Combustible gases, such as propane and methane-based city gas, are widely used in many homes and factories.
However, accidents caused by gas leakage have become a menace to everyday life. Therefore, we have developed a
simple and safe optical sensor for detecting leaking gas, which consists of plastic optical fiber (POF) coated with
swelling polymer as a sensitive cladding layer. In experiments, a gas concentration below 3% was detected for both
propane and methane gas. However, it was also confirmed that this system is influenced by humidity. Therefore, further
improvement of the POF gas-sensing system with a POF humidity calibrator is proposed and discussed in this paper.
The wavelength division multiplexing (WDM) technology effectively increases the bandwidth capacity of a
communication line without installing additional fibers and increasing data bit rate to high levels. Optical add-drop
modules are key components in WDM optical networks.
We propose two types of all-optical tunable filter with a photorefractive planar waveguide. The photo-induced index
grating in the PR waveguide by control beams drops off a part of wavelength components in the WDM signal beam. It
make possible to select the wavelength components of the signal beam by optically adjusting the wave vector of the
grating. It is also possible to control bandwidth of the output signal by adjusting the broadening of the grating in the
waveguide. The photorefractive effect is known as one of the most efficient nonlinear effects, and therefore the device is
controllable by the relative low beam power comparing with the conventional devices using non-linear optical effects.
The channel crosstalk is generated by using uniformly broadened index grating. We note that the nonreciprocal energy
transfer between the two control beams via a photorefractive two-wave mixing causes the nonuniform index grating like
Gaussian profile. We therefore suggest the suppression method of channel crosstalk by adjusting the incident intensity
of the control beams.
A novel plastic-optical-fiber (POF) microphone for discerning devoiced breath, which is based on the detection of
moisture pattern depending on the shape of mouth, have been studied. In the experiment coupled with this microphone
and Dynamic Programming (DP) matching method, recognition rate over 90% was obtained against five devoiced
vowels in Japanese. Therefore, using this system, verbally handicapped people will create sounds with a small effort.
Conversation is the most practical and common form in communication. However, people with a verbal handicap feel a
difficulty to produce words due to variations in vocal chords. This research leads to develop a new devoiced microphone
system based on distinguishes between the moisture patterns for each devoiced breaths, using a plastic optical fiber
(POF) moisture sensor. In the experiment, five POF-type moisture sensors with fast response were fabricated by coating
swell polymer with a slightly larger refractive index than that of fiber core and were set in front of mouth. When these
sensors are exposed into humid air produced by devoiced breath, refractive index in cladding layer decreases by swelling
and then the POF sensor heads change to guided type.
Based on the above operation principle, the output light intensities from the five sensors set in front of mouth change
each other. Using above mentioned output light intensity patterns, discernment of devoiced vowels in Japanese (a,i,u,e,o)
was tried by means of DynamicProgramming-Matching (DP-matching) method. As the result, distinction rate over 90%
was obtained to Japanese devoiced vowels. Therefore, using this system and a voice synthesizer, development of new
microphone for the person with a functional disorder in the vocal chords seems to be possible.
Combustible gases such as propane gas and methane gas are widely used in many homes and factories. However,
accidents caused by gas leakage become a menace to everyday life. Therefore, development of quick and highly
sensitive gas leakage sensor is required strongly. From these backgrounds, we have studied about plastic optical fiber
(POF) gas leakage sensor because the POF have many advantages such as low-cost, light weight, immunity to electromagnetic noise. In this paper, the POF sensing system for multi-point gas leakages and its long term stability have been studied. In the experiment, gas concentration below 1% was detected for both propane gas and methane gas. This operation does not depend on a light wavelength. So, using several LED light sources with different wavelength, the POF sensing
system for multi-point gas leakages was constructed. In the experiment using blue-, green- and red-LED, sensing of
three-point gas leakages could successfully be obtained. Further more, considering its system for real application, long
term stability of the sensor head was also checked and it was confirmed that the sensitivity does not change over 15 days.
Recently, alcohols such as methanol and ethanol have a wide attention as important fuel in next generation. However, As
is known, many alcohols have a toxic and explosive nature. To prevent accidents caused by alcohol, development of a
safety and highly sensitive sensor is required strongly. In addition, it is desired to be simple and low-cost. So, in this
paper, polymer waveguide-type optical alcohol sensors such as fiber-type and channel waveguide-type have been
studied. In these sensor head, refractive index n2 of cladding layer was set at slightly larger value than that of core (n1). Therefore, in the state without alcohol, the sensor head operate as a leaky waveguide. On the other hand in the state with
alcohol, cladding polymer causes swelling and its refractive index becomes lower than n1 in core. Based on this principle,
large change in output light intensity occurs and detection of alcohol concentration becomes possible even for vapor
phase alcohol. In the experiment using a fiber-type sensor with a core size of 0.25 mm, detection of 1% methanol
vapor could easily be obtained. Furthermore, using a channel waveguide-type sensor head with a core size of about
50μm×40μm, large increase in sensitivity was observed.
This paper deals with experimental results on detection of toluene dispersed in water by means of a new and simple
plastic optical fiber (POF) sensor. Its sensing part consists of swelling polymer cladding layer such as high density
polyethylene (HDPE) with slightly larger refractive index n2 than that of poly(methyl methacrylate) (PMMA) core with
n1. When is exposed to toluene dispersed in water, HDPE cladding layer causes swelling and the value of n2 decreases quickly. Then the POF structure in the sensing part changes from leaky-type to guided-one and the output light intensity
increases dramatically. By measuring this light intensity change, it becomes possible to detect toluene concentration. In
addition, as compared with the popular evanescent-wave detection principle type, this sensor operation does not depend
on the wavelength of light source. Therefore, we can use an inexpensive LED or LD in visible region. In experiment,
detection of less than 1 wt% toluene in water was easily obtained with fast response about only 1 s. Furthermore, this
sensor can detect pure toluene even for a small amount below 1 ml.
Holographic technologies for optical memories and interconnection devices have been studied actively because of high
storage capacity, many wiring patterns and high transmission rate. Among multiplexing techniques such as angular,
phase code and wavelength-multiplexing, speckle multiplexing technique have gotten attention due to the simple optical
setup having an adjustable random phase filter in only one direction.
To keep simple construction and to suppress crosstalk among adjacent page data or wiring patterns for efficient
holographic memories and interconnection, we have to consider about optimum randomness of the phase filter. The high
randomness causes expanding an illumination area of reference beam on holographic media. On the other hands, the
small randomness causes the crosstalk between adjacent hologram data.
We have proposed the method of holographic multiplexing, shift-phase code multiplexing with a two-dimensional
orthogonal matrix phase filter. A lot of orthogonal phase codes can be produced by shifting the phase filter in one
direction. It is able to read and record the individual holograms with low crosstalk. We give the basic experimental
result on holographic data multiplexing and consider the phase pattern of the filter to suppress the crosstalk between
adjacent holograms sufficiently.
In this paper, we propose a tunable optical filter using a photorefractive planar waveguide. The index grating
generated by the control beam drops off a part of wavelength components in the wavelength division multiplexed
signal beam. It make possible to select the wavelength components of the signal beam by optically adjusting the
wave vector of the grating. The photorefractive effect is one of the most efficient nonlinear effects, and
therefore the signal beam can be controlled by the relative low beam power. The proposed optical filter can be
applied to an active add-drop module when the signal beam is fed back to the module as a control beam.
Therefore, it contribute to development of the all-optical network systems. It is also able to apply to photonic
label processing technology by multiplexing the index gratings. We investigated the signal beam propagation
and the permittivity distribution in the photorefractive waveguide by using a finite dimensional beam propagation
method (FD-BPM) and analyzed the filtering property. Considering the two optical setups using the
transmission and reflection grating, we compared these performances.
In order to develop a simple system for sensing taste substances, an optical method using polymer/lipid films doped with a voltage-sensitive dye and plastic optical fibers (POFs) has been studied experimentally. The several kinds of polymer/lipid blended membranes doped with rhodamine-B dye with a long hydrocarbon chain were used after transferring on to the glass substrate glued on the end surface of POF. Its fluorescence intensity around 600 nm showed different patterns for the taste substance solutions such as bitter, salty and "umami". These results and a principal component analysis gave the possibility of an optical fiber taste substance sensor.
All-optical interconnections are expected to play an important role in optical computing and neural network systems. Some schemes of the interconnection with a mutually pumped phase conjugate mirror (MPPCM) have been proposed. But it takes long time for reconfiguration of the wiring pattern because the competition among a lot of the index gratings induced by the incident beam and its scattered beams forms MPPCM gradually. In this report, we propose a new optical interconnection by using mutually pumped four-wave mixing (MP-FWM) which is composed of a MPPCM and a degenerate four-wave mixing (FWM). In this method, the two control beams induce the hologram that determines the wiring pattern of the signal beams in the FWM region. On the other hand, the signal beams are transferred to the phase conjugate beam of the one of the control beam through the FWM region by using MPPCM and then the signal beams are diffracted to the desired output channels by the hologram in the FWM region. This scheme can reduce the time to reconfigure the wiring pattern remarkably compared with the conventional interconnection using only MPPCM because the hologram can be reformed by the two control beams arbitrarily. It also can suppress the channel crosstalk that is often generated by the photorefractive fanning effect. This interconnection is effective method to solve the problems of the electrical wiring techniques such as the electro-magnetic interference and the thermal generation. We give the experimental result by using BaTiO3 crystal and Ar+ laser, and investigate the optimum condition of the beams for high connection efficiency.
Simple optic sensors for detecting fuel gases, which consist of plastic optical fibers (POFs), have been studied. The sensing mechanism is based on the swelling phenomena in the rubber-type polymers. The POF-type sensor head was fabricated by coating the swelling polymer on the plastic fiber core and was connected to the normal POFs. When this system was exposed to fuel gases such as gasoline and propane, the light intensity passing through the sensor head changed remarkably depending on the pressure of fuel gases. The sensor response was also found to be fast, stable and reproducible.
Optical fiber sensors for detecting leakage of gasoline have been studied. When exposed to gasoline vapor, certain rubber-type polymers such as polyisoprene cause swelling and their refractive indexes decrease depending on the vapor pressure of gasoline. Based on this effect, the fiber-type sensor heads were fabricated by coating the swelling polymer as a cladding layer on the fiber core with slightly lower refractive index than that of cladding. This sensor head changes its fiber structure from leaky to guided, and then, change in the transmitted light intensity by leakage of gasoline can be observed. The improvement of sensitivity in a wide range of gasoline vapor pressure was attempted.
A new technique for the optical sensing of dissolved oxygen (DO) is proposed here. It is based on the enhancement in fluorescence yield of TPP dye at (lambda) equals 656 nm, when excited by He-Cd blue laser of (lambda) equals 441 nm in the presence of dissolved oxygen. The sensor head was fabricated by cladding the ARTON fiber core with the poly-4-methyl-1- pentene polymer matrix suitably doped with Tetraphenylporphine dye. This sensor head, when placed in a test chamber and end-pumped by He-Cd laser, generates the intense fluorescence at 656 nm. Its intensity was noticed to increase with increasing the amount of DO. A theoretical model of the sensor response was designed and is also discussed.
New optical fiber sensors for detecting leakage of vapor phase alkanes and gasoline have been studied. When exposed to these vapors, certain rubber-type polymers such as polyisoprene and polyisobutylene cause swelling and their refractive indexes decease depending on the vapor pressure of these substances. Based on this effect, the fiber-type sensor heads were fabricated by coating the swelling polymer as a cladding layer on the fiber core with slightly lower refractive index than that of cladding. When was exposed to vapor phase substances, the sensor head changed its fiber structure from leaky to guided one, and then a large change in the transmitted light intensity was observed in a wide range of the vapor pressure. The response was also found to be reversible and reproducible.
An attempt has been made to improve the sensitivity and stability of optical fiber sensor used for the continuous monitoring of gaseous oxygen. It utilizes the quenching phenomena of cladding fluorescence. Two polymers viz. poly cyclohexyl methylacrylate (PCMA) and poly (4-methyl-1-pentene) (PMP) were selected which were doped with 9,10-diphenyl anthracene (DPA) and sensor head was prepared by dipcoating the polymer on a 4.2 cms length of an especially designed ARTONTM plastic fiber with 1 mm core diameter. For dipcoating, polymer matrix containing 3% wt of fluorescent dye was used. The sensor head thus prepared was tested for various oxygen concentrations varied by mixing nitrogen. D2lamp was used for UV side pumping and thus the fluorescence generated in the cladding was coupled to another plastic optical fiber at the output end. The change in fluorescence due to oxygen content was recorded using a photo-multiplier at the (lambda) equals 430 nm. The results obtained have been tabulated in the form of comparative studies. The response was found to be fast, reversible and reproducible with recovery time of the order of few seconds in both the cases. The sensors were found to detect a wide range of oxygen concentration ranging from 0.5% to 100% of O2. In the case of PCMA, better stability in long-term was observed. The effect of cladding thickness on the sensor performance was also explored.
In order to develop a simple sensing system for taste substances, an optical method using an LB film doped with a voltage-sensitive dye was studied experimentally. The blended LB film of arachidic acid and rhodamine B (RBC18) dye with a long hydrocarbon chain, which as a mixture ratio of 75:1, was transferred on to the ITO substrate and was used to measure both the fluorescence intensity around (lambda) f equals 600 nm and the membrane potential of the RBC18-LB film in various taste substance solutions. As a result, for example, it was found that the fluorescence intensity increased as the NaCl concentration increased but on the other hand the membrane potential decreased. The different patterns were obtained for the different taste substance solutions. These experimental results show the possibility of an optical fiber taste substance sensor using blended LB film of arachidic acid and RBC18.
Improvement of the optical fiber oxygen sensor based on the fluorescence quenching by oxygen gas was studied. Using the newly synthesized poly-l-methylmethacrylate (PMtMA) and its blend of the PMtMA/PMP as the cladding layer, in which sensing dye was doped, the plastic optical fiber (POF) O2 sensor with high sensitivity and a fast response time could be realized. In addition this sensor didn't receive any affect by humidity.
A novel TE-TM mode converter using optically active polymers (OAPs), which can be fabricated much more easily than the conventional ones, was proposed. To achieve its phase- matched operation, two methods for controlling birefringence in the OAP waveguides were studied and hence TEo-TMo mode conversion with a high efficiency of about 70 percent was obtained for the first time.
Rhodamine 6G-doped hybrid gels were prepared by a sol-gel route. The inorganic component tetraethyl orthosilicate (TEOS) and the organic component glycerol propoxy triacrylate (GPTA) were simultaneously polymerized to create interpenetrating silica-GPTA networks. Crack-free, transparent dried gels in the shape of rods and fibers were obtained. Lasing properties of the hybrid rod-shaped monoliths were determined as a function of rhodamine concentration. In addition, gels in the shape of fibers were evaluated as fiber lasers for detecting ammonia vapor.
In the films made of p-nitroaniline (pNA) and methacrylate polymers, the highly efficient second harmonic generations (SHGs) were observed. These are due to the spontaneous growth of the noncentrosymmetric pNA crystals in the particular region of the pNA composition. The SHG intensity depended on the film fabrication conditions. Furthermore, the above films showed long-term stability in the SHG property over 400 hours.
Fluorescence properties of the methyl methacrylate solutions of two kinds of aromatic methacrylate monomers: 9-methyl,10-methacryloyloxymethylanthracene and 9- methacryloyloxymethylanthracene were studied. The concentration of anthracene fluors in methyl methacrylate corresponding to the maximum fluorescence yield has been found, and some parameters describing the excitation and deactivation of the excitation energy of the studied system have been calculated. Next polymer rods have been prepared by copolymerization of methyl methacrylate and two studied fluors of anthracene. The absorption and emission spectra, fluorescence lifetimes, quantum efficiency, and Verdet constants were measured for the obtained polymer rods. The studied anthracene fluors can be useful, at small concentrations, as wavelength shifters in polymethyl methacrylate-core polymeric optical fibers whereas higher concentrations of anthracene fluors can be used to get some enhanced magneto-optical properties of the polymers.
Fluorescent, plastic fibers having a dye-doped polymer claddinglayer were fabricated and were used as a smart optical sensor fordetecting atmospheric humidity, breathing conditions and temperature.Under suitable light pumping, the fluorescence intensity of thesefluorescent plastic fibers changed by the above chemical and physicalparameters, and hence, they operaed as excellent fiber sensors withgood sensitivity and a fast response time.
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