JPS58147821A - Optical head - Google Patents

Abstract

PURPOSE:To improve the tracking adjustment and focus adjustment of an optical head remarkably by separating reflected light from a disk into a center and a circumferential light beam through an optical part where a reflective and a transmissive part are formed nearly concentrically. CONSTITUTION:A reflected beam reflected by the recording surface of the optical disk is made into a parallel beam through a convergent lens and the parallel beam is sent to a polarization beam splitter 33 through a quarter-wavelength plate 34. Then, the reflected beam is portioned out by the beam splitter 33 and sent to the optical part 37 consisting of the reflective part 37a and transmissive part 37b. This optical part 37 is arranged at up to 45 degrees to the optical axis of an optical path of reflection as shown in the figure, and while the relatively gentle light intensity distribution in the section of the reflected beam due to an off-tracking phenomenon is considered, the reflected beam is separated into the center light beam near the optical axis and the circumferential light beam at the outside of the center light beam, which are distributed in two directions respectively.

Description

[Detailed description of the invention] The present invention relates to an optical head that improves mixing of signals into signals.

[Background technology]

Conventionally, in the optical head of a video disc player, a half mirror has been used to divide the reflected light from the disc into two parts for tracking adjustment and focus adjustment. The scanning system of this optical video disc player will be explained with reference to FIG. A laser beam generated from a laser light source (semiconductor device laser or He-Ne laser) 1 is converted into a parallel beam by a condenser lens 2 . This parallel light beam passes through the polarizing beam splitter 3 and then passes through the tiger and king mirror (horizontal compensation mirror) 4.
The light is reflected by the converging lens 5 and focused on the recording surface of the disk 6. The beam reflected by the recording surface of the disk 6 returns in the direction in which it came and is distributed by the polarizing beam splitter 3. Thereafter, the optical signal for tracking is divided into two by the half mirror 7 into the optical signal for tracking and the optical signal for focusing. The light is sent to four divided photodiodes 10 through an astigmatism optical section 9 constructed by the following.

Here, detection of a focus signal by the astigmatism optical section will be explained. FIG. 2 shows a normal astigmatism optical section 9 consisting of a condenser lens 9a and a cylindrical lens 9b. In the illustrated example, for convenience of explanation, the reflected light from the recording surface of the optical disc 6 will be considered along the optical axis.

A ray of light in a plane determined by the optical axis and the cylindrical axis of the cylindrical lens 9b focuses the fish in a far distance on the optical axis, and a beam in a plane perpendicular to the ray focuses nearby. From this, the beam passing through the astigmatism optical section 9 is focused between the focal points Fl and F. As a result, the light beam passing through the astigmatism optical section 9 is not focused on one point, but forms a circle of confusion of a certain size as shown in the figure. At this time, if the position of the circle of least confusion is made to correspond in advance to the focal position of the reading laser beam emitted from the optical head to the recording surface of the disk 6,
By detecting the fluctuation of the disk 6 from the positional fluctuation of the circle of least confusion, the focus of the R-cutting laser beam can always be focused on the recording surface of the disk 6.

For example, if the disk 6 is in a normal position and the incident beam is irradiated to a place other than the pit recorded on the recording surface, the reflected beam will be reflected by the objective lens 5° and the tracking mirror 4.
The light passes through a polarizing beam splitter 3 and a half mirror 7 and is guided to a photodiode 10 by an astigmatism optical section 9. As shown in FIG.
Since the center l of d is projected as a circular image as shown in FIG. 4(a), the output from the differential amplifier 11 becomes zero and the servo mechanism is held in a stopped state.

Furthermore, when the disk 6 is located close to the optical head l, the circle of confusion is caused by the four photodiodes 10a to 10.
As shown in FIG. 4(b), a pair of photodiodes 10! is projected onto the center of d as an elongated horizontal circular ring in the vertical direction in the figure. , 10c output is a pair of photodiodes 1
The output is larger than that of 0b and 10d. Therefore, the output from the differential amplifier 11 is ten, and this output drives the servo mechanism to correct the optical head to the correct position.

Furthermore, when the disk 6 is located far away from the optical head i, the circle of confusion is caused by four photodiodes 10a to 1.
This is because it is projected at the center of 0d as an elongated elliptical image in the horizontal direction as shown in Figure 1c).

The output of the pair of photodiodes 10b and 10d is larger than the output of the pair of photodiodes 10a and 100.

Therefore, the output from the differential amplifier 11 becomes -. This output controls the focus servo mechanism to correct the optical head to the correct position.

Next, detection of a tracking optical signal obtained by dividing one reflected beam into two by the half mirror 7 will be briefly described. This is because when the incident beam deviates from the track on the recording surface, the light intensity distribution within the cross section of the two reflected beams becomes uneven.

This tracking optical signal is projected onto two photodiodes 8a and 8b of a tracking control circuit constituted by two photodiodes 851.8b and a differential amplifier 21 as shown in FIG.
A differential amplifier 21 detects the diode output difference between a and 8b. This output controls the tracking servo mechanism to correct the optical head to the correct position.

However, the reflected beam from the disk 6 is not uniform;
Particularly in a state where the track is about to come off, a light intensity distribution occurs within the cross section of the reflected beam. As shown in FIG. 4(a), even though the circle of least confusion is projected at the center of the four photodiodes 10a to 10d, the optical signal for the tratus control circuit is mixed with the optical signal. There is a risk that the output of the differential amplifier 11 will not become zero and the optical head will be out of focus.

[Purpose of the invention]

This invention was made in view of the above-mentioned problems.

It is an object of the present invention to provide an optical head that can significantly improve the accuracy of tracking adjustment and focus adjustment by reducing the mixing of a tracking optical signal into a focusing optical signal with a relatively simple configuration.

[li of the invention [1] This invention is applied to an automatic focusing mechanism of an optical head that reads information recorded on an optical disc using an astigmatism optical part, and a reflecting part is formed within the beam of reflected light from the optical disc. An optical section with a transmitting section formed approximately concentrically is arranged diagonally with respect to the reflected optical axis, and one reflected light is used as a central ray near the optical axis, and one surrounding ray is used as an optical signal for the outer rays of this central ray. This is extracted as a tracking optical signal.

〔Effect of the invention〕

The optical part in which the reflecting part and the transmitting part are formed in substantially concentric circles can separate the reflected light from the disk into a central ray and a surrounding ray, thereby reducing the mixing of the tracking optical signal into the focusing optical signal. This makes it possible to significantly improve the tracking adjustment and focus adjustment of the optical head.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 6, 31 is a laser light source, and this laser light source 31
The laser beam generated is converted into a parallel beam by a condensing lens 32, passes through a polarizing beam splitter 33, passes through a quarter-wave plate 34, and is focused on the recording surface of an optical disk 36 by a converging lens 35. This optical disc 3
The reflected beam that has been reflected on the recording surface of 6 is passed through the converging lens 35.
The beam is converted into a parallel beam by the beam and sent through a quarter-wave plate 34 to a polarizing beam splitter 33.

Here, the reflected beam is separated by a polarizing beam splitter 33 and sent to an optical section 37 having a reflecting section 37a and a transmitting section 37b formed in substantially concentric circles. This optical section 37
is 45° to the optical axis of the reflected optical path as shown in Figure 7.
The beam is disposed at an angle of , and is separated into ambient light rays with a light intensity distribution in the cross section of the reflected beam caused by off-track, and each light ray is divided into two directions. The optical part 37 adopted in this embodiment 1ζ is made by depositing a highly reflective metal film such as gold or aluminum on a flat substrate made of an optically transparent material such as glass or acrylic, and then hot-etching the center of the film. The transparent portion 37b is formed by etching the membrane into an elliptical shape using a method such as etching. At this time, the elliptical shape of the transmitting part 37m- is set to have a ratio of the major axis to the minor axis (E:l), and when the eye shape (the surface perpendicular to the tip) has a circular cross section, it is formed by the concave cylindrical lens 38b. The image is projected through the constructed astigmatism optical section 38 onto a photodiode 39 which is divided into four parts by increasing the diameter of the circle of least confusion.

If the position of this circle of least confusion is made to correspond in advance to the focal position of the reading laser beam that enters the recording surface of the optical disc 36 from the optical pickup, the fluctuation of the optical disc 36 can be detected from the positional fluctuation of the circle of least confusion, and the reading laser The beam can always be focused on the recording surface of the optical disc 36.

Note that the principle of detecting the focus signal in the astigmatism optical section 38 has been described above, so the explanation will be omitted here.

shadowed. Here, the deviation of the light intensity distribution in the cross section of the reflected beam that occurs when the incident beam deviates from the track of the optical disk 36 is detected by the difference in the outputs of a pair of photodiodes using a differential amplifier. This output controls the tracking servo mechanism to correct the optical pickup to the correct position.

Therefore, by taking advantage of the fact that the light intensity distribution in the cross section of the reflected beam caused by off-track is relatively gentle, the reflected beam from the disk 36 is transmitted through the reflecting section 37a and the transmitting section 37b of the optical s37.

Because it can be separated into a central ray and an ambient ray.

A simple four-component configuration can reduce the mixing of the tracking optical signal into the focus signal, and can significantly improve the tracking adjustment and focus adjustment of the optical pickup.

In addition, the shape of the transmitting part 37b formed in the optical part 37 is made to correspond to the arrangement angle of the optical part 37, and the ratio of the major axis and the minor axis is set to v/T.
By setting = 1 and making the cross-sectional shape of the reflected beam circular, the circle of least confusion projected onto the photodiode 39 in a normal state can be made circular, so the diode output difference of the photodiode 39 can be easily reduced to zero. Can be matched.

This invention is not limited to the embodiments described in L, and can be implemented with various modifications without changing the gist.

For example, in the above embodiment, a metal film with high reflectance is deposited on a transparent substrate and the central part is etched to form a transmitting part and a reflective part. However, the present invention is not limited to this. A transparent part and a reflective part can be formed by cutting out the center of the substrate.

Alternatively, a metal film can be deposited in a rectangular shape at the center of a transparent substrate to form a transmissive part and a reflective part.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a row of conventional optical heads, Fig. 2 is an explanatory diagram of the astigmatism optical section, Fig. tx3 is a circuit diagram of the focus control circuit, and Fig. 4 (a) or C1 is an explanatory diagram showing the projection of the circle of confusion of the astigmatism optical section in different states, FIG. 5 is a circuit diagram of a tracking control circuit, and FIG. 6 is a schematic configuration diagram showing an embodiment of the present invention. , FIG. 7 is an explanatory diagram of the optical section of the same embodiment. 1... Laser light source 2... Condensing lens 3...
・Polarizing beam splitter 4...Tracking mirror 5...Converging lens 6
...Disc 7...Half mirror 8,
8m, 8b, 10.10a-10d=Photodiode 9... Astigmatism optical section 9a... Condensing lens 9
b...Cylindrical lens 11, 21...Differential amplifier 3
1... Laser light source 32... Condensing lens 33...
・Polarizing beam splitter 34...1/4 wavelength plate 35...Converging lens 36
...Optical disc 37...Optical section 37s+...
Reflection section 37b... Transmission section 38... Astigmatic optical section 38a... Condensing lens 38b... Concave cylindrical lens 39. 39a to 39d, 40a, 40b - Photodiode applicant Tokyo Shibaura Electric Co., Ltd. Agent Patent Attorney Yuki Komiya - Outside 1 li1WJ Figure 2 et al. 113 Figure 5

Claims (1)

[Scope of Claims] (1) An optical head that reads information from an optical disk includes an optical section in which a reflecting section and a transmitting section are formed substantially concentrically in the optical path of reflected light obtained by irradiating the optical disk. Arranged diagonally to the reflected optical axis. An optical system characterized in that reflected light is separated into a central ray near the optical axis and peripheral rays located outside this ray, and the central ray is used as a focusing optical signal and one peripheral ray is extracted as a tracking optical signal. head. The optical head according to item 1 below. 13) The optical head according to claim fa1, wherein the optical part has a reflective part formed in the center and a transparent part formed around the reflective part. (4) The central ray separated by the optical section is projected onto a 4-split photodiode via an astigmatism optical section and converted into a focus signal.
The optical head according to any one of Items 1 to 3. (5) The optical head according to any one of claims 1 to 3, wherein the ambient light separated by the optical section is projected onto a two-split photodiode and converted into a tracking signal.