Evaluation of high-stability optical beats in laser chaos by plasmonic photomixing

Abstract

The stability of optical beats in a chaotically oscillating laser is compared to that of a free-running continuous-wave laser using a highly efficient plasmonic photomixer. Using a chaotically oscillating laser diode, stable optical beats are observed over an operation current range of 60-90 mA. The optical spectra are stable even with frequent mode hopping. In contrast, optical beats in a free-running continuous-wave laser are not stable compared to those of a chaotically oscillating laser, because of intermittent hopping of the laser modes. The high stability of chaotically oscillating lasers makes these lasers promising candidates for optical pump sources in terahertz time-domain spectroscopy systems.

Transfer characteristics of sub-THz waves in volcanic ash eruption from volcanoes in Japan

“…The scan time of the optical spectrum analyzer is several seconds. In this time scale, the optical spectra of COLD in our condition were stable [17]. With this measurement system, one measurement takes approximately 45 minutes.…”

“…In the spectrum of the generated THz signal of CW-MLD, several discrete lines appeared. These lines correspond to the optical beat between the longitudinal modes of the MLD [17]. In this study, sub-THz waves were also generated at a constant frequency interval, which was equal to the frequency interval of the longitudinal modes of the laser.…”

“…The output from the semiconductor laser was split using beam splitter 1 (BS 1 ) and then fed back to the semiconductor laser by an external mirror M EX to obtain a chaotically oscillating laser diode (COLD). Low-cost, stable, and high-power THz waves can be generated using a COLD [16,17]. The effective reflectivity, R eff , was calculated using the following equation:…”

Stable optical beats in laser chaos near the threshold level for THz waves generation

“…In order to monitor the stability of the optical beats, a plasmonic photomixer was used to down-convert an 87 GHz signal from a frequency multiplier chain to a radio frequency (RF) signal [2]. The frequency of the RF signal equals the frequency difference of the 87 GHz signal and the laser optical beat frequency, which was ~88 GHz for the lasers used in our experiment.…”

Optimal Conditions for a Multimode Laser Diode with Delayed Optical Feedback in Terahertz Time-Domain Spectroscopy

“…Meanwhile, efforts are also being made to improve MMLD-based light sources using chaotically oscillating laser diodes (COLDs) [24][25][26]. COLDs, which involve the simple configuration of adding an external mirror to an MMLD resonator, have been reported to yield more stable and efficient THz-TDS outputs when compared to standalone MMLDs.…”