Mode splitter and magneto-optical signal detection device

A magneto-optical signal detection device, comprising:

• a first waveguide layer;
• a light coupling means disposed on one end portion of said first waveguide layer for simultaneously coupling two polarization components of light reflected from a magneto-optical recording medium, which are perpendicular to each other, into said first waveguide layer to thereby produce a first light of TE mode and a second light of TM mode, each of which propagates toward the opposite end portion of said first waveguide layer;
• and
• a light separating means comprising a second waveguide layer which is disposed on said opposite end portion of said first waveguide layer so as to efficiently separate said first light and said second light propagated through said first waveguide layer,
• said second waveguide layer having a first edge portion for receiving said first and second lights propagating within said first waveguide layer, and a second edge portion from which one of said received first and second lights is emitted, and from which the other of said received first and second lights is reflected, said first and second edge portions crossing each other at a predetermined angle at one end of each of said first and second edge portions, the thickness of each of said first and second edge portions becoming gradually smaller toward the outside of said second waveguide layer,
• said first waveguide layer and said second waveguide layer satisfying the following formulae:
• .beta..sub.Ai >.beta..sub.Bi ( 1)
• .beta..sub.Aj >.beta..sub.Bj ( 2)
• (.beta..sub.Bi /.beta..sub.Ai)>(.beta..sub.Bj /.beta..sub.Aj)(3)
• .theta.>sin.sup.-1 ((.beta..sub.Bi /.beta..sub.Ai) (4)
• sin.sup.-1 {(.beta..sub.Ai /.beta..sub.Bi) sin (.theta.-.theta..sub.ci)}<.alpha.<sin.sup.-1 {(.beta..sub.Aj /.beta..sub.Bj) sin (.theta.-.theta..sub.cj)} (5)
• where .beta..sub.Ai is a propagation constant of one of said first and second lights in said first waveguide layer, .beta..sub.Bi is a propagation constant of said one of said first and second lights in said second waveguide layer, .beta..sub.Aj is a propagation constant of the other of said first and second lights in said first waveguide layer. .beta..sub.Bj is a propagation constant of said other of said first and second lights in said second waveguide layer, .theta. is said predetermined angle, and .alpha. is an incident angle of a light including said TE mode and said TM mode with respect to said first edge portion, wherein .theta..sub.ci is equal to sin.sup.-1 (.beta..sub.Bi /.beta..sub.Ai) and represents a critical angle of said one of said first and second lights, .theta..sub.cj being equal to sin.sup.-1 (.beta..sub.Bj /.beta..sub.Aj) and representing a critical angle of said other of said first and second lights.