We numerically investigated the modulation characteristics of a carrier-depletion InGaAsP optical modulator with a lateral PN junction fabricated on a III-V-on-insulator (III-V-OI) wafer. Owing to the large electron-induced refractive index change in InGaAsP, the InGaAsP optical modulator with a doping concentration of 2 ' 10 18 cm %3 in the PN junction exhibited a phase modulation efficiency V π L of 0.17 Vcm, which was 6 times smaller than that of a Si modulator with the same structure. The

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... ping concentration dependence revealed that αV π L, which is a product of the insertion loss α and V π L, can significantly be improved using InGaAsP when the doping concentration was as high as 1 ' 10 18 cm %3 . Thus, we concluded that the phase modulation efficiency and insertion loss can be improved simultaneously using InGaAsP instead of Si for a carrier-depletion optical modulator with a lateral PN junction.