We propose a technique based on Brillouin optical time domain analysis for measuring loss and crosstalk in few-mode fibers (FMFs). The proposed technique extracts the loss and crosstalk of a specific mode in FMFs from the Brillouin gains and Brillouin gain coefficients measured under two different conditions in terms of the frequency difference between the pump and probe lights. The technique yields the maximum loss and crosstalk at a splice point by changing the electrical field injected into an FMF as the pump light. Experiments demonstrate that the proposed technique can measure the maximum loss and crosstalk of the LP11 mode at a splice point in a two-mode fiber.

The dispersion and the splice characteristics of optical fibers with trench-index profile are investigated. The normalized distance between core and trench is preferably larger than 3.0 to realize complete compatibility with the standard G.652 fiber in terms of chromatic dispersion. The optical fiber realizes compatibility with ITU-T Recommendation G.652 fiber and bend-insensitivity simultaneously. Fabricated fibers with the trench-index profiles can be spliced to standard single-mode fiber with low losses, which have similar values with simulation results.

A single-mode fiber employing a trench index profile for indoor wiring is proposed to realize low-bending loss and low-splice loss simultaneously. The designs and the advantages of the fiber over fibers with conventional step index profiles are described. The characteristics of manufactured fibers with trench index profiles are also described. One of the manufactured fibers realizes a bending loss of 0.018 dB/turn at 1550 nm for a bending radius of 7.5 mm, and a splice loss of 0.19 dB at 1550 nm in mechanical splicing to a conventional single mode fiber simultaneously. Other one of the fibers realizes a bending loss of 0.011 dB/turn at 1550 nm for a bending radius of 5 mm, and the splice loss is 0.37 dB at 1550 nm simultaneously. A total loss of a fiber employing the trench index is small and stable against the fluctuation of MFD.