Patent ID: 8437583

Claim:
An optical module comprising: a circuit board; a flexible substrate connected to the circuit board; and a package including a lead pin, the lead pin being fixedly attached to the flexible substrate, wherein: the flexible substrate includes a transmission path having a signal line, a pair of surface ground lines, and a back-surface ground line, the signal line and the surface ground lines being provided on a first main surface of the flexible substrate, the surface ground lines being arranged on the left and right of the signal line with a gap therebetween, and the back-surface around line being provided on a second main surface of the flexible substrate opposed to the first main surface, the transmission path includes a first region, a second region, and a third region in this order toward the package, the first region, the second region, and the third region include the signal line and the surface around lines, the first region includes the back-surface ground line which is overlapped with the signal line and terminated within the first region; the third region does not include the back-surface ground line in a location overlapped with the signal line, the second region does not include the back-surface ground line in a location overlapped with the signal line or does include the back-surface ground line being arranged so that a distance between the signal line and the back-surface ground line is longer than a distance between the signal line and the surface ground line, and the signal line includes: a part present in the first region and having a first width; a part present in the third region and having a third width; and a part present in the second region and having a width varied from the first width to the third width.