Abstract: A lossless optical link in an optical transmission system comprises an optical fiber that is configured to produce Raman gain and provide for Raman distributed gain, via one or more pump sources, along the fiber so that, as an end result, the gain experienced by one or more propagating signals in the fiber link is made fairly uniform along the link or at least a portion of the optical link, such as not vary, for example, no more than five dB along the length of the optical fiber. The several embodiments disclosed provide for different optical pump/component architectures to achieve this end result.

Abstract: An optical transmission system that employs a Raman amplifier including a Raman pump for introducing depolarized pump light into the fiber. The pump includes an optical source generating a polarized optical pump signal, an optical splitter that splits the pump signal into a first pump portion and a second pump portion, and a beam combiner that combines the first pump portion and the second pump portion into the depolarized pump light. Further, the pump includes a delay device, such as a length of fiber, that causes the first pump portion to propagate farther from the beam splitter to the beam combiner than the second pump portion. The length of fiber is longer than the coherence length of the pump signal.

Abstract: All-fiber coupling architectures include at least one fiber gain media, e.g. a fiber amplifier or a fiber laser, providing for the coupling light from one or more multi-wavelength pump sources propagating in a multimode core fiber at multiple points along a double clad fiber or at least at one point along multiple double clad fibers having their inner claddings fused to the multimode core fiber. The latter arrangement provides for a low cost utility multi-signal fiber amplifier for telecommunication applications.

Abstract: Optical couplers functioning, for example, as fiber optic combiners or fiber optic splitters for multimode fibers are disclosed for coupling, for example, the light output of a plurality of multimode laser sources into a multimode output fiber or fibers. Coupling combinations include multimode fibers to multimode fiber or fibers (MMFs/MMF(s)) or multimode fibers/single mode fiber to double clad fiber (MMFs/SMF/DCF). Improvements are disclosed in coupling efficiency and the power distribution uniformity of optical power into an output fiber, such as double clad fiber inner cladding or multimode fiber core, from multiple multimode input fibers.

Abstract: A Raman optical amplifier for amplifying an optical signal propagating in an optical fiber associated with an optical communications system. The amplifier includes a first Raman pump source including a first pump laser coupled to the fiber to provide first order Raman pump light for amplifying the optical signal, and a second Raman pump source including a second pump laser coupled to the fiber to provide second order Raman pump light for amplifying the first order Raman pump light. The first and second order Raman pump light is introduced into the fiber in either a co-propagating or counter-propagating direction relative to the propagation direction of the optical signal in the fiber. The second pump laser may include first and second pump laser elements that generate the second order Raman pump light, where a center wavelength of the light generated by the first laser element is different than the center wavelength of the light generated by the second laser element.

Abstract: Optical pumping arrangements are provided for the broadband or multiple wavelength pumping of optical sources. Sources may be based on Raman gain media and may use multiple output couplers to couple out different wavelength ranges. Cascaded Raman resonator (CRR) configurations may also be used. Overlapping resonators at different wavelengths may be configured to share gain media, and may have separate portions in separate optical paths. Attenuation filters may also be used that are matched to the gain profile of a gain medium, to flatten the gain spectrum and allow equalization of gain to different output wavelengths. In one embodiment, polarization maintaining fiber is used to develop resonant conditions at different wavelengths in different polarization states. Wideband output gratings may be substituted for narrowband gratings to provide CRR configurations with a broader output band. Broadband amplification may also be provided by using a laser source operating in coherence collapse.

Abstract: A pump source for rare earth and Raman amplifiers or for distributed amplification uses two or more light sources to generate two source beams that are combined by a beam combiner to form the output pump beam. In accordance with one embodiment, the light sources are a diode laser array having be two or more monolithic laser stripes providing dual output beams having substantially the same polarization, such as the TE mode. One of the polarized due outputs is rotated 90° and both beams are applied to a birefringent crystal that combines the beams for insertion into an optical fiber or into a rare earth doped fiber or into a fiber capable of Raman amplification via SRS. The power output of each polarization in the combined beam can be measured and used to drive a feedback circuit that controls the current provided to each diode in order to maintain the power in the two polarization components of the output beam equal.