Optical waveguide element, optical modulation device using optical waveguide element, and optical transmission device using optical waveguide element
Provided is an optical waveguide element including spot size conversion means with suppressed optical insertion loss without complicating a manufacturing process. An optical waveguide element includes an optical waveguide substrate ( 4 ) having a rib-type optical waveguide ( 10 ) formed of a material having an electro-optic effect, and spot size conversion means for changing a mode field diameter of a light wave propagating through the optical waveguide at a position where an input end or an output end of the rib-type optical waveguide ( 10 ) is formed, in which the spot size conversion means includes a first configuration layer ( 1 ) that is connected to the rib-type optical waveguide ( 10 ) and includes a tapered portion ( 11 ) in which a width of the optical waveguide expands, a second configuration layer ( 2 ) that is laminated on the first configuration layer ( 1 ) and has a width narrower than a width of the first configuration layer ( 1 ), and a third configuration layer ( 3 ) that is disposed to cover the second configuration layer ( 2 ) excluding a part of the second configuration layer ( 2 ) close to the rib-type optical waveguide and has a width wider than the width of the second configuration layer ( 2 ).
1 . An optical waveguide element comprising:
an optical waveguide substrate having a rib-type optical waveguide made of a material having an electro-optic effect; and
spot size conversion means for changing a mode field diameter of a light wave propagating through the optical waveguide at a position where an input end or an output end of the rib-type optical waveguide is formed,
wherein the spot size conversion means includes
a first configuration layer that is connected to the rib-type optical waveguide and includes a tapered portion in which a width of the optical waveguide expands,
a second configuration layer that is laminated on the first configuration layer and has a width narrower than a width of the first configuration layer, and
a third configuration layer that is disposed to cover the second configuration layer excluding a part of the second configuration layer close to the rib-type optical waveguide and has a width wider than the width of the second configuration layer.
2 . The optical waveguide element according to claim 1 ,
wherein a refractive index of a material constituting the second configuration layer is higher than a refractive index of a material constituting the first configuration layer or a material constituting the third configuration layer.
3 . The optical waveguide element according to claim 1 ,
wherein a tip end portion of the second configuration layer of a rib-type optical waveguide-side is disposed on the rib-type optical waveguide.
4 . The optical waveguide element according to claim 1 ,
wherein an end surface of the third configuration layer of a rib-type optical waveguide-side is disposed to have an inclination other than 90 degrees with respect to a traveling direction of a light wave propagating through the second configuration layer.
5 . The optical waveguide element according to claim 1 ,
wherein an end surface structure of the spot size conversion means positioned on an end portion side of the optical waveguide substrate is configured such that the first configuration layer and the third configuration layer are disposed to surround the second configuration layer.
6 . The optical waveguide element according to claim 1 ,
wherein an end surface structure of the spot size conversion means positioned on an end portion side of the optical waveguide substrate is configured such that the first configuration layer and the third configuration layer are disposed not to expose the second configuration layer.
7 . The optical waveguide element according to claim 1 ,
wherein the optical waveguide substrate comprises a thin plate in which the optical waveguide is formed, and a holding substrate that holds the thin plate, and a refractive index of a material constituting the holding substrate is lower than a refractive index of a material constituting the thin plate.
8 . The optical waveguide element according to claim 1 ,
wherein the optical waveguide substrate comprises a thin plate in which the optical waveguide is formed, a holding substrate that holds the thin plate, and an intermediate layer between the thin plate and the holding substrate, and a refractive index of a material constituting the intermediate layer is lower than a refractive index of a material constituting the thin plate.
9 . An optical modulation device comprising:
the optical waveguide element according to any one of claims 1 to 8 that includes a modulation electrode for modulating the light wave propagating through the optical waveguide;
an electronic circuit that amplifies a modulation signal to be input to the modulation electrode of the optical waveguide element; and
a case that houses the optical waveguide element and the electronic circuit therein.
10 . An optical transmission apparatus comprising:
the optical modulation device according to claim 9 ; and
an electronic circuit that outputs a modulation signal for causing the optical modulation device to perform a modulation operation.