A novel method for distributionally evaluating the effective refractive index differences, Δ<i>n<sub>eff</sub></i>, in multimode optical fibers is presented based on the Brillouin spectrum analysis. The proposed method is successfully demonstrated in GeO<sub>2</sub>-doped step-index 2-mode fibers, for evaluating Δ<i>n<sub>eff</sub></i> between LP<sub>01</sub> and LP<sub>11</sub> modes, and the method could be straightforwardly expanded to fibers containing higher-order modes, by using a mode demultiplexer supporting the higher-order mode. To the authors’ best knowledge, this is the first report of distributional measurements of the effective refractive index differences in multimode optical fibers.
We describe a novel all-optical hybrid mode-division multiplexing (MDM) -optical code division multiplexing (OCDM) architecture for future flexible access network. We successfully demonstrate, for the first time, an asynchronous on-off keying (OOK) modulation, 2 mode x 4 code x 10 Gbps transmission over 2km two mode fiber (TMF), without dispersion compensation at single wavelength, by using 16-chip (200 Gchip/s), 16-phase-shift keyed (PSK) optical codes (OC) generated by a multiport encoder/decoder (E/D) and an optical mode multiplexer/demultiplexer (MMUX/MDeMUX). We also analytically and experimentally evaluate the mode crosstalk tolerance as a function of the LP<sub>01</sub> and LP<sub>11</sub> modes.
We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable to compensate DMD in wide wavelength range. All fabricated TMFs composed of a graded index core and a depressed inner claddings have low DMD slopes of less than |0.15| ps/km/nm, low optical loss of less than 0.21 dB/km for LP<sub>01</sub> and LP<sub>11</sub> modes respectively and low mode coupling ratio of less than -35 dB at the wavelength of 1550 nm. All TMFs have the similar effective area of 120 μm<sup>2</sup> for LP<sub>01</sub> mode and 160 μm<sup>2</sup> for LP<sub>11</sub> mode at 1550 nm. Moreover, it is clarified that a DMD compensation transmission line composed of the fabricated TMFs can successfully achieve the DMD of below |4.0| ps/km in the C+L band and mode conversion ratio of less than -30 dB at splice points.