JPS6325834A - Optical head - Google Patents

Abstract

PURPOSE:To perform excellent auto-tracking without being practically affected by the change of wavelength of a light source even if the wavelength of the light source is changes, by setting such correspondence relations between the distribution conversion direction of a luminous flux section intensity distribution converting means and the direction of the division line of a tracking optical sensor that they are equal to each other. CONSTITUTION:The light source, a means which converts the section intensity distribution of the luminous flux emitted from the light source to a specific direction, a pickup lens 14, a sensor lens 18, and a two-divided optical sensor 28 which obtains a tracking signal are provided. In this case, the distribution conversion direction of the luminous flux section intensity distribution converting means and the direction of the division line of the tracking optical sensor 28 are in such correspondence relations that they reactically coincide with each other. For example, a two-divided optical sensor 30 which obtains a focusing signal is provided, and the sensor 30 and the tracking optical sensor 28 are arranged in approximately equivalent positions with a beam splitter 26 between them with respect to the sensor lens 18. Thus, good auto-tracking is performed without being practically affected by the change of wavelength of the light source even it the wavelength of the light source is changed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical head with an optical information recording/reproducing bag.

[Background of the Invention] Conventionally, various types of media such as disk-shaped, card-shaped, and tape-shaped media have been known for recording information using light and for reading recorded information. Among these, card-shaped optical information recording media (hereinafter referred to as optical cards) are expected to be in great demand as small, lightweight, easy-to-carry, large-capacity media.

The present applicant has already proposed accurate auto-to-taking (hereinafter referred to as AT) and auto-focusing (
We have proposed an optical information recording/reproducing device and an optical card that can record high-density information at high speed while performing AF (hereinafter referred to as AF) and read out the recorded information at high speed.

:JS3 Figures (a) and (b) are diagrams showing the optical system arrangement of an example of an optical head used in an optical information recording/reproducing device similar to that disclosed in the above application. Figure 3 (a
) is a plan view of the optical head, and FIG. 3(b) is a partial side view of the optical head.

In the figure, reference numeral 2 denotes a semiconductor laser (hereinafter referred to as LD) as a light source, and a diverging light beam emitted from the LD is condensed by a collimator lens 4 into a parallel light beam. 6
is a beam shaping prism. Since the light beam emitted from the semiconductor laser 2 and collimated by the collimator lens 4 has a rotationally asymmetric (for example, elliptical) intensity distribution in its cross section, the parallel state is maintained by placing the shaping prism 6 in the 'A' position. The light beam remains as it is and has a substantially rotationally symmetrical cross-sectional intensity distribution.

Note that by combining a plurality of prisms, it is also possible to make the traveling directions of the light beams parallel before and after beam shaping. Further, in this example, the light beam is reduced by beam shaping, but it is also possible to enlarge the light beam by changing the arrangement of the prisms.

8 is a circular aperture, which is used to narrow down the diameter of the light beam to a desired size. That is, the aperture 8 is provided on the optical card 101 in order to set the diameter of the light beam spot to a desired value. The light beam spot diameter is determined by the orientation characteristics of LI)2,
Since there is a close relationship with the focal length of the collimator lens 4, N, A, the variable power ratio of the beam shaping prism 6, and the focal length of the pickup lens 14, N, A, etc., which will be described later, these should be taken into consideration. It is preferable to determine the shape and size of the aperture 8 in accordance with the desired light beam spot diameter and shape.

Incidentally, such an aperture does not necessarily have to be arranged at the position shown in the figure, and may be arranged, for example, between the collimator lens 4 and the beam shaping prism 6, or between the diffraction grating 10 and the pickup lens 14, which will be described later. Furthermore, it is also possible to use the aperture of the collimator lens 4 to also serve as the aperture 8.

The light beam passing through the circular aperture 8 enters the diffraction grating 10, is diffracted by the diffraction grating, and is converted into three parallel light beams (0-order light and ±1
(next order diffraction light). The zero-order light travels in the same X direction as the traveling direction of the light beam incident on the diffraction grating 10.

The light quantity ratio between the 0th-order light and the ±1st-order diffracted light produced by the diffraction grating 10 is determined in consideration of various conditions. That is, the light amount ratio is the medium sensitivity and reflectance of the optical card 101,
Depending on the sensitivity and exposure time of the optical sensors 28 and 30, the relative movement speed between the optical card lot and the optical head, etc., which will be described later, it is possible to record only with zero-order light during information recording, and the relative It is preferable to determine such a light amount ratio that a good reproduced signal can be obtained in 1 minute even if a relatively small amount of +1st order light is used. For example, such a light amount ratio is -1st order light: 0th order light: +1st order light. Light intensity ratio of 1:2:1 to 1:
An example is about 10:1.

Although either a phase type diffraction grating or an amplitude type diffraction grating can be used, a phase type grating is preferable from the point of view of effective use of the amount of light.

In this example, three light beams obtained by diffraction by the diffraction grating 10 are used, but a different number of light beams may be used depending on the recording/reproducing method and the format of the optical card.

Furthermore, depending on the recording/reproducing method and the format of the optical card, a diffraction grating that divides the light into different light intensity ratios than those exemplified above may be used.

As shown in FIG. 3(b), the three beams of light generated by the diffraction grating 10 are reflected by the left reflecting surface of the roof mirror 12 and are directed toward the left half of the objective lens (pickup lens) 14. and is focused by the lens to form three spots on the optical card 101.

The reflected light from the irradiation spot on the optical card 101 enters the right half side of the pickup lens 14, is focused by the lens, becomes almost parallel light, and is reflected by the right reflective surface of the roof mirror 12. mirror 16
incident on .

As shown in FIG. 3(a), the light beam reflected by the mirror 16 enters the sensor lens 18. The sensor lens is composed of two groups: a front group 18a with positive power and a rear group 18b with negative power.

The light beam exiting the sensor lens 18 passes through mirrors 20, 22 .
beam splitter 26 after being reflected by beam splitter 24.
, the beam splitter splits the amplitude in two directions, and the beam enters a photodetector (photosensor) 28.30. Note that the mirrors 22 and 24 are arranged orthogonally.

The beam splitter 26 is preferably a non-polarizing beam splitter. In other words, the recording surface of the optical card 101 can be sealed with a protective layer to prevent scratches. There are some that change the polarization characteristics of transmitted light. In this case, the light emitted from the LD 2 is generally linearly polarized light, but the light after passing through the optical card protective layer becomes elliptically polarized light having various ellipticities depending on the location of the optical card. For this reason, when a polarizing beam splitter is used as the beam splitter, a phenomenon occurs in which the output level from each sensor differs depending on the location of the optical card, which is undesirable for signal processing. In the wavelength range of hLD2, the transmittance and reflectance of both pt & minute and S components are 5.
A non-polarizing beam splitter of about 0±15% is preferable. Such a non-polarizing beam splitter can be realized, for example, by a structure such as glass-dielectric material (for example, 5 inches)-silver dielectric material-glass. Here, A
Both the sT body layer and the silver layer can be formed by vapor deposition.

Both of the sensors 28 and 30 are connected to the sensor lens 18.
is placed near the focal point.

FIGS. 4(a) and 4(b) show enlarged views of the sensor 28, 30, respectively.

As shown in FIG. 4(a), the sensor 28 has three light receiving sections 28a and 28b arranged in two directions.

It has 28c. Each of these light receiving sections is two light receiving elements A divided by a dividing line along the X direction.

Consists of B. Images of the three light beam spots formed on the optical card surface are formed on these three light receiving sections, respectively. An AT signal can be obtained from the sensor 28.

As shown in FIG. 4(b), the sensor 30 has three light receiving sections 30a and 30b arranged in the X direction.

It has 30c. Each of these light receiving sections is two light receiving elements A divided by a dividing line along the X direction.

Consists of B. Images of the three light beam spots formed on the optical card surface are also formed on these three light receiving sections, respectively. An AF multiplied signal can be obtained from the sensor 30.

In the case of reproducing recorded information, a reproduced information signal can be obtained using either of the sensors 28 and 30.

[Object of the Invention] Incidentally, the wavelength of the LD 2 used as a light source in the optical head as described above generally fluctuates due to mode hops and temperature increases associated with power fluctuations. For example, wavelength fluctuations due to mode hopping are usually about 2 to 3 nm, and wavelength fluctuations due to temperature rise are usually 0.3 nm per 1°C.
It is known that the degree of Therefore, if all factors such as the temperature rise of <LD2 due to changes in the external environmental temperature and the influence of the heat source within the optical head are taken into account, wavelength fluctuations of about 10 nm may actually occur.

In the optical head that converts the beam cross-sectional intensity of the light beam from the LD 2 using the beam shaping prism 6 as described above, if there is a wavelength variation in the LD 2, it will be affected by the wavelength dispersion of the prism 6. Based on this, the refraction angle of the light beam by the prism changes, and as a result, the traveling direction of the emitted light beam changes and
The position t of the light beam spot on 1 changes.

FIG. 5 is a diagram showing a change in the position of the light beam spot image on the optical sensor 28 based on a wavelength change of the LD 2 in the optical head as described above.

That is, in the optical head shown in FIG. 3 above, the direction in which the beam intensity distribution is converted by the beam shaping prism 6 is as shown in FIG. 3(a).
This corresponds to the direction perpendicular to the direction of the information track of the optical card 101, and therefore L
The movement direction of the beam spot image on the optical sensor 28 based on the wavelength fluctuation of D2 is the direction of the arrow perpendicular to the dividing line of each light receiving section 28a, 28b, 28c, which affects the AT multiplication signal and causes an offset error. I understand.

For example, as the glass material of the beam shaping prism 6, L
A5F is used, the apex angle of the prism is 30 degrees, and the light beam enters the prism perpendicularly to the first surface and is refracted by the second surface, and at the same time the beam diameter is reduced in a specific direction. When the beam is emitted with a rotationally symmetric cross-sectional intensity distribution, if the wavelength of the LD 2 changes by 10 nm from 830 nm, the emission angle from the prism changes by about 2 minutes due to the wavelength dispersion of the beam shaping prism 6. Assuming that the focal length of the pickup lens 14 is 5 mm, the optical card 1
The amount of change in the position of the light beam spot on the 01 plane is approximately 3p.
m, and the light beam spot moves by this distance in a direction perpendicular to the information track of the optical card. This distance is a non-negligible amount compared to the size of the information pit recorded on the optical card and the size of a preformat pattern such as a tracking track formed in advance on the optical card. Therefore, due to the above angle change, A
The position of the light spot on the T destination optical sensor 28 also shifts, and therefore the AT control based on the AT multiplied signal obtained from the optical sensor 28 becomes unstable, making it impossible to perform good recording and reproduction.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical head that can realize good AT without being substantially affected by wavelength fluctuations of a light source.

[Summary of the Invention] According to the present invention, in order to achieve the above objects, there are provided a light source, a means for converting the cross-sectional intensity distribution of a light beam emitted from the light source in a specific direction, a pickup lens,
In an optical head having a sensor lens and a two-split optical sensor for obtaining a tracking signal, the distribution conversion direction of the beam cross-sectional intensity distribution conversion means and the direction of the dividing line of the tracking optical sensor are substantially the same. Characterized by being in a relationship. An optical head is provided.

[Example] A specific example of the present invention will be described below with reference to one drawing.

FIG. 1(a) is a plan view showing an example of the optical system arrangement of the optical head according to the present invention, and FIG. 1(b) is a side view of a part of the optical head, and these are respectively Figure 3 (
It is a figure similar to a), (b). Figure 1 (a), (b)
Components similar to those in FIGS. 3(&) and (b) are designated by the same reference numerals, and description 11 of these will be omitted here.

In this embodiment, the arrangement of the blocks consisting of the LD 2, collimator lens 4, and beam shaping prism 6 is different from that shown in FIG. 3 above. That is, in this embodiment, the direction of the beam shaping prism 6 converting the beam cross-sectional intensity distribution is the direction in the plane of the paper of FIG. 1(b). Therefore, the movement direction of the light beam spot image based on the wavelength fluctuation of the LD 2 in the light receiving section of the optical sensor 28 to obtain the AT multiplied signal is the second
As shown in Figure (a), this is the direction indicated by the same arrow as the direction of the dividing line of each light receiving section. Therefore, the AT multiplied signal is not affected at all by the wavelength fluctuation of LD2.

On the other hand, the moving direction of the light beam spot image based on the wavelength fluctuation of the LD 2 in the light receiving section of the optical sensor 30 to obtain the AF multiplied signal is the direction of the dividing line of each light receiving section, as shown in FIG. 2(b). This is the direction indicated by the arrow perpendicular to . Therefore, the AF multiplication signal is affected.

However, the AF multiplication signal change due to the movement of the light beam spot image does not substantially affect the AF. In other words, under the conditions described with respect to the apparatus shown in FIG. Assuming that the traveling direction of the light beam after emission changes by an angle of 2 minutes and further assuming that the focal length of the sensor lens 18 is 150 mm, the amount of movement of the light beam spot image on the light receiving section of the sensor 30 will be approximately 90 JLm.

Since the focal length of the pickup lens 14 is 5 mm, the movement of the focal position at the position of the optical card 101 is approximately 5.6 pm.

By the way, in an optical head like this embodiment, the F value of the sensor lens is generally relatively large, and in particular, as shown in FIG. In such a case, the practical range of the F value for the effective luminous flux is about 3 at most. F value is 3
The depth of focus of the sensor lens is approximately ±15p.
m, which is considerably larger than the amount of movement of the focusing position l based on the wavelength fluctuation of LD2. Even if there is a problem, AF can be performed based on the signal with almost no effect on information recording and reproduction.

In the above embodiment, the beam shaping prism 6 is used as a means for converting the cross-sectional intensity distribution of the light beam, but in the present invention, similar distribution conversion such as a diffraction grating is used as the cross-sectional intensity distribution converting means. It goes without saying that it is equally effective if a means having an effect and wavelength dispersion is used.

[Effects of the Invention] According to the present invention as described above, there is provided an optical head that can realize good AT without being substantially affected by the wavelength fluctuation of the light source even if the wavelength fluctuation occurs.

[Brief explanation of drawings]

Figures 1(a) and 3(a) are plan views showing the optical system arrangement of the optical head, and Figures 1(b) and 3(b) are partially viewed from the side. It is a diagram. FIGS. 2(a), (b), and 5 are diagrams showing changes in the position of the light beam spot image on the optical sensor. FIGS. 4(a) and 4(b) are enlarged views of the optical sensor. 2: Semiconductor laser, 4: Collimator lens, 6: Light beam shaping prism, 8: Circular aperture. 10: Diffraction grating, 12: Roof mirror. 14: Pickup lens, 16.20, 22, 24: Mirror, 18: Sensor lens, 26: Beam splitter. 28, 30: Optical sensor, 101: Optical card. Agent Patent Attorney Minoru Yamashita 2Ba 2B. 28b 28c Fig. 5 28b 28c

Claims (4)

[Claims] (1) In an optical head that has a light source, a means for converting the cross-sectional intensity distribution of the light beam emitted from the light source into a specific direction, a pickup lens, a sensor lens, and a two-split optical sensor for obtaining a tracking signal, the light beam An optical head characterized in that the distribution conversion direction of the cross-sectional intensity distribution conversion means and the direction of the dividing line of the tracking optical sensor are in a correspondence relationship such that they are substantially the same. (2) It has means for dividing the light beam that has passed through the light beam cross-sectional intensity distribution converting means into a plurality of parts, the light beam emitted from the means is made incident on the pickup lens, and the number of tracking optical sensors generated by the light beam splitting means is provided. The optical head according to claim 1, having the same number of light receiving parts. (3) The optical head according to claim 2, wherein the beam splitting direction of the beam splitting means and the distribution conversion direction of the beam cross-sectional intensity distribution converting means are in a substantially orthogonal relationship. (4) The patent claim has a two-split optical sensor for obtaining a focusing signal, and the sensor and the tracking optical sensor are arranged at substantially equivalent positions with respect to the sensor lens via a beam splitter. Optical head in range 1.