808 resultados para OPTICAL-TRANSMISSION
Direction Dependent Transmission Characteristics of Dye Mixture Doped Polymer Optical Fibre Preforms
Resumo:
The direction dependant wavelength selective transmission mechanism in poly (methyl methacrylate)(PMMA) rods doped with C 540 dye and C 540:Rh.B dye mixture as a combination has been investigated. When a polished slice of pure C 540 doped polymer rod was used side by side with a C540:Rh B doped rod with acceptor concentration [A] = 7x10-4 m/l , we could notice more than 100% change in the transmitted intensity along opposite directions at the C 540, Rh B emission and the excitation wavelengths . A blue high bright LED emitting at a peak wavelength 465nm was used as the excitation source.
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The precision of quasioptical null-balanced bridge instruments for transmission and reflection coefficient measurements at millimeter and submillimeter wavelengths is analyzed. A Jones matrix analysis is used to describe the amount of power reaching the detector as a function of grid angle orientation, sample transmittance/reflectance and phase delay. An analysis is performed of the errors involved in determining the complex transmission and reflection coefficient after taking into account the quantization error in the grid angle and micrometer readings, the transmission or reflection coefficient of the sample, the noise equivalent power of the detector, the source power and the post-detection bandwidth. For a system fitted with a rotating grid with resolution of 0.017 rad and a micrometer quantization error of 1 μm, a 1 mW source, and a detector with a noise equivalent power 5×10−9 W Hz−1/2, the maximum errors at an amplitude transmission or reflection coefficient of 0.5 are below ±0.025.
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Molecular beam epitaxy growth of ten-period lattice-matched InAlN/GaN distributed Bragg reflectors (DBRs) with peak reflectivity centered around 400nm is reported including optical and transmission electron microscopy (TEM) measurements [1]. Good periodicity heterostructures with crack-free surfaces were confirmed, but, also a significant residual optical absorption below the bandgap was measured. The TEM characterization ascribes the origin of this problem to polymorfism and planar defects in the GaN layers and to the existence of an In-rich layer at the InAlN/GaN interfaces. In this work, several TEM based techniques have been combined.
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A new proposal to have secure communications in a system is reported. The basis is the use of a synchronized digital chaotic systems, sending the information signal added to an initial chaos. The received signal is analyzed by another chaos generator located at the receiver and, by a logic boolean function of the chaotic and the received signals, the original information is recovered. One of the most important facts of this system is that the bandwidth needed by the system remain the same with and without chaos.
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We discuss the long-distance transmission of qubits encoded in optical coherent states. Through absorption, these qubits suffer from two main types of errors, namely the reduction of the amplitude of the coherent states and accidental application of the Pauli Z operator. We show how these errors can be fixed using techniques of teleportation and error-correcting codes.
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Results of full numerical simulations of a guiding-centre soliton system with randomly birefringent SMF fibre are shown and analysed. It emerges that the soliton system becomes unstable even for small amounts of PMD.
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The transmission of a 10-Gb/s data stream was demonstrated experimentally over a practically unlimited distance in a standard single-mode fiber system using nonlinear optical loop mirrors as simple in-line 2R regenerators. Error-free propagation over 100 000 km has been achieved with terrestrial amplifier spacing. © 2004 IEEE.
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Collision-induced power jitter is theoretically and numerically examined in dispersion-managed wavelength-division-multiplexed optical soliton transmission systems. The variational method is mainly used to develop a time efficient jitter calculation approach. The power jitter causes a serious problem for a singly periodic dispersion managed line having almost zero average dispersion, which can be reduced by applying doubly periodic dispersion management.
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We investigate the use of nonlinear optical loop mirrors as saturable absorbers in picosecond soliton transmission systems. It is found that they allow short (1–5-ps) pulses to be propagated through chains of optical amplifiers spaced at intervals of typically 10 km. The loop mirror removes dispersive waves and stabilizes the peak amplitude of the soliton. An additional advantage is that the self-frequency shift of the soliton may be suppressed by bandwidth filtering without causing growth of dispersive waves at the center of the passband. The timing jitter and soliton interactions present in the scheme are also described.
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This thesis presents several advanced optical techniques that are crucial for improving high capacity transmission systems. The basic theory of optical fibre communications are introduced before optical solitons and their usage in optically amplified fibre systems are discussed. The design, operation, limitations and importance of the recirculating loop are illustrated. The crucial role of dispersion management in the transmission systems is then considered. Two of the most popular dispersion compensation methods - dispersion compensating fibres and fibre Bragg gratings - are emphasised. A tunable dispersion compensator is fabricated using the linear chirped fibre Bragg gratings and a bending rig. Results show that it is capable of compensating not only the second order dispersion, but also higher order dispersion. Stimulated Raman Scattering (SRS) are studied and discussed. Different dispersion maps are performed for all Raman amplified standard fibre link to obtain maximum transmission distances. Raman amplification is used in most of our loop experiments since it improves the optical signal-to-noise ratio (OSNR) and significantly reduces the nonlinear intrachannel effects of the transmission systems. The main body of the experimental work is concerned with nonlinear optical switching using the nonlinear optical loop mirrors (NOLMs). A number of different types of optical loop mirrors are built, tested and implemented in the transmission systems for noise suppression and 2R regeneration. Their results show that for 2R regeneration, NOLM does improve system performance, while NILM degrades system performance due to its sensitivity to the input pulse width, and the NALM built is unstable and therefore affects system performance.
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This thesis examines experimentally options for optical fibre transmission over oceanic distances. Its format follows the chronological evolution of ultra-long haul optical systems, commencing with opto-electronic regenerators as repeaters, progressing to optically amplified NRZ systems and finally solitonic propagation. In each case recirculating loop techniques are deployed to simplify the transmission experiments. Advances in high speed electronics have allowed regenerators operating at 10 Gbit/s to become a practical reality. By augmenting such devices with optical amplifiers it is possible to greatly enhance the repeater spacing. Work detailed in this thesis has culminated in the propagation of 10 Gbit/s data over 400,000 km with a repeater spacing of 160 km. System reliability and robustness are enhanced by the use of a directly modulated DFB laser transmitter and total insensitivity of the system to the signal state of polarisation. Optically amplified ultra-long haul NRZ systems have taken on particular importance with the impending deployment of TAT 12/13 and TPC 5. The performance of these systems is demonstrated to be primarily limited by analogue impairments such as the accumulation of amplifier noise, polarisation effects and optical non-linearities. These degradations may be reduced by the use of appropriate dispersion maps and by scrambling the transmitted state of signal polarisation. A novel high speed optically passive polarisation scrambler is detailed for the first time. At bit rates in excess of 10 Gbit/s it is shown that these systems are severely limited and do not offer the advantages that might be expected over regenerated links. Propagation using solitons as the data bits appears particularly attractive since the dispersive and non-linear effects of the fibre allow distortion free transmission. However, the generation of pure solitons is difficult but must be achieved if the uncontrolled transmission distance is to be maximised. This thesis presents a new technique for the stabilisation of an erbium fibre ring laser that has aUowed propagation of 2.5 Gbit/s solitons to the theoretical limit of ~ 18,000 km. At higher bit rates temporal jitter becomes a significant impairment and to aUow an increase in the aggregate line rate multiplexing in both time and polarisation domains has been proposed. These techniques are shown to be of only limited benefit in practical systems and ultimately some form of soliton transmission control is required. The thesis demonstrates synchronous retiming by amplitude modulation that has allowed 20 Gbit/s data to propagate 125,000 km error free with an amplifier spacing approaching the soliton period. Ultimately the speed of operation of such systems is limited by the electronics used and, thus, a new form of soliton control is demonstrated using all optical techniques to achieve synchronous phase modulation.
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We present the first experimental implementation of a recently designed quasi-lossless fiber span with strongly reduced signal power excursion. The resulting fiber waveguide medium can be advantageously used both in lightwave communications and in all-optical nonlinear data processing.
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We introduce a novel transmission technique of periodic in-line all-optical format conversion between return-to-zero and non-return-to-zero-like aimed at delaying the accumulation of format-specific impairments. A particular realization of this approach using in-line normal dispersion fibre-enhanced nonlinear optical loop mirrors at 40Gbit/s data rate is presented. © 2004 Optical Society of America.