JPS6325843A - Optical head - Google Patents

Abstract

PURPOSE:To obtain an optical head which attains a recording/reproduced signal having good quality, by making the diameter of a spot used for information recording different from that for another purpose with respect to the optical head which uses a diffraction grating to form plural spots on an optical recording medium. CONSTITUTION:The luminous flux from a light source is separated into plural luminous fluxes by a diffraction grating element 1, and they are projected to an optical information recording medium to record and reproduce information. this diffraction grating element 1 has a diffraction grating forming part 3 and a diffraction grating non- forming part 4, and the diffraction grating forming part 3 and the diffraction grating non-forming part 4 are arranged in the optical path from the light source to the recording medium so that they are placed in a luminous flux. Since the luminous flux is made incident on both of the diffraction grating forming part and the diffraction grating non-forming part, the ratio of the synthetized light of the 0th-order diffracted light of the diffraction grating forming part and the transmitted light of the diffraction grating non-forming part to the high-order diffracted light from the diffraction grating forming part is freely set in the shape of the diffraction grating forming part, the area ratio of both parts, etc., are set to prescribed values.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the configuration of an optical head used in an optical information recording and/or reproducing device, and in particular, the present invention relates to the configuration of an optical head used in an optical information recording and/or reproducing device. This invention relates to an optical head that records and reproduces information on and from an optical information recording medium by separating them into separate parts.

[Prior Art] Conventionally, various types of recording media, such as disk-shaped, card-shaped, tape-shaped, etc., have been known for recording information using light and for reading recorded information. Such an optical information recording/reproducing device scans the recording medium relatively with a beam of light that is modulated according to recorded information and narrowed down to a minute spot, thereby generating information as optically detectable pit rows (information tracks). Record. At this time, in order to accurately record information without causing inconveniences such as □ crossing of information tracks, it is necessary to control the irradiation position of the minute spot in a direction perpendicular to the scanning direction (auto tracking control, hereinafter referred to as AT). ). Furthermore,
In order to stably irradiate a minute spot without causing defocus despite bending of the medium, vibration, mechanical processing errors, etc., it is necessary to control the direction perpendicular to the medium surface (autofocusing control, hereinafter referred to as AF). ). Of course, during playback, the above AT, AF f91
11 is required.

FIG. 6 is a schematic diagram of an optical information recording and reproducing bag 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, which is collimated by a collimator 104 and separated into three light beams by a two-diffraction grating 105. After passing through the /4 wavelength plate 107, the light is focused onto the optical card 101 by the objective lens 108 as a minute spot. Note that in this case, usually, by controlling the phase difference given to the light beam by the single diffraction grating 105, the light intensity ratio of the three light beams is varied, and the light intensity is set so that only one light beam can be recorded.

The light beam reflected by the optical card lot passes through the objective lens 1.
08. After passing through the 1/4 wavelength plate 107 and being reflected by the polarizing beam splitter 106, the spherical lens 109.
The light passes through the cylindrical lens 110 and is focused on the sensor 111.

The electrical output 122 photoelectrically converted by the sensor 111 is
Processed by sensor output amplification calculation circuit 112, tracking control circuit 113, focusing control circuit 114
control signals 123. to 123. for AT and AF operations, respectively.
124, and as a result, each control circuit applies a current of 1 to the tracking/king coil 115 and focusing coil 116.
25.126, the objective lens 108 is driven to perform AT and AF. Also, during playback, by lowering the emission power of the semiconductor laser lO3 compared to during recording, in addition to the above-mentioned AT and AF operations, Playback signal 12
7. In addition, the optical card 101 is connected to the motor 1
02 in the direction R in the figure and accessed.

FIG. 7 shows a preformat pattern 141a for AT that is formed in advance on the optical card 101.
141d, information tracks 142a to 142c, and three light spots 1311132a and 132b.

When recording or reproducing information on the information track 142a, the light spots 132a + 132b of the three light spots whose generation method was explained using FIG. 6 are positioned on the preform mat patterns 141a and 141b, respectively. The optical spot 131 is used to perform recording or reproduction as well as AF operation.

For recording and reproducing information on the information tracks 142b and 142c, the optical spots 132a and 132b are set to 141b, respectively.
The above operation is performed by irradiating the beams to 141c and 141c, or 141c and 141d.

By the way, in order to obtain a reproduction signal of good quality from an optical card on which information has been recorded, it is necessary to

It is desirable to provide sufficient exposure energy for the recording sensitivity of the optical card medium. Generally, the exposure energy can be calculated using recording power P [w], recording time T [sec], and recording spot area s [cm2]. , E=P-T/S, but if there is an upper limit to the maximum output rating of the semiconductor laser used or the transmittance of the optical system, then P, and if there is a limit to the specifications of the recording device, T is limited.

In order to increase the exposure energy E under such conditions, a method is used to reduce the spot area S. To do this, the aperture ratio (N, A,) of the objective lens is
The conventional method was to increase .

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

FIG. 8 shows a conventionally used diffraction grating 105, an incident light beam 130, and diffracted lights 131' and 132a'.

132b' is a schematic diagram showing the state of the part 132b'.

As shown in the figure, when the grating forming portion of the diffraction grating 105 is larger than the incident beam system 130, the diffracted light 131',
132a', 132b' (7) The luminous flux diameters are the same size. Therefore, for the above purpose, record spora) 131
If you make it smaller, at the same time, spots 132a, 13
2b also becomes smaller.

However, there are limits to the type of media material and the method of forming the preformat pattern 141, and the spots 132a, 1
If the preformat pattern 141 having a width smaller than the size of the pattern 32b cannot be formed, a significant problem will occur.

The AT method explained using FIGS. 6 and 7 is an arrangement of the so-called 3-beam method, and as is well-known, this method uses a beam having a width at least larger than the width of the Briomat pattern on the preformat patterns 141a and 141b. Using the difference signal representing the difference in the amount of reflected light from the spots 132a and 132b of the diameter, AT is adjusted so that this becomes almost zero.
It controls the operation. FIG. 9 is a diagram showing such an ideal AT error signal pattern. However, when the spot diameter is made smaller than the width of the preformat pattern, the width of the peaks and valleys of the difference signal becomes very narrow, as shown in Figure 10, and the height of the peaks or the depth of the valleys becomes very narrow. This causes a state in which a certain amplitude becomes small, narrowing the range in which accurate AT control can be performed, and making it extremely difficult to obtain a good reproduced signal, which is contrary to the original purpose.

Therefore, in the conventional method, undesirable measures had to be taken such as using a high-output semiconductor laser or lowering the recording speed.

[Means for Solving IFi Problems] In view of the problems of the prior art described above, an object of the present invention is to provide a convenient method for an optical head that forms a plurality of spots on an optical recording medium using one diffraction grating. An object of the present invention is to provide an optical head capable of obtaining recording/reproducing signals of good quality by making the diameter of a spot used for recording information different from the diameter of a spot used for other purposes.

The object of the above is to provide an optical head for recording and/or reproducing information by separating a light beam from a light source into a plurality of light beams using a diffraction grating element and irradiating the light beams onto an optical information recording medium. The diffraction grating element has a diffraction grating forming part and a diffraction grating non-forming part, and the diffraction grating forming part and the diffraction grating non-forming part are both located in the light beam in the optical path from the light source to the recording medium. This is achieved by an optical head characterized in that it is disposed at.

[Function] According to the optical information recording and reproducing device as described above, the light flux is incident on both the diffraction grating forming part and the non-forming part, so that
By setting the shape of the grating forming part and the area ratio between the two to predetermined values, the combined light of the 0th-order diffracted light of the grating forming part and the transmitted light of the grating non-forming part and the light coming from the grating forming part can be combined. The ratio (luminous flux diameter ratio, light amount ratio, etc.) to higher-order diffracted light can be freely set. This means that the diameter of the spot used for recording information and the diameter of the spot used for other purposes, shape 1 intensity, etc. can be made different.

[Example] FIG. 1 is a schematic diagram showing the relationship between the diffraction grating element used in the optical head of the present invention and the diameter of the incident light beam at its arrangement position.

In the figure, ■ indicates the base of the diffraction grating element, 3 indicates the diffraction grating forming portion, 4 indicates the grating non-forming portion, 2 indicates the boundary of the blue portion, and 5 indicates the size of the incident light beam from a laser or the like on the element.

The diffraction grating element according to the invention has a border 2 on a transparent substrate l.
It has a lattice forming part 3 and a lattice non-forming part 4 with the border as a boundary. When a light beam 5 is incident on this element, if the diameter of the light beam 5 is defined as the diameter of the intensity that becomes EXP (-2) of the center intensity, then the 0th order diffracted light after passing through the 1st diffraction grating element (the grating The diameter of the mixed light of the zero-order diffracted light from the grating-forming portion and the transmitted light from the grating-free portion is approximately represented by D, and the diameter of the higher-order diffracted light from the grating-forming portion is approximately represented by d. By setting D) d as in , when these light beams are condensed by an objective lens, the effective N and A are.

Focusing on this, since the O-order diffracted light is larger than the higher-order diffracted light, the spot diameter of the higher-order diffracted light is larger than that of the O-order diffracted light. Therefore, by using the 0th-order diffracted light for recording, It becomes possible to achieve the purpose. FIG. 2 shows light spots 131, 132a, 132b of different sizes using the diffraction grating element shown in FIG.
The preformat pattern 141 on the optical card 101
FIG. 3 is a schematic diagram showing how the light is irradiated upward.

In the detailed design of the diffraction grating element, the ratio of spot diameters is determined by the large contribution of V to the ratio of D and d in FIG. (for example, try to concentrate the diffracted light on a specific order by using a blazed grating), and also take into consideration the intensity distribution of the incident light flux, and perform Fourier transformation to obtain the desired characteristics. All you have to do is find the setting value of the element.

) 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 shape of the boundary 2 of the grating forming part 3 and the shape of the incident light beam 5 are made different. Therefore, it is possible to make the spot of the O-order diffracted light and the spot of the higher-order diffracted light different in shape (that is, in the same embodiment, the former is approximately circular and the latter is elliptical).

FIG. 4 is a schematic diagram showing a third embodiment of the present invention. In the case of this embodiment, compared to FIG. The direction of the long sleeves is different from the oval shape. By doing so, it is possible to handle the diffraction direction of the higher-order diffraction light and the shape of the diffraction spot independently.

FIG. 5 is a schematic diagram showing the state of the light spot according to the embodiment of the present invention shown in FIGS. 3 and 4, respectively, and (a
) corresponds to that in FIG. 3, and (b) corresponds to that in FIG. 4.

As described above, according to the present invention, it is also possible to increase the diameter of the spot in the direction across the tracks of the preformat pattern, and it is possible to easily create a light spot suitable for each information recording medium.

[Effect of the invention 1] As explained above, according to the optical head of the present invention, an element in which a diffraction grating forming part and a diffraction grating non-forming part exist on one diffraction grating element base is manufactured, and the optical path of the optical head is By arranging the diffraction grating element according to the present invention so that both parts are present in the light beam, it is possible to create j4I spots with different diameters and shapes on the optical recording medium. .

As a result, the AT spot is formed with a diameter sufficiently large for the inherent recording sensitivity of the medium, resulting in highly accurate AT.
It is now possible to perform actions.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the diffraction grating element according to the optical head of the present invention, and FIG. 2 is a diagram for explaining the diffraction grating element shown in FIG. Schematic diagram showing how to irradiate the top,
Figures 3 and 4 are respectively 2. FIG. 5 is a diagram showing the third embodiment, and shows how light spots of different sizes are irradiated onto a preformat pattern on an optical card using the diffraction grating elements of the second and third embodiments. FIG. 6 is a schematic diagram of an optical information recording and reproducing apparatus using a conventionally used card-shaped recording medium, and FIG. 7 is a diagram showing a state of a light spot on a conventional optical card. FIG. 8 is a diagram schematically showing the function of the diffraction grating, and FIGS. 9 and 10 are diagrams each showing the ATT difference signal. 1: Diffraction grating element (substrate) according to the present invention, 2: Boundary of grating forming part, 3: Grating forming part, 4: Grating non-forming part, 5: Incident light flux, 101: Optical card, 131: O-th order diffracted light spot, 132a. 132b: High-order diffraction light spot, 141 nib reformat pattern, 142: Information track. Agent Patent attorney Seki Yamashita Figure 1 Figure 3 Figure 4 Figure 2 +01 Figure 5 (0) (b ) = quasi = = (b) = = to 8 4, 5 Figure 7

Claims (1)

[Claims] (1) An optical head that records and/or reproduces information by separating a light beam from a light source into a plurality of light beams using a diffraction grating element and irradiating the beam onto an optical information recording medium, wherein the diffraction grating element is A diffraction grating forming part and a diffraction grating non-forming part are arranged in an optical path from the light source to the recording medium so that both the diffraction grating forming part and the diffraction grating non-forming part are located in the light beam. An optical head characterized by: