Andrew Michie

Temperature independent highly birefringent photonic crystal fibre

A highly birefringent photonic crystal fibre has been characterised as a function of temperature. The modal birefringence has been found to be independent of temperature from -25 to 800 degrees C.

Spun elliptically birefringent photonic crystal fibre

Elliptically birefringent fibre has been fabricated by spinning the preform of a highly linearly birefringent photonic crystal fibre (PCF) during the drawing process. The resulting Spun Highly Birefringent (SHi-Bi) PCF offers intrinsic sensitivity to magnetic fields through the Faraday effect without the high inherent temperature sensitivities suffered by conventional spun stress birefringence fibres. The ellipticity of the birefringence has been measured and temperature independence has been demonstrated.

Electric field and voltage sensing using thermally poled silica fibre with a simple low coherence interferometer

The polarization dependence of the linear electro-optic effect in poled silica is used to measure electric fields applied transversely across the fibre core using a simple low coherence interferometer. The path imbalance arising through the inherent birefringence of the poled fibre is modulated by the applied electric field. 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 spectrometer and the small optical path imbalance is calculated by processing the interferogram in a computer using Fourier transforms. Experimental results for linearity, and an analysis of the methods used are presented.

Electric field and voltage sensing at 50 Hz using a thermally poled silica optical fibre

Lab trials of two simple voltage sensor configurations demonstrate the basis of a field deployable voltage sensor capable of measuring the line voltage of a high voltage electricity transmission line. Sensor operation at 50 Hz is demonstrated with sampling rates up to 1000 Hz in the two separate experiments.

Characterisation of phase-shifts in gratings fabricated by over-dithering and simple displacement

Abstract Several different gratings utilizing phase-shifts in their designs are fabricated and characterised: a uniform grating with a single phase shift in the centre, a sinc-profile grating (with intrinsic phase shifts at the zeros), and a stretched cosine apodised grating with multiple and arbitrary phase shifts. The gratings are fabricated by either over-dithering the phase mask or a simple displacement of the phase-mask. The gratings are then characterised by measuring their spectral and group delay characteristics and using a grating reconstruction algorithm to determine the apodisation and phase profiles of the grating. The relative susceptibility of the different fabrication methods to errors is discussed along with the role of grating reconstruction in characterisation of gratings.

Spun elliptically birefringent photonic crystal fibre for current sensing

Spun elliptically birefringent fibre has been fabricated by spinning the preform of a highly linearly birefringent photonic crystal fibre (PCF) during the drawing process. The resulting spun highly birefringent (SHi-Bi) PCF offers sensitivity to magnetic fields for current measurements with greatly reduced temperature dependence in comparison with conventional spun stress birefringence fibres. The ellipticity of the birefringence has been measured and temperature independence has been demonstrated.

A comparison of Delayed Self-Heterodyne Interference Measurement of Laser Linewidth Using Mach-Zehnder and Michelson Interferometers

Linewidth measurements of a distributed feedback (DFB) fibre laser are made using delayed self heterodyne interferometry (DHSI) with both Mach-Zehnder and Michelson interferometer configurations. Voigt fitting is used to extract and compare the Lorentzian and Gaussian linewidths and associated sources of noise. The respective measurements are wL (MZI) = (1.6 ± 0.2) kHz and wL (MI) = (1.4 ± 0.1) kHz. The Michelson with Faraday rotator mirrors gives a slightly narrower linewidth with significantly reduced error. This is explained by the unscrambling of polarisation drift using the Faraday rotator mirrors, confirmed by comparing with non-rotating standard gold coated fibre end mirrors.

A low coherence interferometric sensing method with analysis and experimental results for voltage sensing

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 interferometers 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.

Polarisation dependence of the linear electro-optic coefficient in thermally-poled twin-hole silica fibre

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.

Eliptically polarizing optical fiber

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.