Compact electro-optic single sideband modulators utilizing miniaturized branch-line couplers on LiNbO3 substrate

Katsuyuki Yamamoto, Tadashi Kawai, Akira Enokihara, Tetsuya Kawanishi

Research output: Contribution to journalArticlepeer-review


Optical single sideband (SSB) modulation with theMach- Zehnder (MZ) interferometer was realized by integrating the modulation electrode with the branch-line coupler (BLC) as a 90-degree hybrid onto the modulator substrate. In this paper, BLCs of the microsrtip-line structure were miniaturized on modulator substrates, LiNbO3 (LN), to realize more compact optical SSB modulators. We introduced two techniques of miniaturizing the BLC, one is using periodically installed open-circuited stabs and the other is installing series capacitors. Compared with a conventional pattern of the BLC, an area of the miniaturized BLC by using periodically installed open-circuited stubs was reduced to about 50%, and that by installing series capacitors was done to about 60%. The operation of these miniaturized BLCs was experimentally confirmed as the 90-degree hybrid at around 10GHz. Output ports of each miniaturized BLC were directly connected with the modulation electrode on the modulator substrate. Thereby, we fabricated two types of compact SSB modulators for 1550nm light wavelength. In the experiments, the optical SSB modulation was successfully confirmed by the output light spectra and the sideband suppression ratio of more than 30dB were observed.

Original languageEnglish
Pages (from-to)769-776
Number of pages8
JournalIEICE Transactions on Electronics
Issue number8
Publication statusPublished - 2015 Aug 1
Externally publishedYes


  • Branch-line coupler
  • Electro-optic modulators
  • Microwavev photonics
  • Single sideband modulation

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


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