Optical pickup diffracting one of two laser beams to a single detector

An optical apparatus for directing first and second laser sources to a media, then directing reflected light to a detector, the improvement comprising:

• a 3-beam grating positioned to split the light from each of said laser sources into 3 beams before contacting said media;
• a beam splitter positioned to split the light from the laser sources and the reflected light so that the laser sources and the detector can be mounted at an angle to each other;
• a collimating lens positioned between said laser sources and said medium;
• an objective lens positioned between said collimating lens and said medium.
• wherein said laser sources have different wavelengths, and an optical axis of each of said laser sources, at a point of entering said objective lens, is parallel to an axis of said objective lens;
• a single four element detector for detecting reflected light from both of said laser sources;
• and
• a grating having a first surface with a grating configured to diffract reflected light from said first laser source to said detector, and having a non grating surface for allowing reflected light from said second laser source to pass directly to said detector without diffraction.