Design and fabrication of ultra-low crosstalk and low-loss multi-core fiber: erratum.

This erratum amends typographical errors in Eq. (1) and Table 2Table 2Optical properties of each core of the fabricated MCF.Attenuation [dB/km]MFD [µm]Aeff [µm2]λcc [nm]CD [ps/nm/km]D. Slope [ps/nm2/km]Bend loss (R = 5 mm) [dB/turn]PMD [ps/√km]λ [nm]1550162515501550N/A1550155015501625C + LDesignN/AN/A9.8679.6149623.30.0630.0100.021N/ACore 10.1760.1969.8380.2150922.20.0620.0110.0200.132Core 20.1790.1979.7680.2150022.20.0620.0100.0200.134Core 30.1810.2029.8881.3150422.20.0620.0100.0200.044Core 40.1770.1999.8580.8149822.20.0620.0110.0210.093Core 50.1750.1929.7479.0148522.20.0620.0110.0220.205Core 60.1790.2009.8079.9148322.10.0620.0110.0220.116Core 70.1770.1979.7278.2149822.20.0620.0100.0190.106 in Opt. Express 19, 16576 (2011).

Effective area measurement of few-mode fiber using far field scan technique with Hankel transform generalized for circularly-asymmetric mode.

We report on a measurement method for the effective area of the few-mode fiber. We derived a transform equation between a near-field pattern and a far-field pattern generalized for circularly-asymmetric higher-order modes of a cylindrical core, and enabled effective area measurement of the higher-order modes using high-dynamic-range far-field scan technique and low-crosstalk mode multiplexer. The measured effective area values agreed well with the values that were numerically predicted using a finite-element method from the refractive index profile, when the modal crosstalk was suppressed.

Temperature response of an all-solid photonic bandgap fiber for sensing applications.

The spectral shift due to temperature in the photonic bandgap (PBG) of an all-solid PBG fiber is investigated, aiming at discrete and distributed temperature sensing. A temperature rise induces a red shift in the bandgap spectra, which can be easily and precisely monitored by measuring the fiber transmission near one of the band edges. Two different situations that are potentially compatible with distributed and quasi-distributed sensing were investigated: heating a 2 m section of a longer (~10 m) fiber, and heating the whole extension of a fiber that is tens of centimeters in length and was spliced to conventional fibers on both sides. The latter setup yielded bandgap spectral shifts up to ~35 pm/°C. Aiming at discrete sensing, a short (~50 mm) fiber section was subjected to a tight bend so as to exhibit increased temperature sensitivity. Choosing the position of the bend allows for reconfiguration, on demand, of the sensor. A semi-analytical method to identify the spectral position of bandgaps was used to model the fiber transmission, as well as the bandgap shift with temperature, with consistent results.

Uncoupled multi-core fiber enhancing signal-to-noise ratio.

We designed and fabricated a low-crosstalk seven-core fiber with transmission losses of 0.17 dB/km or lower, effective areas larger than 120 µm(2), and a total mean crosstalk to the center core of -53 dB after 6.99-km propagation (equivalent to -42.5 dB after 80 km), at 1550 nm. We also investigated the signal-to-noise ratio (SNR) achievable in uncoupled multi-core transmission systems by regarding the crosstalk as a virtual additive white Gaussian noise. The SNR under existence of crosstalk in the fabricated multi-core fiber (MCF) was estimated to be 2.4 dB higher than that in a standard single-mode fiber (SSMF) in the case of 80-km span, and 2.9 dB higher in the case of 100-km span; which are the best values among MCFs ever reported, to the best of our knowledge. The SNR penalties from crosstalk in this MCF were calculated to be 0.4 dB for 80-km span and 0.2 dB for 100-km span. We also investigated SNR penalty from crosstalk in the more ordinary case of an MCF with SSMF cores, and found that the total mean crosstalk to the worst core after one 80-km span should be less than about -47 dB for 0.1-dB penalty, about -40 dB for 0.5-dB penalty, and about -36 dB for 1-dB penalty.

Design and fabrication of ultra-low crosstalk and low-loss multi-core fiber.

We designed and fabricated a multi-core fiber (MCF) in which seven identical trench-assisted pure-silica cores were arranged hexagonally. To design MCF, the relation among the crosstalk, fiber parameters, and fiber bend was derived using a new approximation model based on the coupled-mode theory with the equivalent index model. The mean values of the statistical distributions of the crosstalk were observed to be extremely low and estimated to be less than -30 dB even after 10,000-km propagation because of the trench-assisted cores and utilization of the fiber bend. The attenuation of each core was very low for MCFs (0.175-0.181 dB/km at 1550 nm) because of the pure-silica cores. Both the crosstalk and attenuation values are the lowest achieved in MCFs.