CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese patent application JP2019-227627 filed on Dec. 17, 2019, the contents of which are hereby incorporated by reference into this application.

BACKGROUND

1. Field

This relates to an optical module.

2. Description of the Related Art

A TO-CAN (Transistor Outline Can) Type package, using lead pins held by a dielectric such as glass in through holes of an eyelet, is configured to transmit electrical signals to an optical semiconductor device. The lead pins and electronic components contained in the package are connected by wires, and the lead pins protrude approximately 0.6 mm or more to prevent interference between a wire-bonding tool and the electronic components. The electronic components include a thermoelectric cooler using a Peltier device (JP2011-108939A). There is a bonding portion of the wire, above a heat-absorbing surface of the thermoelectric cooler.

The heat-absorbing surface of the thermoelectric cooler has an unstable potential because it is made of an insulator, and the confinement effect of the electromagnetic field is weak. Therefore, the protruding lead pins become an antenna element, and the high-frequency signal excites the lead pins, resulting in signal transmission loss. In recent years, there has been an increasing demand for modules having high transmission rates. Therefore, stabilization of the ground potential has become important.

SUMMARY

This aims at reducing signal transmission loss.

(1) An optical module includes: a conductive block with a first surface and a second surface, the conductive block having some through holes extending therethrough between the first surface and the second surface; some lead pins including a signal lead pin, the lead pins fixed inside the respective through holes and insulated from the conductive block; a thermoelectric cooler with an upper surface and a lower surface, the lower surface fixed to the first surface of the conductive block, the thermoelectric cooler having a Peltier device therein configured to transfer heat between the upper surface and the lower surface; a metal layer laminated on the upper surface of the thermoelectric cooler; a ground wire connecting the first surface of the conductive block and the metal layer; a photoelectric device adapted to convert an optical signal and an electrical signal at least from one to another; a mounting substrate on which the photoelectric device is mounted, the mounting substrate fixed to the upper surface of the thermoelectric cooler with at least the metal layer interposed therebetween, the mounting substrate having a first wiring pattern electrically connected to the photoelectric device; a relay substrate having a second wiring pattern electrically connected to the signal lead pin; and a signal wire configured to connect the first wiring pattern and the second wiring pattern.

This can reduce the signal transmission loss, due to stabilized potential of the metal layer laminated on the upper surface of the thermoelectric cooler because it is connected to the conductive block with the ground wire.

(2) In the optical module according to (1), the mounting substrate may have a mounting surface on which the photoelectric device is mounted, and the upper surface of the thermoelectric cooler and the mounting surface may face in respective directions intersecting with each other.

(3) In the optical module according to (2), the photoelectric device may be arranged such that an optical axis extends in a direction parallel to the mounting surface.

(4) The optical module according to any one of (1) to (3), may further include a support block interposed between the metal layer and the mounting substrate.

(5) In the optical module according to (4), the support block may have a cuboid shape, the cuboid shape having a surface fixed to the metal layer and another surface fixed to the mounting substrate, which are adjacent to each other.

(6) In the optical module according to (4) or (5), the support block may be made of metal.

(7) In the optical module according to (4) or (5), the support block may be made of non-metal.

(8) In the optical module according to any one of (1) to (3), the metal layer may be part of a metal block interposed between the upper surface of the thermoelectric cooler and the mounting substrate, the metal block may have a projection integral with the metal layer, and the mounting substrate may be mounted on the projection.

(9) In the optical module according to any one of (1) to (8), the signal lead pin may be adapted to single-ended driving of the photoelectric device, and the first wiring pattern may have a ground electrode to which a back side of the photoelectric device is bonded.

(10) In the optical module according to any one of (1) to (8), the signal lead pin may be a pair of signal lead pins adapted to drive the photoelectric device by differential signals, the first wiring pattern may include a pair of first differential signal lines, and the second wiring pattern may include a pair of second differential signal lines bonded to the respective pair of signal lead pins.

(11) In the optical module according to any one of (1) to (10), the ground wire may be two or more ground wires.

(12) In the optical module according to any one of (1) to (11), the conductive block may have a pedestal portion integral with the first surface, and the relay board may rest on the pedestal portion.

(13) The optical module according to any one of (1) to (12), may further include a thermistor mounted on the metal layer.

