Generation of triangular pulses in normally dispersive fibre

In this scheme, nonlinearity and dispersion in the NDF lead to various reshaping processes of an initial, conventional pulse according to the chirping value and power level at the input of the fibre. In particular, we have observed that triangular-shaped pulses can be generated for sufficiently high energies and a positive initial chirp parameter. In our experiments, 2.8 ps-FWHM, transform-limited pulses generated from a mode-locked fibre laser source at a repetition rate of 1.25 GHz were pre-chirped by propagating the pulses through different lengths of standard mono-mode fibre. The chirped pulses were then amplified to different power levels before being launched into a 2.3 km section of True Wave fibre (TWF). The corresponding numerically calculated pulse temporal intensity profile and numerical and experimental second-harmonic generation frequency-resolved optical gating (SHG FROG) spectrograms were also derived. In conclusion, we have presented numerical modelling results which show the system design parameters required for the generation of triangular-shaped pulses in a nonlinear NDF, and experimentally demonstrated triangular pulse shaping in conventional NDF.

Dispersion and nonlinearity-management in mode-locked fibre lasers

In this work we extend theory of dispersion-managed (DM) solitons to dissipative systems with the main focus on applications in mode-locked lasers. In general, pulses in mode-locked fibre lasers experience both nonlinear and dispersion management per cavity round trip. In stretched-pulse lasers, this concept was utilized to obtain high energy pulses. Here we model the pulse propagation in a mode-locked fibre laser with a distributed nonlinear and DM Ginzburg-Landau type equation. We extend existing results on DM solitons and investigate the impact on soliton properties of dissipative perturbations that occur due to the effects of gain amplification, saturable absorption, and loss. In conclusion, in contrast to standard DM solitons in Hamiltonian systems, dissipative DM solitons do exist at high map strengths, thus opening a way for the generation of stable, short pulses with high energy.

Pulse shaping in mode-locked ring-cavity fibre lasers

By means of extensive numerical modelling we have demonstrated the possibility of nonlinear pulse shaping in a mode-locked fibre laser using control of the intra-cavity propagation dynamics by adjustment of the normal net dispersion and integrated gain. Beside self-similar mode-locking, the existence of a novel type of pulse shaping regime that produces pulses with a triangular temporal intensity profile and a linear frequency chirp has been observed.

Quantitative optical coherence tomography for characterization of microscopic structures with varying refractive index

In this paper we have done back to back comparison of quantitive phase and refractive index from a microscopic image of waveguide previously obtained by Allsop et al. Paper also shows microscopic image of the first 3 waveguides from the sample. Tomlins et al. have demonstrated use of femtosecond fabricated artefacts as OCT calibration samples. Here we present the use of femtosecond waveguides, inscribed with optimized parameters, to test and calibrate the sensitivity of the OCT systems.

Performance analysis of 20 Gbit/s RZ-DPSK non-slope matched transoceanic submarine links

This paper studies the performance of a typical non-slope matched transoceanic submarine link using 20Gb/s channel rate and RZ-DPSK modulation with different duty cycles. Through comparison with direct error counting, we have also demonstrated the limitations of the available numerical approaches to the BER estimation for return-to-zero differential phase-shift keying (RZ-DPSK). The numerical results have been confirmed by experiments, and indicate that 20 Gb/s RZ-DPSK transmission is a feasible technique for the upgrade of existing submarine links.

Comparison of BER estimation methods in numerical simulation of 40 Gbit/s RZ-DPSK transmission

This study analyzes the validity of different Q-factor models in the BER estimation in RZ-DPSK transmission at 40 Gb/s channel rate. The impact of the duty cycle of the carrier pulses on the accuracy of the BER estimates through the different models has also been studied.

All-optical passive 2R regeneration of dispersion-managed RZ data at 40 and 80 Gbit/s using in-line NOLMs

We demonstrate that the use of in-line nonlinear optical loop mirrors (NOLMs) in dispersion-managed (DM) transmission systems dominated by amplitude noise can achieve passive 2R regeneration of a 40 and 80 Gbit/s RZ data stream. This is an indication that the use of this approach could obviate the need for full-regeneration in high data rate, strong DM systems, when intra-channel four-wave mixing poses serious problems.

All-optical 40 Gbit/s 2R regeneration in scalable WDM networks

In this paper we propose a 2R regeneration scheme based on a nonlinear optical loop mirror (NOLM) and optical filtering. We numerically investigate wavelength-division multiplexing (WDM) operation at a channel bit rate of 40 Gbit/s. In distinction to our previous work, we focus here on the regenerative characteristics and signal quality after a single transmission section, whose length is varied from 200 to 1000 km. © 2003 IEEE.

Auto-solitons guided by in-line nonlinear optical loop mirrors in dispersion-managed communication systems

Summary form only given. Both dispersion management and the use of a nonlinear optical loop mirror (NOLM) as a saturable absorber can improve the performance of a soliton-based communication system. Dispersion management gives the benefits of low average dispersion while allowing pulses with higher powers to propagate, which helps to suppress Gordon-Haus timing jitter without sacrificing the signal-to-noise ratio. The NOLM suppresses the buildup of amplifier spontaneous emission noise and background dispersive radiation which, if allowed to interact with the soliton, can lead to its breakup. We examine optical pulse propagation in dispersion-managed (DM) transmission system with periodically inserted in-line NOLMs. To describe basic features of the signal transmission in such lines, we develop a simple theory based on a variational approach involving Gaussian trial functions. It, has already been proved that the variational method is an extremely effective tool for description of DM solitons. In the work we manage to include in the variational description the point action of the NOLM on pulse parameters, assuming that the Gaussian pulse shape is inherently preserved by propagation through the NOLM. The obtained results are verified by direct numerical simulations

Time domain all-optical nonlinear signal processing to enhance the performance of a RZ receiver

We have proposed a new technique of all-optical nonlinear pulse processing for use at a RZ optical receiver, which is based on an AM or any device with a similar function of temporal gating/slicing enhanced by the effect of Kerr nonlinearity in a NDF. The efficiency of the technique has been demonstrated by application to timing jitter and noise-limited RZ transmission at 40 Gbit/s. Substantial suppression of the signal timing jitter and overall improvement of the receiver performance has been demonstrated using the proposed method.

Efficiency of energy deposition by fundamental and second harmonics in femtosecond laser inscription

We present the results of numerical modelling of energy deposition in single-shot femtosecond laser inscription for fundamental and second harmonics, which shows that second harmonic is more efficient considering the amount of absorbed energy

Tuneable compensator of dispersion and slope using non-uniformly strained chirped fibre grating

Summary form only given. A novel method for tuning the second and the third order dispersion using a simple multi-point bending device has been demonstrated. A simple model has been developed that allows to calculate the exact bending profile required for compensation for the given values of dispersion and dispersion slope.

Dispersion and nonlinearity-management in mode-locked fibre lasers

In this work we extend theory of dispersion-managed (DM) solitons to dissipative systems with the main focus on applications in mode-locked lasers. In general, pulses in mode-locked fibre lasers experience both nonlinear and dispersion management per cavity round trip. In stretched-pulse lasers, this concept was utilized to obtain high energy pulses. Here we model the pulse propagation in a mode-locked fibre laser with a distributed nonlinear and DM Ginzburg-Landau type equation. We extend existing results on DM solitons and investigate the impact on soliton properties of dissipative perturbations that occur due to the effects of gain amplification, saturable absorption, and loss. In conclusion, in contrast to standard DM solitons in Hamiltonian systems, dissipative DM solitons do exist at high map strengths, thus opening a way for the generation of stable, short pulses with high energy.