Kyozo Tsujikawa

Two-mode PLC-based mode multi/demultiplexer for mode and wavelength division multiplexed transmission

We proposed a PLC-based mode multi/demultiplexer (MUX/DEMUX) with an asymmetric parallel waveguide for mode division multiplexed (MDM) transmission. The mode MUX/DEMUX including a mode conversion function with an asymmetric parallel waveguide can be realized by matching the effective indices of the LP(01) and LP(11) modes of two waveguides. We report the design of a mode MUX/DEMUX that can support C-band WDM-MDM transmission. The fabricated mode MUX/DEMUX realized a low insertion loss of less than 1.3 dB and high a mode extinction ratio that exceeded 15 dB. We used the fabricated mode MUX/DEMUX to achieve a successful 2 mode x 4 wavelength x 10 Gbps transmission over a 9 km two-mode fiber with a penalty of less than 1 dB.

Rayleigh scattering reduction method for silica-based optical fiber

The effect of the thermal treatment of silica-based glasses and glass fibers on their Rayleigh scattering is investigated experimentally. The Rayleigh scattering coefficients of bulk glasses are found to be increased 5-10% by heating them to 1800 /spl deg/C because the density fluctuation is in proportion to their fictive temperature. Based on these results, we propose a method for reducing the Rayleigh scattering losses of silica-based optical fibers by drawing them slowly at low temperatures. We used this method to obtain a GeO/sub 2/ doped silica core single-mode fiber with a minimum loss of 0.16 dB/km at 1.55 /spl mu/m. As a result, we confirmed that the reduction in the fictive temperature of silica-based glasses and glass fibers reduces their Rayleigh scattering.

Mode multi/demultiplexing with parallel waveguide for mode division multiplexed transmission

We propose a planar lightwave circuit (PLC)-based mode multi/demultiplexer (MUX/DEMUX) with an asymmetric parallel waveguide for mode division multiplexed (MDM) transmission. The PLCb-ased mode MUX/DEMUX has advantage of selectively exciting higher-order mode. We realize three-mode (LP(01), LP(11)a, and LP(21)a) multiplexing by using an asymmetric parallel waveguide. We then design and fabricate a PLC-based mode MUX/DEMUX on one chip by using our proposed LP(11) mode rotator to allow us to utilize the LP(11)b mode. We successfully multiplex the LP(01), LP(11)a, and LP(11)b modes and achieve a relatively low insertion loss over the C-band using our fabricated mode MUX/DEMUX. Our results indicate that the PLC-based mode MUX/DEMUX with a uniform height has the potential to increase the mode number by using an LP(11)b mode.

Suppression of Fiber Fuse Propagation in Hole Assisted Fiber and Photonic Crystal Fiber

We suppressed fiber fuse propagation in hole-assisted fiber (HAF) and photonic crystal fiber (PCF) with input powers above 14 W at 1480 and 1550 nm. This result indicates that the threshold power of fiber fuse propagation in HAF and PCF can be at least 10 times larger than that in conventional single-mode fiber (SMF) in the optical communication band. We also observed the dynamics of fiber fuse termination at a splice point between a test fiber (HAF or PCF) and a conventional fiber (SMF or dispersion-shifted fiber (DSF)). Our experimental results show that air holes in HAF and PCF play an important role in suppressing fiber fuse propagation.

Single-Mode Photonic Crystal Fiber Design With Ultralarge Effective Area and Low Bending Loss for Ultrahigh-Speed WDM Transmission

We propose a new photonic crystal fiber design with a W-shaped effective index profile to achieve the largest effective area (<i>A</i>_eff) for telecommunication use. We realized a 220-μ m²<i>A</i>_eff while achieving both a cable cutoff wavelength of less than 1300 nm and a bending loss compatible with ITU-T recommendations G.655 and G. 656.

New SBS suppression fiber with uniform chromatic dispersion to enhance four-wave mixing

A new type of stimulated Brillouin scattering (SBS) suppression fiber has been developed whose dopant concentration and core radius are nonuniform along its length. The chromatic dispersion distribution is kept uniform along its length by varying the core radius in accordance with the /spl Delta/ value to enhance four-wave mixing (FWM) intentionally. The output power of the FWM signal with this fiber was about 15 dB higher than that with a conventional disperion-shifted fiber when the input power was 15 dBm, which is just above the SBS threshold power.

Design of Three-Spatial-Mode Ring-Core Fiber

We investigate the fiber parameters which meet the design conditions for effectively three-spatial-mode transmission and low bending loss in a ring-core fiber for mode-division multiplexing transmission. We also clarify the effective area and the difference of the effective index while satisfying the design conditions.

Penalty-free dispersion-managed soliton transmission over a 100-km low-loss PCF

We successfully fabricated a 100 km-long, low loss (0.3 dB/km) photonic crystal fiber (PCF) with the lowest Rayleigh scattering coefficient. We achieved the first penalty-free dispersion-managed soliton transmission over 100 km PCF at 10 Gb/s.

PLC-based LP 11 mode rotator for mode-division multiplexing transmission

A PLC-based LP11 mode rotator is proposed. The proposed mode rotator is composed of a waveguide with a trench that provides asymmetry of the waveguide. Numerical simulations show that converting LP11a (LP11b) mode to LP11b (LP11a) mode can be achieved with high conversion efficiency (more than 90%) and little polarization dependence over a wide wavelength range from 1450 nm to 1650 nm. In addition, we fabricate the proposed LP11 mode rotator using silica-based PLC. It is confirmed that the fabricated mode rotator can convert LP11a mode to LP11b mode over a wide wavelength range.

Optical Fiber Amplifier Employing a Bundle of Reduced Cladding Erbium-Doped Fibers

We propose a novel optical amplifier that employs a bundle of reduced cladding erbium-doped fibers (EDFs) for multicore fiber transmission and successfully demonstrate the amplification of seven independent signals by employing a bundle of 60-μm cladding EDFs and a planar lightwave circuit integration technique. Average gains of 23 dB with low noise figures of less than 5.1 dB in the C-band were achieved for seven individual EDFs. We also confirmed that low crosstalk characteristics can be achieved for a multicore optical fiber amplifier by using bundled EDF.