JPH03102654A - Optical head device - Google Patents

Abstract

PURPOSE:To eliminate the need for 3 independent optical systems by forming integrally a light collection means and a luminous flux separate means to a multi-function optical element. CONSTITUTION:The device is provided with a semiconductor laser 1 being a light source, a multi-function optical element 2 and a photodetector 3 receiving sets of luminous flux 22a, 22e, 22f reflected from an optical disk 30 and obtained through the multi-function optical element 2 and applying photoelectric conversion to the luminous flux. Thus, a diffraction grating 2b to separate a radiation light generated from the light source 1 by the multi-function optical element 2 into plural sets of luminous flux including the collected light for reproduction and the collected light for position detection, a light collection means collecting the luminous flux diffracted by a diffraction grating and radiating it to an information recording medium 30 and a luminous flux separating means 2c separating the luminous flux reflected from the information recording medium from the radiation luminous flux are formed integrally. Thus, three independent optical systems are not required.

Description

Detailed Description of the Invention [Field of Industrial Application] This invention relates to an optical head device used for reproducing information on an optical information recording medium, and particularly relates to an optical head device used for reproducing information on an optical information recording medium. optical head for reproducing information by irradiating a plurality of focused beams for detecting positional deviations in directions along an optical information recording medium. Regarding equipment.

[Prior Art] FIG. 7 is a schematic diagram showing a conventional optical head device. Referring to FIG. 7, the optical head device includes a semiconductor laser (LD) 1 as a light source, a diffraction grating 4 that diffracts an emitted light beam 20 of the semiconductor laser 1 and separates it into three light beams, and a diffraction grating 4. A reflected light beam 22a that reflects the three light beams separated by the optical disk 30,
22e, 22f and the output light beam 21a. 21e. 2
1f, a condensing lens 6 for condensing the light beam reflected by the flat beam splitter 5 and irradiating it onto the optical disk 30, 6 and a photodetector 3 that receives the light beam transmitted through the beam splitter 5 and photoelectrically converts it.

FIG. 8 is a detailed view of the information track portion when a light beam is incident on the optical disk by the optical head device shown in FIG.

FIG. 9 is a block diagram showing the configuration of the photodetector shown in FIG. 7.

Next, the operation will be explained with reference to FIGS. 7 to 9. The light beam 20 emitted from the semiconductor laser 1 is diffracted by the diffraction grating 4 and opposed by the surface of the beam splitter 5, and then, as shown in FIG. Three light spots 21a, 21e. The light is focused as 21f.

A line connecting the centers of the three light spots 21a, 21e, and 21f is arranged so as to be slightly inclined with respect to the direction of an information track 32 consisting of a row of bits 31, which is recorded information. The light thus focused on the information surface of the optical disc 30 is reflected, passes through the condenser lens 6 again, and then passes through the beam splitter 5, with astigmatism imparted to it as is known in the art. The light enters the photodetector 3.

The photodetector 3 is placed at a position along the optical axis where the center beam, that is, the reflected luminous flux of the 0th order diffracted light forms a circle of least confusion when the condensed spot on the optical disc 30 is in focus. The photodetector 3 has a six-divided configuration, as shown in FIG.
The part that receives the center beam (0th order light) is 10a, 10
It is divided into four parts b, 10c, and 10d. In addition, the portions that receive the beams on both sides, that is, the ±1st order light, are independent photodetectors 10e. It is 10f. Photodetectors 10e, 1 on both sides
By differentially calculating the output of 0f by the subtractor 13, the positional deviation between the central optical spot 22a and the information track 32 can be detected from the terminal 14.

The tracking error signal thus obtained is used to drive a tracking actuator (not shown here) to correct the position of the light spot 21a at the center of the track 32.

The center quadrant detector output is the diagonal component 10a. 10c and 10b. The differential calculation of 10d is taken out from the output terminal 15 by the subtracter 12, used to detect the shift of the focal spot on the optical disk, and correct the focus shift by a focus actuator (not shown) (focus error). signal).

This defocus detection method is called the astigmatism method, and when the spot on the optical disc is in focus, the spot on the detector, which is in the approximately circular state 11a of the circle of least confusion, is As shown by the broken lines, the deformation into a vertically long and horizontally long ellipse is converted into electrical output.

Also, the sum output 17 from the adder 16 of the 4-division detector is:
The signal is processed and used as a reproduction signal for the optical disc 30 by a circuit not particularly shown in the subsequent stage.

[Problems to be Solved by the Invention] As described above, in the conventional optical head device, the diffraction grating 4 is used to create a plurality of light beams to be irradiated onto the optical disk 30.
, a beam splitter 5 for separating the emitted light flux to the optical disc 30 and a reflected light flux from the optical disc, and a condensing lens 6 for focusing the emitted light flux onto the information track of the optical disc. It was a summary of the structure. That is, the conventional optical head device requires three independent optical systems. On the other hand, for optical head devices, there has been a demand in the market for cost reduction and miniaturization of the device. However, with conventional optical head devices,
As mentioned above, three independent optical systems are required, so
This necessitated an increase in cost and was also an obstacle to miniaturizing the device.

In other words, with conventional optical head devices, it has been difficult to reduce costs and downsize the device.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical head device that can reduce costs and downsize the device.

[Means for Solving the Problems] The optical head device according to the present invention includes a light generating means for generating light, and a condensed light for reproducing and a converging light for detecting positional deviation. a diffraction grating for separating the beam into multiple beams including a focused beam, a condensing means for condensing the beam diffracted by the diffraction grating and irradiating it onto the information recording medium, and a beam reflecting the beam reflected by the information recording medium. a multifunctional optical element integrally formed with a beam separating means that separates the emitted beam from the emitted beam; and a light detection means for detecting the beam separated by the beam separating means included in the multifunctional optical element. It is characterized by

[Function] In the optical head device according to the present invention, the multifunctional optical element transforms the emitted light generated from the light generating means into a light beam including a focused light for reproduction and a focused light for detecting positional deviation. A diffraction grating for separating the light beams into the light beams, a light focusing means for focusing the light beams diffracted by the diffraction gratings and irradiating the light beams onto the information recording medium, and a light beam separating means for separating the light beams reflected from the information recording medium from the emitted light beams. Since it is integrally formed, three independent optical systems are not required.

Embodiment J of the Invention FIG. 1 is a schematic diagram of an optical head device showing an embodiment of the invention. Referring to FIG. 1, the optical head device includes a semiconductor laser 1 as a light source, a multifunctional optical element 2, and a light beam 22a. It includes a photodetector 3 that receives the lights 22e and 22f and performs photoelectric conversion.

FIG. 2 is a structural diagram showing details of the multifunctional optical element 2 shown in FIG. Referring to FIG. 2, the multifunctional optical element 2 includes a glass substrate 2a made of glass or the like, and a first surface of the glass substrate 2a on which the emitted light beam 20 from the semiconductor laser 1 is incident. a diffraction grating 2b for diffracting and separating into three beams, and output beams 21a, 21e, 21 formed on a second surface opposite to the first surface.
A beam splitter layer 2c is formed on the beam splitter layer 2c, and is formed on the beam splitter layer 2c to separate the reflected light beams 22a, 22e, and 22f from the reflected light beams 22a, 22e, and 22f. 21a,
While giving astigmatism to 21e and 21f and focusing the light,
It includes a Fresnelson plate 2d for giving astigmatism to the reflected lights 22a, 22e, and 22f and condensing them.
, where the Fresnel Sonpree}2d is opaque between the annular boundary radius rzK−rzx++ (K−0, L 2−) and transparent between r2K+I and r2K+2. In addition, the shading-shaped grating that constitutes the Fresnelson plate 2d is manufactured by applying a known lithography technique and etching to a metal film such as chromium deposited to a thickness that provides an appropriate reflectance, for example, about 1,000 mm. do. Note that the shading pattern is opposite to that of this example, and r2κ~r2
The space between K←, may be transparent, and the space between r2κf, and r2Ky2 may be opaque.

Next, the operation will be explained with reference to FIGS. 1 and 2. The emitted light beam 20 from the semiconductor laser 1 is diffracted by the diffraction grating 2b on the first surface of the multifunctional optical element 2 and separated into 0th-order light and ±1st-order light. The light passes through the beam splitter layer 2C, which is shaped like a plane. Furthermore, three light spots 21a . The light is focused as 21e and 21f. Here, when the emitted light beam 20 of the semiconductor laser 1 passes through the glass substrate 2a of the multifunctional optical element 2, astigmatism generally occurs. However, the grating shape of the Fresnelson plate 2d is designed so that the astigmatism difference generated by passing through the glass substrate 2a is corrected by the Fresnelson plate 2d passing through the glass substrate 2a, and the astigmatism difference becomes 0. There is. Therefore, the focused spots 21a, 2 on the surface of the optical disc 30
1e and 21f have no astigmatism. The light beam reflected by the optical disk 30 is transmitted as it is without being diffracted by the Fresnelson plate 2d on the second surface of the multifunctional optical element 2. The transmitted light beam is reflected by the beam splitter layer 2c and passes through the Fresnelson plate 2d again. The light is subjected to diffraction by the Fresnelson plate 2d and becomes a condensed light beam. At the same time, the light beam enters the photodetector 3 after receiving the astigmatism correction effect given in advance to the Fresnelson plate 2d.

FIG. 3 is a schematic diagram for explaining a method for calculating the annular boundary radius r (of the Fresnel Sonpree}2d shown in FIG. 2. With reference to FIG. For simplicity, the thickness of the substrate glass of the Fresnelson plate is assumed to be zero, and the emitted light beam 20 leaving the emission point O of the semiconductor laser 1 travels along the path 0, B, O' to the converging point O.
It is assumed that the light is focused at ′. Output beam 2 of semiconductor laser 1
0 is incident on the k-th annular boundary radius rκ of the Fresnelson plate 2d, and becomes a focused light beam 21. In order for the luminous flux emitted from the emission point O to be focused on the convergence point O' without aberration,
The difference between the optical path length from point O to O' via B and the optical path length from point O to O' via point A on the optical axis must be an integral multiple of 1/2 wavelength. This condition is expressed by the following formula (1
) can be written as

(Men + So-) - (Shinjumen) - K・λ/2 ... (1)
[K-1.2.3...] Here, λ indicates the wavelength. From Equation 1, the locus of the k-th ring can be written as Equation (2).

1 (2) FIG. 4 is a schematic diagram showing the locus of the annular zone at the k'tF opening of the Fresnelson plate 2d. Referring to FIG. 4, the above equation (2) is an ellipse translated by Δy in the y-axis direction. Also,
rK**rKY is the annular radius of the trajectory I in the X direction and the y direction.

FIG. 5 is a schematic diagram showing the focal state when a luminous flux is emitted from the emission point 0 onto the annular zone formed by the locus I shown in FIG. Referring to figure M5, locus I is the case where the thickness of the substrate glass of the Fresnelson plate 2d is considered to be zero, and in reality, depending on the thickness of the substrate glass, the
An axial focal length difference, that is, an astigmatism difference ΔO' occurs. Therefore, in this embodiment, astigmatism difference ΔO generated in advance is
′ is designed to correct the annular zone. That is, as shown in FIG. 4, the radius of the k-th annular zone of the locus I without considering astigmatism is defined by the radius of the annular zone in the X direction being r'KX. Let the ring radius in the y direction be r'κ.

The radius of the k-th annular zone of the trajectory (■) for correcting astigmatism is defined by the radius of the annular zone in the X direction being rKx. Let rKy be the annular radius in the Y direction.

Furthermore, if the size of correcting the ten diameters of the annular zone corresponding to the astigmatism difference Δ0' is defined as ΔrKY, then the radius of the k-th ring that corrects astigmatism is rKX"'rKX jK, amj' κy+ΔrKy.

FIG. 6 is a schematic diagram showing the state of a fish point when a luminous flux is emitted from the emission point 0 to the annular zone formed by the locus {circle around (2)} shown in FIG. With reference to FIG. 6, the emission point 0 of the semiconductor laser 1
The outgoing light beam 20 is corrected for astigmatism by the glass substrate 2a of the multifunctional optical element 2, and is focused at a point 0'1.

Further, the light beam diffracted by the optical disk 30 is diffracted and focused by the gradation type Fresnelson plate 2d on the second surface of the multifunctional optical element 2, and is given an astigmatism difference ΔC to the photodetector. 3, and a focus error signal is obtained due to this astigmatism. Further, as described above, a tracking error signal is obtained by differential detection of the ±1st-order lights of the three light spots.

In this embodiment, the beam splitter 2c is used as a means for separating the light flux, but since the ratio of transmitted light and reflected light can be determined arbitrarily, the light flux incident on the photodetector 3 has a desired light intensity. If this is possible, it is also possible to set the reflectance ratio to 0, that is, to make the Fresnelson plate 2d serve both the beam splitter function and the light condensing function without using the beam splitter 2c.

In this example, a shading Fresnelson plate}2d was used as a light condensing means, but a blazed Fresnelson plate with a sawtooth cross-section or a binary type with a rectangular cross-section may also be used. A similar function can be obtained by using a Fresnelson plate in combination with a beam splitter and a diffraction grating.

In this embodiment, the Fresnelson plate 2d is used as a condensing means for the light flux, but the present invention is not limited to this, and a condenser lens having an astigmatism function by adjusting the radius of curvature may be used. Good too.

[Effects of the Invention] As described above, according to the present invention, the multifunctional optical element has the following advantages:
A four-fold grating for separating the emitted light from the light generating means into a plurality of light beams including a focused light for reproduction and a focused light for positional deviation detection, and a four-fold grating for condensing the light beam diffracted by the diffraction grating. Three independent optical systems are not required by integrally forming the light condensing means for irradiating the information recording medium and the light beam separation means for reflecting the light beam reflected by the information recording medium and separating it from the emitted light beam. Therefore, the cost and size of the optical head device can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical head device showing an embodiment of the present invention, FIG. 2 is a structural diagram showing details of the multifunctional optical element shown in FIG. 1, and FIG. A schematic diagram for explaining the calculation method of the ring boundary radius of the Fresnelson plate shown in the figure, Figure 4 is a schematic diagram showing the locus of the k-th ring of the Fresnelson plate, ffi5 is Figure 4 A schematic diagram showing the focal state when a luminous flux is emitted from the emission point O to the annular zone formed by the locus I shown in Figure 6. Figure 6 is a schematic diagram showing the focal state when the luminous flux is emitted from the emission point O to the annular zone formed by the locus I shown in Figure 4. Fig. 7 is a schematic diagram showing a conventional optical head device, and Fig. 8 is a schematic diagram showing a state of focus when a light beam is emitted from the optical head device shown in Fig. 7. FIG. 9 is a block diagram showing the structure of the photodetector shown in FIG. 7. In the figure, 1 is a semiconductor laser, 2 is a multifunctional optical element,
2a is a glass substrate, 2b is a diffraction grating, 2C is a beam splitter layer, 2d is a Fresnel zone plate, 3 is a photodetector, 30 is a front disk, 31 is a bit, and 32 is an information track. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 3

Claims (1)

[Scope of Claims] At least a plurality of focused beams for reproducing information on an optical information recording medium and a plurality of beams for detecting a positional shift of the focused beam for reproducing the information in a direction along the optical recording medium. An optical head device that reproduces information by irradiating focused light for detecting positional deviation, the head device comprising: a light generating means for generating light; and a light generating means for emitting light emitted from the light generating means for reproducing information. a diffraction grating for separating the light beam into a plurality of beams including the focused light beam and the focused light beam for detecting positional deviation; and a light focusing beam that focuses the light beam diffracted by the diffraction grating and irradiates the information recording medium. and a light beam separation means that reflects the light beam reflected by the information recording medium and separates it from the output light beam, the light beam separation means included in the multifunction optical element being integrated. 1. An optical head device comprising: a light detection means for detecting a light beam separated by the means.