Opto-magnetic signal reproducing apparatus for reading, by differential detection using a magneto-optical effect, information magnetically recorded on a record medium

Claim 1

A reproducing apparatus for reproducing information recorded on an opto-magnetic recording medium which includes a thin film having at least a magnetic recording layer formed on a transparent substrate, said apparatus comprising: irradiation means for irradiating the medium with a light beam polarized in a predetermined direction, the light beam being modulated by magneto-optic effect according to information recorded on the recording medium; a half mirror for splitting the light beam into a transmitted light beam and a reflected light beam; an optical element for directing the modulated light beam to said half mirror; a plurality of analyzers having different transmission axis directions for transmitting the split light beam therethrough, one of said analyzers for transmitting the transmitted light beam therethrough and one of said analyzers for transmitting the reflected light beam therethrough; a plurality of photodetectors for receiving the split light beam transmitted through said plurality of analyzers, one of said photodetectors receiving a respective transmitted light beam transmitted through a respective one of said analyzers and one of said photodetectors receiving a respective reflected light beam transmitted through a respective one of said analyzers; and a reproducing circuit for reproducing the information recorded on the recording medium by differentiating outputs of said plurality of photodetectors; wherein an arrangement of said optical element and said half mirror satisfies the following conditions: δ.sub.S +δ.sub.M +δ.sub.Q ≈nπ δ.sub.R ≈n.sub.R π δ.sub.T ≈n.sub.T π where δ S , δ M and δ Q are phase differences produced by the transparent substrate, the thin film and said optical element, respectively, between a polarized light component of the modulated light beam in the predetermined direction and a polarized light component of the modulated light beam in a direction orthogonal to the predetermined direction, δ R is a phase difference produced by said half mirror between a polarized light component of the reflected light beam in the predetermined direction and a polarized light component of the reflected light beam in the direction orthogonal to the predetermined direction, δ T is a phase difference produced by said half mirror between a polarized light component of the transmitted light beam in the predetermined direction and a polarized light component of the transmitted light beam in the direction orthogonal to the predetermined direction, and n, n R and n T are each integers.