Paper presents a miniature fiber-optic Pitot tube for gas flow rate measurements created at the tip of an optical fiber. The proposed all-fiber sensor employs two in-fiber Fabry-Perot cavities/chambers. The first chamber is arranged as a differential pressure sensor using a thin flexible silica diaphragm and two side holes for measurement of the difference between stagnation and static pressure, while the second chamber acts as a reference sensor for compensation of changes in the gas refractive index. The entire sensor is fusion-spliced, and is made out of sections of silica fibers and silica capillaries. It is appropriate for mid to high-velocity microfluidic gas flow sensing where miniature size is essential. Sensor operation is demonstrated in a flow velocity range between 0 to 260 m/s with a resolution better than 1.5 m/s. The sensor has a diameter of only 200 µm.
COBISS.SI-ID: 23097878
In this paper, an optical fiber sensor is proposed for measurement of the boiling point and boiling range of liquids. Since boiling point and/or boiling range of liquids correlate directly to chemical composition of liquids, the proposed sensor provides opportunity for on-line and in-situ chemical characterization of various liquids. The proposed sensor is manufactured on the tip of a standard optical fiber, and consists of a Fabry-Perot temperature sensor and short section Vanadium doped fiber, which serves as a microheater. The latter is cyclical and rapidly heated by application of high-power fiber-coupled laser diode, while the Fabry-Perot temperature sensor is used to detect appearance of boiling process and to measure the absolute temperature. The proposed sensor is less than 1 mm long and allows for characterizing samples in quantities of 140 nL in as short time as ten seconds. All-silica/all-fiber design of the sensor provides high chemical inertness, dielectric design and possibility for remote operation. Two sensor types are proposed; the first is intended for measurement of very small samples (140nL). This measurement takes only about 10 seconds. The second sensor type is suitable for online monitoring of binary or multicomponent mixtures, and provides accurate boiling range data of a given mixture.
COBISS.SI-ID: 15011587
This paper presents a method for gas concentration determination based on the measurement of the refractive index dispersion of a gas near the gas resonance in the near-infrared region (NIR). The gas refractive index dispersion line shape is reconstructed from the variation in the spectral interference fringes’ periods, which are generated by a low-finesse Fabry-Perot interferometer during the DFB diode’s linear-over-time optical frequency sweep around the gas resonance frequency. The entire sensing system was modeled and then verified experimentally, for an example of a low concentration methane-air mixture. We demonstrate experimentally a refractive index dispersion measurement resolution of 2 × 10-9 refractive index units (RIU), which corresponds to a change in methane concentration in air of 0.04 vol% at the resonant frequency of 181.285 THz (1653.7 nm). The experimental and modeling results show an excellent agreement. The presented system utilizes a very simple optical design and has good potential for the realization of cost-efficient gas sensors that can be operated remotely through standard telecom optical fibers.
COBISS.SI-ID: 25286403
This paper presents a micro-machined, high-resolution refractive index sensor suitable for monitoring of small changes in the composition of gases. Experimentally demonstrated measurement resolution, induced by gas composition variation, proved to be in the range of 5x10-9 of a Refractive Index Unit (RIU). The proposed all-silica, all-fiber sensor consists of an open-path Fabry-Perot micro-cavity that includes an in-fiber collimation and temperature-sensing segment. It is shown that a sensor’s resolution depends strongly on the signal interrogator’s properties and that, for a given interrogator, there is an optimum Fabry-Perot cavity length that yields the highest system resolution. Furthermore, high-resolution pressure and in situ temperature compositions of measurement results are required to obtain an unambiguous correlation between the gas composition and measured Refractive Index within the presented resolution range.
COBISS.SI-ID: 21660182
This paper proposes an all-optical-fiber sensor for continuous measurements of liquid levels. The proposed sensor utilizes an optically absorbing vanadium doped optical fiber, which is configured as a long-gauge, optically-heated, fiber-optic, Fabry-Perot interferometer that is immersed into the measured liquid. The sensor is excited cyclically by a medium-power 980 nm optical source, which induces periodic temperature variation and, consequently, optical path length modulation within the vanadium doped fiber. The amplitude of this path length variation depends on the liquid level and is measured by an interferometric approach. The relation between the liquid level and the amplitude of optical path length modulation caused by the fiber’s temperature variation were investigated analytically, and the theoretical model proved to be in good agreement with the experimental results. Two versions of level sensors are demonstrated experimentally, the first with single-side optical heating power delivery and 0.45 m measurement range, and the second with dual-side power delivery and 1 m of operational measurement span. Experimental measurement level resolutions achieved for 0.45 m and 1m operational measurement span were approximately 2 and 3 mm, respectively.
COBISS.SI-ID: 21659926