40 Gbit/s 1.55 µm RZ transmission over 109km of non-dispersionshifted fibre with long continuously chirped fibre gratings

Abstract

Chirped fibre gratings are compact and potentially cheap and have become an attractive alternative to technologies such as dispersion compensating fibres for the upgrade of the installed non-dispersion shifted fibre (NDSF) base. In particular the recent demonstrations of 10 Gbit/s transmission over 700 km of NDSF and 40 cm broadband (4 nm) linearly chirped gratings for much-increased source wavelength and operating condition tolerance confirm this potential. These long gratings have essentially flat reflectivity over their usable bandwidth with raised cosine apodisation at both ends of the spectrum. The delay characteristic can be controlled to be linear with less than 2% error with a dispersion slope as high as ~1700 ps/nm (enough for 100 km of standard fibre). At the same time, the broad bandwidth available from the long linearly chirped gratings makes it possible for the first time to achieve dispersion compensation over a significant length of NDSF at several tens of Gbit/s data rates. To date 40 Gbit/s transmission over a significant length of NDSF at 1.55µm has only been demonstrated using dispersion compensating fibres. The best result to our knowledge is an error-free transmission over 150 km of standard fibre. Without any means of dispersion management, the maximum transmission distance is ~4 km for this bit-rate. In this paper we report the first demonstration of 40 Gbit/s transmission over 109 km of NDSF at 1.55µm by employing two continuously-chirped 40 cm long, 4 nm-bandwidth gratings. In addition, a continuously-chirped 5.2 nm bandwidth 1 metre grating is demonstrated