3,102 research outputs found
Noise suppression using optimum filtering of OCs generated by a multiport encoder/decoder
We propose a novel receiver configuration using an extreme narrow band-optical band pass filter (ENB-OBPF) to reduce the multiple access interference (MAI) and beat noises in an optical code division multiplexing (OCDM) transmission. We numerically and experimentally demonstrate an enhancement of the code detectability, that allows us to increase the number of users in a passive optical network (PON) from 4 to 8 without any forward error correction (FEC)
Electronic and photonic switching in the atm era
Broadband networks require high-capacity switches in order to properly manage large amounts of traffic fluxes. Electronic and photonic technologies are being used to achieve this objective both allowing different multiplexing and switching techniques. Focusing on the asynchronous transfer mode (ATM), the inherent different characteristics of electronics and photonics makes different architectures feasible. In this paper, different switching structures are described, several ATM switching architectures which have been recently implemented are presented and the implementation characteristics discussed. Three diverse points of view are given from the electronic research, the photonic research and the commercial switches. Although all the architectures where successfully tested, they should also follow different market requirements in order to be commercialised. The characteristics are presented and the architectures projected over them to evaluate their commercial capabilities.Peer ReviewedPostprint (published version
Optical code-division multiple access system and optical signal processing
This thesis presents our recent researches on the development of coding devices, the
investigation of security and the design of systems in the optical cod-division multiple
access (OCDMA) systems. Besides, the techniques of nonlinear signal processing used
in the OCDMA systems fire our imagination, thus some researches on all-optical signal
processing are carried out and also summarized in this thesis.
Two fiber Bragg grating (FBG) based coding devices are proposed. The first coding
device is a superstructured FBG (SSFBG) using ±π/2-phase shifts instead of
conventional 0/π-phase shifts. The ±π/2-phase-shifted SSFBG en/decoders can not only
conceal optical codes well in the encoded signals but also realize the reutilization of
available codes by hybrid use with conventional 0/π-phase-shifted SSFBG en/decoders.
The second FBG based coding device is synthesized by layer-peeling method, which
can be used for simultaneous optical code recognition and chromatic dispersion
compensation.
Then, two eavesdropping schemes, one-bit delay interference detection and
differential detection, are demonstrated to reveal the security vulnerability of differential
phase-shift keying (DPSK) and code-shift keying (CSK) OCDMA systems.
To address the security issue as well as increase the transmission capacity, an
orthogonal modulation format based on DPSK and CSK is introduced into the OCDMA
systems. A 2 bit/symbol 10 Gsymbol/s transmission system using the orthogonal
modulation format is achieved. The security of the system can be partially guaranteed.
Furthermore, a fully-asynchronous gigabit-symmetric OCDMA passive optical
network (PON) is proposed, in which a self-clocked time gate is employed for signal
regeneration. A remodulation scheme is used in the PON, which let downstream and
upstream share the same optical carrier, allowing optical network units source-free. An
error-free 4-user 10 Gbit/s/user duplex transmission over 50 km distance is reazlied.
A versatile waveform generation scheme is then studied. A theoretical model is
established and a waveform prediction algorithm is summarized. In the demonstration,
various waveforms are generated including short pulse, trapezoidal, triangular and
sawtooth waveforms and doublet pulse.
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In addition, an all-optical simultaneous half-addition and half-subtraction scheme is
achieved at an operating rate of 10 GHz by using only two semiconductor optical
amplifiers (SOA) without any assist light.
Lastly, two modulation format conversion schemes are demonstrated. The first
conversion is from NRZ-OOK to PSK-Manchester coding format using a SOA based
Mach-Zehnder interferometer. The second conversion is from RZ-DQPSK to RZ-OOK
by employing a supercontinuum based optical thresholder
Towards higher scalability of hybrid optical CDMA network
A novel approach for improving the number of simultaneous users in a hybrid OCDMAOTDMA network is proposed and analysed. OCDMA system is based on two-dimensional wavelength-hopping time-spreading codes with multi-wavelengths picosecond carriers. The scalability increase was achieved by adding a third dimension to separate OCDMA user groups within OTDMA time slots by assigning them into different wavelength bands. We have shown this will scale-up the system capacity proportionally to the number of assigned wavelength bands. A self-clocking all-optical time gate was then demonstrated as an effective means for suppressing the growing detrimental multi access interference noise resulted from this capacity increase
A Full-Duplex Diversity-Assisted Hybrid Analogue/Digitized Radio Over Fibre for Optical/Wireless Integration
A duplex Radio Over Fibre (ROF) ring architecture is proposed taking into account the constraints imposed by the cost of fibre laying and of the optical/electronic components, as well as the spectral efficiency and the duplex link performance. It has been shown that relying on Analogue ROF (AROF) and state-of-the-art Digitized ROF (DROF) architectures for downlink and uplink transmission, respectively, attains a high-integrity duplex performance. A sophisticated amalgam of Optical Carrier Suppression (OCS), Code Division Multiplexing (CDM), optical frequency multiplexing, Optical Carrier Reuse (OCR) and distributed antennas is conceived
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