JPS61243953A - Optical head - Google Patents

Abstract

PURPOSE:To decrease a shift of an optical axis shift caused by a temperature variation, and to make a holder small in size by forming the holder for holding a light source of an optical head, and a photodetector, of an organic insulator whose coefficient of thermal expansion is low, and using this holder as a substrate on which an electric circuit pattern has been placed. CONSTITUTION:An information storage medium 21 is placed on a turntable 30, and this table 30 is rotated at a prescribed speed by a driving motor 33. In the radial direction of this medium 21, an optical head having a light source 36, an objective lens 40, and the second photodetector 49 is placed so as to be rotatable. The light source 36 of this head 34 is supported in a frame 54, the frame 54 is used as an electrode, and a signal terminal 56 from the frame is soldered and fixed to a holder 55. This holder 55 is formed by an organic insulator whose coefficient of thermal expansion is low, and an electric circuit pattern 57 is formed on the holder 55. Also, the holder 55 is used as a circuit board, a shift of an optical axis due to a temperature variation is decreased, and the holder 55 is made small in size.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention is a device capable of reading at least information from an information storage medium using focused light.
It is used for playback-only information storage media such as D (compact disc) and video disc, image files, still image files, DOM (computer output memory), etc., and uses focused light to make holes in the recording layer. An optical head that is applied at least when reproducing or recording information on an information storage medium that can record information by causing a state change such as the above, and that can be reproduced from it, as well as an erasable information storage medium. Regarding.

C. Technical background of the invention and its problems] In the above type of device, when reading information from an information storage medium or writing new information to an information storage medium, the convergence point of the focused light is always located at the information storage medium. It must match the position of the recording layer or light reflective layer of the medium.

Therefore, the device has an automatic defocus detection function and its correction function.

However, with this function, when the optical axis shifts, the spot for defocus detection moves on the photodetector that detects defocus, resulting in false detection as if the object is out of focus. Therefore, if the optical axis shifts due to changes in the external environment (temperature changes, humidity changes, mechanical vibrations, shocks, etc.), the focus will be blurred. In particular, it is easily affected by temperature changes.

Therefore, for defocus detection methods that are extremely sensitive to optical axis deviations, such as methods that place a photodetector at the imaging point, it is necessary to avoid optical axis deviations due to external environments such as temperature and humidity. Therefore, it is extremely difficult to reduce the number of parts or change the structure. Therefore, in such an optical system, a method of holding the light source has been devised, but it is still difficult to reduce the number of parts and make it compact.

That is, as shown in FIG. 10, a semiconductor laser 1 serving as a light source is supported within a frame 2 and attached to a holder 3. Furthermore, this holder 3 is attached to the holder 5 of the collimator lens 4 or the optical head body. Here, the frame 2 itself usually serves as an electrode. For this reason, holder 3 and holder 5
Alternatively, an insulating sheet 6 is interposed between the optical head body and the optical head body for the purpose of insulation, and furthermore, insulating screws are used for the mounting screws 7, 7.

Therefore, such a structure has a large number of parts and is complicated and large. Furthermore, if you try to attach the driver circuit board for the semiconductor laser 1, it has to be attached after holding the semiconductor laser 1 as described above, which not only increases the number of parts but also increases the distance between the semiconductor laser 1 and the driver circuit board. A noise problem arises.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its purpose is to prevent the optical axis from shifting due to temperature changes,
Not only can defocus detection be performed stably, but the number of parts can be reduced and the structure can be made simpler and more compact.Moreover, it is possible to arrange an electric circuit on the holder, making it even more compact. Another object of the present invention is to provide an optical head that eliminates concerns about noise.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the holder for holding the light source is made of an organic insulator with a low coefficient of thermal expansion.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 3 shows an information recording/reproducing apparatus using an optical head according to the present invention, and numeral 21 in this figure is an optical disk (information storage medium). This optical disc 21 is formed by bonding a pair of disc-shaped transparent plates 22.23 with an inner and outer spacer 24.25 interposed therebetween, and the transparent plates 22.2
On the inner surface of each of 3, there is a light reflecting layer m as an information recording layer.
26°27 are formed by vapor deposition. A tracking guide 28 (see FIG. 4) is formed helically on each of the light reflecting layers 26, 27, and information in the form of bits 29 is recorded on this tracking guide 28.

A hole is made in the center of the optical disc 21, and when the optical disc 21 is placed on the turntable 30, the center spindle 31 of the turntable 30 is inserted into the hole of the optical disc 21, and the turntable 30 and the optical disc The rotation centers of 21 are matched. turntable 3
A chuck device 32 is further attached to the center spindle 31 of No. 0, and the optical disc 21 is fixed on the turntable 3o by this chuck device 32. The turntable 30 is rotatably supported by a support base (not shown) and rotated by a drive motor 33 at a constant speed.

Reference numeral 34 denotes an optical head that is movable in the radial direction of the optical disk 21 by a linear actuator 35 or a rotating arm.
6 is provided.

When writing information to the optical disc 21,
A laser beam L whose light intensity is modulated according to the information to be written is generated from the semiconductor laser 36, and when reading information from the optical disk 21, a laser beam L having a constant light intensity is generated from the semiconductor laser 36. Ru. The diverging laser beam L generated by the semiconductor laser 36 is converted into a parallel beam by a collimator lens 37 and directed to a polarizing beam splitter 38 . The parallel laser beam L reflected by the polarizing beam splitter 38 passes through the quarter-wave plate 39 and enters the objective lens 40, and is focused by the objective lens 40 toward the light reflection layer 26 of the optical disc 21. The objective lens 40 is supported movably in the direction of its optical axis by a voice coil 41, and when the objective lens 40 is positioned at a predetermined position, the beam waist of the focused laser beam emitted from the objective lens 40 is It is projected onto the surface of the reflective M126, and a minimum beam spot is formed on the surface of the light reflective layer 26. In this state, the objective lens 40
is kept in focus and information can be written and read. When reading the information, a bit 29 is formed on the tracking guide 28 on the light reflection J126 by the laser beam L modulated with light intensity, and when reading the information, the laser beam L having a constant light intensity is The beam L is intensity-modulated by a bit 29 formed on the tracking guide 28 and is reflected.

The diverging laser beam L reflected from the light reflection layer 26 of the optical disk 21 is converted into a parallel beam by the objective lens 40 when it is focused, passes through the quarter-wave plate 30 again, and is returned to the polarizing beam splitter 38. . By the laser beam L going back and forth through the quarter-wave plate 39, the plane of polarization of the laser beam L is rotated by 90 degrees compared to when it is reflected by the polarizing beam splitter 38, and the laser beam L has a plane of polarization rotated by this 90 degrees. L is not reflected by the polarizing beam splitter 38 and passes through the polarizing beam splitter 38. The laser beam L that has passed through the polarizing beam splitter 38 is divided into two systems by a half mirror 42 , one of which is irradiated onto a first photodetector 44 by a first projection lens 43 . The first signal detected by the first photodetector 44 includes information recorded on the optical disc 21, and is sent to the signal processing device 45 and converted into digital data. The other laser beam L separated by the half mirror 42 is extracted asymmetrically with respect to the optical axis 47 by a light shielding plate (light handling member) 46.
Photodetector 49 in the rear tube 2 that has passed through the second projection lens 48
is incident on the The signal detected by the second photodetector 49 is processed by a focus signal generator 50, and this focus signal is given to the voice coil drive circuit 5'1. The voice coil drive circuit 51 drives the voice coil 41 according to the focus signal to maintain the objective lens 40 in a focused state.

Next, the optical system for detecting the focused point shown in FIG. 3 can be simplified as shown in FIG. )(b
) (c). When the objective lens 40 is in focus, the light reflection I! The beam waist is projected onto 26 and a minimum beam spot, namely the beam waist spot 52, is formed on the light reflective layer 26. Normally, the laser beam L incident on the objective lens 40 from the semiconductor laser 36 is a parallel beam of light, so the beam waist is formed on the focal point of the objective lens 40. However, if the laser beam L incident on the objective lens 40 from the semiconductor laser 36 is slightly divergent or convergent, the beam waist is formed near the focal point of the objective lens 40. Here, the light-receiving surface of the photodetector 40 is arranged at the imaging plane of the beam waist spot 52 in a focused state (it may be arranged near the imaging plane). Therefore, when the beam is focused, an image of the beam waist spot 52 is formed at the center of the light receiving surface of the photodetector 49.

That is, as shown in FIG. 5(a), a beam waist spot 52 is formed on the light reflection layer 26, and the laser beam reflected by the light reflection layer 26 is reflected by the objective lens 4.
0, the light is converted into a parallel light beam and directed toward the light shielding plate 46. The beam is then extracted asymmetrically with respect to the optical axis 47 by a light shielding plate 46, converged by a projection lens 48, and focused to a minimum on a photodetector 49, and a beam waist image is formed thereon. Next, when the objective lens 40 approaches the light reflection layer 26, a beam waist is generated as the laser beam L is reflected by the light reflection layer 26, as shown in FIG. 5(1). In other words, the beam waist is the objective lens 4.
0 and the light reflecting layer 26. In such an unfocused state, the beam waist is usually
Since the laser beam L is generated within a focal length of 0, assuming that the beam waist functions as a light spot, it is clear that the laser beam L reflected by the light reflection layer 26 and emitted from the objective lens 40 is diverged by the objective lens 40. is converted into a laser beam L. Since the laser beam L component that has passed through the light shielding plate 46 is also diverging, even if this laser beam L component is focused by the projection lens 48, it is not focused to the minimum on the light receiving surface of the photodetector 49 and is not detected. The light will be focused toward a point farther away than the device 49.

Therefore, the laser beam component is projected upward in the figure from the center of the light receiving surface of the photodetector 49, and a pattern larger than the beam spot image is formed on the light receiving surface. Furthermore, as shown in FIG. 5(C), when the objective lens 40 is separated from the light reflection layer 26, the laser beam L is reflected by the light reflection layer 26 after forming a beam waist. At the time of such an out-of-focus point, the objective lens 40 is outside the focal length of the objective lens 40 and is formed between the objective lens 40 and the light reflection 1i26.
The reflected laser beam L directed from the light shielding plate 46 to the light shielding plate 46 has a focusing property. Therefore, the laser beam L component that has passed through the light shielding plate 46 is further converged by the projection lens 48 to form a convergence point, and then projected onto the light receiving surface of the photodetector 49. As a result, a pattern larger than the image of the beam waist spot 52 is formed on the light receiving surface of the photodetector 49 from the center downward in the figure.

Next, the semiconductor laser 36 will be further explained. As shown in FIGS. 1 and 2, the semiconductor laser 36 is supported within a frame 54.
is itself an electrode.

The frame 54 is soldered to a holder 55 with signal terminals 56 protruding from the frame 54. Here, the holder 55 is made of an organic insulator with a low coefficient of thermal expansion for the purpose of insulation. Further, this holder 55 is used as a circuit board, and an electric circuit pattern 57 is formed on this holder 55, that is, a semiconductor laser 3
A driver circuit for driving 6 is formed. Further, a connector 58 is provided at the end of this electric circuit pattern 57, and input/output signals of the semiconductor laser 36 can be obtained from this connector 58. Roughly speaking, the holder 55 that holds the semiconductor laser 36 in this way has a screw hole or a blank hole for fixing, and the holder 55 connects the holder 59 of the collimator lens 37 with a screw 60.60 through that hole. It is installed by

According to the above configuration, since the holder 55 that holds the semiconductor laser 36 is made of an organic insulator with a low coefficient of thermal expansion, the coefficient of thermal expansion of an organic insulator with a low coefficient of thermal expansion is at the same level as that of metal, so the temperature can be adjusted. This makes it difficult for the semiconductor laser 36 to be misaligned (optical axis misalignment) due to environmental changes caused by this, and it is possible to prevent the photodetector 49 from malfunctioning in defocus detection.

Note that optical axis deviation occurs in glass epoxy and the like that are normally used for electric circuit boards.

Further, since there is no need to provide an insulating sheet or the like as in the conventional case, the number of parts can be reduced and a simple and compact structure can be achieved. Furthermore, since it is possible to directly arrange an electric circuit on the holder 55, the semiconductor laser 36 and its driver circuit are brought closer together, which further reduces the size and eliminates concerns about noise.

In addition to the above embodiments, there are other optical systems for detecting the in-focus state as shown in FIGS. 6 to 9, and the present invention can be applied to such optical systems as well. In addition, a photodetector 49 is placed at or near the imaging position of the light reflective layer 26 of the optical disc 21, and when the focus is out of focus, the center of the spot moves on the photodetector 49 to detect defocus. It can be applied to any optical system. In the optical system shown in FIG. 6, the laser beam L is incident obliquely to the optical axis 47 of the objective lens 40 and is irradiated onto the light reflecting layer 26. In this case as well, a convergent laser beam L is transmitted from the objective lens 40 to the projection lens 48 as shown by the broken line.
When the light reflecting layer 26 approaches the objective lens 40
From there, the projection lens 48 is irradiated with a diverging laser beam L as shown by a chain line. therefore,
The laser beam L directed from the projection lens 48 to the photodetector 49 is deflected according to the degree of defocus, and the size of the spot pattern changes on the light receiving surface of the photodetector 49, and its projection position is deflected. That will happen. In the optical system shown in FIG. 7, a vibrism 71 is provided between the projection lens 48 and the photodetector 49. Therefore, the laser beam L draws a trajectory shown by a solid line when it is in focus, and is deflected by the pipe prism 71 when it is out of focus. In the optical system shown in FIG.
A mirror 72 is provided at the imaging point of the beam waist determined by the beam waist and the projection lens 48, and a lens 73 that forms the image on the mirror 72 onto the photodetector 49 is provided between the mirror 72 and the photodetector 49. It is set in. At a focused point, the laser beam L is focused onto the mirror 72 as shown by a solid line, whereas at an out-of-focus point, a convergent or diverging laser beam L shown by a broken line or a dashed line
will be focused by the projection lens 48, and as a result the laser beam L will be deflected by the mirror 72. Furthermore, in the optical system shown in FIG. 9, the objective lens 40 is irradiated with a laser beam L that passes through a region spaced apart from the optical axis 47 and is parallel to the optical axis 47. Even in this case, the laser beam directed from the projection lens 48 toward the photodetector 49 will be deflected depending on the distance between the objective lens 40 and the light reflection layer 26.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to read at least information from an information storage medium using focused light. In the optical head including an objective lens, a photodetector for detecting light emitted from the information storage medium, and a holder for supporting the light source, the holder is formed of an organic insulator with a low thermal elongation. Not only does the optical axis not easily shift due to temperature changes, making it possible to stably detect defocus, etc., but it also reduces the number of parts and allows for a simple and compact structure.Moreover, the electric circuit is placed on the holder. Since it becomes possible to install the device, it can be made even smaller, and there are excellent effects such as eliminating concerns about noise.

[Brief explanation of the drawing]

Figures 1 to 5 show one embodiment of the present invention.
The figure is a longitudinal side view showing a portion of the semiconductor laser, Figure 2 is a front view showing the holder, Figure 3 is a block diagram schematically showing the information recording/reproducing device, and Figure 4 is a perspective view showing the optical system for detecting defocus. 5(a>(b)(c) are explanatory diagrams showing the trajectory of the laser beam when the same optical system is in focus and out of focus. FIGS. 6 to 9 are other defocus detection methods. FIG. 10 is a longitudinal cross-sectional side view showing a conventional example. 21... Information storage medium (optical disk), 36... Light source (semiconductor laser), 40... Objective lens, 49・
...Second photodetector, 55...Holder, 57...
Electric circuit pattern. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

Claims (3)

[Claims] (1) A light source capable of reading at least information from an information storage medium using focused light; an objective lens for condensing the light emitted from the light source onto the information storage medium; and the information storage medium. 1. An optical head comprising a photodetector for detecting light emitted from the light source and a holder for supporting the light source, wherein the holder is made of an organic insulator with a low coefficient of thermal expansion. (2) The optical head according to claim 1, wherein the holder is used as a circuit board on which an electric circuit pattern is arranged. (3) The optical head according to claim 2, wherein the electric circuit is a circuit that drives a light source.