JPH0465461B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary of the Invention] The pickup according to the present invention has an optical system composed of a phase type hologram, a surface relief type hologram, a λ/4 plate, etc. without using a glass lens, etc. By utilizing these optical properties, especially the incident angle properties of phase-type holograms, the incident light and the reflected light on the information recording medium are separated, and the reflected light is detected, making the optical pickup lightweight and This enables miniaturization and shortens access time.

[Industrial application field]

The present invention relates to an optical pickup for reading information from an information recording medium such as an optical disk.

[Conventional technology]

As shown in FIG. 6, a conventional optical pickup P includes a semiconductor laser 1, a collimator lens 2, a prism 3, a beam splitter 4, a λ/4 plate 5, an objective lens 6, a converging lens 7, a photodetector 8, etc. These optical systems are integrally constructed. As shown in Figure 7, motor M
The above-mentioned access operation of the optical pickup P to the optical disk D rotated by the linear motor LM is performed by the linear motor LM.

[Problem that the invention seeks to solve]

In general, the access time for information recording media such as optical disks, which are large-capacity storage devices, is determined by how fast the optical pickup can be moved by the above-mentioned linear motor LM, and that speed depends on the weight of the optical pickup. to be controlled. Therefore, in order to shorten the access time, research has been carried out to reduce the weight and size of optical pickups.

However, as shown in Figure 6, in the conventional optical pickup mentioned above, each element constituting the optical system is mainly made of glass, and in order to maintain its accuracy, a certain amount of size is required. be done. Therefore, there is a limit to the generally desired reduction in weight and size, and at least the weight reaches tens of grams, making it impossible to obtain access times equivalent to magnetic disks (10 to 20 msec). It was hot.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide an optical pickup that can be made lightweight and compact, and can shorten access time.

[Means for solving problems]

In order to achieve the above object, the present invention enables irradiation of light onto an information recording medium by a light source and detection of reflected light from the information recording medium by a photodetector to a phase type hologram, a surface relief type hologram, or a surface relief type hologram. This is done through a λ/4 plate, and either the light from the light source toward the information recording medium or the light toward the photodetector from the information recording medium is incident on the phase-type hologram at a non-Bragg angle. This is how it was done.

[Effect]

It is known that the incident angle characteristic of a phase hologram is that light incident at a Bragg angle is diffracted, while light incident at a non-Bragg angle is transmitted as is.The present invention specifically utilizes this characteristic. It is. In the present invention, this phase type hologram,
Furthermore, a surface relief type hologram and a λ/4 plate are combined. In the above configuration, if either the light traveling from the light source to the information recording medium or the light traveling from the information recording medium to the photodetector is made to enter the phase hologram at a non-Bragg angle, the other light will It will be incident at the Bragg angle. Therefore, one of the above-mentioned lights will be diffracted by the phase type hologram, and the other will be transmitted as is. Therefore, after the emitted light from the light source is reflected by the information recording medium, the reflected light is separated from the emitted light by a phase type hologram or the like and guided to the photodetector.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an optical system according to an embodiment of the present invention. In the figure, the optical system is
It is composed of a semiconductor laser 11, a phase type hologram 12, a surface relief type hologram 13, a λ/4 plate 14, and a photodetector 15.

The phase type hologram 12 is made of, for example, silver salt, dichromate gelatin, photopolymer, etc., and as shown in _{FIG .} It was created by irradiating the

Phase type hologram 1 created in this way
The incident angle characteristics of 2 are shown in FIG. 3a. As shown in the figure, the diffraction efficiency of the phase type hologram 12 is
It varies greatly depending on the incident angle during reproduction.

When light is input to the lower surface 12b in Figure 2a, the angle of incidence from the same direction as the created wave _L1 is the Bragg angle _θB in Figure 3, and the diffraction efficiency is maximized at this angle. , the incident light is created by the wave shown by the dashed line.
It is diffracted in the direction of the extension line _L3 of _L2 . In addition, when injecting light into the upper surface 12a, the above extension line
The angle of incidence from the same direction as L ₃ is the Bragg angle θ _B , the diffraction efficiency is maximized at this angle, and the incident light is diffracted in the direction of the created wave L ₁ . On the other hand, an angle that is significantly different from the above Bragg angle θ _B (for example, 20~
If light is incident at an angle of 30 degrees (hereinafter referred to as the non-Bragg angle), the diffraction efficiency will decrease and most of the incident light will be transmitted as is.

Surface relief hologram 13 shown in Figure 1
As shown in FIG. 2b, a λ/4 plate 14 is used as a substrate and a photoresist etc. 16 is coated thereon.
It was created by irradiating the created waves L ₄ and L ₅ that diverge and converge, respectively, and further form a plurality of relief grooves in one direction. Note that by using the λ/4 plate 14 as a substrate for the photoresist 16, waste is eliminated in terms of functional integration.

The polarization characteristics of the surface relief type hologram 13 created in this way are shown in FIG. 3b. As shown in the figure, a surface relief hologram 13
The intensity of the diffracted light varies greatly depending on the polarization direction of the incident light. That is, in the case of so-called S-polarized light, in which the direction of the relief groove and the polarization direction match, the intensity of the diffracted light is maximum;
If the incident light is from the same direction as the created wave L ₄ in FIG. b, it will be diffracted in the direction of the extension line L ₆ of the created wave L ₅ shown by the broken line. On the other hand, in the case of so-called P-polarized light, in which the direction of the relief groove and the polarization direction of the incident light are perpendicular to each other, the intensity of the diffracted light is the lowest, and most of the incident light is transmitted as is.

In this embodiment, by utilizing the above characteristics of the phase hologram 12 and the surface relief hologram 13, the semiconductor laser 11 is positioned at a position where the emitted light L ₇ is incident on the phase hologram 12 at a non-Bragg angle. And for the surface relief type hologram 13, the convergence point of the created wave L ₄ in FIG.
It is located at the position corresponding to P ₁ . Furthermore, the polarization direction of the emitted light L ₇ of the semiconductor laser 11 and the direction of the relief groove of the surface relief hologram 13 are made to be the same (in _FIG . ). In addition, the photodetector 15 is connected to the generated waveform shown in FIG. 2a.
It is provided at a position corresponding to the convergence point _P2 of _L1 .

Next, a description will be given of changes in the state of light in this embodiment having the above configuration.

First, in FIG. 1, the emitted light _L7 from the semiconductor laser 11 is incident on the phase type hologram 12 at a non-Bragg angle, so it is transmitted as it is. This transmitted light L ₈ is incident on the surface relief hologram 13, but since its polarization direction and the direction of the relief groove are the same (direction A ₁ ), it is diffracted. The diffracted light is focused on the optical disk D via the λ/4 plate 14. Note that the diffracted light _L9 that has passed through the λ/4 plate 14 has been converted from linearly polarized light to circularly polarized light.

Reflected light L ₁₀ containing that information from optical disk D
is circularly polarized light like the diffracted light _L9 above, but
By passing through the λ/4 plate 14, it is converted into linearly polarized light again, and the surface relief hologram 13
incident on . However, the polarization direction of this incident light is a direction _A2 that is perpendicular to the above-mentioned direction _A1 and parallel to the plane of the paper. Since the direction A ₂ is perpendicular to the direction of the relief groove of the surface relief hologram 13, the above incident light is transmitted as is, and the transmitted light L ₁₁ is directed to the phase hologram 12 at a Bragg angle as described above. incident. Therefore, the above transmitted light
L ₁₁ is diffracted and becomes diffracted light L ₁₂ to the photodetector 15.
guided by.

FIG. 4 is a schematic configuration diagram showing an optical system according to another embodiment of the present invention. In the figure, the optical system includes a semiconductor laser 21 similar to that in FIG. 1, a phase type hologram 22, a surface relief type hologram 23,
It is composed of a λ/4 plate 24, a photodetector 25, and an in-line objective hologram lens 26. Here, the objective hologram lens 26
is movable in the _three directions of arrow A, and by moving this position appropriately, it is possible to focus on the optical disc D.

Furthermore, unlike the embodiment shown in FIG. 1, the semiconductor laser 21 is provided at a position where its emitted light L ₁₃ is incident on the phase type hologram 22 at a Bragg angle, and the polarization direction of the emitted light L ₁₃ is is defined as a direction A ₄ (direction parallel to the plane of the paper) perpendicular to the direction of the relief grooves of the surface relief type hologram 23.

In this embodiment, the emitted light _L13 from the semiconductor laser 21 is incident on the phase type hologram 22 at a Bragg angle, and is therefore largely diffracted. Note that the polarization direction of the emitted light L ₁₃ is in the short axis direction of the ellipse as shown in FIG. It is corrected to The diffracted light L ₁₄ is
The light is incident on the front surface laser type hologram 23, but since its polarization direction is perpendicular to the relief groove, it is transmitted as is. The transmitted light becomes parallel light, λ/4
The light is converted into circularly polarized light by the plate 24, and then focused onto the optical disk D by the objective hologram lens 26.

The reflected light L ₁₅ from the optical disk D becomes parallel light L ₁₆ by the objective hologram lens 26, and is
Surface relief hologram 23 via four plates 24
guided by. However, the above parallel light L ₁₆ is λ/4
The circularly polarized light is converted into linearly polarized light by the plate 24,
Moreover, its polarization direction is the same as the direction of the relief grooves, which is the direction _A6 perpendicular to the plane of the paper. Therefore, the parallel light L ₁₆ is reflected in the surface relief hologram 23.
The diffracted light L ₁₇ enters the phase type hologram 22 at a non-Bragg angle, so it is transmitted as it is and converged on the photodetector 25 .

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to construct an optical system using various holograms, etc., without using glass lenses, etc., so that weight reduction and miniaturization can be easily achieved. , Therefore, the access time can be shortened. Furthermore, since the number of parts is small and the configuration is very simple, it is possible to reduce the price.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an optical system according to an embodiment of the present invention, and FIGS. Figures 3a and b are graphs showing the incident angle characteristics of a general phase type hologram and the polarization characteristics of a surface relief type hologram, respectively.
FIG. 4 is a schematic configuration diagram showing an optical system according to another embodiment of the present invention, FIG. 5 is a schematic diagram showing the polarization direction of the emitted light from a semiconductor laser, and FIG. 6 is a diagram showing the optical system of a conventional optical pickup. FIG. 7 is a schematic diagram illustrating how to access a conventional optical pickup. 11, 21... Semiconductor laser, 12, 22... Phase type hologram, 13, 23... Surface relief type hologram, 14, 24... λ/4 plate, 15, 25... Photodetector, 26... Objective hologram lens.

Claims (1)

[Scope of Claims] 1. In an optical pickup having a light source for irradiating light onto an information recording medium and a photodetector for detecting light reflected by the information recording medium, the light emitted by the light source The irradiation of light and the detection of light by the photodetector are performed via a phase type hologram, a surface relief type hologram, and a λ/4 plate. An optical pickup characterized in that either one of the lights directed toward the photodetector is made incident on the phase type hologram at a non-blagging angle. 2. The light irradiation by the light source sequentially targets the phase type hologram, the surface relief type hologram,
The light is detected through the λ/4 plate, and the light is detected by the photodetector through the λ/4 plate, the surface relief hologram, and the phase hologram in this order. Optical pickup as described in Range 1. 3. When the light directed from the light source toward the information recording medium is made to enter the phase type hologram at a non-Bragg angle, the polarization direction of the light from the light source and the relief groove of the surface relief type hologram may be 3. The optical pickup according to claim 2, wherein the directions are the same. 4. When the light traveling from the information recording medium to the photodetector is made to enter the phase type hologram at a non-Bragg angle, the polarization direction of the light from the light source and the relief of the surface relief type hologram 3. The optical pickup according to claim 2, wherein the direction of the groove is perpendicular to the direction of the groove. 5. The light according to any one of claims 1 to 4, wherein the λ/4 plate is used as a substrate, and the surface relief hologram is formed on the λ/4 plate. Pick up.