Masato Yoshida

We describe 1 Gsymbol/s, 64 and 128 coherent quadrature amplitude modulation (QAM) transmissions over 150 km, in which we employ a frequency-stabilized C(2)H(2) fiber laser, an optical phase-looked loop (OPLL), and a heterodyne detection circuit.

We demonstrate the first 40 Gbit/s single-channel polarization-multiplexed, 5 Gsymbol/s, 16 QAM quantum noise stream cipher (QNSC) transmission over 480 km by incorporating ASE quantum noise from EDFAs as well as the quantum shot noise of the coherent state with multiple photons for the random masking of data. By using a multi-bit encoded scheme and digital coherent transmission techniques, secure optical communication with a record data capacity and transmission distance has been successfully r

A new method for the measurement of the group velocity dispersion (GVD) in optical fibers, based on optical frequency domain reflectometry (OFDR), is proposed and demonstrated. Frequency chirped light is used as a light source, which allows the dispersion to be determined from changes in the frequency chirp rate. Accurate measurement of the average dispersion, at a single terminal, in fibers up to several tens of kilometers, is accomplished using a frequency-shifted feedback fiber laser as a lig

We describe in detail our recent demonstration of a 10 Tbit/s secure physical layer transmission that we achieved by using digital coherent QAM quantum noise stream cipher (QNSC) and injection-locked WDM techniques. We used an FPGA-based transmitter and receiver to demonstrate a 165 channel polarization-multiplexed WDM 5 Gbaud 128 QAM/QNSC (70 Gbit/s) on-line transmission over 160 km with a spectral efficiency of 6 bit/s/Hz. In the present system, the original 128 QAM data were encrypted in a 10

We describe a fused type fan-out device for 7-core fiber based on a bundled structure, which has no taper structure and a highly accurate core arrangement. We evaluated the repeatability of the splice loss characteristics of the fan-out device by splice testing 10 samples, resulting in an average splice loss of as low as 0.3 dB with a deviation of 0.048 dB. The crosstalk between the center and outer cores was less than -52 dB. Furthermore, the power damage threshold was higher than 1 W and the a

We have successfully achieved a mode-hop-free, optical frequency tunable 3-ps 40-GHz mode-locked fiber laser by installing an optical etalon in a 6.8-m laser cavity. The laser frequency was continuously tuned over 1 GHz without mode hopping by tuning the etalon peak frequency. The oscillation wavelength was also tuned over 1535-1560 nm by tuning an optical bandpass filter installed in the laser cavity.

We report the first single-channel 15.3 Tbit/s, 1.28 Tbaud, 64 QAM transmission using 670 fs coherent Nyquist pulses. We newly constructed an optical gate to improve the signal-to-noise ratio (SNR) of the homodyne detection signal, a coherent spectral expansion technique, and an optical phase-locked loop (OPLL) circuit with a 0.6 deg. phase noise. We also constructed an active 70 fs timing stabilization circuit between the OTDM signal and Nyquist LO pulse to realize precise homodyne detection. W

We describe the first on-line 256 QAM digital coherent optical transmission system with an ECLD light source and DFB LD-based injection-locking, and an FPGA-based transceiver. In this system, precise optical phase control was achieved with an optical injection-locking circuit and a phase-locked loop circuit at the receiver, which helped to reduce the complexity of digital signal processing in the FPGA-based receiver. The precise polarization-demultiplexing of a 256 QAM signal was realized by usi

We describe a 1.55 μm hydrogen cyanide (HCN) optical frequency and repetition rate stabilized mode-locked fiber laser, where the optical frequency was locked to the P(10) HCN absorption line and the repetition rate was locked to 9.95328 GHz by using a microwave phase-locked loop. The optical frequency stability of the laser reached 5 x 10^-11 with an integration time τ of 1 s. With a bidirectional pumping scheme, the laser output power reached 64.6 mW. To obtain a short pulse train, th