Michael J. O'Rourke

Temperature sensing by band gap optical absorption in semiconductors

A new sensor for measuring high temperature in harsh environments is presented. The sensor concept is based on the fact that the band gap energy of semiconductors, and accordingly the cut-on optical wavelength, depend strongly on temperature. The optical wavelength at which these semiconductors start transmitting light typically increases as the temperature increases. Durable optical fibers transmit light to and from the semiconductive material. This paper addresses the feasibility of the concept at temperatures up to 800 degrees Celsius, and presents results using different semiconductors including gallium arsenide, silicon, and gallium phosphide.

High-temperature sensors based on thermal radiation integrative waveguides

Blackbody radiation sensors are well known for measuring high temperature in harsh environments. Conventionally, these sensors require materials with high and stable emissivity. Any dimensional changes or shifts in the emissivity over the lifetime of the device would degrade sensor performance. This paper presents a new temperature sensing concept where thermal radiation is integrated over the length of an optical waveguide. Under some easily attainable conditions, it is shown that the new sensor output is independent of both the emissivity of the material and the length of the integrating waveguide.

Lens-type refractometer for on-line chemical analysis

On-line monitoring of the relative chemical content of fluid mixture is needed for a number of industrial applications. This paper describes a lens type refractometer which may be inserted on-line without affecting fluid flow and responds to changes in the refractive index of the fluid and, therefore, to fluid composition. The refractometer includes an optical fiber that delivers light to an optical clear cylindrical fixture through which the chemical mixture flows. The cylindrical fixture/liquid combination acts as a lens whose focal length depends on the refractive index of the medium. Light delivered by the optical fiber is focused on the other side of the lends, at a position that depends on the focal length. Two optical fibers collect the focused light at positions that are selected such as to maximize the sensitivity of the refractometer over the range of interest. For example, for a binary mixture, the tip of one fiber may be positioned at the focal point of the lends when it contains 100% of one chemical species, while the tip of the second fiber may be positioned at the focal point corresponding to the second species.

Linear position sensing by light exchange between two lossy waveguides

Optical position sensors have gained wide popularity in several segments of theindustry over the past few years. They offer a number of advantages overconventional types of sensors such as linear variable differential transformer(LVDT) and potentiometric devices. Specific advantages include immunity to

Optical Control Panel For Automotive Applications

This paper describes a new type of optical control panel that eliminates any electrical contacts and mechanically moving parts. It has potential for low cost, improved reliability, and diagnosability. In its simplest form, the control panel consists of an optically lossy plastic strip that is illuminated from the back side, and that runs parallel to a segmented screen on the front side. Each of the backlit segments acts as a switch. Normally all switches are in the OFF mode. OFF to ON switching is obtained by bringing a finger or reflector close to a segment so as to reflect and couple light into the strip. The back-coupled light divides into two guided waves that attenuate as they propagate towards the extremities of the strip. Two photodetectors detect these attenuated signals. Switch position is inferred from the ratio of the two detected signals. Three early prototypes were tested, each consisting of seven 5 by 15 millimeter switching segments. In all three cases, switch position was inferred without any ambiguity. This type of optical control panel is easy to incorporate in a display.

Microbending Losses Of Metal Coated Single Mode, Multimode, And Cladding-Free Fibers

Under optimized conditions the microbending sensitivity is comparable in metal coated multimode and single mode fibers. Microbending losses in step index fibers may show significant wavelength dependence and this dependence is quite similar for single and multimode fibers. The spectral characteristics of the losses depend not only on the fiber parameters but also on the periodicity of microbending. An inexpensive cladding-free fiber exhibits two-region displacement sensitivity. The maximum sensitivity of the single region fiber can exceed the maximum sensitivities of conventional fibers.