Development of a 64 Gbps Si Photonic Crystal Modulator

A compact silicon photonic crystal waveguide (PCW) slow-light modulator is presented. The proposed modulator is capable of achieving a 64 Gbps bit-rate in a wide operating spectrum. The slow-light enhances the modulation efficiency in proportion to its group index ng. Two types of 200-μm-long PCW modulators are presented. These are lowand high-dispersion devices, which are implemented using a complementary metal-oxide-insulator process. The lattice-shifted PCW achieved lowdispersion slow-light and exhibited ng ≈ 20 with an operating spectrum Δλ ≈ 20 nm, in which the fluctuation of the extinction ratio is ±0.5 dB. The PCW device without the lattice shift exhibited high-dispersion, for which a large or small value of ng can be set on demand by changing the wavelength. It was found that for a large ng, the frequency response was degraded due to the electro-optic phase mismatch between the RF signals and slow-light even for such small-size modulators. Meander-line electrodes, which bypass and delay the RF signals to compensate for the phase mismatch, are proposed. A high cutoff frequency of 55 GHz was theoretically predicted, whereas the experimentally measured value was 38 GHz. A high-quality open eye pattern for a drive voltage of 1 V at 32 Gbps was observed. The clear eye pattern was maintained for 50–64 Gbps, although the drive voltage increased to 3.5–5.3 V. A preliminary operation of a 2-bits pulse amplitude modulation up to 100 Gbps was also attempted. key words: photonic crystal, optical modulator, silicon photonics

提出了一种紧凑型硅光子晶体波导（PCW）慢光调制器。所提出的调制器能够在较宽的工作光谱范围内实现64 Gbps的比特率。慢光的调制效率与其群折射率ng成正比。介绍了两种200μm长的PCW调制器。它们是低色散和高色散器件，采用互补金属 - 氧化物 - 绝缘体工艺实现。晶格移位的PCW实现了低色散慢光，其群折射率ng≈20，工作光谱Δλ≈20 nm，消光比波动为±0.5 dB。无晶格移位的PCW器件表现出高色散，通过改变波长可按需设置较大或较小的ng值。研究发现，对于较大的ng，即使对于这种小尺寸的调制器，由于射频信号和慢光之间的电光相位失配，频率响应也会下降。提出了曲折线电极，它可绕过并延迟射频信号以补偿相位失配。理论上预测的高截止频率为55 GHz，而实验测量值为38 GHz。在32 Gbps、驱动电压为1 V时观察到高质量的眼图张开。尽管驱动电压增加到3.5 - 5.3 V，但在50 - 64 Gbps时仍能保持清晰的眼图。还尝试了高达100 Gbps的2位脉冲幅度调制的初步操作。 关键词：光子晶体，光调制器，硅光子学