Publication IEICE TRANSACTIONS (1976-1990)Vol.E61No.4pp.293-300 Publication Date: 1978/04/25 Online ISSN: DOI: Print ISSN: 0000-0000 Type of Manuscript: PAPER Category: Optical and Quantum Electronics Keyword:
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Summary: With numerical analyses, a design theory of the coupled-waveguide optical modulator with pn junction and planar guides is presented. Some design examples of GaAs homojunction and GaAs-Alx Ga1x As heterojunction devices are also shown. The device is analyzed mainly from the viewpoint of modulating power per bandwidth P/f, and also absorption loss and device dimension. In case of the near-infrared light, it is clear that P/f decreases a great deal with the reduced carrier concentration NB of guide layer. On the contrary, of 10.6 µm and longer wavelength light, P/f decreases by increasing NB. In the former case the modulation is caused mainly by the linear electrooptic effect and in the latter case by the depletion of free carriers in the depletion layer. Heterojunction devices are shown to be superior to homojunction ones because of smaller P/f and smaller absorption loss. The latter advantage is significant at longer wavelength. Smaller P/f and absorption loss are also attained with designing nAnC where nA and nC are refractive indices of p and intermediate layers, respectively. We conclude that this modulator with the pn junction is advantageous not only for near-infrared light but also for longer wavelength.