JPS59201240A - Optical head - Google Patents

Abstract

PURPOSE:To improve the optical performance of an optical head and to reduce the head in thickness and size by arranging an optical head and an objective lens actuator at right angles to the optical axis of an objective lens. CONSTITUTION:A semiconductor laser 21, collimator 22, polarizing prism 23, and reflecting prism 25 are arranged on a line, and the objective lens actuator 31 is arranged on the prolongation of the straight line. An arm 30 is projected from this objective lens actuator 31 and the objective lens is held atop. The polarizing prism 23 and a critical angle prism 28 are united together in crossing relation. Thus, the thin, narrow-width optical head which has high optical performance is obtained while aberrations of an image formation optical system are suppressed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a C head used for recording and reproducing signals on optical discs such as audio discs, video discs, and data discs.

Various types of optical heads have been proposed in the past, including one shown in FIG. 1, for example. This optical head is designed to detect a focus error signal using the critical angle method. The linearly polarized light from the semi-packed laser 1 is made incident on the polarizing prism 8 as a parallel beam by the collimator lens 2, reflected by the polarizing film 4, totally reflected by the reflecting surface 5, and then passed through the λ/4 plate 6. The yC-axis and light It is supported movably in two radial directions of the optical disc 8 perpendicular to the axis, and is driven in the two axial directions by the objective lens actuator 9 so that the original spot follows the center of the track of the optical disc 8 in a focused state. Focus servo and radial servo are performed as follows. The reflected light from the optical disk 8 of the optical spot follows the same yt path as the outgoing path until it reaches the polarizing film 4, but on the return path, the polarization direction is perpendicular to the polarization of the outgoing path and the light direction due to the action of the λ/4 plate 6. In order to do this, the return light from the original disk 8 that passes through the polarizing film 4 is incident on the photodetector 11 through the critical angle prism 1o, as shown in FIG.

The critical angle prism 10 is a
It has two opposing optical surfaces 10a and 10b set so that the incident angle with respect to the optical axis is almost a critical angle, and by reflecting the returned light a total of eight times on these optical surfaces, focus error detection is carried out. is made incident on the photodetector 11. In addition, the original 4 ejector] 1 is a 4-piece ejector divided into two parts in the radial direction and tangential direction of the optical disc 8, respectively.
It has two light receiving areas 11a to lld, and these light receiving areas 1
A data signal, a focus error signal and a radial error signal are generated based on the outputs of 1a to 11(i).

That is, in the optical head shown in FIG. 1, when the optical disk 8 is in the focal point of the objective lens 7, the return light from the optical disk 8 that is incident on the optical angle 71J sum 10 becomes a parallel beam of light; Since the angle of incidence on the optical surfaces 10a and 10b is approximately the critical angle for all '1cf14', all the light rays are totally reflected as shown in No. 214'1A. ll
It is not uniformly incident on d. On the other hand, when the optical disc 8 deviates from the focal point, the stray light incident on the critical angle prism 10 becomes convergent light or the 21st gql as shown in FIG. 2B.
When the divergence becomes C as shown in Ci, the optical surfaces 10a, 1
Since the original angle of incidence on ob is greater than the critical angle on one side of the plane orthogonal to the plane of incidence passing through its optical axis and smaller on the other side, the sum of °C and I output 1 ;, 11, brightness and darkness occur in the tangential direction. The brightness and darkness of the Kunjential direction on the photodetector 1i'W 11 is determined by the relationship between the incident angles of the light rays on both sides of the optical surfaces 10a and 10b, which are perpendicular to the incident plane that traces the optical axis of the returned light. , 1(y flux'yC and the divergent light are reversed, so the brightness and darkness are reversed in FIG. 2B and C. Therefore, each output of the light receiving areas 11a to lld is
+ b , O and d, (a+'b)-(C+
A focus error signal can be obtained by a).

Note that the radial error signal is (, a+c ) −(b+
ci ), and the data signal is (a+b +O+a
) can be obtained respectively.

On the other hand, in order to obtain good optical performance in the optical head shown in Fig. 1, it is necessary to increase the MTF. The long axis direction of the elliptical beam incident on the objective lens 7 should be the tangential direction; ■ To increase the focus error detection sensitivity, the incident light on the critical angle prism 10 should be p-polarized; ■ Focus error signal [Oa] so that the optical surface of the critical angle prism 10 is not affected by push-pull noise caused by pits.

The following conditions are required: the direction of the plane of incidence with respect to the optical disc 10b is in the tangential direction, and (2) the occurrence of aberration in the optical system for forming an image of the original spot on the optical disk 8 is suppressed as much as possible. In the optical head shown in Fig. 1,
The above conditions ■, ■, and ■ can be met, but ■
Regarding the condition (2), since reflection is performed twice in the imaging optical system, there is a drawback that it is difficult to suppress the occurrence of aberrations. The reason for this is that the required level of the surface area of the reflective surface for suppressing the generation of wavefront aberration is several times stricter than that in the transmission direction.

As mentioned above, the °C head shown in FIG. 1 has good performance except for the aberration of the optical system. However, in the VC head shown in FIG. 1, the objective lens 7 is supported within the objective lens actuator 9,
This paired 4 near 1 lens actuator 9 is the optical disk 8.
and the reflective surface 5 of the polarizing prism 3, the semiconductor laser l and the collimator lens 2 are arranged in the vertical force direction with respect to the original disk 8, and the optical disk inside the critical angle prism 10 is It is difficult to make the optical disc 8 thinner in the vertical direction for reasons such as the need to increase the size of the critical angle prism 10 in order to reflect the reflected light from the optical disc 8 several times. For this reason, using such an optical head, for example, if the disk diameter is l 2O1
When constructing a 476 compact disc player, it is not possible to make it large enough to accommodate the compact disc, and therefore a small and thin optical head is desired.

It is an object of the present invention to provide an optical head that satisfies the above-mentioned conditions, has good 'rlIj configuration, yCC note performance, and is thin and small in order to meet the above-mentioned demands. .

The C head of the present invention includes an objective lens, an optical system that irradiates light from a light source onto a recording medium through the objective lens, and guides the reflected light to a photodetector via the objective lens, and an optical system that directs the reflected light to a photodetector via the objective lens. An arm that extends in a direction perpendicular to the optical axis of the lens and holds the objective lens at one end, and is connected to the other end of the arm, and holds the objective lens through the arm in the direction of the optical axis and the arm that holds the objective lens at one end. Pair 91 displaced in a direction substantially perpendicular to the optical axis
/I lens actuator, and the optical system and the objective lens actuator are arranged side by side in a direction perpendicular to the optical axis of the objective lens.

The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a perspective view showing the configuration of an example of the essential parts of the γC head of the present invention. In this example, the linearly polarized light from the semiconductor laser 21 is made incident on the polarizing prism 28 as a parallel light beam by the frimeter lens 22, transmitted through the polarizing films 2 and 4, and the transmitted light is totally reflected at right angles by the reflecting prism 25. After that, the elliptical beam is guided through a λ/4 plate 26 to an objective lens 27 such that the major axis direction of the elliptical beam is in the tangential direction of the original disk (not shown), and is projected onto the optical disk in the form of a spot. The reflected light from the optical disk follows the same optical path as the outgoing path up to the polarizing prism 28 and is incident on the polarizing film 24, but on the returning path, the polarization direction is perpendicular to the polarizing direction of the outgoing path due to the action of the λ/4 plate 26. Therefore, all the returned light is reflected by the polarizing film 24. This polarizing film 24
The return light from the optical disk is reflected once on the optical surface 28a of the critical angle prism 2, and the radial direction and tangential direction of the optical disk are reflected in the radial direction and tangential direction of the optical disk in the same PJ5 as in the j-tight line in Fig. 1. Four light-receiving areas 2 each divided into two
9a to 29 (output powers of these light receiving areas 29a to 29d by making the light incident on the photodetector 29 having i), data signals, focus error (yJ and radial error signals) are detected in the same manner as explained in FIG. get.

As in the case of FIG. 1, the optical surface 28a of the critical angle prism 28 is set so that the angle of incidence of the optical disc onto the optical axis of the optical disc is approximately the critical angle. In order to obtain the same detection sensitivity as the three reflections in the case of FIG. 1 by reflecting the return -yC once at the surface 28a,
As described in Japanese Unexamined Patent Publication No. 57-1224.10-, the optical surface 28a (multiple If3+I@).

Apply anti-reflective coating. In addition, the incident surface of the polarizing prism 23 is arranged such that the incident light on the critical angle prism 28 is p-polarized light and the incident surface with respect to the optical surface 28a is in the tangential direction. When the C-shaped surface 28a and the incident surface are orthogonally crossed, the polarizing prism 28 and the critical angle are The prism 28 is integrated by adhesive or the like.

On the other hand, the objective lens 27 is held at one end of an arm 80 extending in a direction perpendicular to its tip axis, and the other end of this arm 30 is placed on an extension of the optical path from the semiconductor laser 21 to the reflection prism 25. Objective lens actuator 31
Connect to. In this example, the objective lens actuator 31 is connected to the other end of an arm 80, and is capable of sliding a bobbin around which a focusing coil 3z and a radial coil 83 are wound in the optical axis direction of the objective lens 27. The objective lens 27 is rotatably supported on the shaft 34 in a plane perpendicular to the bobbin and the arm 80 by generating magnetic flux in a direction perpendicular to the direction of current flowing through the focus coil 82 and the radial coil 33. The focus servo and radial servo are performed so that the optical spot follows the center of the track of the optical disk in a focused state by displacing it linearly in the optical axis direction and displacing it in a circular arc within a plane perpendicular to the optical axis. Do it like this.

4A and 4B are a sectional view and a plan view showing a specific structure of the optical head shown in FIG. 3. FIG. Semiconductor laser 21
is held in an inner frame 41, and this inner frame 41 is fixed to an outer frame 42 with springs 43 and screws 44 so as to adjust the position in the beam emission direction. This outer frame 42 is provided with an aperture 45 that focuses the beam from the semiconductor laser 21, and a collimator lens 22 that converts the beam into a parallel light beam.
, and fix this outer frame 42 to the substrate 46 with screws 47 so that the position of the collimator lens 22 in the optical axis direction is 4. Further, the integrated polarizing prism 23 and critical angle prism 28 are shown in FIG.
1')- and B, the rotational angle ul' relative to the substrate 46 can be adjusted to adjust the angle of incidence of the return light from the C-task on the optical surface 28a of the critical angle prism 28 with respect to the optical axis. (fit;) is held by the recessed rotating member 48. Furthermore, the reflection prism 25 and the λ/4 plate 26 are integrated with adhesive or the like and fixed to the substrate 46, and the photodetector 2
9 faces the exit surface of the critical angle prism 28, and
It is attached to the holding member 4r9 attached to the screw 50 with the screw 50.

On the other hand, the bobbin 5, which constitutes the objective lens actuator 31 and has a focus coil 82 and a radial coil 88 wound around its outer periphery, is connected to the arm 3 that holds the objective lens 27.
0, and this bobbin 51 is rotatably supported on a shaft 84 provided on the substrate 46 so as to be slidable in the extending direction of the shaft 34, that is, in the optical axis direction of the objective lens 27. Together with these bobbin 51 and arm 8
0 is supported on the substrates 4 and 6 via an elastic member 52 so that its displacement is not hindered. In addition, a ring-shaped magnet 53 is provided around the shaft 34 on the substrate 46, and a cylindrical inner yoke 5711 is provided on the inner circumferential side of the bohin 51 in contact with this magnet 53, and the outer circumferential A pair of outer yokes (11 yokes 55a, 551) are provided facing each other on the side, and the inner yoke 54 and the outer yoke 55a are connected by the magnet 5B.
and 55b, respectively, the focus coil 3
2 and the radial coil 38,
This magnetic flux, focus coil 82, and radial coil 33
Depending on the magnitude and direction of the current flowing through the bobbin 5.
1 is displaced along the shaft 3+ to perform focus servo, and by rotating around shaft 34 to perform radial servo. In addition, the other parts except the pair 9Z lens 27 are 8+ (with case 56). cormorant.

FIG. 4B is a partially cross-sectional plan view with the case 56 removed.According to the embodiment described above, the semiconductor laser 21 and the reflection prism 25 are arranged in a straight line, and the objective A lens actuator 81 is arranged on the extension of the lens actuator 5, an arm 30 is made to protrude from this objective lens actuator 81, and an objective lens 27 is held at its tip, and the polarizing prism 23 and the critical angle prism 29 are arranged in a crossed shape. So, conclusion 1. #,
! It is possible to obtain a thin and narrow optical head that more effectively suppresses the occurrence of aberrations in the optical system and exhibits good optical performance. For example, as shown in FIGS. 6A and 6B, when the height of the optical head 61 is H1, the width is W1, and the length is L, when viewed in the vertical direction of the compact disc 60, in the conventional configuration shown in FIG. ,XL7
Although it was less than 2 decoys, it has the same specifications and performance.
If the head 61 has the configuration of this embodiment shown in FIGS. 31 to 5, H19yy, ry X W 20 qm×L
The width is about 77 degrees, and the width can be significantly increased especially in the U and W directions, making it possible to realize a player that is suitable for thin and small compact discs.

It should be noted that the present invention is not limited to the above-mentioned example, and may be modified in many ways. For example, in the above-mentioned example, the focus servo by the objective lens actuator may be a sliding type, and the radial servo may be rotated. Is it a moving shape, or is it placed on a straight line connecting the semiconductor laser 21 to the offending prism 25? If the objective lens actuator is a fixed type objective lens actuator, from which an arm aO protrudes and the objective lens 27 is held at its tip, a method of supporting the objective lens using a plate, etc. may be used. . ′! ? , by changing the polarizing prism 23 to a semi-transparent prism and using the λ/4 plate 2.
Can I remove 6? ). Furthermore, a mirror may be used instead of the reflecting prism 25.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the j<p configuration of a conventional optical head;
Figures A to C are diagrams for explaining focus errors due to the critical angle method. Figure 8 is a perspective view showing the configuration of an example of the main part of the optical head of the present invention. Figures 4A and B are diagrams shown in Figure 8. 5A and B are partial detailed views thereof, and FIGS. 6A and B are front and bottom views for explaining the present invention in detail. It is. 21... Sitting conductor laser 22... Collimating lens 28... Polarizing prism 24... Polarizing light 1
1・t￥25...Reflection prism 26...λ/
Plate 27... Objective lens 28... Critical angle prism 28a..., optical surface 29... Light detection area; 129a-29d... Light receiving area 30... Arm 3]... Objective lens actuator 32...Focus coil 83...Radial coil 34...Shaft 4]...1゛frame 42...
... Outer frame 4.3 ... Spring 44 ... Screw 45 ... Aperture 46 ... Board
47... Neshi. 48...Rotating member 49...Holding cap 50
...Screw 51...Bobbin 52...
Elastic E'its material 58... Magnet 54...
Inner yoke 55a + 55b, -...Outer yoke 56...Case 60...Compact disc 61...Optical head procedural amendment June 22, 1981 1, Indication of case 1982 Patent Application No. 738 lI・5 No. 2 Title of the invention 9 No. 3, Relationship with the person making the amendment Special feature δ'1. Applicant ((+37) Olympus Optical Industry Co., Ltd. 7, Contents of the amendment (as attached) ■Because there is 1 in page 5, line 8 of the specification r, ``1'' has been omitted.''
Correct. 2.Delete the entire line 9 to IO of page 11 of the same document, "Collimator - so that it can be used." 8 In the same page, page 12, line 6, "installed on the boards 4 and 6" was changed to "the shaft fixing was installed on the board 46 via 57."
Corrected H, and corrected "ring-shaped m-bobbin" in lines 12 and 13 of the same page to "provided with a ring-shaped yoke 53 made of magnetic material and connected to this yoke 53 to form a bobbin", and "Outer circumferential side G-1 and 55b" on page 15-17 lines
1 outer circumference (Ill G, m) A pair of permanent magnets 55a.
, J determined state Q! A pair of permanent magnets 55a, 55b and an inner (ill E-ri 54) are arranged facing each other at
・to" (Correct. 4 Correct "29" on page 13, line 14 of the same document to l-28J. 5 Correct "1-53...magnet" on page 16, line 7 of the same document to 153・
... yoke", and in the 9th line of the same page, the "outer yoke" was corrected to "-permanent magnet". Between the 12th and 13th lines of the same page, it was changed to "57...Shaft fixing collar 58a, 58t). ...Attach the outer yoke 6. Press down B as shown in the drawings, Figures 3 and 4, separate sheet IJ.

Claims (1)

[Claims] 1. An objective lens, an optical system that irradiates light from a light source onto a recording medium through the objective lens, and guides the reflected light to a photodetector through the objective lens, and a direction perpendicular to the optical axis of the objective lens. an arm that extends to and holds the objective lens at one end; and an arm that is connected to the other end of the arm and that holds the objective lens in the direction of its optical axis and in a direction substantially perpendicular to the optical axis. an objective lens actuator for positioning the optical system, and the optical system and the objective lens actuator are arranged side by side in a direction perpendicular to the optical axis of the objective lens.