Shuto Yamamoto

100 × 120-Gb/s PDM 64-QAM transmission over 160 km using linewidth-tolerant pilotless digital coherent detection

We demonstrate 11.2-Tb/s transmission of 12.5-GHz spaced 120-Gb/s PDM 64-QAM signals over 160 km by using a digital coherent receiver with pilotless demodulation algorithms. The spectral efficiency of 9.0 b/s/Hz is the highest reported for 100-Gb/s/ch-class transmission.

Bit-rate-flexible all-optical OFDM transceiver using variable multi-carrier source and DQPSK/DPSK mixed multiplexing

We propose and demonstrate a bit-rate-flexible all-optical OFDM transceiver. Signals were successfully generated at 107, 42.8, 32.1, and 10.7 Gbit/s and received through the transceiver. The 107-Gbit/s signal was successfully transmitted over 40-km-SMF without dispersion compensation.

Achievement of Subchannel Frequency Spacing Less Than Symbol Rate and Improvement of Dispersion Tolerance in Optical OFDM Transmission

We propose a novel optical orthogonal frequency-division multiplexing (OFDM) transmission, where the frequency spacing of subchannels is less than the symbol rate. We show experimentally that the novel OFDM transmission achieves an optical SNR (OSNR) sensitivity level and dispersion tolerance roughly equivalent to those of the conventional OFDM. We also show the influence of chromatic dispersion from the transmission channel on the OFDM signal. The chromatic dispersion causes a desynchronization of the symbol timing between subchannels and breaks the frequency orthogonality in OFDM. We confirm experimentally that it is possible to mitigate the signal degradation due to the chromatic dispersion by optimizing the symbol timing and orthogonally polarizing the subchannels to the neighboring subchannels.

Influence of Intrachannel Crosstalk With Frequency Dependence on Signal Degradation in Optical Switch Network

In this paper, we show the influence of intrachannel crosstalk in an optical switch network. The intrachannel crosstalk is mainly due to a signal that is not sufficiently blocked by the optical switch. The signal has a broadband spectrum and causes coherent crosstalk at the optical switching node. We investigate analytically the relationship between the channel isolation of the optical switching node that the optical switch network comprises and the crosstalk penalty due to the broadband signal. We confirm experimentally that the relationship is suited to the optical switch network that emulates an optical cross-connect system. We also show experimentally that it is important to use the optical switch with a high channel isolation level in the entire range of the signal bandwidth in order to suppress the impairment due to the crosstalk. We confirm that in a 50-GHz spaced system, a 44-Gb/s return-to-zero differential quadrature phase-shift-keying signal is sufficiently transmitted without a crosstalk penalty through 24 optical switching nodes, comprising wavelength selective filters with a high channel isolation level in the entire range of the signal bandwidth.

Phase-transparent flexible waveband conversion of 43 Gb/s RZ-DQPSK signals using multiple-QPM-LN waveguides

We report phase-transparent waveband conversion with polarization insensitivity based on second harmonic (SH) wave pumped difference frequency generation (DFG) using multiple-quasi-phase-matched LiNbO(3) (QPM-LN) waveguides. Flexible waveband conversion is demonstrated over the entire C-band using a tunable DFB-LD array (TLA) as a pump source for a multiple-QPM-LN waveguide. The penalty free waveband conversion of 43 Gb/s return-to-zero differential quadrature phase-shift-keying (RZ-DQPSK) waveband signals is successfully achieved.

In-band OSNR monitor with high-speed integrated Stokes polarimeter for polarization division multiplexed signal.

An in-band optical signal-to-noise ratio (OSNR) monitor is proposed, based on an instantaneous polarization state distribution analysis. The proposed monitor is simple, and is applicable to polarization division multiplexed signals. We fabricate a high-speed Stokes polarimeter that integrates a planar lightwave circuit (PLC) based polarization filter, high-speed InP/InGaAs photodiodes and InP hetero-junction bipolar transistor (HBT) trans-impedance amplifiers (TIA). We carry out proof-of-concept experiments with the fabricated polarimeter, and successfully measure the OSNR dependent polarization distribution with 100-Gb/s dual polarization quadrature phase shift keying (DP-QPSK) signals.

Field trial of differential-phase-shift quantum key distribution using polarization independent frequency up-conversion detectors

We report a field trial of differential phase shift quantum key distribution (QKD) using polarization independent frequency up-conversion detectors. A frequency up-conversion detector is a promising device for achieving a high key generation rate when combined with a high clock rate QKD system. However, its polarization dependence prevents it from being applied to practical QKD systems. In this paper, we employ a modified polarization diversity configuration to eliminate the polarization dependence. Applying this method, we performed a long-term stability test using a 17.6-km installed fiber. We successfully demonstrated stable operation for 6 hours and achieved a sifted key generation rate of 120 kbps and an average quantum bit error rate of 3.14 %. The sifted key generation rate was not the estimated value but the effective value, which means that the sifted key was continuously generated at a rate of 120 kbps for 6 hours.

Hybrid 40-Gb/s and 100-Gb/s PDM-QPSK DWDM transmission using real-time DSP in field testbed

We demonstrate hybrid 40-Gb/s and 100-Gb/s PDM-QPSK DWDM transmission using real-time DSP in 580-km DSF-installed field testbed. The nonlinear crosstalk penalty due to the hybrid transmission of less than 0.5 dB is confirmed.

Scalable Photonic Interconnection Network With Multiple-Layer Configuration for Warehouse-Scale Networks

A scalable and flexible photonic interconnection network architecture suitable for warehouse-scale networks is proposed. The architecture comprises three functional layers: physical, optical, and logical layers. The network topologies achieved at the layers are tree in the physical layer; hypercube in the optical layer; and relatively lower dimensional topologies like two-dimensional mesh, tree, and ring in the logical layer. The application of the appropriate network configuration in each layer by making good use of wavelength division multiplexing technology realizes a truly scalable and flexible network. Evaluation of the physical link requirements reveals the scalability of the proposed network architecture.

Field trial of simultaneous 100-Gbps and 400-Gbps transmission using advanced digital coherent technologies

We achieve double the performance in 400-Gbps optical transmission employing advanced digital coherent technologies based on field trials. Additionally, we show stable transmission of 400-Gbps channels that does not affect the existing 100-Gbps channels.