Magneto-optical information reproducing apparatus

Claim 1

A magneto-optical information reproducing apparatus comprising means (10,12,21-24) for applying a light beam polarized in a predetermined direction onto a recording medium (26) on which information is magnetically recorded, means (30) for dividing the reflected or transmitted light beam from said recording medium modulated into a polarized state in conformity with said information by the magneto-optical effect, a pair of analyzer means (27₁,27₂) having their optic axes inclined in opposite directions with respect to said predetermined direction and analyzing said divided light beams, a pair of photodetectors (29₁,29₂) having no amplifying action and photoelectrically detecting the light beams transmitted through said pair of analyzer means, and a signal processing means (15₁, 15₂, 16₁, 16₂, 18) for amplifying the detection signals of said pair of photodetectors, subtracting them from each other and reproducing said information, characterized in that the angle ϑ A formed between the optic axes of said plurality of analyzer means and said predetermined direction satisfies the following conditions: S = 2e κ ε|t A |²|R|²I₀·ΔB where I₀ is the quantity of light of the incident light beam on said recording medium, R is the amplitude reflectance of said recording medium, ε is the light utilization efficiency of the optical system from the recording medium to the photodetectors except said analyzer means, K is the photoelectric conversion efficiency of said photodetectors, e is the amount of charge, S is the shot noise of said photodetectors, T is the thermal noise of said amplifying means in a magneto-optical signal observation frequency, ΔB is the band width of the magneto-optical signal observation frequency, t A is the amplitude transmittance of said analyzer means, and η A is the extinction ratio of said analyzer means.