| 摘要 |
PURPOSE:To make the utilizing efficiency of an optical fiber doubled by adopting a bidirectional transmission line for the transmission line and using the same optical fiber to loop back a loopback signal. CONSTITUTION:An optical signal whose wavelength is lambda1 made incident through an optical fiber 171 on an optical loopback circuit 100 is collimated by a lens 111 and made incident on a polarized light demultiplexer 110, in which the signal is separated into P polarized light and S polarized light. Normally the light made incident on the 1st terminal 131 of a 2X2 optical switch 130 is emitted to a 3rd terminal 133 and the light made incident on a 2nd terminal 132 is emitted to a 4th terminal 134. When a control signal representing the switching of the connection between terminals of the 2X2 optical switch 130 is inputted to a control signal input terminal 135, the connection state between the 2X2 optical switch 130 is switched and the 1st terminals 131 and the 2nd terminal 132, and the 3rd terminal 133 and the 4th terminal 134 are connected respectively. |
