Edvard Cibula

All-fiber high-sensitivity pressure sensor with SiO 2 diaphragm

The design and fabrication of a miniature fiber Fabry-Perot pressure sensor with a diameter of 125 microm are presented. The essential element in the process is a thin SiO2 diaphragm that is fusion spliced at the hollow end of an optical fiber. Good repeatability and high sensitivity of the sensor are achieved by on-line tuning of the diaphragm thickness during the sensor fabrication process. Various sensor prototypes were fabricated, demonstrating pressure ranges of from 0 to 40 kPa to 0 to 1 MPa. The maximum achieved sensitivity was 1.1 rad/40 kPa at 1550 nm, and a pressure resolution of 300 Pa was demonstrated in practice. The presented design and fabrication technique offers a means of simple and low-cost disposable pressure sensor production.

Miniature fiber-optic pressure sensor with a polymer diaphragm.

The fabrication and experimental investigation of a miniature optical fiber pressure sensor for biomedical and industrial applications are described. The sensor measures only 125 microm in diameter. The essential element is a thin polymer diaphragm that is positioned inside the hollow end of an optical fiber. The cavity at the fiber end is made by a simple and effective micromachining process based on wet etching in diluted HF acid. Thus a Fabry-Perot interferometer is formed between the inner fiber-cavity interface and the diaphragm. The fabrication technique is described in detail. Different sensor prototypes were fabricated upon 125 microm-diameter optical fiber that demonstrated pressure ranges from 0 to 40 and from 0 to 1200 kPa. A resolution of less than 10 Pa was demonstrated in practice. The fabrication technique presented facilitates production of simple and low-cost disposable pressure sensors by use of materials with that ensure the required biocompatibility.

In-line short cavity Fabry-Perot strain sensor for quasi distributed measurement utilizing standard OTDR.

This paper presents an in-line, short cavity Fabry-Perot fiber optic strain sensor. A short air cavity inside a single-mode fiber is created by the fusion splicing of appropriately micro machined fiber tips. A precise tuning of the cavity length is introduced and used for the setting of the sensor static characteristics within the quasi-linear range around a quadrature point, which significantly simplifies signal processing. Sensor insertion losses achieved by short cavity design and optimized fusion splicing proved to be below 1 dB. Low insertion loss allows for effective cascading of the proposed strain sensors into a quasi-distributed sensor array. A practical 10-point quasi-distributed strain sensor array was demonstrated in practice, where each in-line sensor was tuned to the same operating point in the static characteristics, thus allowing for simple interrogation of the sensor array by using standard telecommunication OTDR. In addition, precise tuning of the short cavity Fabry Perot sensor was applied for an effective compensation of temperature-induced strain errors and for an increase in the unambiguous measuring range, while improving the overall linearity of the sensor system.

Miniature all-glass robust pressure sensor

This paper describes a newly designed all-glass miniature (Ø 125 microm) fiber-optic pressure sensor design that is appropriate for high-volume manufacturing. The fabrication process is based on the chemical etching of specially-designed silica optical fiber, and involves a low number of critical production operations. The presented sensor design can be used with either single-mode or multi-mode lead-in fiber and is compatible with various types of available signal processing techniques. A practical sensor sensitivity exceeding 1000 nm/bar was achieved experimentally, which makes this sensor suitable for low-pressure measurements. The sensor showed high mechanical stability, good quality of optical surfaces, and very high tolerance to pressure overload.

Micromachining of Optical Fibers Using Selective Etching Based on Phosphorus Pentoxide Doping

This paper presents a maskless micromachining process that can reform or reshape a section of an optical fiber into a complex 3-D photonic microstructure. This proposed micromachining process is based on the etching rate control achieved by the introduction of phosphorus pentoxide into silica glass through standard fiber manufacturing technology. Regions within a fiber cross section doped with phosphorus pentoxide can etch up to 100 times faster than pure silica when exposed to hydrofluoric acid. Various new photonic devices can be effectively and economically created by design and production of purposely doped fibers that are spliced at the tip or in-between standard lead-in fibers, followed by etching into a final structure.

Low-loss semi-reflective in-fiber mirrors

This paper presents a method for the efficient production of all-fiber semi reflective mirrors suitable for fiber sensors and other all-fiber device applications. The mirrors are obtained by the short duration etching of a standard single mode fiber in hydrofluoric acid, followed by an on-line feedback-assisted fusion splicing process. Fiber mirror reflectance up to 9.5% with excess losses below 0.25 dB were produced in practice, which is in good agreement with provided theoretical and modeling analyses. Control over the etching time and fusion splicing process allows for balancing between reflectance and transmittance, while maintaining low excess loss of experimentally produced mirrors.

In-Line Fabry–Pérot Refractive Index Sensor

An in-line intrinsic Fabry-Perot refractive index (RI) sensor is demonstrated. The sensor consists of a short single-mode fiber (SMF) section with removed cladding that is fusion spliced between two lead fibers containing in-fiber mirrors. The measured medium surrounding the decladed fiber section affects the fundamental modes effective index and, consequently, the optical path length of the Fabry-Perot interferometer (FPI). Sensors with different diameters of decladed regions were produced and experimentally evaluated within an RI range of between 1.33 and 1.444. The proposed sensor can be interrogated by standard spectrally resolved interrogators.

All-fiber Fabry-Perot strain sensor

The fiber-optic strain sensor based on Fabry-Perot air cavity, made inside single-mode fiber by simple micromachining technique is presented. The sensor features near-linear response, low transmission loss, low temperature dependence, easy fabrication and it can be applied in quasi-distributed networks by using standard OTDR interrogation.

Remote monitoring of water salinity by using side-polished fiber-optic U-shaped sensor

In this paper, a remote water salinity measurement system based on a simple and low-cost intensity based side-polished fiber-optic U-shaped sensor is presented. The sensor system utilizes a side-polished U-shaped configuration in order to maximize the sensitivity and expand the measurement range. The implemented salinity sensor is made of a multimode plastic optical fiber, and sensor determines the salinity by measuring the refractive index. Measurement resolution and uncertainty of proposed salinity sensor are 0.001 and 0.002, respectively. Wireless electronics based on ZigBee protocol is also implemented. Therefore, the sensor has the possibility of wireless measurements. The main advantages of this sensor are simplicity, lightness and flexibility. This sensor is also electrically safe and immune to electromagnetic interferences. In LabVIEW software package client and server applications are implemented, which gives a possibility of remote monitoring of water salinity over the internet.

In-line optical fiber-sensors based on low-loss semi-reflective in-fiber mirrors

This paper presents the design and fabrication of semi-reflective in-fiber mirrors and their usage for the realization of different miniature fiber sensors. The fabrication of a semi-reflective in-fiber mirror is based on the selective chemical etching and splicing of standard single-mode fibers (SMF). The mirrors reflectance can be set precisely in between any range between 0.1% and 9.5 %. The practical usability of the produced in-fiber mirrors was evaluated by the fabrication of an in-line temperature sensor and evanescent field refractive index (RI) sensor. A temperature sensor is an intrinsic type of in-line FPI, formed between an in-fiber mirror and a flat-cleaved optical fiber tip. As an example, a temperature sensor that was optimized within a range from 0 to 100°C showed a temperature resolution better than 0.1 °C, and a repeatability better than 0.2 °C. The evanescent RI sensor was created by the splicing of a small-diameter SMF between two in-fiber mirrors and removing of the intermediate fiber-cladding by chemical etching. The effective index of the fundamental mode depended on the surrounding-medium RI, which was interrogated by a spectrally-resolved technique. A high sensitivity of 830 nm/RIU was measured at RI of 1.444.