Apparatus and method for polarization switching of a readout beam in a magneto-optic storage system

A playback apparatus for playing back information recorded in a magnetic recording layer of a magneto-optic recording device, wherein said recording layer exhibits a differential absorption for vertically magnetized magnetic domains of opposite orientation, said playback apparatus comprising:

• a laser unit having first and second excitation radiation modes which are linearly polarized and which have planes of polarization which are substantially orthogonal;
• first conversion and focusing means for converting said modes of linear polarization into circularly polarized radiation and focusing said circularly polarized radiation onto said recording layer:
• second conversion and focusing means for converting modulated circularly polarized radiation which has interacted with said recording layer into first and second linearly polarized components parallel with said first and second modes and focusing said modulated linearly polarized components into said laser unit;
• a first radiation path means including a first mirror means and a first adjustable loss element for applying said first linearly polarized mode and said first linearly polarized component from said laser unit to said first mirror means and applying radiation reflected from said first mirror to said laser;
• and
• a second radiation path means including a second mirror means and a second adjustable loss element for applying said second linearly polarized mode and said second linearly polarized component to said second mirror means and applying radiation reflected from said second mirror to said laser unit.

A playback apparatus for playing back information recorded on a recording layer of a magneto-optic material, wherein vertically magnetized domains of said recording layer have a differential absorption to circularly polarized radiation depending on the orientation of said magnetized domains, said playback apparatus comprising a laser having two linearly polarized modes of radiation excitation, said two linearly polarized radiation modes having planes of polarization generally orthogonal, said playback apparatus comprising an extended cavity for said laser, said extended cavity including said recording layer wherein interaction of laser radiation with magnetized domain of said recording layer determines which radiation mode is currently excited, wherein the playback apparatus is characterized by:

• a first portion of said extended cavity in which only a first mode of radiation is present;
• a second portion of said extended cavity in which only a second radiation mode is present;
• and
• at least one controllable loss element controlling a radiation loss in said first portion.

A method for equalizing excitation of a first and a second mode of generally orthogonal radiation modes from a laser, said laser having an extended cavity wherein said two radiation modes are coupled to vertically magnetized domains of a magneto-optic storage layer, an orientation of said magnetized domains providing a differential absorption to circularly polarized applied to said recording layer, wherein an orientation of said magnetized domains determines which radiation mode is currently excited in said laser, said method comprising the steps of:

• a.) converting said linearly polarized radiation from said laser to circularly polarized radiation and applying said circularly polarized radiation to said recording layer;
• b.) converting said circularly polarized radiation which has interacted with said recording layer to two linearly polarized components parallel to polarizations of said radiation modes and applying said radiation components to said laser;
• c.) separating a first radiation mode and parallel radiation component and applying said separated first radiation to a first portion of said extended cavity, wherein a separated second radiation mode and parallel radiation is applied to a second extended cavity portion;
• and
• d.) controlling a radiation loss in said first portion whereby excitation of said first and said second radiation modes become substantially equally probable in an absence of differential absorption by said recording layer.