Embedded type optically irreversible circuit

An optical isolator comprising an optical element comprised of a plurality of incoming side optical members, a Faraday rotator and a plurality of outgoing side optical members superposed in this order in the direction of an optical path, an optical fiber or optical waveguide having a light axis, a slot defined by a pair of walls extending across the optical fiber or optical waveguide in a direction slanted at a slant angle with respect to the light axis, the optical element being inserted in the slot, and spaces between the optical element and the walls defining the slot being filled with optical adhesive portions, at least one of interfaces between the incoming side optical members, the Faraday rotator, the outgoing side optical members and the optical adhesive portions being inclined at an angle opposite to the wall on an incoming side of the slot as measured from a plane normal to the light axis, in such manner tat the following relationship is satisfied:

• nf<n1*L1/L+n2*L2/L+n3*L3/L+ . . . <nr
• where nf:
• refractive index of the optical fiber,
• L:
• distance from an incoming side optical fiber
• to the Faraday rotator,
• n1, n2, n3. . .:
• refractive indexes of the optical members inserted between the incoming side optical fiber and the Faraday rotator,
• L1, L2, L3. . .:
• Thickness of materials inserted between the incoming side optical fiber and the Faraday rotator,
• nr:
• refractive index of the Faraday rotator, the materials inserted between the incoming side optical fiber to the Faraday rotator are comprised of a polarizer and refractive index of the polarizer is no more than refractive index of the Faraday rotator.