We developed a compact InP-based DP-IQ modulator for small-form-factor pluggable coherent transceivers. The modulator achieves 112-Gb/s DP-QPSK modulation with a driving voltage of 6 Vppd. In addition, it provides 86-Gb/s DP-16 QAM signal generation and 240-km transmission with negligible degradation of BER performance. The halfwavelength voltage of our recent device is 1.9 V, and a high median extinction ratio of over 32 dB was achieved for more than 1,400 child MZ modulators. We have also proposed an athermal InP-based twin IQ modulator that enables us to use a modulator in a TEC-free operation. It contributes to lowering the power consumption of transceivers. Under a constant driving condition, there is little change in 56-Gb/s x 2 QPSK modulation characteristics in the range of 20 to 80°C.
We realized high-speed and low driving voltage InP-based Mach Zehnder modulators with an npin high-mesa waveguide
structure and traveling-wave electrodes. A full C-band 40-Gbit/s DPSK signal was successfully generated using a
compact tunable wavelength transmitter module, which incorporated a tunable DFB laser array as a wavelength tunable
laser and an InP MZM in one package. The MZM had a low driving voltage of 3 Vpp in a push-pull driving
configuration. We have demonstrated 112 Gbit/s RZ-DP-QPSK modulation using two InP MZM modules. One
modulator was used as a pulse carver in a push-pull configuration, and the other was used as an IQ modulator in a dual-drive
configuration. Since we used an RZ pulse carver to remove the transient region, we obtained clear eye openings
without any amplitude ripple. We also demonstrated 50 Gbit/s (12.5 GSymbol/s x 4) 16QAM signal generation
employing a novel dual-drive modulation method consisting of a single MZM. We utilized the electro-absorption
characteristics of an InP semiconductor to adjust the QPSK amplitude. We confirmed that a single MZM operated as a
DPSK, a QPSK, and a 16QAM modulator with the same device. We believe these modulators to be suitable for next
generation optical transmission systems.
We propose a novel InP-based traveling-wave electrode Mach-Zehnder modulator. It has an n-i-n isotype heterostructure to reduce both electrical signal loss and the optical loss caused by the p- type cladding layer. This device provides a large modulation bandwidth of more than 40 GHz. We have also developed a compact
push-pull driven modulator module. We obtained error-free operation for a 40-Gbit/s NRZ signal in a push-pull configuration with a very low driving voltage of 1.3 Vpp. We also confirmed that the modulator has low chirp characteristics by demonstrating a 100-km SMF transmission with a penalty of less than 1.5 dB for a 10-Gbit/s NRZ signal.
Recent progress on soliton transmission is described, in which dispersion management plays an important role in increasing the power margin and the dispersion tolerance in TDM and WDM systems. The quality of the dispersion-managed soliton is compared with RZ and NRZ pulses.