Patent ID: 8401351

Claim:
A 90-degree hybrid, comprising: a planar lightwave circuit (PLC) chip having a planar lightwave circuit; and a 90-degree hybrid circuit formed within the planar lightwave circuit and mixing a modulated signal light and a local oscillation light to output, the 90-degree hybrid circuit including: a first Y-branch coupler branching the signal light; a second Y-branch coupler branching the local oscillation light; a first coupler causing interference between one of two signal lights branched by the first Y-branch coupler and one of two local oscillation lights branched by the second Y-branch coupler; a second coupler causing interference between the other one of two signal lights branched by the first Y-branch coupler and the other one of two local oscillation lights branched by the second Y-branch coupler; a first path for connecting the first Y-branch coupler and the first coupler and for causing one of the two branched signal lights to propagate therethrough, the first path having at least one bend waveguide and at least one straight waveguide; a second path for connecting the first Y-branch coupler and the second coupler and for causing the other one of the two branched signal lights to propagate therethrough, the second path having the same number of bend waveguides as the first path and the same number of straight waveguides as the first path; a third path for connecting the second Y-branch coupler and the first coupler and for causing one of the two branched local oscillation lights to propagate therethrough; and a fourth path for connecting the second Y-branch coupler and the second coupler and for causing the other one of the two branched local oscillation lights to propagate therethrough, wherein the first path and the second path are configured so as to have the same optical path length, the third path and the fourth path are configured so that an optical path difference between one of the two branched local oscillation lights and the other one of the two branched local oscillation lights becomes 90 degrees in terms of phase, at least one of the bend waveguides of the first path and the bend waveguide of the second path are in a one-to-one correspondence relationship, respectively, and at least one straight waveguide of the first path and the straight waveguide of the second path are in a one-to-one correspondence relationship, respectively, the bend waveguide of the second path has the same shape as or an inverted shape of the bend waveguide of the first path, the both waveguides being in a one-to-one correspondence relationship, the straight waveguide of the second path has the same shape as the straight waveguide of the first path, the both waveguides being in a one-to-one correspondence relationship, the second path and the third path intersect with each other, and an intersection angle α at which the second path and the third path intersect with each other is set to a range from 60° to 90°.