Widely tunable laser diodes are attractive devices for the next generation wavelength-division-multiplexing (WDM) systems, as they have potential to increase the capacity and the flexibility of the networks. Multi-section tunable laser wavelength switching dynamics, are determined by carrier density and temperature effects. After fast wavelength switching has taken place, a thermal transient induced by the tuning current(s) causes a slow wavelength drift towards a steady state value. Thermal effects on the frequency shift keying (FSK) modulation and wavelength switching dynamics are investigated for a GCSR laser, using the phase section. Thermal effects on wavelength switching dynamics of the device are measured by a time-resolved spectral (TRS) technique, based on a scanning Fabry-Perot Interferometer (FPI). The experimental setup has the ability to measure thermal transients at an increased temporal resolution, over previously reported measurements. A model of the FM response has been developed, which is in close agreement with experimental results.
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.
This paper gives an overview of the European ACTS project AC329-ACTUAL. This project was carried out during 1998 and 1999. The stated main objective of the project was: TO sue the state-of-the-art technology on widely tunable lasers available within the Consortium, to bring this to full maturity on a subsystem level and to demonstrate that wavelength agile transmitters based on widely tunable lasers can open the way to the next generation WDM and wavelength switching systems. This paper will give a description of the result from the project.
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