Misao Sakano

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.

Investigation of a Downsized Silica Highly Nonlinear Fiber

Theoretical influences of reducing the cladding diameter for silica highly nonlinear fiber (HNLF) have been investigated by the finite-element method. Downsized HNLF with 56-mum cladding was fabricated, and certain reliability was confirmed through mechanical and environmental tests. A coin-sized module was obtained using over 200 m of 56-mum HNLF.

External Synchronization of 160-GHz Optical Beat Signal by Optical Phase-Locked Loop Technique

We have synchronized a 160-GHz optical beat signal with a 40-GHz reference optical pulse train by using an optical phase-locked loop (OPLL). The OPLL consists of an optical beat signal source, comprising a pair of three-electrode distributed feedback laser diodes that works as a voltage controlled oscillator, and an all-optical phase detector based on the two-photon absorption in a silicon avalanche photodiode. Phase-locking operation is confirmed through phase-error measurement and cross-correlation trace measurement. The residual timing jitter of the 160-GHz optical beat signal relative to the reference pulse train, in the bandwidth of 80 MHz, is measured to be as small as 126 fs

Generation of 80-nm Wavelength-Tunable 100-fs Pulse Based on Comblike Profiled Fiber Comprised of HNLF and Zero Dispersion-Slope NZDSF

To realize extremely wideband wavelength-tunable femtosecond (fs) pulse generation, we propose a dispersion-flattened comblike profiled fiber that is a pulse compressor comprised of low dispersion-slope highly nonlinear fiber and zero dispersion-slope nonzero dispersion-shifted fiber (ZDS-NZDSF). We also apply ZDS-NZDSF to a soliton converter to reshape and compress a seed pulse train generated from a tunable laser source and an intensity modulator. Using the proposed scheme, we successfully generate 100-fs optical pulse from the seed pulse with the varied wavelengths of 1530, 1570, and 1610 nm

Repetition rate variable and wavelength-tunable picosecond optical pulse source employing square-wave-driven intensity modulator and comb-like profiled fiber

We present a picosecond optical pulse source with repetition rate variability and wavelength tunability. The key to realize the repetition rate variability in our proposal is the method of generating seed pulse, where an intensity modulator is driven by a half-clock square wave. The advantage of this method is that the duration of the seed pulse is approximately half of the rise time and independent of repetition rate. In the experiment, we obtain a 15-ps seed optical pulse train, which is successfully compressed down to less than 1 ps with a 4.2-km-long comb-like profiled fiber. We confirm the repetition rate tunability of 9-15 GHz and the wavelength tunability of 1530-1560 nm.

Electrooptic spectral shearing interferometry using a Mach-Zehnder modulator with a bias voltage sweeper

We propose a novel implementation of electrooptic spectral shearing interferometry (EOSSI) for complete characterization of optical pulses. We measure the spectrum of the output pulse of a Mach-Zehnder intensity modulator by sweeping the bias voltage. By doing this, we can synthesize a spectral fringe, with which we can reconstruct the waveform of the pulse under test. Compared to the previous EOSSI, our proposal simplifies the setup and enables us to measure high-repetition rate trains of optical pulses. In the experiment, we characterize picosecond optical pulse trains at a repetition rate of 10 GHz with high sensitivity and reliability.

Novel NZ-DSF with ultra-low dispersion slope lower than 0.020 ps/nm/sup 2//km

A novel NZ-DSF with dispersion slope lower than 0.020 ps/nm/sup 2//km and /spl lambda//sub 0/ shorter than 1400 nm has designed and fabricated. The adaptability of a Raman amplifier and dispersion compensator was improved. A BER lower than 10/sup -9/ both in the C- and L-bands was obtained without dispersion compensation.

Generation of 160-GHz sub-picosecond in-phase pulse train from optical beat signal

We propose a method to generate in-phase optical pulse train from optical beat signal based on four-wave mixing and asymmetric spectral filtering. A 160-GHz repeating, 0.7-ps-FWHM, nearly transform-limited, in-phase sech pulse train is successfully generated.

Supercontinuum spectrum broadening by one-bobbin compact modules comprised of re-coated comb-like profiled fiber and HNLF

We demonstrated SC spectrum broadening from the original value of 25 nm to 100 nm without changing output power and module size by the efficient pulse compression and novel package of a 6-step CPF and a 500 m HNLF.

Synchronization of a 160-GHz Optical Beat Signal with a 2-ps Optical RZ Signal by Phase-Locked Loop Technique

We demonstrate a phase-locking of 160-GHz beat signal, which is generated by an optical comb generator and a polarization-stable, high-extinction optical filter, to a 10-Gb/s RZ signal with a residual timing jitter of 69 fs.