| 摘要 |
PURPOSE:To decrease absorption loss by setting the thickness of a Faraday rotator within a range where the total loss of light absorption loss and loss due to deviation in the angle of rotation of linear polarized light on a return way. CONSTITUTION:When the thickness of the Faraday rotator 4 is expressed by mum while the absorption coefficient of a magnetooptic material constituting the Faraday rotator 4 is denoted as A db/mum and an angle of Faraday rotation per mum is denoted as B deg./mum, the absorption loss to the quantity of light arriving at a detector D and the loss due to deviation in the angle of rotation of the light on the return way are so represented that the absorption loss of the Fara day rotator is 2AT (dB) and the loss due to the deviation from 90 deg. of the plane of polarization of light on the return way is -10log cos<2>(90-2Bt). In this case, the magnetooptic material whose thickness t(mum) is set to a minimum value -10log cos<2>(90-2Bt)+2AT is used. The angle of rotation is set to <=90 deg. and the thickness is set so that the total loss of the absorption loss and loss due to the deviation in angle of rotation is minimum. Consequently, the absorption loss is suppressed and a low-loss Faraday rotator for an optical head is obtained.
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