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Chinese Optics Letters

Coverage of coherent output states in parallel-coupled dual-racetrack microresonators

Wei Jiang, Yating Zhou

Published Jan 1, 2016• 0 citations
Publisher

Abstract

Parallel-coupled dual-racetrack silicon microresonators can potentially be used for quadrature amplitude modulation. We analyze the evolution of the coverage of coherent output states of devices with varying device parameters. As the coupling constant increases, the coverage of coherent states initially improves then degrades, which is unexpected based on a prior preference for overcoupling. Increasing the quality factor generally improves the coverage. The influence of the refractive index modulation is found to saturate after reaching a certain level. Analytic formulas are developed to provide insight into the coverage evolution. These results are fairly robust against a small asymmetry of device parameters.

DOI
10.3788/col201614.102304

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Parallel-coupled dual-racetrack silicon microresonators can potentially be used for quadrature amplitude modulation. We analyze the evolution of the coverage of coherent output states of devices with varying device parameters. As the coupling constant increases, the coverage of coherent states initially improves then degrades, which is unexpected based on a prior preference for overcoupling. Increasing the quality factor generally improves the coverage. The influence of the refractive index modulation is found to saturate after reaching a certain level. Analytic formulas are developed to provide insight into the coverage evolution. These results are fairly robust against a small asymmetry of device parameters.
We demonstrate a high-brightness on-chip photon pair source based on a high-Q racetrackshaped silicon microresonator, achieving a quality factor of approximately 1.75×1051.75 \times 10^{5}1.75×105 and an on-chip photon pair generation brightness of 9.8MHz⋅mW−1⋅nm−19.8 \text{MHz} \cdot \text{mW}^{-1} \cdot \text{nm}^{-1}9.8MHz⋅mW−1⋅nm−1 .
In this thesis I study in detail the quantum dynamics of several nonlinear optical processes in microresonator systems. A Heisenberg-picture input-output formalism is developed from first principles that includes the effects of scattering losses and independent quality factors and coupling ratios for different resonances. The task of calculating the device output is then reduced to solving a set of driven, damped, ordinary differential equations for the resonator mode operators alone. This theoretical framework is used to study photon pair generation via spontaneous four-wave mixing in the weakly pumped regime, on which the effects of scattering losses are appraised. A more strongly driven regime is studied for continuous wave pumps, demonstrating when self- and cross-phase modulation and multi-photon pair generation become important, and their effects on the spectral and power scaling properties of the system are examined; A detuning strategy is presented that compensates for some of these effects. The results of the weak-pump regime are applied to study microresonator-based her- alded single photon sources. The impact of scattering losses is studied, revealing that typical systems suffer from low heralding efficiency due to these losses. A technique to improve heralding efficiency is presented through over-coupling the resonator-channel system, and a resultant trade-off between heralding rate and heralding efficiency is un- covered. Limitations to the spectral purity of the heralded single photon output for conventional microresonator systems are also analysed, and a more sophisticated cou- pling scheme presented to overcome the upper bound for spectral purity of 93% that exists in typical systems, permitting the generation of single photons with spectral pu- rity arbitrarily close to 100% without spectral filtering or sophisticated phase-matching techniques. The theory of quantum frequency conversion in microresonators using four-wave mix- ing is then developed in detail, and the spectral conversion probability and conversion efficiency studied. Efficiencies exceeding 90% using less than 100 mW of pump power are predicted to be achievable with current technology. A dressed mode picture is developed to better understand the conversion dynamics. Rabi-like spectral splitting and temporal oscillations of the intraresonator mean photon number are predicted, exhibiting a novel regime of strongly coupled photonic modes.
We investigate the dynamical evolution of quantum discord, entanglement and purity in an open quantum system of two coupled asymmetric harmonic oscillators interacting with a thermal environment. Using the Kossakowski-Lindblad master equation we analyze the time evolution starting with a squeezed vacuum state. In contrast to our previous study on entanglement evolution in asymmetric oscillators, the present work introduces XY-type position-position coupling together with a systematic joint analysis of quantum discord and purity alongside entanglement. We examine the combined effects of the squeezing parameter, asymmetry parameter, coupling constant, dissipation rate and temperature. We find that quantum discord and entanglement exhibit, in general, a non-monotonic decrease over time. Increasing temperature consistently accelerates the degradation of both quantum correlations and purity, whereas increasing dissipation accelerates the degradation of quantum correlations but leads to higher steady-state purity. Increasing the squeezing parameter provides a protective effect by enhancing initial correlations and prolonging entanglement survival time, while increasing the coupling constant leads to higher quantum correlations. The asymmetry parameter exhibits only a weak influence on the correlation evolution. Our analysis reveals that quantum discord demonstrates stronger resilience than entanglement, which can present more complex behaviour including entanglement sudden death and possible temporary revivals and re-suppressions. These findings provide valuable insights for developing robust quantum information protocols and strategies for preserving quantum correlations in realistic open quantum systems, with potential extensions to non-Markovian regimes and multi-mode architectures.
Silicon on insulator (SOI) waveguides are the most used waveguides in photonic components and devices, primarily because of their low losses and compatibility with complementary metal oxide semiconductor (CMOS) manufacturing. This compatibility enables the use of electronic fabrication facilities to produce photonic circuits. In SOI waveguides, most of the photonic mode is contained within the silicon core, while an exponentially decaying evanescent tail extends into the surrounding cladding. Racetrack-resonators are pivotal in advancing silicon photonics, enabling the creation of compact resonators that support high-quality factors (Q-factors). A typical racetrack resonator consists of an optical waveguide that loops back on itself, creating resonance when the optical path length corresponds to an integer multiple of the wavelength. In this paper, we introduce an optical gas sensor based on electromagnetically induced transparency (EIT), a quantum interference effect arising from the interaction of two nearby resonant modes. Our design features a double racetrack with varying radii that resonate at1.55μm1.55 \mu \mathrm{m}1.55μm. By placing the smaller racetrack inside the larger one, we achieve the EIT phenomenon, resulting in the absence of resonant spectral lines at the same wavelength and the emergence of two shifted resonance lines. This sharp and narrow transmission peak enhances gas detection accuracy, making this sensor a promising tool for environmental monitoring and industrial applications, where precise measurements of gas concentrations are essential.