Celebrating the 20th anniversary of Optics Express, this paper reviews the evolution of optical fiber communication systems, and through a look at the previous 20 years attempts to extrapolate fiber-optic technology needs and potential solution paths over the coming 20 years. Well aware that 20-year extrapolations are inherently associated with great uncertainties, we still hope that taking a significantly longer-term view than most texts in this field will provide the reader with a broader perspective and will encourage the much needed out-of-the-box thinking to solve the very significant technology scaling problems ahead of us. Focusing on the optical transport and switching layer, we cover aspects of large-scale spatial multiplexing, massive opto-electronic arrays and holistic optics-electronics-DSP integration, as well as optical node architectures for switching and multiplexing of spatial and spectral superchannels.

Fiber-optic transmission and networking: the previous 20 and the next 20 years [Invited]

The Erbium-Doped Tiber Amplifier (EDFA) has had a profound impact on the design, operation and performance of transoceanic cable transmission, and is central to the expected proliferation of cable systems. Laboratory experiments have demonstrated 100 Gb/s over transoceanic distances using Wavelength Division Multiplexing (WDM) techniques. These large transmission capacity experiments have resulted from an increased understanding of the effects that can limit performance of WDM systems. Important strides have been made in areas of dispersion management, gain equalization, and modulation formats which have made possible the demonstration of large data transmission capacity. This paper reviews experimental techniques developed to improve the performance of long-haul WDM transmission systems based on the Non-Return-to-Zero (NRZ) format, and other non-soliton methods.

Wavelength Division Multiplexing in Long-Haul Transmission Systems

Wavelength division multiplexing shows great promise for the next generation of long-haul undersea cable transmission systems. WDM techniques will allow for greater transmission capacity and network flexibility compared to the present single-channel optical amplifier systems. The transmission of many WDM channels over transoceanic distances can be limited by a variety of phenomena, including the finite bandwidth of the erbium-doped fiber amplifier repeaters, the nonlinear interactions between channels, and the noise accumulation along the chain of amplifiers. Significant progress has been made over the past few years in understanding the nature of these impairments for long-distance transmission. This paper describes techniques used to transmit many WDM channels over transoceanic distances using the nonreturn-to-zero format and other nonsoliton methods. Data is presented for several WDM experiments including the transmission of 100 Gb/s (20 channels of 5 Gb/s) over 9100 km.

Wavelength division multiplexing in long-haul transmission systems

The work described in this thesis details the development of a multicore fibre device that can be used to optically trap multiple cells and particles. The optical trapping of multiple cells at close proximity allows for cell-to-cell interactions to be studied. Current methods available for creating arrays of traps are free space optical systems that use diffractive optics, laser scanning techniques or the interference of multiple beams to create the multiple traps. A fully integrated, fibre optic based, multiple particles, optical trapping device could be used in non-optical research facilities such as biological laboratories to aid with their research into cellular processes. In order to create the multiple traps, the distal end of the multicore fibre needs to be modified to induce a lensing effect. The multicore fibre device presented in this thesis was lensed in a fusion splicer; this refracts the outputs from the four cores to a common point in the far field where interference fringes are formed. The initial investigation demonstrated one-dimensional interferometric optical trapping through coupling light into two of the diagonal cores of the lensed multicore fibre. This produced linear interference fringes approximately 250 ± 25 μm from the end of the fibre with a fringe spacing of 2 ± 0.3 μm. The linear interference fringes were used to optically trap polystyrene microspheres with diameters of 1.3 μm, 2 μm and 3 μm in the high intensity regions of the fringes. Coupling into all four cores using a diffractive optical element produced an array of intensity peaks across the interference pattern with high visibility fringes greater than 80 %. Each intensity peak, spaced 2.75 μm apart could trap a single particle in two dimensions. The optical trapping of multiple microspheres and Escherichia coli bacterial cells was demonstrated proving that the lensed multicore fibre has the potential to be used to trap cells in biological experiments. The active manipulation of trapped 2 μm microspheres was also demonstrated through the rotation of the input polarisation to the multicore fibre. Finally, work towards creating a “turn-key” optical trapping device was demonstrated through the fabrication of a fully integrated multicore fibre device using an ultrafast laser-inscribed fan-out to couple light into each core. Single mode operation of the device was demonstrated at 1550 nm, using a weaker lensed MCF device. The two dimensional trapping of 4.5 μm polystyrene microspheres was shown in an array of peaks spaced 11.2 μm apart at a distance of 400 ± 25 μm from the end of the fibre.

Integrated multicore fibre devices for optical trapping

The fast-paced evolution of long-haul and high-bit-rate terrestrial and submarine optical transmission links requires powerful analysis tools that take into account all the relevant phenomena in the fiber. To provide such a tool, we developed a time-domain optical system simulation package, integrated in the TOPSIM simulation environment. The fiber simulation module makes use of the vector form of the propagation equations to account for the quasi-degenerate two-mode (the two polarizations) medium propagation characteristics. This way, all polarization-related effects and their interplay with the other linear and nonlinear phenomena in the fiber can be accurately modeled. In particular, the fiber third-order susceptivity, responsible for all major nonlinear effects, is expressed in its actual vector form, so that nonlinear polarization mode coupling could be accounted for. Conventional birefringence and PMD are generated using appropriate random models. A novel feature of the simulator is that it uses time-domain digital filters to simulate dispersion effects, as opposed to the usual FFT-based algorithms. This approach leads to more efficient computing for a wide range of bandwidth and dispersion values. We present the fiber simulation module in detail. As an example of the use of the simulation package, the analysis of a long-haul two-channel transoceanic WDM transmission system is presented.

A time-domain optical transmission system simulation package accounting for nonlinear and polarization-related effects in fiber

The TAT-12/13 Cable Network will provide a 10 Gb/s capacity between the United States, the United Kingdom, and France. By using ring switching equipment, this capacity is fully restorable within the network without dropping calls in the process. The undersea repeaters in this network use optical amplifier technology to transport a single 5 Gb/s optical signal on each fiber pair. With the upgrade potential already demonstrated, TAT-12/13's transport capacity may at least double before the end of its 25-year design life.

M. Colas

Papers

The TAT-12/13 Cable Network