arXiv subjects

Gordon K. L. Wong

Publications and source records attributed to Gordon K. L. Wong.

8 recordsLinked to original sources

arXiv2026

Spatial delocalization of cold oscillators in hollow-core fibers

Trapped particles in hollow-core fibers enable long-range sensing, though advanced control of their in-fiber motion, such as multimodal cooling and squeezing, remains challenging. Here, we present optical interference-based adaptive techniques for controlling the motion of a fringe-trapped silica nanoparticle inside a fiber. After feedback-cooling its axial and radial motion, we induce axial delocalization (position anti-squeezing) via two complementary approaches. First, non-adiabatic fringe suppression expands the position variance by 11.83 ($\pm$0.7) dB to that of the initial cold-state while retaining Gaussian statistics. Second, multi-pass particle positioning at dark fringes increases the delocalization to 13.23 ($\pm$0.5) dB relative to the cold-state's variance via dark inverted optical potentials, in agreement with our Wiener stochastic model. Stronger delocalization produces non-Gaussian states of motion. Unlike prior inverted-trap implementations, our method requires neither auxiliary optical traps nor charged particles in Paul traps. Our results demonstrate fringe-trapped particles in hollow-core fibers as a versatile platform for long-range sensing and macroscopic quantum physics.

physics.optics↗

arXiv2026

Viscoelastic dynamics of nanoparticles optically trapped in moving fringe pattern in air-filled hollow-core fiber

We report optical trapping and transport of nanoparticles in a moving interference pattern in hollow-core photonic crystal fiber at atmospheric pressure, when competition between trapping and drag forces causes the particle velocity to oscillate as it is momentarily captured and accelerated by each passing fringe, followed by release and deceleration by viscous forces. As a result the average particle velocity is lower than the fringe velocity. We refer to this phenomenon as drag-trapping. An analytical model of the resulting motion shows excellent agreement with experiment. Additional control is possible by introducing an imbalance in the backward and forward powers. The high precision of this new technique makes it of interest for example in characterizing nanoparticles, exploring viscous drag forces in different gases and liquids, and temperature sensing.

physics.optics↗

arXiv2026

Optomagnetic forces on YIG/YFeO3 microspheres levitated in chiral hollow-core photonic crystal fibre

We explore a magnetooptomechanical system consisting of a single magnetic microparticle optically levitated within the core of a helically twisted single-ring hollow-core photonic crystal fibre. We use newly-developed magnetic particles that have a core of antiferromagnetic yttrium-ortho-ferrite (YFeO3) and a shell of ferrimagnetic YIG (Y3Fe5O12) approximately 50 nm thick. Using a 632.8 nm probe beam, we observe optical-torque-induced rotation of the particle and rotation of the magnetization vector in presence of an external static magnetic field. This one-of-a-kind platform opens a path to novel investigations of optomagnetic physics with levitated magnetic particles.

physics.optics↗

arXiv2025

Phase-adaptive cooling of fringe-trapped nanoparticles at room temperature in hollow-core photonic crystal fiber

Active feedback cooling of levitated dielectric particles is a pivotal technique for creating ultrasensitive sensors and probing fundamental physics. Here we demonstrate phase-adaptive feedback cooling of silica nanoparticles optically trapped in standing-wave potential formed by two co-linearly polarized counterpropagating diffraction-free guided modes in a hollow-core photonic crystal fiber at room temperature. Unlike standard laser intensity- or Coulomb force-based feedback, our approach modulates the relative optical phase between the counterpropagating fundamental modes proportionally to the particle's axial momentum. This generates a Stokes-like dissipative force which effectively damps the center-of-mass motion without introducing excess heating and can also work with uncharged particles. At 2 mbar air pressure, the axial center-of-mass temperature of a 195 nm silica particle is reduced by half upon application of the feedback and to 58.6 K at 0.5 mbar. The measured mechanical spectra agree well with our analytical model, validating the cooling mechanism. We envision this approach will open up pathways towards long-range, coherent control of mesoscopic particles inside hollow-core fibers, offering a fiber-integrated versatile platform for future quantum manipulation.

physics.optics↗

arXiv2022

Optical vortex Brillouin laser

Optical vortices, which have been extensively studied over the last decades, offer an additional degree of freedom useful in many applications, such as optical tweezers and quantum control. Stimulated Brillouin scattering, providing a narrow linewidth and a strong nonlinear response, has been used to realise quasi-continuous wave (CW) lasers. Here, we report stable oscillation of optical vortices and acoustic modes in a Brillouin laser based on chiral photonic crystal fibre, which robustly supports helical Bloch modes (HBMs) that carry circularly-polarized optical vortex and display circular birefringence. We implement a narrow-linewidth Brillouin fibre laser that stably emits 1st- and 2nd-order vortex-carrying HBMs. Angular momentum conservation selection rules dictate that pump and backward Brillouin signals have opposite topological charge and spin. Additionally, we show that when the chiral PCF is placed within a laser ring cavity, the linewidth-narrowing associated with lasing permits the peak of the Brillouin gain that corresponds to acoustic mode to be measured with resolution of 10 kHz and accuracy of 520 kHz. The results pave the way to a new generation of vortex-carrying SBS systems with applications in quantum information processing, vortex-carrying nonreciprocal systems.

physics.optics↗

arXiv2022

Nonreciprocal vortex isolator by stimulated Brillouin scattering in chiral photonic crystal fibre

Optical non-reciprocity, which breaks the symmetry between forward and backward propagating optical waves, has become vital in photonic systems and enables many key devices, such as optical isolators, circulators and optical routers. Most conventional optical isolators involve magneto-optic materials, but devices based on optical nonlinearities, optomechanically induced transparency and stimulated Brillouin scattering (SBS) have also been demonstrated. So far, however, they have only been implemented for linearly or randomly polarized LP01-like fundamental modes. Here we report a light-driven nonreciprocal isolator for optical vortex modes, based on topology-selective SBS in chiral photonic crystal fibre. The device can be reconfigured as an amplifier or an isolator by adjusting the frequency of the control signal. The experimental results show vortex isolation of 22 dB, which is at the state-of-the-art in fundamental mode isolators using SBS. This unique device may find applications in optical communications, fibre lasers, quantum information processing and optical tweezers.

physics.optics↗

arXiv2021

Stimulated Brillouin scattering in chiral photonic crystal fiber

Stimulated Brillouin scattering (SBS) has many applications, for example, in sensing, microwave photonics and signal processing. Here we report the first experimental study of SBS in chiral photonic crystal fiber (PCF), which displays optical activity and robustly maintains circular polarization states against external perturbations. As a result, circularly polarized pump light is cleanly back-scattered into a Stokes signal with the orthogonal circular polarization state, as is required by angular momentum conservation. By comparison, untwisted PCF generates a Stokes signal with an unpredictable polarization state, owing to its high sensitivity to external perturbations. We use chiral PCF to realize a circularly polarized continuous-wave Brillouin laser. The results pave the way to a new generation of stable circularly polarized SBS systems with applications in quantum manipulation, optical tweezers, optical gyroscopes and fiber sensors.

physics.optics↗

arXiv2017

Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre

Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon-phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with 1 μm diameter are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to 6 mbar gas pressure, the collective mechanical modes of the bound-particle array could be observed. The measured inter-particle distance at equilibrium and mechanical eigen-frequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.

physics.optics↗