Akihiro Maruta

NRZ-OOK-to-RZ-BPSK modulation-format conversion using SOA-MZI wavelength converter

A novel all-optical modulation-format conversion from nonreturn-to-zero on-off keying (NRZ-OOK) to return-to-zero binary phase-shift keying (RZ-BPSK) is proposed. A Mach-Zehnder interferometric (MZI) wavelength converter consisting of integrated semiconductor optical amplifiers (SOAs) is utilized to implement the proposed format conversion. Error-free operation at a bit rate of 10.7 Gb/s is experimentally demonstrated in order to show the feasibility of the proposed scheme. The received sensitivity of the converted signal is improved by 2.9 dB compared with a back-to-back NRZ-OOK signal at BER=10 -9. In addition, a reasonable dispersion tolerance of the converted signal up to plusmn500 ps/nm is observed. The numerical simulation based upon the carrier-rate equation verifies the experimental results

All-optical modulation format conversion from on-off-keying to multiple-level phase-shift-keying based on nonlinearity in optical fiber

We propose an all-optical modulation format conversion scheme from non-return-to-zero on-off-keying (NRZ-OOK) to return-to-zero (RZ) multiple-level phase-shift-keying (PSK) based on nonlinearity in optical fiber. The proposed conversion scheme is numerically investigated and experimentally demonstrated. We experimentally demonstrate error-free operation of NRZ-OOK/RZ- binary PSK conversion at 10.7 Gb/s. The operation of the NRZ-OOK/RZ-quadrature PSK conversion is shown by eye opening after balanced receiving at a symbol rate of 10.7 Gsymbol/s. In addition, we demonstrate the feasibility of the modulation format conversion from NRZ-OOK to RZ-8-levels PSK by numerical simulation.

All-optical modulation format conversion from NRZ-OOK to RZ-QPSK using parallel SOA-MZI OOK/BPSK converters

A novel all-optical modulation format conversion from non-return-to-zero on-off-keying (NRZ-OOK) to return-to-zero quadrature-phase-shift-keying (RZ-QPSK) is proposed and experimentally demonstrated. The proposed format conversion scheme is based on parallel Mach-Zehnder interferometric (MZI) OOK/binary-PSK (BPSK) converters, consisting of integrated semiconductor optical amplifiers (SOAs). We experimentally demonstrate that in both decoded channels of the converted RZ-QPSK signal bit error rate (BER) curves show almost the same receiver sensitivity at a symbol-rate of 10.7 Gsymbol/s. In addition, a reasonable dispersion tolerance of the converted signal up to +295 ps/nm is observed. The numerical simulation based upon carrier rate equation verifies the experimental results.

All-optical quantization scheme based on fiber nonlinearity

We have proposed a novel all-optical quantization scheme that may be useful for analog-to-digital conversion. The preprocess of optical sampling is performed by four-wave mixing, and optical quantizing is realized by soliton phenomena. We have conducted a simple proof-of-principle experiment, and demonstrated the optical multilevel thresholding to show the feasibility of the proposed method.

Digital Coherent Technology for Optical Fiber and Radio-Over-fiber Transmission Systems

Current status and the future perspective of digital coherent technology for optical fiber and radio-over-fiber (RoF) transmission systems will be reviewed. For the starter, we will review two key digital coherent techniques; the coherent receiver and compensation techniques for the fiber nonlinearity-induced impairments. Next, we will present a commercial deployment of 100 G digital coherent long-haul optical fiber transmission system and the R&D challenge to 400 G and beyond transmission systems. Finally, we will turn our focus on digital coherent RoF transmission systems. We will introduce an ongoing government-funded R&D program in Japan, entitled “Agile deployment capability of highly resilient optical and radio seamless communication systems.” It was initiated after the disaster in Japan in March 2011, aiming at optical fiber and millimeter-wave-band radio seamless transmission system. It would be a good use case of cutting-edge radio-over-fiber technology for an immediate social need.

Experimental demonstration of optical performance monitoring for RZ-DPSK signals using delay-tap sampling method

The emerging transparent optical networks, employing spectrally-efficient modulation formats require new methods for supervision of signal quality in the optical domain. In this paper we demonstrate the optical performance monitoring (OPM) of optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD) in return-to-zero differential phase-shift keying (RZ-DPSK) signals using asynchronous delay-tap sampling and pattern recognition algorithms. We experimentally show noise measurement of OSNR from 8.7 dB to 32 dB with low optical input power requirement. Moreover, residual CD can be evaluated in the range from -600 to +600 ps/nm. The results indicate that careful adjustment of delay is necessary in order to ensure accurate measurement.

Chirped nonlinear pulse propagation in a dispersion-compensated system

We study nonlinear pulse propagation in an optical transmission system with dispersion compensation. A chirped nonlinear pulse can propagate in such a system, but eventually it decays into dispersive waves in a way similar to the tunneling effect in quantum mechanics. The pulse consists of a quadratic potential that is due to chirp in addition to the usual self-trapping potential and is responsible for the power enhancement and the decay.

All-optical digital-to-analog conversion using nonlinear optical loop mirrors

We propose a novel ultrafast all-optical digital-to-analog conversion (DAC) scheme consisting of nonlinear optical loop mirrors, which can be applied to both a standard binary code and a Gray code. We conducted a proof-of-principle experiment and successfully demonstrated a 2-bit all-optical DAC with a Gray code, which indicates that the proposed scheme is feasible.

On the dispersion managed soliton

We review various methods used to study the dispersion managed soliton for nonlinear return-to-zero pulse propagation in optical fibers. A numerical averaging method, the guiding center soliton, the variational method both with a simple and with an extended ansatz, as well as the multiscale theory are discussed and numerically compared, allowing us to show their domains of applicability. Their relative merits and demerits are then exposed. (c) 2000 American Institute of Physics.

Optimal dispersion management for a wavelength division multiplexed optical soliton transmission system

Solitons frequency shift arising from the pulse collision between wavelength division multiplexed (WDM) channels in an optical transmission line may be reduced by dispersion management technique. The reduction mechanism is due to a cancellation between the shifts in normal and anomalous dispersion fibers. With a proper management of the dispersion, the effect of lumped amplifiers on the frequency shift may also be canceled out. In this paper, we give a detailed analysis of the frequency shift in dispersion managed systems, and explain the reduction mechanism of the shift. We then propose optimal dispersion management schemes by means of minimizing the frequency shift. We also present a statistical analysis of the collision induced timing jitter for a two-channel WDM system.