Novel Fiber-Optical Refractometric Sensor Employing Hemispherically-Shaped Detection Element
We present the theoretical and experimental data on the performance of the novel fiber-optic refractometric sensor that employs the hemispherical optical detection element. We exploit the sensitivity of internal reflection of light on the element’s spherical surface to the refractive index of the surrounding medium, several internal reflections in series, and the focussing properties of the concave spherical surface to achieve the enhanced sensitivity and reduce the intrinsic optical loss in the sensor. We show that the transmission function of the new sensor can easily be modified in the wide interval of the refractive index of the surrounding medium. This new sensor may find applications in different instruments. Key-Words:Optoelectronics, instrumentation, refractive index measurement, liquid level measurement.
Analysis of refractometric optical fiber sensors: comparison between different forms of optical detection elements
The state of the art in the area of optical-fiber refractometric sensors includes a large number of different proposals about sensor designs and applications. However, there are few works that compare the transducer response to the refractive index of refractometric sensors with different geometrical shape. This makes it difficult to design the refractometric sensors optimized for particular applications. In addition, the existing knowledge relates mainly to the refractometric sensors with perfectly clean surfaces, while the surface of real sensors is frequently contaminated. In this work, we analyzed the response of optical-fiber refractometric sensors of ellipsoidal shape and the effect of the residual film of liquid (water, oil, etc.) on the transducer's surface on the transducer's response. Also, we determined the sensibility of the response to small variations of the geometrical parameters, in turn, allowed us to determine the tolerance margin in sensor fabrication. We obtained data on the effect of the liquid film of different thickness on the response of the optical detection element as well. These data allow one to make an optimal choice between different possible shapes of detection elements.
Digital fiber-optic liquid level sensor
A fiber-optic liquid level sensor is presented which directly outputs digitally encoded liquid level information. The sensor operates on selective coupling at the liquid surface between a source waveguide and an array of digitally masked receiving waveguides. The receiving waveguides carry optical "high/low" signals to a remote detector and discriminator circuit. The sensor is capable of liquid level resolution of ± 2 mm over a range of up to several meters. A 40-cm-long prototype sensor has demonstrated an optical signal-to-noise ratio of 10-20 dB for several different transparent and semi-transparent liquids. The digital nature of the sensor provides good isolation from drift and the effect of tilt, source intensity fluctuations, and variations in liquid characteristics. Optical fibers are the only connections to the liquid tank, providing complete electrical isolation. The associated electronics are relatively simple and inexpensive.