1,720,997 research outputs found
Applications of superstructure fibre Bragg gratings for optical code division multiple access and packet switched networks
No full textThis thesis describes the research on the implementation of all-optical code generation and recognition based on superstructure fibre Bragg grating (SSFBG) for use in Optical Code Division Multiple Access (OCDMA) systems and also in high-speed all-optical packet switched networks.These results highlight the precision and flexibility of the continuous grating writing process and show that the SSFBG technology represents a promising technology not just for OCDMA but an extended range of other pulse shaping, and associated optical processing applications such as required within optical packet switched networks
8-channel bi-directional spectrally interleaved OCDMA/DWDM experiment employing 16-chip four-level phase coding gratings
No full textWe demonstrate a full-duplex bi-directional OCDWD WDM experiment comprising 8-coded channels in each direction incorporating 16-chip, 20 Gchip/s quaternary phase coding gratings. Error free performance was obtained over a transmission distance of 44km without requiring dispersion compensation
All-optical modulation and demultiplexing systems with significant timing jitter tolerance through incorporation of pulse-shaping fiber Bragg gratings
Full text linkIn this letter, we demonstrate the use of a superstructured fiber Bragg grating to preshape optical pulses to obtain optimal operation of nonlinear all-optical switches. Specifically, we demonstrate the conversion of 2.5 ps soliton pulses into 20 ps rectangular pulses at the input to both fiber and semiconductor optical amplifier-based switches, and show that rectangular switching windows can be achieved thereby providing a 5-10-fold reduction in timing jitter sensitivity. Error free penalty free optical time-division-multiplexing switching was readily achieved over a ±7 ps timing mismatch range for the square pulse driven fiber nonlinear optical loop mirror switch versus a ±1 ps range for the switch driven directly with 2.5 ps laser pulses
All-optical TDM demultiplexing systems with significant timing jitter tolerance through incorporation of square pulse generating fiber Bragg gratings
No full textAs OTDM data rates increase, and the pulses used get correspondingly shorter, the synchronization requirements placed on the locally generated pulses used to control the switch operation can become a limiting practical issue. The key to reducing time jitter tolerance in such devices is to establish a rectangular temporal switching window [1]. This reduces the absolute accuracy for temporal bit alignment and provides optimal resilience to timing jitter-induced errors. In this paper we report the use of superstructured fiber Bragg gratings (SSFBGs) to convert the output of an actively mode-locked, 2.5ps fiber laser, a reliable source of short pulses of a well-defined soliton shape, to 20ps square pulses [2]. These pulses are then used to control the operation of two sorts of nonlinear switch. High quality, ~15-20ps rectangular switching windows are obtained, providing ±7ps, 15ps timing jitter tolerance, in switches based on both the Kerr effect in dispersion shifted fiber (nonlinear optical loop mirror (NOLM)), and on four-wave mixing in a semiconductor amplifier (SOA). This approach is particularly attractive for use with SOA based switching devices for which there is no ready way of shaping the switching window other than through direct control of the pulse shape
The use of nonlinear element for signal enhancement in a grating based all-optical pattern recognition system
No full textWe demonstrate an elementary grating-based OCDMA code generation and - recognition system incorporating a nonlinear optical loop mirror (NOLM) within the receiver. We show that the NOLM can act as a nonlinear processing element capable of reducing both the pedestal associated with conventional matched-filtering, and the width of the associated code-recognition pulse. The pedestal rejection allows for an improved code recognition signal to noise ratio relative to simple matched filtering alone and reduced intra- and inter-channel interference noise due to code overlap. The system benefits of using the NOLM are experimentally demonstrated under both single and multi user operation within a variety of both 7- and 63-chip, 160 Gchip/s code generation, recognition and transmission experiments based on the use of bipolar SSFBG coding:decoding pairs. Incorporation of the NOLM is shown to allow error-free, penalty free operation at data rates as high as 2.5Gbit/s under single user operation, and to provide error-free performance with reduced power penalty in two-user experiments. The narrowed pulse recognition signature offers major advantages in terms of the further all-optical processing of decoded signals, such as code regeneration and recoding. In our experiments we used a fibre based NOLM however, semiconductor based nonlinear devices should offer similar benefits
Self-routing edge-to-edge optical packet switched network based on superstructured fibre Bragg gratings
No full textA simple self-routing edge-to-edge optical packet switched network based on all-optical recognition of a 20 Gchip/s cascaded header using fibre Bragg gratings is presented. Self-routing of optical packets through two network switching nodes is demonstrated
A novel distributed ODCMA architecture based on simultaneous transmission of 16-chip OCDMA signals and clock pulses
No full textWe demonstrate a distributed bi-directional OCDMA architecture suitable for secured access networks, incorporating a fast 16-chip code-tunable encoder based on a uniform fibre Bragg grating and fixed-code superstructure fibre Bragg grating. This simple architecture eliminates the requirement for expensive laser transmitters at the subscribers' terminal
The use of fibre Bragg gratings for advanced optical signal processing
No full textThe development of ultrafast laser technology and high-speed fibre-optic communications, has resulted in the need to develop all-optical techniques for implementing many network operations. Superstructured fibre Bragg grating (FBG) technology has advanced to the point that the design and fabrication of passive filters of highly complicated optical responses is feasible. Thus, FBGs can be used for applications involving coherent control of short or ultrashort pulses, such as pattern generation and pulse shaping at high speeds. Key benefits offered by this filtering approach are full integration with fiberised systems, and precise control of the amplitude and phase of the filter responses. Due to their coherence properties, superstructured FBGs are monolithic devices, and consequently their operation does not require any external configurations (e.g. adjustable delay lines, etc.). We have demonstrated this powerful signal processing technique in a series of different experiments, including the generation of a 40GHz pulsed signal by repetition rate multiplication of 10GHz pulses, and shaping of solitons into square pulses. In this talk I will focus mainly on our more recent results, concerning pulse encoding and decoding schemes suitable for optical code-division multiple access (OCDMA) systems. Bipolar codes of a chip rate of 160Gchip/s are written in single superstructured FBGs. An incoming 10Gbit/s signal is encoded, transmitted and then decoded using a second, matched-filter FBG
Optical code division multiple access encoders and decoders based on superstructured fiber Bragg gratings
No full textWe report a range of elementary optical coding and decoding experiments employing superstructured fiber Bragg grating (SSFBG) components for optical code division multiple access (OCDMA) system. Firstly, we perform a comparative study of the relative merits of bipolar and unipolar coding:decoding schemes and show that the SSFBG approach allows high quality Unipolar and bipolar coding. A performance close to that theoretically predicted for 7-chip, 160 Gchip/s M-sequence codes is obtained. Secondly, we report the fabrication and performance of 63-chip, 160 Gchip/s, bipolar Gold sequence grating pairs. These codes are at least 8 times longer than those generated by any other scheme based on fiber grating technology so far reported. Finally, we describe a range of transmission system experiments for both the 7 and 63-bit bipolar grating pairs. Error-free performance is obtained over transmission distances of ~25km of standard fiber. In addition, we have demonstrated error-free/penalty-free performance under multi-user operation (two simultaneous users). Our results highlight the precision and flexibility of our particular grating writing process and show that SSFBG technology represents a promising technology not just for OCDMA but an extended range of other pulse shaping, optical processing applications
A 10 Gbit/s, 160 Gchip/s superstructured fibre Bragg gratings for OCDMA coding:decoding system
No full textOptical Code Division Multiple Access (OCDMA) is capable of providing future local area networks with higher connectivity, asynchronous multiple access and flexible bandwidth management. Much of the increased activity in this area has resulted from improvements in Fibre Bragg grating (FBG) fabrication technology driven mainly by the stringent requirements of DWDM. It is now possible to design and reliably fabricate superstructured fibre Bragg gratings (SSFBGs) with truly complex amplitude and phase responses [1], opening the possibility of using SSFBG components to perform fundamental OCDMA functions such as the coding and decoding of chip patterns described herein. In earlier work we demonstrated the generation of seven-chip, direct sequence, unipolar (amplitude) code OCDMA bits at 125 MHz using a SSFBG, and demonstrated optical pattern recognition using a matched SSFBG filter as a decoder [2]. In this paper we present results on upgrading the SSFBG approach to both far higher data rates (10Gbit/s) and far shorter chip-lengths (6.4ps) with far higher grating reflectivity (up to 50%) than previously demonstrated by fabricating bipolar (phase) coding and decoding SSFBGs using our continuous scanning technique. We present the results of BER measurements at 10 GBit/s on a decoded pulse sequence both before and after transmission through 25km of standard fibre which show there to be no noise-penalty associated with the either the coding:decoding process, or due to transmission of the coded pulse itself. Our experimental set-up is shown in Fig. 1a and comprises a 10 Gbit/s, ~2ps pulse transmitter (based on a regeneratively mode-locked, soliton fibre ring laser operating at 10 GHz), bipolar coding and decoding gratings, and an (optional) 25km standard fibre transmission span which had its dispersion compensated with a chirped FBG. We fabricated seven-chip M-sequence, bipolar coding and decoding gratings. The total grating length in each instance was 4.64mm (corresponding to a temporal code length of 44.8µs) and the individual chip width was 0.66mm (corresponding to a chip length of 6.4ps). The bipolar grating design is shown inset in Fig.1a, and is a pure phase-encoded structure with discrete n phase shifts at the (NRZ) chip transition boundaries. The experimental and theoretical plots are shown in Fig.lb. The agreement between the theoretical and experimental spectral responses of the bipolar SSFBG is seen to be excellent, highlighting the precision of our grating writing process. The decoder grating is essentially identical to the encoder grating other than it has a spatially-reversed refractive index superstructure. Note that all of gratings used in these experiments (including the dispersion compensating FBG) were written by appropriate W exposure through the same, uniform period phase mask. Since the SSFBGs are relatively weak and within the Fourier theory grating design limit, the impulse response of the grating in the time domain is given by the superstructure modulation profile used to write the grating. We examined the intensity autocorrelation functions of the incident 2ps pulses on reflection from the individual coding:decoding gratings, and found the profiles to be in excellent agreement with our theoretical predictions as shown in Fig.2a. This includes the decoder response to the code after it has propagated over the 25km dispersion-compensated transmission line, there is evidence of some correlation signal degradation, however the effects are slight, and in fact negligible in terms of overall system performance. The spectral response of the decoded signal is also compared to the theoretical plot as shown inset in Fig 2a. BER measurements were taken on the code:decode process, both with and without the 25km transmission. The results are summarised in Fig.2b where it is seen that no power penalty associated with code-decode process is observed in either instance. Eye diagrams for both the simple code:decode and transmitted code:decode case are shown inset within Fig.2b. No evidence of temporal features away from the main, chip-length long, correlation peak is observed as expected. In conclusion we have demonstrated high-quality, 10 Gbit/s bipolar OCDMA coding and decoding using superstructured FBGs with a code chip rate of 160 Gbit/s. Error-free operation with no power penalty was obtained for the coding:decoding process after propagation of the code through 25km of fibre. These results highlight the precision and flexibility of our particular grating writing process and point to further applications of SSFBGs in future high-speed optical networks. For example our results demonstrate the possibility of using SSFBGs for header recognition in 160 Gbit/s OTDM based networks. Fig 1 (a) Experimental set up. The pseudorandom sequence is 231-1 bits long. LCFBG - Linearly Chirped Fibre Bragg Grating. Fig. 1 (b) Bipolar grating reflectivity spectrum (theoretical and experimental). The refractive index phase superstructure is shown inset. The peak reflectivity of this grating was ~50%. Fig. 2 (a) Theoretical and experimental pulse intensity autocorrelation functions for the code:decode process both before and after transmission through 25km of (dispersion compensated) standard fibre. The theoretical and experimental frequency responses of the decoded signal are shown inset. Fig. 2 (b) BER curves for back-to-back (open circles), and decoded signal before (closed circles) and after (triangles) transmission; the corresponding eye diagrams (without and with transmission) are shown inset
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