Koji Enbutsu

A coherent Ising machine for 2000-node optimization problems

Taking the pulse of optimization Finding the optimum solution of multiparameter or multifunctional problems is important across many disciplines, but it can be computationally intensive. Many such problems defined as computationally difficult can be mathematically mapped onto the so-called Ising problem, which looks at finding the minimum energy configuration for an array of coupled spins. Inagaki et al. and McMahon et al. show that an optical processing approach based on a network of coupled optical pulses in a ring fiber can be used to model and optimize large-scale Ising systems. Such a scalable architecture could help to optimize solutions to a wide range of complex problems. Science, this issue pp. 603 and 614 An optical-based processor is developed to solve a broad class of complex optimization problems. The analysis and optimization of complex systems can be reduced to mathematical problems collectively known as combinatorial optimization. Many such problems can be mapped onto ground-state search problems of the Ising model, and various artificial spin systems are now emerging as promising approaches. However, physical Ising machines have suffered from limited numbers of spin-spin couplings because of implementations based on localized spins, resulting in severe scalability problems. We report a 2000-spin network with all-to-all spin-spin couplings. Using a measurement and feedback scheme, we coupled time-multiplexed degenerate optical parametric oscillators to implement maximum cut problems on arbitrary graph topologies with up to 2000 nodes. Our coherent Ising machine outperformed simulated annealing in terms of accuracy and computation time for a 2000-node complete graph.

PDM Signal Amplification Using PPLN-Based Polarization-Independent Phase-Sensitive Amplifier

We demonstrate the first polarization-independent phase-sensitive amplification of a polarization-division multiplexing (PDM) signal. A novel polarization-diversity loop configuration using periodically poled LiNbO3 waveguides is proposed to achieve the polarization-independent amplification of both a single-polarized signal and a PDM signal. The proposed configuration provides two independent optical parametric amplification processes for two orthogonal polarization components in the loop, while preventing the amplification of the reflection noise by a counter-propagating pump. Polarization-independent error-free operation was confirmed with a bit-error-rate measurement for a 40-Gb/s quadrature phase-shift keying (QPSK) signal. We then demonstrated the phase regenerative amplification of an 80-Gb/s PDM-QPSK signal with artificial phase noise.

ParaBIT-1: 60-Gb/s-throughput parallel optical interconnect module

We previously proposed ParaBIT (parallel inter-board optical interconnection technology), and developed a prototype front-end module, called ParaBIT-0, with a total throughput of 28 Gb/s (700 Mb/s/spl times/40 ch). Aiming at higher throughput, lower cost, and further miniaturization, we are now developing a version, called ParaBIT-1, which is designed to achieve a total throughput of 60 Gb/s (1.25 Gbit/s/spl times/480-ch). To achieve a compact and high-throughput module, we developed a new compact high-density packaging structure and cost-effective optical coupling system for ParaBIT-1. This packaging structure enabled us to reduce the volume of ParaBIT-1 to 9 cc, which is about one-third that of ParaBIT-0 (25 cc). The optical coupling system consists of a new structure 24-fiber BF (bare fiber) connector whose main parts are made of molded plastic and a 24-channel optical coupling component using new polymeric optical waveguide film. The optical coupling component is composed of a 24-ch waveguide film with 45/spl deg/ mirrors and the 24-fiber BF connector interface, and can be assembled by passive alignment. The film has high thermal stability to allow soldering reflow processes, and is fabricated by direct photo-patterning. ParaBIT-1 met the design target of 1.25 Gb/s per channel.

Multimode optical waveguide fabricated by UV cured epoxy resin for optical interconnection

We have fabricated low loss multimode polymeric optical waveguides with high thermal stability for a parallel optical interconnect module using UV cured epoxy resins. The propagation loss of the waveguide at 830 nm was 0.08 dB/cm and no increment was observed after a solder bumps melting test.

Real-Time N2O Gas Detection System for Agricultural Production Using a 4.6-µm-Band Laser Source Based on a Periodically Poled LiNbO3 Ridge Waveguide

This article describes a gas monitoring system for detecting nitrous oxide (N2O) gas using a compact mid-infrared laser source based on difference-frequency generation in a quasi-phase-matched LiNbO3 waveguide. We obtained a stable output power of 0.62 mW from a 4.6-μm-band continuous-wave laser source operating at room temperature. This laser source enabled us to detect atmospheric N2O gas at a concentration as low as 35 parts per billion. Using this laser source, we constructed a new real-time in-situ monitoring system for detecting N2O gas emitted from potted plants. A few weeks of monitoring with the developed detection system revealed a strong relationship between nitrogen fertilization and N2O emission. This system is promising for the in-situ long-term monitoring of N2O in agricultural production, and it is also applicable to the detection of other greenhouse gases.

Individual fiber line testing technique for PONs using TLS-OTDR enhanced with reflected backward light analysis method

We describe a fiber line testing technique for PON that uses backscattered light reflected at FBGs with several wavelengths and a TLS-OTDR. We demonstrate the ability to test 8-branched fibers individually.

Polymeric optical waveguide with high thermal stability and its application for optical interconnection

We have realized multimode optical waveguides with low loss and high thermal stability by a simple fabrication process using UV-cured epoxy resin, and also proposed useful and low-cost waveguide film devices for optical interconnection.

Integrated quasi-phase-matched second-harmonic generator and electro-optic phase modulator for low-noise phase-sensitive amplification.

We propose a quasi-phase-matched second-harmonic generator integrated with an electro-optic phase modulator in a directly bonded LiNbO3 (DB-LN) waveguide to obtain high signal-to-noise ratio (SNR) pump light for a phase-sensitive amplifier (PSA). This integrated device exhibits 1-MHz modulation and 1-W second-harmonic-generation properties sufficient for phase-locking between the signal and pump and for PSA gain, respectively. A novel PSA configuration based on the high-input-power tolerance of the device helps to suppress the noise from the erbium-doped fiber amplifier used for pump-light generation and leads to an improvement of the SNR of the pump light. The SNR improvement was confirmed by comparing the noise figure of a PSA employing the DB-LN waveguide with that of a PSA using a Ti-diffused LN waveguide modulator.

Low-noise phase-sensitive amplifier for guard-band-less 16-channel DWDM signal using PPLN waveguides

A X(2)-stage SHG/OPA configuration enabled low-crosstalk and guard-band-less DWDM signal amplification. We demonstrated a 5.6-dB link-SNR improvement and a low NF of 2.1 dB below the 3-dB quantum limit in simultaneous 16-channel-signal amplification.

Optical parametric amplifiers based on PPLN waveguides for long-Haul transmission

We review the capabilities of optical parametric amplifiers based on periodically poled LiNbO3 (PPLN) waveguides for optical communication. Specifically, we discuss phase and amplitude regeneration using a phase sensitive amplifier and nonlinearity mitigation using an optical phase conjugator in multi-span transmissions.