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

All-optical passive regeneration of 40 Gbit/s soliton data stream using dispersion-management and in-line nonlinear optical loop mirrors

We numerically demonstrate for the first time that dispersion management and in-line nonlinear optical loop mirrors can achieve all-optical passive regeneration and distance-unlimited transmission of a soliton data stream at 40 Gbit/s over standard fibre.

Optimal dispersion maps for multichannel soliton transmission with distributed Raman amplification

Using an asymptotic theory and a momentum method, we identify a family of dispersion management schemes with distributed Raman amplification, which are advantageous for massive multichannel soliton transmission. For the case of two-step dispersion maps, special schemes are found that have optimal (chirp-free) launch point locations that are independent of the fibre dispersion. Despite the variation of dispersion with wavelength due to the fibre dispersion slope, the transmission in several different channels can be optimized simultaneously using the same optimal launch point. The theoretical results are verified by direct numerical simulations.

Normal dispersion fibre-enhanced nonlinear optical loop mirror for 2R regeneration and phase margin improvement

A novel all-optical regeneration technique using loop-mirror intensity-filtering and nonlinear broadening in normal-dispersion fibre is described. The device offers 2R-regeneration function and phase margin improvement. The technique is applied to 40Gbit/s return-to-zero optical data streams.

Dispersion-dominated nonlinear fiber-optic channel

We propose to apply a large predispersion (having the same sign as the transmission fiber) to an optical signal before the uncompensated fiber transmission in coherent communication systems. This technique is aimed at simplifica- tion of the following digital signal processing of nonlinear impairments. We derive a model describing pulse propagation in the dispersion-dominated nonlinear fiber channel. In the limit of very strong initial predispersion, the nonlinear propagation equations for each Fourier mode become local and decoupled. This paves the way for new techniques to manage fiber nonlinearity.

An RZ DPSK receiver design with significantly improved dispersion tolerance

We show an improved DPSK receiver design which can increase useful dispersion tolerance by up to a factor of two. The increased dispersion tolerance is achieved through optimization of the optical filter at the receiver and the delay of the Mach-Zehnder interferometer. In this paper we fully explain the concept, quantify the gain and provide an explanation for the operation of the receiver. © 2007 Optical Society of America.

Experimental verification of the dispersion tolerance improvement of partial DPSK with optimised filtering

We experimentally confirm the optimum combination of modulator delay and filter bandwidth to maximize the dispersion tolerance of partial DPSK.

Stabilization of a passively mode-locked laser by continuous wave optical injection

We investigate numerically and experimentally the properties of a passively mode locked quantum dot semiconductor laser under the influence of cw optical injection. We demonstrate that the waveform instability at high pumping for these devices can be overcome when one mode of the device is locked to the injected master laser and additionally show spectral narrowing and tunability. Experimental and numerical analyses demonstrate that the stable locking boundaries are similar to these obtained for optical injection in CW lasers. © 2010 American Institute of Physics.

Sub-50 fs Yb-doped laser with anomalous-dispersion photonic crystal fiber

We report on the generation of 42 fs pulses at 1 µm in a completely fiber-integrated format, which are, to the best of our knowledge, the shortest from all-fiber-integrated Yb-doped fiber lasers to date. The ring fiber cavity incorporates anomalous-dispersion, solid-core photonic crystal fiber with low birefringence, which acts as a broadband, in-fiber Lyot filter to facilitate mode locking. The oscillator operates in the stretched-pulse regime under slight normal net cavity dispersion. The cavity generates 4.7 ps long pulses with a spectral bandwidth of 58.2 nm, which are dechirped to 42 fs via a grating pair compressor outside of the cavity. Relative intensity noise (RIN) of the laser is characterized, with the integrated RIN found to be 0.026% in the 3 Hz-250 kHz frequency range.

Trans-oceanic 80Gbit/s single channel transmission using short period dispersion management

The authors demonstrate dispersion managed soliton transmission using short-period dispersion management, which is characterised by having a dispersion management period that is much shorter than the amplification period. Simulation results indicate that by optimisation of the system parameters single channel transmission at 80Gbit/s is possible over trans-oceanic distances. © IEE, 2000.

Impact of third-order dispersion on the evolution of parabolic pulses

We present a perturbation analysis that describes the effect of third-order dispersion on the similariton pulse solution of the nonlinear Schrödinger equation in a fibre gain medium. The theoretical model predicts with sufficient accuracy the pulse structural changes induced, which are observed through direct numerical simulations.

All-fiber normal-dispersion single-polarization passively mode-locked laser based on a 45°-tilted fiber grating

An all-fiber normal-dispersion Yb-doped fiber laser with 45- tilted fiber grating (TFG) isto the best of our knowledgeexperimentally demonstrated for the first time. Stable linearly-chirped pulses with the duration of 4 ps and the bandwidth of 9 nm can be directly generated from the laser cavity. By employing the 45 TFG with the polarization-dependent loss of 33 dBoutput pulses with high polarization extinction ratio of 26 dB are implemented in the experiment. Our result shows that the 45 TFG can work effectively as a polarizerwhich could be exploited to singlepolarization all-fiber lasers.

Chromatic dispersion effect in a microwave photonic filter using superstructured fiber Bragg grating and dispersive fiber

In this paper a microwave photonic filter using superstructured fiber Bragg grating and dispersive fiber is investigated. A theoretical model to describe the transfer function of the filter taking into consideration the spectral width of light source is established. Experiments are carried out to verify the theoretical analysis. Both theoretical and experimental results indicate that due to chromatic dispersion the source spectral width introduces an additional power penalty to the microwave photonic response of the filter.

Ultra-long mode-locked Er-droped fibre lasers

The development of ultra-long (UL) cavity (hundreds of meters to several kilometres) mode-locked fibre lasers for the generation of high-energy light pulses with relatively low (sub-megahertz) repetition rates has emerged as a new rapidly advancing area of laser physics. The first demonstration of high pulse energy laser of this type was followed by a number of publications from many research groups on long-cavity Ytterbium and Erbium lasers featuring a variety of configurations with rather different mode-locked operations. The substantial interest to this new approach is stimulated both by non-trivial underlying physics and by the potential of high pulse energy laser sources with unique parameters for a range of applications in industry, bio-medicine, metrology and telecommunications. It is well known, that pulse generation regimes in mode-locked fibre lasers are determined by the intra-cavity balance between the effects of dispersion and non-linearity, and the processes of energy attenuation and amplification. The highest per-pulse energy has been achieved in normal-dispersion UL fibre lasers mode-locked through nonlinear polarization evolution (NPE) for self-modelocking operation. In such lasers are generated the so-called dissipative optical solitons. The uncompensated net normal dispersion in long-cavity resonatorsusually leads to very high chirp and, consequently, to a relatively long duration of generated pulses. This thesis presents the results of research Er-doped ultra-long (more than 1 km cavity length) fibre lasers mode-locked based on NPE. The self-mode-locked erbium-based 3.5-km-long all-fiber laser with the 1.7 µJ pulse energy at a wavelength of 1.55 µm was developed as a part of this research. It has resulted in direct generation of short laser pulses with an ultralow repetition rate of 35.1 kHz. The laser cavity has net normal-dispersion and has been fabricated from commercially-available telecom fibers and optical-fiber elements. Its unconventional linear-ring design with compensation for polarization instability ensures high reliability of the self-mode-locking operation, despite the use of a non polarization-maintaining fibers. The single pulse generation regime in all-fibre erbium mode-locking laser based on NPE with a record cavity length of 25 km was demonstrated. Modelocked lasers with such a long cavity have never been studied before. Our result shows a feasibility of stable mode-locked operation even for an ultra-long cavity length. A new design of fibre laser cavity – “y-configuration”, that offers a range of new functionalities for optimization and stabilization of mode-locked lasing regimes was proposed. This novel cavity configuration has been successfully implemented into a long-cavity normal-dispersion self-mode-locked Er-fibre laser. In particular, it features compensation for polarization instability, suppression of ASE, reduction of pulse duration, prevention of in-cavity wave breaking, and stabilization of the lasing wavelength. This laser along with a specially designed double-pass EDFA have allowed us to demonstrate anenvironmentally stable all-fibre laser system able to deliver sub-nanosecond high-energy pulses with low level of ASE noise.