JPS632125A - Optical head - Google Patents

Abstract

PURPOSE:To attain miniaturization and to relieve in weight by arranging an aperture lens while making a direction in which a comatic aberration is left on an axis of the aperture lens coincident with a direction corresponding to a direction in parallel with the junction of a semiconductor laser so as to eliminate the need for the tilt adjusting mechanism of an actuator. CONSTITUTION:The light emitted from the semiconductor laser 1 is converted into a collimated light beam by a condenser lens 2, made incident to a recording medium protecting transparent parallel plate of an optical disk through a beam splitter 3 and the aperture lens 4 to form a minute diameter light spot for recording/reproducing information on a recording face 6. The reflected light from the recording face 6 including an information signal is reflected in the beam splitter 3, made incident in a photodetector 8 via a signal detection optical system 7, where the information signal is reproduced and the focusing/tracking signal is detected. The detected signal is fed back to the actuator 9'. Thus, an excellent spot is obtained, the need for the tilt adjustment of the actuator is eliminated, and no tilt adjusting mechanism is required.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical disc that records information signals at high density on an optical disc having a recording medium that can optically record and reproduce information, and reproduces the recorded information. This invention relates to an optical head for an information recording/reproducing device.

BACKGROUND OF THE INVENTION Conventionally, in an optical head used for the above purpose, as shown in FIG. After passing through the aperture lens 4, the light enters a transparent parallel plate 6 for protecting the recording medium of the optical disc, and forms a minute diameter light spot for recording and reproducing information on the recording surface e. The reflected light from the recording surface 6 containing the information signal is reflected by the beam splitter 3, passes through the signal detection optical system 7, and enters the photodetector 8.
Here, reproduction of information signals and signal detection for focusing and tracking are performed. The detected signal is fed back to the actuator 9. This actuator 9 holds the aperture lens 4 and drives it axially in a direction perpendicular to the optical axis and the track. Further, the actuator 9 is attached to the base 10 by a set screw 11 and a spring 12, and has a structure in which the inclination of the aperture lens 4 can be adjusted by the action of the set screw 11 and spring 12.

In the optical head having the above configuration, the periphery of the light beam having an elliptical Gaussian distribution peculiar to a semiconductor laser is blocked by the aperture of the aperture lens, thereby shaping the light spot imaged onto the disk into a substantially circular shape. The cross-sectional shape of the light spot at this time is shown in FIG. In the direction perpendicular to the junction surface of the semiconductor laser, a side rope, that is, an annular zone formed near the main spot, occurs, but the half-value diameter of the optical spot is small. Furthermore, in the direction parallel to the junction surface of the semiconductor laser, the half-value diameter of the optical spot is slightly larger;
No side ropes occur.

Problems to be Solved by the Invention Now, the diaphragm lens used in the above-mentioned optical head generally has a high N and A of 0.46 to 0.63, and is a combination of three to four spherical lenses. Many structures are used. - An example is shown in FIG. Assembling such an aperture lens is performed in the following steps. A single spherical lens is placed into the lens barrel, and light is passed through it to observe a spot image. In a state where eccentricity adjustment is not performed, when the lens barrel is rotated with reference to the outer circumference, the spot image moves on a certain circumference. The radius of this circle represents the amount of eccentricity, and the basic idea of lens assembly is to adjust this amount so that it approaches a circle.

Spherical aberration and axial coma aberration cannot be corrected by adjusting the eccentricity of the lens as described above. - In general, spherical aberration increases the amount of annular light in a spot image, and axial coma aberration causes a deviation in the amount of annular light. The occurrence of spherical aberration can be suppressed to some extent by controlling the spherical precision and center wall thickness of a single lens.

It is also possible that an error occurs in the distance between single lenses due to assembly, resulting in spherical aberration, but when measuring wavefront aberration using an interferometer, the measured value will clearly deteriorate, so it is difficult to distinguish between good and defective products. It's easy.

On the other hand, axial coma aberration may remain even if the decentering accuracy of a single lens is good, or even if decentering is perfectly adjusted during assembly. Possible reasons why axial coma aberration cannot be completely corrected by eccentric adjustment include, for example, poor coaxiality between the outer diameter and inner diameter of the lens barrel, poor coaxiality between the inner diameter cylindrical parts, or paris in the lens holder. . This is illustrated in FIGS. 6(a), (b), and (c). If these factors are included in the lens barrel, a lens that is adjusted so that eccentricity is 0 will be mounted at an angle, which causes axial coma aberration.

Further, in wavefront aberration measurement, residual axial coma aberration does not appear as a noticeable feature, and no deterioration of measured values is observed, so it is difficult to distinguish.

As mentioned above, the annular light amount of the spot image where axial coma aberration remains is biased, and the light amount increases locally, which causes deterioration of recording and playback signals, that is, deterioration of signal frequency characteristics, and crosstalk. Phenomena such as an increase in

Conventionally, in order to solve the problem caused by the axial coma aberration of the diaphragm lens, the actuator 9 that holds the diaphragm lens has been provided with an adjustment mechanism to correct the deviation of the spot image annular light amount. With this method, the structures of the actuator and optical head are complicated, making it difficult to make the optical head smaller and lighter.Furthermore, since the aperture lens is driven while being tilted with respect to the optical axis, there is a risk of deterioration of the mold dynamic characteristics. It was also the cause.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides an aperture lens by aligning the direction in which the axial zoom aberration of the aperture lens remains with the direction corresponding to the direction parallel to the cemented surface of the semiconductor laser. is arranged.

Function: The above means has the effect of redirecting the axial coma aberration remaining in the aperture lens in a direction in which side ropes do not appear in the light spot, thereby suppressing an increase in the side rope light intensity due to the axial coma aberration. This is what we are trying to do.

Example Embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a principle diagram showing the basic configuration of the present invention.

The light emitted from the semiconductor laser 1 is converted into a parallel light beam by the condensing lens 2, passes through the beam splitter 3 and the aperture lens 4, and then enters the transparent parallel plate 6 for protecting the recording medium of the optical disc, and the recording surface θ A minute diameter optical spot for recording and reproducing information is formed on the top. Recording surface 6 containing information signals
The reflected light from 1. The light is reflected by the beam splitter 3, passes through the signal detection optical system 7, and enters the photodetector 8, where information signal reproduction and signal detection for focusing and tracking are performed. The detected signal is transmitted to actuator 9'
will be given feedback. The actuator 9' holds the aperture lens 4 and drives it in a direction perpendicular to the optical axis and the track. Note that this actuator 9' does not need to be provided with a tilt adjustment mechanism.

The aperture of the diaphragm lens is used to shape the light spot into a substantially circular shape, as in the conventional example, but in this embodiment, based on the gist of the present invention, the aperture lens is shaped in a direction parallel to the cemented surface of the semiconductor laser and The direction of residual axial coma aberration is made to match. This suppresses the increase in sidelobe light intensity due to axial coma aberration, as shown in FIG. 6.

It can be seen that extremely good spots are obtained compared to the defective spots that may occur with the configuration shown in FIG. 7 that does not satisfy the gist of the present invention. Therefore, in this embodiment, there is no need to adjust the tilt of the actuator, and therefore, the actuator 9' is not provided with a tilt adjustment mechanism.

Effects of the Invention As described above, the present invention eliminates the need for an actuator tilt adjustment mechanism, making it possible to realize a compact, lightweight optical head with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of an optical head in an embodiment of the present invention.
Fig. 2 is a diagram showing the principle of the optical head in the conventional example, Fig. 3 is a diagram showing the principle of light spot shaping by the aperture of the diaphragm lens, and a cross section of the light spot, Fig. 4 is a sectional view of the diaphragm lens, and Fig. 6 ( a), (b), and (C) are cross-sectional views showing the factors that cause axial coma aberration, Fig. 6 is a cross-sectional view showing an extremely small light spot of a side rope obtained by the present invention, and Fig. 7. is a cross-sectional view of a defective spot that may be generated by a configuration other than the present invention. 1... Semiconductor laser, 2... Condensing lens, 3... Beam splitter, 4...
Aperture lens, 6...Transparent flat plate (disc), 6
...Recording surface, 9,9'...Actuator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 ■ To 〇 noodles, direction of Komahiro 1

Claims (1)

[Claims] a semiconductor laser, a collimator lens that condenses the light generated from the semiconductor laser and converts it into a parallel light beam, a beam splitter, and an aperture lens that images the parallel light beam as a micro-diameter light spot on a disk recording surface; a photodetector that receives the light beam reflected on the disk recording surface, and a direction parallel to the bonding surface of the semiconductor laser;
An optical head characterized in that the direction of axial coma aberration remaining in the aperture lens is made to coincide with the direction.