Abstract: This invention relates to optical fiber systems where light is launched into and propagated in the fundamental mode of graded-index multimode fiber. Generally, it is not possible to launch light exclusively into the fundamental mode of graded-index multimode fiber by butt-coupling the multimode fiber to an arbitrary fiber carrying light from a source; several other modes may be launched. By inserting a length of a special singlemode fiber between an arbitrary fiber carrying light from a source and the graded-index multimode fiber, light can be launched exclusively into the fundamental mode of the graded-index multimode fiber. The special singlemode fiber has a modal pattern that matches the fundamental Gaussian modal pattern of the graded-index multimode fiber, which permits launching of the light into only the fundamental mode of the multimode fiber. Several applications for propagation in the fundamental mode of graded-index multimode fiber arises.

Abstract: This invention relates to optical fiber systems where light is launched into and propagated in the fundamental mode of graded-index multimode fiber. Generally, it is not possible to launch light exclusively into the fundamental mode of graded-index multimode fiber by butt-coupling the multimode fiber to an arbitrary fiber carrying light from a source; several other modes may be launched. By inserting a length of a special singlemode fiber between an arbitrary fiber carrying light from a source and the graded-index multimode fiber, light can be launched exclusively into the fundamental mode of the graded-index multimode fiber. The special singlemode fiber has a modal pattern that matches the fundamental Gaussian modal pattern of the graded-index multimode fiber, which permits launching of the light into only the fundamental mode of the multi mode fiber. Several applications for propagation in the fundamental mode of graded-index multimode fiber arises.

Abstract: This invention relates to optical fiber communication systems where data light is launched into a very small set of the lowest order propagation modes of multimode graded-index fibers, resulting in very high data rate transmission capability. We have determined, experimentally and theoretically, that light launched into a small set of a few lowest order propagation modes, or launched only into the fundamental propagation mode of multimode graded-index fiber, converts into and within a limited small set of lowest order modes due to severe bending perturbations that may occur in deployed multimode graded-index fiber transmission cable. Low modal time dispersion of the limited small set of lowest order modes is much less than when all modes of the multimode graded-index fiber are launched, yielding a much higher data rate transmission capability. Added advantages are: low transmission loss, low modal noise, and data security.

Abstract: An optical planar waveguide wavelength division demultiplexer for separating multiple wavelengths received in a wavelength division multiplexed communication system is disclosed, with each wavelength launched into a separate output waveguide channel. Wavelength separation is performed by wavelength-selective angular back-reflection from Bragg gratings, which are fabricated into the channel junctions of the planar germania-enriched silica waveguide by applying short wavelength light past a mask. A second Bragg reflection, reflecting the same wavelength as the first Bragg grating, is introduced into each output channel circuit, in order to attenuate residual backscattered light at non-desired wavelengths. The Bragg grating is extended beyond the channel junctions into the merged channel for greater reflectivity, if required, for the double Bragg grating geometry.

Abstract: An intrusion-alarmed optical fiber communication system, where light from two or more sources are launched with a planar channel waveguide launcher into two or more modes of a multimode graded-index transmission fiber, is disclosed. Input fibers containing the source light waves and the output fibers are in direct contact with the waveguide channels. Waveguide channels redistribute the light from input channels to output channels by rerouting, crossing, merging, or splitting channels. Waveguide launcher precisely launches data light into the fundamental mode and intrusion monitor light into high order modes of a multimode graded-index fiber. Fiber intrusion attenuates light in high order modes, but much less of the data in the fundamental mode, thereby forming a basis for the intrusion-alarmed system.