The Best Paper Award
Dual Evanescently Coupled Waveguide Photodiodes with High Reliability for over 40-Gbps Optical Communication Systems
Kazuhiro Shiba 　・　Yasuyuki Suzuki 　・　Sawaki Watanabe　・　Tadayuki Chikuma
Takeshi Takeuchi 　・　Kikuo Makita
（英文論文誌C　平成22年12月号掲載）
　Over 40-Gbps optical communication systems are required by a demand of high throughput multimedia service networks. In those communication systems, advanced optical modulation formats like differential phase shift keying (DPSK) and quadrature phase shift keying (QPSK) are needed because of their high frequency efficiency. In such systems, dual Photo Diode (dual PD) is one of the key semiconductor devices which dominate the receiver performance. High speed performance, high responsivity and high reliability are required to dual PDs. Highly symmetrical characteristics between the two PDs should also be achieved to improve a signal-noise ratio, thus the dual PDs are desired to be integrated monolithically into one chip. Moreover, robustness against high input power is also required to the PDs, because an EDFA must be deployed in the transmission line.
　 In their paper, the novel evanescently coupled waveguide PDs (EC-WG-PDs) were proposed for the purpose described above and shown the transfer matrix method to calculate optimum design. In addition, excellent characteristics (50-GHz bandwidth with a responsivity of 0.95 A/W) were demonstrated experimentally.
　 Utilizing the waveguide structure which enables a low capacitance and a short carrier transit time, dual PDs with both a high responsivity and a high speed performance were realized. Furthermore, EC-WG structure, where the light is gradually coupled into InGaAs absorption layer on the waveguide layer, was useful. In the EC-WG structure, photo-generated carriers are distributed along the whole waveguide. This allows for more robust operation than conventional waveguide PIN-PDs under high input power operation.
　 Thus, it is great significance for next generation high speed communication systems to show the theoretical analysis of novel high speed photodiodes and demonstrate the high speed performance experimentally. Moreover, compact and low power consumption RZ-DPSK receiver modules including the dual EC-WG-PDs and differential transimpedance amplifiers (TIAs) newly developed were also presented. Furthermore they demonstrated ultra high speed operation up to 100-Gbps. As mentioned above, their paper is worthy of the best paper award.

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