1,721,102 research outputs found
Integrated planar Bragg grating sensors: Towards an oxygen sensor
No full textSensors play an important role in measuring changes in the environment. Optical sensors operating at well established telecoms wavelengths demonstrate many benefits over electronic sensors. These include immunity to EM interference, absence of spark risk in flammable environments and remote interrogation of large arrays over many tens or even hundreds of kms
Mapping phase and amplitude of optical field distributions in fiber Bragg gratings
No full textDevelopments in the technique of Near-field Scanning Optical Microscopy (NSOM) [1] have made possible the mapping of both amplitude and phase of electric fields in photonic devices using simple interferometry. Combined with heterodyne techniques, this gives very high sensitivity within the technologically important 1.5µm wavelength regime. We describe experiments that use this capability to study one of the most important telecommunications components, the fiber Bragg grating. Interferometric SNOM allows us to measure the amplitude and phase of the optical field within the fiber Bragg gratings directly. The evanescent fields, which are usually protected by the fiber cladding, are exposed by polishing off the cladding on one side of the fiber. These fields are measured using photon scanning tunneling microscopy (PSTM), and detection is achieved using a heterodyne fiber interferometer. The laser source is tunable across the first order stop band region of the grating. The low index contrast and high degree of perfection of the periodic structure, combined with its long length, mean that measurements are not dominated by out-of-plane scattering or scattering from the beginning and end of the grating, which have been problematic in many NSOM investigations of photonic crystals. The reflection spectrum of the fiber Bragg grating is complex, and shows bands due to the structure of the 1D photonic crystal formed by the refractive index variation along the core, as well as other bands due to the interaction of the core and cladding modes. Each of these bands has been studied by tuning the probe laser to the appropriate wavelength. The standing wave along the grating can be considered to be the sum of two counterpropagating waves. The application of heterodyne techniques allows us to deconvolve the amplitudes and relative phases of the two counterpropagating components, and show that they agree well with predictions based on grating theory [2]. In addition, the variation of the physical positions of field antinodes can be measured as a function of wavelength. As the laser wavelength is increased through the grating stop band, the antinode position is predicted to shift from the high index to the low index grating regions, a shift of -λ/4, or λ/2. As an example of what can be achieved using this mode of imaging, we have measured this position shift directly, and the composite image of field antinodes at wavelengths above and below the stop band shown in figure 1. This technique will be applicable to study the more complex structures possible in fiber gratings, such as deliberately introduced defects, or phase slips
Precision dicing of optical materials
Full text linkDuctile regime dicing has been used to machine a variety of optical materials to produce waveguides for lasers, multi-mode interference devices and non-linear devices. However, few papers discuss the properties of the machining, either qualitatively or quantitatively. In this work ductile regime dicing of germanium, Yttrium Aluminum Garnet (YAG), lithium niobate and silicon for photonic applications are reported. Machining parameters are discussed, surface micrographs shown, and surface roughnesses are calculated for each sidewall machined. The sidewall average surface roughnesses (Sa) were measured to be 2.1 nm for germanium, 3.5 nm for YAG, 7.9 nm for lithium niobate and 8.6 nm for silicon
Measurement of the local optical phase and amplitude in photonic devices using scanning near-field microscopy
No full textThis thesis presents the optical characterisation of various photonic devices using scanning near-field microscopy (SNOM). The SNOM technique has a unique capability of achieving a resolution beyond the diffraction limit. Placing the SNOM into the arm of a heterodyne interferometer also enables the measurement of both the optical phase and amplitude in the near infrared. In this work three different photonic devices are investigated. The optical field distribution within a fibre Bragg grating is investigated as a function of wavelength. This work details the direct observation of the spatial shift of the standing wave across the stop band of a fibre grating. The shift is an explicit feature of fibre Bragg gratings and has previously only been theoretically predicted. The thesis also details three analytical techniques for measuring the microscopic loss of planar or channel waveguides. Two of the techniques are experimentally tested. The techniques exploit a standing wave generated within the waveguide, the visibility of the standing wave provides sufficient information to determine to loss between two points. The present limitations of the techniques are presented. The SNOM technique has also been applied to the measurement of a large mode holey fibre. The work details the accurate characterisation of the mode at the end face of the fibre and as it propagates into free space. The results are compared to theoretically predicted modes
Planarised optical fiber composite using flame hydrolysis deposition demonstrating an integrated FBG anemometer
No full textThis paper reports for the first time a planarised optical fiber composite formed using Flame Hydrolysis Deposition (FHD). As a way of format demonstration a Micro-Opto-Electro-Mechanical (MOEMS) hot wire anemometer is formed using micro-fabrication processing. The planarised device is rigidly secured to a silicon wafer using optical quality doped silica that has been deposited using flame hydrolysis and consolidated at high temperature. The resulting structure can withstand temperatures exceeding 580K and is sensitive enough to resolve free and forced convection interactions at low fluid velocity
Review of photonic Hilbert transformers
No full textThis paper reviews the demonstrations of photonic Hilbert transformers (PHTs), describing their progress and recent developments. The physical operating principles of PHTs including fractional Hilbert transformers are discussed, together with device applications in all-optical signal processing. Versatile approaches to realize PHTs are discussed, e.g., discrete free space optics, fiber-based schemes and integrated planar geometry. The numerical designs and experimental performances of these PHTs are analyzed in terms of spectral quality, operating bandwidth, system integration, and mechanical and thermal stability. Recent developments of the monolithically integrated photonic Hilbert transform (HT) devices include directional couplers and planar Bragg gratings which allow all-optical single-sideband (SSB) suppression and sideband switching.Erratum: The author of Ref. [1] Frederick W K should be King F W
Novel technique for measuring dispersion and detuning of a UV written silica-on-silicon waveguide
No full textWe shall present a new method of measuring the dispersive properties of UV written waveguides in the silica-on-silicon platform used to fabricate planar Bragg gratings. The technique involves direct measurement of the modal refractive index of a waveguide produced in the material. The data obtained also provides additional information about the spectral range of Bragg grating inscription. This direct writing technique reported previously differs from fibre Bragg grating fabrication by the small spot size of the writing beam and permits detuning of the Bragg wavelength from 1250nm to 1625nm. The fabrication technique provides the exact period of the grating and thus interrogation of the gratings produces information on the effective index of the mode. A series of integrated gratings were fabricated in a direct UV written waveguide via the direct grating writing technique in order to measure the wavelength dependence of the refractive index of the material. The Sellmeier curve obtained is shown
Monitoring the deflection of a membrane using direct UV written planar Bragg gratings
No full textA thin (~100 µm thick) silica-on-silicon square membrane (10 mm x 10 mm) has been fabricated and its deflection monitored through a 100 Bragg grating array defined within the membrane
Evanescent field sensing in novel flat fiber
No full textRecently developed novel 'flat fiber' substrate promises flexible, long-haul integrated optical devices. Here, we present the first demonstration of one such device; an evanescent field sensor, based upon direct UV written Bragg gratings
Analysis of dispersion characteristics of planar waveguides via multi-order interrogation of integrated Bragg gratings
No full textWe demonstrate experimentally a simple technique to measure the wavelength-dependent effective refractive index of a waveguide utilizing integrated Bragg grating structures. A broadband measurement of the Bragg wavelengths yields the effective index of the waveguide and, thus, an accurate total dispersion relationship. An empirical calculation of the waveguide component of the dispersion yields both the waveguide and material dispersion components of the measured total dispersion. The technique allows direct measurement of the effective index of the waveguide and yields a zero dispersion wavelength at 1220.5 nm in our silica-on-silicon platform. Importantly, inclusion of second-order Bragg reflections improves the accuracy of modal refractive index for near-visible wavelengths
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