Nobuo Kuwaki

Two mode optical fibers with low and flattened differential modal delay suitable for WDM-MIMO combined system

We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable for wavelength division multiplexing and multiple input multiple output (MIMO) combined transmission system. We designed and fabricated three different kinds of TMF, nearly zero-DMD (zTMF), positive-DMD (pTMF) and negative-DMD (nTMF) with a graded index core and a depressed inner cladding. We confirmed that the fabricated zTMF has DMD of below 15 ps/km in the C band and the fabricated pTMF and nTMF have the same degree of effective areas. We also confirmed that a DMD compensation line with a length of 100 km composed of pTMF and nTMF can successfully achieve the best properties of low DMD in the C + L band and low mode conversion.

Optimized graded index two-mode optical fiber with low DMD, large A eff and low bending loss

An optimized two-mode optical fiber (TMF) with the graded index (GI) profile is designed and fabricated. We clarify an appropriate region of GI-TMF satisfying DMD = 0 ps/km, the large effective area A(eff), and the low bending loss for LP(11) at 1550 nm. According to our fiber design, GI-TMF is successfully fabricated to have the large effective area A(eff) of 150 μm(2) for LP(01) mode, and low DMD below 36 ps/km including zero in the C-band. We expect that our design GI-TMF is suitable for MDM and can reduce MIMO-DSP complexity.

Characteristics of dispersion-shifted dual shape core single-mode fibers

The structural design, bending loss, and dispersion characteristics of the dual shape core (DSC) single-mode fiber with zero dispersion at 1.55 μm are described. It is clarified that the bending loss of the DSC fiber is less than one tenth of that of a step-index fiber, and that the dispersion sensitivity due to a small change of the core radius is less than half of that of a step-index fiber. The explanation for the small bending loss is presented. A greater reduction of bending loss is expected from the replacement of the center core profile with a Gaussian or triangular profile.

Evaluation of longitudinal chromatic dispersion

The relationship between changes in the refractive index along a fiber and chromatic dispersion is investigated theoretically. The variance of the chromatic dispersion along a fiber is approximately proportional to that of longitudinal structural fiber parameters. To control the dispersion to within +or-1 ps/km/nm, theoretical results indicate that the longitudinal deviations of the core radius and relative index difference must be less than 0.04 mu m and 0.014%, respectively, for W-type dispersion-flattened fiber. Measurements of the standard deviation of the change in the longitudinal parameter for W-type dispersion-flattened fiber fabricated by the vapour axial deposition VAD method show that chromatic dispersion deviation is mainly caused by longitudinal core radius deviation. The effective standard deviation of the core radius is estimated to be within 0.03 mu m. >

Experimental investigation of relation between mode-coupling and fiber characteristics in few-mode fibers

We experimentally clarify that relation between mode-coupling coefficient h and effective-index difference Δn_eff in few-mode fibers (FMFs) by impulse response technique and h in our fabricated FMFs with Δn_eff ≥ 1.7 × 10^-3 converges to 7.4×10^-5 1/km.

Experimental Evaluation of Mode Conversion Ratio at Splice Point for Two-Mode Fibers and its Simulated Effect on MIMO Transmission

We evaluate experimentally mode conversion ratio at a splice point (Cs) for two-mode fibers which degrades transmission performance. We confirm the measured results are consistent with the calculated ones by an overlap integral on field distributions of individual modes and clarify the precise connection value with an offset and an end face angle of the fiber which are required for suppressing the degradation due to Cs by MIMO transmission simulation.

Suitable definition of mode field diameter in view of splice loss evaluation

The definition of the mode field diameter is investigated theoretically and experimentally from a practical viewpoint of the splice loss estimation. The difference of mode field diameter defined by various definitions becomes larger as the V -value decreases. This tendency agrees with the experimental result. As a result, the definition of mode field diameter obtained from RMS width of far-field intensity is useful.

Mode-selective optical packet switching in mode-division multiplexing networks

A novel mode-selective optical packet switching, based on mode-multiplexers/demultiplexers and multi-port optical micro-electro-mechanical systems (MEMS) switches, has been proposed and experimentally demonstrated. The experimental demonstration was performed using the LP(01), LP(11a) and LP(11b) modes of a 30-km long mode-division multiplexed few-mode fiber link, utilizing 40 Gb/s, 16-QAM signals.

Mode dispersion compensating optical transmission line composed of two-mode optical fibers

We fabricated mode dispersion compensating optical transmission line composed of two different kinds of two-mode optical fibers with the opposite signs of mode dispersion. Its mode dispersion was successfully controlled within ±700 ps/km at C-band.

Mode-division multiplexed W-Band RoF transmission for higher-order spatial multiplexing

20Gb/s seamless 2×2 MIMO transmission of W-Band millimeter-wave signals over a 30-km modal-dispersion-compensated mode-division multiplexed link and a 2.5-m wireless path, is demonstrated for enhancing the transmission capacity in radio-over-fiber systems.