Abstract: A system and method for providing eye-safety protection during operation of distributed Raman amplifiers based on the application of continuous out-of-band amplified spontaneous scattering (ASS) monitoring in an optical communication network span coupled to the Raman amplifier, and real-time detection and analysis of changes in the monitored ASS power level, The system includes at least one Raman pump for introducing Raman energy into the span, a monitoring unit for performing the continuous ASS monitoring, and a control unit operative to detect and analyze in real-time changes in the ASS power, and upon determination that such changes indicate an open span, to reduce the level of the Raman pump energy entering the span to a safe level.

Abstract: An apparatus for optical amplification that imparts to a narrow band optical amplifier, specifically an Erbium dope fiber amplifier (EDFA), gain properties found in wide band optical amplifiers. In one preferred embodiment, the apparatus comprises an EDFA and an externally attachable (to the EDFA) module that includes a single un-pumped Erbium doped fiber (EDF) connected to a gain flattening filter (GFF). The GFF may be internal or external to the module. In another embodiment, the apparatus comprises an EDFA and an externally attachable module having a plurality of un-doped EDFs with different lengths, switchably connectable to the GFF and the EDFA to provide the required wide-band gain properties.

Abstract: An apparatus for optical amplification that imparts to a narrow band optical amplifier, specifically an Erbium dope fiber amplifier (EDFA), gain properties found in wide band optical amplifiers. In one preferred embodiment, the apparatus comprises an EDFA and an externally attachable (to the EDFA) module that includes a single un-pumped Erbium doped fiber (EDF) connected to a gain flattening filter (GFF). The GFF may be internal or external to the module. In another embodiment, the apparatus comprises an EDFA and an externally attachable module having a plurality of un-doped EDFs with different lengths, switchably connectable to the GFF and the EDFA to provide the required wide-band gain properties.

Abstract: A limited mode dispersion compensating optical fiber supporting at least one high order spatial mode comprising a plurality of core areas. The refractive index profile of the fiber are selected to result in an optical waveguide providing in the LP02 mode dispersion more negative than −300 ps/nm/km at a representative wavelength within an operative waveband, a projected zero dispersion (PZD) less more than 75 nm less than the representative wavelength and third order dispersion less than 2% over the operative waveband. Third order dispersion is defined as the maximum deviation from a best line fit for dispersion divided the best fit dispersion at the representative wavelength, with the best fit line being chosen to minimize the maximum deviation. In one embodiment the PZD lies between 1340 nm and 1420 nm, and in another embodiment the PZD lies between 1420 nm and 1475 nm.

Abstract: A family of fiber profiles is disclosed which exhibit only three well guided modes in the operative “band”. The reduction in the number of modes is accomplished with a change in the refractive index in the core area. The change in refractive index in the core area changes the order of the appearance of the modes, thus leading to fewer guided modes, and less MPI. In one embodiment the refractive index ring comprises an area of depressed refractive index, and the null energy point of one of the guided modes is found therein. In another embodiment, the change in the refractive index in the core is located coincidentally with the null point of a desired mode. In some embodiments negative dispersion on the order of −400 ps/nm/km is experienced, while MPI is minimized. In another embodiment the fiber profile is further characterized by a negative slope suitable for compensating a link of transmission fiber.

Abstract: The invention relates to method and apparatus for transmitting an optical signal having optical energy substantially in a high order spatial mode. The optical waveguide, in one embodiment, includes a few mode fiber designed to have specific transmission characteristics for supporting the single high order spatial mode, and the few mode fiber transmits the single high order spatial mode. The optical waveguide, in one embodiment, has a dispersion and a dispersion slope for a given transmission bandwidth. Another aspect of the invention includes a method for transmitting an optical signal having optical energy substantially in a single high order spatial mode. The method includes the steps of providing a few mode fiber, which supports optical energy in the single high order spatial mode. In one embodiment, the single high order spatial mode is the LP02 spatial mode In another embodiment, the few mode fiber supports an optical signal having optical energy having less than twenty spatial modes.

Abstract: A variable dispersion compensation device utilizing temperature control of the dispersion compensating fiber. Both a high order mode fiber, or a conventional dispersion compensating fiber are utilized. Use of a high order mode fiber with a trimming fiber, each being separately temperature controlled is also described. A method for controlling a system containing the apparatus is also described.

Abstract: An Erbium-doped fiber amplifier wherein the signal and/or the laser pump source are introduced into the erbium-doped fiber in a high order spatial mode. A mode transformer is utilized to transform the optical signal or the laser pump source to a second spatial mode. A coupler and erbium-doped profile are also described.