Patent ID: 7684451

Claim:
An optical transmitter module comprising: a semiconductor laser configured to output forward outgoing light and backward outgoing light; a temperature control device configured to control a temperature of the semiconductor laser; a beam splitter plate configured to receive the backward outgoing light and to output split light which is reflected part of the backward outgoing light and transmitted light which is transmitted part of the backward outgoing light; a first photoelectric conversion element configured to convert the split light into an electric signal; a wavelength filter configured to receive the transmitted light and to change transmittance continuously depending on the wavelength of the transmitted light; and a second photoelectric conversion element configured to receive filter-transmitted light transmitted through the wavelength filter and to convert the filter-transmitted light into an electric signal, wherein the beam splitter plate includes an anti-stray-light structure configured to prevent the transmitted light reflected by an incident surface of the wavelength filter from entering the first photoelectric conversion element through a side end surface portion of the beam splitter plate, and wherein the anti-stray-light structure has a configuration in which an angle between the side end surface of the beam splitter plate and a plane perpendicular to a light-exit surface of the beam splitter plate is greater than a light-exit angle from the beam splitter plate which the reflected light from the filter enters.