No abstract

To enable optimum network transmission, the ideal is to launch as high laser power as possible into the optical fiber, to overcome the effects of fiber attenuation and maintain an acceptable signal to noise ratio. Launching high powers into a fiber however, results in unwanted nonlinear effects. Stimulated Brillouin scattering (SBS) is one of the nonlinear effects which reflects a significant proportion of the transmitted optical power back to the transmitter, degrading the system severely. This paper reports the development of a digitally selected supermode distributed Bragg reflector monolithic laser chip which can provide significant linewidth broadening using a pure frequency modulation technique by application of a dither current. By modifying a small segment of the laser chip material refractive index, it produces a modulation of the longitudinal mode and hence laser frequency; the monolithic laser chip has reduced the effects of SBS significantly with very little parasitic amplitude modulation.

This paper reports the development of an infra-red circa 193THz (~1.5µm) frequency tunable laser source selected and evaluated for photonic environment sensing systems. LIDAR (LIght Detection And Ranging) offers a method of remote wind speed measurement. Widespread deployment of the technique has been limited by the expense and complexity of LIDAR systems. However development of systems based on optical fiber and photonic components from the telecommunications industry promises improvements in cost, compactness, and reliability, so that it becomes viable to consider deployment of such systems on large wind turbines for the advance detection of fluctuations of wind speed. A monolithic multi-section laser, originally designed as a tunable source for telecommunications applications, has been modified and re-evaluated as a source for sensing applications, based on the technique of coherent laser radar (CLR), and coherent doppler LIDAR (CDL). A tunable frequency optical source should fulfil specific technical criteria to fulfil the applications requirements; speed of frequency selection, absolute accuracy of emitted frequency, spectral purity, and stability. Custom electronics and firmware were developed to realise an improvement in frequency switching speed by a factor of 10 relative to equivalent commercially available telecoms (DBR) sources, satisfying the target application requirements. An overview of the sensing architecture is presented, a detailed description of the fast tuning process described, including the custom hardware and firmware, and specifically the laser energising sequence. The results of the laser module are then presented with detailed consideration of the target application.