InP-Based Photodetectors Monolithically Integrated with 90° Hybrid toward Over 400Gb/s Coherent Transmission Systems

Hideki YAGI  Takuya OKIMOTO  Naoko INOUE  Koji EBIHARA  Kenji SAKURAI  Munetaka KUROKAWA  Satoru OKAMOTO  Kazuhiko HORINO  Tatsuya TAKEUCHI  Kouichiro YAMAZAKI  Yoshifumi NISHIMOTO  Yasuo YAMASAKI  Mitsuru EKAWA  Masaru TAKECHI  Yoshihiro YONEDA  

IEICE TRANSACTIONS on Electronics   Vol.E102-C   No.4   pp.347-356
Publication Date: 2019/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.2018ODI0006
Type of Manuscript: INVITED PAPER (Special Section on Progress in Optical Device Technology for Increasing Data Transmission Capacity)
digital coherent transmission,  InP,  90° hybrid,  multimode interference structure,  p-i-n photodiode,  

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We present InP-based photodetectors monolithically integrated with a 90° hybrid toward over 400Gb/s coherent transmission systems. To attain a wide 3-dB bandwidth of more than 40GHz for 400Gb/s dual-polarization (DP)-16-ary quadrature amplitude modulation (16QAM) and 600Gb/s DP-64QAM through 64GBaud operation, A p-i-n photodiode structure consisting of a GaInAs thin absorption and low doping n-typed InP buffer layers was introduced to overcome the trade-off between short carrier transit time and low parasitic capacitance. Additionally, this InP buffer layer contributes to the reduction of propagation loss in the 90° hybrid waveguide, that is, this approach allows a high responsivity as well as wide 3-dB bandwidth operation. The coherent receiver module for the C-band (1530nm - 1570nm) operation indicated the wide 3-dB bandwidth of more than 40GHz and the high receiver responsivity of more than 0.070A/W (Chip responsivity within the C-band: 0.130A/W) thanks to photodetectors with this photodiode design. To expand the usable wavelengths in wavelength-division multiplexing toward large-capacity optical transmission, the photodetector integrated with the 90° hybrid optimized for the L-band (1565nm - 1612nm) operation was also fabricated, and exhibited the high responsivity of more than 0.120A/W over the L-band. Finally, the InP-based monolithically integrated photonic device consisting of eight-channel p-i-n photodiodes, two 90° hybrids and a beam splitter was realized for the miniaturization of modules and afforded the reduction of the total footprint by 70% in a module compared to photodetectors with the 90° hybrid and four-channel p-i-n photodiodes.