Optical sources for the forthcoming terabit/s era of optical communications and networking will require multiple frequency-locked carriers, each with low phase noise, in order to minimize the spectral occupancy of the overall channel bandwidth. One method to construct a highly reconfigurable version of such a source is to use an optical frequency comb from a gain-switched laser to simultaneously injection-lock many different single mode lasers. The outputs from the single-mode lasers are all mutually frequency locked and possess the same low-phase noise properties of the gainswitched comb. In this submission, we present numerical simulation results from the entire system of simultaneously injection-locked single mode lasers by firstly simulating an optical frequency comb from the gain-switched laser and then using that frequency comb to injection lock the single-mode lasers. The simulation approach is to use lumped rate equations with the appropriate stochastic Langevin terms for spontaneous carrier recombination and for spontaneous emission. The inclusion of the stochastic terms are vital when identifying the locked states of the entire system. Using the simulator we are able to identify important criteria to maximize the frequency locking range that suppresses the cross talk from adjacent comb lines to greater than 30 dB, and avoiding the carrier-photon resonance of the single mode lasers is vital to achieve this. The relative simplicity of the simulator has the advantage of being exploited within optical communication simulators to predict the communication system performance when using these sources, which would be of advantage to designers of such systems.
Photopolymer materials are practical materials for use as holographic recording media. In order to further develop such
materials, a deeper understanding of the photochemical mechanisms present during the formation of holographic
gratings in these materials has become ever more crucial. This is especially true of the photoinitiation process, which
has already received much attention in the literature. Typically the absorption mechanism varies with exposure time.
This has previously been investigated in association with several effects taking place during recording. Since
holographic data storage requires multiple short exposures, it is necessary to verify the temporal change in
photosensitizer concentration. Post exposure effects have also been discussed in the literature; however, they do not
include post exposure effects such as the photosensitizer recovery. In this paper we report experimental results and
theoretical analysis to examine the effects of the recovery and bleaching mechanisms which arise during exposure.
Abstract: Evolving optical communication systems are leading towards an all-optical network, where destination and routing information is incorporated in the carrier wavelength of the signal. It is possible to extend the agility and flexibility of the network by including a Frequency Shift Keyed (FSK) header to all data packets, this can provide additional routing information which can be processed entirely and instantly in the wavelength domain. Thus reducing the queuing required at individual nodes within the network. However, in such a network, due to the number of co-propagating channels and the tight frequency tolerances that are necessary, the optical fibre nonlinearities become very significant and can be detrimental to the use of FSK in such a system. The nonlinear effect under consideration in this paper is Cross Phase Modulation (XPM). This effect occurs when amplitude changes on one channel induce frequency changes on all the others. In a network that simultaneously employs both amplitude and frequency modulation, (where AM is used to transmit payload data and FSK transmits the routing information), the FSK header on one signal can be greatly influenced by the frequency changes induced on it due to the amplitude changes of other signals. In this paper, simulations of the effects of XPM on an FSK signal will be presented. This will include the effects as the number of channels, input optical powers and bitrates are increased. As well as a method to alleviate the effect of the induced frequency variations on the FSK signal.
This paper investigates the effect that Four Wave Mixing (FWM) has on Frequency Shift Keyed (FSK) optical signals. The paper will show how an optical FSK modulated signal can be implemented using a widely tunable laser. These lasers will have a bigger impact in future optical transmission systems due to their agile wavelength capabilities. Then measurements of FWM in a Semiconductor Optical Amplifier (SOA) and in Zero Dispersion Shifted Fiber (DSF) will be presented. SOAs are of crucial importance in modern & future transmission systems as many operations can be implemented using their highly nonlinear properties, such as wavelength conversion, pulse reshaping & format conversion can be implemented. While Zero DSF is less popular these days, due to its nonlinearities, nevertheless the fiber still forms the core of many networks and thus its ability to handle many different WDM signals without introducing potential interference needs to be investigated.
Due to the continuous growth of data traffic current telecommunications systems are being pushed to the extremes of their capacity. Bottlenecks are particularly evident at the routers, where optical to electrical conversion must take place to read the routing information. Using optical only routing, traffic flow would be much more streamlined. Central to this optical routing is the tunable laser, the speed of the routing is obviously dependent on the speed at which the laser can switch between different wavelengths. Wavelength switching is achieved through the application of currents to the front, back and phase sections of the laser. With each change in current there is a corresponding change in the temperature of the laser. It is extremely important to quantify and minimise the temperature effects for stable accurate wavelength output. A measurement rig which had been previously used for high speed switching has been setup under labview control to study these transients. The laser is tuned to a wavelength and then is switched to another wavelength by applying currents to the three sections quickly. A fabry perot interferometer is used to quickly determine the wavelength of the laser.
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