Resin optical waveguide
A resin optical waveguide containing a core, an under cladding and an over cladding having refractive indices lower than that of the core, in which the resin optical waveguide has, at one end side of, a core-exposed section at which the over cladding is not present and the core and the under cladding nearby the core are exposed and, of the under cladding, a portion corresponding to the core-exposed section has a first layer and a second layer that satisfy a certain condition.
1. A resin optical waveguide comprising a core, an under cladding and an over cladding having refractive indices lower than that of the core,
wherein the resin optical waveguide comprises, at one end side thereof, a core-exposed section at which the over cladding is not present and the core and the under cladding nearby the core are exposed and,
of the under cladding, a portion corresponding to the core-exposed section comprises a first layer and a second layer that satisfy the following (1) to (3):
(1) the first layer and the second layer differ from each other in a distance from an interface with the core or an exposed surface of the under cladding, and the first layer is positioned on a near side to these surfaces and the second layer is positioned on a far side from the interface with the core or the exposed surface of the under cladding;
(2) the first layer is positioned within 15 μm in the distance from the interface with the core or the exposed surface of the under cladding; and
(3) the first layer and the second layer differ from each other in refractive index, and the first layer has a refractive index higher than that of the second layer,
wherein the first layer has a thickness t of 15 μm or less, and wherein the resin optical waveguide has a product (t×(n 1,max -n 2,max )) of the thickness t of the first layer and a difference (n 1,max -n 2,max ) between a maximum value n 1,max of the refractive index of the first layer and a maximum value n 2,max of the refractive index of the second layer being from 0.001 to 0.2 μm.
2. The resin optical waveguide according to claim 1 , wherein the core-exposed section has a length of 100 μm or more in a light propagation direction.
3. The resin optical waveguide according to claim 1 , having a difference (n 1,max -n 2,max ) between a maximum value n 1,max of the refractive index of the first layer and a maximum value n 2,max of the refractive index of the second layer being 0.001 or more.
4. The resin optical waveguide according to claim 1 , having a difference (n′ ,max -n 1,max ) between a maximum value n′ ,max of a refractive index of the core and a maximum value n i,max of the refractive index of the first layer being from 0.008 to 0.02.
5. The resin optical waveguide according to claim 1 , wherein the resin optical waveguide is a single-mode optical waveguide at a wavelength of at least one of 1,310 nm and 1,550 nm.
6. The resin optical waveguide according to claim 1 , wherein the resin optical waveguide has a core size of from 1 to 10 μm.
7. The resin optical waveguide according to claim 1 , wherein the core of the resin optical waveguide is composed of a resin containing fluorine.
8. A resin optical waveguide chip, comprising the resin optical waveguide according to claim 1 connected with a silicon optical waveguide at the core-exposed section of the resin optical waveguide.