Keisuke Kasai

256-QAM (64 Gb/s) Coherent Optical Transmission Over 160 km With an Optical Bandwidth of 5.4 GHz

We report a polarization-multiplexed (Pol-Mux) 4-Gsymbol/s 256 quadrature amplitude modulation (QAM) coherent optical transmission over 160 km. A 64-Gb/s data signal was successfully transmitted with an optical bandwidth of 5.4 GHz. We also describe a Pol-Mux, 10-Gsymbol/s, 128- and 64-QAM (140 and 120 Gb/s) transmission over 150 km.

Performance improvement of an acetylene (C2H2) frequency-stabilized fiber laser

An erbium-doped fiber laser with a high Er-ion concentration generally causes output power fluctuation and self-pulsing resulting from relaxation oscillation. In this work, we employed a new EDF with high Er- and Al-ion concentrations in order to suppress the relaxation oscillation and increase the output power of the laser. As a result, the output power was more than doubled and the power fluctuation halved. The linewidth was narrowed to 4kHz. Furthermore the frequency stability of the 13C2H2 frequency-stabilized erbium fiber laser reached as high as 1.3 × 10-11 for τ = 1s and 2.0 × 10-11 for τ = 102s. The short-term stability of τ = 1s was also improved.

64 and 128 coherent QAM optical transmission over 150 km using frequency-stabilized laser and heterodyne PLL detection

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.

2048 QAM (66 Gbit/s) single-carrier coherent optical transmission over 150 km with a potential SE of 15.3 bit/s/Hz.

We have successfully achieved a 2048 QAM transmission (66 Gbit/s) with a potential spectral efficiency of 15.3 bit/s/Hz in a single carrier coherent transmission over 150 km.

512 QAM (54 Gbit/s) coherent optical transmission over 150 km with an optical bandwidth of 4.1 GHz

We report the first demonstration of 512 QAM coherent optical transmission by using an optical PLL. A polarisation-multiplexed 54 Gbit/s data signal was successfully transmitted at 3 Gsymbol/s with an optical bandwidth of 4.1 GHz including a tone signal.

1-Gsymbol/s 64-QAM Coherent Optical Transmission Over 150 km

Quadrature amplitude modulation (QAM) is an excellent modulation format for realizing optical communication systems with a high spectral efficiency of much greater than 1bit/s/Hz. We describe QAM coherent optical communication that we achieved by using heterodyne detection with a frequency-stabilized fiber laser and an optical phase-locked loop (OPLL) technique. The phase error variance of the intermediate frequency signal of the OPLL was 6.1times10-3 rad. A 1-Gsymbol/s 64-QAM coherent signal was successfully transmitted over 150km

1 Gsymbol/s, 64 QAM coherent optical transmission over 150 km with a spectral efficiency of 3 bit/s/Hz

A 1 Gsymbol/s, 64 QAM coherent signal was successfully transmitted over 150 k m using heterodyne detection with a frequency-stabilized fiber laser and an optical phase-locked-loop technique. The spectral efficiency reached as high as 3 bit/s/Hz.

Mode-Hop-Free, Optical Frequency Tunable 40-GHz Mode-Locked Fiber Laser

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.

Single-Channel 400-Gb/s OTDM-32 RZ/QAM Coherent Transmission Over 225 km Using an Optical Phase-Locked Loop Technique

A single-channel 400-Gb/s transmission with a polarization-multiplexed , 10-Gsymbol/s, four-optical time-division multiplexed (OTDM) 32 return-to-zero/quadrature amplitude modulation (RZ/QAM) scheme is demonstrated for the first time. By using an optical phase-locked loop technique and a clock recovery circuit, we have successfully obtained a very stable pulsed-local oscillator whose phase was locked to the transmitter, and achieved precise demultiplexing and demodulation simultaneously. As a result, 400-Gb/s data were transmitted over 225 km with a bit-error-rate performance below the forward-error correction limit. Furthermore, we also realized a 320-Gb/s to 450-km transmission with an OTDM 16 RZ/QAM scheme.

Optical phase-locked loop for coherent transmission over 500km using heterodyne detection with fiber lasers

We have developed an optical phase-locked loop (OPLL) that can operate over 500km. The coherent transmitter is a 1.54µm 13C2H2 frequency-stabilized CW fiber ring laser with a frequency stability of 2.0 × 10-11 and a linewidth of 4kHz. To obtain wide band operation with a bandwidth of 1GHz, we fabricated a high-speed fiber laser as a local oscillator. By using these fiber lasers, the OPLL circuit successfully generated an intermediate frequency signal with a phase error variance of 7.9 × 10-3 rad.