LEAKY SURFACE-PLASMON MODE DIRECTIONAL COUPLER AND POLARIZATION DETECTION MODULE FOR MAGNETO-OPTICAL PICKUP HEAD USING SAME

A leaky surface-plasmon mode directional coupler and a polarization detection module for a magneto-optical pickup head using same are provided to reduce size and weight of the coupler by monolithic-integrating the coupler on a circuit board. A planar waveguide(100) includes a substrate(105), a core layer(110), and a cladding layer. The planar waveguide propagates a TM mode and a TE mode from an input terminal to an output terminal. A leaky surface-plasmon mode waveguide(130) uses the cladding layer and a lower cladding layer and includes a metal film layer and an upper cladding layer. The metal film layer and the upper cladding layer cover a portion of the cladding layer to generate a leaky surface-plasmon mode. A first photo diode(410) is provided on the leaky surface-plasmon mode directional coupler(90) having the planar waveguide and the leaky surface-plasmon mode waveguide. A second photo diode(420) is provided on an output terminal of the core layer. A polarization detection module measures a polarization angle using detected power difference between the first and second photo diodes.