32 research outputs found
High Dimensional Modulation and MIMO Techniques for Access Networks
Exploration of advanced modulation formats and multiplexing techniques
for next generation optical access networks are of interest as promising
solutions for delivering multiple services to end-users. This thesis addresses
this from two different angles: high dimensionality carrierless amplitudephase
(CAP) and multiple-input multiple-output (MIMO) radio-over-fiber
(RoF) systems.
High dimensionality CAP modulation has been investigated in optical
fiber systems. In this project we conducted the first experimental demonstration
of 3 and 4 dimensional CAP with bit rates up to 10 Gb/s. These
results indicate the potentiality of supporting multiple users with converged
services. At the same time, orthogonal division multiple access
(ODMA) systems for multiple possible dimensions of CAP modulation has
been demonstrated for user and service allocation in wavelength division
multiplexing (WDM) optical access network.
2 x 2 MIMO RoF employing orthogonal frequency division multiplexing
(OFDM) with 5.6 GHz RoF signaling over all-vertical cavity surface
emitting lasers (VCSEL) WDM passive optical networks (PONs). We have
employed polarization division multiplexing (PDM) to further increase the
capacity per wavelength of the femto-cell network. Bit rate up to 1.59 Gbps
with fiber-wireless transmission over 1 m air distance is demonstrated.
The results presented in this thesis demonstrate the feasibility of high
dimensionality CAP in increasing the number of dimensions and their potentially
to be utilized for multiple service allocation to different users.
MIMO multiplexing techniques with OFDM provides the scalability in increasing
spectral effciency and bit rates for RoF systems.
High dimensional CAP and MIMO multiplexing techniques are two
promising solutions for supporting wired and hybrid wired-wireless access
networks
Mode division multiplexing in radio-over-free-space-optical system incorporating orthogonal frequency division multiplexing and photonic crystal fiber equalization
Radio over free space optics (Ro-FSO) is a revolutionary technology for seamlessly integrating radio and optical networks without expensive optical fiber cabling. RoFSO
technology plays a crucial role in supporting broadband connectivity in rural and remote areas where current broadband infrastructure is not feasible due to geographical and economic inconvenience. Although the capacity of Ro-FSO can be increased by mode division multiplexing (MDM), the transmission distance and capacity is still limited by multipath fading and mode coupling losses due to atmospheric turbulences such as light fog, thin fog and heavy fog. The main intention of this thesis is to design MDM system for Ro-FSO for long and short haul
communication. Orthogonal frequency division multiplexing (OFDM) is proposed for long haul communication to mitigate multipath fading and Photonic Crystal Fiber (PCF) is proposed for short haul communication to reduce mode coupling
losses. The reported results of the proposed scheme for long haul communication show a significant 47% power improvement in deep fades from multipath propagation with the use of OFDM in MDM-Ro-FSO systems as compared to without OFDM. The results of the proposed scheme for short haul communication show 90.6% improvement in power in the dominant mode with the use of PCF in MDM-Ro-FSO as compared to without PCF. The reported results in the thesis show
significant improvement in Ro-FSO systems as compared to previous systems in terms of capacity and transmission distance under clear weather conditions as well as under varying levels of fog. The contributions of this thesis are expected to provide seamless broadband services in remote areas
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
Hybrid Dy-NFIS & RLS equalization for ZCC code in optical-CDMA over multi-mode optical fiber
For long haul coherent optical fiber communication systems, it is significant to precisely monitor the quality of transmission links and optical signals. The channel capacity beyond Shannon limit of Single-mode optical fiber (SMOF) is achieved with the help of Multi-mode optical fiber (MMOF), where the signal is multiplexed in different spatial modes. To increase single-mode transmission capacity and to avoid a foreseen “capacity crunch”, researchers have been motivated to employ MMOF as an alternative. Furthermore, different multiplexing techniques could be applied in MMOF to improve the communication system. One of these techniques is the Optical Code Division Multiple Access (Optical-CDMA), which simplifies and decentralizes network controls to improve spectral efficiency and information security increasing flexibility in bandwidth granularity. This technique also allows synchronous and simultaneous transmission medium to be shared by many users. However, during the propagation of the data over the MMOF based on Optical-CDMA, an inevitable encountered issue is pulse dispersion, nonlinearity and MAI due to mode coupling. Moreover, pulse dispersion, nonlinearity and MAI are significant aspects for the evaluation of the performance of high-speed MMOF communication systems based on Optical-CDMA. This work suggests a hybrid algorithm based on nonlinear algorithm (Dynamic evolving neural fuzzy inference (Dy-NFIS)) and linear algorithm (Recursive least squares (RLS)) equalization for ZCC code in Optical-CDMA over MMOF. Root mean squared error (RMSE), mean squared error (MSE) and Structural Similarity index (SSIM) are used to measure performance results
Enabling Technology in Optical Fiber Communications: From Device, System to Networking
This book explores the enabling technology in optical fiber communications. It focuses on the state-of-the-art advances from fundamental theories, devices, and subsystems to networking applications as well as future perspectives of optical fiber communications. The topics cover include integrated photonics, fiber optics, fiber and free-space optical communications, and optical networking
Time and frequency offsets in all optical OFDM systems
Ultra-high-speed data transmission (terabit-per-second per channel) is urgently required in
optical communication systems to fulfill the emerging demands of 3D multimedia applications,
cloud computing, and bandwidth-hungry applications. In one way by using singlecarrier
optical communication systems for the data transmission rates 1 Tb/s, we need the
high baud rate and/or the high-order modulation formats (i.e. 512-QAM, 1024-QAM). Another
way is to group the data carrying subcarriers without a guard bands (tightly spaced)
to form a superchannel which gives increase in channel capacity. In a superchannel, the
requirements of high-order modulation formats and high baud rates are relaxed. In an alloptical
orthogonal frequency division multiplexing (AO-OFDM) system, the subcarriers are
orthogonal and closely packed which gives more suitability to form superchannel. This thesis
focuses on the time and frequency offsets in AO-OFDM systems.
A theoretical model to investigate the performance of on-off-keying (OOK) modulated
AO-OFDM system is developed for analytical simulation. The analytical (statistical) model
considers the random characteristics of time and frequency offsets in adjacent subcarriers
as well as the common noise sources such as shot and thermal noises to calculate the interference
variances for evaluating the BER performance. The effects of time and frequency
offsets on the BER performance of AO-OFDM system is evaluated with the number of optical
subcarriers (NSC), receiver bandwidth (BWRX), and cyclic prefix (CP)
We further develop an analytical model to evaluate the performance of AO-OFDM system
with advanced modulation format (M-QAM) in the presence of time and frequency offsets,
and the performance is compared with numerical simulations of other emulation setups (oddand-
even subcarriers and decorrelated systems). The performance is investigated with NSC,
BWRX, and CP in AO-OFDM system. A delay-line interferometer based all-optical method
to reduce the effects of time and frequency offsets is proposed and evaluated.
Finally, performance of demultiplexed subcarriers from an optical discrete Fourier transform (O-DFT) in AO-OFDM system in the presence of chromatic dispersion and limited
modulation bandwidth is evaluated. The fiber Bragg grating (FBG) based passive device is
proposed to reduce the interference and the results are compared with existing method using
sampling gates. The proposed method using FBG for interference reduction provides a
cost-effective design of AO-OFDM system
FBG-Based Filtering Optical Clock and Data Recovery Enhancement for Optical Access Networks
Data transmission using optical fiber can be affected by nonlinear effects, dispersion, and crosstalk. These effects are causing the optical signal to be degraded. Optical clock and data recovery are necessary to synchronize and regenerate the affected signal and consequently achieving a good BER value. In this paper, a system with optical clock and data recovery function using FBG and FP-FBG filter technique is tested and analyzed using OptiSystem software. Eye diagram for both configurations is observed. Some parameters are also being manipulated such as the data rate and transmission distance to compare both FBG filtering effect. Clock data recovery signal with FBG filtering shows better performance compare to FP-FBG filtering at 10 Gbps
Orthogonal frequency division multiplexing for optical access networks
Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme with numerous advantages that has for years been employed as the leading physical interface in many wired and wireless communication systems. Recently, with advancements made in digital signal processing, there has been a surge of interest in applying OFDM techniques for optical communications. This thesis presents extensive research on optical OFDM and how it is being applied in access networks. With the aid of theoretical analysis, simulations and experiments, it is shown that the system performance of direct-detection optical OFDM (DD-OOFDM) in the presence of MZM non-linear distortion can be improved by proper biasing and selection of appropriate drive to the MZM. Investigations are conducted to illustrate how a variation in the number of subcarriers and the modulation format influences the sensitivity of the DD-OOFDM system to the MZM non-linear distortion. The possibility of improving the spectral efficiency by reduction of the width of the guard band is also investigated. This thesis also looks into the radio-over-fibre (RoF) transmission of Multiband OFDM UWB as a transparent and low-cost solution for distributing multi-Gbit/s data to end-users in FTTH networks. Due to relaxed regulatory requirements and the wide bandwidth available, UWB operation in the 60-GHz band is also considered for this FTTH application scenario. Four techniques for enabling MB-OFDM UWB RoF operation in the 60-GHz band are experimentally demonstrated. The impacts of various parameters on the performance of the techniques as well as the limitations imposed by fibre distribution are illustrated. Finally, a digital pre-distorter is proposed for compensating for the MZM non-linearity. Experimental demonstration of this digital pre-distortion in an UWB over fibre transmission system shows an increased tolerance to the amplitude of the driving OFDM signal as well as an increase in the optimum modulation index of the OFDM signal