Abstract: An optical communication system is provided comprising a first optical fiber having a first end and a second end, a plurality of line units optically coupled to the first optical fiber for amplification of an optical signal propagating along the first optical fiber, and a power cable for the line units. The power cable is terminated between the first end and the second end of the first optical fiber, preferably at about a midpoint of the first optical fiber.

Abstract: Optical transmission systems of the present invention includes at least one double pass Mach Zehnder filter, which includes a first optical coupling section coupling at least one input/output port to a first end of two or more optical communication paths, or Mach-Zehnder legs, having different effective lengths. A second optical coupling section is provided to couple at least one output/input port to a second end of the optical communication paths. The first and second optical coupling sections and the two communication paths form a Mach-Zehnder interferometer. The double pass Mach-Zehnder filter is configured such that the output from at least one of the output/input port is coupled back into one of the one output/input ports and passes through the Mach-Zehnder interferometer a second time.

Abstract: A system and method of providing a transmission span that compensates for signal attenuation, dispersion, and nonlinearity of an optical signal communicated between two line units of a transmission link includes dividing the transmission span into a plurality of fiber segments and selecting a particular fiber for each of the segments. The fiber selection and arrangement of fibers within the span can be selected in accordance with the nonlinearity, dispersion conditions, and distributed gain conditions of the constituent fibers. In a three segment map, the first segment can provide low non linearity, the third segment can provide distributed gain, and the second segment can compensate for the dispersion of the first and third segments. The span can be used, e.g., for distributed Raman amplification. The span can alternatively include a two segment map, a four segment map, or a map with additional segments.

Abstract: A method of increasing usable bandwidth on a long-haul cable system having at least one optical fiber, the method comprising the steps of: (a) effecting counter-propagating first and second signals of different bands on a common long-haul optical fiber having cascaded optical amplifiers; and (b) band amplifying the first and second signals while reducing BRS in the bands.

Abstract: A collapsed ring fiber optic system includes a service path and a protection path provides at a shallow water portion of the fiber optic system, to deal with any fiber cuts that may occur at the shallow water portion without loss of main trunk bandwidth. The service and protection paths meet at a branch point, which is preferably located at a deep water portion of the fiber optic system. A passive combiner or a 1×2 switch is provided at the branch unit, along with a detector and a processor, to determine whether any signals are being received from the service path, and if not, to reconfigure the system to accept signals from the protection path. At another shallow water portion of the fiber optic system, nearby where a destination is located, the signal provided on the optical path over the deep water portion is split into a service path and a protection path, to provide redundancy to deal with any fiber cuts that may occur.

Abstract: An optical amplifier having redundancy and a dynamic range of pump power is provided. The amplifier contains a plurality of optical pump sources which are adapted to emit a plurality of pumps. The amplifier also contains a P×V coupler containing P inputs and V outputs, which is adapted to receive the pumps and to output V pump profiles, where P and V are positive integers >1 and P=V or P≠V. The pump profiles include a first set of pumps having a first set of wavelengths and having a first power and a second set of pumps having a second set of wavelengths different from the first set of wavelengths and having a second power different than the first power. The amplifier optionally contains at least one spare optical pump source which is adapted to be turned off during operation of the amplifier unless at least one of the plurality of optical pump sources becomes non operational during the operation of the amplifier.

Abstract: A method and apparatus for performing error correction is described. A stream of data is encoded using concatenated error correcting codes. The encoded data is communicated over a transmission system. The encoded data is decoded using the codes and three levels of decoding.

Abstract: A method and apparatus is provided for determining the gain profile of a path through an optical amplifier disposed in a first optical transmission path of an optical transmission system supporting bi-directional communication between first and second terminals along the first optical transmission path and a second optical transmission path. The method begins by generating an optical tone at a given wavelength within the bandwidth of the optical amplifier. The wavelength of the optical tone is modulated about the given wavelength. The modulated optical tone is transmitted from the first terminal along the first optical transmission path and through the optical amplifier. A portion of the modulated optical tone is received after it traverses the optical amplifier and FM to AM conversion is performed on the received portion to form an amplitude modulated optical tone. The amplitude modulated optical tone is transmitted back to the first terminal along the second transmission path via an optical loop-back path.

Abstract: An optical amplifier includes first, second and third amplifier stages, a first equalizer coupled between the first and second amplifier stages, a second equalizer coupled between the second and third amplifier stages, and a third equalizer coupled between an amplifier output and the third amplifier stage. The first stage includes a length of first erbium doped fiber coupled between an input and the first equalizer. The second stage includes a second erbium doped fiber coupled between the first equalizer and the second equalizer. The third stage includes a third erbium doped fiber coupled between the second equalizer and the third equalizer.

Abstract: A method and apparatus to perform automatic gain equalization for a lightwave communications system is described. A first amplifier amplifies an optical signal to produce a first gain curve having a first gain maxima and a first gain minima of a first period. A second amplifier amplifies the optical signal to produce a second gain curve with a second gain maxima and a second gain minima of a second period, with the second gain maxima substantially coinciding with the first gain minima.

Abstract: A branching unit is provided for directing individual wavelengths of a WDM optical communication signal among a transmitting terminal, a receiving terminal and a branch terminal. The branching unit includes first and second cross bar switches each having at least a first, second and third port such that in a first state the first cross bar directs an optical signal appearing on the first port to the second port and in a second state the first cross bar directs the optical signal from the first port to the third port. A reflective filter couples the third port of the first switch to the third port of the second switch. The reflective filter is configured to reflect a prescribed wavelength and to transmit therethrough all remaining wavelengths forming the WDM signal. An optical fiber couples the second port of the first switch to the second port of the second switch. First and second circulators are also provided, which each have an input, output and an intermediate port.

Abstract: A WDM optical communication system is provided that includes a transmitter and a receiver. An optical fiber transmission path couples the transmitter to the receiver. The transmission path includes at least one repeater having an optical amplifier located therein. A dispersion compensator is disposed at an intermediate point along the transmission path. The intermediate point is located outside of the repeater. The compensator includes a wavelength routing device for dividing a signal having a prescribed bandwidth into a plurality of distinct sub-bands. A plurality of output paths is provided for respectively receiving the plurality of distinct sub-bands. The dispersion compensator also includes a dispersion compensating optical element coupled to each of the output paths. Each dispersion compensating optical element substantially compensates for dispersion at a prescribed wavelength within the bandpass of its respective sub-band.

Abstract: A WDM optical communication system is provided that includes a transmitter and a receiver. An optical fiber transmission path couples the transmitter to the receiver. The transmission path includes at least one repeater having an optical amplifier located therein. A dispersion compensator is disposed at an intermediate point along the transmission path. The intermediate point is located outside of the repeater. The compensator includes a wavelength routing device for dividing a signal having a prescribed bandwidth into a plurality of distinct sub-bands. A plurality of output paths is provided for respectively receiving the plurality of distinct sub-bands. The dispersion compensator also includes a dispersion compensating optical element coupled to each of the output paths. Each dispersion compensating optical element substantially compensates for dispersion at a prescribed wavelength within the bandpass of its respective sub-band.

Abstract: An optical signal processing method and apparatus for providing a noise feedback loop that uses existing noise within the optical system to saturate a chain of amplifiers after the branching unit, thereby preventing information channels in a WDM signal containing empty channels from becoming overamplified as they pass through downstream amplifiers. The method and apparatus uses an existing drop amplifier which emits ASE noise as a side effect. A coupler connects the ASE noise to a filter. The filtered ASE noise is fed into an existing trunk amplifier by a second coupler. The trunk amplifier increases gain to the filtered ASE noise to a level high enough to saturate the amplifier chain, without requiring an external noise generating device.