NTT Research and Development 2009 Review of Activities

Overview

In regards to NTT back-bone networks, 40-Gbit/s high-speed transmission is now available. Further improvement in bit rate and capacity, however, is required. At NTT Laboratories, PLC^*1-LN^*2 hybrid-integration technology — utilizing both the high-performance PLCs and LN modulator arrays — was developed. This technology creates an efficient multi-level modulator, such as a compact 40Gbit/s RZ^*3 integrated DQPSK^*4 modulator and a 100Gbit/s DP-QPSK modulator.

Features

• Integration of versatile PLCs and high-performance LN phase shifters
• Very low coupling loss (0.2 dB) between PLC and LN waveguide
• Realization of a low-loss ultra-high-speed modulator (which cannot be realized by using a conventional LN modulator alone)
• Realization of various multi-level modulators based on the same LN phase shifter arrays
• Applicable to various modulation formats (DQPSK, DP-QPSK, OFDM^*5, 64 QAM^*6, etc.)

Application scenarios

• Current high-speed (40-Gbit/s) transmission system
• Near-future very-high-speed (100-Gbit/s) transmission system
• Future ultra-high-speed modulation system and optical signal processing

• *1 PLC: Planar Lightwave Circuit
• *2 LN: LiNbO₃
• *3 RZ: Return to Zero
• *4 DQPSK: Differential Quadrature Phase Shift Keying
• *5 OFDM: Orthogonal Frequency Division Multiplexing
• *6 QAM: Quadrature Amplitude Modulation