Abstract: A method and apparatus for amplifying optical transmission signals is described. A bi-directional amplifier utilizes a pump feed-through signal from one of the optical pumps used to pump a first amplifying fiber to provide pump power to a second amplifying fiber. If an optical pump within the amplifier fails, this feed-through signal is used to pump the amplifying fiber directly pumped by the failed pump source.

Abstract: In accordance with the present invention, a land-based cable station is provided for an undersea optical transmission system. The cable station includes submarine line terminal equipment (SLTE) for processing terrestrial traffic received from an external source, power feed equipment for supplying electrical power to active undersea components of the transmission system, an element management system for configuring and obtaining status information from the transmission system, and a cable termination box in which an undersea cable terminates. The SLTE includes terrestrial optical transmission equipment receiving the terrestrial traffic and generating optical signals in response thereto. The SLTE also includes an interface device providing signal conditioning to the optical signals received from the terrestrial optical transmission equipment so that the optical signals are suitable for transmission through the undersea optical transmission system.

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 method and apparatus is provided for monitoring optical signal quality between land-based terminal equipment and an undersea optical transmission path. The method begins by receiving an analog optical signal in which information is embodied in digital form from either of the terminal equipment or the undersea optical transmission path. The method continues by measuring a parameter such as the Q-factor, which reflects signal quality by analysis of the analog optical signal and not the information digitally embodied therein.

Abstract: A method and apparatus is provided for using optical time-domain reflectometry (OTDR) with a WDM transmission system that includes a plurality of terminals interconnected by at least two pairs of unidirectional optical transmission paths each of which has at least one repeater therein. The method begins by transmitting an optical probe signal from a first OTDR unit associated with a first terminal into the repeater over a first optical path in a first of the at least two pairs of unidirectional optical transmission paths. The first OTDR unit receives a first returned OTDR signal over a second optical path in the first optical path pair. The first OTDR signal contains status information concerning the first optical path in the first optical path pair. The optical probe signal from the first optical path in the first optical path pair is coupled to a second optical path in the second optical path pair.

Abstract: An optical repeater includes a plurality of optical amplifiers and a plurality of pump sources for providing pump energy to the plurality of optical amplifiers. The optical repeater also includes a coupling arrangement coupling the pump energy from the plurality of pump sources to the plurality of optical amplifiers so that the pump energy from each pump source is distributed among at least two of the plurality of optical amplifiers in a substantially unequal manner.

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: A method and apparatus is provided for using optical time-domain reflectometry (OTDR) with a WDM transmission system that includes a plurality of terminals interconnected by at least two pairs of unidirectional optical transmission paths each of which has at least one repeater therein. The method begins by transmitting an optical probe signal from a first OTDR unit associated with a first terminal into the repeater over a first optical path in a first of the at least two pairs of unidirectional optical transmission paths. The first OTDR unit receives a first returned OTDR signal over a second optical path in the first optical path pair. The first OTDR signal contains status information concerning the first optical path in the first optical path pair. The optical probe signal from the first optical path in the first optical path pair is coupled to a second optical path in the second optical path pair.

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: 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: An optical transmission system has an optical transmission terminal with first and second optical interfaces. The first interface is configured to communicate in accordance with an industry-standard, network level protocol. The second interface is configured to communicate in accordance with a first optical layer transport protocol. The optical transmission span includes an optical interface device that has a third interface communicating with the second interface of the optical transmission terminal in accordance with the first optical layer transport protocol and a fourth interface configured to communicate in accordance with a second optical layer transport protocol. The optical interface device also has a signal processing unit for transforming optical signals between the first and second optical layer transport protocols.

Abstract: An optical transmission system has an optical transmission terminal with first and second optical interfaces. The first interface is configured to communicate in accordance with an industry-standard, network level protocol. The second interface is configured to communicate in accordance with a first optical layer transport protocol. The optical transmission span includes an optical interface device that has a third interface communicating with the second interface of the optical transmission terminal in accordance with the first optical layer transport protocol and a fourth interface configured to communicate in accordance with a second optical layer transport protocol. The optical interface device also includes a signal processing unit for transforming optical signals between the first and second optical layer protocols. A test system is coupled to the signal processing unit for monitoring optical signal quality.

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: A system and method for controlling gain shape in a Raman amplifier including a plurality of pumps. The pumps produce a spectral distribution of output power characteristic. A feedback control system provides one or more feedback control signals in response to the amplifier output for adjusting pump parameters to achieve a desired spectral distribution of output power characteristic.

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 optical communication system including a transmitter, an optical information channel, and a receiver. The transmitter is configured to transmit a plurality of optical signals in L-band wavelengths or between about 1560 nm and about 1630 nm. Use of the L-band in long-haul optical systems permits transmission over at least about 2,000 kilometers from an originating light source such as a transmitter or another regenerator. A method of modulating and transmitting data signals in the L-band is also provided.

Abstract: An optical amplifier achieves multistage amplification with a four port optical circulator with fiber amplifiers and Faraday rotators and mirrors connected to at least two of the ports. The fiber amplifiers permit the signal to pass through the fiber amplifiers twice.

Abstract: The present invention is an in-line multi-stage erbium doped fiber amplifier system for use in fiber optic communication systems. The system comprises two cascaded erbium doped fiber amplifiers (12), (14) separated by an drop/add device (20) for filtering out the amplifier spontaneous emission noise and the existing telemetry channel and for adding a new telemetry channel before the second amplifier (14). The invention also provides a method for providing a telemetry signal to in-line erbium doped fiber amplifier sites without affecting the signal capacity of the system, and also provides a method for monitoring the performance of a link in an optical fiber communication system.

Abstract: High output power, high gain, and low noise are achieved in a two-stage optical amplifier, suitable for use as a repeater for a long haul lightwave communication system, in accordance with the principles of the invention, by employing a first amplifying stage having a signal gain sufficiently small to prevent self-saturation by amplified stimulated emission (ASE) that uses counter-propagating pump light to cause maximum inversion of the first stage amplifying medium. In an illustrative embodiment of the invention, EDFAs are used in each of two amplifying stages. The length of the EDFA in the first stage is short enough to ensure nearly complete inversion of the EDFA from pump light that counter-propagates with the signal. The counter-propagating pump light allows the invention to advantageously avoid the significant noise figure penalty from the input loss associated with co-propagating pump light.

Abstract: The present invention relates to a method of mitigating gain peaking in a chain of fiber amplifiers by pumping the amplifiers at a predetermined wavelength to produce gain over a specified wavelength range.