Masatoshi Kagawa

EA-Modulator-Based Optical Time Division Multiplexing/Demultiplexing Techniques for 160-Gb/s Optical Signal Transmission

In this paper, 160-Gb/s optical-time-division-multiplexing (OTDM) techniques employing electroabsorption (EA)-modulator-based optical multiplexer are described. The optical multiplexer integrates four EA modulators with free-space optics and enables, stably, to generate an authentic 160-Gb/s OTDM signal. The optical multiplexer possesses a switching capability of modulation format, which originates in the thermo-optic effect in EA waveguide, so that it is possible to generate various phase-coded OTDM signals such as carrier-suppressed return-to-zero (CS-RZ) signal by tuning operation temperatures of the EA modulators. By employing the novel 160-Gb/s optical multiplexer, prototypes of 160-Gb/s OTDM transmitter and receiver were developed. EA modulators are also adopted to optical short pulse source at transmitter side, optical time division demultiplexer, and phase-locked loop (PLL) circuit for clock recovery at the receiver side. The 160-Gb/s system prototype exhibited a superior performance maintaining high stability, and its applicability to practical use is discussed, showing experimental results of 160-Gb/s 635 km field trial on Japan Gigabit Network II (JGN II) optical testbed

EA Modulator-Based Optical Multiplexing/Demultiplexing Techniques for 160 Gbit/s OTDM Signal Transmission

160 Gbit/s optical-time-division-multiplexing (OTDM) transmitter/receiver employing electroabsorption (EA) modulators are described. In the 160 Gbit/s OTDM transmitter, the optical multiplexer, which implemented four EA modulators, is used and the generation of authentic 160 Gbit/s OTDM signal is realized. The optical multiplexer also enables to generate the phase-coded OTDM signal such as carrier-suppressed return-to-zero (CS-RZ) signal at 160 Gbit/s by changing driving temperatures of the EA modulators. In the 160 Gbit/s receiver, the EA modulator is also used in an optical demultiplexer and a phase-locked-loop (PLL) for clock extraction. As both optical demultiplexer and PLL are insensitive to polarization state of incoming signal, highly stable operation is achieved. We also show some results of transmission experiment using the developed OTDM transmitter/receiver and discuss the advantage of a switching capability of modulation format in the 160 Gbit/s signal transmission.

Regenerative SPM-Based Wavelength Conversion and Field Demonstration of 160-Gb/s All-Optical 3R Operation

In this paper, we describe a 160-Gb/s all-optical 3R regenerator consisting of a wavelength converter based on self-phase-modulation (SPM) and a non-linear optical loop mirror (NOLM). Particularly, we focus on the simple method to improve the performance of dual-stage wavelength conversion. The dual-stage configuration is useful to alleviate pulse-to-pulse interaction, which degrades both conversion bandwidth and regenerative effect. Total conversion performance, however, strongly depends on waveform distortion at the 1st-stage conversion. Against this, we found that when setting the wavelength shifts of the 1st -stage: ¿¿1 and the 2nd-stage: ¿¿2 to be ¿¿1¿¿2 < 0, i.e., reversing a wavelength shift at the 2nd-stage, the impact of waveform distortion was suppressed and the conversion performance was dramatically improved in comparison with a monotonic shift over both stages (¿¿1¿¿2 > 0). The physical mechanism proving the benefit of the proposed conversion scheme is discussed through both numerical simulations and wavelength conversion experiments. The 3R performance assisted by the regenerative wavelength converter was evaluated by 160-Gb/s field transmission experiments which were conducted in the optical test-bed of Japan Gigabit Network II (JGN II). At a 3R-interval of 380 km, a Q-factor improvement of greater than 7 dB was achieved by applying the wavelength-converter assisted all-optical 3R regenerator.

80-Gb/s error-free transmission over 5600 km using a cross absorption Modulation based optical 3R regenerator

Transoceanic transmission at 80 Gb/s was successfully demonstrated by introducing an optical retiming, reshaping, reamplifier (3R)-signal regenerator using cross-absorption-modulation gate and self-phase-modulation-based wavelength converter. At the 3R repeater spacing of 160 km, 80-Gb/s error-free transmission over 5600 km was achieved. The power penalty at 5600 km was 2 dB, and very clear eye-opening was observed even after 11 200-km transmission.

Control and Stabilization of bit-wise phase correlation in 160 (4 x 40) Gbit/s OTDM signal and its impact on transmission.

Detail of control technique of bit-wise phase correlation in 160 (4 x 40) Gbit/s optical time division multiplexing (OTDM) signal using a phase-correlation monitor based on 1-bit delay asymmetric interferometers (AIFs) is described. The 1-bit delay AIF transforms a bit-by-bit optical phase discontinuity to an optical power variation, so that it enables to quantify the phase-jump between adjacent bits. By use of this unique technique, we experimentally demonstrated stable generation of bitwisely phase-controlled 160 Gbit/s periodical alternate-phase return-to-Zero (APRZ) signal in addition to other different modulation formats such as conventional RZ, carrier suppressed RZ (CS-RZ), pair-wise alternate-phase CSRZ (PAP-CSRZ) and pi/2-APRZ. And long term stability was observed with CS-RZ signal. Also, we show some experimental results of 120 km un-repeatered transmission using standard single mode fiber (SSMF) and then discuss the impact of bit-wise phase change on 160 Gbit/s OTDM transmission performance.

All-optical 3R-signal regeneration at 80 Gbit/s using high-speed electro-absorpsion modulator

An all-optical 3R-signal regeneration using cross-absorption modulation in EAM was investigated and the error free signal regeneration at the bit rate of 80 Gbit/s was achieved with a proper operating condition.

Highly stable 160-Gb/s field transmission employing adaptive PMD compensator with ultra high time-resolution variable DGD generator

We demonstrate highly stable field transmission of 160-Gb/s signal utilizing adaptive PMD compensator, which employing variable DGD generator with ultra high time-resolution of 0.053 fs.

Optical waveguide fabrication by combination of spin-on-glass and plasma-enhanced chemical vapor deposition for optoelectronic integration

Low-loss optical waveguides for optoelectronic integration were realized by the combination of spin-on- glass (SOG) and plasma-enhanced chemical vapor deposi- tion (PECVD). Undercladdings of 20-mm thickness together with cores of 6-mm height and 8-mm width were formed on Si substrates by PECVD and reactive ion etching. Overclad- dings were formed by a combination of SOG and PECVD SiO2 films. This method successfully filled narrow gaps be- tween cores of optical circuits. The refractive index of over- claddings was adjusted by SOG curing and fluorine incorpo- ration in PECVD SiO2 films. A buried-type optical waveguide formed by the combination of SOG and PECVD showed single-mode propagation. Propagation losses and polariza- tion dependent losses at the 1.3-mm wavelength were mea- sured to be 0.3 dB/cm and below 0.15 dB, respectively.

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

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.

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

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.