Wide vector solitons in systems with time- and space-modulated nonlinearities

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Stable and mobile excited two-dimensional dipolar Bose-Einstein condensate solitons

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Demonstration of the spatial separation of the entangled quantum sidebands of an optical field

Quantum optics experiments on bright beams are based on the spectral analysis of field fluctuations and typically probe correlations between radio-frequency sideband modes. However, the extra degree of freedom represented by this dual-mode picture is generally ignored. We demonstrate the experimental operation of a device which can be used to separate the quantum sidebands of an optical field. We use this device to explicitly demonstrate the quantum entanglement between the sidebands of a squeezed beam.

Many-body quantum dynamics of polarization squeezing in optical fibers

We report new experiments that test quantum dynamical predictions of polarization squeezing for ultrashort photonic pulses in a birefringent fiber, including all relevant dissipative effects. This exponentially complex many-body problem is solved by means of a stochastic phase-space method. The squeezing is calculated and compared to experimental data, resulting in excellent quantitative agreement. From the simulations, we identify the physical limits to quantum noise reduction in optical fibers. The research represents a significant experimental test of first-principles time-domain quantum dynamics in a one-dimensional interacting Bose gas coupled to dissipative reservoirs.

Stable propagation of solitons with increased energy through the combined action of dispersion management and periodic saturable absorption

It is shown, through numerical simulations, that by using a combination of dispersion management and periodic saturable absorption it is possible to transmit solitonlike pulses with greatly increased energy near to the zero net dispersion wavelength. This system is shown to support the stable propagation of solitons over transoceanic distances for a wide range of input powers.

Dispersion-managed solitons: a new paradigm for high data rate

The WDM properties of dispersion managed (DM) solitons and the reduction in Gordon-Haus jitter means that it is possible to contemplate multiple channels each at 10 Gbit/s for transoceanic distances without the need for elaborate soliton control. This paper will concentrate on fundamental principles of DM solitons, but will use these principles to indicate optimum maps for future high-speed soliton systems.

Picosecond soliton propagation using nonlinear optical loop mirrors as intensity filters

The authors show that by inserting nonlinear optical loop mirrors into an optical fibre transmission line, 1.5 ps solitons may be transmitted over at least 750 km, with amplifiers spaced at 15 km intervals.

Solitons: permanent waves

Communications engineers are learning to create an electromagnet wave at will, to transmit information. This wave, the optical soliton, is the subject of astounding recent developments in nonlinear optics and lasers. The author describes the principles behind the use of solitons in optical communications and shows that in the context of such communications the most important property of solitons is that they are extremely stable. Not only do they not disperse, but an encounter with a perturbation (e.g. a joint in optical fibre) will usually leave the soliton unaltered.

WDM of solitons in dispersion managed transmission systems

This thesis investigates the physical behaviour of solitons in wavelength division multiplexed (WDM) systems with dispersion management in a wide range of dispersion regimes. Background material is presented to show how solitons propagate in optical fibres, and key problems associated with real systems are outlined. Problems due to collision induced frequency shifts are calculated using numerical simulation, and these results compared with analytical techniques where possible. Different two-step dispersion regimes, as well as the special cases of uniform and exponentially profiled systems, are identified and investigated. In shallow profile, the constituent second-order dispersions in the system are always close to the average soliton value. It is shown that collision-induced frequency shifts in WDM soliton transmission systems are reduced with increasing dispersion management. New resonances in the collision dynamics are illustrated, due to the relative motion induced by the dispersion map. Consideration of third-order dispersion is shown to modify the effects of collision-induced timing jitter and third-order compensation investigated. In all cases pseudo-phase-matched four-wave mixing was found to be insignificant compared to collision induced frequency shift in causing deterioration of data. It is also demonstrated that all these effects are additive with that of Gordon-Haus jitter.

Experimental transmission of dispersion managed solitons

This thesis investigates the feasibility of soliton transmission at 1150nm over standard fibre. This is done using a dispersion compensating fibre module in each amplifier span to compensate for the high dispersion. The basic principles of soliton propagation in optical fibre are discussed within this thesis, followed by an introduction to advantages of dispersion management. In the experimental chapter single channel transmission results are presented in 10Gbit/s and 40Gbit/s. At 10Gbit/s the effects of dispersion management on the power dispersion relationship for solitons are investigated. The detrimental effects of soliton-soliton interactions, which are increased due to the greater overlap breathing solitons are discussed. A technique for reducing the soliton-soliton interactions through amplifier positioning is presented as a solution to this problem. The experiments demonstrate the feasibility of using standard fibre for transmission over trans-oceanic distances at 10Gbit/s. The 40Gbit/s experiment demonstrates transmission over sufficient distance for an terrestrial system. Also contained within this thesis are experimental results showing transmission of solitons over dispersion shifted fibre using a novel technique that makes use of the non-linear polarisation rotation of the soliton in the fibre. This is used to generate the effect of saturable absorption, allowing transmission distances of 200,000km to be achieved.

Ultra high-speed transmission using dispersion managed solitons

This thesis presents the results of numerical modelling of ultra high-speed transmission using DM solitons. The theory of propagation in optical fibres is presented with specific reference to optical communication systems. This theory is then expanded to. incorporate dispersion-managed transmission and the dispersion managed soliton. The first part of this work focuses on ultra high-speed dispersion managed soliton propagation in short period dispersion maps. Initially, the cbaracteristics .of dispersion managed soliton propagation in short period dispersion maps are contrasted to those of the more conventional dispersion managed regime. These properties are then utilised to investigate transmission at single channel data rates of 80 Gbit/s, 160 Gbit/s and 320 Gbit/s. For all three data rates, the tolerable limits for transmission over 1000 km, 3000 km and·transoceanic distances are defined. A major limitation of these higher bjt rate systems arises from the problem of noise-induced interactions, which is where the.accumulation of timing jitter causes neighbouring dispersion-managed solitons to interact. In addition, the systems become more sensitive to initial conditions as the data rate increases, .. The second part of the work focuses on contrasting the performance of a range of propagation regimes, from quasi-linear through to soliton-like propagation at 40 Gbit/s for both single channel and WDM dispersion managed transmission. The results indicated that whilst the optimal single channel performance was achieved for soliton-like propagation, the optimal WDM performance was achieved for propagation regime that lay between quasi-linear and soliton-like.

Ultra-long haul optical fibre transmission systems

This thesis examines experimentally options for optical fibre transmission over oceanic distances. Its format follows the chronological evolution of ultra-long haul optical systems, commencing with opto-electronic regenerators as repeaters, progressing to optically amplified NRZ systems and finally solitonic propagation. In each case recirculating loop techniques are deployed to simplify the transmission experiments. Advances in high speed electronics have allowed regenerators operating at 10 Gbit/s to become a practical reality. By augmenting such devices with optical amplifiers it is possible to greatly enhance the repeater spacing. Work detailed in this thesis has culminated in the propagation of 10 Gbit/s data over 400,000 km with a repeater spacing of 160 km. System reliability and robustness are enhanced by the use of a directly modulated DFB laser transmitter and total insensitivity of the system to the signal state of polarisation. Optically amplified ultra-long haul NRZ systems have taken on particular importance with the impending deployment of TAT 12/13 and TPC 5. The performance of these systems is demonstrated to be primarily limited by analogue impairments such as the accumulation of amplifier noise, polarisation effects and optical non-linearities. These degradations may be reduced by the use of appropriate dispersion maps and by scrambling the transmitted state of signal polarisation. A novel high speed optically passive polarisation scrambler is detailed for the first time. At bit rates in excess of 10 Gbit/s it is shown that these systems are severely limited and do not offer the advantages that might be expected over regenerated links. Propagation using solitons as the data bits appears particularly attractive since the dispersive and non-linear effects of the fibre allow distortion free transmission. However, the generation of pure solitons is difficult but must be achieved if the uncontrolled transmission distance is to be maximised. This thesis presents a new technique for the stabilisation of an erbium fibre ring laser that has aUowed propagation of 2.5 Gbit/s solitons to the theoretical limit of ~ 18,000 km. At higher bit rates temporal jitter becomes a significant impairment and to aUow an increase in the aggregate line rate multiplexing in both time and polarisation domains has been proposed. These techniques are shown to be of only limited benefit in practical systems and ultimately some form of soliton transmission control is required. The thesis demonstrates synchronous retiming by amplitude modulation that has allowed 20 Gbit/s data to propagate 125,000 km error free with an amplifier spacing approaching the soliton period. Ultimately the speed of operation of such systems is limited by the electronics used and, thus, a new form of soliton control is demonstrated using all optical techniques to achieve synchronous phase modulation.

Intermediate asymptotics in nonlinear optical systems

Using a fiber laser system as a specific illustrative example, we introduce the concept of intermediate asymptotic states in finite nonlinear optical systems. We show that intermediate asymptotics of nonlinear equations (e.g., coherent structures with a finite lifetime or distance) can be used in applications similar to those of truly stable asymptotic solutions, such as, e.g., solitons and dissipative nonlinear waves. Applying this general idea to a particular, albeit practically important, physical system, we demonstrate a novel type of nonlinear pulse-shaping regime in a mode-locked fiber laser leading to the generation of linearly chirped pulses with a triangular distribution of the intensity.