Self-diagnosis alarm device and method of optical path fault for optical fiber current transformer

The invention discloses a self-diagnosis alarm device and method of an optical path fault for an optical fiber current transformer. The device comprises a first coupler; a first port, a second port, athird port and a fourth port of the first coupler are connected with a light source, a first detector, a Y waveguide and a second detector correspondingly and respectively; the Y waveguide is furtherconnected to a third detector and a lambda/four wave plate through a second coupler; and the first detector, the second detector, and the third detector are connected to a modem module. Light entering the lambda/four wave plate through the second coupler is transformed into two beams of circularly polarized light and then the two beams of circularly polarized light enters a sensitive fiber directly; after the sensitive fiber transmits the light to a reflecting mirror, the light is reflected and then passes through the sensitive fiber and the lambda/four wave plate successively and then returns to the Y waveguide to fo