Shigehiro Takasaka

Nearly exact optical beat-to-soliton train conversion based on comb-like profiled fiber emulating a polynomial dispersion decreasing profile

We show that an optical beat signal is almost exactly converted to a soliton train through the propagation along a fiber with a polynomial dispersion decreasing profile, which is numerically optimized through iterative calculation. In the experiment, we demonstrate the 160-GHz beat-to-soliton conversion with a 40-pair comb-like profiled fiber, which is designed to emulate the optimized dispersion profile. The optical beat is compressed to a 324-fs soliton train with a high peak-to-pedestal ratio of more than 21 dB, and its spectral envelope is almost completely converted into a sech/sup 2/ shape.

Counter-Dithering Pump Scheme for Cascaded Degenerate FWM Based Wavelength Converter

We demonstrate counter-dithering of pumps between two cascaded FWM processes for highly-efficient format-independent wavelength conversion. Up-to -1.2dB FWM conversion efficiency is obtained over 32-nm. 86-Gbps DP-QPSK are converted with OSNR penalty below 0.3dB at 10-3 BER.

Polarization insensitive arbitrary wavelength conversion in entire C-band using a PM-HNLF

Polarization insensitive pump-wavelength-tunable FWM in a zero dispersion and dispersion slope PM-HNLF was demonstrated. Polarization scrambled 10Gbit/s NRZ and DPSK signals in entire C-band were converted into entire C-band with power penalties less than 0.3dB and 0.5dB, respectively.

Phase noise mitigation of QPSK signal utilizing phase-locked multiplexing of signal harmonics and amplitude saturation.

We demonstrate an all-optical phase noise mitigation scheme based on the generation, delay, and coherent summation of higher order signal harmonics. The signal, its third-order harmonic, and their corresponding delayed variant conjugates create a staircase phase-transfer function that quantizes the phase of quadrature-phase-shift-keying (QPSK) signal to mitigate phase noise. The signal and the harmonics are automatically phase-locked multiplexed, avoiding the need for phase-based feedback loop and injection locking to maintain coherency. The residual phase noise converts to amplitude noise in the quantizer stage, which is suppressed by parametric amplification in the saturation regime. Phase noise reduction of ∼40% and OSNR-gain of ∼3  dB at BER 10(-3) are experimentally demonstrated for 20- and 30-Gbaud QPSK input signals.

Arbitrary wavelength conversion in entire CL-band based on pump-wavelength-tunable FWM in a HNLF

Pump-wavelength-tunable FWM was demonstrated using a zero dispersion and dispersion slope HNLF. Signal in CL-band was converted to any wavelength in entire CL-band and measured power penalties were less than 1 dB for 10 Gbit/s NRZ signals.

Duration-tunable 100-GHz sub-picosecond soliton train generation through adiabatic Raman amplification in conjunction with soliton reshaping

We demonstrate generation of 100-GHz soliton train with tunability of temporal duration from 0.84 to 2.1 ps by adiabatic Raman amplification with soliton reshaping, while keeping near transform-limit, low pedestal level and low stimulated Brillouin scattering.

On the Cascadability of All-Optical Wavelength Converter for High-Order QAM Formats

With the evolution to ever more complex modulation formats for optical signals, all-optical wavelength converters offer great benefits to optical networks, thanks to the possibility of translating the wavelength of an optical signal regardless of its data rate or modulation format. To deliver its full advantages over conventional optical-electrical-optical conversion, an all-optical wavelength converter has to possess important features in terms of transparency, bandwidth, and cascadability for practical applications in real systems. In this paper, we review a recent development of an all-optical wavelength converter, which exhibits seamless conversion in the C-band with a low noise figure of 6.2 dB for dual-polarization (DP) phase-modulated signals. We then carry out an investigation by both experiment and calculation of the cascaded operation of the developed wavelength converter for high-order quadrature amplitude modulation (QAM) formats. A cascadability comparable to an erbium-doped fiber amplifier is achieved for DP-QPSK, DP-16QAM, and DP-64QAM signals, thanks to the exemplary characteristics of the wavelength converter.

Polarization insensitive fiber optical parametric amplifier using a SBS suppressed diversity loop

We suppress stimulated Brillouin scattering occurred in a polarization diversity loop by restricting pumps propagation in highly nonlinear fibers to one-way so that we obtain fine polarization insensitive operation of a fiber optical parametric amplifier.

Cladding-Pumped L-Band Multicore EDFA with Reduced Power Consumption

Seven-core MC-EDFA pumped with single MM-LD optimized for L-band is developed. Output power of 19 dBm for each core is realized between 1576-1603nm with 33% reduced power consumption.

Sub-millisecond timing-jitter-free tuning of parametric dispersion compensator.

We demonstrate sub-millisecond tuning of a prototype parametric tunable dispersion compensator (P-TDC) based on cascaded polarization-diverse four-wave mixing (FWM) process with a fast tunable and highly wavelength-stable pump light source. The pump light source is developed using a tunable distributed amplification chirped sampled grating distributed reflector laser that is fully wavelength tunable by on-chip heaters with a 3-dB frequency response of 45 kHz, resulting in fast dispersion tuning of less than 50 μs without additional timing jitter. The P-TDC is developed as the first prototype to satisfy essential requirements for practical network uses: stable input-polarization diversity, input-wavelength preservation, and seamless dispersion tunability for entire C-band input wavelengths are simultaneously achieved.