Re-entry-type fiber-optic gyroscope

The invention provides a re-entry-type fiber-optic gyroscope. The fiber-optic gyroscope comprises a light source, a photoelectric detector, a first coupler with two ports, an MIOC (memory input/output controller) with three ports, a second coupler with four ports, and a Sagnac-effect fiber-optic sensitive ring, wherein each two of the four ports of the second coupler are communicated with each other; the light source and the photoelectric detector are connected with a port of the first coupler through an optical fiber; the other port of the first coupler is connected with one port of the MIOC through an optical fiber; the other two ports of the MIOC are respectively connected with two ports, which are not communicated with each other, of the second coupler through an optical fiber; and the Sagnac-effect fiber-optic sensitive ring is connected with other two ports of the second coupler. The fiber-optic gyroscope can meet directional conditions, so that the detection accuracy is improved.