Optical subassembly and optical module

An optical subassembly comprising:

• an eyelet including a first surface and a second surface arranged opposite the first surface,
• a first through hole penetrating from the first surface to the second surface;
• a first lead terminal inserted into the first through hole and transmitting an electrical signal;
• a dielectric filled in the first through hole;
• a device mounting substrate on which an optical device converting at least one of an optical signal and the electrical signal into another is mounted;
• a relay substrate including a first conductor pattern transmitting the electrical signal to the optical device;
• and
• a pedestal protruding from the first surface to an extending direction of the first through hole, on which the relay substrate and the device mounting substrate are placed,
• wherein the device mounting substrate is arranged on a different level of the pedestal than the relay substrate,
• wherein the first lead terminal includes a small-diameter part and a large-diameter part provided at an end of the small-diameter part,
• wherein a diameter of the large-diameter part is larger than a diameter of the small-diameter part,
• wherein at least part of the large-diameter part is exposed from the dielectric on a first surface side, and
• wherein the first lead terminal and the first conductor pattern are connected by brazing and soldering.