Complex optical networks demand high levels of functionality from optical components requiring high density integration in low cost, compact, plug and play format. Technologies at the forefront of this move to higher integration are MEMs and planar waveguide options. In all cases the components are interfaced with the transmission medium, generally through precision alignment to individual fibres. All-fibre technologies offer good performance but are not in general appropriate for multi-functional integration. One all-fibre approach that offers the potential for integration is the fibre evanescent field technology. This technology creates a waveguide substrate from the transmission optical fibre onto which the optical circuit can be built. This paper describes a VOA-power monitor device formed using evanescent field approach, to assess its performance and the potential for full integration.
KEYWORDS: Sensors, Temperature metrology, Signal attenuation, Polarimetry, Polarization, Modulation, Polarizers, Transmitters, Temperature sensors, Fiber optics
This paper describes a remote polarimetric low coherence temperature sensing system employing intensity and wavelength compensation mechanisms. Possible interconnection interference effects and system polarisation dependent losses are minimized using a broadband (low coherence) optical source followed by a fibre Lyot-type depolariser. The sensor was optimized to operate over a temperature range of 160° C corresponding to the linear region of the interferometric response. A high extinction broadband fibre polariser (>40 dB) was fabricated to achieve maximum modulation depth. The intensity referencing scheme employed allows the remote operation of the sensor and can compensate up to 90% attenuation along the fibre line without any loss of resolution. The wavelength referencing scheme discriminates against temperature dependent shift of the source spectra and minimizes possible measurement errors. The modular structure of the system can be expanded to accommodate a number of sensors.
Composite materials are vulnerable to damage, and this can result in conservatism in design and increased maintenance costs. One way of reducing these costs is by integrating a system into the composite material which can sense the damage condition and provide an assessment of its size, location and significance. This is a difficult task, and one of the main challenges is to develop sensor systems that can detect damage reliably while not compromising the material properties of the composite or significantly increasing its weight. A sensor system will be described which fulfills some of these requirements. It is based on the use of a highly birefringent optical fiber. The whole length of the fiber is used as the sensor, which minimizes additional weight. It also enables information to be obtained on the position of the damage along its length. The mechanical properties of the composite material are not degraded when the fiber is embedded, as long as some simple precautions are taken. The sensor utilizes the propagation of low coherence polarized light in highly birefringent optical fiber. Light is launched into one of the polarization states of the fiber and is coupled into the orthogonal state in the presence of damage. The sensor is interrogated interferometrically. Its operation will be described in detail and results will be presented which illustrate its perforce in detecting impact induced damage in a number of different composite material systems. Benefits of the system will be described together with areas which need further development.
The construction and evaluation of single-mode optical fibre tunable couplers are described with the emphasis on the polarisation maintaining fibre devices. The couplers operate via an evanescent field coupling mechanism and are produced based on the polishing technique. General characteristics including polarisation property, wavelength tunability and limitations are described. Applications of tunable fibre couplers are discussed.
Two novel quasi-distributed optical fiber sensor systems are presented using 'Optical Coherence Domain Polarimetry'. This technology utilizes the two polarization axes of a single length of hi-bi fiber as two independent optical paths and detects the positions of the discrete sensing units along the fiber with 'white-length' interferometry. The two systems presented can be classified as intensity and interferometric type, respectively by the way the system measures the relevant measurand amplitudes. Experimental results with the two systems performed as a distributed pressure and temperature sensor, respectively are also given.
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