Abstract
We have developed an optical pick-up with a liquid crystal shutter that can read both digital video discs (DVDs) and compact discs (CDs). An objective lens which is designed for reading DVDs with a numerical aperture ( NA ) of 0.6 is used in this optical pick-up. The pick-up can be used to read CDs by changing the diameter of the laser beam which enters the objective lens, using the liquid crystal shutter. The wavelength of the laser diode is 635 nm. When a CD is read, the NA of the objective lens is 0.35. For focus error detection when reading CDs, an astigma method was used, and for tracking error detection, a 3-beam method was used. We have confirmed that both DVDs and CDs can be successfully read by changing the NA of the objective lens according to the thickness of the disc substrate.
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