Koji Inafune

Highly efficient phase-sensitive parametric gain in periodically poled LiNbO 3 ridge waveguide

We have developed a periodically poled LiNbO3 (PPLN) ridge waveguide device and experimentally demonstrated a phase-sensitive optical parametric amplification. The highly efficient net phase-sensitive parametric gain of +18.6  dB is obtained in a cascaded second harmonic generation and difference frequency generation configuration. The phase-sensitive gain is greater by +5.8  dB in comparison with the phase-insensitive gain. We successfully confirmed the phase-sensitive amplification with a high gain in the PPLN ridge waveguide.

Chirped Periodically Poled

We developed a periodically poled LiNbO3 wavelength converter with its nonlinear coupling strength changed along the propagation length to improve the quasi-phase-matched (QPM) wavelength bandwidth. The apodization is realized by sampling the QPM grating to attain fabrication easiness. The wavelength response showed a broad and flat-top wavelength conversion characteristic in a second harmonic generation. The QPM bandwidth of the wavelength conversion was 2.2 nm, which is sufficiently broad to convert optical pulses for a 160-Gb/s system.

{\rm LiNbO}_{3}

We demonstrate stabilization of a delay interferometers (DI) for variable bit-rate DPSK receiver from 40 Gbit/s up to 160 Gbit/s using a wavelength tunable CW laser. The phase difference is continuously tunable by tuning the CW laser. The BER of the received 41.25 Gbit/s DPSK signal was successfully stabilized. No noticeable degradation was observed in the eye patterns when the bit rate is 82.5 Gbit/s and 165 Gbit/s.

Wavelength Converter With Apodization Structure

The performance monitoring technique using pre-scaled clock-tone detection was proposed and the principle of the technique was explained. The technique has advantage of simple contracture with very low electrical bandwidth. In addition, applicability of proposed techniques to 160-Gb/s RZ-BPSK signal and 40-Gb/s NRZ-OOK signal was discussed. In spite of the lack of clock-tone spectra in BPSK signal, the proposed technique generates the pre-scaled signal and is able to detect waveform distortion by chromatic dispersion and OSNR degradation. Furthermore, possibility to separate the distortion origin of 40-Gb/s NRZ-OOK signal was reveled by adding revealed 25-ps and 12.5-ps delayed interferometer.

Stabilization of a delay interferometer for variable bit-rate DPSK receiver from 40 Gbit/s up to 160 Gbit/s

We demonstrate a 160 Gbit/s RZ/CS-RZ OTDM multiplexer, where optical phase between adjacent channels was stabilized. The use of optical bandpass filter to pick up carrier or sideband component of the multiplexer output eliminates the needs for a tunable CW laser. The optical spectrum of the output was stabilized with temperature change between 26 °C and 32 °C.

Application of performance monitor using pre-scaled clock-tone detection technique to 160-Gb/s RZ-BPSK signal and 40-Gb/s NRZ-OOK signal

We have designed and developed a nonlinear-optic wavelength converter with periodically poled LiNbO3 (PPLN) waveguides for optical fiber communication systems. The wavelength conversion module comprises two parallel PPLN ridge waveguide devices for a polarization-independent operation. We demonstrate highly efficient wavelength conversions and amplifications based on a cascaded second harmonic generation (SHG) and difference frequency generation (DFG), and optical parametric amplifier (OPA). The wavelength conversion efficiencies and the signal gains more than 20 dB are achieved for both orthogonal transverse magnetic (TM) polarization and transverse electric (TE) polarization in the module.

Active bit-wise phase stabilization in 160 Gbit/s RZ/CS-RZ OTDM multiplexer

We demonstrate a stabilization of 40 Gbit/s optical DQPSK receiver using a wavelength tunable CW laser. The BER of the received data was successfully stabilized.