The achievable rate region related to the problem of generating mutually independent random sequences is determined. Furthermore, it is proved that the output distribution of lossless source encoders with correlated side information is asymptotically independent of the side information. Based on this, we can realize a random number generator that produces mutually asymptotically independent random sequences from random sequences emitted from correlated sources.

Advanced optical transmission fibers have enabled 40-Gb/s transmission over distances of up to 5200km with 100-km amplified spans. This paper will discuss a number of the enabling fiber properties including dispersion, dispersion slope, Raman gain efficiency, and polarization mode dispersion.

An 80 Gbit/s conventional and carrier-suppressed return-to-zero optical time-division multiplexing signal transmission over a 208 km standard single-mode fiber was experimentally demonstrated. This was achieved by using mid-span optical phase conjugation based on four-wave mixing in semiconductor optical amplifiers. In addition, it was confirmed that the transmitted carrier-suppressed return-to-zero optical signal's carrier phase-relation was held.

Self-pulsation of Nd3+-doped fluoride fiber laser is experimentally and theoretically demonstrated using a Tm3+-doped fluoride fiber pumped at 808 nm as a saturable absorber. Self-pulsation at finite pump power predicted by linear stability analysis is confirmed through experiments, achieving a pulse width and peak power of 4.5µs and 1.5mW when the Nd3+-doped fiber was pumped at 230mW.

An optical fiber line testing system is essential for reducing maintenance costs and improving service reliability in optical access networks. NTT has already developed such a system called AURORA (AUtomatic optical fibeR opeRAtions support system). As we already use the 1310 and 1550nm wavelengths for communication, we use the 1650nm wavelength for maintenance testing in accordance with ITU-T recommendation L.41. Recently, a long wavelength band (L-band) that extends to 1625nm has begun to be used for WDM transmission. With a view to monitoring optical fiber cables transmitting L-band communication light, an attractive way of separating the U-band wavelength of the test lights from the L-band wavelength of the communication light is to use a chirped fiber Bragg grating (FBG) filter because of its steep optical spectrum. However, it is difficult to measure fiber characteristics with an optical time-domain reflectometer (OTDR), because multi-reflections appear in the OTDR trace when FBG filters are installed at both ends of an optical fiber line. In this paper, we consider this problem and show that the reflection loss at the port of a test access module (TAM) must be more than 36.6dB. We also describe the system design for an extended optical fiber line testing system using an L/U-band optical coupler, which has two chirped FBGs between two 4-port circulators for L-band WDM transmission. In this system, the reflection loss at a TAM port was 38.1dB, and we confirmed that there was no degradation in the OTDR trace caused by multi-reflections at the optical filters.

We will present a novel core mode blocker fabricated with hydrogen loaded Ge-B co-doped fiber exposed to the electric arc discharge using local heat exposure. Tunable bandpass filter based on cascaded LPFGs with a core mode blocker inserted between the LPFGs will be also described. The characteristics are: 6.5-nm bandwidth, 30-nm tuning range, and 15-dB dynamic range, respectively. It can be very useful for application to wavelength stabilization and physical sensors.

In a previous study about a combinatorial optimization problem solver using neural networks, since the Hopfield method, convergence to the optimum solution sooner and with more certainty is regarded as important. Namely, only static states are considered as the information. However, from a biological point of view, dynamical systems have attracted attention recently. Therefore, we propose a "dynamical" combinatorial optimization problem solver using hysteresis neural networks. In this paper, the proposed system is evaluated by the N-Queen problem.

We propose a new algorithm for blind source separation (BSS), in which frequency-domain independent component analysis (FDICA) and time-domain ICA (TDICA) are combined to achieve a superior source-separation performance under reverberant conditions. Generally speaking, conventional TDICA fails to separate source signals under heavily reverberant conditions because of the low convergence in the iterative learning of the inverse of the mixing system. On the other hand, the separation performance of conventional FDICA also degrades significantly because the independence assumption of narrow-band signals collapses when the number of subbands increases. In the proposed method, the separated signals of FDICA are regarded as the input signals for TDICA, and we can remove the residual crosstalk components of FDICA by using TDICA. The experimental results obtained under the reverberant condition reveal that the separation performance of the proposed method is superior to those of TDICA- and FDICA-based BSS methods.

A soft-decision decoding scheme of low-density parity-check codes (LDPC) is proposed for hard-detected signals of optical fiber communication (OFC) systems. Based on the error detection, the proposed scheme converts the received hard-decision into soft reliability for the input of the LDPC decoder, and soft-decision decoding is performed. Simulation results under OFC channels are shown and superior performance is obtained by using the proposed decoding scheme of the LDPC codes.

We propose a method to realize soft-decision decoding for hard-detected signals. In this paper, a novel concept is introduced as "error-detected reliability. " The method is very useful for optical fiber communications (OFC) as hard detection is the only detection method for the OFC systems. We demonstrate our proposed method using the turbo code in which soft information is required for decoding. As a result, the simulation shows slight difference in the range of moderate to high signal-to-noise ratio between the proposed decoding scheme and the conventional turbo decoding scheme. Moreover, the bit error rate of 10-11 can be achieved by serial concatenation of a Reed-Solomon code and a turbo code for Q-factor lower than 8.0 dB with a bandwidth expansion ratio of 33.3%.

We have developed a fiber physical contact (FPC) connector for the high-density connection of optical fibers. This connector individually aligns multiple bare fibers in micro-holes without ferrules and realizes physical contact by using the buckling force of the fibers themselves. The fiber endfaces must be tapered to allow the fibers to be inserted into the micro-holes. The endfaces must also be polished so that they realize physical contact (PC) with excellent optical performance. For each process, we examined the required shape and processing condition of the fiber endface for the FPC connector. As regards tapering, we determined the processing condition for achieving a target tapering angle and developed a non-breaking process with the optical fibers bent. In terms of polishing, we revealed that it is important for the fiber endface angle error to be less than 0.7 degrees if we are to achieve excellent optical performance. These results allowed us to fabricate an FPC connector that exhibited excellent levels of optical performance.

The characteristics of 155 Mbps optical propagation through atmosphere at the wavelengths of 0.78 and 1.55 m over a 72 m range were measured. Two propagation characteristics were compared to examine the wavelength dependence on the rain rate and the aperture size of a receiver. An enhanced intensity exceeding the signal level measured in the absence of rain was observed at both wavelengths during 7.2 mm/h rain. The resultant bit error rate is shown to be dominated mainly by the rain-induced scintillation rather than the attenuation.

Ray tracing is an efficient method for analyzing transmission characteristic of indoor wireless systems. However for simulating the transmission characteristic, using a path profile obtained by ray tracing, calculation times become enormous and there is no good theoretical model which can link a path analysis result with digital transmission characteristics evaluation. To overcome such problems, in this paper, a simple calculation method on spatial distribution of error occurrence due to intersymbol interference (ISI) based on "the equivalent transmission-path (ETP) model" is proposed. The ETP model is a technique that can simply estimate statistics of errors due to ISI that arise in Rayleigh and Nakagami-Rice fading environments. If a simple calculation method proposed in this paper is used, calculation time of digital transmission characteristics evaluation become tremendously shorter and results of this method agree with those of exact simulations with sufficient accuracy.

We newly propose an optical coherence domain reflectometry for optical subscriber networks with measurement range enhancement. This reflectometry is based on our own technique to synthesize an optical coherence function. An optical switch after a light source generates optical pulses, which select the measuring region, in which one coherence peak is scanned with high spatial resolution. An optical fiber loop delay line including a frequency shifter is placed in a reference-path of the interferometer. In this method, the measuring region could be easily changed by the hetelodyne intermediate frequency selected at the electronic band pass filter. In the basic experiments, the reflections at 5 km distance are measured with a spatial resolution of 8 cm, and the change of the measuring region is successfully demonstrated.

We propose and demonstrate a novel method to measure the polarization mode dispersion (PMD) of optical devices. The device under test (DUT) is installed in a fiber laser cavity which can operate at multiwavelength. PMD can be evaluated by the wavelength spacing of the multiwavelength laser output spectrum. In our method, the maximum extrema wavelength is easier to be identified than in the conventional fixed-analyzer (FA) method. We measure the PMD of polarization maintaining fibers (PMFs) and the ITU-T round robin KDD samples.

This paper proposes a new algorithm to achieve about two-times speedup of modular exponentiation which is implemented by Montgomery multiplication based on Residue Number Systems (RNS). In RNS Montgomery multiplication, its performance is determined by two base transformations dominantly. For the purpose of realizing parallel processing of these base transformations, i. e. "duplicate processing," we present two procedures of RNS Montgomery multiplication, in which RNS bases a and b are interchanged, and perform them alternately in modular exponentiation iteration. In an investigation of implementation, 1.87-times speedup has been obtained for 1024-bit modular multiplication. The proposed RNS Montgomery multiplication algorithm has an advantage in achieving the performance corresponding to that the upper limit of the number of parallel processing units is doubled.

In this paper, we evaluate the average bit error rate (BER) and bits per symbol (BPS) performances of CDMA system employing the adaptive modulation according to the position of mobile station since the performance of CDMA system is highly dependent on user location especially in the downlink, and further we evaluate the overall performance by considering the user distribution at the level of cell. To evaluate the performance of the considered system in the forward link, we derive the distribution of the received signal to noise ratio (SNR) by Mobile Station located at arbitrary cell position with which we investigate the average BER and BPS performances of the common shared channel, one of the downlink channels of beyond IMT-2000 systems such as 1xEV-DO, 1xTEME and HSPDA. As a result, we observe that the CDMA system adopting the adaptive modulation can get about 2.47 bits per symbol at the cell level, while satisfying the required BER performance over all cell area.

Due to saturable nature of gain or absorption of Er doped fiber, a dynamic grating is formed by standing wave produced by interference between two laser beams traveling in opposite directions in the fiber. In this letter, we propose a variable optical filter using the dynamic grating in Er doped fiber controlled by synthesis of optical coherence function. Simulations and experimental verifications are also shown.

We clarify the effectiveness of receiver-side compensation in offsetting fiber Bragg grating (FBG) dispersion induced-electrical signal-to-noise ratio (SNR) degradation in a 10 Gb/s 8-channel wavelength-division multiplexing (WDM) 6,400 km transmission system. The receiver-side compensation greatly improves the SNR degradation. The allowable accumulated FBG dispersion is -400 1000ps/nm for the worst arrangement, a single FBG at the transmitter, which is about half the accumulated fiber dispersion permissible with receiver-side compensation.

We investigate dispersion compensation using dispersion-compensating fibers (DCFs) for ultrashort light pulse code division multiple access (CDMA) communication systems in a multi-user environment. We employ fiber link that consists of a standard single-mode fiber (SMF) connected with two different types of DCFs. Fiber dispersion can be effectively decreased by adjusting the length ratios of DCFs to SMF appropriately. Some criteria for dispersion compensation are proposed and their performances are compared. We theoretically derive a bit error rate (BER) of ultrashort light pulse CDMA systems including the effects of the dispersion and multiple access interference (MAI). Moreover, we reveal the mutual relations among BER performance, fiber dispersion, MAI, the number of chips, a bandwidth of a signal, and a transmission distance for the first time. As a result, we show that our compensation strategy improves system performance drastically.