Optical module

1. An optical module comprising:

an optical subassembly for converting an optical signal and an electric signal at least from one to another, the optical subassembly having a stem;

a flexible printed circuit board having an insulation film with a first surface and a second surface opposite to each other and with a first portion and a second portion extending in a direction opposite to each other from a central portion, the flexible printed circuit board having a first ground plain on the second surface; and

a printed circuit board having an insulation layer with a third surface and a fourth surface opposite to each other, the printed circuit board having a second ground plain,

wherein

the optical subassembly is connected to the flexible printed circuit board with the stem opposed to the second surface at the central portion,

the flexible printed circuit board curves with the second surface facing outward at least at the central portion,

the printed circuit board intervenes between edges of the first portion and the second portion and is connected to the flexible printed circuit board, and

the first portion and the second portion of the flexible printed circuit board curves in a shape to avoid mutual contact and three-dimensionally intersect with each other, and the first portion and the second portion on the second surface are opposed to the printed circuit board.

2. The optical module according to claim 1 , wherein

the flexible printed circuit board on the second surface has a first ground terminal connected to the first ground plain,

the printed circuit board on the third surface has a second ground terminal connected to the second ground plain,

the first ground terminal and the second ground terminal are connected to each other.

3. The optical module according to claim 1 , wherein

the flexible printed circuit board at the central portion and the first portion on the first surface has a first interconnect pattern, the flexible printed circuit board at the first portion on the second surface having a first terminal connected to the first interconnect pattern,

the printed circuit board has a third interconnect pattern, the printed circuit board on the third surface having a third terminal connected to the third interconnect pattern, and

the first terminal and the third terminal are connected to each other.

4. The optical module according to claim 3 , wherein

the first ground plain is at the central portion and at the first portion and overlaps with the first interconnect pattern, and

the first interconnect pattern includes a high-frequency signal line.

5. The optical module according to claim 3 , wherein

the flexible printed circuit board at the central portion and the second portion on the first surface has a second interconnect pattern, the flexible printed circuit board at the second portion on the second surface having a second terminal connected to the second interconnect pattern,

the printed circuit board has a fourth interconnect pattern, the printed circuit board on the fourth surface having a fourth terminal connected to the fourth interconnect pattern, and

the second terminal and the fourth terminal are connected to each other.

6. The optical module according to claim 5 , wherein the second interconnect pattern includes a direct-current signal line.

7. The optical module according to claim 1 , wherein one of the first portion and the second portion of the insulation film has an opening or a cutout.

8. The optical module according to claim 7 , wherein

the second portion has the opening or the cutout, and

the first portion is situated inside the opening or the cutout.