In this paper we propose a new approach to fibre optic voltage sensors via voltage-controlled Liquid Crystals (LC),
which would allow direct measurement of up to 400 kV/m electric fields at multiple points. In addition, a novel
polarization independent fibre optic sensor configuration is presented that exhibits a linear electro-optic (EO) response
to variations of the electrical field under test.
Liquid crystal (LC) cells can be used in conjunction with optical fibres to develop cheap and efficient sensors, such as
voltage sensors or hydrophones. In this paper we apply an effective tensor model to describe reflection from gold-coated
deformed-helix ferroelectric liquid crystal (DHFLC) cells. We show that, depending on the polarisation of the incident
light, it is possible to obtain a linear electro-optical response to the voltage applied to the cell. Theoretical results are
compared with experimental results yielding accurate agreement.
We describe a fibre optic hydrophone array system that could be used for underwater acoustic surveillance applications
e.g. military, counter terrorist and customs authorities in protecting ports and harbors, offshore production facilities or
coastal approaches as well as various marine applications. In this paper we propose a new approach to underwater sonar
systems using voltage-controlled Liquid Crystals (LC) and simple multiplexing method. The proposed method permits
measurements of sound under water at multiple points along an optical fibre using low cost components (LC cells),
standard single mode fibre, without complex interferometric measurement techniques, electronics or demodulation
software.
The use of Faraday rotator mirrors in a Michelson interferometer configuration is shown to
significantly improve resolution and coherence for delayed self-heterodyne interferometry.
This paper studies torsion of air-hole microstructured fibers induced by fiber packaging. The twist of
two-hole optical fiber induced while the fibers were coiled into a helix along the surface of a cylinder was
experimentally observed and simulated using the Finite Element Analysis. Both experiment and simulation reveal
periodic twisting patterns when two holes fibers were coiled along the surface of a cylinder.
A distributed feedback laser was fabricated in Er3+-doped photonic crystal fibre. Single mode lasing is obtained with
<10kHz linewidth. The output was amplified to 12mW using a commercial erbium doped fibre amplifier (EDFA).
KEYWORDS: Sensors, Electrodes, Silica, Signal processing, Sensing systems, Electro optics, Polarization, Optical fibers, Interferometry, Signal to noise ratio
All fibre voltage sensing using helically coiled lengths of thermally poled twin-hole silica optical fibre is presented. The
thermally poled optical fibre possesses a small electro-optic response and forms the basis of an intrinsic sensor for
electric fields. The helical arrangement of the poled silica fibre, from the ground to the high voltage conductor, allows an
approximation to a tangential line integral of the electric field i.e. the voltage, to be calculated. The interferometric
interrogation system combined with the high speed digital signal processing system allowed voltage measurements at an
effective sampling rate of approximately 5000 samples per second. Preliminary lab system test results are presented.
The ongoing development of a fibre optic voltage sensor requires a self-aligning fibre. We experimentally demonstrate
fibre designs with preferential bending directions which self-align when coiled as part of a voltage sensor device. Such a
fibre has much wider applications.
Polarisation maintaining fibres used for sensing and interferometry typically have high birefringence [1-3] and are known as HiBi fibres. Since photonic crystal fibre (PCF) was first reported [4,5], HiBi PCFs with birefringence comparable to and greater than conventional highly stressed bow-tie and PANDA fibre have been demonstrated [6-10]. Very high levels of form birefringence in PCFs have been possible due to the flexibility in geometry and the high refractive index contrast offered by making a fibre with an air silica structure (ASS). In this paper we present experimental results that show effective temperature independent, or athermal, birefringence in a HiBi-PCF [11-14]. This is expected to be beneficial for a number of sensing and interferometric applications. For example, fibre optic gyroscopes (FOG) generally use very long lengths of coiled HiBi fibre in a Sagnac configuration to attain suitable sensitivity. FOG cost is, however, a significant driving factor in limiting the expansion of FOGs into new lower cost applications. FOG performance has been primarily limited by environmental temperature sensitivity [15,16] and stabilisation routes, using temperature-stabilised packaging, add too much to their cost. The use of a passive, temperature insensitive HiBi-PCF is a much lower cost alternative that does not require active stabilisation, thereby potentially overcoming these limitations and potentially opening up a new low cost market for FOG technology whilst retaining high performance.
A 3-Section Lyot Fibre Depolariser was used to substantially reduce the degree of polarisation of an Er-doped superfluorescent fibre source. The residual degree of polarisation of this improved Er-doped superfluorescent fibre source is found to be 0.05% (-33dB).
In this paper a low coherence interferometric sensing method is presented. The magnitude of a small optical path length imbalance is monitored by measuring the wavelength dependence of the interferometer's output. The interferometer produces a spectral modulation, or interferogram, imposed on the background spectrum of the broadband light source used to illuminate the sensor. The interferograms are then recorded using a high-speed spectrometer and the small optical path imbalance is calculated by processing the interferogram in a computer using a Fast Fourier Transform (FFT).
This sensing system has been configured to form the basis for an optical fibre voltage sensor. The system monitors the total retardance of a section of thermally poled twin hole silica fibre (sensing fibre). Transverse electric fields applied to the sensing fibre will then modulate its total retardance due to the polarisation dependence of the induced linear electrooptic effect. Experimental results for linearity, and an analysis of the methods used are presented.
The polarization dependence of the linear electro-optic coefficient (LEO) in thermally poled twin-hole silica fiber has been characterized by two separate interferometric methods and the results compared. Firstly the magnitudes of the individual LEO values for the two separate polarization states of the thermally poled twin-hole silica fiber were measured and the difference in the LEO values was calculated by subtraction. Secondly a direct measurement of the difference was made using an interferometric technique by monitoring the total retardance of the birefringent poled twin hole fiber section while applying various electric fields to the internal electrodes. The second method, which directly measures the differential LEO, has strong potential as an interferometric method for the measurement of electric fields. The intended application is the measurement of line voltage in high voltage electricity distribution and transmission systems.
Elliptically polarizing optical fiber has been fabricated. Measurements show an extinction of the lossy mode relative to the transmitted mode of around 10 dB/m. The preform is spun during drawing and the ellipticity of the transmitted polarization state is as expected from the measured beat length of the unspun fiber and the pitch length of the spun fiber. This fiber is expected to be useful for interferometric or laser-based electric-current sensing, and perhaps in other applications for an in-line polarizer.
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