<p> This thesis deals with the limiting factors in the design of a long-haul fiber-optic communication
system, and the techniques used to suppress their resulting impairments. These
limiting factors include both linear and nonlinear effects, such as fiber chromatic dispersion
and the Kerr nonlinearity, and the modulator-induced nonlinearity. </p> <p> In Chapter 3, the conditional probability density function (PDF) of the received elect
rical signal given transmitted bit '1 '/'0' for a coherent fiber-optic transmission system
based on binary phase shift keying (BPSK) is mathematically derived. Both amplified
spontaneous emission (ASE) noise and fiber nonlinearity are taken into account . The
results show that the conditional PDF of given bit '1' or '0' is asymmetric when intrachannel
four-wave mixing (IFWM) is dominant, while it becomes nearly symmetric when
the variance of ASE is much larger than that due to IFWM. The standard deviation of
the received signal is calculated analytically. The system parameters, including optimum
dispersion map and pre-compensation ratio, are optimized by analytically calculating
variance of IFWM. Significant computation efforts can be saved using this approach as
compared to full numerical simulations of the nonlinear Schrodinger equation, without
losing much accuracy. </p> <p> In Chapter 4, an improved 4-f time-lens configuration is proposed. Fourier transform
(FT) and inverse Fourier transform (IFT) can be realized using time lenses such that
there is no need for time reversal at the end. A typical 4-f configuration consists of two
2-f systems and a temporal filter. The first 2-f system consisting of a time lens and two
dispersive elements produces the Fourier transform (FT) of the input signal. The temporal filter modifies the spectrum. The next 2-f system produces the inverse Fourier transform
(IFT). A wavelength division demultiplexer and a higher-order dispersion compensator
based on 4-f configuration are numerical implemented. One of the advantages of the
time-lens-based temporal filtering technique is that the transfer function of the temporal
filter can be dynamically altered by changing the input voltage to the temporal filter
(amplitude/phase modulator) and therefore, this technique could be used for dynamic
switching and multiplexing in optical networks. </p> <p> In chapter 5, a direct-detection optical orthogonal frequency division multiplexing
(DD-0-0FDM) is realized using time lenses. Typically, in OFDM systems, discrete
Fourier transform (DFT) is used at the transmitter and inverse discrete Fourier transform
(IDFT) is used at the receiver. In this chapter, it is proposed to use continuous Fourier
transform (FT) and inverse Fourier transform (IFT) using time lenses that replace DFT
and IDFT in the electrical domain. The third- and higher-order dispersive effects can be
considerably reduced using the proposed DD-0-0FDM scheme. </p> <p> In Chapter 6, a coherent optical orthogonal frequency division multiplexing (OFDM)
(C0-0-0FDM) scheme using time lenses is analyzed. The comparison of performance
between the proposed scheme and the conventional optical OFDM scheme using fast
Fourier transform (FFT) and inverse FFT in the electrical domain is made. Both the
Mach-Zehnder modulator (MZM) induced and fiber induced nonlinearities are investigated.
Results show that the time-lens-based C0-0-0FDM performs almost the same as
the FFT-based C0-0-0FDM when the message signal launched to MZM is low so that
MZM operates in the linear region. The nonlinearity of MZM degrades the performance
of FFT-based C0-0-0FDM drastically when the power of message signal becomes sufficiently
large, but only has negligible impact on the time-lens-based C0-0-0FDM. A
periodical driving voltage has been proposed to set up the time lens such that the maximally
required driving voltage level is kept low within the time frame. The advantages
using the time-lens-based C0-0-0FDM are that (i) FT can be done in optical domain
almost instantaneously, whereas the FFT in digital domain is slow and requires significant computational efforts, (ii) optical domain Fourier transform has a large bandwidth
(~THz) and therefore, FT /IFT can be performed at a large symbol rate. </p> <p> In Chapter 7, the digital backward propagation (DBP) has been studied both in
orthogonal frequency-division multiplexing ( OFDM) and single-carrier (SC) fiber-optic
transmission systems. 16 quadrature amplitude modulation (QAM) is used for both
systems with the bit rate of 100 Gbjs. The results show that OFDM and SC with
Nyquist pulses (SC-Nyquist) have a superior performance as compared to SC with raisedcosine
pulses (SC-NRZ) when the DBP is used. The impact of electrical filter bandwidth
and nonlinear phase/amplitude noise has also been investigated. The performance
of perfect-BP-based OFDM/SC initially improves when the electrical filter bandwidth
increases at high signal-to-noise ratio (SNR). The comparison of the effects of nonlinear
phase/amplitude noise among OFDM, SC-Nyquist and SC-NRZ systems is made
and it is shown that SC-NRZ systems significantly suffer from the effects of nonlinear
phase/amplitude noise, which explains the performance advantage of OFDM/SC-Nyquist
over SC-NRZ when the DBP used. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19402 |
| Date | 08 1900 |
| Creators | Yang, Dong |
| Contributors | Kumar, Shiva, Electrical and Computer Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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