| 摘要 |
An optical head comprising of a laser source, a collimating lens, a focusing lens, a beam splitter, two polarizers, a quarter wave retarder, three detector lenses, and three photo detectors can be used to detect the polarization change of reflected light from an optical memory. Linear polarized light emerging from the laser source is collimated by the collimating lens and then is focused through the beam splitter and focus lens on the optical memory. Reflected light, which is elliptically polarized upon reflection from optical memory, is subdivided by the beam splitter into three parts: The first part goes through the quarter wave phase retarder followed by a polarizer whose transmission axis is set at 45 degrees, to reach a photo detector through a detector lens. The second part goes through a second polarizer, which has its transmission axis also set at 45 degrees, and then through the second detector lens to reach another photo detector. The third part of light that emerges from beam splitter goes directly to the third detector lens to reach the last photo detector. A simple and elegant equation is derived which relates the three light intensities detected by the photo detectors to the change of phase between the orthogonal electrical components of reflected light from optical memory. Such information is sufficient to detect the recorded information on the optical memory.
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