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Abstract

The invention relates to an optical integrated circuit for bidirectional communications which is able to achieve a downsizing and high integration with the production cost thereof decreased. An optical waveguide circuit is formed on a substrate and a photo diode (PD) is connected to the outgoing end side thereof. The optical waveguide circuit has a circuit of an optical wavelength division multiplexer which causes communication signal light (.lambda.1) inputted from a bidirectional light input/output port to be transmitted through a communication light selective transmission filter and to be outputted from a communication light output port and causes non-communication light (.lambda.2) to be reflected by the communication light selective transmission filter and to outgo through a non-communication light output port. A piezoelectric element is provided on the upper part at the outgoing side of the communication light output port. When the communication signal light passing through the optical waveguide circuit is inputted into the PD 8, the PD 8 is actuated in the reception mode to receive communication signal light and is not driven in the transmission mode to reflect communication signal light toward the optical waveguide circuit side by a high reflection coating film. The reflection light is given polarization plane modulation by the piezoelectric element, and the polarization plane modulated light is transmitted from the bidirectional light input/output port.

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First Claim