Toshiyuki Tokura

70-GHz-spaced 40/spl times/42.7 Gb/s transpacific transmission over 9400 km using prefiltered CSRZ-DPSK signals, all-Raman repeaters, and symmetrically dispersion-managed fiber spans

70-GHz-spaced 40/spl times/42.7 Gb/s prefiltered carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) signals have been transmitted over transpacific distances for the first time, using all-Raman repeaters with two pump-wavelengths, dispersion-managed fiber commercially available in volume, and an ETDM receiver. In this paper, first, in order to enhance the spectral efficiency, the impact of bandlimitation to a CSRZ-DPSK signal was experimentally investigated in comparison to a conventional CSRZ-on-off-keying (OOK) signal, and we found that the bandlimitation tolerance of CSRZ-DPSK signal was smaller than that of CSRZ-OOK signal in back-to-back condition. We also confirmed that the prefiltering CSRZ-DPSK signal with up to 65 GHz bandlimitation potentially had better transmission performance than the prefiltered CSRZ-OOK signal. In addition, we found that, although the nonlinear transmission penalty was increased by bandlimitation, this penalty for CSRZ-DPSK signal was smaller than that for CSRZ-OOK signal. Through this study, long-term stability of the transmission performance was also evaluated with low-speed signal polarization scrambling without using any polarization mode dispersion (PMD) compensation.

Bidirectional unrepeatered 43 Gb/s WDM transmission with C/L band-separated Raman amplification

A novel wavelength arrangement using C- and L-band-separated Raman preamplification is proposed for application to bidirectional unrepeatered transmission systems operating with multiple 43 Gb/s channels. The proposed wavelength allocation makes it possible to greatly mitigate Raman gain depletion by the counter-propagating signals. The authors have achieved bidirectional unrepeatered transmission of 32 /spl times/ 43 Gb/s channels (= 1.28 Tb/s) over 200 km with Raman preamplifiers using the proposed technique. They found that the system performance of bidirectional transmission with C/L band-separated Raman preamplification is degraded by nonlinear interactions between the high power Raman pump lights and the WDM signals. The root cause can be described in terms of nondegenerate four-wave mixing induced by beating between the WDM signals and two longitudinal modes of the Raman pump light. A solution avoiding ND-FWM was demonstrated in a 32 /spl times/ 43 Gb/s transmission experiment.

Pump light depolarization method for low PDG Raman amplification

In order to reduce polarisation dependence of gain (PDG) of Raman amplification, pump depolarization method with polarisation maintaining fibre (PMF) depolarizer is discussed. PMD of the depolarizer should be designed to optimum value determined by pump LDs longitudinal mode spacing.

Efficient Pump Depolarizer Analysis for Distributed Raman Amplifier With Low Polarization Dependence of Gain

This paper discusses a method of reducing the polarization dependence of gain (PDG) of a distributed Raman amplifier. Reducing its PDG is important for a Raman amplifier because it is higher than that of an erbium-doped fiber amplifier and can degrade transmission performance. Raman PDG is determined primarily by two factors, namely 1) polarization-mode dispersion (PMD) of the transmission fiber and 2) degree of polarization (DOP) of the pump source. The authors propose a simple analytical model to show the required pump light DOP for a given transmission fibers PMD and the allowable PDG. For instance, a low pump DOP of 5% produces a low PDG of 0.2 dB under typical fiber PMD conditions, in which the analytical model agrees well with experiment. Subsequently, to achieve the required DOP, the pump source configuration is investigated in detail. The authors used one length of polarization-maintaining fiber (PMF) as an efficient pump depolarizer and evaluated its performance for various pump light spectra. It has been shown that the DOP following the depolarizer is determined simply by Fourier transformation of the pump light spectrum. The analysis in this paper has led to the important result that a Fabry-Perot laser diode pump with a short piece of PMF is effective in achieving a low pump DOP due to its multimode spectrum when the length of the PMF is properly adjusted for the longitudinal-mode spacing frequency. It has been verified that a Raman amplifiers PDG can be reduced by the proposed efficient depolarizer sufficiently for a PDG-reduced Raman amplifier repeater to be applicable to long-haul transmission systems

65 /spl times/ 22.8 Gb/s WDM transmission over 8,398 km employing symmetrically collided transmission with Aeff managed fiber

Two proposed methodologies, Aeff management and symmetrically collided transmission, were discussed for long haul transmission systems. 65 /spl times/ 22.8 Gb/s WDM transmission over 8398 km was achieved by employing these techniques.

Reliable WDM telemetry transmission system for next generation scientific underwater cable network "ARENA"

A novel telemetry transmission system for next generation scientific underwater cable networks is proposed. The design concept features: (1) simple undersea Raman-effect transmitters employing only field-proven optical devices, (2) high capacity wavelength division multiplexing (WDM), (3) wavelength source distribution from the terrestrial terminal for flexibility and upgradeability and (4) per-node optical add-drop multiplexing with loop-back transmission for superior robustness against cable failures. To demonstrate the concept we conduct transmission experiments using a prototype node, four optical repeaters and 210 km of fiber. One challenge is to achieve high-speed Raman gain modulation, for which, under optimum conditions, we see the capability exceeding 100 Mb/s. Using WDM, more than 16 Gb/s of total capacity is achievable for a system a couple of thousand kilometers long with hundreds of observation nodes. The potential performance of the proposed system is expected to support next generation scientific underwater cable networks, such as the ARENA project proposed by IEEE OES Japan Chapter

High-speed optical telemetry system with 310 Mb/s Raman modulators for scientific underwater cable networks

We report recent progress of a novel telemetry transmission system for next generation scientific underwater cable networks. Our proposed system is based on reliable Raman modulation for telemetry transmission. The design concept features: (1) simple undersea Raman-effect transmitters employing reliable optical devices, (2) high capacity wavelength division multiplexing (WDM), (3) flexible and upgradeable optical add-drop multiplexing (OADM), and (4) loop-back transmission robust against cable failures. In our previous work, we experimentally demonstrated the feasibility of our proposed system. In this paper, we investigate methods to improve the modulation speed. The modulation speed in our previous experiment was limited by chromatic dispersion of the modulation fiber. Therefore, we compare several types of fiber having different dispersion values from the points of view of the achievable modulation speed and unwanted nonlinear effects. We have experimentally verified that Raman modulation speed can be successfully improved to up to 310 Mb/s by using highly nonlinear dispersion shifted fiber (HNL-DSF) and field-proven reliable pump LD modules. We believe that the demonstrated Raman-modulated transmission speed of 310 Mb/s is adequate to support a range of sensors and HDTV (high definition television) cameras. For example, 160 observation nodes (8 fiber pairs and 20 waves) with 300 Mb/s Raman modulators can handle 48 Gb/s of data. The proposed transmission system concept using Raman modulation with HNL-DSF is promising for the high speed, highly reliable scientific underwater cable networks of the next generation

High Speed Raman Modulation for Reliable Scientific-Observatory Undersea Cable Networks

A telemetry transmission system for next generation scientific-observatory underwater cable networks is discussed. Raman modulation using a highly nonlinear fiber achieves transmission capacity adequate for cost-effective undersea observatories that are simple, reliable and upgradable.