Abstract: An optical pickup using a holographic optical element includes a light source, a lens system for converting an optical beam outputted from the light source onto a recording carrier, a photodetector for detecting reflected light from the recording carrier and a diffraction grating for introducing the reflected light from the recording carrier to the photodetector in a light path connecting the recording carrier and the light receiving element. The photodetector includes a photodiode and a signal processing circuit which at least amplifies the output signal of the photodiode.

Abstract: A photo detecting device has a photoelectric converting element formed on a semiconductor chip with the photoelectric converting element being divided into first and second light receiving regions. The photo detecting device further has a signal processing circuit formed on the same semiconductor chip. The signal processing circuit includes a subtracting element for subtracting an output signal from the second light receiving region from an output signal from the first light receiving region.

Abstract: The present invention presents a beam converting apparatus which comprises a semiconductor laser element,means for converting the laser beam from the semiconductor laser element into a parallel beam, anda prism possessing a first plane for receiving the parallel beam and a second plane for fully reflecting so that the beam entering from the first plane may be emitted from the first plane, wherein the apex angle of the first plane and second plane is defined so that the sum of the incidence angle (.theta.1) to the normal of the first plane and the exit angle (.theta.2) to the normal of the first plane of the beam fully reflected from the second plane emitted from the first plane, (.theta.1+.theta.2), may be about 90 degrees.