Yuta Wakayama

2.05 Peta-bit/s super-nyquist-WDM SDM transmission using 9.8-km 6-mode 19-core fiber in full C band

We demonstrate ultra-dense SDM transmission of 360-channel Super-Nyquist-WDM DP-QPSK signals over 9.8-km 6-mode 19-core fiber, achieving the record fiber capacity of 2.05 Pbit/s (360WDM×114SDM×50Gbit/s) with the highest aggregate spectral efficiency of 456 bit/s/Hz.

Selective multimode excitation using volume holographic mode multiplexer.

We propose a mode multiplexer based on volume holograms to realize a simple and efficient mode-division-multiplexed transmission system that supports a large number of modes. Selective multiexcitation of three spatial modes into a conventional multimode fiber is experimentally demonstrated. This device could potentially multiplex 10 or more modes. Future perspectives of the mode multiplexer for application in mode-division multiplexing are also discussed.

Mode demultiplexer using angularly multiplexed volume holograms

This study proposes a volume holographic demultiplexer (VHDM) for extracting the spatial modes excited in a multimode fiber. A unique feature of the demultiplexer is that it can separate a number of multiplexed modes output from a fiber in different directions by using multi-recorded holograms without beam splitters, which results in a simple configuration as compared with that using phase plates instead of holograms. In this study, an experiment is conducted to demonstrate the basic operations for three LP mode groups to confirm the performance of the proposed VHDM and to estimate the signal-to-crosstalk noise ratio (SNR). As a result, an SNR of greater than 20 dB is obtained.

Ultra-dense spatial-division-multiplexed optical fiber transmission over 6-mode 19-core fibers.

Ultra-dense spatial-division multiplexing (SDM) is achieved by mode multiplexed technique with multiple cores in a single fiber, namely few-mode multi-core fiber. Using a 9.8-km six-mode nineteen-core fiber, we demonstrate an ultra-dense SDM transmission of 16-channels wavelength-division-multiplexed (WDM) dual-polarization quadrature phase shift keying signals, achieving a record spatial multiplicity of 114. With the help of ultra-dense Super-Nyquist WDM techniques in the 4.5-THz bandwidth of the full C-band, we demonstrate 2.05 Pbit/s transmission over 9.8-km six-mode nineteen-core fibers. In this experiment, the highest aggregate spectral efficiency of 456 bit/s/Hz is achieved.

Multi-excitation of spatial modes using single spatial light modulator for mode division multiplexing

With the goal of establishing mode division multiplexing techniques, we performed experiments on the multi-excitation of spatial modes by combining first-order diffracted beams generated from hologram patterns indicated in different regions using a single SLM.

Mode division multiplex communication technique based on dynamic volume hologram and phase conjugation

We propose mode division multiplex communication technique that can split a specific spatial mode in light from a spatial mode multiplexed in an optical fiber by fusion of a phase conjugation technique with spatial filtering processing by multiplexed volume holograms and random diffusers. In mode division multiplexing, the optical signal outgoing from the multimode optical fiber is in a condition that optical information of plural spatial modes is overlapped, therefore it is difficult to de-multiplex electrically after light detection. Our technique enables to split it into each mode all optically and to compensate temporal modal shift dynamically. Mode de-multiplexing is realized by multiplexed holographic arithmetic device and phase matching of a wave surface for the spatial mode orthogonal to time. Therefore, if we use indices in conventional electronic processing, a very high-speed operation equivalent to that of 10-100PFLOPS can be realized without causing any delay in light information to be transmitted. Moreover, it can realize constructions of a system that can dynamically respond to temporal mode variations and distortions with fiber transmissions by using a photorefractive medium. Separating of around 60-70% was achieved in an experiment of separating three multiplexed spatial modes by controlling a volume type dynamic reconfigurable device based on LiNbO3. It was clarified that the separation performance improved by an appropriate random phase mask in the numerical analysis.

6-Mode 19-core fiber for weakly-coupled mode-multiplexed transmission over uncoupled cores

Design and fabrication results of a 6-mode 19-core fiber with the highest relative core multiplicity factor of 30 for weakly-coupled mode-multiplexed uncoupled-core-multiplexed transmission are detailed. Technical challenges for long-haul transmission are also discussed.

DMD measurement of 114-SDM transmission fibre using low-coherence interferometry with digital holographic processing

We observe mode fields of a 6-mode 19-core fibre used in 114-SDM transmission experiment by digital holographic approach. Total DMDs are within 1.6-2.2 ns/km for all the cores as designed for the weakly-coupled few-mode multi-core fibre.

Photorefractive Splicing Device with Double Phase Conjugate Mirror Using Sn2P2S6:Sb Crystal

We develop a splicing device for photonic crystal fibers (PCFs) based on a double phase conjugate mirror (DPCM) using a novel photorefractive (PR) Sn2P2S6:Sb 1.5% crystal. This PR splicer has many attractive characteristics including modal field compensation and the automatic reconfiguration of the optical path. Utilizing a DPCM as the splicer, our device can adapt to misalignments automatically since the incident beams continuously rewrite an index grating which formed in the crystal. By the implementation of the Sn2P2S6:Sb crystal, the response time for the characteristic of dynamic reconfiguration is improved several-hundred-fold compared with conventional materials, e.g. BaTiO3. We demonstrate that the high angular tolerance is provided using the DPCM with the Sn2P2S6:Sb crystal. When the misalignment of the incident angle is from -7° to 8°, the increment of coupling loss is less than 0.6dB. This is several-ten-fold compared with the fusion splicing. We reveal the dependence of the coupling loss on the position of the incident beams and also the dependence of the energy flow on the propagation distance for the first time with the two-dimensional finite-difference beampropagation method. Using our numerical simulation tool, we can visually investigate the beam propagation property considering the influence of the fanning effect in the Sn2P2S6 crystals.

Six-Mode 19-Core Fiber With 114 Spatial Modes for Weakly-Coupled Mode-Division-Multiplexed Transmission

This paper describes a six-mode 19-core fiber with 114 spatial modes, which was designed and fabricated for weakly-coupled mode-division-multiplexed (MDM) transmission over uncoupled cores. The 19 identical graded-index cores were packed on a hexagonal lattice with a 62-μm pitch in a ∼318-μm-diameter cladding. The cladding diameter is large, but still mechanically reliable by assuming a 2% proof test and 40-mm minimum fiber bend radius. The inter-core crosstalk is negligibly suppressed and the calculation indicated that a 50-μm core pitch (corresponding to the 266-μm-diameter cladding) is achievable without significant crosstalk degradation. Though the fiber was intended for the weakly-coupled MDM transmission, the differential mode delay (DMD) within a degenerated mode group of LP21 and LP02 modes was not well suppressed. Thus, further DMD suppression within each mode group or splitting the degeneracy of the modes is required to realize multiple-input multiple-output (MIMO) digital signal processing with reduced complexity. Additionally, a numerical investigation revealed that the intra-core inter-modal crosstalk at a butt coupling was induced not only by the misalignment, but also by the refractive index profile mismatch between the butt-coupled cores. Therefore, the tight tolerance on the refractive index profile is important both for DMD control and modal crosstalk suppression.