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Results in Physics

Investigation of the dynamic features of a moveable ultrahigh-Q nanocavity

Jiahui Chen, Yuan‐Bao Zhang, Chao Li, Jun-Fang Wu

Published Jul 6, 2022• 1 citation

Abstract

Although the approach of forming an ultrahigh-Q nanocavity via local refractive index tuning in a PC waveguide was proposed a decade ago, it has not yet been employed to realize a moveable ultrahigh-Q nanocavity, so the dynamic physics related to a moving resonator remain unknown. Here we demonstrate that a dynamically-formed cavity is essentially moveable, so we can use this nanocavity to trap, store, and transfer signal photons, enabling greater photon control. For a high cavity moving speed, we find the trapped signal energy will radiate out of the moving cavity. We think this interesting phenomenon originates from Doppler-effect-induced resonant frequency split in a moving resonator and the accompanied Purcell-like effect, which has never been reported before, to the best of our knowledge. In addition, we present an analytical model to reveal why and how the trapping and storing processes are accompanied by significant spectral bandwidth compression and dynamic wavelength conversion, which are critical for achieving dynamic ultrahigh-Q nanocavity. This approach may find application in photon memories, quantum computing, and controllable light-matter interactions.

DOI: 10.1016/j.rinp.2022.105796

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We analytically and numerically investigate a signal light storing mechanism based on the controllable electromagnetically induced transparency (EIT) effect. We demonstrate that the isolation between the waveguide and the cavities cannot be achieved instantly as soon as the two cavities are tuned into resonance, no matter the index tuning rate is ultrafast or slow. We also investigate the temporal evolution features of the intracavity energy when the pulse during time is prolonged. We find many periodical oscillations of the trapped energy in both cavities, and they are entirely complementary. Our analysis shows that the adiabatic wavelength conversion in both cavities and a phase difference π between them play critical roles in this phenomenon.

Abstract A refractive index step, moving at the speed of light, can serve as a trap for weak light waves. Here we shed light on highly unusual features of such trapping, making it fundamentally different from conventional “resting” cavities. First, such trapping can be described as time-tapping rather than space-trapping. Trapping in time provides superior quality Q, but this quality does not anymore impose very narrow spectral lines, breaking thereby the fundamental time-bandwidth limit inherent to most traps of any physical nature. Although the trapped states are almost entirely disconnected from the outer world, a nonreciprocal connection channel involving resonant radiation can be opened and tunably manipulated. Nonreciprocity breaks the balance between the energy currents directed into the trap and back, allowing to load the trap faster than it is possible for reciprocal systems. Exotic, up to now unobserved in optics states such as halo states, and phenomena as anomalously huge delays in transmission occur naturally in a time trap. Beatings between the trapped-in-time modes provide a novel tool for ultrafast shaping of both spectral and temporal waveforms for arbitrary weak wavepackets, even for single photons. Altogether, this promises a highly eﬀicient platform for energy storage, pulse compression, waveform shaping and frequency conversion for ultrafast classical and quantum optics.

This article overviews our recent studies of ultrahigh-Q and ultrasmall photonic-crystal cavities, and their applications to nonlinear optical processing and novel adiabatic control of light. First, we show our latest achievements of ultrahigh-Q photonic-crystal nanocavities, and present extreme slow-light demonstration. Next, we show all-optical bistable switching and memory operations based on enhanced optical nonlinearity in these nanocavities with extremely low power, and discuss their applicability for realizing chip-scale all-optical logic, such as flip-flop. Finally, we introduce adiabatic tuning of high-Q nanocavities, which leads to novel wavelength conversion and another type of optical memories.

We demonstrate numerically that the wavelength conversion of light is possible by the simple dynamic refractive index tuning of an optical cavity in a photonic crystal. We also clarify the mechanism and conservation rule for this conversion process. In addition, we discuss the observability of this phenomenon in realistic cavities. Our results indicate that this linear adiabatic wavelength conversion process can be observed for various high-

Q

microcavities.

Multiwavelength optical storage is critical in signal processing and optical computing. However, so far, most of the proposed light storage systems support only a single working band. Here, we propose a multiwavelength light storage mechanism based on dynamic waveguide phase modulation in a system composed of several pairs of nanocavities side-coupled to a waveguide. Unlike methods based on modulating intrinsic cavity parameters, our approach dynamically manipulates the waveguide propagation phase by introducing local refractive index modulation on a single common waveguide section, triggering all coupled resonator subsystems for multiwavelength light control. This simple approach offers a promising venue for high-density on-chip optical buffering.