Patent ID: 8781272

Claim:
A monolithic optical non-micro-structured fiber, comprising: a multimode (“MM”) core configured to support multiple modes (“MM”) along an entire length thereof between opposite input and output core ends, the core having a double bottleneck-shaped cross-section which includes: spaced end regions with respective substantially uniformly-shaped cross-sections, the input end region of the MM core being configured to receive an input signal light at a desired wavelength in a single transverse mode which is launched into the MM core so as to excite only a fundamental transverse mode (“FTM”) with a first mode field diameter (“MFD”), a central region spaced inwards from the input and output end regions and having a substantially uniformly-shaped cross-section greater than that one of each end region, input and output frustoconical regions bridging opposite ends of the central region and respective input and output end regions, the input frustoconical region being configured to gradually expand the first MFD of the FTM to a second MFD greater than the first MFD so as to increase an optical threshold for nonlinear effects, the output frustoconical region being configured to decrease the second MFD to the first MFD so as to output the signal light in the fundamental mode at the desired wavelength, wherein the core guides the FTM without splice losses between the end regions; and at least one cladding surrounding the monolithic core.