Highspectralpurity frequencyagile roomtemperature sources in the terahertz spectrum are foundational elements for imaging, sensing, metrology, and communications. Here we present a chipscale optical parametric oscillator based on an integrated nonlinear microresonator that provides broadly tunable singlefrequency and multifrequency oscillators in the terahertz regime. Through opticaltoterahertz downconversion using a plasmonic nanoantenna array, coherent terahertz radiation spanning 2.8octaves is achieved from 330 GHz to 2.3 THz, with ≈20 GHz cavitymodelimited frequency tuning step and ≈10 MHz intracavitymode continuous frequency tuning range at each step. By controlling the microresonator intracavity power and pumpresonance detuning, tunable multifrequency terahertz oscillators are also realized. Furthermore, by stabilizing the microresonator pump power and wavelength, sub100 Hz linewidth of the terahertz radiation with 10^{−15}residual frequency instability is demonstrated. The roomtemperature generation of both singlefrequency, frequencyagile terahertz radiation and multifrequency terahertz oscillators in the chipscale platform offers unique capabilities in metrology, sensing, imaging and communications.
Advanced LIGO and other groundbased interferometric gravitationalwave detectors use high laser power to minimize shot noise and suspended optics to reduce seismic noise coupling. This can result in an optomechanical coupling which can become unstable and saturate the interferometer control systems. The severity of these parametric instabilities scales with circulating laser power and first hindered LIGO operations in 2014. Static thermal tuning and active electrostatic damping have previously been used to control parametric instabilities at lower powers but are insufficient as power is increased. Here we report the first demonstration of dynamic thermal compensation to avoid parametric instability in an Advanced LIGO detector. Annular ring heaters that compensate central heating are used to tune the optical mode away from multiple problematic mirror resonance frequencies. We develop a singlecavity approximation model to simulate the optical beat note frequency during the central heating and ring heating transient. An experiment of dynamic ring heater tuning at the LIGO Livingston detector was carried out at 170 kW circulating power and, in agreement with our model, the third order optical beat note is controlled to avoid instability of the 15 and 15.5 kHz mechanical modes. We project that dynamic thermal compensation with ring heater input conditioning can be used in parallel with acoustic mode dampers to control the optical mode transient and avoid parametric instability of these modes up to Advanced LIGO’s design circulating power of 750 kW. The experiment also demonstrates the use of three mode interaction monitoring as a sensor of the cavity geometry, used to maintain the
 NSFPAR ID:
 10195533
 Publisher / Repository:
 IOP Publishing
 Date Published:
 Journal Name:
 Classical and Quantum Gravity
 Volume:
 37
 Issue:
 20
 ISSN:
 02649381
 Page Range / eLocation ID:
 Article No. 205021
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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