An optical information transmitting device for transmitting information on a light beam emitted by a light source, includes an electronic circuit board, and an optical input/output port mounted on the electronic circuit board. The optical input/output port has a glass substrate attached to the electronic circuit board, a first array of optical sensors for absorbing a portion of a light beam applied thereto from the light source and photoelectrically converting the portion of the light beam, and for transmitting the remainder of the light beam therethrought, and a second array of spacial light modulators for modulating the transmittance with respect to a light beam applied thereto, the first and second arrays being disposed on a surface of the glass substrate in superposed relationship to each other. A motherboard comprises a substrate and a coaxial lens array of lenses spaced at equal intervals along an optical axis on the substrate, with conjugate focusing planes of equal magnification being disposed between adjacent ones of the lenses. A method of manufacturing the motherboard is also disclosed.