Traveling-Wave Mach-Zehnder Modulator Integrated With Electro-Optic Frequency-Domain Equalizer for Broadband Modulation
Yuya Yamaguchi, Pham Tien Dat, Shingo Takano, Masayuki Motoya, Shotaro Hirata, Yu Kataoka, Junichiro Ichikawa, Satoshi Oikawa, Ryo Shimizu, Naokatsu Yamamoto, Kouichi Akahane, Atsushi Kanno, Tetsuya Kawanishi
Abstract
Broadband modulator is a key component of future high-capacity and high-baud-rate optical fiber communication. An electro-optic (EO) frequency-domain equalizer is proposed and investigated to increase the 3-dB bandwidth of optical modulators. The equalizer can be integrated with conventional traveling-wave modulators using a crossing waveguide, U-turn waveguide, or ferroelectric-domain-inversion. The 3-dB bandwidth of the modulator can be doubled by integrating the equalizer. As a theoretical consideration, we modeled several types of EO equalizers and investigated the function and parameter dependency of the equalizers in detail. For the experimental demonstration, a titanium-diffused lithium niobate optical waveguide modulator integrated with the EO equalizer was fabricated. The optical loss including fiber-coupling was as low as 5.4 dB, and the half-wave voltage was 3.7 V. The measured electro-optic response at 110 GHz is –0.4 dB, and that of the 3-dB bandwidth is larger than 110 GHz, which is the upper frequency limit of our measurement equipment. The 3-dB bandwidth of the modulator estimated using the fitting curve obtained from the measured electrical propagation loss of the modulator electrode was approximately 200 GHz.