Magneto-optical pickup device having phase compensating circuitry

A magneto-optical pickup device, comprising:

• a) a substrate;
• b) a light emitting device;
• c) a filter polarizing light emitted by said light emitting device to generate a first polarized component of light;
• d) a differential photo-detecting unit which separates light into first and second polarized components of light;
• e) an optical waveguide operatively configured and disposed on said substrate to guide said first polarized component of light from said filter onto a magneto-optical recording medium, and to guide light reflected back from said medium to said differential photo-detecting unit;
• f) a differential amplifying circuit coupled to an output of said differential photo-detecting unit, said differential amplifying circuit providing an output signal which varies according to a magnetization direction of magnetization information recorded on the magneto-optical recording medium;
• g) a feedback circuit coupled to said differential amplifying circuit, which feedback circuit is configured to generate a phase compensating signal that correlates to a phase difference between said first and second polarized components of light in said light reflected from said magneto-optical recording medium;
• and
• h) phase compensating means for receiving said phase compensating signal and minimizing said phase difference,
• wherein,
• said waveguide comprises a first path that guides said polarized light from said filter to said magneto-optical recording medium and a returning path that branches out from said first path thereby to guide said light reflected from said magneto-optical recording medium to said differential photo-detecting unit,
• said differential photo-detecting unit comprises a split optical waveguide with first and second parallel paths, the first parallel path including a first filter with a polarizing plane with a first angle of inclination, and said second parallel path including a second filter with a polarizing plane with a second angle of inclination opposite of the first angle of inclination,
• said feedback circuit comprises a reproduced signal output at which is generated an electronic output signal corresponding to said magnetization information recorded on said magneto-optical recording medium and a first low pass filter coupled between said reproduced signal output and said differential amplifying circuit, a frequency modulator which generates a frequency modulated signal, a band pass filter coupled to said differential amplifying circuit whose center frequency is the same as that of said frequency modulated signal, a multiplier unit coupled to an output of said bandpass filter and an output of said frequency modulator, a second low pass filter operatively connected to an output of said multiplier unit to generate a phase difference signal, and an adder unit coupled to said output of said frequency modulator and to said phase difference signal to generate said phase compensating signal,
• said means for receiving said phase compensating signal and minimizing said phase difference comprises an electrode unit operatively positioned about said waveguide to effect a change in a refraction width in said waveguide when an electrical signal is applied thereto, and
• said substrate is made of silicon.