Amplified spontaneous emission in index-guided multimodal waveguide structures

This paper describes a theory of amplified spontaneous emission in index-guided multimodal waveguide structures. It is based on a perturbation approach taking into account the correlated excitation of the different guided modes of the unperturbed waveguide. The coupling between these modes due to the propagation through a perturbed waveguide is taken into account by deducing evolution equations of the cross correlations between the modal amplitudes. Eventually, a beam propagation method program, including the spontaneous emission model, has been used for a comparison of the noise characteristics of a single-mode SOA with a 1-by-1 multimode interference semiconductor optical amplifier. Experiments have been performed confirming the obtained simulation results.     

Optimization of multiple exposure gratings for widely tunablelasers

A theoretical study of the reflection spectra of multiple holographic exposure distributed Bragg reflector gratings is presented. We will show that such a grating can exhibit a uniform reflection comb if the relative phases of the superimposed gratings are well chosen. The tolerances on the optimal phases are of the order of 0.09 radians for six superimposed gratings to 0.04 radians for ten gratings     

Numerical and theoretical study of the crosstalk in gain clampedsemiconductor optical amplifiers

A rate equation model of a gain clamped semiconductor optical amplifier (GCSOA) is presented. Both a time-domain and a small-signal analysis of those rate equations are used to investigate the crosstalk between different signal channels. It is shown that the crosstalk of GCSOA's strongly depends on the bit rate of the amplified signals and is lower at both very high bit rates and low bit rates. This crosstalk is proportional with the input power and, approximately, with the amplification     

An accurate rate-equation description for DFB lasers and someinteresting solutions

Starting from the coupled-wave equations, we have derived an alternative set of rate equations which are valid for most single-section distributed feedback (DFB) lasers. These rate equations are in many respects more useful than the conventional rate equations and have also been used to derive the influence of spatial hole burning on characteristics such as the chirp, the linewidth, or the harmonic distortion. Numerical results are presented for a DFB laser with both facets cleaved, AR-coated, and for a λ/4-shifted DFB laser     

Sampled grating tunable twin-guide laser diodes with over 40-nm electronic tuning range

Device and tuning characteristics of sampled grating tunable twin-guide laser diodes are presented. The vertically integrated, monolithic widely tunable laser requires only two tuning currents to fully cover a wavelength range of more than 40 nm by electrooptic tuning. Its tuning behavior is quasi-continuous with up to 8.2-nm broad continuous tuning regions. High sidemode suppression (SMSR /spl ges/ 35 dB) as well as large output power (P /spl ges/ 10 mW) are obtained over the wavelength range from 1520.5 to 1561.5 nm.     

Improved performance of AR-coated DFB lasers for the introductionof gain coupling

Antireflection (AR)-coated distributed-feedback (DFB) lasers with both gain- and index-coupled distributed feedback are studied numerically with respect to mode losses, mode suppression, and spatial hole burning. The mode losses and the spatial hole burning decrease with increasing gain coupling, while the mode suppression increases. It is shown that a large improvement in performance can already be obtained for small fractions of gain coupling     

All-optical 2R regeneration based on integrated asymmetricMach-Zehnder interferometer incorporating MMI-SOA

2R regeneration is proposed with an integrated Mach-Zehnder interferometer containing a monomodal semiconductor optical amplifier (SOA) and an SOA with a 1 × 1 multimode interference (MMI) coupler-SOA in the arms. Simulations and measurement of the static transfer function show a digital shape with a high extinction ratio improvement     

Improvement of the direct modulation behavior of semiconductor lasers by using a holding beam

We show theoretically that the direct modulation properties of semiconductor lasers can be significantly improved by the injection of a so-called holding beam-a continuous-wave beam at the transparency wavelength of the gain medium. Both the small-signal and the large-signal behavior are investigated.     

Yield analysis of non-AR-coated DFB lasers with combined index and gain coupling

The threshold gain difference for DFB lasers with various degrees of gain coupling and different strengths of facet reflectivities is calculated as a function of the random phases between grating and facet reflectivities. From this, the yield for single mode behaviour is determined. It is shown that even for cleaved facets a relevant improvement in terms of threshold gain difference is obtained by introducing a small fraction of gain coupling.<>     

Proposal for an All-Optical Flip-Flop Using a Single Distributed Feedback Laser Diode

We introduce a new concept for an all-optical flip-flop based on a single distributed feedback laser. The injection of external light into the laser results in a nonuniform carrier distribution. We will show numerically that this nonlinear effect of the carriers gives rise to a bistability that can be exploited for fast flip-flop operation.