Showing papers by "Kunimasa Saitoh published in 2015"
22 Mar 2015
TL;DR: Recent progress on the MCFs for space-division multiplexing to be utilized in future large capacity long-distance transmission systems are described and prospect of large-space multiplicity of MCFs is discussed.
Abstract: • Due to the limitation of the outer cladding size of MCFs related to their mechanical reliability, the number of cores as well as the core arrangement have to be carefully determined based on the required modulation format and transmission distance. • By introducing heterogeneous core arrangement, further decrement of core-to-core distance is possible with keeping lower crosstalk level compared with the homogeneous MCFs. • The combination of MCF and FMF, which is FM-MCF, is a very promising approach to realize space multiplicity over 50. • Further development on related devices such as Fan-in/Fan-out and amplifier for FM-MCF transmission is highly expected. • Investigation towards cost saving by using MCF transmission system is underway and further development on devise integration is expected for deploying MCFs in the real network.
137 citations
22 Mar 2015
TL;DR: A 30-core fiber with heterogeneous cores that achieved large spatial multiplicity and low crosstalk of less than -40 dB at 100 km was demonstrated.
Abstract: A 30-core fiber with heterogeneous cores that achieved large spatial multiplicity and low crosstalk of less than −40 dB at 100 km was demonstrated. The correlation lengths were estimated to be more than 1 m.
89 citations
TL;DR: In this paper, the design and characteristics of a three-mode 12-core fiber with low intercore crosstalk (IC-XT) and low differential mode group delay (DMD) were demonstrated.
Abstract: The design and characteristics of a novel three-mode 12-core fiber are demonstrated. This fiber has low intercore crosstalk (IC-XT) and low differential mode group delay (DMD). In order to produce such a fiber, three new techniques are introduced to few-mode multicore fiber. A heterogeneous core arrangement with two types of cores, is used to minimize IC-XT; a multistep index, which can control DMD without sacrificing intermode crosstalk, is adopted as a core profile to reduce DMD; and a square lattice structure allows for the inclusion of 12 cores within a cladding diameter of 230 μm. Optimum design of the fiber using these techniques is determined from calculations. Finally, detailed characteristics of a three-mode 12-core fiber based on the design are reported. A fabricated 40-km fiber is confirmed to have a DMD of less than |530| ps/km over the C + L band and an estimated worst-case IC-XT of less than –55 dB/100 km at 1550 nm. This low IC-XT allows for the transmission of 32 QAM signals.
32 citations
03 Dec 2015
TL;DR: In this paper, the highest relative core multiplicity factor of more than 22 was achieved by arranging a 6-mode 12-core fiber in 227-μm cladding, and a quadratic double ring core arrangement realized sufficiently low crosstalk and enabled use of advanced multi-level modulation.
Abstract: The highest relative core multiplicity factor of more than 22 is achieved by arranging a 6-mode 12-core fibre in 227-μm cladding. A quadratic double ring core arrangement realizes sufficiently low crosstalk and enables us to use advanced multi-level modulation.
29 citations
03 Dec 2015
TL;DR: In this article, a six-spatial-mode multiplexer using effective index matching and adiabatic mode transition was demonstrated. Butler et al. used a fabricated PLC on one chip.
Abstract: We demonstrated a six-spatial-mode multiplexer using effective index matching and adiabatic mode transition. Six-mode multiplexing including the equal effective indices of LP 21 b and LP 02 was successfully achieved with a fabricated PLC on one chip.
21 citations
TL;DR: In this paper, a PLC-based mode multi/demultiplexer (MUX/DEMUX) for mode-division multiplexing was proposed, which achieved a relatively low-wavelength dependence over the C-band.
Abstract: We propose a PLC-based mode multi/demultiplexer (MUX/DEMUX) for mode-division multiplexing. We show numerically that the PLC-based mode MUX/DEMUX with a uniform height on one chip can multi/demultiplex four modes (LP01, LP11a, LP11b, and LP21a) by using our proposed LP11 mode rotator and a parallel waveguide. We successfully multi/demultiplex the four modes and achieve a relatively low-wavelength dependence over the C-band by using our fabricated four-mode MUX/DEMUX.
20 citations
22 Mar 2015
TL;DR: By introducing a square lattice structure for bidirectional core assignments in multi-core fibers, the effectiveness of propagation-direction interleaving for crosstalk reduction can be increased, realizing a 24-core fiber with -30.6 dB crosStalk over 100 km.
Abstract: By introducing a square lattice structure for bidirectional core assignments in multi-core fibers, the effectiveness of propagation-direction interleaving for crosstalk reduction can be increased, realizing a 24-core fiber with −30.6 dB crosstalk over 100 km.
20 citations
TL;DR: An Yb-doped polarizing all-solid photonic bandgap fiber for single-polarization and single-mode operation with an effective mode area of ~1150µm(2) is demonstrated, a record for all- solid photonicBandgap fibers.
Abstract: We demonstrate an Yb-doped polarizing all-solid photonic bandgap fiber for single-polarization and single-mode operation with an effective mode area of ~1150µm2, a record for all-solid photonic bandgap fibers. The differential polarization mode loss is measured to be >5dB/m over the entire transmission band with a 160nm bandwidth and >15dB/m on the short wavelength edge of the band. A 2.6m long fiber was tested in a laser configuration producing a linearly polarized laser output with a PER value of 21dB without any polarizer, the highest for any fiber lasers based on polarizing fibers.
17 citations
03 Dec 2015
TL;DR: This work experimentally evaluates the relationship between mode dependent loss (MDL) and Q penalty for few-mode fibre transmission with a low-MDL recirculating loop and free-space-optics type MDL equaliser and 3-mode signals with PDM-16QAM modulation.
Abstract: We experimentally evaluate the relationship between mode dependent loss (MDL) and Q penalty for few-mode fibre transmission. We employ a low-MDL recirculating loop and free-space-optics type MDL equaliser and transmit 3-mode signals with PDM-16QAM modulation.
16 citations
TL;DR: In this paper, the material gain of GeSn/SiGeSn quantum wells, which can be grown on Si substrate using a buffer layer, is analyzed based on microscopic many-body theory (MBT) for mid-infrared light sources based on Si photonics.
Abstract: Material gain of GeSn/SiGeSn quantum wells, which can be grown on Si substrate using a buffer layer, is analyzed based on microscopic many-body theory (MBT) for mid-infrared light sources based on Si photonics MBT can consider a gain spectrum broadening associated with scattering phenomena, such as Coulomb scattering, based on quantum field theory, and does not need any artificial fitting parameters, such as a relaxation time, used in conventional analysis Not only $\Gamma $ - but also carrier distributions in L-points are considered for the gain analysis Using MBT, the quantum well structures maximizing the material gain and the differential gain at the threshold are investigated in terms of the well thickness, the strain, and the energy difference of quantum states between $\Gamma $ - and L-points
16 citations
TL;DR: In this article, a rigorous definition of nonlinear parameter γ for high-index-contrast (HIC) periodic optical waveguides, such as photonic crystal (PC) optical waveguide, is proposed.
Abstract: A rigorous definition of nonlinear parameter γ for high-index-contrast (HIC) periodic optical waveguides, such as photonic crystal (PC) optical waveguides, is proposed. The definition is fully vectorial, and approximations assumed in previous works are unnecessary. The γ values calculated by the proposed definition are compared with those obtained by previous definitions, the rigorous nonlinear mode solver, and measured values for weakly guiding optical fibers, HIC Si-nanowire waveguides, and PC waveguides. It is demonstrated that the γ values calculated by proposed definition agree well with those of the rigorous nonlinear mode solver and experiments for all three waveguides, showing the validity of the definition.
03 Dec 2015
TL;DR: Two high-spatial-multiplicity multi-core fibres with low differential mode delay have been realized with low-crosstalk characteristics through optimisation of core structure and core arrangement.
Abstract: Design and fabrication results of high-spatial-multiplicity multi-core fibres are presented. A 30-core single-mode multi-core fibre and a 36-spatial-channels multi-core fibre with low differential mode delay have been realized with low-crosstalk characteristics through optimisation of core structure and core arrangement.
TL;DR: A kind of heterogeneous trench-assisted graded-index few-mode multi-core fiber with square-lattice layout with Absolute value of differential mode delay is smaller than 100 ps/km over C + L bands, which can decrease the complexity of digital signal processing at the receiver end.
Abstract: We propose a kind of heterogeneous trench-assisted graded-index few-mode multi-core fiber with square-lattice layout. For each core in the fiber, effective area (A(eff)) of LP(01) mode and LP(11) mode can achieve about 110 μm(2) and 220 μm(2). Absolute value of differential mode delay (|DMD|) is smaller than 100 ps/km over C + L bands, which can decrease the complexity of digital signal processing at the receiver end. Considering the upper limit of cladding diameter (D(cl)) and cable cutoff wavelength of LP(21) mode in the cores located at the inner layer, we set core pitch (Λ) as 43 μm. In this case, D(cl) is about 220.4 μm, inter-core crosstalk (XT) is lower than -40 dB/500 km and the relative core multiplicity factor (RCMF) reaches 15.93.
03 Dec 2015
TL;DR: In this paper, a homogeneous 31-core fiber with a cladding diameter of 230 μm for quasi-single-mode transmission is designed and fabricated, achieving LP 01 -crosstalk of −38.4 dB/11 km at 1550 nm.
Abstract: A homogeneous 31-core fibre with a cladding diameter of 230 μm for quasi-single-mode transmission is designed and fabricated. LP 01 -crosstalk of −38.4 dB/11 km at 1550 nm is achieved by using few-mode trench-assisted cores.
TL;DR: In this article, the Quantum Controlled Stark Effect (QCSE) of group IV Ge(Sn)/SiGe(Sn) quantum wells (QWs) on Si substrate is analyzed by microscopic many-body theory for mid-infrared (mid-IR) Si-based electroabsorption devices.
Abstract: Quantum-confined Stark effect (QCSE) of group IV Ge(Sn)/SiGe(Sn) quantum wells (QWs) on Si substrate is analyzed by microscopic many-body theory for mid-infrared (mid-IR) Si-based electroabsorption devices. To show the validity of the theory, QCSE of Ge/SiGe QW is investigated and very good agreement between theory and reported measured results is obtained. Next, the QCSE of GeSn/SiGeSn QWs is analyzed and the QW design for electroabsorption modulators to obtain large extinction ratio in mid-IR region is presented. It is shown that compressive and tensile strained well and barrier layers is preferable to obtain large extinction ratio due to its large conduction band offset.
01 Sep 2015
TL;DR: In this article, the group delay spread of strongly-coupled 3-core fibres was investigated through principal mode analysis and the results were in good agreement with the results obtained by adding an air-hole to the centre of the fiber.
Abstract: Group delay spread of strongly-coupled 3-core fibres is investigated through the principal mode analysis. Calculated and measured results are in good agreement and group delay spread can be further reduced by adding an air-hole to the centre of the fibre.
TL;DR: In this paper, a multicore fiber (MCF)-based mode multiplexer/demultiplexer (MUX/DEMUX) that can overcome the alignment issue of the fiber-based mode MUX and DEMUX is proposed.
Abstract: A multicore fiber (MCF)-based mode multiplexer/demultiplexer (MUX/DEMUX) that can overcome the alignment issue of the fiber-based mode MUX/DEMUX is proposed. Design concept and fabrication results of the MCF-based mode MUX/DEMUX for two-spatial-mode operation (LP 01 and LP 11 ) (2M-MUX/DEMUX) and for three-spatial-mode operation (LP 01 , LP 11a , and LP 11b ) (3M-MUX/DEMUX) are presented. The fabricated 2M-MUX/DEMUXes for C-band or L-band, using the same MCF with different elongation ratios demonstrate a coupling efficiency of greater than 90% over each band. Finally, a 3M-MUX/DEMUX with a fan-in/fan-out device is presented. The selective excitation of LP 01 , LP 11a , and LP 11b modes depending on input ports is experimentally demonstrated.
TL;DR: In this article, a 3D finite-element beam propagation method is described for the first time, to the best of our knowledge, for the analysis of transmission characteristics of any kind of photonic structures.
Abstract: A 3-D finite-element time-domain beam propagation method is described for the first time, to the best of our knowledge, for the analysis of transmission characteristics of any kind of photonic structures. In order to avoid nonphysical reflections from computational window edges, the perfectly matched layer boundary condition is introduced. Furthermore, the present method can treat wideband optical pulses owing to the use of Pade approximation. The validity of this method is verified by numerical simulations of a photonic crystal cavity and a microring resonator. In addition, in order to demonstrate the usefulness of the developed method, a taper waveguide for a highly efficient connection between a straight waveguide and a 1-D photonic crystal-coupled resonator optical waveguide is designed.
01 Jun 2015
TL;DR: A kind of heterogeneous trench-assisted graded-index few-mode multi-core fiber (Hetero-TA-GI-FM-MCF) that can be smaller than 100 ps/km over C+L bands is proposed.
Abstract: We propose a kind of heterogeneous trench-assisted graded-index few-mode multi-core fiber (Hetero-TA-GI-FM-MCF). For each core in the fiber, absolute value of differential mode delay (| DMD |) can be smaller than 100 ps/km over C+L bands.
TL;DR: In this article, a coupled resonator optical waveguide (CROW) based on a slotted 1-D photonic crystal (1-D PC) cavity is proposed, and its enhancement of the optical nonlinearity due to the slow-light effect of the CROW and the small effective area of the slotted PC cavities is demonstrated.
Abstract: A coupled resonator optical waveguide (CROW) based on a slotted 1-D photonic crystal (1-D PC) cavity is proposed, and its enhancement of the optical nonlinearity due to the slow-light effect of the CROW and the small effective area of the slotted 1-D PC cavities is demonstrated. Setting the appropriate slot configuration in terms of the tradeoff between the nonlinear parameter and the leakage loss, a large nonlinear parameter exceeding $10^4\ \text{m}^{-1}\text{W}^{-1}$ can be obtained.
TL;DR: In this article, the authors analyzed the impulse response of strongly coupled 3-core fibers from weak to strong coupling regime based on multimode generalized nonlinear Schrodinger equation, and measured and calculated impulse responses were in good agreement, showing the validity of discussion.
Abstract: Impulse response of strongly-coupled 3-core fibers is analyzed from weak to strong coupling regime based on multimode generalized nonlinear Schrodinger equation. Measured and calculated impulse responses are in good agreement, showing the validity of discussion.
Journal Article•
TL;DR: In this paper, a high performance polarization splitter-rotator based on a mode-conversion taper and a mode sorting asymmetric Y-branch waveguides is designed by wavefront matching method.
Abstract: A high-performance polarization splitter-rotator based on a mode-conversion taper and a mode-sorting asymmetric Y-branch waveguides is designed by wavefront matching method. A high transmission in a wide wavelength range is demonstrated.
TL;DR: A broadband, large fabrication tolerance LP01/LP11 PLC-based mode multi/demultiplexer design is presented by using wavefront mathing method and the low-loss bandwidth of the optimized structure is 4-times wider than that of conventional structure.
Abstract: A broadband, large fabrication tolerance LP01/LP11 PLC-based mode multi/demultiplexer design is presented by using wavefront mathing method. The low-loss bandwidth of the optimized structure is 4-times wider than that of conventional structure.
TL;DR: In this paper, the authors compare homogeneous and heterogeneous 2LP-mode multicore fibers and find that the heterogeneous MCF can improve a tradeoff relationship between low inter-core crosstalk and short cutoff wavelength, resulting in high spatial multiplicity.
Abstract: We compare homogeneous and heterogeneous 2LP-mode multicore fibers (MCFs) and find that the heterogeneous MCF can improve a tradeoff relationship between low inter-core crosstalk and short cutoff wavelength, resulting in high spatial multiplicity.
TL;DR: In this paper, a 50μm core Yb-doped polarizing photonic bandgap fiber (PBF) was demonstrated for single-polarization operation throughout the entire transmission band from 1010nm to 1170nm with a polarization extinction ratio (PER) of >5dB/m.
Abstract: Polarizing optical fibers are important components for building compact fiber lasers with linearly polarized laser output. Conventional single-mode optical fibers with birefringence can only preserve the polarization when the incident beam is launched properly. Recent reports demonstrate that the birefringence in photonic bandgap fibers (PBFs) can provide single-polarization operation near the edge of transmission band by shifting the transmission band for the light with orthogonal polarizations. Here, we demonstrate a 50μm core Yb-doped polarizing photonic bandgap fiber (PBF) for single-polarization operation throughout the entire transmission band from 1010nm to 1170nm with a polarization extinction ratio (PER) of >5dB/m, which is >15dB/m near the short wavelength edge of the transmission band. The polarizing effect is due to the differential polarization transmission loss presented in this fiber, which is benefited from the fiber birefringence of 3.2x10 -4 , obtained by incorporating low-index boron-doped rods on either side of the core. The achievement is based on the fact that light at fast axis has lower effective mode index which is closer to the modes in the photonic cladding and thus to be easily coupled into cladding. A 2.6m long straight fiber was tested in a laser configuration without any polarizers to achieve single polarized laser output with a PER value of 21dB at 1026nm lasing wavelength.
19 Nov 2015
TL;DR: In this paper, a two-mode supporting multi-core fiber with dual-ring structure was proposed, which achieves −33 dB/100km, maximum Rpk is 11.03 cm, and RCMF reaches 15.28.
Abstract: We proposed a two-mode supporting multi-core fiber with dual-ring structure. The maximum XT11–11 achieves −33 dB/100km, maximum Rpk is 11.03 cm, and RCMF reaches 15.28.
TL;DR: In this paper, a review of the recent progress in photonic bandgap fiber suppression is presented, with a focus on higher-order mode suppression in large-mode-area designs, making them well suited for further power scaling of fiber lasers.
Abstract: All-solid photonic bandgap fibers have unsurpassed higher-order-mode suppression in large-mode-area designs, making them well suited for further power scaling of fiber lasers. We will review of some of the recent progress in this invited talk.
01 Sep 2015
TL;DR: In this paper, the inter-core crosstalk of a fabricated few-mode multicore fiber is theoretically and experimentally investigated, and the direction of the LP 11 mode was investigated.
Abstract: The inter-core crosstalk of a fabricated few-mode multicore fibre is theoretically and experimentally investigated. By changing the direction of the LP 11 mode, the crosstalk between the LP 11 mode and the LP 01 mode decreased by more than 10 dB.
10 May 2015
TL;DR: In this article, the effect of Ge(Sn)/SiGe(Sn) quantum wells (QWs) was analyzed by many-body theory and calculated absorption spectra of Ge/SiGe-QWs were in good agreement with the experiment.
Abstract: Quantum-confined Stark effect of Ge(Sn)/SiGe(Sn) quantum wells (QWs) is analyzed by many-body theory. Calculated absorption spectra of Ge/SiGe-QWs are in good agreement with the experiment. Also, the effect of Sn-incorporation is investigated for mid-infrared applications.