We investigate geometries for efficient coupling of single ions to fiber-coupled light fields for applications in quantum sensing, quantum metrology, and quantum information processing. Specifically, we discuss the integration of fiber-tip microcavities into radio-frequency ion traps. The distortions of the trapping fields induced by the presence of the optical fibers are simulated for a range of ion trap geometries and the most promising arrangements are identified. Finally, we investigate the use of fiber-tip microcavities with non-spherical mirrors for enhanced ion-light coupling at the center of the trap by appropriate shaping of the cavity modes.
We have demonstrated Raman frequency conversion and supercontinuum light generation in a hollow core Kagomé fiber filled with air at atmospheric pressure, and developed a numerical model able to explain the results with good accuracy. A solid-state disk laser was used to launch short pulses (~6ps) at 1030nm into an in-house fabricated hollow core Kagomé fiber with negative core curvature and both ends were open to the atmosphere. The fiber had a 150 THz wide transmission window and a record low loss of ~12 dB/km at the pump wavelength. By gradually increasing the pulse energy up to 250 μJ, we observed the onset of different Kerr and Raman based optical nonlinear processes, resulting in a supercontinuum spanning from 850 to 1600 nm at maximum input power. In order to study the pulse propagation dynamics of the experiment, we used a generalized nonlinear Schrödinger equation (GNLSE). Our simulations showed that the use of a conventional damping oscillator model for the time-dependent response of the rotational Raman component of air was not accurate enough at such high intensities and large pulse widths. Therefore, we adopted a semiquantum Raman model for air, which included the full rotational and vibrational response, and their temperature-induced broadening. With this, our GNLSE results matched well the experimental data, which allowed us to clearly identify the nonlinear phenomena involved in the process. Aside from the technological interest in the high spectral density of the supercontinuum demonstrated, the validated numerical model can provide a valuable optimization tool for gas based nonlinear processes in air-filled fibers.
While hollow core-photonic crystal fibres are now a well-established fibre technology, the majority of work on these speciality fibres has been on designs with a single core for optical guidance. In this paper we present the first dual hollow-core anti-resonant fibres (DHC-ARFs). The fibres have high structural uniformity and low loss (minimum loss of 0.5 dB/m in the low loss guidance window) and demonstrate regimes of both inter-core coupling and zero coupling, dependent on the wavelength of operation, input polarisation, core separation and bend radius. In a DHC-ARF with a core separation of 4.3 μm, we find that with an optimised input polarisation up to 65% of the light guided in the launch core can be coupled into the second core, opening up applications in power delivery, gas sensing and quantum optics.
UV generation via four-wave-mixing (FWM) in optical microfibres (OMFs) was demonstrated. This was achieved by exploiting the tailorable dispersion of the OMF in order to phase match the propagation constant of the four frequencies involved in the FWM process. In order to satisfy the frequency requirement for FWM, a Master Oscillator Power Amplifier (MOPA) working at the telecom C-band was connected to a periodically poled silica fibre (PPSF), producing a fundamental frequency (FF) at 1550.3 nm and a second harmonic (SH) frequency at 775.2 nm. A by-product of this second harmonic generation is the generation of a signal at the third harmonic (TH) frequency of 516.7 nm via degenerate FWM. This then allows the generation of the fourth harmonic (FH) at 387.6 nm and the fifth harmonic (5H) at 310nm via degenerate and nondegenerate FWM in the OMF.The output of the PPSF was connected to a pure silica core fibre which was being tapered using the modified flame brushing technique from an initial diameter of 125 μm to 0.5 μm. While no signal at any UV wavelength was initially observed, as the OMF diameter reached the correct phase matching diameters, signals at 387.6 nm appeared. Signals at 310 nm also appeared although it is not phase matched, as the small difference in the propagation constant is bridged by other nonlinear processes such as self-phase and cross phase modulation.
We present the design and fabrication of a dual air-bridge waveguide structure integrated with MEMS functionality. The structure is designed to function as a tunable optical buffer for telecommunication application.
The optical buffer structure is based on two parallel waveguides made of high refractive index material with subwavelength dimensions. They are suspended in air, and are separated by a sub-micron air gap. Due to the fact that the size of the waveguides is much smaller than the wavelength of light that propagates in the structure, a significant fraction of the optical mode is in the air gap between the waveguides. By changing the size of the air gap using MEMS techniques, we can vary this fraction and hence the effective refractive index of the waveguide structure, thus generating tunable optical delay.
The optical buffer structure was grown on an InP substrate by molecular beam epitaxy, and the device layer was made of InGaP. An InGaAs layer was sandwiched between the device layer and the substrate to serve as a sacrificial layer. The sub-micron waveguides, their supports in the form of side pillars with tapered shapes in order to minimize optical losses, and the MEMS structures were patterned using electron beam lithography and plasma etching. Electrodes were integrated into the structure to provide electrostatic actuation. After the sample patterning, the waveguide structure was released using HF etch. Our simulations predict that by varying the waveguide separation from 50 nm to 500 nm, we could achieve a change in propagation delay by a factor of two.
We present the design and fabrication of a tunable optical buffer device based on III-V semiconductor platform for
telecommunication applications. The device comprises two indium phosphide suspended parallel waveguides with cross
sectional dimension of 200 nm by 300 nm, separated by an air gap. The gap between the waveguides was designed to be
adjustable by electrostatic force. Our simulation estimated that only 3 V is required to increase the separation distance
from 50 nm to 500 nm; this translates to a change in the propagation delay by a factor of 2. The first generation of the
suspended waveguide structure for optical buffering was fabricated. The sample was grown on an InP substrate by
molecular beam epitaxy. The waveguide pattern is written onto a 300 nm thick InP device layer by electron beam
lithography and plasma etching. Electrodes were incorporated into the structure to apply voltages for MEMS actuation.
We investigate theoretically and experimentally the possibility of electrostatic actuation of nanomechanical optical fibers with integrated electrodes. The fiber has two optically guiding cores suspended in air by thin flexible membranes. This fiber structure allows for control of the optical properties via nanometer-range mechanical core movements. The electrostatic actuation of the fiber is generated by electrically charged electrodes embedded in the fiber cladding. Fiber designs with one to four electrodes are analyzed and, in particular, a quadrupole geometry is shown to allow for all-fiber optical switching in a 10cm fiber with an operating voltage of 25 - 30V. A multi-material fiber draw technique is demonstrated to fabricate a fiber with well-defined dual core structure in the middle and four continuous metal electrodes in the cladding. The fabricated fiber is analyzed and compared with the modeled requirements for electrostatic actuation.
We present a scattering model which enables us to describe the mechanical force, including the velocity dependent
component, exerted by light on polarizable massive objects in a general one-dimensional optical system. We show
that the light field in an interferometer can be very sensitive to the velocity of a moving scatterer. We construct
a new efficient cooling scheme, 'external cavity cooling', in which the scatterer, that can be an atom or a moving
micromirror, is spatially separated from the cavity.
We report recent advances in the development of fibers for the delivery and generation of both single-mode and heavily
multimode laser beams as well as recent progress in fibers for supercontinuum generation in spectral regimes spanning
the visible to mid-IR.
Whispering gallery modes of a microdisk resonator are useful for the optical detection of single rubidium and cesium atoms near the surface of a substrate. Light is coupled into two high-Q whispering-gallery modes of the disk which can provide attractive and/or repulsive potentials, respectively, via their evanescent fields. The sum potential, including van der Waals/Casimir-Polder surface forces, may be tuned to exhibit a minimum at distances on the order of 100 nm from the disk surface. Simultaneously optically trapping and detecting is possible, with the back-action of an atom held in this trap on the light fields being suffciently strong to provide a measurable effect. Atom trapping and detection depend on a variety of system parameters and experimental realizations differ for different atoms.
We report the generation of white light comprising red, green, and blue spectral bands from a frequency-doubled
fiber laser in submicron-sized cores of microstructured holey fibers. Picosecond pulses of green light are launched
into a single suspended core of a silica holey fiber where energy is transferred by an efficient four-wave mixing
process into a red and blue sideband whose wavelengths are fixed by birefringent phase matching due to a slight
asymmetry of the structure arising during the fiber fabrication. Numerical models of the fiber structure and
of the nonlinear processes confirm our interpretation. Finally, we discuss power scaling and limitations of this
white light source.
The Q-factor of the optical nanowire microcoil resonator is calculated and compared for different geometries. The results suggest that the Q-factor is very sensitive to the coupling conditions and high-Q resonators can be obtained more easily when the geometry of the nanowire microcoil resonator or its coupling contour has a bi-conical profile.
We investigate simultaneous optical trapping and optical detection of a single Rb atom near the
surface of a toroidal microdisk. Light is coupled into two high-Q whispering-gallery modes of the
disk which provide attractive and repulsive potentials, respectively, via their evanescent fields. The
sum potential including van-der-Waals and Casimir-Polder surface forces exhibits a minimum at
distances of the order of 100 nm from the disk surface. The back-action of an atom held in this trap on the light fields is sufficiently strong to provide a measurable effect. We discuss atom trapping
and detection properties in dependence on a variety of system parameters.
The anomalous linewidth behavior in a DFB fiber laser is investigated. It is shown that not only does the linewidth deviate drastically from the Schawlow-Townes linewidth formula by increasing with pump and laser power, but it also varies significantly with the pumping configuration used. These results have potentially important implications for the design and operation of such fiber lasers.
We investigate the bound and evanescent fields of the optical whispering gallery modes which are supported by a toroid microcavity and which may be used for a wide range of applications. Results of simulations using finite-difference time domain solutions of Maxwell's equations are compared with semi-analytical solutions based on coupled mode theory. Key parameters such as resonance frequencies, transmittance characteristics, coupling efficiencies, and bending/scattering losses are analyzed as a function of experimental variables such as size, distance, and fabrication roughness. Finally, the feasibility of single-atom detection is discussed.