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.
Several network testbeds use optical labels as a means of routing data through a network. The EU funded IST project STOLAS is producing one such network testbed which uses an optical label carried by a frequency shift keyed (FSK) modulation of the optical carrier at 75 Mb/s as an orthogonal channel to the 10 Gb/s intensity modulation used to carry the data. This paper presents the results of some transmission experiments on one of the laser transmitters used to supply the IM and FSK modulated signal within the network. In particular the paper investigates the cross-talk between the two theoretically orthogonal modulation channels of IM and FSK and the effect on bit error rate (BER).
Widely tunable lasers support certain characteristics which out perform DFB technology for the sensing of gas species in the NIR spectral region. Reduced frequency tuning variation and almost zero residual amplitude modulation (RAM) are investigated. The current report illustrates how 18 individual gas absorption lines can be interrogated using a single laser source over a 40nm wavelength range, where RAM and FM non-linearity never exceed 5% and 13 % respectively. Comparison with DFB technology is made.
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.
A new interrogation system for a large number of strain sensors is presented. In the residential building sensor market some facts have to be dealt with: low cost, networks with a large number of sensors, reliability, passive devices, amongst others. We have accomplished all of these with the new interrogation system we are going to present.
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.
COST 240 is a pan-European action collaborating on the investigation of techniques for modeling and measuring photonic components. This action has concentrated on inter- laboratory comparison of measurement and modeling techniques using round-robin measurement of sample devices. The present paper reviews the work performed within this action on measurement of and parameter extraction from single frequency semiconductor laser diodes. Specifically, those measurements that have been made in order to estimate laser parameters include; Relative Intensity Noise, modulation response, emission linewidth, several static characteristics and amplified spontaneous emission below threshold. Some of the parameters that can be estimated from these measurements include; threshold current, external efficiency, diode resistance, internal loss, characteristic temperature, differential gain, gain compression parameter, facet reflectivities, facet phases, index and gain coupling coefficients, and group refractive index. Following a review of the typical measurements performed on circulated lasers within the COST 240 Action by participating laboratories, a brief description will be presented of the physical models adopted to extract the laser diode parameters. Examples will be presented and conclusions given as to the suitability of certain techniques for the extraction of diode parameters for single frequency lasers.
We give an overview of near IR laser diode based methods for gas sensing discussing both the devices enabling this technology and the techniques utilized. Of particular importance for this technology is development of single frequency laser diodes for laser based gas sensing. We discuss and present results on laser diode based gas sensing using sources such as distributed feedback laser diodes, vertical cavity laser diodes and other novel single frequency devices. Detection limits for particular gases of interest, e.g. methane, oxygen and hydrogen sulphide are discussed.
By suitably modulating a single multielectrode semiconductor laser and processing the optical output, a wideband frequency-swept signal from near-dc to millimeter frequencies can be generated. Initial results reveal that a usable sweep range from 60 MHz to 22 GHz (receiver-bandwidth-limited) can be achieved with low-residual amplitude modulation, with bandwidths of greater than 125 GHz being possible. Generated frequency resolution is limited in laser frequency stability and linewidth.
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