| 摘要 |
PROBLEM TO BE SOLVED: To provide a cross waveguide with a filter function which can reduce noise and stabilize an LD generating signal light. SOLUTION: A multi-layered film filter 116 is used in the center of the cross waveguide 110. An optical fiber 113 connected to a port 2 is provided with a grating 112 having a characteristic of reflecting test light. The test light generated by an OTDR device 115 is made incident from a port 4, reflected by the multi-layered film filter 116, and transmitted from a port 3 to an optical line 120. At this time, return test light which passes through the multi-layer film filter 116 is also transmitted to the port 2 although it is a little, but a fiber grating 112 reflects the return test light, so that none of the return test light is made incident on a transmitter 114. |
