JPH0673195B2 - Light pickup - Google Patents

Description

DETAILED DESCRIPTION [Overview] A conventional optical pickup having a large shape and heavy weight is difficult to access at a high speed. Therefore, by using a hologram for the main part of the optical pickup, it is possible to make the optical disc memory device smaller and lighter by reducing the size and weight of the optical disc memory device.

[Industrial application field]

The present invention relates to an optical disk memory device that uses light for writing and reading information, and more particularly to an optical pickup that can be made compact and lightweight.

As a means for increasing the capacity of a storage device that constitutes an information processing device, an optical disk memory device that uses light for writing and reading information has been actively developed.
The optical pickup for writing information to the optical disc and reading the information stored in the optical disc in such an optical disc memory device must be small and lightweight in order to make the entire device compact and shorten the access time. . Therefore, it is required to develop an inexpensive optical pickup that can be made compact and lightweight.

[Conventional technology]

FIG. 5 is a schematic diagram showing a main part of a conventional optical pickup.

In the figure, a conventional optical pickup 1 includes a semiconductor laser (hereinafter abbreviated as LD) 11, a collimator lens 12, and a prism 1.
3, polarizing beam splitter 14, quarter wave plate 15, objective lens
The divergent light emitted from the LD11 is converted into parallel light by the collimator lens 12, the cross section is enlarged by the prism 13, and the light is incident on the polarization beam splitter 14. To do.

The light emitted from the LD 11 is polarized in the direction of passing through the polarization beam splitter 14, and the parallel light incident on the polarization beam splitter 14 passes through the polarization beam splitter 14 and
Objective lens 16 after being converted into circularly polarized light by the four-wave plate 15
The light is focused on the optical disc 2 by.

On the other hand, the signal light from the optical disk 2 is the opposite of the above light,
It enters the polarization beam splitter 14 via the objective lens 16 and the quarter-wave plate 15. The signal light is polarized in the direction in which it is diffracted by the polarization beam splitter 14, and the signal light diffracted by the polarization beam splitter 14 is collected by a condenser lens 17.
The light is focused on the photodetector 18 by.

[Problems to be solved by the invention]

An optical pickup for writing information to an optical disk and reading information stored in the optical disk in an optical disk memory device must be small and lightweight in order to enable downsizing of the entire device and shortening of access time. Therefore, research is being conducted to reduce the size and weight of the conventional optical pickup by integrating the optical components shown in FIG. However, these optical parts, which are mainly made of glass, are limited in downsizing and weight saving, and the volume is about 4 cm × 3 cm × 2 cm, the weight is several tens of grams, and the access time is the same as that of the magnetic disk device. There was a problem that (10 to 20 msec) could not be obtained.

[Means for solving problems]

FIG. 1 is a perspective view showing the principle of the optical pickup according to the present invention. Note that the same object is denoted by the same symbol throughout the drawings.

The above problem is caused by a light source that emits coherent light, such as LD11.
And two surface relief holograms (hereinafter abbreviated as holograms) arranged so that the lattice groove directions are substantially orthogonal to each other 3
1, 32, a quarter-wave plate 15, and a photodetector 18 for detecting the signal light from the optical disk 2, and the coherent light emitted from the light source 11 is a first surface relief hologram 32, a second surface. The relief type hologram 31 and the 1/4 wavelength plate 15 are sequentially incident on the irradiation target, and the signal light is inverted to the 1/4 wavelength plate 15,
This is solved by the optical pickup of the present invention configured to enter the photodetector 18 via the second surface relief hologram 31 and the first surface relief hologram 32 in sequence.

[Action]

In FIG. 1, the Z axis is taken in the direction of irradiating the optical disk 2 with light, and the quarter wave plate 15 and the two holograms 31 and 32 are arranged perpendicularly to the Z axis. LD11 is a photo detector on the X axis.
18 is arranged on the Y axis, and the grating groove direction of the hologram 31 is approximately Y.
The lattice groove direction of the hologram 32 is aligned with the axis substantially along the X axis.
The polarization of the LD 11 is set so that the vibration plane is parallel to the plane including the Y axis and the Z axis.

The spherical wave from light emitting point P ₁ of the grating pattern LD11 of the hologram 31, are formed to converge to a point P ₂ on the optical disc 2, the grating pattern of the hologram 32 from the point P ₂ on the optical disc 2 It is formed to focus the spherical wave on the photodetector 18. Therefore, the hologram 31 and the hologram 32 have a lattice pattern in an arc shape having a large radius of curvature.

The divergent light emitted from the light emitting point P _{1 of the} LD 11 is reflected by the hologram 32.
Is P-polarized, and the hologram 31 is S-polarized. Therefore, the hologram 32 is transmitted as it is, diffracted by the hologram 31, and converged on the point P ₂ on the optical disc 2. On the way, linearly polarized light is converted into circularly polarized light by passing through the 1/4 wavelength plate 15 placed in the convergent wave.

On the other hand, the reflected and diffracted light from the optical disk 2 goes backward in the outward path and becomes 1/4.
The wave plate 15 converts the light traveling from the LD 11 to the optical disc 2 into linearly polarized light whose polarization direction is orthogonal. This light is P-polarized for the hologram 31 and S-polarized for the hologram 32. Therefore, the hologram 31 is transmitted as it is, diffracted by the hologram 32, and converged on the photodetector 18.

The hologram 32 is added with an appropriate aberration and the photodetector 18
By dividing into four, focus error and tracking error of the optical pickup can be detected at the same time.

That is, the LD 11 and the grating groove direction are arranged so as to be substantially orthogonal to each other.
Holograms 31, 32, quarter wave plate 15, and photodetector 18
An optical pickup can be configured with. The hologram is an extremely thin film, and by using the hologram on the main part, the size and weight of the optical pickup can be significantly reduced, and the cost of the optical pickup can be reduced by reducing the parts cost and assembly time. Can be realized.

〔Example〕

Examples of the present invention will be described below with reference to the addition diagrams. 2 is a side sectional view showing an embodiment of the optical pickup according to the present invention, FIG. 3 is a view showing a modification of the optical pickup according to the present invention, and FIG. 4 is a view for explaining the operation of the modification. is there.

In FIG. 2, a transparent substrate 33 is coated with a photosensitive resin and exposed and developed to form a hologram 32. Also 1/4 wave plate 1
A hologram 31 is formed by directly coating a photosensitive resin on the surface of the 5 and exposing and developing it. The two holograms 31 and 32 are adhered to the frame 35 so as to face each other via the air layer 34. The LD 11 and the photodetector 18 are fixed to the container 36, and the frame 35 is fitted to the container 36 so as to seal them. A mirror 37 is attached to the side surface of the container 36, and the optical path from the LD 11 to the photodetector 18 is bent to make the optical pickup compact.

The optical pickup according to the present invention thus configured has a volume of about 1 cm × 1 cm × 1 cm and a weight of several grams or less.
An access time equal to or longer than that of the magnetic disk device can be obtained.

In the side view of FIG. 3 (a) and the plan view of FIG. 3 (b), the modification of the present invention is such that when the X-axis direction in FIG. The hologram 32 for condensing light is divided into two by a plane perpendicular to the track groove direction, that is, a plane including the Y axis and the Z axis, and the signal light incident from the optical disc 2 is divided into two and diffracted in different directions. Photodetector 18A with different signal light
And 18B so as to focus light.

One photodetector 18A is composed of two elements parallel to the Y-axis, and a light non-detection region is provided in the center. The other photodetector 18B is composed of two elements orthogonal to the Y axis. By splitting the signal light into two and focusing them on different photodetectors 18A and 18B, respectively, one photodetector 18A can detect a focus error and the other photodetector 18B can detect a tracking error.

The operation of this modified example will be described with reference to FIG. 4 (in the figure, the hatched lines indicate non-irradiation elements).

As shown in FIG. 4 (a), one element of the photodetector 18A is
₁ and 18A ₂ for the other element, if there is no focus error, as shown in FIG. 4 (b), the signal light is focused on the non-detection region and both elements of the photodetector 18A cannot be irradiated. There is no. However, if the optical disk surface is far from the focal point, the fourth
As shown in FIG. 6C, the signal light converges once and then starts to diverge, and the element 18A ₁ is irradiated. When the optical disk is close to the focal point, as shown in FIG. 4 (d), the element 18A ₂ is irradiated before the signal light converges. Therefore, the focus error can be detected from the difference between the output signals of the respective elements.

Next, assuming that one element of the photodetector 18B is 18B ₁ and the other element is 18B ₂ as shown in FIG. 4 (e), if there is no tracking error, as shown in FIG. Bowl 18B
The signal light converged on illuminates the elements 18B ₁ and 18B ₂ evenly. However, when a tracking error occurs, as shown in FIG. 4 (g) or FIG. 4 (h), the signal light converged on the photodetector 18B irradiates a large amount of either the element 18B ₁ or the element 18B ₂ , The tracking error can be detected from the difference between the output signals of the elements.

As described above, by using the four-division type photodetector 18, it is possible to detect a focus error and a tracking error even in the optical pickup shown in FIG.
However, in this method, it may be difficult to distinguish between the case where only the focus error occurs and the case where the tracking error occurs in addition to the focus error. However, the modification shown in FIG. 3 does not cause such an inconvenient problem.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide an inexpensive optical pickup that can be reduced in size and weight.

[Brief description of drawings]

FIG. 1 is a perspective view showing the principle of the optical pickup according to the present invention, FIG. 2 is a side sectional view showing an embodiment of the optical pickup according to the present invention, and FIG. 3 is a modification of the optical pickup according to the present invention. FIG. 4 is a diagram for explaining the operation of the modified example, and FIG. 5 is a schematic diagram showing a main part of a conventional optical pickup. In the figure, 2 is an optical disk, 11 is a light source (semiconductor laser), 15 is a quarter-wave plate, 18, 18A and 18B are photodetectors, 18A ₁ , 18A ₂ , 18B ₁ and 18B ₂ are detector elements, 31, 32 is a surface relief hologram, 33 is a transparent substrate, 34 is an air layer, 35 is a frame, 36 is a container, and 37 is a mirror.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Ikeda, 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor, Yushi Inagaki 1015, Kamikodanaka, Nakahara-ku, Kawasaki, Kanagawa, Fujitsu Limited ( 56) References JP-A-59-160166 (JP, A)

Claims (2)

[Claims] 1. A light source (11) for emitting coherent light,
It comprises two surface relief holograms (31, 32) arranged so that the grating groove directions are substantially orthogonal to each other, a 1/4 wavelength plate (15), and a photodetector (18) for detecting signal light, The coherent light emitted from the light source (11) is passed through the first surface relief hologram (32), the second surface relief hologram (31), and the quarter wavelength plate (15) to the irradiation target. The incident signal light, on the contrary, passes through the quarter-wave plate (15), the second surface relief hologram (31), and the first surface relief hologram (32) in order, and the photodetector ( 18) An optical pickup which is configured to be incident on. 2. One surface relief so that the incident signal light is divided into two and diffracted in different directions, and the respective signal lights are condensed on different photodetectors (18A, 182B). The optical pickup according to claim 1, wherein a type hologram (32) is formed.