FIBER-OPTIC COMPENSATION FOR DISPERSION, GAIN TILT, AND BAND PUMP NONLINEARITY

摘要

An apparatus and method are describedfor combining optical amplification anddispersion compensation in a Ramanampli-fier. A Dispersion-Managing RamanAm-plifier (DMRA) combines Ramanamplification with dispersion compensation byselect-ing the length and dispersion of the gain fiberto balance the dispersion of the link. Thisgain fiber is also single-mode at the signaland pump wavelengths. The pumping levelis adjusted to balance the losses from thegain fiber and transmission link, while thepumping configuration is selected to remainwithin the 3dB loss length for the pumpinglight. When the amplifier is split into twosegments, the two segments may be joinedby an isolator, a gain equalization element,and/or an optical add/drop multiplexer. ForWDM transmission systems based ondispersion-shifted fiber (DSF), operation in the"vi-olet band" between 1430-1530 nm is based on Raman amplification. By usinga DMRA, a dispersion and nonlinearity managed systemcan be implemented. In particular, 4WM does not phase match in such a system,and modulation instability is absent in the transmissionlink. Furthermore, gain equalization can be added to the DMRA by cascading oneor two Mach-Zehnder frequency filters. The inventionalso includes a method for symmetrically adding channels below and above the C-band, the gain tilt within the C-band can be minimized.Therefore, a roughly equal number of channels should be placed in the short-wavelength S-band and the long-wavelength L-band tominimize the Raman energy exchange in the C-band. Also, whereas C- and L-bandscan be amplified using erbium-doped fiberamplifiers, the S-band can use either discrete or distributed Ramanamplifiers. To minimize the interaction between pumps for different bands,alternate band pumps can be spatially dispersed and/or cross-polarized. Thedistributed Raman amplification can be achieved by pumpingthe transmission line with discrete laser diodes or by a Raman oscillator.