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Efficient Power Transfer via Induced Virtual Critical Coupling in an Overcoupled Silicon Nitride Microresonator

Jakob Hinney, Seunghwi Kim, Graydon J. K. Flatt, Ipshita Datta, Andrea Alù, Michal F. Lipson

Published Jan 1, 2023• 0 citations
Publisher

Abstract

We induce virtual critical coupling in an overcoupled photonic microresonator using complex-frequency pulses. We observe efficient cavity storage as an incident pulse of time constant 138 ps suppresses the resonant transmission from 0.58 to 0.11.
DOI
10.1364/cleo_at.2023.jth2a.69

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Abstract Critical coupling in integrated photonic devices enables the efficient transfer of energy from a waveguide to a resonator, a key operation for many applications. This condition is achieved when the resonator loss rate is equal to the coupling rate to the bus waveguide. Carefully matching these quantities is challenging in practice, due to variations in the resonator properties resulting from fabrication and external conditions. Here, we demonstrate that efficient energy transfer to a non-critically coupled resonator can be achieved by tailoring the excitation signal in time. We rely on excitations oscillating at complex frequencies to load an otherwise overcoupled resonator, demonstrating that a virtual critical coupling condition is achieved if the imaginary part of the complex frequency equals the mismatch between loss and coupling rate. We probe a microring resonator with tailored pulses and observe a minimum intensity transmission T=0.11T=0.11T=0.11 T = 0.11 in contrast to a continuous-wave transmission T=0.58T=0.58T=0.58 T = 0.58 , corresponding to 8 times enhancement of intracavity intensity. Our technique opens opportunities for enhancing and controlling on-demand light-matter interactions for linear and nonlinear photonic platforms.
Integrated nonlinear microring resonators are promising sources of bright twin-beams exhibiting intensity difference squeezing. To take advantage of the noise reduction of these quantum states, many applications require high squeezing levels. However, the attainable on-chip squeezing is constrained by the ratio of intrinsic to coupling loss, which is strongly related to design and fabrication limits. Here, we demonstrate a silicon nitride microring resonator engineered to enable a set of periodic strongly overcoupled resonances from which the estimated on-chip intensity difference squeezing is 11.8 dB, exceptionally high for an integrated device. Due to significant setup loss, we directly measure 1.4±0.2 dB of squeezing, corresponding to an on-chip level of 9.2±5.1 dB. In addition, the new, to the best of our knowledge, design inherently suppresses mode competition in the modes surrounding the twin-beams, enabling a constant high squeezing level up to moderate powers. These results represent a significant step toward the miniaturization of integrated devices whose performance benefits from surpassing the quantum noise limit using squeezed states, with particular relevance to sensing applications.
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We describe a dynamically tuned system capable of capturing light pulses incident from a waveguide in a pair of microcavities. We use coupled mode theory to design a method for determining how to tune the microcavity resonant frequencies. The results show that pulses can be captured almost completely, with arbitrarily small reflected power. We optimize the pulse capture bandwidth by varying the cavity coupling constants and show that the maximum bandwidth is comparable to the resonant-frequency tuning range. Our system may be implemented using refractive-index tuning in a 2-D silicon photonic crystal slab. Current technology would allow for capture of pulses with widths as low as ~100 ps, with a holding time limited only by cavity loss rates.