Takamasa Imai

An over 2200-km coherent transmission experiment at 2.5 Gb/s using erbium-doped-fiber in-line amplifiers

A 2223 km transmission distance was achieved with a 2.5-Gb/s heterodyne detection system that used erbium-doped-fiber in-line amplifiers and dispersion-shifted single-mode fibers. Twenty-five amplifiers, placed at approximately 80-km intervals, offered a total gain of more than 440 dB. Receiver sensitivity was -42.0 dBm, with only a 4.2-dB penalty from the initial sensitivity achieved by the back-to-back configuration. >

A remote supervisory system based on subcarrier overmodulation for submarine optical amplifier systems

A supervisory (SV) signal transmission scheme for long haul optical amplifier systems is described. The scheme is based on subcarrier overmodulation of the line signal and features simple configuration; due to the use of EDFA gain modulation, no additive optical components are required in a submarine repeater to transmit a response signal. This paper discusses the subcarrier modulation index and frequency used for the SV signaling, the most significant design parameters. The dependence of the signal-to-noise ratio (SNR) on the modulation index in SV signal transmission is analyzed to clarify the modulation index value required for reliable SV signaling. In addition, the line signal impairment caused by subcarrier overmodulation is also analyzed to show the systems in-service feasibility. The subcarrier frequencies used for command and response signal transmission are discussed from the experimental results on the frequency response of an optical amplifier system and EDFA gain modulation efficiency.

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.

A new single-fiber 10-gb/s optical loopback method using phase Modulation for WDM optical access networks

This paper proposes a new single-fiber 10-Gb/s optical loopback method for wavelength-division-multiplexing (WDM) optical access networks. The proposed method improves the tolerance of backreflection that causes interferometric crosstalk with the loopback method on a single fiber. Furthermore, bit synchronization is used to avoid the problem of wavelength dispersion caused in optical access networks. The authors simulated the available distance, received eye patterns at 10 Gb/s, and confirmed the excellent eye opening. 10-Gb/s back-to-back experiments show that the proposed method provides a 17-dB improvement in backreflection tolerance compared with the direct method. The paper reports the first successful results for 10- and 20-km transmission experiments using a standard single-mode optical fiber. The measured eye patterns agreed well with the simulation results. The paper also shows measured bit-error rates (BERs) equivalent to those of a back-to-back configuration.

WDM upgrading of an installed submarine optical amplifier system

This paper describes the WDM upgrading of a submarine optical amplifier system installed for single-channel transmission in commercial use. The key technologies used include 10-Gb/s high-speed forward error correction, preemphasis to overcome the optical passband-width constraint, optimized signal pulse format that leads to partial return-to-zero (PRZ) signaling, and dispersion compensation to suppress the degradation caused by fiber nonlinearity and dispersion. It also reports field experimental results on upgraded system performance. The results confirm that simply upgrading the terminal equipment allows the transmission capacity of a submersed line consisting of submarine repeaters and cables to be flexibly increased from 10 Gb/s to 40 Gb/s per fiber pair.

Long-haul WDM transmission using higher order fiber dispersion management

We propose a fiber dispersion management scheme for large-capacity long-haul wavelength division multiplexing (WDM) transmission systems that considers not only second- but also third-order dispersion characteristics using transmission fibers with opposite dispersion signs. It eliminates the waveform distortion of WDM signals that originates from the existence of third-order dispersion, which is a constraint placed on WDM capacity in conventional dispersion management, while reducing the interchannel interaction caused by the interplay of fiber nonlinearity and second-order dispersion. Design concept of the scheme is discussed to show the feasibility of using actual fiber parameters. An experimental investigation on transmission performance regarding the signal pulse format, nonreturn-to-zero (NRZ) and return-to-zero (RZ), and interchannel interaction caused by four-wave mixing (FWM) and cross-phase modulation (XPM) is described for optimizing WDM system performance. It is experimentally shown that RZ pulse transmission is possible without significant spectral broadening over a wide wavelength range in dispersion managed fiber spans. Using these results together with a wideband optical amplifier gain-bandwidth management technique, yields long-distance WDM transmission with the capacity of 25/spl times/10 Gb/s over 9288 km.

Over 10,000 km Straight Line Transmission System Experiment at 2.5 Gb / s Using In-Line Optical Amplifiers

Many recent transmission experiments have demonstrated the potential of long distance transmission systems using erbium-doped amplifiers [1],[2],[3]. However, to confirm the realization of a transoceanic system, the evaluation of a full-length straight line transmission experiment is essential. Also, supervisory(SV) signal transmission over the transoceanic distance has to be confirmed to realize a practical system. In this paper, we report for the first time a 10,073 km straight line transmission experiment at 2.5 Gb/s with supervisory signal transmission.

Quarter terabit (25/spl times/10 Gb/s) over 9288 km WDM transmission experiment using nonlinear supported RZ pulse in higher order fiber dispersion managed line

We experimentally show that RZ pulse transmission with narrow spectral broadening over a wide wavelength range is possible in higher order dispersion managed fiber spans. WDM transmission with total capacity of 25/spl times/10 Gb/s is also demonstrated.

Polarization fluctuations in a single-mode optical fiber

Polarization fluctuation characteristics of single-mode optical fiber output are examined theoretically and experimentally. A fiber model for studying these characteristics from the perspective of probability on the Poinare sphere is proposed. The relationship of the degree of polarization fluctuation to time and fiber length is shown theoretically. Measurements of submarine and underground cables and long-haul fibers up to 270 km in length generally support the proposed model. >

Limitations imposed by Rayleigh backscattering in closely interleaved, bidirectional WDM transmission systems

By deriving signal-backscattering and backscattering-backscattering beat noises, this letter quantifies the performance impairment due to backscattering produced by closely spaced counterpropagating signals. Experiments using 10-Gb/s data signals verify the theoretical analysis. The interference between signal and backscattering induces significant impairment when their channel separation is less than the sum of the data rate and signal spectrum width. The spectral efficiency limitation imposed by backscattering is clarified for closely spaced, interleaved bidirectional transmission systems.