Kristie L. Cooper

All-fused-silica miniature optical fiber tip pressure sensor

An all-fused-silica pressure sensor fabricated directly onto a fiber tip of 125 microm diameter is described. Simple fabrication steps include only cleaving and fusion splicing. Because no chemical processes are involved, the fabrication is easy, safe, and cost effective. Issues in sensor design and loss analysis are discussed. The sensor has been tested for static pressure response, showing a sensitivity of 2.2 nm/psi, a resolution of 0.01 psi (68.9 Pa), a hysteresis of 0.025%, and capability of operation at temperatures up to 600 deegrees C. This miniature sensor may be suitable for medical diagnostics, environmental monitoring, and other industrial applications.

Miniature all-silica fiber optic pressure and acoustic sensors

We present a miniature diaphragm-based Fabry-Perot (F-P) interferometric fiber optic sensor fabricated by novel techniques for pressure or acoustic wave measurement that is only approximately 0.32 mm in diameter. By choosing different diaphragm thicknesses and effective diameters, we obtain a sensor measurement range from 5 to 10,000 psi (1 psi = 51.72 Torr) and a frequency response up to 2 MHz. In addition, the sensors F-P cavity can be set from micrometers to millimeters with a precision of several nanometers. With the all-silica structure, the sensor is reliable, biocompatible, and immune to electromagnetic interference and has high-temperature sensing capability.

Miniature fiber-optic multicavity Fabry-Perot interferometric biosensor

A fiber-optic sensor is designed based on multicavity Fabry-Perot interferometry for the study of optical thickness in self-assembled thin-film layers. This miniature sensor is applicable not only to the measurement of self-assembled polyelectrolyte layers but also to the immobilization of proteins such as immunoglobulin G (IgG). The binding of IgG and the corresponding antigen is observed, and the nonspecific binding characteristics are investigated. The optical thickness changes are used to evaluate the immobilization of the IgG and the immunological activities of the immobilized layers.

High-temperature fiber-tip pressure sensor

This paper presents a miniature fiber-optic high-temperature pressure sensor fabricated on the tip of a singlemode (SM) fiber by means of fusion splicing, cleaving, and wet chemical etching. A new approach was developed to simplify the fabrication and greatly improve the sensitivity. The sensor is made entirely of fused silica, whose high-temperature sensing capability is explored in detail for the first time. Two sensors were tested up to 611/spl deg/C and 710/spl deg/C, respectively, showing excellent repeatability better than 0.62% and 1.4%. The maximum operating temperature is limited by the mechanical creep of the fused silica diaphragm.

A novel temperature-insensitive optical fiber pressure sensor for harsh environments

A novel diaphragm-based miniature optical fiber pressure sensor has been shown to work at temperatures up to 700/spl deg/C with a sensitivity of 2.93 nm/psi and a resolution of 0.01 psi (68.9 Pa). A passive temperature compensation scheme was used to reduce the temperature dependence to 0.0076 psi//spl deg/C (52.4 Pa//spl deg/C). The sensor exhibited a linear response in the available testing range from 0 to 200 psi (1.38 MPa), and being composed entirely of fused silica, the sensors structure is very reliable, corrosion resistant, and immune to electromagnetic interference.

Microgap Multicavity Fabry–Pérot Biosensor

This paper presents a microgap multicavity Fabry-Perot interferometric sensor fabricated by wet etching and fusion splicing of single-mode optical fibers. The temperature dependence of the optical thickness measurement of self-assembled thin films can be compensated by extracting the temperature information from the multiplexed temperature sensor. Experimental results demonstrate that thin-film characteristics under temperature variations can be examined accurately. The high-temperature sensitivity of the temperature sensor also enables biosensing under temperature variations. This greatly improves the flexibility in sample handling and provides the opportunity to investigate temperature effects in biological applications.

Simultaneous measurement of humidity and temperature by combining a reflective intensity-based optical fiber sensor and a fiber Bragg grating

A novel sensor capable of simultaneously measuring temperature and humidity has been fabricated and demonstrated using optical fiber waveguides. The sensor head is composed of a fiber Bragg grating and a low-finesse Fabry-Perot interferometric cavity. The Fabry-Perot cavity was fabricated using the electrostatic self-assembled monolayer process for the molecular-level deposition of materials of different thicknesses that form a humidity-sensitive coating on the end of the fiber, while the in-line Bragg grating fiber element is used to monitor temperature. Experimental results for a humidity range from 11% to 97% RH and for a temperature range from 10/spl deg/C to 85/spl deg/C are shown.

Label-free DNA sequence detection using oligonucleotide functionalized optical fiber

The authors present a label-free method for direct detection of deoxyribonucleic acid (DNA) sequences. The capture DNA is immobilized onto the surface of a silica optical fiber tip by means of the layer-by-layer electrostatic self-assembly technique. Hybridization of target DNA with complementary capture DNA increases the optical thickness of the fiber tip. This phenomenon can be detected by demodulation of the spectrum of a Fabry-Perot cavity fabricated in the optical fiber. Experimental results demonstrate sequence specificity and sensitivity to nanogram quantities of target DNA sequences with short (∼5min) hybridization time.

Fabrication of microgratings on the ends of standard optical fibers by the electrostatic self-assembly monolayer process.

The electrostatic self-assembly monolayer process has been utilized for what is believed to be the first time to deposit quarter-wavelength stacks on the end faces of cleaved and polished optical fibers. Standard multimode optical fibers as well as single-mode optical fibers were used as substrates with different coating materials to fabricate broadband filters, and the experimentally measured spectral responses of these devices are shown. These optical filter structures were employed to develop chemical sensors that use an unperturbed reference wavelength to normalize the output signal.

Optical fiber gas sensor based on self-assembled gratings

The electrostatic self-assembled monolayer synthesis process is used to fabricate gas sensors by building up grating sensor elements on the ends of multimode optical fibers. These novel sensors can be designed to operate in the transmission windows of standard optical fibers and implemented using specific reference wavelengths to normalize the output signals. Experimental results for such sensors designed to detect dichloromethane gas are presented.