Recent advances in developing nonlinear optical techniques for processing serial digital information at high speed are reviewed. The field has been transformed by the advent of semiconductor nonlinear devices capable of operation at 100 gigabits per second and higher, well beyond the current speed limits of commercial electronics. These devices are expected to become important in future high-capacity communications networks by allowing digital regeneration and other processing functions to be performed on data signals “on the fly” in the optical domain.

https://science.sciencemag.org/content/sci/286/5444/1523.full.pdf

Nonlinear Optics for High-Speed Digital Information Processing.

We introduce a traffic model for circuit switched all-optical networks (AONs) which we then use to calculate the blocking probability along a path for networks with and without wavelength changers. We investigate the effects of path length, switch size, and interference length (the expected number of hops shared by two sessions which share at least one hop) on blocking probability and the ability of wavelength changers to improve performance. Our model correctly predicts unobvious qualitative behavior demonstrated in simulations by other authors.

Models of blocking probability in all-optical networks with and without wavelength changers

Semiconductor optical amplifiers are useful building blocks for all-optical gates as wavelength converters and OTDM demultiplexers. The paper reviews the progress from simple gates using cross-gain modulation and four-wave mixing to the integrated interferometric gates using cross-phase modulation. These gates are very efficient for high-speed signal processing and open up interesting new areas, such as all-optical regeneration and high-speed all-optical logic functions.

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Semiconductor optical amplifier-based all-optical gates for high-speed optical processing

The investigation of nonlinear wave phenomena has been one of the main direc tions of research in optics for the last few decades. Soliton concepts applied to the description of intense electromagnetic beams and ultrashort pulse propagation in various media have contributed much to this field. The notion of solitons has proved to be very useful in describing wave processes in hydrodynamics, plasma physics and condensed matter physics. Moreover, it is also of great importance in optics for ultrafast information transmission and storage, radiation propagation in resonant media, etc. In 1973, Hasegawa and Tappert made a significant contribution to optical soliton physics when they predicted the existence of an envelope soliton in the regime of short pulses in optical fibres. In 1980, Mollenauer et al. conducted ex periments to elucidate this phenomenon. Since then the theory of optical solitons as well as their experimental investigation has progressed rapidly. The effects of inhomogeneities of the medium and energy pumping on optical solitons, the interaction between optical solitons and their generation in fibres, etc. have all been investigated and reported. Logical devices using optical solitons have been developed; new types of optical solitons in media with Kerr-type nonlinearity and in resonant media have been described.

Optical Solitons

The processing of optical signals in the optical domain is an important issue resulting from the desire to take advantage of the full bandwidth of the optical fiber. In this paper, we present detailed investigations on a device, which utilizes a semiconductor laser amplifier in a loop mirror configuration (SLALOM). Different modes of operation are reported like nonlinear single pulse switching and two-pulse switching at different operation speeds (1-100 Gb/s). Furthermore, a number of applications of the SLALOM in photonic systems, like pulse shaping, decoding, retiming and time-division demultiplexing, are presented. In addition, the SLALOM can be used for an estimate of the linewidth enhancement factor /spl alpha/ and the carrier lifetime /spl tau//sub e/ in an SLA. >

SLALOM: semiconductor laser amplifier in a loop mirror

A device capable of demultiplexing Tb/s pulse trains that requires less than 1 pJ of switching energy and can be integrated on a chip is presented. The device consists of an optical nonlinear element asymmetrically placed in a short fiber loop. Its switching time is determined by the off-center position of the nonlinear element within the loop, and therefore it can use the strong, slow optical nonlinearities found in semiconductors, which all other fast demultiplexers seek to avoid. The switch's operation at 50 Gb/s is demonstrated, using 600-fJ control pulses. >

A terahertz optical asymmetric demultiplexer (TOAD)

The first demonstration of all-optical demultiplexing of TDM data at 250Gbit/s is reported. The demultiplexer, called a 'TOAD', is compact and requires sub-picojoule switching energy. Crosstalk measurements of pseudorandom data in adjacent, 4ps-width time slots, exhibit a BER of less than 10-9, with strong jitter immunity.

Demonstration of all-optical demultiplexing of TDM data at 250 Gbit/s

Bit error rate measurements were performed on a 50 Gbit/s optical time domain multiplexed system which utilized the newly developed terahertz optical asymmetric demultiplexer (TOAD) device as the front end of a receiver. Bit error rates of less than 10/sup /spl minus/9/ were measured when 800 fj control pulses were used to gate the demultiplexer. These measurements, which were made on a 50 Gbit/s peak line-rate train, also quantified the tolerance of the TOAD to signal-control pulse jitter. >

Performance of a 50 Gbit/s optical time domain multiplexed system using a terahertz optical asymmetric demultiplexer

We present an analysis of the optical loop mirror in which a nonlinear optical element is asymmetrically placed in the loop. This analysis provides a general framework for the operation of a recently invented ultrafast all-optical switch known as the terahertz optical asymmetric demultiplexer. We show that a loop with small asymmetry, such as that used in the terahertz optical asymmetric demultiplexer, permits low-power ultrafast all-optical sampling and demultiplexing to be performed with a relatively slow optical nonlinearity. The size of the loop is completely irrelevant to switch operation as long as the required degree of asymmetry is accommodated. This is therefore the first low-power ultrafast all-optical switch that can be integrated on a single substrate.

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Asymmetric optical loop mirror: analysis of an all-optical switch

An optical demultiplexer includes an optical loop having first and second terminals and a mid point A non-linear optical element is positioned in the loop at a distance Δx from the mid point A first coupler is positioned in the loop and has a gating pulse applied which causes a change in the optical property of the non-linear optical element from a first state to a second state A second coupler is optically coupled to the first and second terminals and has an input terminal for receiving a series of input optical pulses The second coupler responds by inducing, for each input pulse, a pair of counter-propagating pulses in the optical loop Control circuitry causes a gating pulse to be applied to the optical loop and to be timed to switch the non-linear optical element to from a first to a second state after one of the pair of counter-propagating pulses has passed through the non-linear optical element, but before the other counter-propagating pulse has reached the non-linear optical element In this manner, one counterpropagating pulse is affected by the second state of the non-linear optical element and the other counterpropagating pulse is not, thereby enabling a differential signal to exit from the output of the second coupler to a detector

Jason P. Sokoloff

Papers

A terahertz optical asymmetric demultiplexer (TOAD)

Demonstration of all-optical demultiplexing of TDM data at 250 Gbit/s

Performance of a 50 Gbit/s optical time domain multiplexed system using a terahertz optical asymmetric demultiplexer

Asymmetric optical loop mirror: analysis of an all-optical switch

Terahertz optical asymmetric demultiplexer