A rigorous semi-analytical approach for the scalar field in a microstructured optical fiber, which is formed of layered cylindrical arrays of circular rods symmetrically distributed on each concentric cylindrical layer, is presented. The method uses the T-matrix of a circular rod in isolation and the generalized reflection and transmission matrices of cylindrical arrays. Numerical examples of the mode index for three-layered hexagonal structure of circular air holes are demonstrated and compared with those obtained by a variational method.

This paper analyzes transient behaviors of the polarization-mode-dispersion (PMD) vector for the Foschini and Poole's birefringence vector model. We find an asymptotic solution of the corresponding Fokker-Planck equation representing the solution as a superposition of angular components characterized by the Legendre polynomials. The distribution tail for the PMD vector magnitude evolves slowly to the Maxwellian owing to the residual couplings between adjacent angular components. Of particular interest, the distribution tail for the PMD vector magnitude lies well below the Maxwellian fit during the transient.

Fiber access network architectures such as active optical networks (AONs) and passive optical networks (PONs) have been developed to support the growing bandwidth demand. Whereas particularly Swedish operators prefer AON, this may not be the case for operators in other countries. The choice depends on a combination of technical requirements, practical constraints, business models, and cost. Due to the increasing importance of reliable access to the network services, connection availability is becoming one of the most crucial issues for access networks, which should be reflected in the network owner's architecture decision. In many cases protection against failures is realized by adding backup resources. However, there is a trade off between the cost of protection and the level of service reliability since improving reliability performance by duplication of network resources (and capital expenditures CAPEX) may be too expensive. In this paper we present the evolution of fiber access networks and compare reliability performance in relation to investment and management cost for some representative cases. We consider both standard and novel architectures for deployment in both sparsely and densely populated areas. While some recent works focused on PON protection schemes with reduced CAPEX the current and future effort should be put on minimizing the operational expenditures (OPEX) during the access network lifetime.

Adaptive polarization mode dispersion (PMD) compensation is required for the speed-up and advancement of the present optical communications. The combination of a tunable PMD compensator and its adaptive control method achieves adaptive PMD compensation. In this paper, we report an effective search control algorithm for the feedback control of the PMD compensator. The algorithm is based on the hill-climbing method. However, the step size changes randomly to prevent the convergence from being trapped at a local maximum or a flat, unlike the conventional hill-climbing method. The randomness depends on the Gaussian probability density functions. We conducted transmission simulations at 160 Gb/s and the results show that the proposed method provides more optimal compensator control than the conventional hill-climbing method.

The polarization dependence of the resonance wavelength of long period fiber gratings (LPFGs) that employ the photoelastic effect is investigated based on a simple model. The proposed model for estimating the birefringence of these LPFGs provides a good explanation of the experimental results.

We propose and demonstrate a scheme enhancing the performance of optical access networks with Manchester coded downstream and re-modulated NRZ coded upstream. It is achieved by threshold level control of a limiting amplifier at a receiver, and the minimum sensitivity of upstream is significantly improved for the re-modulation scheme with 5 Gb/s Manchester coded downstream and 2.488 Gb/s NRZ upstream data rates.

This paper describes a novel optical fiber line testing system operating at 1.65 µm using test light bypass modules. We show a new testing configuration for add/drop multiplexer (ADM) ring networks. The test light bypass modules were installed in individual customer buildings so the test light can bypass the ADMs. We evaluated the bit-error performance with a 2.48832 Gbit/s ADM ring network using a prototype test light bypass module. We confirmed that this testing system can monitor the optical fiber cables of an ADM ring network, and that it causes no degradation in transmission quality. We show the operating area provided by the system dynamic range expressed in terms of fiber length and customer building number. The prototype system could monitor an ADM ring network linking five buildings with a 5 km loop. We also performed an in-service monitoring field trial in a 2.6 km ring network with three ADM nodes. This testing system enables us to reduce the operating, administration, and maintenance cost and improves the transmission quality of ADM ring networks.

An all-optical phase multiplexing scheme for phase-modulated signals is proposed and experimentally demonstrated using four-wave mixing (FWM) in a highly-nonlinear fiber (HNLF). Two 10-Gb/s π/2-shifted differential phase-shift keying (DPSK) wavelength-division multiplexing (WDM) signals are experimentally demonstrated to be converted and phase-multiplexed into a 20-Gb/s differential quadrature phase-shift keying (DQPSK) signal with non-return-to-zero (NRZ) and return-to-zero (RZ) formats, respectively. Experimental results show that, due to phase-modulation-depth doubling effect and phase multiplexing effect in the FWM process, a DQPSK signal is successfully generated through the proposed all-optical phase multiplexing with improved receiver sensitivity and spectral efficiency.

Transmission performance of amplitude and phase shift keying (APSK) format is studied theoretically. The extinction ratio of the amplitude shift keying (ASK) signal of the APSK format causes a trade-off of the performance between the ASK and the phase shift keying (PSK) signal of the APSK format. Then, zero-nulling method is proposed to improve the performance of the APSK format, and its effectiveness is confirmed by the numerical simulation.

For the construction of photonic crystal fiber (PCF) systems using their unique properties, a PCF coupler (PCFC) is one of the key components of the systems. The characteristics of the PCFC depend on the state of air holes in the tapered region of the PCFC because the state of air holes in the tapered region affects light propagation in the PCFC taper. In this paper, coupling characteristics of PCFCs were theoretically investigated. In PCFCs with air hole remaining tapers, we found that a smaller elongation ratio i.e. a stronger elongation is required to obtain optical coupling as an air hole pitch or a ratio of air hole diameter to pitch is larger. In PCFCs with air hole collapsed tapers, it was clarified that a dependence of extinction ratio on air hole collapsed elongation ratio is higher for smaller elongation ratio. It was also clarified that an air hole remaining PCFC has slow wavelength characteristics in extinction ratio compared to an air hole collapsed PCFC. Air hole remaining PCFCs and air hole collapsed PCFCs were fabricated using a CO2 laser irradiation technique. We could successfully control whether air holes in the PCFC taper were remaining or collapsed by adjusting the irradiated laser power in the elongation process of the PCFC fabrication. It was experimentally clarified that the air hole remaining PCFC has slow wavelength characteristics in extinction ratio compared to the air hole collapsed PCFC. The tendencies of the measured wavelength characteristics of PCFCs agree with those of numerical results.

The number of broadband users is rapidly increasing worldwide. Japan already has over 10 million FTTH users. Another trend is the rapid digitalization of home electrical equipment e.g. digital cameras and hard disc recorders. These trends will encourage the emergence of the next generation home network. In this paper, we introduce the next generation home network image and describe the five domains into which home devices can be classified. We then clarify the optimum medium with which to configure the network given the requirements imposed by the home environment. Wiring cable lengths for three network topologies are calculated. The results gained from the next generation home network implemented on the first phase testbed are shown. Finally, our conclusions are given.

This paper proposes a novel fiber endface preparation tool for optical fiber joints that employs thermal surface cleaning and thermal endface cutting. This tool has great advantages in terms of fiber endface preparation time, and fiber endface stability when fiber is cut repeatedly. Stable thermal surface cleaning and thermal endface cutting are achieved by selecting suitable heating conditions. The fiber endface preparation time can be reduced to 50% of that required with conventional tools. The fiber endface stability obtained using thermal cutting is more than five times better than that obtained with the conventional tool using a blade.

In this paper, a fiber with two inhomogeneous sector holes around the core is proposed, and propagation characteristics of polarization maintaining region and single-polarization region are numerically analyzed by circular Fourier expansion method. In each case of the single-polarization region and the polarization maintaining region, a fiber is designed so as to satisfy the zero total dispersion at wavelength of 1.55 µm. Then, the single-polarization bandwidth for the single-polarization region and the modal birefringence for the polarization maintaining region are examined as the specific characteristics in each region. In addition, the power concentrating into the core region and distributions of Poynting vector is also discussed.

We experimentally demonstrated polarization-mode dispersion (PMD) compensation by distributing polarizers with only 1 degree of freedom (DOF) along the transmission line. The average power penalty was measured to be 0.4 dB by inserting four compensators, where average differential group delay was 47% of bit period.

A passive optical network (PON) that provides fiber to the home (FTTH) services is a fundamental access network topology in Japan. An optical fiber line monitoring and testing system is essential if we are to improve service reliability and reduce the maintenance costs of optical access networks. PONs have optical splitters in their optical fiber lines. It is difficult to find a fault in an optical fiber line equipped with an optical splitter by using a conventional optical fiber line testing system, which uses optical time-domain reflectometer (OTDR) in a central office (CO), because Rayleigh backscattering from the branched fibers accumulates in the OTDR trace. This paper describes a newly developed optical fiber line testing method that employs bi-directional OTDRs with two wavelengths at branched fiber regions in a PON to locate a fault precisely. Optical fiber line testing is conducted by two OTDRs that are installed in a CO and on a customer's premises, respectively. The OTDR in the CO has a U-band maintenance wavelength. We present two kinds of maintenance wavelength allocation for OTDRs on a customer's premises, which are in the U-band and C-band respectively. An OTDR whose maintenance wavelength is in the U-band enables us to test in-service PON lines simply by filtering the U-band wavelength. For the maintenance wavelengths in the C-band, we can use a cost-effective conventional OTDR to test the PON from the customer's premises on condition that we clarify the peak pulse power limit and dynamic range. We describe the test procedures for both cases. We also clarify the insertion loss design for an optical filter in the CO when using the U-band to provide the maintenance wavelength and the criteria for in-service line testing when the using C-band to provide the maintenance wavelength. To confirm the feasibility of our approach, we demonstrate a bi-directional OTDR method using the U-band and the C-band, and the test procedure, which successfully detected fault locations in branched fiber regions. We also describe the use of packet loss measurements to investigate the effect of in-service line testing with an OTDR in the C-band on data communication quality.

We achieved the first 10 Gb/s WDM transmission at 1064 and 1550 nm over 24 km of photonic crystal fiber (PCF). We confirmed an improvement in the bit error rate (BER) performance after the transmission, namely "negative power penalties" of -0.5 and -0.3 dB at 1064 and 1550 nm, respectively. Our experimental result and theoretical estimation revealed that the signal degradation induced by the chromatic dispersion can be effectively suppressed by employing the pre-chirp technique with a conventional Z-cut lithium niobate (LN) modulator. We also show theoretically that we can expect to realize 10 Gb/s transmission over a 24 km PCF with negligible BER degradation in the 1060 to 1600 nm wavelength range by using the pre-chirp technique.

This paper proposes the most effective deployment scenario of the passive double-star (PON) system to provide multiple broadband services, such as high speed Internet access and broadcast services. The deployment costs of the two major PON technologies, wavelength division multiplexing (WDM) and 10 Gbps time division multiplexing (TDM), are analyzed using the latest cost trend and the most popular access network architecture. These two technologies are compared using the cost analysis results to identify the cost-effective scenarios of PON system deployment. Based on the comparison, this paper reveals that the WDM network becomes cost effective when the service penetration and the shift ratio becomes high.

A nonlinear optical fiber loop mirror (NOLM) adapted for all-optical 2R operation at ultrahigh bit-rates was experimentally and theoretically investigated. The proposed NOLM was created by adding inline/external fiber polarizers and also an inline optical phase-bias compensator (OPBC) to a standard NOLM. A theoretical investigation revealed that the operation of the standard NOLM became unstable due to residual polarization crosstalk of the polarization-maintaining optical components making up the NOLM, and that it could be dramatically improved with the inline/external polarizers. The NOLM with the polarizers ensured stable switching operation with high switching-dynamic-range (>30 dB) against the change of the wavelength of the input clock pulses, and the change of the environment temperature. We also experimentally verified that the OPBC played a dramatic role to ensure excellent dynamic switching performance of the NOLM, and to achieve signal-Q-recovery of the regenerated signals. All optical 2R experiments at 40 Gb/s and 160 Gb/s were performed with the modified NOLM. Signal regeneration with improved extinction ratio and signal Q value was successfully demonstrated. Q-recovery to the input of the control pulses degraded with ASE noise accumulation was also successfully achieved.

Optical fiber communications require multiple-access schemes to access a shared channel among multiple users. The coherent ultrashort light pulse code-division multiple-access (CDMA) system is one such scheme, and it also offers asynchronous-access communication. This system usually employs 2-level, i.e., binary, m-sequences as signature codes because of their low correlation. If the number of active users is greater than the length of the m-sequence, i.e., code length, distinct m-sequences are used. However, the distinct 2-level m-sequences do not exhibit low correlation, resulting in performance degradation. We therefore propose a coherent ultrashort light pulse CDMA communication system with distinct 4-level, i.e., quaternary, m-sequences to improve system performance when the number of users is greater than the code length. We created the 4-level m-sequences from 2-level m-sequences, and assess the correlation of the 4-level m-sequences. We also theoretically derive the bit error rate (BER) of the proposed system taking into account multiple-access interference (MAI), beat noise, amplified spontaneous emission (ASE), shot noise, and thermal noise. The numerical results show that BER for distinct 4-level m-sequences is more than an order of magnitude smaller than that for distinct 2-level m-sequences. BER is limited by MAI and beat noise when the power of the received signal is high, otherwise BER is limited by ASE, shot noise, and thermal noise.

This paper describes a low-loss submarine optical fiber cable for a long-distance submarine repeaterless transmission system that employs remote pumping. The features of this system are that it has an increased signal power budget and is cost effective and easy to maintain. First, we investigated the relationship between the signal and pump losses and the Raman gain efficiency of optical fiber needed to achieve a submarine repeaterless transmission system operating at 2.5 Gbps and over a distance exceeding 370 km. We manufactured a submarine optical fiber cable based on the results and confirmed that it had low-loss characteristics. Second, we evaluated the long-term loss stability of the optical fiber with a high-power continuous wave (CW) laser light as the pump source. We confirmed that the loss remained unchanged after 1900 hours of exposure to 8 W CW laser light at a wavelength of 1.48 µm. This submarine optical fiber cable is being employed in a commercial submarine repeaterless transmission system between Okinawa and Miyakojima.