1,721,134 research outputs found
Opportunities in chemical sensing
No full textThis talk will introduce the technology being commercialised by Stratophase Ltd, which has been developed at the Optoelectronics Research Centre, University of Southampton. The company produces sources and sensors, with the sources based on periodically poled lithium niobate, and sensors utilising planar Bragg gratings for measuring refractive index. The underlying technology will be reviewed, and then applications and opportunities will be discussed in the field of chemical sensing. The nonlinear materials produced by Stratophase - periodically poled lithium niobate allow phasematching for nonlinear generation at virtually any wavelengths within the transmissions range of Lithium Niobate (approx 450nm to 4.5 microns - with operation under certain regimes at wavelengths up to 7 microns). The company is also commercialising planar Bragg grating waveguide sensors. These provide a highly integrated approach to refractive index sensing. The technology offers a number of unique features including remote fibre access, high sensitivity, self calibration, multiwavelength operation. Results will be reviewed for various phase change systems including liquid crystals and condensation, water, ice
Self-assembled axicon lens in integrated optical fiber
No full textThis work reports the fabrication of an integrated axicon lens within a monolithic fiber-upon-planar format. The lens is self-assembled around a tapered optical fiber during flame hydrolysis planarization. The formed lens approximates an oblate axicon that upon launch generates a quasi-Bessel beam, guided in the planar optical layer of the substrate. Experimental observations are theoretically concurred using Fourier-based beam propagation
Planar waveguide water state sensor allowing detection of supercooling
No full textA sensor believed to be the first truly integrated optical sensor demonstrating the detection of the liquid-solid phase transition of water is presented. The condensation, freezing, melting and evaporation of water are all detected with a planar silica Bragg grating operating in the 1.5 micron telecommunications window. Additionally, use of the sensor allows recognition of supercooled liquid at temperatures below the melting point of water. The device is fabricated by direct UV writing with simultaneous definition of the grating, a method inherently suited to integration with other technologies. The Bragg grating is exposed and water is allowed to condense over it. Interaction with the evanescent field causes small changes in effective index (5x10-6) which can be detected, a sufficient sensitivity to identify the phase transitions of water clearly
Investigation into bulk optical Bragg deflectors based on an electro-optically induced grating in periodically poled lithium niobate
No full textMany solutions exist for making laser modulators including acousto-optic (AO) and bulk electro-optic (EO) devices. However, another class of modulators based on Bragg diffraction in periodically poled materials offers the potential to overcome disadvantages inherent in the more conventional types, such as low efficiency in the infra-red and high drive voltages. These devices are an extension of early work on grating based EO devices, for example those by Hammer and Barros & Wilson, but by making use of periodic poling they allow additional design freedom. This in turn allows fast switching, high efficiency and simple construction as demonstrated in periodically poled lithium niobate at 633nm
Electro-optically controlled TIR switching in domain-engineered LiNbO<sub>3</sub>
No full textWe have developed a novel electro-optically addressable total internal reflection (TR) switch in a sample of Limos that has been engineered to have a sharp boundary between two anti-parallel domain regions [1]. Such a switch can provide numerous advantages including ease of fabrication, the possibility of high contrast ratios (TIR is a 100% efficient process), relatively low drive voltages, and a wavelength dependence that is superior to other electro-optic devices such as Pockels cells. The LiNbO3 sample is z-cut, and has been patterned and electric-field poled to produce equal areas of oppositely oriented domain regions. The boundary region should ideally be very smooth, and free from residual poling-induced strain. In our case we observe a static index difference at the boundary, this affects the choice of angle for the grazing incidence beam and hence the contrast achievable experimentally. When an external electric field is applied to this boundary, equal magnitude refractive index changes of opposite sign will occur between the adjacent domain regions. If the value of index change is sufficiently large TIR can occur for the incident beam, thereby leading to switching of beam direction at the boundary from transmission to reflection. A schematic for the switch can be seen below in figure 1. (Schematic of switch.) Light incident on the boundary at an angle that is less than the angle for TIR will be transmitted through it. If however the light is incident on the boundary at angles greater than the TIR angle then it will be reflected with a theoretical efficiency of 100%. As the device consists of anti-parallel regions within a single electro-optic composite crystal the incident beam will only see a change in refractive index when a suitable field is applied. We will discuss results achieved for electro-optically modified reflectivity versus applied electric field, for light of s and p polarisations, and wavelengths in the visible and the near I.R. Initial results have already shown a contrast ratio of greater than 20dB which we expect to be improved with the optimization of annealing, manufacturing and design parameters.To conclude, we have constructed a domain engineered electro-optic total internal reflection switch in a sample of LiNbO3. This novel switching approach can be further improved and optimized, but already shows a good switching contrast ratio and the possibility for practical device implementation
Gouy phase compensation in quasi-phase matching
Full text linkIn any focussed nonlinear interaction the focus induced phase shift, known as the Gouy phase shift, provides an imperfection in phase matching for any linearly invariant material. However, using an appropriately designed quasi-phase matched structure it is theoretically possible to compensate for the deleterious effects of the Gouy phase shift, allowing a symmetric frequency response and tighter optimal focussing than in a uniform material
Direct refractive index measurement technique to observe waveguide dispersion
No full textMeasuring the dispersion characteristics of a planar waveguide is typically difficult due to the short lengths of waveguides involved. Traditional dispersion measurement techniques were developed in fibre [1] and bulk glass [2], and thus do not take into account the intricacies of the short planar waveguide. The fibre techniques typically require far more material than is available in a short planar waveguide, resulting in an imprecise measurement. The bulk measurement techniques do not take into account the specific structure and dimensions of the waveguide under test, so again do not provide a realistic interpretation of the dispersion characteristics of a specific waveguide
Planarised optical fiber composite using flame hydrolysis deposition demonstrating an integrated FBG anemometer
Full text linkThis 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
Planar micromachined glass cantilevers utilising integrated Bragg Fabry-Perot cavities
No full textHere we demonstrate a glass cantilever based on a unique micromachining and etching approach, combined with UV written Bragg gratings. We shall also discuss the increase in sensitivity by using two Bragg gratings to form Fabry-Pérot cavity. Cantilevers are in ultra sensitive force sensors used in applications such as Atomic Force Microscopy, mass sensing and acoustic transducers
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