JPH0799591B2 - Optical head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a configuration of an optical head used in an optical information recording and / or reproducing apparatus, and particularly relates to a plurality of light fluxes from a light source using a light flux splitting element. The present invention relates to an optical head that separates a light beam and records and reproduces information on an optical information recording medium.

[Prior Art] Conventionally, various types of recording media, such as a disc, a card, and a tape, are known as a form of a recording medium that records information by using light and reads the recorded information. Such an optical information recording / reproducing apparatus relatively scans the recording medium with a light beam which is modulated according to the recording information and is narrowed down to a minute spot, whereby information is formed as an optically detectable pit train (information track). To record. At this time, in order to accurately record information without causing inconvenience such as intersection of information tracks, the irradiation position of the minute spot is controlled with respect to a direction perpendicular to the scanning direction (auto tracking control, hereinafter referred to as AT). Need to be called). Furthermore, in order to irradiate a minute spot stably without causing defocusing despite curve of the medium, vibration, mechanical processing error, etc., control is also performed in the direction perpendicular to the medium surface (auto focusing). Control, hereinafter referred to as AF).
Of course, the above-mentioned AT and AF controls are also required during playback.

FIG. 5 is a schematic configuration diagram of an optical information recording / reproducing apparatus using a conventional card-shaped recording medium. In the figure, a semiconductor laser 103 emits a modulated light beam in accordance with a recording signal 121, the light beam is collimated by a collimator 104, and then separated into three light beams by a diffraction grating 105, and polarized beam splitters 106, 1 / After passing through the four-wave plate 107, the objective lens 108
As a result, it is condensed as a minute spot on the optical card 101. In this case, normally, by controlling the phase difference given to the light beams by the diffraction grating 105, the light amount ratios of the three light beams are made different so that only one light beam can be recorded.

The light flux reflected by the optical card 101 is the objective lens 108,
After passing through the quarter-wave plate 107 and reflected by the polarization beam splitter 106, the light passes through the spherical lens 109 and the cylindrical lens 110 and is condensed on the sensor 111.

The electrical output 122 photoelectrically converted by the sensor 111 is processed by the sensor output amplification arithmetic circuit 112, and is sent to the tracking control circuit 113 and the focusing control circuit 114, respectively AT and
Control signals 123 and 124 for AF operation are applied, and as a result, each control circuit applies currents 125 and 126 to the tracking coil 115 and focusing coil 116 to drive the objective lens 108 to perform AT and AF. . Further, at the time of reproduction, the emission power of the semiconductor laser 103 is lowered as compared with that at the time of recording, so that the reproduction signal 12
Is what you get 7. Further, the optical card 101 is driven by the motor 102 in the R direction in the figure and accessed.

FIG. 6 shows a pre-formed A on the optical card 101.
Preformat patterns 141a to 141d for T, information tracks 142a to 142c, and three light spots 131, 132a, 1
It is the figure which showed 32b.

When information is recorded on or reproduced from the information track 142a, the three light spots 132a and 132b of which the generation method has been described with reference to FIG. 5 are positioned so as to be located on the pre-phon mat patterns 141a and 141b, respectively. The optical spot 131 is used to perform recording or reproduction and AF operation.

For recording / reproducing to / from the information tracks 142b and 142c, the light spots 132a and 132b are respectively directed to 141b and 141c, or 141c.
And 141d are irradiated to perform the above operation.

By the way, in order to obtain a reproduction signal of good quality from the recorded optical card, it is desirable to give sufficient exposure energy to the recording sensitivity of the optical card medium at the time of recording. Generally, the exposure energy is the recording power P
[W], recording time T [sec], recording spot area S [c
m ² ] can be expressed as E = P · T / S, but if the maximum rating of the output of the semiconductor laser used and the upper limit of the transmittance of the optical system have an upper limit, then P is the device specification for recording. If T is limited, T is limited.

In order to increase the exposure energy E under such a condition, a method of reducing the area S of the spot is used. For that purpose, conventionally, the aperture ratio (NA) of the objective lens is increased. It was a way of being.

[Problems to be Solved by the Invention] However, the conventional method has the following problems.

FIG. 7 shows a diffraction grating 105 and an incident light beam 13 which are conventionally used.
0 is a schematic diagram showing the states of 0 and diffracted light 131 ′, 132a ′, 132b ′.

As shown in the figure, when the grating forming portion of the diffraction grating 105 is larger than the incident light beam system 130, the diffracted light 131 ′, 132a ′, 13
The light flux diameter of 2b 'is the same size. Therefore, if the recording spot 131 is reduced for the above purpose, the spots 132a and 132b are also reduced at the same time. However, there are limitations on the type of medium material and the method of forming the preformat pattern 141, and if the preformat pattern 141 having a width smaller than the sizes of the sports 132a and 132b cannot be formed, a serious problem will occur. The AT method described with reference to FIGS. 5 to 6 is a so-called three-beam method, which is a well-known method. The AT operation is controlled so that the difference signal representing the difference in the amount of reflected light from 132a and 132b becomes almost zero. FIG. 8 is a diagram showing such an ideal AT error signal pattern. However, when the spot diameter is made smaller than the width X of the pre-format pattern in FIG. 6, the width of the peaks and valleys of the difference signal becomes very narrow as shown in FIG.
The controllable range becomes narrow, and it becomes extremely difficult to obtain a good reproduction signal, contrary to the original purpose.

Therefore, in the conventional method, it has been necessary to take an unfavorable measure such as using a high output semiconductor laser or reducing the recording speed.

[Means for Solving Problems] An object of the present invention is, in view of the above problems of the prior art, a simple method in an optical head that uses a diffraction grating to form a plurality of spots on an optical recording medium. An object of the present invention is to provide an optical head capable of obtaining a recording / reproducing signal of good quality by making the diameter of a sport used for recording information different from the diameter of a spot for other purposes.

According to the present invention, in order to achieve the above object, a light beam from a light source is divided into a plurality of light beams by using a light beam splitting element, and the light beam is applied to an optical information recording medium to record and / or reproduce information. In the optical head for performing the above, the light beam splitting element is made of a hologram, and the hologram has a configuration in which the diameter of the imaged spot formed by the diffracted light among the plurality of spots condensed on the recording medium is formed by the non-diffracted light. It is formed so as to be larger than the diameter of the image spot, and information is recorded using the image spot formed by the non-diffracted light, and auto-tracking control is performed by using the image spot formed by the diffracted light in the previous period. An optical head, characterized in that

[Operation] With the above-described optical head, the state of the wavefront of the diffracted light can be easily changed depending on the type of hologram to be formed, and as a result, the beam diameter of the diffracted light with respect to the non-diffracted light (0th-order diffracted light). The ratio, the light amount ratio, etc. can be freely set. This means that the size, shape, strength, etc. of the diameter of the spot used for recording information and the diameter of the spot for other purposes can be made different.

[Example] FIG. 1 is a schematic diagram showing the relationship between a hologram element used in the optical head of the present invention and an incident light beam at the position where the hologram element is arranged. In the figure, 1 is the base of the hologram element, and 5 is the size of the incident light flux from the laser or the like on the element.

In the hologram element according to the present invention, the hologram is formed over the entire surface of the transparent substrate 1. If the diameter of the light beam 5 is made to be EXP (-2) of the central intensity when the light beam 5 is made incident on this element, the diameter of the image spot of the 0th-order diffracted light after passing through the hologram element is defined. Is approximately represented by d. Further, assuming that the hologram element used in this embodiment is formed so as to generate spherical aberration for high-order diffracted light, flare due to spherical aberration occurs in the spot imaged by the high-order diffracted light. Therefore, the diameter D at the EXP (-2) strength is larger than d. Therefore, it is possible to achieve the above object by using the spot of the 0th-order diffracted light for recording.

FIG. 2 is a schematic diagram showing how the light spots 131, 132a, 132b formed by using the hologram element shown in FIG. 1 are irradiated onto the preformat pattern 141 on the optical card 101.

In manufacturing the hologram element, it is possible to use a known method such as a method of forming a hologram by causing a wavefront having a desired spherical aberration to interfere with a reference wavefront, or a computer hologram.

FIG. 3 is a schematic diagram showing a second embodiment of the present invention. The feature of the embodiment shown in the figure is that the hologram element is formed so as to generate a spherical wave for the high-order diffracted light and give defocus to the image spot. Therefore, the spot due to the non-diffracted light (0th order diffracted light) is in focus on the surface of the information recording medium, and the spot due to the diffracted light has a larger spot diameter on the surface of the information recording medium than the 0th order diffracted light due to defocusing. It will be possible.

In addition, the hologram element of the present invention utilizes the feature of being able to form diffracted light having an arbitrary wavefront, and for example, imparts astigmatism to the diffracted light to increase the diameter of the preformat pattern in the direction crossing the tracks. For example, only diffracted light can be independently operated. FIG. 4 is a schematic diagram showing an example of a light spot formed by such a hologram element. In the figure, the light spots 132a and 132b condensed on the pre-format patterns 141a and 141b have an elliptical shape whose diameter in the direction crossing the tracks is increased by the above-mentioned operation.

[Effects of the Invention] As described above, according to the optical head of the present invention, for example, the wavefront of the diffracted light is adjusted so that the shape of the spot imaged by the diffracted light is made larger than the shape of the spot formed by the non-diffracted light. It is possible to form a plurality of spots having different diameters on the optical recording medium by producing a hologram element for converting the light and arranging the hologram element in the optical path of the optical head. As a result, an AT spot with a diameter large enough for the recording sensitivity of the medium is formed,
It has become possible to perform highly accurate AT operations.

Also, by the same operation, the size of the diameter on the optical recording medium,
It is possible to form a plurality of spots having different shapes and light intensities, and as a result, it is possible to form spots that are suitable for the optical recording medium and the optical information recording / reproducing apparatus.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a hologram element according to an optical head of the present invention, and FIG. 2 is a diagram showing a hologram element shown in FIG. 1 in which light spots having different sizes are formed on a preformat pattern on an optical card. FIG. 3 is a schematic diagram showing the state of irradiation, FIG. 3 is a diagram for showing the second embodiment, and FIG. 4 is a diagram showing the spots of different sizes and shapes on the optical card using the hologram element of the present invention. FIG. 5 is a schematic diagram showing how a format pattern is irradiated, FIG. 5 is a schematic configuration diagram of an optical information recording / reproducing apparatus using a conventionally used card-shaped recording medium, and FIG. 6 is a conventional optical card. FIG. 7 is a diagram showing a state of a light spot in FIG. 7, FIG. 7 is a diagram schematically showing a function of a diffraction grating, and FIGS. 8 and 9 are diagrams showing AT error signals. 1: hologram element (base) according to the present invention, 5: incident light flux,
101: Optical card, 131: 0th order diffracted light spot, 132a, 132b: Higher order diffracted light spot, 141: Preformat pattern, 14
2: Information track.

Claims (1)

[Claims] 1. An optical head for recording and / or reproducing information by splitting a light beam from a light source into a plurality of light beams by using a light beam splitting element and irradiating the optical information recording medium. The element is a hologram, and the hologram is formed such that the diameter of the image spot formed by the diffracted light is larger than the diameter of the image spot formed by the non-diffracted light among the plurality of spots condensed on the recording medium. An optical head is characterized in that information is recorded by using an image spot formed by the non-diffracted light and auto-tracking control is performed by using the image spot formed by the diffracted light.