Abstract: Consistent with the present disclosure, an optical communication system is provided in which client data is input to a first node and output from a second node, spaced from the first node, with little delay. In one example, the delay is reduced by including higher order Raman amplifiers that provide a substantially uniform gain along the length of a fiber optic link, thereby reducing the number of EDFAs that may otherwise be installed along the optical fiber link or eliminating such EDFAs entirely. In another example, FEC encoding and decoding are not employed, thereby reducing the delay even further.

Abstract: Consistent with the present disclosure, an optical communication system is provided in which client data is input to a first node and output from a second node, spaced from the first node, with little delay. In one example, the delay is reduced by including higher order Raman amplifiers that provide a substantially uniform gain along the length of a fiber optic link, thereby reducing the number of EDFAs that may otherwise be installed along the optical fiber link or eliminating such EDFAs entirely. In another example, FEC encoding and decoding are not employed, thereby reducing the delay even further.

Abstract: An optical system includes a number of substantially identical, tunable, wavelength-preserving, optical regenerators 10. Each of the regenerators 10 is tuned to a different wavelength so that when a regenerator 10 is tuned to a given wavelength that regenerator will generate a regenerated, reshaped and retimed optical signal at the same given wavelength. The system also includes a multiplexer 32 coupled to receive and combine regenerated optical signal from each of regenerators. A filtering system (34) is provided, either internal or external to regenerators 10, to demultiplex different wavelength signals from an aggregate WDM optical signal.

Abstract: A spectral polarization separator (SPS) designed to separate two wavelength-separated signals applied to the SPS with the same state of polarisation (SOP) into signals with orthogonal SOP's comprises two or more birefringent fibre elements optically in series. The differential delays and relative orientations of these elements are chosen so that polarisation separation is effected without introducing any polarisation mode dispersion (PMD). This contrasts with a prior art single birefringent element SPS whose operation necessarily does introduce PMD. A particular application for the SPS is in a dual wavelength transmitter designed for overcoming polarization hole-burning effects in a long-haul optically amplified transmission system.

Abstract: An arrangement for reducing the effects of four-wave-mixing in an optically amplified WDM optical fiber communication system employing dissimilar wavelength channel spacing, comprising means for effecting spectral regeneration of the optical signals at intervals along the system transmission medium.

Abstract: The spectral-gain characteristics of an erbium-doped fibre amplifier have been tailored by incorporating a gain-shaping-filter within the amplifier. The filter is chosen to modify the natural gain spectrum of the amplifier so as to suppress the gain peak and thus flatten the overall spectral-gain profile. Because the amplifier is distributed, it is possible to insert one or more filters along the length of the fibre. It is shown that there are considerable advantages to locating the filter within the length of the amplifier, rather than at the end, which is the more obvious choice. Advantages are that the amplifier pump efficiency is almost unaffected and the output saturation power is similar to that of the unshaped amplifier. In addition, the flat spectral gain provides an amplifier ideally-suited for use at a number of signal wavelengths, as required for wavelength-division multiplexing (WDM).

Abstract: A laser is characterized by a glass gain medium which contains trivalent samarium Sm.sup.3+ ions and which, when optically pumped on one or a number of absorption bands to achieve excitation at or above the metastable .sup.4 G.sub.5/2 level, radiates light at a wavelength substantially corresponding to transitions from the .sup.4 G.sub.5/2 level of samarium.