An All-Fiber Fabry-Pérot Sensor for Emulsion Concentration Measurements.

This paper describes a Fabry-Pérot sensor-based measuring system for measuring fluid composition in demanding industrial applications. The design of the sensor is based on a two-parametric sensor, which enables the simultaneous measurement of temperature and refractive index (RI). The system was tested under real industrial conditions, and enables temperature-compensated online measurement of emulsion concentration with a high resolution of 0.03 Brix. The measuring system was equipped with filtering of the emulsion and automatic cleaning of the sensor, which proved to be essential for successful implementation of a fiber optic RI sensor in machining emulsion monitoring applications.

Nano-strain resolution fiber-optic Fabry-Perot sensors compatible with moderate/low resolution VIS-NIR spectrometers.

This paper reports on nano-strain resolution fiber-optic Fabry-Perot sensors produced by an improved selective etching method. The presented sensors exhibit high spectral sensitivity, low intrinsic temperature response, small size and mounting comparable to conventional Fiber Bragg gratings. Furthermore, the proposed sensors can be read-out by a combination of cost-efficient and widely available VIS/NIR spectrometers and LEDs used in lighting/automotive applications. A strain resolution of 1 nɛ was demonstrated when using a high-end FBG signal interrogator, while the application of a cost-efficient VIS spectrometer still yielded a strain resolution of about 20-70 nɛ. When applying suitable temperature compensation, absolute measurements with the nano-strain range are also plausible.

Miniature magneto-optic angular position sensor.

This Letter describes a miniature Fabry-Perot, contactless, magneto-optic sensor for angular position measurement. The sensor utilizes a magneto-optic fluid comprising barium hexaferrite nanoplatelets that become birefringent in the presence of an external magnetic field and a compact fiber-optic sensor system for tracking the liquid's optical axis direction. An efficient temperature compensation system is provided which allows the use of otherwise highly temperature-sensitive magneto-optic liquids. An unambiguous measurement range of 90° and a resolution of better than 0.05° are demonstrated experimentally.

Resonant-Opto-Thermomechanical Oscillator (ROTMO): A Low-Power, Large Displacement, High-Frequency Optically Driven Microactuator.

A light-driven micromechanical oscillator is presented, which can be operated by a low optical power (in the mW, or even the µW range), can produce large mechanical displacements (>5-100 µm), and can be designed to operate at frequencies from sub-kHz up to more than 200 kHz. The actuation of the oscillator is achieved by an asymmetrically metal-coated optical microwire configured into a silica micromechanical oscillator. The metalized optical microwire confines and absorbs the light strongly over a short distance, which results in a controlled optical power conversion into heat, and, consequently, into mechanical actuation through the temperature rise and the difference in thermal expansions of the silica microwire and the asymmetrically applied metal layer. Mechanical displacements are amplified further by the resonance operation of the oscillator, which is driven by a low-power, harmonic optical excitation signal generated by a current-modulated laser diode. Proper selection of the micromechanical oscillator's geometrical configuration and materials allows for a high-frequency operation at large mechanical displacements of the oscillator, while relying on low excitation optical power. The presented concept of a fully optically driven micromechanical oscillator may, thus, present a basis for realization of new classes of actuated micro-opto-mechanical Systems and similar photonics microdevices.

Optical Micro-Wire Flow-Velocity Sensor.

This paper presents a short response time, all-silica, gas-flow-velocity sensor. The active section of the sensor consists of a 16 µm diameter, highly optically absorbing micro-wire, which is heated remotely by a 980 nm light source. The heated microwire forms a Fabry-Perot interferometer whose temperature is observed at standard telecom wavelengths (1550 nm). The short response time of the sensor allows for different interrogation approaches. Direct measurement of the sensor's thermal time constant allowed for flow-velocity measurements independent of the absolute heating power delivered to the sensor. This measurement approach also resulted in a simple and cost-efficient interrogation system, which utilized only a few telecom components. The sensor's short response time, furthermore, allowed for dynamic flow sensing (including turbulence detection). The sensor's bandwidth was measured experimentally and proved to be in the range of around 22 Hz at low flow velocities. Using time constant measurement, we achieved a flow-velocity resolution up to 0.006 m/s at lower flow velocities, while the resolution in the constant power configuration was better than 0.003 m/s at low flow velocities. The sensing system is constructed around standard telecommunication optoelectronic components, and thus suitable for a wide range of applications.

Miniature all-fiber force sensor.

A miniature all-fiber Fabry-Perot sensor for measurement of force is presented in this Letter. The sensor consists of a thin silica diaphragm created at the tip of the fiber. The central part of the diaphragm is extended into a silica pole, which is ended with a round-shaped probe or a sensing cylinder apt for asserting measured force. The entire sensor is made of silica glass and has a cylindrical shape with a length of about 800 µm and a diameter of about 105 µm. Force sensing resolution of about 0.6 µN was demonstrated experimentally while providing an unambiguous sensor measurement range of about 0.6 mN. The sensor is shown for measurements of surface tension of liquids and biological samples examination.

PECVD of Hexamethyldisiloxane Coatings Using Extremely Asymmetric Capacitive RF Discharge.

An extremely asymmetric low-pressure discharge was used to study the composition of thin films prepared by PECVD using HMDSO as a precursor. The metallic chamber was grounded, while the powered electrode was connected to an RF generator. The ratio between the surface area of the powered and grounded electrode was about 0.03. Plasma and thin films were characterised by optical spectroscopy and XPS depth profiling, respectively. Dense luminous plasma expanded about 1 cm from the powered electrode while a visually uniform diffusing plasma of low luminosity occupied the entire volume of the discharge chamber. Experiments were performed at HMDSO partial pressure of 10 Pa and various oxygen partial pressures. At low discharge power and small oxygen concentration, a rather uniform film was deposited at different treatment times up to a minute. In these conditions, the film composition depended on both parameters. At high powers and oxygen partial pressures, the films exhibited rather unusual behaviour since the depletion of carbon was observed at prolonged deposition times. The results were explained by spontaneous changing of plasma parameters, which was in turn explained by the formation of dust in the gas phase and corresponding interaction of plasma radicals with dust particles.

Deposition Kinetics of Thin Silica-Like Coatings in a Large Plasma Reactor.

An industrial size plasma reactor of 5 m3 volume was used to study the deposition of silica-like coatings by the plasma-enhanced chemical vapor deposition (PECVD) method. The plasma was sustained by an asymmetrical capacitively coupled radio-frequency discharge at a frequency of 40 kHz and power up to 7 kW. Hexamethyldisilioxane (HMDSO) was introduced continuously at different flows of up to 200 sccm upon pumping with a combination of roots and rotary pumps at an effective pumping speed between 25 and 70 L/s to enable suitable gas residence time in the plasma reactor. The deposition rate and ion density were measured continuously during the plasma process. Both parameters were almost perfectly constant with time, and the deposition rate increased linearly in the range of HMDSO flows from 25 to 160 sccm. The plasma density was of the order of 1014 m-3, indicating an extremely low ionization fraction which decreased with increasing flow from approximately 2 × 10-7 to 6 × 10-8. The correlations between the processing parameters and the properties of deposited films are drawn and discussed.

Optically controlled fiber-optic micro-gripper for sub-millimeter objects.

A miniature, fully optically controlled, dielectric, opto-thermally actuated tweezer/micro-gripper that is suitable for the manipulation of small objects is presented. The tweezer/micro-gripper is formed at the tip of an optical fiber and utilizes a mid-power laser diode for its actuation. The manipulation of small objects such as short pieces of optical fibers is demonstrated. Small dimensions, fully dielectric design, non-electric actuation, remote operation through the fiber, and good harsh environment compatibility (chemical, radiation, and temperature) might provide opportunities for micromanipulation in a system and areas where current solutions are inadequate.

Miniature fiber-optic Fabry-Perot refractive index sensor for gas sensing with a resolution of 5x10-9 RIU.

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.

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.

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.

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 temperature's effect on the fluid's refractive index change and consequently provides opportunities for the detection of very small changes in the surrounding fluid's composition. A measurement resolution of 2x10(-7) RIU was demonstrated experimentally for a component of the refractive index that is related purely to the fluid's 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 sensor's optical spectrum.

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.

Miniature micro-wire based optical fiber-field access device.

This paper presents an optical fiber-field access device suitable for use in different in-line fiber-optics' systems and fiber-based photonics' components. The proposed device utilizes a thin silica micro-wire positioned in-between two lead-in single mode fibers. The thin micro-wire acts as a waveguide that allows for low-loss interconnection between both lead-in fibers, while providing interaction between the guided optical field and the surrounding medium or other photonic structures. The field interaction strength, total loss, and phase matching conditions can be partially controlled by device-design. The presented all-fiber device is miniature in size and utilizes an all-silica construction. It has mechanical properties suitable for handling and packaging without the need for additional mechanical support or reinforcements. The proposed device was produced using a micromachining method that utilizes selective etching of a purposely-produced phosphorus pentoxide-doped optical fiber. This method is simple, compatible with batch processes, and has good high-volume manufacturing potential.

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 sensor's pressure response. The second resonator exploits the refractive index dependence of silica fiber in order to provide the proposed sensor's 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.

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 µÎµ, and strain-resolution better than 1 µÎµ were demonstrated by the application of a commercial, multimode fiber-based signal processor.