Optical pickup head using multiple laser sources

Details Optical pickup head using multiple laser sources Optical pickup head using multiple laser sources

1999-05-03

2001-11-27

Young, W. R. (Department: 2651)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S112210

Reexamination Certificate

active

06324150

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to an optical pickup head, and more particularly to an optical pickup head which utilizes several laser beams of different wavelengths for reading or writing data on different kinds of optical disc.
An optical pickup records and reproduces information such as video or audio data onto/from recording media, e.g., laser discs. A disc has a structure that an information-bearing surface is formed on a substrate. Regular compact disc drivers are designed subject to the specifications of the laser discs. Currently, a DVD (digital versatile disc) driver is designed to read/write data on different kinds of optical disc, such as CD (compact disc) or DVD. The reading or writing is made by an optical pickup head which can provide two focusing points on an information-bearing surface of the disc which has a specific thickness. The thickness of the disc is defined as a distance from the surface of the disc to the information-bearing surface. When reading, the laser beam reflected from the disc and bearing the data signal is transformed by a photo detector into recognizable electrical signal. A similar process is generated for data writing.
The following is a table listing the specifications of the disc and the laser light for a CD and a DVD:
NA
THICKNESS
TRACK
WAVELENGTH
(numerical
(mm)
PITCH (&mgr;m)
(nm)
aperture)
CD
1.2
1.6
780
0.45
DVD
0.6 * 2
0.74
635-650
0.6
Because the thickness of a CD is different from that of a DVD, for the requirement of compatibility, a DVD driver must be designed to read discs of different thickness. There are several methods which achieve this requirement. These methods include:
1) using two objective lenses with different focuses, and selecting one of them corresponding to the CD or DVD by a driving mechanism such as a rotary mechanism. But the two objective lenses greatly increase the weight of the pickup head and the price of the product;
2) providing a diffraction member for the objective lens and performing two focuses;
3) using a HOE (holographic optical element) to provide two focusing points. But the efficiency of usage of laser light is decreased, and the HOE is difficult and expensive to be manufactured;
4) using an LCD (liquid crystal display) shutter as an NA controller which produces two numerical apertures from a single wavelength laser. However, it is difficult to be installed since the polarization of the laser light source must be properly arranged relative to the LCD and polarizer. Moreover, the LCD needs continuous power supply to maintain shutter effect;
5) providing an objective lens having a near axial region which includes a center of the light path and a far axial region located radially outward from the intermediate region, using electric signals corresponding to the near axial region converted in only the inner photodetector when the light is reflected from a CD; and using electric signals corresponding to both near and far axial regions converted in both the inner and outer photodetector when the light is reflected from a DVD. This is disclosed in U.S. Pat. No. 5,665,957. It has the disadvantages of higher manufacturing cost, lower acceptable tolerance or higher precision demand of installation, and decreasing the laser efficiency about 15%;
6) as disclosed in U.S. Pat. No. 5,777,970, providing a first optical system which leads the laser beam output from a first laser diode and a second optical system which leads the laser beam output from a second laser diode, providing an optical element which has refractivity to either the first optical system or the second optical system, and driving either the first laser diode or the second laser diode according to the type of the loaded optical disc. The drawbacks are that it is expensive and complicated in structure; and
7) adjusting an electronic aperture ring to change the numerical aperture, and change the distance between the disc and the object lens subject to type of the disc used. Similar designs are disclosed in U.S. Pat. No. 5,659,533 and U.S. Pat. No. 5,281,797.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to provide an optical pickup head which utilizes two or three laser beams of different wavelengths for reading or writing data on different kinds of optical recording media through a same optical output path.
According to the present invention, a beam shaper located in optical output paths of multiple laser beams is used. The beam shaper is composed of two prisms in which several laser beam interfaces are formed. Each laser beam interface is furnished with a specific coating for reflecting laser beam of a specific wavelength and transmitting and refracting laser beams of other wavelengths. By accommodating the angles and the material of the prisms, laser beams in different wavelengths can be shaped into a same optical output path for reading and writing data from optical recording media of different densities.
Another objective of the present invention is to provide an optical pickup head which utilizes multiple laser sources and is constructed as a compact unit with small size.
According to the invention, several laser beams of different wavelengths are incident to a beam shaper from different planes individually, then reflected or refracted via some optical interfaces and composed into an output path, therefore, no complicated components or complicated optical paths are needed.
A further objective of the present invention is to provide an optical element of a pickup head in which laser beams can be enlarged, and a higher usage efficiency of laser beam can be obtained.


REFERENCES:
patent: 4694447 (1987-09-01), Cohen et al.
patent: 4716283 (1987-12-01), Ando
patent: 5311496 (1994-05-01), Whitehead
patent: 5684781 (1997-11-01), Jeong
patent: 6084841 (2000-07-01), Sugiura et al.

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