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Quantum cascade lasers (QCLs) have emerged as promising candidates for generating chip-scale frequency combs in mid-infrared and terahertz wavelengths. In this work, we demonstrate frequency comb formation in ring terahertz QCLs using the injection of light from a distributed feedback (DFB) laser. The DFB design frequency is chosen to match the modes of the ring cavity (near 3.3 THz), and light from the DFB is injected into the ring QCL via a bus waveguide. By controlling the power and frequency of the optical injection, we show that combs can be selectively formed and controlled in the ring cavity. Numerical modeling suggests that this comb is primarily frequency-modulated in character, with the injection serving to trigger comb formation. We also show that the ring can be used as a filter to control the output of the DFB QCL, potentially being of interest in terahertz photonic integrated circuits. Our work demonstrates that waveguide couplers are a compelling approach for injecting and extracting radiation from ring terahertz combs and offer exciting possibilities for the generation of new comb states in terahertz, such as frequency-modulated waves, solitons, and more.
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Cnoidal Waves for Accessible High Power and Wide-Band Microresonator Frequency Combs
Pumped Kerr microresonators have recently emerged as a promising source of optical frequency combs. The production of octave-spanning spectrum by dispersive waves and consequent demonstration of carrier-envelope phase locking has paved the way toward a wide fi eld of comb applications. Nevertheless, there remain some obstacles before the goal of a simple off-the-shelf comb source is achieved. Current microcomb implementations rely on cavity solitons, and several of the present limitations of microcombs are tied to those of soliton waveforms. Cavity solitons exist only in a small red-detuned region of the pump parameters, where waveforms suffer from thermal instabilities. Furthermore, solitons are always obtained in the multistable regime, and therefore cannot be continuously connected to cw, so that elaborate, often non-deterministic, access protocols are needed to produce them. Another issue is that because solitons are accompanied by a strong pedestal, their comb power efficiency is low.
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- Award ID(s):
- 1807272
- PAR ID:
- 10095788
- Date Published:
- Journal Name:
- FRISNO15: FRench-Israel Symposium on Non-Linear & Quantum Optics
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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