JPH02306441A - Optical head and its production - Google Patents

Abstract

PURPOSE:To improve the recording/reproducing characteristic and also to attain the recording of information with high density by positioning the optical axis of an objective lens and the center value of the light quantity distribution of the incident light of the objective lens. CONSTITUTION:A light source 1 is separated from a holding member 19 for a collimator lens 2, and the center value of the light quantity distribution of the incident light is positioned to the optical axis of an objective lens 6 with high accuracy. Thus the member 19 is separated form the light source 1 and can be moved horizontally to a fixed optical base 18. At the same time, the optical axis of the lens 6 and the center value of the light quantity distribution of the incident light are positioned with high accuracy. As a result, the diameter of a beam spot image-formed on an information recording medium is approximately equal to a circular beam. Furthermore the beam diameter can be reduced. Thus the recording/reproducing characteristics can be improved in a wide range of the lens 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used in compact discs, laser discs, image document file devices, external storage devices for computers, etc., and reproduces information using a light beam of a semiconductor laser. The present invention also relates to an optical head used in an optical recording and reproducing apparatus for storing and reproducing data.

Conventional technology In recent years, optical storage devices with high density, large capacity, and non-contact characteristics have been attracting attention as external storage devices for computers, but the development of magneto-optical recording is the most promising because it is rewritable. has been done. (1) In principle, a light beam emitted from a light source is irradiated onto an information recording medium made of an amorphous perpendicularly magnetized film with perpendicular anisotropy, and when the temperature is raised to near the cue point, magnetization occurs. It is recorded by being magnetized in the opposite direction by an external magnetic bias.During reproduction, due to the magnetic light and optical effects on the surface of the information recording medium, the vibration direction of the light is shifted to the left and right by the magnetization direction of the information recording medium. The information signal is extracted by rotating the information signal by about .3 to 0.5 degrees.During erasing, the information recording medium is irradiated with a light beam emitted from a light source in the same way as during recording. It will be erased by applying an external magnetic bias in the direction.

A conventional magneto-optical reproducing device will be explained using FIGS. 5 and 6.

In FIG. 5, 1 is a semiconductor laser, and the light beam emitted from this semiconductor laser 1 is a diverging and elliptical beam. Therefore, this diverging beam is converted into a parallel beam by the collimating lens 2. Also, since this parallel beam is an elliptical beam, it is corrected into a circular beam by the shaping prism 3, then transmitted through the non-polarizing beam splitter 4, and the optical axis is bent at a right angle by the 45-degree reflecting mirror 5. . The light beam bent at right angles enters the objective lens 6 and is focused onto the information recording medium 7. At this time, as shown in FIG. 6, if the light beam incident on the objective lens 6 is made to be larger than the effective diameter of the objective lens 6, the light beam focused by the objective lens 6 will be narrowed down by the diffraction effect. It exhibits an Airy disk distribution, and the beam diameter is converged to a small value.Also, if the converged beam is made to have a uniform beam diameter in the nine circumferential directions, the diameter of the parallel beam incident on the objective lens 6 will be a circular beam. It is necessary to make the light amount distribution uniform in the radial direction and the circumferential direction. Information recording medium 7
If the beam diameter becomes a circular beam and can be narrowed down to a small diameter, the recording and reproducing characteristics will be good and at the same time high-density recording and reproducing will be possible. Further, the light beam irradiated onto the information recording medium 7 is reflected and enters the objective lens 6 again to become a parallel beam. In addition, this parallel beam is again incident on the non-polarizing beam splitter 4, and the amount of light is reflected according to the reflectance RP and ps of P-polarized light and S-polarized light, and 1/2
The light passes through the wavelength plate 8 and enters the polarizing beam splitter 9, where it is separated into P-polarized light and S-polarized light beams. The 1/2 wavelength plate 8 has the function of shifting the phase of P-polarized light and S-polarized light by 180 degrees, and cancels common-mode noise in the differential detection method that is commonly used for detecting playback signals in magneto-optical disk drives. It is a frequently used retardation plate because it can double the signal output and improve the CN ratio by about 3 dB.

Further, the transmitted beam of the light beam separated by the polarizing beam splitter 9 is focused by a focusing lens 10, generates astigmatism by a cylindrical lens 11, and is imaged on a 4-split photodetecting element 12. , a focus error signal is detected. Further, the beam reflected by the polarizing beam splitter 9 is imaged by a focusing lens 13 onto a two-split photodetecting element 14, and a tracking error signal is detected. Using these focus error signals and tracking error signals, even if the information recording medium 7 has some degree of surface deflection or eccentricity, positioning control of about ±1 μm in the focus direction can be performed by driving the objective lens 6 with the lens drive coil 15. Achieved. The objective lens 6 is held by a rubber damper 17 via a lens holder 16 having a lens drive coil 15 on its outer periphery, and the semiconductor laser 1.
Collimating lens 2. The photodetecting elements 12, 14 and various optical components are mounted on a fixed optical base 18 made of metal.

Problems to be Solved by the Invention In order to achieve miniaturization and large capacity, which is a feature of optical recording devices, it is essential to form a beam with a small diameter and uniformity to form an image on an information recording medium. Generally, in order to reduce the beam diameter, it is necessary to shorten the laser wavelength or increase the aperture (NA) of the objective lens. Intensity distribution and wavefront aberration greatly influence this. Since it takes a considerable amount of time to develop a short wavelength laser and a high NA objective lens, it is important to first make the intensity distribution of the light incident on the objective lens uniform. However, in the prior art, the optical axis tilt of the semiconductor laser 1 and the optical axis position of the objective lens 6 are held by the rubber damper 17.
Since highly accurate positioning is not possible during assembly, the light intensity distribution of the incident light with respect to the optical axis of the objective lens 6 is non-uniform and has large variations. As a result, the beam spot diameter and its dispersion are large, which adversely affects the recording and reproducing characteristics such as the CN ratio and crosstalk.

In addition, when the objective lens 6 is moved left and right, the larger the amount of movement (the more uneven the beam spot diameter becomes, resulting in deterioration of recording and reproducing characteristics such as CNR and crosstalk, In practice, it could only be moved within a narrow range of about 100 μm.

The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide an optical head with excellent recording and reproducing characteristics over a wide range of objective lenses.

Means for Solving the Problems In order to solve the above problems, the present invention separates the holding member that holds the light source and the collimating lens, and sets the central value of the light intensity distribution of the incident light with respect to the optical axis of the objective lens. This configuration allows for highly accurate positioning.

Function As described above, the holding member that holds the light source and the collimating lens can be separated and made movable in the horizontal direction with respect to the fixed optical base, and the center value of the light intensity distribution of the objective lens and the incident light can be separated. By positioning with high precision,
The beam spot diameter formed on the information recording medium becomes a nearly circular beam, and the beam diameter can be made small.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram of a magneto-optical optical head according to the present invention, and FIG. 2 is a block diagram of a holding member that holds a light source and a collimating lens. The principles of recording, reproducing, and erasing are exactly the same as the conventional example, and the light source and the holding member that holds the collimating lens are separated, and the optical axis of the objective lens and the center value of the light intensity distribution of the incident light are positioned with high precision. This is different from conventional methods.

The light beam emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2, as in the conventional example.
The semiconductor laser 1. The collimating lens 2 is the holding member 1
9, the x-y optical axes are adjusted, and parallel light is emitted. The emitted parallel light is converted into a circular beam by a shaping prism 3 provided on a fixed optical base 18, passes through a non-polarizing beam splitter 4, and the optical axis is converted to a right angle direction by a 45-degree reflecting mirror 5. Objective lens 6
An image is formed on the surface of the information recording medium. The objective lens 6
is held by a rubber damper 17 via a lens holder 16 having a lens drive coil 15 on its outer periphery as in the conventional example, so the optical axis position of the objective lens 6 cannot be positioned with high accuracy due to assembly variations. It is possible.

Therefore, the semiconductor laser 1. which emits the parallel beam with respect to the optical axis of the objective lens 6. By moving the holding member 19 equipped with the collimating lens 2 in the horizontal direction with respect to the fixed optical base 18, highly accurate positioning is achieved. The light beam focused on the information recording medium surface is reflected by the information recording medium surface, passes through the objective lens 6 again, and is reflected by the non-polarizing beam splitter 4 according to the reflectance, and then passes through the 1/2 wavelength plate. 8. After passing through the 1/2 wavelength plate 8, the light beam is incident on the polarizing beam splitter 9, and among the light beams separated by the polarizing beam splitter 9, the transmitted beam is focused by the focusing lens 10, and is focused by the cylindrical lens 11. Astigmatism is generated, an image is formed on the four-split photodetecting element 12, and a focus error signal is detected. The beam reflected by the polarizing beam splitter 9 is imaged by a focusing lens 13 onto a 110-2 split photodetecting element 14 to detect a tracking error signal.

FIGS. 3 and 4 are schematic diagrams of a method for precisely positioning the optical axis of the objective lens and the center value of the light amount distribution of the light incident on the objective lens. Next, the basic principle will be explained. In FIG. 3, the optical axis of the objective lens is located at the left side (A) and at the center (B) with respect to the light intensity distribution of the incident light.

At the right end, the objective lens is driven at a low frequency of about 107 to 207 via an actuator drive circuit. Further, a light detection element is provided in the light output section of the objective lens, and the waveform of a detection signal representing a change in the amount of light is measured with an oscilloscope through an amplifier circuit. On the other hand, the waveform of the driving current of the objective lens is similarly measured. When the objective lens is driven on the left side (A) and the right side drive is set to 10, the detection signal, which is a change in light amount, also increases to 10, and the waveforms of the lens drive current and detection signal have the same frequency and are in phase. . In the right side (A), the light intensity change is opposite to the lens drive current, and the waveforms of the lens drive current and the detection signal have the same frequency but are in opposite phases. At the center, the light intensity changes as the objective lens optical axis passes through the maximum value of the incident light intensity, and the detection signal becomes a waveform with a frequency twice that of the lens drive current. The principle described above allows the positioning of the objective lens optical axis and the center value of the light intensity distribution of the incident light to be
This has become possible with high precision of 0 μm or less.

FIG. 4 is a schematic diagram of another method for similarly positioning the optical axis of the objective lens and the center value of the light intensity distribution of the incident light. An objective lens replacement member 20 having an opening smaller than the effective diameter of the objective lens and having approximately the same weight as the objective lens 6 is inserted into the lens holder 16 and driven at a low frequency via an actuator drive circuit 21. In addition, a sensor section of the photodetecting element 22 or the power meter 23 is provided on the output light side of the opening, and the center value of the light intensity distribution of the incident light is positioned so that the light intensity becomes the maximum value. 20 and the objective lens 6 are replaced.

By the above method, it has become possible to position the objective lens optical axis and the center value of the light intensity distribution of the incident light with high precision.

In optical playback-only and optical recording/playback drive devices equipped with optical heads, not only the recording and playback characteristics, such as the SN ratio and crosstalk characteristics, are improved (the beam spot can be narrowed down to a small size and uniformly, so the frequency characteristics are improved and the size is small. It is possible to provide a drive device with a large capacity.Furthermore, in the drive device, the access mechanism generally uses a linear motor to perform rough access to the optical head, and fine seek is performed by driving an objective lens. The SNR increases as the movable range of the objective lens increases.

Generally, the movable range of the objective lens for close seek is ±
It is generally used at a thickness of 100 μm or less. but,
Although linear motors are suitable for high-speed access, they are not suitable for small, low cost, and low power consumption drive devices. Therefore, a stepping motor is suitable as the head rough access mechanism for providing the above-mentioned compact, low cost, low power consumption drive device. However, if you try to achieve a fairly fast access using a stepping motor, you will need to perform rough feed, and considering the poor feed accuracy of the stepping motor, the range of movement of the objective lens that can be used with conventional optical heads is narrow, making it unusable. do not have. However, with the optical head of the present invention, the deterioration of the CN ratio in a range of about ±250 μm can be suppressed to about 0.5 dB, stable servo characteristics can be obtained, and a stepping motor suitable for small size, low cost, and low power consumption can be used. Therefore, it is possible to provide a drive device exclusively for optical reproduction and for optical recording and reproduction that is small in size, low in cost, and has low power consumption. Furthermore, external storage devices for computers and image two-document filing systems that use the drive device described above are equipped with the drive device with the features described above, so they are reliable, small and large, with a low error rate. We can provide a high-capacity, low-cost system.

Effects of the Invention As described above, according to the present invention, the optical axis of the objective lens and the light intensity distribution of the incident light can be easily positioned without changing the configuration of the optical head, and the objective lens can be adjusted over a wide range (±
By using an optical head with excellent recording/reproducing characteristics (250 μm) and suitable for high-density recording, and the optical head of the present invention, a stepping motor with features of small size, low cost, and low power consumption can be used as a coarse access mechanism. can be used,
It is possible to provide an optical drive device having the features of small size, low cost, and low power consumption, and a system such as an image file and document file device using the drive device.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an optical head in an embodiment of the present invention, Fig. 2 is a sectional view of a holding member for a semiconductor laser and a collimating lens, and Figs. 3 and 4 are the optical axis of the objective lens and the amount of incident light. FIG. 3 is an explanatory diagram showing a light amount distribution of high-definition incident light and a center value of the distribution. 1... Semiconductor laser, 2... Collimating lens, 3... Shaping prism, 4...
・Non-polarizing beam splitter - 15...45 degree reflection mirror, 6...Objective lens, 7...
Information recording medium, 8...1/2 wavelength plate, 9...
... Polarizing beam splitter 110 ... Focusing lens, 11 ... Cylindrical lens, 12
...Four-split light detection element, 13... Condensing lens, 14... Two-split light detection element, 15...
... Lens drive coil, 16 ... Lens holder, 17 ... Rubber damper, 18 ...
...Fixed optical base, 19... Holding member.

Claims (4)

[Claims] (1) A light source as a radiation means for emitting a light beam, a 45-degree reflecting mirror for irradiating the radiation light from the light source at right angles to the information recording medium, and for forming an image on the information recording medium. The objective lens is composed of an objective lens, an objective lens driving section, and a photodetecting element that receives reflected light from the information recording medium and converts it into an electrical signal, and the optical axis of the objective lens and the center value of the light intensity distribution of the light incident on the objective lens are The optical head that has been positioned. (2) Holding the light source and a collimating lens that converts the elliptically divergent light emitted from the light source into parallel light in a holding member,
2. The optical head according to claim 1, wherein the holding member is movable in a horizontal direction with respect to a fixed optical base comprising a degree reflection mirror, an objective lens, an objective lens drive unit, and the like. (3) The objective lens is driven in the tracking direction, and the change in the amount of light emitted from the objective lens is 2 times the frequency of the objective lens drive current.
A method of manufacturing an optical head that positions it to double the frequency. (4) Attach an objective lens replacement component with an aperture smaller than the effective diameter of the objective lens to the objective lens holding component, drive it in the tracking direction, and position it so that the amount of light emitted from the aperture is close to the maximum value. A method for manufacturing an optical head in which the objective lens and the objective lens replacement part are replaced after the objective lens is removed.