| Increased data traffic demands, along with a continual push to minimize cost per bit, have recently motivated a paradigm shift away from traditional on-off keying (OOK) fiber transmission links towards systems utilizing more advanced modulation formats. In particular, modulation formats that utilize the phase of the optical signal, including differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK) along with polarization multiplexing (Pol-MUX), have recently emerged as the most popular means for transmitting information over long-haul and ultra-long haul fiber transmission systems. DPSK is motivated by an increase in receiver sensitivity compared to traditional OOK. DQPSK is motivated by a doubling of the spectral efficiency, along with increased tolerance to dispersion and nonlinear distortions. Coherent communications has also emerged as a primary means of transmitting and receiving optical data due to its support of formats that utilize both phase and amplitude to further increase the spectral efficiency (bits/sec/Hz) of the optical channel, including quadrature amplitude modulation (QAM). Polarization multiplexing of channels is a straight forward method to allow two channels to share the same wavelength by propagating on orthogonal polarization axis and is easily supported in coherent systems where the polarization tracking can be performed in the digital domain. Furthermore, the forthcoming IEEE 100 Gbit/s Ethernet Standard, 802.3ba, provides greater bandwidth, higher data rates, and supports a mixture of modulation formats. In particular, Pol-MUX (D)QPSK has grown in interest as the high spectral efficiency allows for 100 Gbit/s transmission while still occupying the current 50 GHz/channel allocation of current 10 Gbit/s OOK fiber systems. In this manner, 100 Gbit/s transfer speeds using current fiber links, amplifiers, and filters may be possible.;In addition to advanced modulation formats, it is expected that optical signal processing may play a role in the future development of more efficient optical transmission systems. The hope is that performing signal processing in the optical domain may reduce optical-to-electronic conversion inefficiencies, eliminate bottlenecks and take advantage of the ultrahigh bandwidth inherent in optics. While 40 to 50 Gbit/s electronic components are the peak of commercial technology and 100 Gbit/s capable RF components are still in their infancy, optical signal processing of these high-speed data signals may provide a potential solution. Furthermore, any optical processing system or sub-system must be capable of handling the wide array of data formats and data rates that networks may employ. It is also worth noting that future networks may use a combination of data-rates and formats while it has been estimated that "we may start seeing the first commercial use of Terabit Ethernets by 2015". -Robert Metcalfe.;To this end, the work presented in this Ph.D. dissertation is aimed at addressing the issue of optical processing for advanced optical modulation formats. All optical multiplexing and demultiplexing of Pol-MUX and phase and QAM encoded signals at the 100 Gbit/s Ethernet standard is addressed. The creation and development of an extremely large continuously tunable all-optical delay capable of handling a variety of modulation formats and data rates is presented. As optical delays are viewed as a critical element to achieve efficient and reconfigurable signal processing, the presented delay line is also utilized to enable a tunable packet buffer capable of handling data packets of varying rate, varying size, and multiple modulation formats. |
