Optical instability and self-pulsing in silicon nitride whispering gallery resonators

Abstract

We report time domain observations of optical instability in high Q silicon nitride whispering gallery disk resonators. At low laser power the transmitted optical power through the disk looks chaotic. At higher power, the optical output settles into a stable self-pulsing regime with periodicity ranging from hundreds of milliseconds to hundreds of seconds. This phenomenon is explained by the interplay between a fast thermo-optic nonlinearity within the disk and a slow thermo-mechanic nonlinearity of the structure. A model for this interplay is developed which provides good agreement with experimental data and points out routes to control this instability.

MHz-level self-sustained pulsation in polymer microspheres on a chip

“…The period of the pulsation is of the order of microsecond, much smaller than that in previous reports of mechanical movement involved SSP on silicon nitride microdisks (of the order of second) (Ref. 31), and PMMA-coated silica microtoroids (of the order of millisecond) (Ref. 32).…”

“…32 Generally, the SSPs in silica or silica/polymer microcavities have relatively small frequencies, usually at the Hz or kHz level. [30][31][32] In this work, we report SSP in a polymer microsphere on a silicon chip, excited by a fixed-frequency continuous laser, with a MHz-level oscillation frequency, much faster than previously reported silica or silica/polymer microcavities. A theoretical model is built to interpret the physical origin of the SSP, based on the thermal and optical dynamics of the cavity, by taking into account the modification of the thermal expansion coefficient and the temperature distribution within the mode volume.…”

“…[16][17][18][19] Studies have shown abundant nonlinear behaviors promoted by the highly localized optical field inside the microcavities, such as optical bi-stability, 20,21 deformation and abnormal oscillation [22][23][24][25][26][27] of the transmission spectra. Recently, periodic self-sustained pulsation (SSP) [28][29][30][31][32] in the transmission spectrum has been reported in various microcavity systems, excited by a fixed-frequency continuous laser, different from that excited by frequency-scanned lasers 26 or by pulsed lasers 27 in previous studies. For instance, very fast SSPs at the GHz level have been reported in silicon microcavities 28,29 resulting from coupled electron-photon dynamics.…”

“…Moreover, in silica microcavities or silica/polymer hybrid microcavities where there are no free carriers, SSPs have also been observed, formed by the interplay between thermo-optic effect and Kerr effect, 30 or between thermo-optic effect and mechanical motion. 31,32 The phenomenon of SSP in various WGM microresonators provides a simple optical oscillator, which for example can be used to generate continuous pulse lasers in Er-doped microcavities 33 and has also led to certain other sensing applications. 32 Generally, the SSPs in silica or silica/polymer microcavities have relatively small frequencies, usually at the Hz or kHz level.…”

Refractometric sensing of Li salt with visible-light Si3N4 microdisk resonators

“…27,28 Si 3 N 4 is a desirable material for optical sensing due to its CMOS compatibility, 29 transparency to visible light, and lower refractive index than silicon resulting in less mode confinement. 30 Si 3 N 4 refractometric sensors have been described previously in optical ring and slot geometries, 23,25,31 and with optimization have achieved sensitivities of 246 nm/RIU and detection limits of 5 × 10 −6 RIU.…”