We propose and experimentally demonstrate a low cost, low power consumption technique for ultra-wideband pulse shaping. Our approach is based on thermal apodization of two identical linearly chirped fiber Bragg gratings (LCFBG) placed in both arms of a balanced photodetector. Resistive heating elements with low electrical power consumption are used to tune the LCFBG spectral responses. Using a standard gain switched distributed feedback laser as a pulsed optical source and a simple energy detector receiver, we measured a bit error rate of 1.5×10−4 at a data rate of 1 Gb/s after RF transmission over a 1-m link.
In this paper we present our study of all optical label encoding and ultrafast processing to route packets through optical
networks. Our investigations include new network topologies, novel photonic components and performance analysis. We
propose a <i>label stacked</i> packet switching system using spectral amplitude codes (SAC) as labels. We have developed
enabling technologies to realize key photonic components for generation, correlation (identification) and conversion
(swapping) of SAC-labels. We generate and identify the labels with fibre Bragg gratings (FBGs) encoders used in
transmission. Furthermore, we demonstrate a static, all-photonic code-label converter based on a semiconductor fiber
ring laser that can be used for label swapping of SAC-labels. We also address the design of dedicated receivers for
optical burst detection. For this, we propose a novel architecture for a burst mode receiver module. In the system studies,
we have shown by simulations that the throughput of standard Ethernet passive optical networks (E-PONs) can be
substantially increased by the use of data encoded with SACs to achieve optical code division multiple access over
passive optical networks (OCDMA-PONs). In the paper, we present recent results for all of these photonic technologies
and we discuss how they can enable flexible packet switched networks.
Numerical simulations of semiconductor optical amplifiers (SOA) often are time consuming. Making simplifying assumptions, we obtain a fast model based on the <i>reservoir</i>, representing the total number of useful carriers. In this paper, we explain how this model is developed and how the gain is parameterized. We demonstrate that the scattering losses, dropped in the derivation of the reservoir model, can be re-introduced by applying a simple transformation to the gain coefficient. In this way, the accuracy of the model is greatly increased, but its level of complexity remains low.
In optical code division multiple access (OCDMA), the optical bandwidth is accessed simultaneously by multiple users, leading to intensity noise in photodetection. In this article we focus on spectral amplitude encoded CDMA for access networks. We examine efficient system architectures, practical implementations, compare the impact of different system designs on spectral efficiency and bit error rates. We draw on both experimental and simulation results. We discuss the use of two types of optical sources, a broadband incoherent source and a multi-laser source. We examine the capacity that can be achieved for these systems and the design goals we are shooting for in our laboratory.
In this paper, we review first, the different noise terms involved in amplified and filtered spontaneous emission detection using the standard beating theory (or the semi-classical field expansion theory) of the noise in optical amplifiers. We derive BER calculations using the following approaches: 1) non-ideal electrical and optical filters combined with a Gaussian approximation for the resultant noise process and an ideal integrate and dump electrical filter and an ASE source combined with non-Gaussian Erlang noise statistics.
A serious problem facing wavelength division multiplexed (WDM) networks with fiber amplifier
cascades is transient cross saturation or gain dynamics of fiber amplifiers. Attention has been focused
primarily on circuit-switched scenarios. When the number of WDM channels transmitted through a
circuit-switching network varies, channel addition/removal will tend to perturb signals at the surviving
channels that share all or part of the route. Even more serious bit error rate deterioration can arise in
WDM packet switched burst mode networks. In this contribution we present experimental results
demonstrating the effect of fast power transients in erbium-doped fiber amplifiers (EDFAs) on packetized
traffic transmitted through a chain of five EDFAs. Traffic of a LAN has been transmitted over one
channel, the effect of EDFA cross gain saturation due to the bursteness of the traffic has been observed in
a cw channel. The stabilizing effect of gain clamping the first EDFA in the cascade has been investigated.
Multiple Bragg gratings are written in a single fibre strand with accurate positioning to achieve predetermined time delays
between optical channels. Applications of fibre Bragg grating arrays include encoders/decoders with series of identical
gratings for optical code-division multiple access.
The gain of an EDFA (erbium doped fiber amplifier) is in general wavelength-dependent, leading to different amplification
levels among WDM (wavelength division multiplexing) channels. The use of Optical FFH-CDMA (fast frequency hopped
code division multiple access) offers a natural diversity of wavelength, and therefore gain, thus eliminating the requirement
of an equalization stage to achieve flat gain on all channels. Computer simulations are developed to analyze and compare
equalization performance of these two transmission approaches (CDM and WDM) in EDFAs, especially in situations where
the EDFA operating point is subject to change (i.e., variable input traffic). We find that WDM requires an equalization stage
that fails when packetized traffic characteristics shift, whereas optical FFH-CDMA presents the advantage of more robust,
hence truly dynamic, gain equalization.
In this paper, we present a new method to equalize the optical signal-to-noise ratio (OSNR) of all
wavelength division multiplexed channels at the end of a cascade of several erbium-doped fiber
amplifiers (EDFAs), by use of pre-emphasis and the proper choice of EDFA design parameters.
Identical OSNR at the end of the cascade ensures better signal detection and quality of service
Simple analytical expressions for determining the characteristic time of a single EDFA and evaluating the 1 dB time response of a cascade of EDFA are given in a form of a difference equation. It is shown that the expressions are in remarkable agreement with the results obtained through solving numerically the differential equations for chains of EDFAs. Simulations of the transient time response to channel drop/add are also included.
We propose a new architecture for an optical fast frequency- hop code division multiple access system using tunable Bragg gratings. Previously proposed architectures called for a series of in-fiber Bragg gratings, each independently tunable with a piezo-electric device. We propose a system where the entire fiber of multiple Bragg gratings uses one piezo-electric device to tune to a particular code. We introduce a new set of codes to take advantage of the new architecture and increase the bit rate of each user, as well as the total number of users and hence aggregate bit rate.
This paper presents a summary of some of the research activities conducted at the Centre d'optique, photonique et laser from Universite Laval that find applications in the field of optical communications. The subjects considered are: absolute frequency control, compensation of dispersion and nonlinear effects within dense wavelength division multiplexed systems, writing of in-fiber Bragg gratings, optical fast frequency-hopped code division multiple access, gain dynamics in Erbium doped fiber amplifiers, short pulsed emission at high repetition rates, dual wavelength operation of semiconductor lasers, applications of Fourier-transform spectrometers and holographic interconnections.
Optical code division multiple is one of the candidates for future broadband optical networks. We investigate here the performance of such systems from the security point of view. We demonstrate that 2D coding can enhance the security aspect while still maintaining the multiuser ability. Analysis of the eavesdropping activity in the presence of multiuser interference is presented and ways to further strengthen the security aspects are discussed.