Abstract: A fiber-optic WDM ring carries communication traffic among a plurality of nodes, each node associated with respective subscriber premises. Remote gain is provided in at least one link of the ring. In specific embodiments of the invention, the remote gain is applied preferentially to those wavelength channels most in need of amplification. In specific embodiments of the invention, the remote gain is Raman gain.

Abstract: A lightwave communication system is provided that includes first and second optical transmitters/receivers remotely located with respect to one another. First and second optical transmission paths couple the first transmitter/receiver to the second transmitter/receiver for bidirectionally transmitting optical information therebetween. First and second doped optical fibers are respectively disposed in the first and second optical transmission paths. Optical pump energy is supplied by first and second optical pump sources. The first optical pump source generates Raman gain in the first transmission path and the second optical pump source generates Raman gain in the second transmission path. A first optical coupler is provided for optically coupling pump energy from the first pump source to the second-doped optical fiber and a second optical coupler is provided for optically coupling pump energy from the second pump source to the first doped optical fiber.

Abstract: An optical transmission system is formed to include an optical phase conjugator at alternate repeater sites to minimize the presence of four-wave mixing and other Kerr effect nonlinearities in systems using optical fiber transmission paths (particularly in systems using DWDM and launching relatively high power signals into the low dispersion fiber). Raman gain is included in each fiber span (or in alternate fiber spans) so as to provide a “negative absorption” along the length of the fiber and thereby provide for essentially symmetrical power distribution along the length of each span, where the presence of such a symmetric,power distribution on each side of an optical phase conjugator has been found to significantly improve its performance.

Abstract: A Raman amplified transmission includes at least two pump sources to provide amplification to optical signals residing in the C-band (1530-1562 nm) and L-band (1574-1604 nm). The pump signals are chosen so as to provide for a relatively flat and wide composite gain spectrum with a width at least 50% greater than that generated by a monochromatic pump, while also chosen so as to prevent any four-wave mixing products from being in either the C- or L-bands.

Abstract: The use of a co-propagating fiber Raman amplifier in an optical WDM transmission system has been found to be practical in the situation where the fiber amplifier is operated into depletion and the characteristics of the input signals are controlled to exhibit a reduced integrated relative intensity noise (RIN) over the fiber crosstalk bandwidth. In particular, the reduction in the integrated RIN can be achieved by increasing the number of input channels (by adding more messages or simply using dummy channels), encoding the data in a particular fashion to reduce the integrated RIN, or decorrelating the plurality of N input signals below a predetermined, relatively low frequency (for example, 2 MHz).

Abstract: The use of a co-propagating fiber Raman amplifier in an optical WDM transmission system has been found to be practical in the situation where the fiber amplifier is operated into depletion and the characteristics of the input signals are controlled to exhibit a reduced integrated relative intensity noise (RIN) over the fiber crosstalk bandwidth. In particular, the reduction in the integrated RIN can be achieved by increasing the number of input channels (by adding more messages or simply using dummy channels), encoding the data in a particular fashion to reduce the integrated RIN, or decorrelating the plurality of N input signals below a predetermined, relatively low frequency (for example, 2 MHz).

Abstract: A fiber Raman amplifier is configured to use a co-propagating Raman pump source, which may be beneficial in a variety of system configurations (for example, in bidirectional communication systems). By carefully configuring the pump source characteristics, sufficient optical gain can be achieved in the co-propagating arrangement, the characteristics including: (1) using an optical pump power of at least 50 mW, (2) having a relatively large spectral bandwidth within the pump (to suppress SBS); and (3) a frequency difference between all longitudinal pump modes of each pump laser being separated by at least the walk-off frequency between the pump laser frequency and the signal frequency, and all intense longitudinal modes between different pump lasers being separated by at least the electrical bandwidth of the communication system.

Abstract: In accordance with the invention, an optical fiber communication system comprises one or more Nd doped fiber amplifiers for amplified transmission in the 1400 nm window. The amplifier is designed with a combination of waveguide effects and selective absorption to reduce amplified spontaneous emission to acceptable levels.

Abstract: A Raman amplifier is provided that includes at least a portion of optical fiber in which an optical signal travels. The optical fiber portion may encompass all or part of the optical transmission path of an optical communication system. A pump energy unit is provided that includes first and second pump sources providing pump power at first and second wavelengths, respectively. The first and second wavelengths generate first and second gain profiles in the optical fiber portion. The first and second gain profiles overlap in wavelength. An optical coupler couples the pump power to the optical fiber portion. Since the gain profiles overlap, the Raman amplifier has a greater bandwidth than can be achieved with a pump operating at a single wavelength.

Abstract: A fiber Raman amplifier is configured to use a co-propagating Raman pump source, which may be beneficial in a variety of system configurations (for example, in bidirectional communication systems). By carefully configuring the pump source characteristics, sufficient optical gain can be achieved in the co-propagating arrangement, the characteristics including: (1) using an optical pump power of at least 50 mW, (2) having a relatively large spectral bandwidth within the pump (to suppress SBS); and (3) a frequency difference between all longitudinal pump modes of each pump laser being separated by at least the walk-off frequency between the pump laser frequency and the signal frequency, and all intense longitudinal modes between different pump lasers being separated by at least the electrical bandwidth of the communication system.

Abstract: A method and apparatus is provided for providing pump energy to a doped optical fiber located along an optical transmission path. The doped optical fiber imparts amplification to an optical signal when pumped at a pump wavelength. In accordance with the method, pump energy is generated in the transmission fiber by introducing a power at a wavelength one Raman Stokes order below the desired pump wavelength. The pump energy is transmitted along the transmission path such that first order Raman Stokes-shifted light is applied to the doped optical fiber. For example, if the optical fiber is doped with erbium, which has a pump wavelength of about 1485 nm, pump energy is provided at a wavelength of 1390 nm.

Abstract: A high-powered optical pump includes at least two sub-pumps. Each sub-pump generates light at different wavelengths. The outputs of the sub-pumps are coupled to a remote pump fiber. The resulting light transmitted on the remote pump fiber results in a lower Raman gain and Raman noise spectral peak than that generated by existing single wavelength high-powered optical pumps at the same power level. Therefore, increased power can be transmitted on the remote pump fiber in contrast to a single wavelength pump. Additionally, the total gain spectrum available for the amplification of signals is increased.

Abstract: A Raman amplifier is provided that includes at least a portion of optical fiber in which an optical signal travels. The optical fiber portion may encompass all or part of the optical transmission path of an optical communication system. A pump energy unit is provided that includes first and second pump sources providing pump power at first and second wavelengths, respectively. The first and second wavelengths generate first and second overlapping gain profiles in the optical fiber portion. An optical circulator has a first port receiving the pump power, a second port providing the pump power to the optical fiber and receiving the optical signal, and a third port transmitting the optical signal received from the second port. As a result of this arrangement, a Raman amplifier is provided in which the bandwidth is substantially increased over the bandwidth that can be achieved by the previously mentioned Raman amplifier.