Silica based fibre-optic refractive index sensors are gaining acceptance over conventional refractometers and finding
applications in chemical/biological sensing due to many of their desirable properties. Here we present an optical fibre-based
refractive index sensor that uses the power transmission through etched D-shaped fibres. The sensor's operating
point and resolution can be tailored for a specific application by selecting the correct combination of the operating
wavelength and the cladding thickness of the etched fibre. The sensor's power transmission depends on the surrounding
refractive index in which the sensor head is immersed. The sensor presented has a maximum resolution on the order of
10-6 in its "high resolution" region and on the order of 10-4 in its "low resolution" region. The refractive index at which
the maximum resolution occurs in the high resolution region can be shifted by ~0.012 and by ~0.027 in the low
resolution region. To date, such high resolutions have been reported over narrow ranges and/or for fibre Bragg grating
based sensors, which require optical spectral analysis which typically, is costly.
A liquid level sensor based on etched D-shaped silica optical fibers is presented. The optical transmission of the sensor depends on the liquid level. The sensor can be realized as a continuous level sensor with a high resolution and requires only one fiber and one optical source and detector. We have demonstrated a sensor with a resolution of ~1 mm. The sensor works for liquids with refractive indices greater than ~1.45. We show that the sensor response is the same for increasing and decreasing liquid levels.
Cladding-reduced fibers with elliptical cores can be used in the fabrication of fiber-optic sensors. Here we analyze the power transmission ratio in cladding reduced D-shaped optical fibers for the purpose of determining the cladding thickness, in a non-destructive manner, when the fibers have been etched to reduce their cladding thicknesses to allow interaction of the optical evanescent field with an external medium having a refractive index greater than the mode effective index of the fiber. Parameters needed to determine the cladding thickness are determined empirically using the measured power transmission ratio of a few calibration fibers. We show that one can estimate the cladding thickness by fitting the measured transmission ratio curves for the fiber of interest to the curves generated for the calibration fibers.
Optical electric field sensors have been used for the measurement of high-voltages found in power substations. Typical
sensors are based on electro-optic crystals and hence require the coupling of light into and out of the crystals from optical
fibers. This coupling is difficult and costly. The objective of the work presented here is the design and implementation of
an optical electric field sensor that uses an entirely fiber-based sensor-head. The sensor-head is comprised of a D-shaped
optical fiber with its flat side coated with liquid crystals. D-fibers allow easy access to the evanescent optical field and
replacement of part of the cladding with an external medium allows for modulation of this optical field. We are
investigating the use of chiral Smectic A liquid crystals, which respond linearly to electric fields through the electroclinic
effect. The propagation characteristics of the D-fiber for various distances between the fiber core edge and flat and for
various refractive indices of the external medium are theoretically investigated and experimentally verified. Preliminary
experimental results for a prototype electric field sensor are presented. The sensor responds in a linear fashion to an
applied electric field.