There are many public key cryptosystems that require random inputs to encrypt messages and their security is always discussed assuming that random objects are ideally generated. Since cryptosystems run on computers, it is quite natural that these random objects are computationally generated. One theoretical solution is the use of pseudorandom generators in the Yao's sense. Informally saying, the pseudorandom generators are polynomial-time algorithms whose outputs are computationally indistinguishable from the uniform distribution. Since if we use the Yao's generators then it takes much more time to generate pseudorandom objects than to encrypt messages in public key cryptosystems, we relax the conditions of pseudorandom generators to fit public key cryptosystems and give a minimal requirement for pseudorandom generators within public key cryptosystems. As an example, we discuss the security of the ElGamal cryptosystem with some well-known generators (e. g. , the linear congruential generator). We also propose a new pseudorandom number generator, for random inputs to the ElGamal cryptosystem, that satisfies the minimal requirement. The newly proposed generator is based on the linear congruential generator. We show some evidence that the ElGamal cryptosystem with the proposed generator is secure.

Biological object could be trapped by a single laser beam from an optical fiber end inserted at an angle to a sample chamber. Separation/coupling of an individual biological cell was easily achieved using plural optical fibers. From these experimental results, we verify that fiber optic trapping technology can provide new and novel tools for the manipulation of microorganisms and cells without physical contact.

In modems for burst transmission of digital data, rapid carrier and clock synchronization are essential. Typically, frequency correction occurs prior to phase recovery since estimators are sensitive to frequency offsets. In this paper, we derive the bit error rate (BER) performance of a M-ary phase shift keying (MPSK) receiver in a closed form when there is no frequency offset estimator. Then we derive a relationship of the required burst length for certain BER with frequency offset estimator. To obtain the BER=10-4, approximately we need the burst length of 101 at Eb/N0=10 dB and 69 at Eb/N0=15 dB.

A novel polarimetric fiber optics current sensor configuration using an in-line 22.5 degree Faraday rotator is proposed on this paper. The introduction of the 22.5 degree Faraday rotator allows to obtain a sensor configuration that does not require adjustment on most optical elements, resulting in an accuracy immune to manufacturing issues. Two prototypes are presented in this paper that are designed to measure AC current, yielding in an excellent accuracy over more than 3 decades.

An improvement of the fiber-optic transceiver having both transmitter and receiver functions of optical time-domain reflectometers is examined. The improvement is achieved by introducing an external optical amplifier without changing the previously reported configuration. The characteristics of the transmitted Q-switched pulse and the receiver gain is studied theoretically and experimentally to estimate the performance improvement. It is found that the introduction of the external optical amplifier is a simple and effective way to the performance improvement.

The technique used is based on thermal optical activity measurement of temperature combined with electric-field-induced polarization modulation of the input light. Quartz is used as the sensing element. A 1/4 wave plate is placed behind the quartz so that a single sensing head can simultaneously output two signals: one includes the Pockels effect for voltage measurement; the other optical activity for the temperature measurement. The operating principle of the sensor which detects voltage and temperature is presented theoretically and experimentally. The technique for separating voltage and temperature from the signals is analyzed theoretically and experimentally. It was found that the sensitivity of the voltage sensor to temperature depends on the magnitudes of voltage applied to it. To realize temperature compensation over a full range, two key parameters must be obtained: one is the response of the voltage sensor to temperature when the applied voltage is zero; another is the response of the sensing material to temperature when a certain voltage is applied. In the absence of electrogyration the effect of voltage on the temperature sensor may be neglected. The technique was demonstrated using a fiber-optic voltage sensor with temperature compensation. The sensor offered a voltage measurement range of 0-10 kV, and a temperature stability of 0.4% within the temperature range of 20-70.

A correlation-based technique for measuring Brillouin gain spectrum distribution along an optical fiber is proposed, which employs frequency-modulated pump and probe lightwaves. The spatial-resolution of about 40 cm is demonstrated, which cannot be realized by the conventional pulse-based technique.

Attempts have been made to evaluate and investigate the radiated emissions from fiber optical modules that are currently available in the market. Far electric field strength measurements show that the radiated emission has a peak at a high-order harmonic wave of the fundamental pulse frequency and reaches a level exceeding the limiting values of the CISPR noise specifications. Near magnetic field distribution measurements show that the source of the interference noise lies between a light emitting diode (LED) module and an LED driver. These measurements are compared with those of electromagnetic field calculations based on a high-frequency equivalent circuit. As a result, it was established that both the peaking effects of deformed pulse waves transmitted between an LED module and an LED driver and the radiation characteristics of the optical transmitter circuit act as factors for increasing the radiation level of the peak frequencies in the radiated emission from fiber optical modules.

A novel temperature sensor device based on a conventional long-period fiber grating but having an improved sensing resolution is presented. By forming a reflector at one cleaved end of the fiber embedding a long-period grating, a fine interference fringe pattern was obtained within the conventional broadband resonant spectrum of the grating. Due to the fine internal structure of the reflection spectrum of the proposed device, the accuracy in reading the temperature-induced resonant wavelength shift was improved. The formation of the self-interference fringe is analyzed and its properties are discussed in detail. The performance of the proposed device is analyzed by measuring the resonant wavelength shift of the device placed in a hot oven under varying temperature. The rate of the fringe shift is measured to be 551 pm/. The rms deviation is 10 pm over a 100 dynamic range, which corresponds to 0.2 in rms temperature deviation. The thermal variation of the differential effective index of the fiber is calculated to be (0.3 0.1)10-6/ by comparing the analytic calculations with the experimental results. The interference fringe shift is revealed to be inversely proportional to the differential effective group index of the fiber, which implies that the shifting rate strongly depends on the type of fibers and also on the order of the involved cladding mode.

This paper describes a fiber-optic level sensor designed to measure the level of liquid propane-butane in a relatively short range (60 cm) in the top part of storage tanks at oil refineries with the purpose of monitoring the level of this product in the filled or slightly underfilled or overfilled tanks during various measuring operations. A discrete multi-element device employing novel refractometric transducers was selected because it yields both a large measurement range and high resolution. Several innovations offer a competitive advantage to industrial users: 1) Special micro-optical refractometric transducer; 2) Efficient and economical sensor multiplexing scheme; 3) Fast level-tracking operational algorithm. The vertical resolution of the sensor -1 cm, the maximum excess pressure in the tank -40 atm (4 MPa). The sensor has the spark-proof and explosion-proof design and optical fiber interface for the transmission of the output data. The sensor successfully measured liquid propane-butane level in storage tanks during numerous cycles of measuring operations.

Characteristics of an FBG hydrophone are described under various conditions. The developed FBG hydrophone detects an acoustic field in water with good performances: linear response,high sensitivity,high stability,wide dynamic range as large as 90 dB and wide operation frequency range from a few kHz to a few MHz. A WDM FBG hydrophone consisting of two FBGs in serial connection can detect simultaneously amplitudes and phases of acoustic fields at different points,which in turn allows a directive measurement of an acoustic field in water.

Since river levee collapse causes great damage, it is socially very important to prevent such disasters by using a monitoring system which can detect changes in the state of a river levee. To investigate the possibility of detecting the collapse of a levee slope at an early stage, we performed an experiment in which we used artificial rainfall and penetration to collapse a full-scale levee model, and measured the change in the levee state using a detection system during collapse. The system consists of sensor plates, a distributed fiber optic strain sensor, and a personal computer. With this system, the stretching produced in the sensor plates by the force resulting from the movement of the soil on the levee slope face is detected as strain by a sensing optical fiber fixed to the plates. Since the distributed fiber optic strain sensor can measure strain continuously and for a long distance along a fiber, it is suitable for monitoring civil structures such as river levees. The experiment confirmed that a change in a levee can be clearly detected when the slope face collapse progresses near the place where the sensor plates are buried. The results suggest the feasibility of being able to foresee the collapse of a levee slope.

This paper describes a load carrying test for a concrete pipe designed to study the effectiveness of distributed strain measurement using an optical fiber sensor. We performed a load carrying test on a concrete pipe and attempted to detect the distributed strain inside it using an optical fiber sensor mounted inside the pipe. We confirmed that it was possible to detect the strain in a concrete structure by using an optical fiber sensor after a crack had occurred on the concrete surface. This paper shows that measurement using the optical fiber sensor was effective despite great changes in the strain conditions of the measured object over a short distance.

Macrobending characteristics of a newly developed hetero-core splicing sensor is investigated from the viewpoint of the practical use intended both for relatively large distortion monitoring and for liquid adhesion detection. The hetero-core sensor can be simply fabricated by fusion splicing of a hetero-core fiber portion as short as approximately 5 mm in length, which is inserted in a typical low-transmission-loss single mode fiber with a 9-µm core diameter for the wavelength of 1.3 µm as a fiber network line. Two types of the sensor are typically realized in terms of the core diameters of 3 and 5 µm for the inserted hetero-core portion which are referred to as 9-3-9 and 9-5-9 types, respectively , with showing their distinct bending loss characteristics. This paper deals with the explorative applications of the two types of hetero-core sensors in which a bending-to-linear displacement converter and a liquid adhesion sensor are successfully examined using a 9-5-9 structure with its low insertion loss and a cladding interactive 9-3-9 structure with its high sensitivity, respectively. The low-insertion loss 9-5-9 sensor has shown the capability of monitoring millimeters-order distortion in low transmission loss fiber networks. On the other hand, the 9-3-9 type has found to be a prospective sensor for liquid adhesion detection. Operational mechanisms for these two sensors are also discussed in terms both of optical leaks occurring at the hetero-core interfaces and of the build-up of cladding modes which might interrogate the outer cladding boundary conditions of the hetero-core sensor.

For a wireless communication system to work effectively without interference, the electromagnetic environment needs to be controlled. We experimentally and analytically investigated the requirements for controlling the electrical field strength and delay spread so as to achieve the best communication without electromagnetic interference in selected regions for a 2.4-GHz-band wireless LAN system. To control the coverage, partitions were placed around desks in a test environment and covered on the inside with electromagnetic absorbing board from the top of the desks to the top of the partitions; four indoor environments that combined one of two wall-material types and one of two partition heights were used. The transmission loss and delay spread were measured, then calculated using ray tracing to verify the effectiveness of using ray-tracing calculation. The throughput and BER characteristics were measured for the same environments to clarify the requirements for controlling the coverage. We found that covered and uncovered regions could be created by using partitions with absorbing boards and that the delay spread must be less than 15 ns and the received-signal must be stronger than -75 dBm for a region to be covered. We verified that the delay spread can be calculated to within 5 ns and the received-signal level can be calculated to within 5 dB of the measured data by using ray tracing. Therefore, ray tracing can be used to design antenna positions and indoor environments where electromagnetic environments are controlled for 2.4-GHz-band wireless LAN systems.

In this paper, design and experimental results are described about a newly developed highly flexible fiber Faraday effect current sensor using the flint glass fiber as the sensor element. In the new type, a mirror is coated at an end of the flint glass fiber, and light takes round trip transmission in it. By the round trip transmission, the effect of rotation of polarization plane due to the torsion of the fiber is automatically canceled. Because of the low photo-elastic constant of the flint glass fiber, and the automatic canceling of the rotation, the polarization state of light passed through the fiber is stable. Therefore, in the new reflection type, it is not necessary to support the flint glass fiber with a durable circular frame to maintain accuracy. And so, the sensor head is small, light, and can be easily installed to existing power apparatus by winding the flint glass fiber around the current conductor without pulling out or cutting it. Experiments were done to verify the stable characteristics using the developed sensor model. In the experiments, relation between the final output signal of the sensor and shape of the curve of the flint glass fiber were examined. From the experiments, it became clear that the final output is almost perfectly independent on shape of the curve of the fiber. It was also confirmed that accuracy of the sensor conform to the standard of conventional current transducers for protection of power systems in Japan.

An optical fiber humidity sensor was fabricated forming a nanometer-scale Fabry-Perot interferometer by using the Ionic Self-Assembly Monolayer (ISAM) method. The materials used were Poly R-478 and poly(diallyldimethyl ammonium chloride). Taking advantage of the precision that the ISAM method can achieve in controlling the length of the nano cavity, the length was fit to obtain a maximum variation of 8.7 dB of reflected optical power between 11.3% and 85% RH. The sensor exhibited a fast response time and was able to monitor the human breathing.

In this study, a simple chaos communication system including modulation-demodulation circuits is studied. The influence of modulation-demodulation circuits to chaos synchronization is investigated. For the estimation of communication quality, bit error rate (BER) is calculated by computer simulation when a sequential random pulse information signal is transmitted via this proposed system.

Compact intra-cavity spectroscopic measurements may be obtained with any material that has an absorption signature under the gain bandwidth of a fiber laser. Experiments have demonstrated that compared with a regular absorption scheme, an increase in sensitivity is achieved when using the intra-cavity configuration. The practical limit for this enhancement is given by the fiber laser noise. Since intra-cavity spectroscopy is essentially a single beam technique, the application of dual-beam noise reduction techniques is not possible. However, considering that a single-mode fiber can support two modes of polarization, we have used a polarization beam splitter to create two independent cavities (x and y polarization) with the same noise, one cavity of which contains the absorber. For the first time, this permits the convenient use of Balanced Ratiometric Detection in conjunction with an intra-cavity absorption arrangement.

A new sensing method for measuring directly flow velocity by using low coherence interference techniques is proposed and demonstrated. In this method, a temporally fluctuating signal, not the Doppler frequency shift, is detected. Theoretical analysis shows that a spectrum of light backscattered from a particle takes a Gaussian form whose width is simply proportional to the flow velocity. The measured velocity is in good agreement with the actual flow velocity derived from the flow rate. The dynamic range of this sensing method is governed by the frequency range of the FFT processor used and is estimated to be 1.4 10-4 14 m/s. The depth position can be adjusted with an accuracy of approximately 30 µm which is determined by the coherence length of the light source. The velocity distribution along the depth is easily measured by changing mechanically the length of the reference arm in the low coherence interferometer.