Simon Pevec

Miniature all-fiber Fabry–Perot sensor for simultaneous measurement of pressure and temperature

This article presents a miniature, high-sensitivity, all-silica Fabry-Perot fiber-optic sensor suitable for simultaneous measurements of pressure and temperature. The proposed sensor diameter does not exceed 125 μm and consists of two low-finesse Fabry-Perot resonators created at the tip of an optical fiber. The first resonator is embodied in the form of a short air cavity positioned at the tip of the fiber. This resonator utilizes a thin silica diaphragm to achieve the sensors pressure response. The second resonator exploits the refractive index dependence of silica fiber in order to provide the proposed sensors temperature measurement function. Both resonators have substantially different lengths that permit straightforward spectrally resolved signal processing and unambiguous determination of the applied pressure and temperature.

High resolution, all-fiber, micro-machined sensor for simultaneous measurement of refractive index and temperature

This paper presents a highly-sensitive, miniature, all-silica, dual parameter fiber-optic Fabry-Perot sensor, which is suitable for independent measurement of the refractive index and the temperature of the fluid surrounding the sensor. The experimental sensor was produced by a micromachining process based on the selective etching of doped silica glass and a simple assembly procedure that included fiber cleaving, splicing and etching of optical fibers. The presented sensor also allows for direct compensation of the temperatures effect on the fluids refractive index change and consequently provides opportunities for the detection of very small changes in the surrounding fluids composition. A measurement resolution of 2x10(-7) RIU was demonstrated experimentally for a component of the refractive index that is related purely to the fluids composition. This resolution was achieved under non-stabilized temperature conditions. The temperature resolution of the sensor proved to be about 10(-3) °C. These high resolution measurements were obtained by phase-tracking of characteristic components in a Fourier transform of sensors optical spectrum.

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.

All-fiber, long-active-length Fabry-Perot strain sensor

This paper presents a high-sensitivity, all-silica, all-fiber Fabry-Perot strain-sensor. The proposed sensor provides a long active length, arbitrary length of Fabry-Perot cavity, and low intrinsic temperature sensitivity. The sensor was micro-machined from purposely-developed sensor-forming fiber that is etched and directly spliced to the lead-in fiber. This manufacturing process has good potential for cost-effective, high-volume production. Its measurement range of over 3000 µε, and strain-resolution better than 1 µε were demonstrated by the application of a commercial, multimode fiber-based signal processor.

Miniature fiber-optic sensor for simultaneous measurement of pressure and refractive index

This Letter presents a fiber-optic sensor created at the tip of an optical fiber for simultaneous measurements of pressure and refractive index. The sensor diameter does not exceed the standard fiber diameter and is shorter than 300 μm. Measurement resolutions of 0.2 mbar and 2×10(-5)  RIU were demonstrated experimentally by using spectral interrogation and Fourier-transform-based measurement algorithms (interrogation system bandwidth corresponded to 1 Hz). A micromachining process based on selective chemical etching of specially designed phosphorus-doped fibers, and a sequence of splice and cleave steps were used to fabricate the sensor.

Focused ion beam post-processing of optical fiber Fabry-Perot cavities for sensing applications.

Focused ion beam technology is combined with chemical etching of specifically designed fibers to create Fabry-Perot interferometers. Hydrofluoric acid is used to etch special fibers and create microwires with diameters of 15 μm. These microwires are then milled with a focused ion beam to create two different structures: an indented Fabry-Perot structure and a cantilever Fabry-Perot structure that are characterized in terms of temperature. The cantilever structure is also sensitive to vibrations and is capable of measuring frequencies in the range 1 Hz - 40 kHz.

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.

Nanowire-based refractive index sensor on the tip of an optical fiber

This letter presents a refractive index sensor created at the tip of an optical fiber that utilizes silica nanowire within a radius of between 225 nm and 600 nm, as a sensing element. Sensitivity in excess of 800 nm/RIU was demonstrated within an aquatic medium, while the entire sensor structure was shorter than 1 mm with a diameter equal to or less than the standard fiber diameter. The presented sensor structure is made entirely from silica and provides the mechanical protection of sensitive nanowire. The proposed sensor is thus a robust and self-sustained structure, which does not require any complex packing.

Miniature all-silica fiber-optic sensor for simultaneous measurement of relative humidity and temperature

This Letter presents a miniature fiber-optic sensor created at the tip of an optical fiber suitable for simultaneous measurement of relative humidity and temperature. The proposed sensor is based on two cascaded Fabry-Perot interferometers, the first configured as a relative humidity sensing element made from silica micro-wire coated with thin porous SiO2 layer, and the second as a temperature sensing element made from a segment of a standard single-mode fiber. The sensor has linear characteristics for both measurement parameters and a sensitivity of 0.48 deg/%RH and 3.7 deg/°C.

Optical fiber Fabry-Pérot sensor fabrication based on focused ion beam post-processing

A combination of focused ion beam milling and chemical etching is proposed for the creation of Fabry-Pérot cavities in microwires. Both simple cavities and cantilevers are created on 15 μm-diameter microwires and characterized in temperature. The cantilever structure shows sensitivity to vibration and is capable of measuring frequencies in the range 1 Hz – 40 kHz.