Tatsuhiko Watanabe

Large Spatial Channel (36-Core × 3 mode) Heterogeneous Few-Mode Multicore Fiber

We describe the design and characterization of a heterogeneous 36-core, three-mode fiber with three core types. Intercore crosstalk for LP11 modes is estimated to be below -31 dB for 5.5 km propagation at a core pitch of 34 μm. Feasibility of 108 space/mode division multiplexed transmission is investigated using free-space multiplexing/demultiplexing technologies, 40-wavelength division multiplexed, 25 GBd, 93.4-Gb/s dual-polarization QPSK signals, and coherent detection with a sparse 6 × 6 MIMO equalizer. The total transmission capacity amount to 403.7 Tb/s.

Laminated polymer waveguide fan-out device for uncoupled multi-core fibers

A compact waveguide-type fan-out device for uncoupled multi-core fibers was demonstrated using laminated polymer waveguide. The measured coupling losses from a 7-core fiber to seven single-core fibers were as low as 0.2 - 4.4 dB.

Ultra-large number of transmission channels in space division multiplexing using few-mode multi-core fiber with optimized air-hole-assisted double-cladding structure

The ultimate number of transmission channels in a fiber for the space division multiplexing (SDM) is shown by designing an air-hole-assisted double-cladding few-mode multi-core fiber. The propagation characteristics such as the dispersion and the mode field diameter are almost equalized for all cores owing to the double cladding structure, and the crosstalk between adjacent cores is extremely suppressed by the heterogeneous arrangement of cores and the air holes surrounding the cores. Optimizing the structure of the air-hole-assisted double-cladding, ultra dense core arrangements, e.g. 129 cores in a core accommodated area with 200 μm diameter, can be realized with low crosstalk of less than -34.3 dB at 100km transmission. In this design, each core supports 3 modes i.e. LP(01), LP(11a), and LP(11b) as the transmission channels, so that the number of transmission channels can be 3-hold greater than the number of cores. Therefore, 387 transmission channels can be realized.

Low-loss plasmon-assisted electro-optic modulator

For nearly two decades, researchers in the field of plasmonics1—which studies the coupling of electromagnetic waves to the motion of free electrons near the surface of a metal2—have sought to realize subwavelength optical devices for information technology3–6, sensing7,8, nonlinear optics9,10, optical nanotweezers11 and biomedical applications12. However, the electron motion generates heat through ohmic losses. Although this heat is desirable for some applications such as photo-thermal therapy, it is a disadvantage in plasmonic devices for sensing and information technology13 and has led to a widespread view that plasmonics is too lossy to be practical. Here we demonstrate that the ohmic losses can be bypassed by using ‘resonant switching’. In the proposed approach, light is coupled to the lossy surface plasmon polaritons only in the device’s off state (in resonance) in which attenuation is desired, to ensure large extinction ratios between the on and off states and allow subpicosecond switching. In the on state (out of resonance), destructive interference prevents the light from coupling to the lossy plasmonic section of a device. To validate the approach, we fabricated a plasmonic electro-optic ring modulator. The experiments confirm that low on-chip optical losses, operation at over 100 gigahertz, good energy efficiency, low thermal drift and a compact footprint can be combined in a single device. Our result illustrates that plasmonics has the potential to enable fast, compact on-chip sensing and communications technologies.Ohmic losses in plasmonic devices can be reduced by exploiting ‘resonant switching’, in which light couples to surface plasmon polaritons only when in resonance and bypasses them otherwise.

Demonstration of Mode-Evolutional Multiplexer for Few-Mode Fibers Using Stacked Polymer Waveguide

Mode-evolutional multi/demultiplexer for few-mode fibers was demonstrated using stacked polymer waveguides. Owing to the stacked structure, TE00, TE10, and TE01 modes, which correspond to LP01, LPeven11 , and LPodd 11 modes, respectively, were selectively excited by the fabricated multiplexer. The mode excitation ratio was evaluated from the near-field patterns of excited modes using a mode analysis method called the averaged interference component method that we have developed. The evaluated mode excitation ratio was ranging from 6.4 to 9.7 dB for both transverse electric (TE) and transverse magnetic (TM) polarizations of first-order TE modes within the center and long wavelength (CL)-band.

What is a mode in few mode fibers? : Proposal of MIMO-free mode division multiplexing using true eigenmodes

The evolution of electromagnetic field profile of LP modes along with the propagation owing to the difference of propagation constants between constituent true eigenmodes is accurately analyzed. It is shown that the mode demultiplexer can’t accurately discriminate the LP mode at the output end and so the MIMO-DSP is inevitable for the mode division multiplexed transmission using LP modes. From the accurate analysis, a transform matrix between LP modes and constituent true eigenmodes is derived and a novel method to configure true eigenmode multi/demultiplexer is proposed to realize MIMO-free transmission.

Full-set mode analysis of three-mode fibers calculated from polarization components of near-field pattern

We propose and demonstrate a novel mode analysis method that can provide a full set of amplitudes, phases, and polarization states of guided modes including degenerate modes in few-mode fibers. The method is based on the calculation of amplitude components and phase differences from the intensity profiles that passed through a polarizer with angles of 0, 45, and 90°. The accuracies of calculation formulas are shown by simulation to be less than 10−10 for amplitudes and 10−3 rad for phase differences. The method was applied to a graded-index three-mode fiber, and the off-axis mode excitation ratio characteristics were compared with theoretical ones.

Serial branching mode multi/demultiplexer for homogeneous multi-core fibers

Mode-evolutional serial branching mode multi/demultiplexer (SBMM) for homogeneous coupled multi-core fiber was demonstrated. This multi/multiplexer has some advantages such as the high fabrication tolerance and small wavelength and polarization dependences owing to the principle of adiabatic mode-evolutional phenomenon. The SBMM was fabricated using polymer materials. The selective four mode excitation with the low crosstalk of less than −10 dB and small wavelength dependence were realized within the CL-band.

Full mode analysis of vector components of degenerated LP modes in Few Mode Fibers from intensity profile through angled polarizer

We propose and demonstrate a novel mode analysis method which can obtain a full set of amplitude, phase, and polarization state of transmitted modes including degenerate modes in few mode fibers. The method is based on the calculation of all modal components from the intensity profiles through an angled polarizer.

Proposal of MIMO-free mode divison multiplexed transmission using true eigenmodes

The evolution of electromagnetic field profile of LP modes along with the propagation is accurately analyzed and the transform matrix between LP modes and true eigenmodes is derived. Using this matrix, a novel method to configure true eigenmode multi/demultiplexer is proposed to realize MIMO-free transmission.