Makoto Tsubokawa

Mode couplings due to external forces distributed along a polarization-maintaining fiber: An evaluation

A new interferometric scheme for measuring mode conversion distributed locally along a polarizationmaintaining fiber is presented. Using this technique the power coupling coefficient, varying with magnitude and angle of external pressure transversely applied to a fiber, was evaluated both theoretically and experimentally. The coupling point location is determined with +/- 1.5-cm accuracy and resolution of better than 10 cm for a 220-m long fiber having modal birefringence of 4.4 x 10 (- 4). The coupling coefficient was proportional to the external force in the range from 5 x 10 (- 3) to 0.1 kg/mm. The relationships determined experimentally reflected those predicted by theory.

A Burst-Mode 3R Receiver for 10-Gbit/s PON Systems With High Sensitivity, Wide Dynamic Range, and Fast Response

The burst-mode 3R receiver using monolithic ICs for 10-Gbit/s-class optical access networks is reported. In a point-to-multipoint access system like a passive optical network (PON), the receiver at the optical line terminal (OLT) must be able to handle burst-mode optical packets with significantly different powers and phases. An OLT receiver with high sensitivity with instantaneous response to burst inputs is desired for widening the accommodation area and for high efficiency in PON uplinks. Currently, the diffusion of high-speed Internet connection services represented by fiber to the home services at 1.25 Gbit/s is remarkable and the standardization of the next-generation system operating at 10 Gbit/s has started in IEEE. We first discuss the issues in the implementation of 10-Gbit/s-class PON systems, focusing on securing the accommodation area and the quality of the service comparable with those of the deployed system. Against that background, we propose target specifications for sensitivity, a dynamic range and response speed of the 10-Gbit/s-class burst-mode receiver so as to secure the power budget and the upstream efficiency comparable with those of the already-installed systems. Our burst-mode 3R receiver was designed to meet the above requirements and developed using monolithic ICs of transimpedance amplifier, limiting amplifier, and clock and data recovery circuit fabricated by using SiGe BiCMOS technologies along with a p-i-n photodiode. High sensitivity of , a wide dynamic range of over 16.5 dB, and quick response time of 75 ns were confirmed for burst inputs with extremely different powers.

Security in Photonic Networks: Threats and Security Enhancement

We address emerging threats to the security of photonic networks as these networks become heterogeneous being opened to the upper layers, other operators, and end users. We review the potential threats, mainly loss of the confidentiality of user data transmitted through optical fibers and disturbances of network control, both of which could seriously damage the entire network. We then propose a novel conceptual model of a secure photonic network by introducing a quantum key distribution (QKD) network to its legacy structure. Secure keys generated by the QKD network are managed by key management agents (KMAs) and used to encrypt not only user data but also control signals. The KMAs cooperate with the generalized multiprotocol label-switching controller for secure path provisioning and drive photonic and modern crypto engines in appropriate combinations. Finally, we present a roadmap of a deployment scenario, starting from niche applications such as mission critical and business applications and the next. Digital cinema distribution through a photonic network is presented as an example of a niche application.

Suppression of Fiber Fuse Propagation in Hole Assisted Fiber and Photonic Crystal Fiber

We suppressed fiber fuse propagation in hole-assisted fiber (HAF) and photonic crystal fiber (PCF) with input powers above 14 W at 1480 and 1550 nm. This result indicates that the threshold power of fiber fuse propagation in HAF and PCF can be at least 10 times larger than that in conventional single-mode fiber (SMF) in the optical communication band. We also observed the dynamics of fiber fuse termination at a splice point between a test fiber (HAF or PCF) and a conventional fiber (SMF or dispersion-shifted fiber (DSF)). Our experimental results show that air holes in HAF and PCF play an important role in suppressing fiber fuse propagation.

Single-Mode Photonic Crystal Fiber Design With Ultralarge Effective Area and Low Bending Loss for Ultrahigh-Speed WDM Transmission

We propose a new photonic crystal fiber design with a W-shaped effective index profile to achieve the largest effective area (<i>A</i>_eff) for telecommunication use. We realized a 220-μ m²<i>A</i>_eff while achieving both a cable cutoff wavelength of less than 1300 nm and a bending loss compatible with ITU-T recommendations G.655 and G. 656.

Temporal coherence properties of a dispersively propagating beam in a fiber-optic interferometer

The temporal coherence properties of a dispersively propagating optical beam are clarified experimentally by means of a two-beam interferometer composed of optical fibers with 1.3- and 1.5-μm zero-chromatic-dispersion wavelengths. Experimental results fully explain and reflect theoretically predicted ones concerning both the magnitude of the degree of coherence and the shape of the coherence curve with respect to the optical path difference.

AC-Coupled Burst-Mode Transmitter Using Baseline-Wander Common-Mode-Rejection Technique for 10-Gbit/s-Class PON Systems

We propose and demonstrate an AC-coupled burst-mode transmitter with a differential interface for 10-Gbit/s-class passive optical network (PON) systems by using a novel baseline-wander common-mode-rejection (BLW-CMR) technique. This technique can cancel the transient responses of capacitors at the AC-coupled differential interface, and produce an optical burst-mode signal with a fast response. We confirmed the feasibility of this technique experimentally with the prototype we developed. The response time of the optical burst-mode signal was 500 ps, which is the fastest response time reported for a burst-mode transmitter. Good temperature dependences were also observed. Moreover, we conducted a burst-mode upstream experiment using a burst-mode avalanche photodiode (APD) receiver that we developed for 10 G-EPON systems. We obtained a large loss budget of 33 dB and a wide dynamic range of 25.5 dB at a bit error rate (BER) of 10-3.

Evaluation of polarization mode coupling coefficient from measurement of polarization mode dispersion

Polarization mode coupling coefficient is evaluated from the measurement of polarization mode dispersion as a function of fiber length in a single-mode fiber having an elliptical-core with 10-percent ellipticity. The modal dispersion measurement are carried out by the improved spatial technique based on an optical heterodyne detection at the wavelengths of 0.85 and 1.3 μm. The coupling coefficients are evaluated from the measurements to be 3.4 \times 10^{-3} and 4.6 \times 10^{-3} m-1for modal-birefringence magnitudes of 8 \times 10^{-6} and 3 \times 10^{-6} , respectively. The coupling coefficients obtained from the dispersion measurement are coincident with those evaluated from the extinction-ratio measurements. In addition, dependence of the coupling coefficient on propagation constant difference between the two orthogonally polarized HE 11 modes is investigated based on Lorentzian power spectrum model.

First demonstration of fast automatic-gain-control (AGC) PDFA for amplifying burst-mode PON upstream signal

The effectiveness of installing fast AGC in a PDFA for amplifying burst mode PON upstream signals is reported for the first time. The technique has the potential to realize high-gain/high-power burst-mode PON repeaters.

Evolution of Next Generation Access

Deployment strategy of access systems is described toward next generation access (NGA). Considering service requirements and consecutive evolution to NGA, we think that 10 Gbit TDM-PON will be the most promising system among several technologies. The other systems like WDM-PON, for which we have not yet found a suitable segment of users, can contribute to high-end access services with scalability and reliability.