Nondestructive determination of cladding thickness in D-fibers

2007

Opt. Eng

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 ϳ1 mm. The sensor works for liquids with refractive indices greater than ϳ1.45. We show that the sensor response is the same for increasing and decreasing liquid levels.

Section: Operating Principlementioning

confidence: 99%

Optical fiber-based liquid level sensor

2007

Opt. Eng

“…The cladding thickness after etching can be determined accurately 33,34,37 . We used standard thermo-optic oils to measure the sensor's response.…”

Section: Experimental Setup and Resultsmentioning

confidence: 99%

“…Consequently, the transmission through the sensor head depends on n s and thus an intensity-based refractive index sensor can be realized. The D-fibre/SRI structure can be theoretically modeled by first replacing the fibre with a three-layer equivalent planar waveguide by matching modal fields and propagation constants 33,34 . This equivalent planar waveguide is then extended to a four-layer planar waveguide to take into account the SRI, which acts as a superstrate.…”

Section: Operating Principlesmentioning

confidence: 99%

Refractive index sensor based on etched D-fibres with wavelength adjustable operating point and resolution

2008

SPIE Proceedings

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 fibrebased 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.

“…There is excellent agreement between measured and calculated values indicating that the model can correctly predict our structures' propagation characteristics. We have further validated our model by imaging the cross-section of the etched region using a scanning electron microscope 22 .…”

Section: Experimental Verificationmentioning

confidence: 96%

In-line D-fiber electric field sensor using chiral liquid crystals

Shao

et al. 2006

Photonics North 2006

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.