Noboru Edagawa

Analysis of laser phase noise to intensity noise conversion by chromatic dispersion in intensity modulation and direct detection optical-fiber transmission

Laser phase noise conversion to intensity noise due to fiber chromatic dispersion is analyzed by deriving the noise power spectral density. Theory predicts that the phase-modulation-amplitude-modulation conversion noise is a principal limiting factor of the gigabit-per-second nonregenerative transmission using an external modulator when the linewidth of the laser transmitter is above several tens of megahertz and the total chromatic dispersion of fibers exceeds several thousand picoseconds per nanometer. This fact is confirmed by the 2.4-Gb/s transmission experiments using multiple inline Er-doped fiber amplifiers. The system penalty due to this noise in the intensity modulation and direct detection (IM-DD) optical transmission using an external modulator is evaluated. >

Transform-limited optical pulse generation up to 20-GHz repetition rate by a sinusoidally driven InGaAsP electroabsorption modulator

The authors propose and demonstrate a simple technique for generating a transform-limited optical short pulse with variable repetition rates by using a sinusoidally driven InGaAsP electroabsorption modulator without any optical resonators. Using the pulse compression effect due to nonlinear attenuation characteristics of the modulator, a transform-limited optical pulse can be generated just with sinusoidal modulation. Theoretical calculations and experimental results show that the pulse shape is very close to the sech/sup 2/ shape, and the pulse width can be easily varied by varying the bias and modulation voltages. Transform-limited optical pulse generation with a minimum pulse width of 11 ps was achieved up to 20-GHz repetition rate. The time-bandwidth product was as small as 0.32. >

40 Gb/s single-channel soliton transmission over transoceanic distances by reducing Gordon-Haus timing jitter and soliton-soliton interaction

Forty Gb/s single-channel soliton transmission experiments using periodic dispersion compensation were conducted. The impact of the dispersion map on the transmission performance was experimentally investigated. The transmission performance was significantly varied with the dispersion map. The improvement of the transmission performance by the polarization division multiplexing, which reduced soliton-soliton interaction furthermore, was also confirmed. By using the polarization division multiplexing in the optimum dispersion map, 40 Gb/s single-channel transmission over 10200 km has been successfully demonstrated without any active inline transmission control.

A multiwavelength fiber ring-laser employing a pair of silica-based arrayed-waveguide-gratings

A multiwavelength fiber ring-laser employing a pair of silica-based arrayed-waveguide-gratings (AWGs) is proposed to easily implement a stable multiwavelength operation for a variety of research needs. A fixed multiwavelength operation is available when the free-spectral-range (FSR) of the AWGs is wide enough to cover the gain bandwidth of deployed erbium-doped fiber amplifiers (EDFAs). A tunable multiwavelength operation is also available when the FSR is narrower than the gain bandwidth. 15 channels with 1.6-nm spacing in the fix type, and five channels with about 40-nm discretely tunable range at 1.4-nm spacing in the tunable type and almost 50-dB signal to amplified spontaneous emission (ASE) ratio in both types are demonstrated.

New applications of a sinusoidally driven InGaAsP electroabsorption modulator to in-line optical gates with ASE noise reduction effect

The authors propose new applications of a sinusoidally driven InGaAsP electroabsorption modulator to an inline optical gate for a 2R (reshape and retiming) repeater in optical amplifier systems, an n:1 optical demultiplexer in time division multiplexing systems, and an optical switch. The small polarization dependence of the modulator is essential for inline use. By utilizing the monotonic increase of the extinction ratio with increasing applied voltage, the electroabsorption modulator driven by a large-signal sinusoidal voltage can produce a time domain square-shaped gate function with variable gate width. Furthermore, amplified spontaneous emission noise of optical amplifier systems can be reduced in both time and wavelength domains at the off-state of the modulator, due to noninterferometric wide wavelength operation of the modulator. Experimental results for a 2R repeater, an n:1 (n=4, 8) optical demultiplexer, and optical gates for switching are also demonstrated at over 10-Gb/s repetition rate. >

Novel wavelength converter using an electroabsorption modulator: conversion experiments at up to 40 Gbit/s

We have proposed a novel wavelength converter using an electroabsorption modulator. High-quality conversion has been demonstrated at 20 Gbit/s over 30 nm of wavelength range. The potentialities for high speed (>40 Gbit/s) and broadcasting applications were also demonstrated.

Dispersion-managed high-capacity ultra-long-haul transmission

The recent progress of dispersion-managed transmission technologies for ultra-long-haul wavelength-division-multiplexing (WDM) systems is reviewed. First, we discuss the dispersion-management technologies for 10 Gb/s-based WDM systems. Next, dispersion-managed technologies for higher bit rate applications are reviewed, including dispersion-managed soliton transmission. Finally, we compare the effectiveness of different modulation formats for achieving ultradense WDM transmission for future applications.

Amplified spontaneous Raman scattering in fiber Raman amplifiers

Amplified spontaneous Raman scattered light power in forward and backward Raman amplifiers is theoretically and experimentally studied under the assumption of the constant Raman gain coefficient in the bandwidth of an optical filter. On the basis of the results, the power ratio of the amplified signal to amplified spontaneous scattering is discussed. As a result, it is clarified that the effect of amplified spontaneous Raman scattering on the signal to noise ratio for backward Raman scattering is larger than for forward Raman scattering.

70-GHz-spaced 40/spl times/42.7 Gb/s transpacific transmission over 9400 km using prefiltered CSRZ-DPSK signals, all-Raman repeaters, and symmetrically dispersion-managed fiber spans

70-GHz-spaced 40/spl times/42.7 Gb/s prefiltered carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) signals have been transmitted over transpacific distances for the first time, using all-Raman repeaters with two pump-wavelengths, dispersion-managed fiber commercially available in volume, and an ETDM receiver. In this paper, first, in order to enhance the spectral efficiency, the impact of bandlimitation to a CSRZ-DPSK signal was experimentally investigated in comparison to a conventional CSRZ-on-off-keying (OOK) signal, and we found that the bandlimitation tolerance of CSRZ-DPSK signal was smaller than that of CSRZ-OOK signal in back-to-back condition. We also confirmed that the prefiltering CSRZ-DPSK signal with up to 65 GHz bandlimitation potentially had better transmission performance than the prefiltered CSRZ-OOK signal. In addition, we found that, although the nonlinear transmission penalty was increased by bandlimitation, this penalty for CSRZ-DPSK signal was smaller than that for CSRZ-OOK signal. Through this study, long-term stability of the transmission performance was also evaluated with low-speed signal polarization scrambling without using any polarization mode dispersion (PMD) compensation.

Long-haul coherent optical fiber communication systems using optical amplifiers

Studies on long-haul coherent optical fiber communication systems with in-line optical amplifier repeaters are made theoretically and experimentally. By theoretical calculation it was found that coherent systems can achieve wider dynamic range for an amplifier input power as compared with the intensity-modulation direct-detection (IM-DD) systems. The feasibility of such systems using traveling-wave semiconductor laser amplifiers (TWSLAs) and erbium-doped fiber amplifiers (EDFAs) was investigated, and 546 km, 140 Mb/s CPFSK transmission using TWSLAs and 1028-km, 560-Mb/s CPFSK transmission using EDFAs were successfully demonstrated. >