Abstract: Methods and systems for higher-order PMD compensation are implemented by developing an effective mathematical model and applying economical design techniques to the model. By assuming a constant precession rate for a narrow band of frequencies in an optical signal, a simplified model of a higher-order PMD compensator can be derived. The model can be used produce an economical compensator by making multiple uses of selected optical components.

Abstract: Methods and systems for PMD compensation in an optical communication system are implemented by transmitting multiple optical signals through a common optical conduit to an optical compensator that adjustably rotates the polarization states of the multiple optical signals and transmits the rotated optical signals to an optical receiver. The receiver, upon sensing an excessive error condition, commands the optical compensator to change the polarization state of rotation, which changes the PMD profile of the received optical signals.

Abstract: A system, amplifier and method are provided for amplifying an optical signal in an optical communications system where spans between amplifiers may vary. The system includes a Raman amplifier variable gain portion and an EDFA gain portion. The amount of Raman amplifier gain is chosen to trade off accumulation of noise with accumulation of multi-path interference. This variable Raman gain is used to equalize the loss of each span so that the amount of optical power supplied at the input of the EDFA gain portion is substantially constant throughout the system.

Abstract: Methods and systems for higher-order PMD compensation are implemented by developing an effective mathematical model and applying economical design techniques to the model. By assuming a constant precession rate for a narrow band of frequencies in an optical signal, a simplified model of a higher-order PMD compensator can be derived. The model can be used produce an economical compensator by making multiple uses of selected optical components.

Abstract: A method of compensating for chromatic dispersion in an optical signal transmitted on a long-haul terrestrial optical communication system including a plurality of spans, including: allowing chromatic dispersion to accumulate over at least one of the spans to a first predetermined level; and compensating for the first pre-determined level of dispersion using a dispersion compensating fiber causing accumulation of dispersion to a second predetermined level. There is also provided a hybrid Raman/EDFA amplifier including a Raman portion and an EDFA portion with a dispersion compensating fiber disposed therebetween. An optical communication system and a method of communicating an optical signal using such a Raman/EDFA amplifier are also provided.

Abstract: An optical interface device is provided for use in an undersea optical transmission system that includes an undersea optical transmission path, a plurality of optical repeaters located along the optical transmission path, and a selected one of any of a plurality of different vendor supplied optical transmission terminals each of which has a vendor-specific interface. The optical interface device includes a signal processing unit providing signal conditioning to optical signals received from the vendor-specific interface of the selected optical transmission terminal so that the optical signals are suitable for transmission through the undersea optical transmission path. A gain monitoring arrangement is also provided for determining a change in gain provided by any one of the optical repeaters.

Abstract: A method of compensating for chromatic dispersion in an optical signal transmitted on a long-haul terrestrial optical communication system including a plurality of spans, including: allowing chromatic dispersion to accumulate over at least one of the spans to a first predetermined level; and compensating for the first pre-determined level of dispersion using a dispersion compensating fiber causing accumulation of dispersion to a second predetermined level. There is also provided a hybrid Raman/EDFA amplifier including a Raman portion and an EDFA portion with a dispersion compensating fiber disposed therebetween. An optical communication system and a method of communicating an optical signal using such a Raman/EDFA amplifier are also provided.

Abstract: An optical and electrical isolating unit for use with a branching unit located in an undersea optical transmission system is provided. The unit includes a pressure vessel adapted for use in an undersea environment. First, second and third ports are located in the pressure vessel for receiving first, second and third undersea transmission cables, respectively. The first cable includes an electrical power conductor and at least one optical fiber. The second cable includes an electrical conductor, and the third cable, which is electrically unpowered, includes at least one optical fiber. An electrical power conductor segment is provided for electrically coupling the conductor in the first cable received in the first port to the conductor in the second cable received in the second port. At least one optical fiber segment is located in the pressure vessel, which segment optically couples the optical fiber of the first cable to the optical fiber of the third cable.

Abstract: A method and apparatus is provided for obtaining status information concerning an optical transmission path. The method begins by generating a COTDR probe signal having a prescribed wavelength and transmitting optical traffic signals and the COTDR probe signal over an optical transmission path having a length corresponding to those used in regional undersea market applications. The prescribed wavelength of the COTDR probe signal is separated from wavelengths at which the optical traffic signals are located by a distance at least equal to a predetermined guard band. A backscattered and/or reflected portion of the COTDR probe signal in which status information concerning the optical path is embodied is received over the optical path. The backscattered and/or reflected portion of the COTDR probe signal is detected to obtain the status information.

Abstract: In an optical communication system that includes a transmitting terminal, a receiving terminal, and an optical transmission path optically coupling the transmitting and receiving terminals and having at least one rare-earth doped optical amplifier therein, a second optical amplifier is provided The second optical amplifier includes a first portion of the optical transmission path having a first end coupled to the transmitting terminal and a second end coupled to a first of the rare-earth doped optical amplifiers. In addition, the second optical amplifier includes a pump source providing pump energy to the first portion of the optical transmission path at one or more wavelengths that is less than a signal wavelength to provide Raman gain in the first portion at the signal wavelength.

Abstract: Methods and systems for higher-order PMD compensation are implemented by developing an effective mathematical model and applying economical design techniques to the model. By assuming a constant precession rate for a narrow band of frequencies in an optical signal, a simplified model of a higher-order PMD compensator can be derived. The model can be used produce an economical compensator by making multiple uses of selected optical components.

Abstract: An undersea WDM optical transmission system is provided. The system includes first and second land-based cable stations, at least one of the cable stations includes power feed equipment (PFE) supplying electrical power to the cable at a voltage of no more than about 6 kv or less. The PFE is located in at least one of the cable stations. The system also includes an undersea WDM optical transmission cable having a length corresponding to those required in the undersea regional market. The cable includes at least one optical fiber pair for supporting bidirectional communication between the first and second cable stations. At least one repeater is located along the optical transmission cable. The repeater includes at least two optical amplifiers each providing optical gain to one of the optical fibers in the optical fiber pairs. The optical gain is in a range from about 12 to 20 dB.

Abstract: A method and apparatus is provided for obtaining status information concerning an optical transmission path. The method begins by generating a cw probe signal having a frequency that is swept over a prescribed frequency range in a prescribed time period. The cw probe signal is transmitted over the optical path and a returned COTDR signal in which status information concerning the optical path is embodied is received over the optical path. A predetermined frequency is detected within the prescribed frequency range of the returned COTDR signal to obtain the status information.

Abstract: A method and apparatus is provided for obtaining status information from a given location along an optical transmission path. The method begins by generating a cw probe signal having a prescribed frequency that is swept over a prescribed frequency range. The cw probe signal is transmitted over the optical path and a returned COTDR signal in which status information concerning the optical path is embodied is received over the optical path. A receiving frequency within the prescribed frequency range of the returned COTDR signal is detected to obtain the status information. The detecting step includes the step of sweeping the receiving frequency at a rate equal to that of the prescribed frequency. A period associated with the receiving frequency is temporally offset from a period associated with the prescribed frequency.

Abstract: A method is provided for locating a fault arising in one or more optical amplifiers from among a plurality of optical amplifiers operating in saturation and located along an optical transmission path. The method begins by generating a COTDR trace representing a backscattered and/or reflected optical power level along the transmission path and comparing the COTDR trace to a previously obtained reference COTDR trace to generate a difference trace that represents a change in gain. The change in gain is assigned to at least one of the plurality of optical amplifiers based on the difference trace.

Abstract: A branching unit is provided for interconnecting at least three undersea optical transmission cables. The branching unit includes first, second and third ports for receiving first, second and third undersea optical transmission cables, respectively. The first and second cables each include an electrical power conductor and a plurality of first optical fibers. The third cable is electrically unpowered and includes at least one drop optical fiber and at least one add optical fiber. An electrical power conductor segment is provided for electrically coupling the conductor in the first cable received in the first port to the conductor in the second cable received in the second port. A first optical fiber segment optically couples a first of the plurality of first optical fibers in one of the first or second cables to the drop optical fiber of the third cable.

Abstract: A system, amplifier and method are provided for amplifying an optical signal in an optical communications system where spans between amplifiers may vary. The system includes a Raman amplifier variable gain portion and an EDFA gain portion. The amount of Raman amplifier gain is chosen to trade off accumulation of noise with accumulation of multi-path interference. This variable Raman gain is used to equalize the loss of each span so that the amount of optical power supplied at the input of the EDFA gain portion is substantially constant throughout the system.

Abstract: An optical repeater is provided that includes at least four optical amplifiers each supplying optical amplification to an optical signal traveling in a different unidirectional optical fiber that collectively form at least two bi-directional pairs of optical fibers. The repeater also includes a first plurality of pump sources for providing pump energy to a first optical fiber located in a first of the optical fiber pairs and a second optical fiber located in a second of the optical fiber pairs. The first optical fiber and the second optical fiber support optical signals traveling in a common direction. A first combiner arrangement combines the pump energy from the first plurality of pump sources and distributes it to the optical amplifiers supplying amplification to optical signals traveling in the first and the second optical fibers.

Abstract: A method for entering a market with high barriers to entry and a plurality of proprietary business elements includes converting at least one of the business elements into a universal business element that can accept a wide variety of inputs from other business elements, while converting a remaining one of the plurality of business elements to commoditized business elements. For example, one exemplary embodiment of the present invention employs an optical repeater that can accept any existing submarine cable, in combination with an optical line interface terminal that can accept existing terrestrial terminal equipment. Regarding market division, this embodiment is specifically limited to spans of less than 5000 kilometers, and preferably between 350 and 4000 kilometers, thereby straddling both the long-haul and short-haul markets while providing highly desirable services and capability.

Abstract: A system and method for controlling noise in a Raman amplifier including a plurality of pumps. A control system provides one or more control signals in response to an amplifier input or output signal. Pump parameters are adjusted in response to the control signals to achieve a desired noise figure characteristic.