Optical module and fabrication method
An optical module includes an optical waveguide that transmits and outputs signal light; a circuit board that transmits the signal light output from the optical waveguide, and includes a low refractive-index portion that neighbors and surrounds a transmissive portion and has a lower refractive index than the transmissive portion, which transmits the signal light; and a light-receiving element that includes, on a side toward the circuit board, a light-receiving portion that receives the signal light that has transmitted through the circuit board, where the signal light is reflected toward the light-receiving element at a boundary surface between the transmissive portion and the low refractive-index portion.
1. An optical module comprising:
an optical waveguide that transmits and outputs signal light;
a circuit board that transmits the signal light output from the optical waveguide, and includes a low refractive-index portion that neighbors and surrounds a transmissive portion and has a lower refractive index than the transmissive portion, which transmits the signal light; and
a light-receiving element that includes, on a side toward the circuit board, a light-receiving portion that receives the signal light that has transmitted through the circuit board, wherein
the signal light is reflected toward the light-receiving element at a boundary surface between the transmissive portion and the low refractive-index portion,
the circuit board includes a ground electrode at a surface on a side opposite of a circuit board surface toward the light-receiving element,
the low refractive-index portion is provided up to a bottom of the circuit board, and
the transmissive portion is fixed by the ground electrode provided on the circuit board.
2. The optical module according to claim 1 , wherein
a circuit pattern is formed on the circuit board, and
the light-receiving element is connected to the circuit pattern formed on the circuit board.
3. The optical module according to claim 1 , wherein a cross section of the transmissive portion perpendicular to a traveling direction of the signal light becomes smaller toward the light-receiving element.
4. The optical module according to claim 1 , wherein
the light-receiving portion has a circular light-receiving surface, and
the transmissive portion has a circular cross section perpendicular to the traveling direction of the signal light.
5. The optical module according to claim 1 , further comprising another circuit board that is layered on the circuit board, on a side toward the optical waveguide and transmits the signal light output from the optical waveguide to the light-receiving portion.
6. The optical module according to claim 1 , wherein
the circuit board is provided in plurality and layered one on another, and
the light-receiving element receives the signal light that has been transmitted through a plurality of transmissive portions.
7. The optical module according to claim 1 , wherein the circuit board is a flexible printed circuit board that includes a polyimide thin film.
8. The optical module according to claim 1 , wherein the low refractive-index portion is an air layer formed by removing a part of the circuit board.
9. A fabrication method of an optical module that includes an optical waveguide that transmits and outputs signal light, a circuit board that transmits the signal light output from the optical waveguide, and a light-receiving element that includes, on a side toward the circuit board, a light-receiving portion that receives the signal light that has been transmitted through the circuit board, the fabrication method comprising:
making a circuit pattern on the circuit board;
forming, on the circuit board, a low refractive-index portion that neighbors and surrounds a transmissive portion and has a lower refractive index than the transmissive portion, which transmits the signal light; and
mounting the optical waveguide and the light-receiving element on the circuit board after the making and the forming, wherein
the circuit board includes a ground electrode at a surface on a side opposite of a circuit board surface toward the light-receiving element, and
the low refractive-index portion is formed at the forming by removing the circuit board around the transmissive portion such that the circuit board is penetrated and the transmissive portion is fixed onto the ground electrode.
10. The fabrication method according to claim 9 , wherein at the mounting, the light-receiving element is connected to the circuit pattern made on the circuit board at the making.
11. The fabrication method according to claim 9 , wherein the low refractive-index portion is formed at the forming by removing the circuit board around the transmissive portion.