Large Electro-Optical Modulation of a Field-Effect Transistor-Type Waveguide Modulator Using α-Sexithienyl

An optical waveguide modulator having a held-effect transistor-type electrode using a thiophene oligomer, alpha-sexithienyl, has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The device also functions as a field-effect transistor (FET). The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced or injected by negative bias.