Multi-stage combined optical device

A multi-stage combined optical device having an improved structure which can perform a function as a plurality of optical isolator and can detect incident light power using a single optical isolator. The multi-stage combined optical device includes a first collimator (51) for collimating a ray emitted from a first optical fiber (10), an optical isolator (60) having a first polarizer (61), a Faraday rotator (63), and a second polarizer (65) sequentially disposed on an optical path, a second collimator (55) for focusing the light transmitted through the second polarizer onto a second optical fiber (20), a third collimator (53) facing the light receiving plane of the first polarizer and disposed at a position different from that of the first collimator, for focusing a ray emitted from a third optical fiber (30), and a fourth collimator (57) facing the light emitting plane of the first polarizer and disposed at a position different from that of the second collimator, for focusing a ray emitted from the third collimator via the optical isolator onto a fourth optical fiber (40). Also, the multi-stage combined optical device further includes a tap (67) formed on a light receiving plane (61a) facing the first collimator of the first polarizer, and first and second photodetectors (71, 75) detecting the optical power of rays reflected from the tap (67).