半導体マッハツェンダ変調器の吸収平衡化変調の検討

摘要

半導体マッハツェンダ（MZ）変調器は，変調導波路において変調電圧に応じて屈折率変化と同時に吸収量変化を生じる.そのためMZ変調器を構成する2アーム間で，吸収量変化に非平衡がある場合，位相変調出力光の強度が符号によって異なり，伝送特性を劣化させる.本稿ではこの課題に対し，2アーム間で吸収量変化を平衡化し，変調時の符号の強度を等しくすることで，伝送特性を改善する手法を提案し，その妥当性を理論的，実験的に示す.10GbpsDPSK変調において，提案手法により符号間の強度差を0.1dB以下に抑えることでQ値が1．4dB改善した．%Semiconductor Mach-Zehnder (MZ) Modulators generally use quantum-confined-Stark effect (QCSE) at the phase modulation waveguides. The QCSE causes light absorption corresponding to refractive index change. Because this relation is owing to Kramers-Kronig relation, the absorption is inevitable in phase modulation by semiconductor MZ modulators. Unbalance of the absorption change between two arms of MZ Modulator results in difference between output light intensities of different symbols and deterioration of the Q factor of the modulator. In this paper, we propose a novel method of balancing light absorption at two arms of a semiconductor MZ modulator, and confirmed it both theoretically and experimentally. It depressed the symbol intensity difference within 0.1 dB and the Q factor was improved in lOGbps differential-phase-shift-keying format by 1.4dB.