The operation of several singlemode erbium doped polymer waveguide amplifiers was demonstrated. Optical gain of 5 dB was achieved at two different signal laser wavelengths, using a 1.48 micrometers pump. The two polymer host in which gain was demonstrated were gelatin and polystyrene - both prepared in a waveguide structured with high doping levels.
Two distributed fiber optic sensors for use in the prevention and monitoring of corrosion in aircraft are described. These sensors, based on optical fibers that are intrinsically sensitive to either water or changes in pH, will alert maintenance personnel to the presence of water in lap joints and other inaccessible critical areas. Furthermore, the sensors can also locate precisely where the moisture infiltration has occurred. In a typical application, a sensor fiber would be embedded in a lap joint along the bottom panel of an aircraft's body, or on a wing, where water is likely to collect. Changes in the optical transmission through the fiber can be monitored either periodically or continuously to determine the extent of water penetration.
In our ongoing work developing a reversible optical chemical sensor (OCS) for CO, we have produced a greatly simplified and improved sensor design. Chemically impregnated porous optical fiber has been replaced with impregnated porous Vycor glass; a battery powered blue LED has replaced a compact Hg lamp and power supply; optical fibers are no longer necessary; The Vycor acts as both chemical transducer and optical waveguide. The CO OCS now consists of five components: a 9 V battery and a blue LED; a transition metal impregnated porous Vycor matrix/waveguide; a short pass interference filter or a colloidally colored glass bandpass filter; and a large area, resin coated Si photodetector. The CO OCS responds reversibly to the presence of [CO] in both air and in N<SUB>2</SUB>, over the 40 to 950 ppm range at STP. The sensor has shown a lower limit of detection of approximately 40 ppm at STP. In terms of the transmitted intensity, the sensor is very slow in responding to very slow changes or buildups in the [CO]<SUB>ambient</SUB>. Yet, in the presence of rapid changes in the [CO]<SUB>ambient</SUB>, the sensor displays a 100% time constant of 60 to 70 seconds irrespective of the delta [CO]<SUB>ambient</SUB>. The new design simplifies sensing greatly in that optical fibers (and the various problems associated with their use), bulky light sources, and extremely fragile porous optical fibers have been supplanted by small, durable, inexpensive, commercially available components. The sensor could find application in environments in which the [CO] can or does change rapidly.
Advances in integrated optics devices require the development of materials and technologies that can transmit, guide, receive, multiplex, demultiplex, modulate, and demodulate optical signals. These requirements are crucial for the realization of advanced integrated optic devices that fully employ the potentially wide bandwidth (approximately THz) of optical signal processing and computing. The authors are developing an innovative new technology for the photolithographic fabrication of sol-gel derived integrated optic devices (sol-gel IODs). The fabrication procedure is based on direct photolithographic writing of IODs onto a photoactive sol-gel glass matrix. Sol-gel glasses are made by a two-step process: first a gel film is chemically formed and dried to a porous state, and second the porous film is densified into solid glass at high temperature. An organometallic photosensitizer is doped into the porous matrix after the first step. Waveguide patterns are then formed by straightforward photolithographic techniques, and the unexposed sensitizer is removed. The final densification step locks in the waveguide patterns, creating a durable, impermeable integrated optic device. Depending on the choice of sensitizer, these waveguide patterns can be passive (simply having a higher index of refraction than the surrounding host glass) or active (possessing optical properties that can be influenced by the application of electric fields). The uncomplicated nature of this process makes this a very promising approach for the fabrication of commercially viable integrated optic devices.
A distributed fiber optic moisture sensor based on intrinsic changes in the optical properties of the cladding is reported. A 10-meter-long fiber sensor was fabricated that demonstrated a response to humidity in less than 5 minutes. The humidity-sensitive cladding was fabricated on-line during fiber draw by continuously coating a multimode glass core fiber with a polyvinyl acetate cladding, in which a water-sensitive indicator had been dissolved. The indicator was a solvatochromic dye that showed a pronounced hypsochromic shift in its absorption spectrum in the presence of water. The moisture response of the sensor was monitored by measuring changes in the optical attenuation of the fiber in the region between 580 nm and 650 nm. This spectral region facilitates the use of commercially available solid state optoelectronic devices such as LEDs, laser diodes, and PIN photodiode detectors, in order to produce a low-cost, compact, lightweight humidity sensor.
We report here experimental results for a nitrogen dioxide sensor based on optical transmission through porous silica fiber. The NO<SUB>2</SUB> optrode is activated by using a proprietary chemical pretreatment process on the porous silica. Light is coupled to and from the porous silica optrode via 600 micrometers diameter optical fibers. The peak response of the sensor is at approximately 420 nm and therefore can be monitored using a blue LED. The sensor demonstrated a reversible, full-range response from 0 to 10,000 ppm NO<SUB>2</SUB> in a balance of nitrogen. The sensor also demonstrated a sensitivity of 10 ppm. The range and sensitivity of this sensor make it suitable for monitoring nitrogen dioxide emission from combustion stacks.
A completely reversible fiber optic chemical sensor (FOCS) for carbon monoxide (CO) has been recently developed at Physical Optics Corporation (POC). The sensor, consisting of an organometallic complex adsorbed in a short segment of porous optical fiber, demonstrated spectroscopic changes upon exposure to CO. The sensor exhibits a strong absorption peak centered at 435 nm that disappears upon exposure to CO. The absorption peak reappears as the ambient CO partial pressure is reduced. This paper reports the results from testing a FOCS for CO based on the optical transmission at this absorption peak.
This paper describes a series of experimental results in the development of fiber optic oxygen sensor with excellent immunity to quenching by water vapor. The sensor exhibits good oxygen response (4 dB quenching when P<SUB>O(2</SUB>) changes from 0 to 190 torr) identically in both 0% and 100% relative humidity environments. To develop this sensor the solution spectra of several organic fluorescent compounds were characterized for oxygen quenching efficiency. The most promising of these fluorophores were coated onto porous substrates using a proprietary process and tested for their sensitivity to oxygen and the potential interference from water vapor. The presence of oxygen quenches the fluorescence radiated by many compounds. Since water is also commonly found to quench fluorescence, a humidity insensitive oxygen sensor would be of great value in most applications. Each of the sensors was characterized for its fluorescence excitation and emission wavelengths, sensitivity for oxygen, and quantum efficiency. The most promising fluorophores, decacyclene and benzo[g,h,i]perylene, demonstrated the best overall results of the compounds tested. These fluorophores were characterized for their response to oxygen, as well as a cross- sensitivity to water vapor, carbon monoxide and carbon dioxide.
This paper treats some of the general requirements of optoelectronic instrumentation systems for fiber optic chemical sensors and points out how nonimaging optical elements can be used to meet those requirements. Passive fiber optic chemical sensors, specifically remote spectroscopic absorbance, fluorescence, and Raman systems are discussed. The operation of nonimaging optics (NIOs) is explained, as are applications of these optical elements in fiber illumination, sample light collection, and filtering subsystems. Optical signal detection methodologies are also presented. The above topics are treated in an introductory or "tutorial" fashion.
This paper treats some of the general requirements of optoelectronic instrumentation systems for fiber optic chemical sensors and points out how non-imaging optical elements can be used to meet those requirements. Passive fiber optic chemical sensors, specifically remote spectroscopic absorbance, fluorescence, and Raman systems, are discussed. The operation of non-imaging optics (NIOs) is explained, as are applications of these optical elements in fiber illumination, sample light collection, and filtering subsystems. Optical design detection methodologies are also presented. The above topics are treated in an introductory or 'tutorial' fashion.