We propose a volume holographic mode demultiplexer incorporating a dual-wavelength method, which enables us to
easily and flexibly set up the receiving system in mode division multiplexing for a large number of mode multiplexing.
This demultiplexer can separate a lot of multiplexed modes with different wavelengths through angularly hologram
multiplexing by appropriate angular difference between the two holographic writing beams. Thereby, the proposed
method can be applicable to wavelength division multiplexing systems. In this study, we demonstrated the mode
separation using the proposed demultiplexer with dual-wavelength. The results showed that the separation ratios of three
LP modes reached around 90%.
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.
We develop a tunable optical wavelength filter with PR (photorefractive) materials applied the external field for
achieving higher sensitivity and efficiency. In the past, the diffraction efficiency of the PR tunable filters with
transmission gratings has been much lower than other conventional wavelength filters, such as the array wavelength
gratings filter, the thin film filter, and the fiber Bragg gratings filter. By applying the external field to PR materials, we
can obtain the refractive index modulation depth of 13 times larger than that without applied field, specifically in lithium
niobate with the acceptor density of ~1022 [1/m3] and the voltage of 10 [kV/cm]. Our PR tunable filter provides
reconfigurable wavelength routing of the signal beam since the various diffraction gratings can be immediately induced
and multiplexed by changing incident conditions of two coherent writing beams viewpoint in comparing experimental
results to numerical simulations, and can be rewritten dynamically through the PR effect. These advantages allow us to
achieve more flexible optical net work based on the wavelength division multiplexing technique. In this work, we
calculate the relationship between the diffraction efficiency and the magnitude of the applied external field by solving
coupled wave equations in the case of lithium niobate, respectively.
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.
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.
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.
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.
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.
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.
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.
Recently, the scheme of bi-directional optical communication with a mutual-pumped phase conjugate mirror (MPPCM) has attracted attention. Bi-directional communication enables the integration of devices because input port and output port can be shared. We propose a new design for all-optical bi-directional interconnection with double MPPCMs. This interconnection is composed of two photorefractive crystals and a polarized beam splitter which is located between two crystals. The bi-directional connection is formed via two MPPCMs produced by illumination of the signal beams and the control beam. In this interconnection, the wiring pattern can be reconfigured flexibly by changing the spatial distribution of the control beam without any adjustment of the signal beams. The signal beams and the control beam are orthogonal polarized, so the signal beams can be transmitted without energy loss in dividing with control beam. In addition, the signal beams transmitting through the two crystals enhance the MPPCMs efficiently under the appropriate condition. After the buildup of MPPCMs, the connection is maintained without consecutive illumination of the control beam. Therefore the self-holding is achieved and it enables the interconnection with lower power consumption. In this paper, we analyze the optimum intensity ratio of the control beam for the signal beam in order to obtain high connection efficiency. Moreover, we confirm the self-holding of connection experimentally using BaTiO3 crystals and Ar+ laser without consecutive illumination of the control beam and show the connection can be maintained for several hundred times as long as the time constant of the crystal.
We propose an all-optical interconnection with double mutual-pumped phase conjugate mirrors (MPPCM). The bi-directional interconnection is possible by using single MPPCM, however it is difficult to reconfigure the wiring pattern because the incident angle or location of the signal beams must be readjusted to buildup the new communication lines. In our interconnection, the bi-directional connection between channels is formed by the two MPPCMs produced by the illumination of the signal beams and the control beam. Therefore, the wiring pattern can be reconfigured flexibly by changing the spatial distribution of the control beam without any adjustment of the signal beams. In addition, the self-holding of connection can be achieved because the signal beams diffracted by the MPPCM illuminate the other MPPCM and the holograms in MPPCMs are maintained even if the control beam is cut off. It enables the suppression of control beam power consumption. We investigate the connection efficiency of this interconnection in order to estimate the optimum beam splitter reflectivity and intensity ratio of signal beams for obtaining higher connection efficiency and lower coupling strength threshold for the establishment of connection. We also confirm the self-holding of connection experimentally using the BaTiO3 crystals and the Ar+ laser and show that the connection is maintained for several hundred times as long as the time constant of the crystal.
We propose an all-optical interconnection with cross-polarized double phase conjugate mirrors (CP-DPCMs). In the interconnection, spatially arrayed signal beams from an input port two-dimensionally intersect with control beams from an output port in the photorefractive crystal (PRC) where polarizations of these two beams are orthogonal each other. The CP-DPCM can function as the switching element by adjusting the intensity ratio of these two beams because it strongly depends on the intensity ratio of crossing two beams whether the CP-DPCM is built up in the PRC or not. Thus the signal beam is diffracted by the CP-DPCM and propagated to the output port, when the intensity ratio of signal beam and control beam is adjusted to proper value for buildup of the CP-DPCM. This technique offers the point-to-point interconnection in two-dimensional plane. It implies the possibility of miniaturization and the integration by stacking the planes with different wiring pattern in layers compared to the conventional interconnections with DPCMs. For configuring the arbitrary wiring pattern, it is important to determine the intensities of the signal beams and the control beams, so we investigate the optimum intensities of these beams for effective switching. We carry out basic experiment on 1x2 interconnection with BaTiO3 and Ar+ laser.
We have proposed the all-optical interconnection, in which the photorefractive four wave mixing (FWM) is used as the core, by full-linear resonator (FR) with a beam splitter (BS) and a self-pumped phase conjugate mirror (CAT). The index grating of the FWM region inside the photorefractive crystal (PRC), which determines the connection pattern, was maintained by the rewriting effect of the input signal beam and the resonance beam between the CAT and the BS. But the power of the resonance beam was wasted by the optical reflection at the crystal surface of the CAT and the PRC. Therefore the rewriting effect of the connection pattern could not be obtianed sufficiently. In this report, we propose the integrated full-linear resonator (IFR), in which a self-pumped phase conjugation (SPPC) region and the FWM region are formed in one PRC, to solve this problem. Compared with the conventional FR, the power loss of the resonance beam by the optical reflection can be prevented and the resonance beam can be used efficiently for the maintenance of the connection pattern. We experiment on the 2×2 all-optical interconnection with the IFT by using BaTiO3 crystals and Ar+ laser. It is shown that the maintenance time of the connection pattern can be extended sufficiently by using IFR.
We propose a bidirectional multi-channel cross-connector for two-way optical communications with array of the photorefracttinve crystal. The communication channels are connected bidirectionally by double phase conjugation in each photorefractive crystal. The wiring pattern is possible to determine by the beam that controls whether it generates the double phase conjugation in the crystal. This all-optical switching is effective method to solve the problems of the electrical wiring techniques such as the electro-magnetic interference and the thermal generation. We analyze the connection efficiency for coupling strength of the two four-wave mixing interaction region in the double phase conjugation and investigate teh intensity of control beams for sufficiently switching. We also experiment on the bidirectional connection switch and estimate the connection efficiency and the transmission efficiency.
We propose a new type of the fault tolerant all-optical router (FTAR) by using an all-optical switch with photorefractive two-wave mixing. FTAR can detect a cutoff of a main transmitting line and automatically reroute a signal beam from the main line to a backup line. These functions can increase communication reliability of optical wireless. FTAR is composed of ony all-optical devices without any electronic devices or any mechanical operations. In the new type of FTAR, the routing of the signal beam is controlled by a control beam transmitting on the main line from a different light source at a receiver in the opposite direction with the signal beam. Compared with the previous type of FTAR composed of two photorefractinve crystals, the new configuration offers the simplification of the construction and high transmission efficiency of the signal beam. In this report, we experiment on the FTAR by usign a BaTiO3 and Ar+ laser whose wavelength is 514.5nm, and confirm the fundamental fucntin of FTAR. We give comparison of the result with the numerical analysis. We also analyze the dependence of the switching time on the input beam intensity of the crystal by a numerical analysis and an experiment.
In this paper, we propose an application of the mutually pumped phase conjugation to the all-optical connection switch and present the two type of the bi-directional cross connector with the photorefractive crystals, the polarized beam splitters and the half-wave plates in terms of the control method. In the type 1 connector, the bypass mode or the exchange mode can be selected by the external control beam whose polarization is orthogonal with those of the signal beams. In the type 2 connector, these modes can be controlled by rotating the polarization of the signal beams. We give the basic experimental result of these connectors with BaTiO3 crystals and Ar+ laser, and discuss about the results.
We have studied PRCM as a basic device that could achieve a free-space optical communication with the spatial parallelism using mainly photorefractive crystal and four-wave mixing technique. The asynchronous PRCM, which is newly introduced in this paper, has the diffraction grating generated by two control beams independent of the signal beam. Thus, the signal is transmitted at the velocity of light and can be branched with no delay from the multiple nodes connected on the transmission bus line. We also propose a new two-way communication device, to which double phase conjugator technology was applied, as opposed to the one-directional device of optical signals from the transmitting side to the reception side. We conduct a basic evaluation on the branching and transmission characteristics of signals at the spatial optical switch element.
We propose an all-optical interconnection with pattern memory function by a photorefractive full-linear resonator with a beam splitter(BS) and a self-pumped phase conjugate mirror(CAT). This interconnection utilizes the oscillation phenomenon between the BS and the CAT. This resonance beam rewrites and sustains the connection pattern continuously, which is once configured by the writing beam, after the writing beam is turned off. We analyze the optimum reflectivity of the BS and the CAT, which determines the feedback rate of the resonation, for high connection efficiency. We also analyze the coupling strength threshold of the photorefractive crystal for the sustentation of the connection. We experiment on the photorefractive full-linear resonator in order to examine the efficiency and the sustentation time of the connection.
This study suggests an optical fault-tolerant system using all-optical sensing and feedback circuits with photorefractive crystals. The first example is a fault- tolerant system in which the system independently detects a cutoff of the optical transmission line and converts its routing to the backup line. Next, while practical application of holographic optical memory is currently being developed, under proposing system, the memory system automatically detects the loss of information (dropout) in optical memory, and reloads and eventually restores the corresponding data from the backup memory.
We propose an optical demodulator with photorefractive cross-polarized duplex two-wave mixing, in which the phase- modulated signal beam is converted into the intensity- modulated output signal beams. We calculate the intensity variations of the output signal beams when phase-modulated signal beam input to photorefractive cross-polarized duplex two-wave mixing.
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