Patent ID: 7317854

Claim:
A waveguide comprising: first and second transmission areas which transmit an input optical signal; and a coupling area provided between the first transmission area and the second transmission area; wherein a width of the coupling area is less than a width of the first and second transmission areas; and wherein each of the first transmission area, the second transmission area, and the coupling area comprises: a core through which an optical signal is transmitted; and a cladding layer provided on an upper portion, a lower portion, and a side surface of the core, the cladding layer having a refractive index lower than a refractive index of the core; and wherein the coupling area weakens a mode confinement of the optical signal and at least part of the optical signal transmitted through the transmission areas is branched to a neighboring optical member; wherein a gap between the coupling area and the neighboring optical member is approximately equal to or greater than a width of the coupling area; and wherein a difference between the refractive index of the core and the refractive index of the cladding layer is 2 or more.