Munehiko Nagatani

160-Gbps Nyquist PAM4 transmitter using a digital-preprocessed analog-multiplexed DAC

We proposed an ultra-wide-band DAC configuration consisting of a digital preprocessor, two sub-DACs, and an analog multiplexer. The output bandwidth is nearly doubled from that of the sub-DACs. The idea was verified by a 160-Gbps Nyquist PAM4 transmission.

5 × 1-Tb/s PDM-16QAM transmission over 1,920 km using high-speed InP MUX-DAC integrated module

We demonstrate WDM transmission of 75-Gbaud PDM-16QAM signals over 1,920 km. InP-based high-speed and compact MUX-DAC integrated modules (bandwidth exceeds 40 GHz) enable the long haul transport of 1-Tb/s superchannels composed of just two subcarriers.

Single-carrier 1-Tb/s PDM-16QAM transmission using high-speed InP MUX-DACs and an integrated OTDM modulator.

We generated a 1-Tb/s single-carrier PDM-16QAM signal using a single optical modulator with external PDM emulation. To achieve the high symbol rate of 125 Gbaud, we used high-speed InP MUX-DAC modules, each consisting of six 2:1 MUXs and a 6-bit DAC in a single package, and an integrated optical modulator, which contains a generator of two orthogonal CSRZ pulse trains for spectrally efficient OTDM followed by IQ modulators for each tributary. The signal was received and demodulated without using any time-domain demultiplexing. Transmission over 80-km SSMF was demonstrated.

Coded Eight-Dimensional QAM Technique Using Iterative Soft-Output Decoding and Its Demonstration in High Baud-Rate Transmission

We proposed coded eight-dimensional (8-D) quadrature amplitude modulation (QAM) and experimentally demonstrated in high baud-rate transmission. Both high baud rate and multilevel modulation techniques are necessary for large capacity long haul transmission without increasing the number of transponders. However, optical signal-to-noise ratio (OSNR) tolerance of higher order modulation is low due to the short minimum Euclidean distance. Therefore, to relax OSNR tolerance by enlarging minimum Euclidean distance, we proposed 8-D modulation formats. The spectral efficiency of the proposed coded 8-D-16QAM, 8-D-32QAM, and 8-D-64QAM is equivalent to polarization division multiplexed (PDM)-8QAM, PDM-16QAM, and PDM-32QAM, respectively. To confirm the applicability of the proposed 8-D modulation to high baud rate transmission, we experimentally demonstrated 96-GBaud 8-D-16QAM wavelength division multiplexed transmission over 5,-252 km using iterative soft output decoding. The line data rate is 576-Gbps and a net rate 478-Gbps. At the same spectral efficiency, 8-D-16QAM using iterative soft output decoding can expand the transmission reach by 1212 km compared to conventional PDM-8QAM.

High-performance compound-semiconductor integrated circuits for advanced digital coherent optical communications systems

Communications traffic over photonic networks is exponentially increasing due to the spread of broadband applications. To cope with the rapid growth, novel 100-Gb/s digital coherent systems have been deployed recently in optical core networks. Further research and development of digital coherent technologies with channel rates of beyond 100Gb/s is now being conducted. Optical transceivers for such high-speed communications systems need high-performance analog and mixed-signal electronic circuits such as optical modulator drivers, transimpedance amplifiers (TIAs), analog-to-digital converters (ADCs), and digital-to-analog converters (DACs). Compound-semiconductor integrated circuits (ICs) have played key roles in this technical field. This paper reviews recent trends in compound-semiconductor ICs for such advanced digital coherent optical communications systems and presents our latest results based on InP heterojunction bipolar transistor (HBT) technology.