We present two new designs of optoacoustic waveguides supporting nonlinear Brillouin scattering (SBS). The first design, optimized for forward SBS, comprises a rectangular core supporting a low-loss optical mode, suspended in air by a series of transverse ribs. The ribs are engineered to exhibit a complete acoustic stopband and suppress the transverse leakage of acoustic waves. The second design we discuss here is a realization of an Anti-Resonant Reflecting Acoustic Waveguide, which are analogues of optical ARROWs. These waveguides, capable of co-localization and guiding of both the optical and GHz acoustic waves in simple, translationally invariant waveguides, are shown to support backwards SBS.
We fabricate a series of reconfigurable waveguide interferometers using laser machining techniques and charac- terize them classically. The 3D nature of the ultrafast laser writing technique allows for the fabrication of unique multi-arm interferometers not possible in planar platforms. We demonstrate selectivity between multiple phase shifters in a single interferometer by patterning the chip surface using picosecond laser ablation in a separate step. Microfluidic elements for making practical measurements on-chip are incorporated by machining channels within the substrate to interact with waveguide modes. Our results provide a path toward practical implementation of quantum metrology protocols requiring multiple interferometer arms and tunable phases.
We perform a rigorous characterisation of multiport waveguide circuits. These devices were fabricated using an ultrafast laser inscription process which permits uniquely three-dimensional circuit fabrication not possible using standard lithographic means. To infer device manipulation of an arbitrary input state of light (i.e. intensity and phase transformations), we perform device interrogation with coherent input states. We demonstrate that the inscription process, and output from coherent state interrogation combined with a maximum likelihood estimation algorithm, provide a rapid prototyping system for waveguide circuits acting on quantum states of light. This opens the way for more advanced multiport structures exploiting additional paths, input states and arbitrary phase relationships.
Femtosecond laser direct writing (FLDW) is developing rapidly but to date, there is no native optical isolator (needed to
mitigate reflections in any optical system) for the platform. As a step towards integrated glass isolators, we have
investigated FLDW in kHz and MHz pulse rate regimes for two magneto-optical glasses (TG20 and MR3-2) to
ultimately create one-way structures based on the Faraday effect.
Previously, we fabricated basic waveguides obtaining single-mode guidance at 632 nm (the Faraday effect is strongest
near the Tb3+ resonance at 485 nm) in both regimes. kHz regime waveguides were isotropic but had high propagation
loss due to associated photodarkening (which could be post-annealed). The propagation loss of the MHz regime
waveguides was acceptable due to lower photodarkening, but the waveguides were too narrow to confine light properly
because of the very strong focus of the writing beam.
To try to combine the lower loss with larger waveguide width, we created overlapping structures using a series of
superposed waveguides arranged in rings in MHz regime. The confinement in these multi-ring structures was indeed
improved and the structure propagation loss was intermediate between that of one-path waveguides created in kHz and
MHz regimes. For most other glasses, MHz FLDW systems operate in a heat-accumulation regime, producing
waveguide diameters much larger than the writing laser spot size and superposed waveguides that merge into one by
melting. Here, the sub-unit waveguides maintained their individual identity indicating that the heat-accumulation effect
was absent.
We discuss the hybrid integration of multiple components for the production of telecom band single photon sources. We implement four, on-chip, waveguide channels capable of producing four spatially separated collinear pairs of single photons. Using laser inscribed waveguide circuits and point-by-point bre Bragg gratings (FBG), we interface, separate and lter generated photon pairs. We propose using fast switches to actively route multiple heralded single photons to a single output producing an enhanced rate while maintaining a xed noise level.
Since the discovery, that a tightly focused femtosecond laser beam can induce a highly localized and permanent refractive index change in a wide range of dielectrics, ultrafast laser inscription has found applications in many elds due to its unique 3D and rapid prototyping capabilities. These ultrafast laser inscribed waveguide devices are compact and lightweight as well as inherently robust since the waveguides are embedded within the bulk material. In this presentation we will review our current understanding of ultrafast laser - glass lattice interactions and its application to the fabrication of inherently stable, compact waveguide lasers and astronomical 3D integrated photonic circuits.
With in-built advantages (high quantum efficiency and room temperature photostability1) for deployment in quantum technologies as a bright on-demand source of single photons, the nitrogen vacancy (NV) center is the most widely studied optical defect in diamond. Despite significant success in controlling its spontaneous emission2, the fundamental understanding of its photo-physics in various environments and host material remains incomplete. Studying NV photoemission from nanodiamonds on a glass substrate, we recently pointed out a disparity between the measured and calculated decay rates (assuming near unity quantum efficiency)3. This indicates the presence of some strong nonradiative influences from factors most likely intrinsic to nanodiamond itself. To obtain a clearer picture of the NV emission, here we remove the substrate contributions to the decay rates by embedding our nanodiamonds inside silica aerogel, a substrate-free environment of effective index n ~ 1.05.
Nanodiamond doped aerogel samples were fabricated using the “two-step” process4. Time-resolved fluorescence measurement on ~20 centers for both coverslip and aerogel configurations, showed an increase in the mean lifetime (~37%) and narrowing of the distribution width (~40%) in the aerogel environment, which we associate with the absence of a air/cover-glass interface near the radiating dipoles3. Finite difference time domain (FDTD) calculations showed the strong influence of the irregular nanodiamond geometry on the remaining distribution width. Finally a comparison between measurements and calculations provides an estimate of the quantum efficiency of the nanodiamond NV emitters as ~0.7. This value is apparently consistent with recent reports concerning the oscillation of the NV center between negative and neutral charge states5.
The development of an Yb-doped distributed Bragg reflector (DBR) waveguide laser fabricated in phosphate glass using the femtosecond laser direct-write technique is reported. The laser has the slope efficiency of 31% with the output power up to 81 mW at a pump power level of 378 mW. A theoretical model for the waveguide laser (WGL) is presented which gives emphasis to transverse integrals to investigate the energy distribution in a homogenously doped glass which is opposed to the fiber laser. The model was validated with experiments comparing a DBR WGL, and then used to study the influence of distributed rare earth dopants on the performance of such lasers. Approximately 15% of the pump power was absorbed by the doped “cladding” in the femtosecond laser inscribed Yb doped WGL case.
Focussing ultrashort laser pulses allows for inscribing fiber Bragg gratings (FBGs) directly into rare earth doped
fiber cores - without prior photosensitivity treatment. High reflective FBGs can be written into active Large
Mode Area (LMA) Fibers with 20 micron core diameter using a phase mask scanning technique. Here, we
demonstrate fiber Bragg gratings (FBGs), which cover only a fraction of the core. With this additional degree
of freedom it is possible to taylor the reflectivity of individual modes. We show for example how those FBGs
can be used in few mode LMA fibers to suppress reflections into higher order modes.
In this paper we demonstrate a simple temperature and strain discriminating sensor based on a single fibre Bragg grating
inscribed by a femtosecond laser via the point-by-point technique. These gratings exhibit strong and extensive cladding
mode structures and by simultaneously monitoring both the Bragg wavelength and a cladding mode spaced by ~ 40 nm
from the Bragg peak, as a function of both temperature and strain, it is possible to distinguish between the two effects
and potentially obtain and increased sensitivity over prior reports for similar systems. In preliminary experiments the two
parameters were determined with an accuracy of 1°C and 40 με respectively. Due to the close spectral separation of the
two peaks that were monitored, quick and simultaneously measurements of the two parameters was possible, allowing
for real time measurements of the temperature and strain and making the device practical for use in various applications.
All optical switching devices based on kerr-effect, where light switches light, are enjoying renewed interest. The dream of ultra compact devices operating at very low power and integrable on a chip is entering the realm of reality thanks to the advent of photonic crystal, enabling high Q/V ratio. We show that marrying photonic crystal and a new class of highly non linear material, Chalcogenide glasses, is a very promising way to achieve an all-optical chip. We describe the fabrication techniques we have developed for manufacturing two-dimensional Chalcogenide photonic crystal. Different types of photonic crystal resonances are investigated. Coupling technique to chalcogenide based photonic crystal waveguides and cavities via tapered nanowires is thoroughly described. We demonstrate resonant guiding in a chalcogenide glass photonic crystal membrane using a fano probe technique. We observe strong resonances in the optical transmission spectra at normal incidence, associated with Fano coupling between free space and guided modes. We obtain good agreement with modeling results based on three-dimensional finite-difference time-domain simulations, and identify the guided modes near the centre of the first Brillouin zone responsible for the main spectral features.
In this paper we review the fabrication and characterisation techniques of m icrostructured optical fibre (M OF) tapers, their fundam ental waveguiding properties and potential applications. W e fabricate photonic crystal fibre tapers without collapsing the air-holes, and confirm this along the taper with a non-invasive probing technique. We then describe the fundam ental property of such tapers associated with the leakage of the core m ode that leads to long wavelength loss. We also revisit the waveguiding properties in another form of tapered MOF photonic wires, which transition through waveguiding regimes associated with how strongly the mode is isolated from the external environment. We explore these regimes as a potential basis for evanescent field sensing applications, in which we can take advantage of controlled airhole collapse as an extra dimension to these photonic wires.
We apply the Finite-Difference Time-Domain algorithm to the problem of calculating modal loss in microstructured optical fibers. We use periodic boundary conditions in the longitudinal direction to isolate a mode that decays through transverse perfectly-matched layer
boundaries. The loss coefficient is extracted by a direct monitoring of the energy enclosed in the simulation domain. Predictions of the method are compared to results from beam propagation and multipole approaches, and finally the tool is applied to fibers containing elliptical air holes.
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