulse emitted from the graphene‐coupled QCL is directly measured employing a terahertz pump–probe technique. The enhanced passive frequency comb operation is attributed to the saturable absorption behavior of the graphene‐integrated saturable absorber mirror, as well as the dispersion compensation introduced by the graphene sample. The results provide a conceptually different graphene‐based approach for passive comb formation in terahertz QCLs, opening up intriguing opportunities for fast and high‐precision terahertz spectroscopy and nonlinear photonics.

Investigation of Phonon Scattering on the Tunable Mechanisms of Terahertz Graphene Metamaterials

“…The terahertz (THz) frequency range lies in the microwave and infrared wavelength ranges of the electromagnetic spectrum, showing potential applications in the practical fields of spectral analysis, imaging, homeland security detection, and high-speed wireless communication (in the range of several hundred Gbit s −1 ) [1][2][3][4][5][6][7][8]. But to further substantial development of THz science and technology, there is a high demand for well-performing functional waveguide devices and components.…”

Acoustic frequency combs using gas bubble cluster oscillations in liquids: a proof of concept

“…Optical frequency combs-optical spectra composed of equidistant narrow peaks-enable precision measurement in both fundamental and applied contexts [1][2][3][4][5][6] . An optical frequency comb acts as a spectrum synthesizer that enables the precise transfer of phase and frequency information from a stabilised reference to optical signals.…”

Tunable, Grating‐Gated, Graphene‐On‐Polyimide Terahertz Modulators

“…[ 65 ] The Fabry–Pérot device operates as frequency comb synthesizer over ~1.05 THz bandwidth, and shows a stable and narrow (4.15 kHz) beatnote over a continuous current range ~106 mA, corresponding to 15% of the laser operational range. Different to previous approaches, [ 66 ] we then engineer an etalon‐like interferometric scheme, in which the modulator is tightly coupled to the back facet of the THz QCL, at a distance ~50 µm, as required for an on‐resonance GTI. [ 58 ] The THz radiation is injected in the laser cavity after being back‐reflected by the modulator, operating as the external cavity active mirror of a GTI.…”