40 Gbit/s 1.55 [micro sign]m RZ transmission over 109 km of non-dispersion shifted fibre with long continuously chirped fibre gratings

Abstract

We report the first demonstration of 40 Gbit/s transmission over 109 km of standard fibre at 1.55 µ µm with dispersion compensating linearly chirped continuous fibre gratings and a ~0.5 nm source wavelength tolerance, demonstrating the feasibility of fabricating such gratings for use at very high data rate. Background: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 fibres (NDSF). In particular the recent demonstration of 10 Gbit/s transmission over 700 km of NDSF [11] and 40 cm broadband (4 nm) linearly chirped gratings for much increased source wavelength and operation condition tolerance [2] 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 in delay and with a dispersion slope as high as ~1700 ps/nm (equivalent to ~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 1.55 µm has only been demonstrated using dispersion compensating fibres [3,4]. The best result to our knowledge is an error-free transmission over 150 km of NDSF [4]. Without dispersion compensation, the maximum transmission distance is limited to ~4 km at this bit rate.In this paper we report the first demonstration of 40 Gbit/s transmission over 1.09 km of NDSF at 1.55 µm by employing two continuously chirped 40 cm long, 4 nm bandwidth gratings. Experiment:Two linearly chirped gratings were employed in combination with a 4 port circulator. The characteristics are shown in figure 1. Grating 1 exhibits ~98% reflectivity with < ±0.1 dB amplitude deviation over 3.8 nm, dispersion slope of 837 ps/nm and maximum delay deviation from linear fit of < ±50 ps. Whilst comparable figures for grating 2 are ~98% reflectivity, < ±0.1 dB amplitude deviation over 3.5 nm, dispersion slope of 870 ps/nm with < ±40 ps delay deviation from linear fit.

Chirped Fiber Bragg Gratings

“…A novel offset core fiber grating has also been reported for strain tuned dispersion compensation of 270 km of standard fiber at 10 Gb/sec [55,56]. Longer gratings, up to 400 mm [58], have been used at 40 Gb/sec over 109 km of fiber, and in excess of 1-m-long gratings with a bandwidth of $10 nm at 10 Gb/sec over 100 km of standard fiber in a WDM transmission system with up to 11 wavelengths simultaneously [48]. Longer gratings, up to 400 mm [58], have been used at 40 Gb/sec over 109 km of fiber, and in excess of 1-m-long gratings with a bandwidth of $10 nm at 10 Gb/sec over 100 km of standard fiber in a WDM transmission system with up to 11 wavelengths simultaneously [48].…”

Long continuously chirped fibre Bragg gratings for compensation of linear- and 3

“…In particular chirped fibre Bragg gratings have already proven their suitability as chromatic dispersion compensators in a series of experiments [ 1,2] where they have been incorporated in real systems at 10 Gbit/s with excellent results. Furthermore they have been shown to allow 40 Gbit/s error-free transmission at 1.55 pm over 109 km of non-dispersion shifted fibre as we recently reported [3]. As the bit rates are being increased the effect of higher order dispersion and polarisation mode dispersion starts to become a limiting factor on the recovery of the data after transmission over long distances.…”

Optimization of apodized linearly chirped fiber gratings for optical communications

“…They basically constitute generalized distributed reflectors whose reflection spectra and dispersion characteristics are wavelength-dependent and can be accurately adjusted by proper design. They can be effectively used for dispersion compensation in high-bit-rate, long-haul fiber communication links [1]- [7] and short-pulse generation and restoration [8], [9]. On the other hand, fiber Bragg gratings can be used for the implementation of high-quality fiber laser cavities of various geometries [10], [11] and semiconductor diode stabilization [12], [13].…”