JPH02294944A - Optical head adjusting device - Google Patents

Abstract

PURPOSE:To execute best satisfactory image field detection in a minimum blurring circle and to reduce the adjusting error of a focus deviation detecting system by using a second half mirror, disposed while being inclined to the optical axis of an objective lens by 45 deg., and a second cylindrical lens. CONSTITUTION:XYZ adjustment is executed to an optical head 30 and the optical head is adjusted to a position where a beam spot appearing on a second TV monitor 13 from a semiconductor laser beam source 3 is the minimum blurring circle. At this a time, the best satisfactory laser beam spot is formed on the upper surface of a first half mirror 6 and reflected light from a semitransparent film is returned to a focus deviation detecting system 31, passes through the second half mirror 8 and can be observed on a TV monitor 10. The optical axial direction position and XY position on a plane vertical to the optical axis of four elements of a first cylindrical lens 1 are adjusted so that outputs from the four elements of a quadripartite detector 2 can be equal. At the time of best focusing, a focus deviation signal is made 0.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical system for reproducing information on a recording medium or for recording and reproducing information on a recording medium using a light beam emitted from a light source. This is a dispute regarding an optical head adjustment device that adjusts the position of a focus shift detection optical system of a head.

Conventional technology In optical information recording and reproducing devices using optical disks, etc., it is necessary to focus the laser beam onto the disk to a diameter of 1 μm or less, but since the rotating disk has surface runout, it is necessary to Is going. Methods for detecting defocus include astigmatism method, knife edge method,
Various methods have been proposed, such as the critical angle method, but in any of these methods, it is necessary to adjust the optical position so that the defocus signal becomes O when focusing on the disk. In the head assembly process, it is difficult to reduce costs.

FIG. 2 shows a conventional optical head adjustment device. In FIG. 2, 100 is an optical head, 51 is a light source, 52 is a focusing lens, 53 is a cylindrical lens, and 5
4 is a four-division photodetector element.

The focus shift detection system of this optical head 100 consists of a cylindrical lens 1, a linear lens 53, and a four-part light detection element 54, and uses the so-called astigmatism method.

The principle of defocus detection is described in numerous documents, so it will not be described here. A half mirror 55 has the same optical thickness as the disk, and is positioned in advance on the object plane of the objective lens 56 of the enlarging optical system 101. A TV camera 57 and a TV monitor 58 are used to observe the laser beam spot 1 focused on the half mirror 55. A semi-transparent film is deposited on the upper surface of the half mirror 55, and approximately half of the light is returned to the defocus detection system of the optical head 100.

In such a configuration, a method for adjusting the positions of the cylindrical lens 53 and the four-split photodetecting element 54 will be described below. Adjust the optical head 100 in XYZ, and set the TV monitor 58.
Adjust to the position where the upper laser beam spot is best. Since the laser beam spot has a diameter of approximately 1 μm, the optical magnification of the enlarging optical system 101 must be 500 times or more.

In this state, the position of the cylindrical lens 53 in the optical axis direction and the Adjust the position. As a result, the focus shift signal becomes O when the best focus is reached on the disk.

Problems to be Solved by the Invention However, with the above configuration, the best focus position is adjusted so that the diameter of the laser beam spot on the TV monitor is minimized, so it is easy for visual errors to occur, resulting in adjustment errors. It had the problem of becoming large.

In view of the above problems, the present invention provides an optical head adjustment device with small adjustment errors.

Means for Solving the Problems In order to solve the above problems, the optical head adjusting device of the present invention includes an objective lens and a first /'t- a second half mirror installed at an angle of approximately 45 degrees to the optical axis, a first TV camera installed on the image plane of the objective lens, a cylinder 1 linear lens, and an objective lens and a cylinder lens. A second T camera, a first TV monitor, and a second T camera installed on a surface where a circle of least confusion is formed by
It has a V monitor.

Operation With the above configuration, the optical head is adjusted in XYZ so that the laser beam spot on the second TV monitor becomes the circle of least confusion. At this time, the laser beam spot on the second TV monitor is optically adjusted in advance to be optimal. In this state, the reflected light from the first half mirror is received by the 4-split photodetector element of the optical head, and the position of the cylindrical lens in the optical axis direction and the light of the 4-split photodetector element are adjusted so that the outputs of the 4 elements are equal. Adjust the XY position in the plane perpendicular to the axis. As a result, the focus shift signal becomes O when the disc is in the lowest focus. Further, on the second TV monitor, the laser beam spot on the best image plane can be observed simultaneously, and the optical characteristics of the optical head can be evaluated.

Example Embodiments of the present invention will be described below with reference to FIG.

30 is an optical head to be adjusted, and 31 is a focus shift detection system. In this example, it consists of a first cylindrical lens 1 and a four-part light detection element 2. 3 is a semiconductor laser light source, 4 is a collimator lens, and 5 is a focusing lens. A first half mirror 6 has the same optical thickness as the disk plate, and is preliminarily positioned on the object plane of the objective lens 7. A semi-transparent film is deposited on the upper surface of the first mirror 6, and approximately half of the light is returned to the defocus detection system 31 of the optical head 30. Reference numeral 8 denotes a second half mirror, which is installed at an angle of approximately 45 degrees with respect to the optical axis of the objective lens 7. 9 is the first TV camera,
Reference numeral 10 denotes a first TV monitor for observing the laser beam spot 1 focused on the upper surface of the first half mirror 6.

11 is the second cylindrical lens, 12 is the second T
V camera 13 is a second TV monitor. The laser beam focused by the objective lens 7 is subjected to astigmatism by the second silica lens 11. The position of the second cylindrical lens 11 is fixed in advance at a position where the circle of least confusion is observed on the second TV monitor 13 when the laser beam spot 1 becomes the best image plane on the first TV monitor 10. In this configuration, a method for adjusting the positions of the first cylindrical lens 1 and the four-split photodetecting element 2 will be described below. The optical head 30 is adjusted in XYZ to a position where the laser beam spot on the second TV monitor 13 becomes the circle of least confusion. At this time, the best laser beam spot is formed on the second surface of the first half mirror 6, and the reflected light from the semi-transparent film is returned to the defocus detection system 31.

In this state, the position of the first cylindrical lens 1 in the optical axis direction and the
Adjust the Y position. As a result of the above, the defocus signal becomes O when the best focus is achieved on the disc.

Furthermore, the shape of the laser beam spot on the best image plane can be observed on the first TV monitor 10, and the optical characteristics of the optical head 30 can be evaluated at the same time.

Effects of the Invention As described above, the optical head adjustment device of the present invention uses the second cylindrical lens to achieve the following effects:
The best image plane detection can be easily performed with the smallest circle of confusion, and the adjustment error of the focus shift detection system can be kept small. In addition, optical characteristics evaluations of multiple optical units can be performed at the same time.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical head adjustment device according to an embodiment of the present invention, and FIG. 2 is a configuration diagram of a conventional optical head adjustment device. 6...First half mirror, 7...Objective lens, 8...Second half mirror, 9...
...First TV camera, 10...First T
V monitor, 11... Second cylindrical lens, 12... Second TV camera, 13...
. . . second TV monitor, 30 . . . optical head 1, 31 . . . focus shift detection system.

Claims (1)

[Claims] an objective lens, a first half mirror fixed with a reflecting surface aligned with the object plane of the objective lens, a second half mirror installed at an angle of approximately 45 degrees with respect to the optical axis, and an image plane of the objective lens. A first TV camera installed on a cylindrical lens, a second TV camera installed on a plane where a circle of least confusion is formed by an objective lens and a cylindrical lens, and connected to the first and second TV cameras, respectively. An optical head adjustment device having a first TV monitor and a second TV monitor.