Tadashi Sakamoto

1.58-/spl mu/m broad-band erbium-doped tellurite fiber amplifier

This paper describes the development of a 1.58-/spl mu/m broad-band and gain-flattened erbium-doped tellurite fiber amplifier (EDTFA). First, we compare the spectroscopic properties of various glasses including the stimulated emission cross sections of the Er/sup 3+4/ I/sub 13/2/ /sup 4/I/sub 15/2/ transition and the signal excited-state absorption (ESA) cross sections of the Er/sup 3+4/ I/sub 13/2/ - /sup 4/I/sub 9/2/ transition. We detail the amplification characteristics of a 1.58-/spl mu/m-band EDTFA designed for wavelength-division-multiplexing applications by comparing it with a 1.58-/spl mu/m-band erbium-doped silica fiber amplifier. Furthermore, we describe the 1.58-/spl mu/m-band gain-flattened EDTFA we developed using a fiber-Bragg-grating-type gain equalizer. We achieved a gain of 25.3 dB and a noise figure of less than 6 dB with a slight gain excursion of 0.6 dB over a wide wavelength range of 1561-1611 nm. The total output power of the EDTFA module was 20.4 dBm and its power conversion efficiency reached 32.8%.

Hybrid fiber amplifiers consisting of cascaded TDFA and EDFA for WDM signals

The detailed gain characteristics of hybrid fiber amplifiers that consist of cascaded thulium-doped fiber amplifiers (TDFAs) and erbium-doped fiber amplifiers (EDFAs) are reported. The experimental results showed that the hybrid amplifiers have gains of over 20 dB with the bandwidth of more than 80 nm in the wavelength range between 1460 and 1560 nm. The low noise figure (NF) below 7 dB was obtained in 1460-1540 nm when placing a TDFA in the first stage followed by an EDFA and in 1480-1560 nm when placing amplifiers in a reversed order. The gain of TDFA and EDFA was optimized for minimizing the gain variation ratio (GVR=(maximumgain-minimumgain)/minimumgain: in the unit of decibels) of the hybrid amplifiers, and it could be minimized to less than 0.4 for the amplifiers that have gain in the wavelength region from 1460 to 1537 nm. The gain-equalization technique was applied, and the hybrid amplifier that had an average gain of 20 dB, a gain excursion of less than 2 dB, an output power of 14.5 dBm, and an NF of less than 7 dB in the 77-nm gain band was achieved.

1580-nm band, equally spaced 8 x 10 Gb/s WDM channel transmission over 360 km (3 x 120 km) of dispersion-shifted fiber avoiding FWM impairment

Optically repeated wavelength-division multiplexed (WDM) transmission over dispersion-shifted fibers (DSFs) in the novel 1580-nm wavelength band is reported. WDM systems operating on DSFs are severely impaired by nonlinear crosstalk caused by four-wave mixing (FWM). We avoid this impairment by using novel 1580-nm band instead of the conventional 1550-nm band. Newly developed erbium-doped fiber amplifiers (EDFAs) for 1570-1600-nm wavelength band (gain-shifted EDFAs) are used as pre- and post amplifiers as well as in-line amplifiers. We demonstrate, for the first time, that long in-line amplifier span (120 km, span loss /spl sim/30 dB), high-bit rate (10 Gb/s), optically repeated WDM transmission over a 360 km (3/spl times/120 km) DSF is possible by using 1580-nm band channels without FWM impairment.

Gain-clamped S-band discrete Raman amplifier

In summary, we have demonstrated, for the first time to our knowledge, a gain-clamped discrete Raman amplifier in the S-band. The device achieves peak net gain over 22 dB, and a gain variation of only 0.3 dB for signal input power ranging from -20 dBm to 2.7 dBm. Unlike conventional gain-clamping designs, an extinction ratio between signal and lasing wavelength of over 30 dB is achieved. This new technique suppresses instability due to randomly-polarized ASE and double Rayleigh scattering (DRS) (hence noise figure) for small signal input power under high pump power, as well as power surges due to transient effects in Raman amplifiers. This promises a viable technology to provide gain bands not currently available from traditional doped fiber amplifiers.

S-band fiber optic amplifiers

This paper reviews S-band fiber optic amplifiers including thulium-doped fiber amplifiers (TDFA), gain-shifted thulium-doped fiber amplifiers and Raman amplifiers describe TDFA, gain shifted (GS) TDFA and Raman amplifiers. The TDFAs or GS-TDFA seem to have a slight advantage over Raman amplifiers in terms of power conversion efficiency, but we must make further improvements in power conversion efficiency if we wish to employ all these amplifiers under practical conditions.

Terabit-scale compact hierarchical optical cross-connect system employing PLC devices and optical backplane

The first practical hierarchical optical cross-connect system is developed and its feasibility confirmed using field-installed fibers. Fully-implemented equipment requires a 16-U chassis to manage 4.8-Tbit/s signals from 8 WDM lines and 160 client ports.

Development of Terabit-Scale Compact Hierarchical Optical Cross-Connect System Using Planar Device Integration

The first practical terabit-scale hierarchical optical cross-connect system is realized by employing silica-based planar lightwave circuit devices. The system is scalable to 320 line cross connects + 160 client cross connects, and fully implemented equipment would require a 16-U-high chassis and only a 350-W power consumption. The potential of node cascadability is discussed and experimentally confirmed using partially implemented equipment that has four wavelength-division-multiplexed ports and one waveband switching capability. Stable operation was also confirmed using field-installed fibers.

Wavelength Path Reconfigurable AWG-STAR Employing Coprime-Channel-Cycle Arrayed-Waveguide Gratings

We propose a novel flexible AWG-STAR system that employs two kinds of cyclic-frequency AWGs whose repetition channel numbers are coprime. We demonstrate that we can reconfigure all the wavelength paths in a network independently.

Tunable wavelength converter using cross-gain modulation in fiber optical parametric amplifier

We have demonstrated a novel wavelength conversion scheme based on XGM in fiber OPA. The scheme enables the tunable wavelength conversion with a simple configuration, and it is free from linewidth broadening caused by the phase modulation of OPA pump. The signal at 1554 nm was converted anywhere into a 13 nm wavelength range, in either the C band (1548-1556 nm) or the L band (1574-1580 nm), with high extinction ratio and high signal to noise ratio.

Fast transient response of L-band tellurite-based EDFAs and their optically gain-clamped behavior

We reported on the fast transient response of EDTFAs. The transient time of EDTFAs can be one-ninth as short as that of the EDSFAs with similar gain shape in L-band. We also demonstrated optically gain-clamped EDTFAs and showed that the power excursion due to SHB is comparable to or smaller than that in EDSFAs. The relaxation oscillation frequencies also give us information about the fast dynamics within EDTFAs. In summary, EDTFAs show superior controllability over EDSFAs for automatic gain control via either electrical or optical schemes. Further research will include modeling of the dynamic behavior of EDTFAs.