Patent ID: 7626825

Claim:
An optical transmitter module comprising: a housing that houses a semiconductor laser element, and an optical modulation element for modulating a laser beam by an electrical signal; lead pins for electrically connecting the inside and outside of the housing; and a flexible printed circuit board connected to the lead pins, wherein said flexible printed circuit board includes: a signal pattern to be connected to the optical modulation element; first and second ground conductor patterns provided on both sides of the signal pattern; a third ground conductor pattern provided on the back side of the signal pattern; a first insulating layer for covering the signal pattern as well as the first and second ground conductor patterns; a second insulating layer for covering the third ground conductor pattern; a first covering conductive layer for covering the first insulating layer; and a second covering conductive layer for covering the second insulting layer, and wherein said first covering conductive layer at least has a slit formed over the portion of the signal pattern.