40 Gbit/s or higher bit-rate DWDM has been seen as a promising candidate for next generation optical transport networks for some years because it reduces the number of wavelengths, resulting in easier operation and maintenance. It can also potentially reduce the cost and footprint of equipment. However, the reality is that even 40 Gbit/s DWDM has not yet appeared in commercial long-haul systems. This seems to be due not only to financial depression in the market but also to technical difficulties with 40 Gbit/s. The most significant difficulty in 40 Gbit/s systems is that an additional 6 dB of optical signal-to-noise ratio (OSNR) is required compared to 10 Gbit/s systems. One way to gain the 6 dB needed for 40 Gbit/s is by combining (1) the 3 dB provided by the DPSK, with (2) the 3 dB available from the stronger forward error correction technique (FEC). Recent advance in opt-electrical devices and high-speed LSI technologies have made it possible to employ advanced modulation formats and powerful and complex FEC techniques. Another challenge in higher bit-rate transport systems is to extend tolerance against the unwanted waveform distortion due to the wavelength chromatic dispersion and polarization mode dispersion. Various kinds of adaptive delay equalizing technologies have also been proposed to mitigate this issue. In this paper, these enabling technologies will be reviewed and discussed for the near future high-speed and flexible transport networks.

Date Published: 25 October 2005
PDF: 11 pages
Proc. SPIE 6012, Optical Transmission Systems and Equipment for WDM Networking IV, 60120H (25 October 2005); doi: 10.1117/12.632015

Published in SPIE Proceedings Vol. 6012:
Optical Transmission Systems and Equipment for WDM Networking IV
Ken-ichi Sato; Werner Weiershausen; Achyut K. Dutta; Benjamin B. Dingel, Editor(s)