Diffraction optical element and optical pickup device

Abstract

An optical pickup with a simplified structure in which, according to the type of optical disc, diffracted light from three types of laser light can be directed efficiently onto a photodetector and appropriate focus control can be performed based on the signals detected by the photodetector, and a diffractive optical element that can be used in the optical pickup, which has a semiconductor laser 10 that can emit three types of laser light, a diffractive optical element 42 that diffracts the laser light reflected from the optical disc 31, and a single photodetector 43 that detects the diffracted light exiting the diffractive optical element 42. The diffractive optical element 42 is structured so that 0-order light is the maximal component of the diffracted light generated from each of two of three types of laser light, the two having close wavelengths (with a small wavelength difference), and +1-order light or −1-order light is the maximal component of the diffracted light generated from the remaining one type of laser light.

Description

Technical field [0001] The present invention relates to an optical pickup device that can correspond to three optical disc standards, and a diffractive optical element that can be mounted on the optical pickup device. Background technique [0002] As optical discs, there are CDs (compact discs) that use infrared lasers with a center wavelength of 0.78 μm to record or reproduce information, and DVDs that use red lasers with a center wavelength of 0.65 μm to record or reproduce information. (Digital versatile disc: digitalversatile disc). In addition, HD-DVD and Blu-ray discs (hereinafter collectively referred to as "blue laser discs" or "Blu-ray discs") that use a blue laser with a center wavelength of 0.405 μm to record or reproduce information are also beginning to be available Practical application. [0003] Generally, a recording and reproducing device for a blue laser disc is configured to be capable of recording or reproducing information for conventional DVDs and CDs. Rega...

AI Technical Summary

Problems solved by technology

[0009] However, when the linear range of the focus error signal is reduced, focus control for CDs that allow a large disc surface wobble in the focus direction (that is, have a large focus shift allowable value) becomes difficult

[0010] Conversely, when the linear range of the focus error signal is increased, focus control for CD becomes easy, but the accuracy of focus control for Blu-ray discs and DVDs decreases, and each signal recording surface of a dual-layer disc cannot be recognized

[0011] In this way, since the depth of focus of the CD standard is about 7 times that of the Blu-ray standard, it is very difficult to set the linear range of the focus error signal that satisfies both standards

Images