JPS60119644A - Optical head - Google Patents

Abstract

PURPOSE:To detect stably out-of-focus by connecting a frame supporting a collimate optical system and a connecting member connecting the said frame and a light source at a position to make hardly an optical axis shifted against external temperature changes. CONSTITUTION:A semiconductor laser 30 is supported by the 1st frame 74 and collimator lenses 32, 34 are supported to the 2nd frame 76 respectively. The 1st and 2nd frames 74, 76 are fixed at the same time by a connecting member 72. The 2nd frame 76 and the connecting member 72 are connected by a mounting member 78 at one position in this case and the connected position is a position where a lens face of the collimator lenses 32, 34 closest to the semiconductor laser 30 is moved only within a permissible range to the semiconductor laser 30 due to thermal expansion and contraction, that is, a position in the vicinity of the lens face of the collimator lenses 32, 34 closest to the semiconductor laser 30.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an apparatus capable of reading at least information from an information storage medium using focused optical sound, such as a C for DAD.
Playback-only information storage media such as D (computer disc) and video disc, image files, still image files, and COM (computer output memory)
At least for information storage media, which can be used for information storage media that can completely record information by causing state changes such as completely drilling holes in the recording layer with focused light, and playback from there, as well as erasable information storage media. The present invention relates to an optical head used for reproduction or recording.

[Technical background of the invention and its problems]

In the above type of optical head, when reading all the information from the information storage medium or adding all the new information, the focal point of the focused light always matches the position of the recording layer or the light reflection layer of the information storage medium. There must be. Therefore,
An optical information reproducing device or an optical information recording and reproducing device equipped with this optical head has an automatic focus detection function and all its correction functions.

However, with this function, if the optical axis shifts, the spot moves on the photodetector, resulting in false detection as if the spot is out of focus.

Therefore, if the optical axis is shifted due to changes in the external environment (humidity changes, humidity changes, mechanical vibrations, shocks, etc.), the focus will be blurred. It is particularly susceptible to temperature changes.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its purpose is to provide an optical head in which the optical axis is difficult to shift due to external temperature changes, and defocus detection can be performed stably. It's about doing.

[Summary of the invention]

In order to achieve the above object, the present invention includes a light source, a collimating optical system that includes a plurality of frimeter lenses that have a light focusing function, and that collimates the light sound emitted from the light source, and a collimating optical system that supports the entire collimating optical system. comprising a frame and a connecting member connecting the frame and the light source,
It is characterized in that the frame and the connecting member are connected at VT11 points.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to all the drawings. 1 shows an entire information recording and reproducing apparatus to which the optical head of the present invention is applied, and 2 shows an optical disk as an information storage medium. This optical disc 2 is formed by laminating a pair of disk-shaped transparent plates 4.6 with inner and outer spacers 8, 1θ interposed therebetween, and an optical disc as an information recording layer is formed on the inner surface of each of the transparent plates 4, 6. A reflective layer 12.14 is formed by vapor deposition. A tracking guide 16 is formed helically on each of the light reflecting layers 12, 14, and information is recorded on the tracking guide 16 in the form of pits. A hole is bored in the center of the optical disc 2, and when the optical disc 2 is placed on the turntable 18, a center spindle 2o of the turntable 18 is formed.
is inserted into the hole of the optical disc 2, and the rotation centers of the turntable 18 and the optical disc 2 are aligned. A chuck device 22 is further attached to the center spindle 20Vc of the turntable 18, and the optical disc 2 is fixed on the turntable 18 by this chuck device 22.

The turn cheagle 18 is rotatably attached to a support base (not shown).
and is rotated at a constant speed by a drive motor 24.

The optical head 26 is movable in the radial direction of the optical disc 2 by a linear actuator 28 or a rotating arm! This optical head 26 includes a laser beam.
A semiconductor radar 3o is provided as a light source that generates a beam.

When writing information onto the optical disk 2, a laser beam whose light intensity is modulated according to the information to be written is generated from the semiconductor laser 3o, and the information is written onto the optical disk 2.
When reading from the semiconductor radar 30, a laser beam having a constant light intensity is generated. A diverging laser beam generated by the semiconductor radar 3° is converted into a parallel light beam by a collimating optical system, ie, a collimator lens 32° 34, and is directed to a polarized beam beam 36. The collimated laser beam A reflected by the polarized beam sgelitter 36 passes through the 1/4 wavelength plate 3
8 and enters the objective lens 40, and is focused toward the light reflection layer 14 of the optical disc 2 by the objective lens 4o. The objective lens 40 is supported by a voice coil 42 so as to be movable in its front axis direction.
0 is positioned at a predetermined position, the beam waist of the focused laser beam emitted from this objective-lens 40 is projected onto the surface of the light reflective layer 14, and the minimum beam spot is projected onto the surface of the light reflective layer 140. is formed. In this state, the objective lens 40 can be kept in focus and information can be written and read. When writing all the information, the light reflecting layer 1 is
A pit is formed in the tracking guide 16 on 4,
When reading information sound, a laser beam with a constant light intensity is used.
The beam is intensity modulated by a bit formed on the tracking guide 16 and reflected.

The diverging laser beam reflected from the light reflection layer 14 of the optical disk 2 is converted into a parallel beam by the objective lens 40 when focused, passes through the entire 174 wavelength plate 38 again, and is returned to the polarizing beam splitter 36. . By reciprocating the laser beam through the 1/4 wavelength plate 38't, the plane of polarization of the laser beam is rotated by 90 degrees compared to when it is reflected by the polarizing beam splitter 36, and the plane of polarization is changed by this 90 degrees. The rotated Rade beam is not reflected by the polarizing beam splitter 36, and is not reflected by the polarizing beam splitter 3.
All 6 will be passed. The Rade beam that has completely passed through the polarizing beam splitter is divided into two systems by a half mirror 44 , one of which is irradiated onto a first photodetector 48 by a convex lens 46 . This first photodetector 4
The first signal detected at step 8, which contains all the information recorded on the optical disc 2, is sent to a signal processing device and converted into digital data. From the other laser beam separated by the half mirror 44, only the component that passes through a region separated from the optical axis 53 is extracted by the light shielding plate 52, and after passing through the projection lens 54't, it is incident on the mirror 56. Ru. Here, the light shielding plate 52 may be formed of any one of a prism, an anode, a knife edge, and the like.

The signal detected by the second photodetector 58 is processed by a focus signal generator 60.
A focus signal generated from 0 is given to the chair/coil drive circuit 62. The chair coil drive circuit 62 drives the chair coil 42 in accordance with the focus signal to maintain the objective lens 40 in a fully focused state. Note that in order to accurately trace the tracking guide 16 formed on the light reflective layer 14 of the optical disc 2, the second
The signal from the photodetector 48 may be processed to operate the linear actuator 28, the objective lens 40 may be moved laterally, or a galvanometer mirror (not shown) may be operated.

The optical system for full detection during focusing shown in Fig. 1 is simplified as shown in Fig. 2, and the trajectory of the laser beam related to focus detection is shown in Fig. 3. It can be drawn as shown. When the objective lens 40 is in focus, the beam waist is projected onto the light reflective layer 14, and the minimum beam
A beam waist spot 64 is formed on the light reflecting layer 14. Normally, the laser that enters the objective lens 40 from the radar device 30 is a parallel beam of light.
．． The beam waist is formed on the focal point of the objective lens 40. However, the radar device 30 is attached to the objective lens 40.
If the laser incident from the laser beam is slightly diverging or converging, the beam waist will be formed near the focal point of the objective lens 40. Figures 1, 2 and 3 (a)
In the optical system shown in (C) to (C), the light receiving surface of the photodetector 58 is arranged on the imaging plane of the beam waist spot 64 in the focused state. Therefore, during focusing, an image of the beam waist spot 64 is formed at the center of the light receiving surface of the photodetector 58.

iQ] H, as shown in Figure 3 (A), the beam waist f! , a laser beam 4 is formed on the light reflection layer 14 , and the laser beam reflected by the light reflection layer 14 is converted into a parallel beam by the objective lens 40 and directed toward the light shielding plate 52 . Only the light components that pass through the entire area away from the optical axis 53 are extracted by the light shielding plate 52, focused by the projection lens 54, and minimized on the photodetector 58 to form a beam.
West Su4. image is formed thereon.

Next, when the objective lens 40 approaches the light reflective layer 14, a beam waist is generated as the laser beam is reflected by the light reflective layer 14, as shown in FIG. That is, a beam waist occurs between the objective lens 40 and the light reflective layer 14. In such an out-of-focus state, the beam waist normally occurs within the focal length of the objective lens 40, so assuming that the beam waist functions as a light spot, it is clear that the beam is reflected by the light reflecting layer 14. The ray-f beam emitted from the objective lens 40 is
0 into a diverging laser beam. Since the laser beam component that has completely passed through the light shielding plate 52 is also diverging, this laser beam component is transmitted through the projection lens 5.
4, the light is not focused to the minimum on the light-receiving surface of the photodetector 58, but is focused toward a point farther than the photodetector 58. Therefore, the laser beam component is projected upward in the figure from the center of the light-receiving surface of the photodetector 58, and a pattern larger than the beam spot image is formed on the light-receiving surface. Furthermore, when the objective lens 40 is separated from the light reflection layer 14 as shown in FIG. In such an out-of-focus state, the beam waist is usually outside the focal length of the objective lens 40 and is formed between the objective lens 40 and the reflection M74. The beam will have full convergence. Therefore, the light shielding plate 5
The laser beam component that has passed through 2 is further converged by a projection lens 54, and a rear photodetector 58 with a full convergence point is formed.
is projected onto the light-receiving surface of. As a result, a pattern larger than the image of the beam waist spot is formed on the light receiving surface of the photodetector 58 from the center upward and downward in the figure.

In the coil, as mentioned above, since the Radhe beam generated from the semiconductor laser 30 is diverging, it is converted into a parallel beam by the collimator lens 92, 4 (see FIGS. 1 and 4). However, these semiconductor lasers 3
0 and collimator lenses 32, 34 are integrated by a connecting member 72 as shown in FIG. That is, the semiconductor laser 30 is supported by the first frame 74, and the collimator lens 32.34 is supported by the second frame 76, and these first and second frames 74.7
6 are simultaneously fixed by a connecting member 72. In this case, the second frame 76 and the connecting member 72 are connected to the mounting member 7
The collimator lenses 32 and 34 are connected at one point by 8, and the lens surfaces closest to the semiconductor laser 30 of the collimator lenses 32 and 34 are connected to the semiconductor laser 3 due to thermal expansion and contraction.
The position is such that there is only movement within an allowable range with respect to 0, that is, near the lens surface of the collimator lens 32, 34 that is closest to the semiconductor laser 3°. Note that the connection using the mounting member 78 can be achieved by placing taps on all the connecting members 72 near the collimator lens surface, and pressing the second frame 76 with screws to secure the joint. This is done by making a hole in the connecting member 72 near the lens surface closest to the lens surface, and pouring adhesive through the hole and fixing it.

Here, in such a configuration, the connecting portion between the second frame 76 and the connecting member 72 is connected to the collimator lens 32.3.
Since it is located near the lens surface closest to the semiconductor laser 30 of the collimator lenses 32 and 34, the distance from this coupling part to the lens surface of the collimator lenses 32 and 34 closest to the semiconductor laser 30 may change due to temperature changes. Conceivable. So now,
As shown in FIG. 6, the distance from the semiconductor laser 30 to the connecting portion between the second frame 76 and the connecting member 72 is
If we consider the case where the coefficient of thermal expansion of the connecting member 72 is α and the temperature changes by Δt°C, the connecting member 72 will thermally expand and contract around the position of the attachment part 78.
Therefore, the amount of change ΔX in response to temperature change in the distance a between the semiconductor laser 30 and the lens surface of the collimator lens 32, 34 closest to the semiconductor laser 30 is Δx = aα
Δt.

By the way, when the temperature changes in this way, if the distance p between the lens surface of the collimator lens e32, e34 closest to the semiconductor laser 30 and the semiconductor laser 30 changes,
The light that exits the collimator lens will have either divergent or convergent properties, and the greater the absolute value of ΔX, the greater the deviation from parallelism of the light that exits the collimator lens 32, 34, and eventually the focus will be It blurs.

Therefore, in order to keep the value of ΔX within the allowable amount of defocus (the range in which it is okay for the focus to shift),
The material of the connecting member 72 and the semiconductor laser 30 at room temperature
What is necessary is to determine the distance between and the lens surface of the collimator lens 32, 34 that is closest to the semiconductor laser 30.

For example, the allowable defocus amount of an optical head in an optical disk device is as follows. In other words, when we examine the maximum allowable value for defocus, we find that the diffraction of the reflected light from the tracking guide of the focused laser beam is
Pu5h-P detects track deviation using turns
In the u1l method, if a large amount of defocus occurs, the track deviation detection signal does not appear. Figures 7 and 8 show a groove (continuously extending in a spiral shape) used as a tracking guide.
This shows the track deviation detection signal that appears for each groove when the radar switch crosses the groove (groove group) in the right angle direction. Each drawing represents the state of the track deviation detection signal when the focus is blurred in each direction. In addition, in the figure, a is the objective lens 4.
The amount of deviation of the light reflective layer 14 from the focal point of the emitted light from 0,
The side far from the objective lens 40 is defined as positive. Further, the upper curve shows the tracking signal 50A, and the lower curve shows the total signal 50B, and both zero points are 2 dl from the top, and anything below this is positive. From the figure, it can be seen that if the focus is out of focus by 3.0 μm or more, or at most 5.0 μm, the Pu5h-Pu1l method signal cannot detect the track deviation (note that the smoother the waveform of signal 5 (IIA), the more
Also, the larger the amplitude, the better. ).

Further, when recording is performed by causing a state change such as making a hole in the light reflection layer 14 of the optical disc 2, defocusing occurs and the spot on the light reflection layer 14 becomes larger, making it difficult to perform recording.

The suit size at (for example, the numerical aperture (NA) value of the light reflecting layer 14 at the time of focusing is NA (here, NA is treated as a symbol in the mathematical formula), and the lens has ideally no aberrations. Assume that a parallel laser beam whose distribution is uniform everywhere is incident, and the spot size at) at the point where the beam is condensed after passing through this lens is given by the wavelength of the laser beam being λ. Also, assuming that the intensity distribution at this time is similar to a Gaussian distribution, let ωG be the radius of the annular zone where the intensity at the beam waist is 1/e2 of the center intensity, and ωG is the radius of the ring zone where the intensity at the beam waist is 1/e2 of the center intensity. This formula can be used to determine the radius ω(6) on the light reflecting layer when the focus is out of focus. Therefore, the spot center intensity at this time decreases to 1. If the lowest central intensity that can be recorded is lm1n, now λ = 0.83 μm, N A = 0.6, 1
When m1n=0.7, =0.79μm λ=0.83/jm, NA=0.5, 1
When m1n=0.7, 0.44 X O,65 121≦□=1.16 fim o,25.

By the way, the values of λ and NA can be changed before and after the above-mentioned preparation, and considering how to take lm1n, etc., it is considered that the allowable defocus amount should be set at 2°0 μm above. Therefore, for an optical disk device, the value of ΔX is determined so that the change is within the allowable defocus amount described above, and the value of ΔX is determined based on the material of the connecting member 72 and the collimator lens 32° from the semiconductor radar 3o at room temperature. What is necessary is to determine the distance a to the lens surface closest to the semiconductor laser 3o of No. 34.

That is, the semiconductor laser 3o and the recording film (light reflective layer 14)
Since there is an image formation relationship on the surface, when the vertical magnification is M, the amount of movement d of the semiconductor radar 30 when the defocus δ occurs on the recording film surface is given by d=Mδ.

As mentioned above, since the allowable defocus amount is 2°0, the collimator lens 3 in the semiconductor laser 30
The allowable amount of movement with respect to the lens surface closest to the semiconductor laser 30 of 2.34 is given by ±2XM. Therefore, the semiconductor laser 30 and collimator lens 3 due to temperature change
The amount of movement of the semiconductor laser 30 may be suppressed so that the amount of change ΔX in the distance a from the lens surface closest to the semiconductor laser 30 of 2.34 falls within this allowable range. That is, each position may be determined so that 1aαΔt I <, M x δ (where δ = 2.0 μtn). Here, since the temperature usually only needs to be changed by changing from 0° C. to 40° C., Δt=±20° C. for room temperature. Therefore, 1.1aα1×M×δ
/1Δt1 (however, δ=2 urn r lΔtl=20) = In short, the connecting member 72 should be made of a material with as small a coefficient of thermal expansion as possible, and the semiconductor laser 30 and collimator lens 32 at room temperature should be determined. The distance to the lens surface closest to the semiconductor lens 30 of .34 may be made as close as possible.

According to the above configuration, even if a temperature change occurs, the distance between the semiconductor radar 30 and the lens surface of the collimator lens 32.degree. Since .34 is synthesized, it is considered that the distance between the front principal point of the collimator lens 32.34 and the lens surface of the collimator lens 32.34 closest to the semiconductor laser 30 does not change. The collimated state (parallel) of the light coming out of the meter lens 32.34.

The convergence and divergence states) can also be kept unchanged.

Therefore, it is possible to suppress the deviation from parallelism of the light that has passed through the collimator lenses 32 and 34 due to temperature changes, for example, and to keep the amount of defocus within an allowable range.

The above can be applied to any defocus detection, regardless of the defocus detection method. In addition to the above-mentioned example, it is also possible to apply the astigmatism method, for example.

Note that the means for detecting defocus by moving the center position of the spot on the photodetector is shown in FIGS. 2 and 3 (a) to 3.
(Not limited to the optical system shown above, various optical systems, such as
The optical systems shown in FIGS. 9 to 12 may also be used. In the optical system shown in FIG. 9, a laser beam is incident on the optical axis 90 of the objective lens 40 from a direction oblique to the light reflecting layer 1.
4 is irradiated with a laser beam. Even in this case, when the light reflection layer 14 moves away, the projection lens 54 is irradiated with a convergent laser beam as shown by the broken line, and when the light reflection layer 14 approaches, the projection lens 54 is irradiated with a focused laser beam as shown by the broken line. The lens 54 is irradiated with a diverging laser beam as shown by the dashed line. Therefore, the laser beam directed from the projection lens 54 to the photodetector 58 is deflected by the projection lens 54 according to the degree of defocus, and the size of the pattern changes on the light receiving surface of the photodetector 58. At the same time, the projection position is displaced. In the optical system shown in FIG. 10, a pipe rhythm 92 is provided between the projection lens 54 and the photodetector 58.
is provided. Therefore, when in focus, it draws a trajectory as shown by the solid line, and when out of focus, it is deflected by the pipe rhythm 92. In the optical system shown in FIG. 11, the beam determined by the objective lens 40 and the projection lens 54
A mirror 94 is provided at the imaging point of the waist, and a lens 96 is provided between the mirror 94 and the photodetector 58 for forming an image on the mirror 94 onto the photodetector 58. When in focus, the laser beam is focused onto the mirror 94 as shown by the solid line, while when out of focus, the laser beam is focused by the projection lens 54 as shown by the dashed line and the dashed line. As a result, the laser beam will be deflected by mirror 94. Furthermore, in the optical system shown in FIG.
The beam is irradiated onto the objective lens 40. Even in this case, the Rade beam directed from the projection lens 54 toward the photodetector 58 will be deflected depending on the distance between the objective lens 4σ and the reflective layer 14.

〔Effect of the invention〕

As explained above, according to the present invention, a collimating optical system includes a light source and a plurality of collimator lenses having a light condensing function and collimates the light emitted from the light source;
It is equipped with a frame that supports this collimating optical system and a connecting member that connects this frame and the light source, and since the frame and the connecting member are connected at one place, the optical axis is fixed against external temperature changes. It has excellent effects such as being difficult to shift and stably detecting defocus.

[Brief explanation of the drawing]

Figures 1 to 8 show one embodiment of the present invention.
The figure is a block diagram showing the information recording and reproducing device, Figure 2 is a diagram showing the defocus detection system, and Figure 3 shows the trajectory of the Radhe beam when in focus and when out of focus. Fig. 4 is a diagram showing the collimating optical system, Fig. 5 is a perspective view showing the support structure for the light source and collimator lens, and Fig. 6 is a diagram showing the support structure for analyzing the influence of temperature changes. Figure, Figure 7(f)~(Kalpa and Figure 80)~
(G) is a diagram showing a track deviation detection signal with respect to the amount of defocus, and FIGS. 9 to 12 are diagrams showing other different embodiments of the defocus detection system. 26... Optical head, 30... Light source (semiconductor laser), SZ, S4... Collimating optical system (collimator lens), 72... Connecting member, 76... Second frame. Applicant's agent Patent attorney Takehiko Suzue Figure 9 1/. Figure 10 Figure 11 Figure 12

Claims (3)

[Claims] (1) A light source, a collimating optical system consisting of a plurality of collimator lenses that perform a light focusing function and collimating the light sound emitted from the light source, a frame that supports this collimating optical system, and a frame that supports the collimating optical system, and a frame that supports the collimating optical system, and a frame that supports the collimating optical system, and a frame that supports the collimating optical system. a connecting member that connects the frame and the connecting member 1-1.
An optical head characterized by being joined at certain points. (2) The lens surface of the collimating optical system that is closest to the light source should be connected to the frame near the lens surface of the collimating optical system that is closest to the light source so that the lens surface that is closest to the light source of the collimating optical system only moves within the allowable range relative to the light source due to thermal expansion and contraction. The optical head according to claim 1, characterized in that the optical head is connected to the connecting portion side. (3) Distance from the light source to the joint between the frame and the connecting member ktz Thermal expansion overtone α of the connecting member, vertical double overtone due to the imaging relationship between the light source and the recording film surface on which the light from the light source is imaged When M, 1aα1≦δxM/Δt (however, δ
=211 m, Δt is a temperature change with respect to room temperature, and is ±20°C. The optical head according to claim 1 or 2, characterized in that the optical head is constructed so as to satisfy all of the following relationships.