Proton irradiation was carried out on emerging semiconductor laser technologies, including Distributed Bragg Reflector (DBR) and Sampled Grating (SG)- DBR lasers at 1550 nm, as well as Distributed Feedback (DFB) lasers at 935 nm and 1550 nm. Two separate exposure sessions, at low and high doses, were performed, the first to mimic a typical 2-year Earth Observation mission, and the second for more comprehensive radiation hardness assessment. Low dose exposure yielded minimal damage to all lasers, but the 935 nm DFBs did exhibit small changes in tuning efficiency. In-situ measurements on the 1550 nm DFB and DBR lasers show degradation in lasing threshold by 15% and 4% respectively, and the DBR mode structure is maintained but shifts by more than one mode width.
Due to the development of Fibre Bragg Grating sensors for the measurement of temperature, strain and pressure many markets can benefit from optical technology. These markets are the oil and gas industry, structural and civil engineering, rail and aerospace to name a few. The advantages of using optical sensing technology are that high accuracy measurements can be performed with a passive optical system. By running one fibre along the structure or down the well, multiple points along the fibre can be tested to measure strain, temperature and pressure. Of importance with these systems is the reach that can be obtained while maintaining accuracy. A major problem with long reach system is the back reflection due to SBS and Rayleigh scattering processes which reflect part of the laser light back into the receiver which affect the sensitivity of system. This paper shows a technique to enable a reach of >70km by using a tunable laser and receiver. Techniques for the suppression of receiver noise from SBS and Raleigh scattering are implemented. In addition polarisation dependence of the FBG is considered and results of techniques to limit the effect of polarisation at long and short reaches are shown.
Widely tunable lasers that have been developed for the telecommunications industry have many applications in the sensing industry and bring the advantages of technology robustness, volume low cost potential, ultra fast tuning capabilities and high performance. These traits are now being further exploited in sensing applications such as gas sensing, sensor interrogation systems, optical frequency domain reflectometry based systems and interformeteric sensing. The current paper gives an overview of a number of these areas and how tunable laser technologies, particularly those based on monolithic tunable lasers, are being successfully deployed in real world sensing scenarios.
Full coverage, wavelength switching over the entire C band on the 100 GHz ITU frequency grid, from any channel to any channel in a single microsecond, is presented here for the first time. This switching time is achieved whilst ensuring that the terminal lasing frequency is within +/- 2.5GHz of the target ITU 1 us after the switching event. The current paper presents the key parameters associated with such a laser transmitter and how these are unaffected by the addition of the wavelength switching functionality, i.e. linewidth, switching time, SMSR and transient frequency error. Next generation networks will move from physical path managed optical networks to logical wavelength managed networks where, efficient utilisation of the network on the wavelength level will be demanded. Fast and robust switching of the wavelengths is a key technological requirement for delivering on this.
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