We demonstrate theoretically that discrete Raman amplifiers operating in the O-band region (1260–1360 nm) are more efficient than in any other band if we consider the fiber attenuation. Compared with the C-band (1530–1565 nm), the net gain is 3 dB higher. We present also theoretically two types of discrete Raman amplifiers which can be used in the O-band with a course wavelength division multiplexing system. The first amplifier has a bandwidth of 70 nm that was designed with four pump lasers operating at 12XY nm. The second one has a bandwidth of 100 nm and needed six pump lasers to obtain a flattened gain across the O-band. In addition, we have analyzed the gain saturation in both optical amplifiers.

Dispersion compensating fibers (DCF) are the most widely used technology for dispersion compensation. A DCF without Raman amplification introduces extra loss in the system, thus increasing the need for gain in the discrete amplifiers and degrading the noise performance. The idea to additionally use the DCF as a Raman gain medium was originally proposed by Hansen et al. in 1998. [1] This was quickly followed by Emori et al., who demonstrated a broadband, loss less DCF using multiple-wavelength Raman pumping. [2] DCF is a good Raman gain medium, due to a relatively high germanium doping level and a small effective area. To get sufficient gain with a reasonable pump power, a discrete Raman amplifier has to contain several kilometers of fiber, adding extra dispersion to the system that must be handled in the overall dispersion management. Dispersion compensating Raman amplifiers integrates two key functions: dispersion compensation and discrete Raman amplification into a single component.

By optimizing the fiber design for both dispersion compensation and Raman amplification, the pump efficiency can be improved by 35% for a fiber compensating for NZDF.

Optical fiber networks currently operate in the C and L-bands with no usage of the O- band. We demonstrate theoretically that discrete Raman amplifiers operate more efficiently in the O-band than in the other wavelength bands.

Distributed Raman amplification in the transmission fiber is an important technology for advancing the system performance. Co-directionally pumped Raman amplifiers can enhance the performance and allow more flexibility in the system design. However, several sources of non-amplified spontaneous emission noise need to be carefully considered in the amplifier design. The intrinsic cross gain modulation associated with the transient nature of Raman effect can impair the system performance, if the amplifier is not properly designed. We have isolated and measured the impairment due to cross gain modulation in 200-km bi-directionally pumped fiber spans. The penalty depends on the fiber dispersion characteristics and can be small for up to 20 dB on-off co-gain. The benefit of co-directionally pumped Raman amplifiers can be used in multiple long-span transmission to compensate the high loss while maintaining a low nonlinear impairment. It can also be used to extend the length of a single span and achieve a simple system configuration for unrepeatered applications. As opposed to using a span containing multiple fiber types and remotely pumped erbium-doped fiber amplification to achieve transmission over spans with > 60 dB loss, we have demonstrated an unrepeatered link over a single type of fiber with bi-directional Raman pumping. Using the simple conventional non-return-to-zero data format, we achieved transmission of 20 × 10Gb/s channels over a 300-km span of non-zero dispersion-shifted fiber. This simple system configuration provides an important option for terrestrial transmission in remote areas where service access is difficult.

We have measured the DGD induced by bending in both active and passive erbium doped fibers. We demonstrate, both theoretically and experimentally, non-trivial behaviour of PMD in spun erbium doped fiber (EDF) when coiled to small diameters. (2 pages)

We have demonstrated the unrepeatered transmission of 20×10.66Gbit/s over 300km non-zero dispersion-shifted fiber with conventional NRZ modulation format by using bi-directionally pumped Raman amplification, as opposed to hybrid fiber types or remotely pumped EDF.

We have isolated and measured the impairment due to cross gain modulation in 200-km bidirectionally pumped fiber spans. The penalty depends on fiber dispersion characteristics and can be small for up to 20 dB on-off co-gain.

We have developed a Raman gain efficient fiber with positive dispersion. In combination with a negative dispersion fiber we have built Raman amplifiers with zero total dispersion and present results on gain, noise figure and MPI.

A parameter is defined to monitor variations in spectral response of Erbium-doped fibers. Production statistics are given for more than one Mm EDF. The standard deviation is 0.7%, attained by using highly optimized production equipment.

We present an optimally designed dispersion compensating Raman amplifier (DCRA). The dispersion and dispersion-slope can be simultaneously compensated for non-zero dispersion fiber TrueWave(R)RS (TWRS) by extra-high-slope dispersion compensating fiber (EHS-DCF). For C-band 38.4nm range centered at 1548nm, the optical link residual dispersion is within +/-0.1ps/nm(.)km. An average net gain of 8 dB with optimized flatness of +/-0.13dB can be achieved with average NF of 5.6dB and DRB induced MPI of -46dB. (C)2002 Optical Society of America

A single DCF module capable of compensating the dispersion in the full C+L-band of a prototype Raman optimized NZDF has been demonstrated. The residual dispersion from 1530 to 1610 nm was controlled within /spl plusmn/0.07 ps/(nm/spl middot/km). The dispersion margin for 40 Gbit/s transmission is around /spl plusmn/60 ps/nm/sup 3/. Therefore, It will be possible to transmit DWDM 40 Gbit channels in the full C+L-band for around 850 km without any per channel dispersion trimming. The module is also an ideal lumped Raman amplifier. Using a total pump power of 1042 mW an average net gain of 10.1 dB was demonstrated from 1530 to 1607 nm. Noise figure was less than 6 dB in whole wavelength range, and OSNR from double Rayleigh scattering was better than 40 dB. The module will be ideal for use together with the Raman optimized transmission fiber in all Raman systems. Such a system will compared to a conventional system with EDFA's not require any band splitting and therefore support more channel with less loss and lower cost.

We present a bi-directionally pumped dispersion compensating Raman amplifier. The link residual dispersion (1570 nm-1607 nm) is within plusmn0.023 ps/km-nm for non-shifted transmission fibre. MPI of plusmn46.2 dB can be obtained for 8 dB net gain with 5 dB noise figure

Eighty 42.7-Gb/s, 100-GHz-spaced WDM channels weretransmiffed over52x100kmofUltraWaveTM fiber. We employed dispersion-managed