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J. Stewart Aitchison

Publications and source records attributed to J. Stewart Aitchison.

11 recordsLinked to original sources
arXiv2025

Noise-Induced Limits on Responsivity and SNR for Nonlinear Exceptional Point Sensing

Exceptional points (EPs) have been suggested for ultra-sensitive sensing because the eigenfrequency splitting grows as the nth-root of a perturbation, suggesting divergent responsivity. In ideal linear devices, however, this responsivity gain is reconciled by a matching divergence in the quantum shot-noise floor, so the net signal-to-noise ratio remains unchanged. Recent work has extended this argument to nonlinear devices, such as above-threshold lasers, predicting other divergences at an EP that is shifted by the interplay of noise and saturation effects. Here we analyze a system of two coupled saturable resonators and show analytically that a self-consistent treatment of fluctuation dynamics removes these divergences entirely. Islands of instability arise in the parameter space surrounding the EP due to the coupling of phase noise into the amplitude dynamics, dictating a maximum responsivity and maximum noise that can be experimentally observed. Stochastic Langevin simulations of the full nonlinear system corroborate our analytical results down to zero detuning.

physics.optics↗
arXiv2024

Responsivity and Stability of Nonlinear Exceptional Point Lasers with Saturable Gain and Loss

The responsivity of perturbation sensing can be effectively enhanced by using higher-order exceptional points (HOEPs) due to their nonlinear response to frequency perturbations. However, experimental realization can be difficult due to the stringent parameter conditions associated with these points. In this work, we study an EP laser composed of two coupled nonlinear resonators that uses nonlinearity to simplify these tuning requirements. This system demonstrates a distinct cube-root response in the steady-state lasing frequency, with a constant of proportionality that depends on the distribution of linear and saturable gain and loss. This design freedom enables several orders of magnitude higher responsivity than systems with a single nonlinear resonator, which have been previously explored. Maximizing responsivity also improves the robustness of sensing performance against parametric errors. These features are derived from coupled mode theory and further supported by steady-state ab initio laser theory (SALT) results at several nonlinear EPs. Through linear stability analysis, we also identify regions of instability within the class-A regime that arise due to mode competition, which can be induced by asymmetric passive losses. In the class-B regime, we show that the interplay between gain dynamics and detuning can lead to restabilization at slow relaxation rates or higher inter-resonator coupling rates. This regime could be used to increase the maximum achievable responsivity of the system.

physics.optics↗
arXiv2017

Polarization-entangled photon pair sources based on spontaneous four wave mixing assisted by polarization mode dispersion

Photonic-based qubits and integrated photonic circuits have enabled demonstrations of quantum information processing (QIP) that promises to transform the way in which we compute and communicate. To that end, sources of polarization-entangled photon pair states are an important enabling technology, especially for polarization-based protocols. However, such states are difficult to prepare in an integrated photonic circuit. Scalable semiconductor sources typically rely on nonlinear optical effects where polarization mode dispersion (PMD) degrades entanglement. Here, we directly generate polarization-entangled states in an AlGaAs waveguide, aided by the PMD and without any compensation steps. We perform quantum state tomography and report a raw concurrence as high as 0.91$\pm$0.01 observed in the 1100-nm-wide waveguide. The scheme allows direct Bell state generation with an observed maximum fidelity of 0.90$\pm$0.01 from the 800-nm-wide waveguide. Our demonstration paves the way for sources that allow for the implementation of polarization-encoded protocols in large-scale quantum photonic circuits.

quant-ph↗
arXiv2016

An Efficient and Compact Excitation of Surface Plasmons Using a Si Gable Tip

We propose a novel technique to efficiently excite a surface plasmon polariton (SPP) mode at a gold-glass interface by exploiting the near field excitation of an engineered high index (silicon) gabled tip at the telecom wavelengths. The proposed structure can theoretically convert 49% of the input optical power to a SPP mode. The device is compact, it will facilitate the on-chip excitation of the SPP, its fabrication is compatible with the standard Si fabrication processes, and as such, it is expected to be useful in the design of future integrated sensors.

physics.optics↗
arXiv2016

Correlated photon pair generation in AlGaAs nanowaveguides via spontaneous four-wave mixing

We demonstrate a source of correlated photon pairs which will have applications in future integrated quantum photonic circuits. The source utilizes spontaneous four-wave mixing (SFWM) in a dispersion-engineered nanowaveguide made of AlGaAs, which has merits of negligible two-photon absorption and low spontaneous Raman scattering (SpRS). We observe a coincidence-to-accidental (CAR) ratio up to 177, mainly limited by propagation losses. Experimental results agree well with theoretical predictions of the SFWM photon pair generation and the SpRS noise photon generation. We also study the effects from the SpRS, propagation losses, and waveguide lengths on the quality of our source.

physics.optics↗
arXiv2016

Low-power continuous-wave four-wave mixing wavelength conversion in AlGaAs-nanowaveguide microresonators

We experimentally demonstrate enhanced wavelength conversion in a Q=7500 deeply etched AlGaAs-nanowaveguide microresonator via degenerate continuous-wave four-wave mixing with a pump power of 24 mW. The maximum conversion efficiency is -43 dB and accounts for 12 dB enhancement compared to that of a straight nanowaveguide. The experimental results and theoretical predictions agree very well and show optimized conversion efficiency of -15 dB. This work represents a step toward realizing a fully integrated optical devices for generating new optical frequencies.

physics.optics↗
arXiv2014

Photonic Integrated Devices for Nonlinear Optics

We review our recent progresses on frequency conversion in integrated devices, focusing primarily on experiments based on strip-loaded and quantum-well intermixed AlGaAs waveguides, and on CMOS-compatible high-index doped silica glass waveguides. The former includes both second- and third-order interactions, demonstrating wavelength conversion by tunable difference-frequency generation over a bandwidth of more than nm, as well as broadband self-phase modulation and tunable four-wave mixing. The latter includes four-wave mixing using low-power continuous-wave light in microring resonators as well as hyper-parametric oscillation in a high quality factor resonator, towards the realization of an integrated multiple wavelength source with important applications for telecommunications, spectroscopy, and metrology.

physics.optics↗
arXiv2012

Low-voltage broadband hybrid plasmonic-vanadium dioxide switches

Surface plasmon polaritons can substantially reduce the sizes of optical devices, since they can concentrate light to (sub)wavelength scales. However, (sub)wavelength-scale electro-optic plasmonic switches or modulators with high efficiency, low insertion loss, and high extinction ratios remain a challenge due to their small active volumes. Here, we use the insulator-metal phase transition of a correlated-electron material, vanadium dioxide, to overcome this limitation and demonstrate compact, broadband, and efficient plasmonic switches with integrated electrical control. The devices are micron-scale in length and operate near a wavelength of 1550 nm. The switching bandwidths exceed 100 nm and applied voltages of only 400 mV are sufficient to attain extinction ratios in excess of 20 dB. Our results illustrate the potential of using phase transition materials for highly efficient and ultra-compact plasmonic switches and modulators.

physics.optics↗
arXiv2007

Generation of slow intense optical solitons in a resonance photonic crystal

We demonstrate interesting and previously unforeseen properties of a pair of gap solitons in a resonant photonic crystal which are predicted and explained in a physically transparent form using both analytical and numerical methods. The most important result is the fact that an oscillating gap soliton created by the presence of a localized population inversion inside the crystal can be manipulated by means of a proper choice of bit rate, phase and amplitude modulation. Developing this idea, we are able to obtain qualitatively different regimes of a resonant photonic crystal operation. In particular, a noteworthy observation is that both the delay time and amplitude difference must exceed a certain level to ensure effective control over the soliton dynamics.

physics.optics↗
arXiv2005

Gap soliton gating, dissociation, and retrieval via defect mode excitation in a resonant photonic crystal

We consider the interaction within a bunch of two coherent optical pulses in a one dimensional, resonant photonic crystal which includes a defect produced by a coherent pump. Using numerical methods, the defect is shown to provide a selective reversible trap for a gap soliton mediated by the long-range coupling. This opens up new opportunities for signal transmission control and light localization.

nlin.PS↗