Hiroji Masuda

Review of wideband hybrid amplifiers

The configurations and characteristics of several types of wideband hybrid amplifiers are presented. Each of the amplifiers consists of an EDFA and a Raman amplifier (distributed or discrete type) and yields low noise in WDM systems.

High-performance distributed Raman amplification systems: practical aspects and field trial results

We introduce high-performance distributed Raman amplification (DRA) systems employing a DRA/EDFA hybrid amplifier scheme with practical aspects based on safety considerations. We also describe successful field trial results using the scheme with high pump-efficiency.

Recent progress on optical fiber amplifiers and their applications

I review recent progress on optical fiber amplifiers and their applications in fiber-optic communication systems. This study focuses on rare-earth doped fiber amplifiers (RDFAs) and fiber Raman amplifiers (FRAs). There are three types of RDFA, namely erbium, thulium, and praseodymium doped fiber amplifiers (EDFAs, TDFAs, and PDFAs, respectively) and EDFAs have been widely deployed in trunk networks for about a decade. EDFAs have wideband, low noise, and high pumping efficiency characteristics, and are key components of high-capacity and cost-effective wavelength-division-multiplexing (WDM) transmission systems in the low loss 1.5 μm band. In contrast, distributed Raman amplification (DRA) has been recognized as a powerful and practical technology in long-haul trunk networks in recent years. DRA/EDFA or DRA/lumped FRA hybrid-amplification systems yield significantly higher signal-to-noise ratios than lumped optical amplification systems that use EDFAs or FRAs. The latter are hybrid systems called all-Raman systems. As regards the bandwidth enhancement of optical fiber amplifiers, which is indispensable for cost-effectively realizing a rapid increase in communication traffic, silica Raman amplifiers have seamless single band bandwidths (Δλ) up to ~100 nm wider than those of RDFAs (~30 to ~80 nm). Further bandwidth enhancement can be achieved by using tellurite-based Raman amplifiers with Δλ up to ~160 nm or multi-band amplifiers. Each multi-band amplifier uses plural single-band RDFAs and/or FRAs in the parallel configuration in the low loss wavelength region (1.3-1.6 μm band) of silica transmission fibers.

Ultra-wideband tellurite-based fiber Raman amplifiers

We review recent research on ultra-wide-band tellurite-based fiber Raman amplifiers and discuss their future prospects. These amplifiers are superior to silica-based fiber Raman amplifiers in that they provide wideband operation with short fibers and only a few pump LDs.

Recent Progress in High-Speed and Large-Capacity Optical Transmission Technologies

This paper describes 100-Gb/s-class high-speed and large-capacity optical transmission technologies with focus on the modulation formats and high-speed optical/electrical devices. First, we review the recent progress of 100-Gb/s-class transmission technologies. We then discuss the transmission characteristics of several promising modulation formats with the line rate of 111 Gb/s. Next, we show the results of a 20.4-Tb/s transmission experiment using the 111-Gb/s CSRZ-DQPSK format and gain-flattened hybrid Raman/EDFAs.

Advanced transmission systems using distributed Raman amplification technologies

This paper introduces practical and high-performance transmission systems that employ distributed Raman amplification (DRA) technologies. The systems incorporate DRA/EDFA hybrid amplifiers as inline amplifiers with limited DRA pump powers. These powers are determined with respect to the practical safety and reliability of the systems against intense pump light. The practical aspects and merits of our systems are described both in detail and qualitatively. It is shown that a hybrid amplifier system using DSF performs better than one using SMF with limited pump powers. The use of DRA means that the optical SNR of the former system is typically about 2-3 dB higher than that of the latter. Moreover, this paper reports successful results of long-haul transmission field trials using the hybrid amplifier scheme in the L-band over installed DSF with an aggregate capacity of 1.28 Tbit/s (32 x 43 Gbit/s).