A inteligibilidade da palavra em igrejas católicas, através de análises de carácter objectivo e subjectivo
Lencastre, Margarida Maria Mendes de Freitas de Queiroz e
1988-01-01
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237 records were found.
Using a recently developed inverse scattering layer-peeling algorithm and a modified stroboscopic grating writing technique, we have designed and successfully demonstrated novel grating devices, such as 50GHz-bandwidth dispersion compensators and square dispersionless filters, suitable for future high performance DWDM optical systems.
Fibre Bragg grating design and writing technologies offer unique flexibility and can provide a wide range of high performance all-fibre passive and active devices that can dramatically increase the performance of current and future telecommunication systems.
Optical microresonators of different configurations have been studied extensively over the last two decades and applied successfully in various fields in photonics, such as light-atom interactions, quantum electrodynamics, sensing and telecommunications. In general, they rely on light trapping in small volumes, primarily by whispering-gallery mode (WGM) excitation. The resulting high-Q resonances show significant internal intensity build-up and tremendous increase of the effective propagation lengths. These attributes facilitate a number of optical functions, such as low threshold lasing, efficient non-linear interactions, controlled dispersion, and make optical microresonators very good candidates as building blocks in miniaturised, highly-efficient integrated circuits.
In this presentation, we review various advanced microresonato...
A layer-by-layer analysis of the time delay of both reflected and transmitted light in one-dimensional photonic band-gap structures is developed and applied to uniform Bragg gratings. An effective Fabry-Pérot cavity is associated with every layer along the Bragg grating, multiple paths with a well defined layer traversal time are identified, and the average time is computed, introducing an appropriate weighting factor that accounts for interference between different paths. The analysis presented leads directly to a complex-valued time delay whose real part is shown to be equivalent to the classic phase time delay. Physical meaning is also given to the imaginary part. The local dwell time, interpreted as the average time spent by light in the layer independently of the final (transmitted or reflected) state, is proved analytically to be...
The effect of periodic loss on the performance of refractive-index gratings has been studied in detail. It is shown that the loss periodicity and relative phase strongly affects the symmetry of the reflection, transmission, and loss spectra. This asymmetry is explained successfully through consideration of the overlap between the standing-wave intensity distribution and the periodic loss pattern.
This paper studies the influence of random phase and amplitude fabrication errors on the performance of optical filters based on fiber Bragg gratings (FBG's). In particular, we analyze two effects of particular importance for optical communications: the excess crosstalk induced in apodized gratings commonly used in wavelength-division-multiplexing (WDM) systems, and the time-delay fluctuations that appear in chirped gratings employed to compensate the fiber dispersion. A statistical model is presented to explain these effects in terms of the coherence length of the grating fabrication procedure
The performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry (V2 /V1 ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should he optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet stringent telecom specifications
We demonstrate a novel application for DFB fibre laser temperature sensors, i.e. characterization of the pump induced temperature distribution along another DFB fibre laser, with high temperature and spatial resolution. This provides valuable information for improving DFB fibre laser performance.
Characterization of Optical Add Drop Multiplexers (OADMs) in High Bit Rate Wavelength Division Multiplexing (WDM) systems is presented using theoretical systems simulations. Firstly the interferometric full-coupler based OADM is modelled in various configurations using coupled mode theory. Implications of the inherent non-optimum overall performance of this device in conjunction with additional system issues like filter misalignments and cascading are analysed. Filters with typical degraded spectral characteristics in the Drop or Add action exhibits at least 0.15 dB higher Eye Opening Penalty (EOP) compared to filter with optimized flat spectral response. For this kind of OADMs we found also that the Intra-Band dispersion EOP performance in a cascaded 'Add-and-Drop operation' - in a single-wavelength-processing-node - for a specific OA...
The effects of time-delay-ripple period and amplitude in 25GHz and 100GHz filters for operation at 10Gb/s and 40Gb/s, respectively, are studied. It is shown that maximum transmission penalties occur at time-delay periods of ~75% of the -20dB data bandwidth.
