The Experts below are selected from a list of 3183 Experts worldwide ranked by ideXlab platform
Gilberto Brambilla - One of the best experts on this subject based on the ideXlab platform.
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long period fiber Grating fabrication by high intensity femtosecond pulses at 211 nm
Journal of Lightwave Technology, 2005Co-Authors: Alexey I Kalachev, D N Nikogosyan, Gilberto BrambillaAbstract:Using high-intensity (110-200 GW/cm/sup 2/) 250-fs 211-nm laser pulses and a point-by-point technique, the efficiency of long-period Grating inscription in H/sub 2/-loaded standard telecom Corning SMF-28 and H/sub 2/-free photosensitive B-codoped Fibercore fibers was studied and compared with those at other existing recording methods (low-intensity 157-nm, 193-nm, 248-nm or high-intensity 264-nm fabrications). It was shown that at high-intensity 211-nm laser inscription, two-quantum photoreactions are responsible for long-period fiber Grating (LPFG) formation, which results in a significant photosensitivity enhancement in comparison with conventional low-intensity 248-nm exposure (by 45 times for SMF-28 fiber). It was found that the Grating Strength in the case of SMF-28 fiber, irradiated with high-intensity 211-nm pulses, reaches 28 dB, which is the highest value among all known photochemical approaches. The thermal studies of the recorded Gratings were also conducted.
Paul R. Stoddart - One of the best experts on this subject based on the ideXlab platform.
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A low-cost and temperature-insensitive fibre Bragg Grating sensor for monitoring localized strain concentrations
Measurement Science and Technology, 2009Co-Authors: C.e. Davis, H. C H Li, A. F. Dethlefsen, A Thompson, Paul R. StoddartAbstract:A simple, self-diagnostic strain sensor is described, based on a strongly reflective optical fibre Bragg Grating illuminated by a broadband source. The total reflected power from these Gratings is shown to be a function of the strain gradient experienced by the Grating. This is because a change in pitch within a section of the Grating results in the emergence of reflected energy in other spectral regions, without any significant reduction in the peak intensity at the Bragg wavelength. Thus, the presence of a localized strain can be inferred directly from an intensity measurement without the need for an optical filter or other more complex interrogation schemes. For spectrally flat light sources, the measurement is relatively insensitive to environmental temperature changes. The sensing mechanism can also be considered ‘self-diagnostic’ as a signal is returned by the Grating even under zero load unless the sensor has failed. Modelling results are presented to determine the minimum Grating Strength required to achieve this effect, while the technique has been experimentally verified by measuring the strain transfer on a loaded scarf repair joint at room and elevated temperatures. The scarf repair was loaded to failure and a reduction in strain transfer was observed as the failure grew along the bondline, in accordance with finite element modelling results.
J. Gonzalo Wangüemert-pérez - One of the best experts on this subject based on the ideXlab platform.
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Waveguide Grating coupler with subwavelength microstructures
Optics Letters, 2009Co-Authors: Robert Halir, Dan-xia Xu, Siegfried Janz, Íñigo Molina-fernández, Pavel Cheben, J. Gonzalo Wangüemert-pérezAbstract:We propose a silicon waveguide-fiber Grating coupler that uses a subwavelength microstructure to achieve a continuously variable Grating Strength yet can be fabricated using only a single etch step. By adjusting the subwavelength microstructure at every point along the Grating, the Grating coupler can be optimized to give high field overlap with the optical fiber mode and also minimize backreflections along the incident waveguide path. Our design example is optimized for quasi-TM mode in a silicon photonic-wire waveguide, as required for waveguide evanescent-field-sensing applications. A field overlap of up to 94% with a standard single-mode optical fiber (SMF-28) is achieved by coupler apodization. Backreflection from the Grating is reduced to ~0.1%, and the total predicted photonic wire to fiber coupling efficiency is 50%.
William Shieh - One of the best experts on this subject based on the ideXlab platform.
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low dmd few mode fiber with distributed long period Grating
Optics Letters, 2015Co-Authors: Jian Fang, William ShiehAbstract:We propose a distributed Grating-assisted few-mode fiber (DG-FMF) to reduce the differential mode delay (DMD). By introducing asymmetric long-period fiber Gratings with random exposure directions in a step-index few-mode fiber during fiber manufacture process, the strong random mode coupling is generated along the entire length of the fiber. Simulation results show that mean DMD in the DG-FMF can be reduced to less than 12 ns at a distance of 100 km with a period of 514 μm and Grating Strength of 1×10−6. The DMD reduction in our DG-FMF is guaranteed within the entire C-band, and in a wide temperature range from −20°C to +60°C.
Siegfried Janz - One of the best experts on this subject based on the ideXlab platform.
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highly efficient optical antenna with small beam divergence in silicon waveguides
Optics Letters, 2020Co-Authors: Pablo Ginelmoreno, Siegfried Janz, Robe Hali, A Ortegamonu, D Pereiramarti, Abdelfettah Hadijelhouati, Daniele Melati, Gonzalo J Wanguemertperez, I Molinafernandez, Jens H SchmidAbstract:Optical antennas are key components in optical phased arrays for light detection and ranging technology requiring long sensing range and high scanning resolution. To achieve a narrow beam width in the far-field region, antenna lengths of several millimeters or more are required. To date, such long antennas have been impossible to achieve in silicon waveguides because currently demonstrated technologies do not allow accurate control of Grating Strength. Here, we report on a new type of surface-emitting silicon waveguide with a dramatically increased antenna length of L=3.65mm. This is achieved by using a subwavelength metamaterial waveguide core evanescently coupled with radiative segments laterally separated from the core. This results in a far-field diffracted beam width of 0.025°, which is a record small beam divergence for a silicon photonics surface-emitting device. We also demonstrate that by using a design with L-shaped surface-emitting segments, the radiation efficiency of the antenna can be substantially increased compared to a conventional design, with an efficiency of 72% at the wavelength of 1550 nm.
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Waveguide Grating coupler with subwavelength microstructures
Optics Letters, 2009Co-Authors: Robert Halir, Dan-xia Xu, Siegfried Janz, Íñigo Molina-fernández, Pavel Cheben, J. Gonzalo Wangüemert-pérezAbstract:We propose a silicon waveguide-fiber Grating coupler that uses a subwavelength microstructure to achieve a continuously variable Grating Strength yet can be fabricated using only a single etch step. By adjusting the subwavelength microstructure at every point along the Grating, the Grating coupler can be optimized to give high field overlap with the optical fiber mode and also minimize backreflections along the incident waveguide path. Our design example is optimized for quasi-TM mode in a silicon photonic-wire waveguide, as required for waveguide evanescent-field-sensing applications. A field overlap of up to 94% with a standard single-mode optical fiber (SMF-28) is achieved by coupler apodization. Backreflection from the Grating is reduced to ~0.1%, and the total predicted photonic wire to fiber coupling efficiency is 50%.
