JPH04255921A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the influence of stray light which occurs in the head of a separation type optical system and to prevent the deterioration of signal quality. CONSTITUTION:In an optical information recording and reproducing device provided with the separation type optical system consisting of a movable part and a stationary part, a reflection preventing layer against the relevant laser beam is provided on a laser beam incident plane 22 of a movable part 8 or the relevant laser beam incident plane is provided obliquely.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical information recording/reproducing device, and more specifically, an optical information recording/reproducing device such as an optical disk device using a CD-ROM, a write-once optical disk device, or a magneto-optical disk device. Regarding.

0002

4 to 9 are diagrams showing conventional examples, in which FIG. 4 is an explanatory diagram of a bulkhead, FIG. 5 is an explanatory diagram of a separated optical system, FIG. 6 is a block diagram of a servo circuit, FIG. 7 is an explanatory diagram of stray light in the separation optical system head, FIG. 8 is an explanatory diagram of an error signal, and FIG. 9 is an explanatory diagram of FES and TES when there is a stray light component.

In the figure, 1 is a bulkhead, 2 is a medium, 3 is an actuator section, 4 is an objective lens, 5 is a semiconductor laser, 6 is an optical system, 7 is a reflection mirror, 8 is a movable section, 9 is a fixed section, 11 is a semiconductor laser control circuit, 12 is an optical head,
13 is a track control circuit, 14 is a track drive unit, 15
16 is a focus control circuit; 16 is a focus drive unit; 20 is a focus control circuit;
indicates a window, and 21 indicates stray light.

Conventionally, as an optical information recording/reproducing device,
For example, optical disk devices using CD-ROMs, write-once optical disk devices, magneto-optical disk devices, and the like have been known.

[0005] These devices irradiate an information recording medium with a minute light beam spot to reproduce or record information on the medium.

An example of an optical disc device will be explained below. Conventionally, a bulkhead as shown in FIG. 4 has been used in an optical disk device.

[0007] The bulkhead 1 includes an actuator section 3.
, an objective lens 4, a semiconductor laser 5, an optical system 6, a reflection mirror 7, etc. are provided. This bulkhead 1 is moved in the radial direction (ST direction) of the medium 2 by a VCM (voice coil motor), a stepping motor, or the like.

[0008] The actuator section 3 moves on the bulkhead 1 in the X-Y directions shown in the figure, and performs positioning to a track on the medium 2, etc. Also, the objective lens 4 is moved to focus on the medium 2.

In such a bulkhead 1, a laser beam emitted from a semiconductor laser 5 passes through an optical system 6, an objective lens 4, etc., and irradiates the recording surface of the medium 2.

By the way, since the bulkhead 1 as described above is equipped with a heavy optical system 6 and the like, it cannot be moved at high speed. For this reason, a head portion having a separate optical system as shown in FIG. 5 has been used.

In this separated optical system, the head portion is separated into a movable portion 8 and a fixed portion 9, and only the movable portion 8 is moved.

In this case, a heavy optical system 6 and a semiconductor laser 5 are mounted on the fixed part 9, and an actuator 3, an objective lens 4, a reflecting mirror 7, etc. are mounted on the movable part 8.

In the head of such a separated optical system, only the movable part 8 needs to be moved, and this movable part 8 is
Since it is lighter than the bulkhead, high-speed access is possible.

A servo circuit as shown in FIG. 6 is connected to the above head (optical head) to perform various servo controls.

The servo circuit includes a semiconductor laser control circuit 11, an optical head 12, a track control circuit 13, a track drive section 14, a focus control circuit 15, a focus drive section 16, and the like.

The track control circuit 13 controls the track drive section 14, and the track drive section 14 positions the medium 2 on the track.

In this case, the track control circuit 13 receives the track error signal (TES) from the optical head 12 and performs servo control so that this signal falls within a predetermined range.

The focus control circuit 15 also controls the focus drive section 16 to drive the optical lens, etc.
Focus on medium 2.

In this case, the focus control circuit 15:
A focus error signal FES from the optical head 12 is input, and servo control is performed so that this signal falls within a predetermined range.

In the above-mentioned bulk head (see FIG. 4), stray light did not pose a problem due to the optical path, but in the head with a separate optical system (see FIG. 5), stray light becomes a problem due to the optical path. This point will be explained based on FIG.

FIG. 7(A) is an external view of the head, FIG. 7(B)
shows a partial cross-sectional view. In a head with a separate optical system,
It consists of a movable part 8 and a fixed part 9, and a semiconductor laser is mounted in the fixed part 9.

Therefore, the laser beam emitted from inside the fixed part 9 enters the inside of the movable part 8 through the window 20 provided on one surface of the movable part 8 and exits from the objective lens 4 to the outside.

At this time, the optical axis of the laser beam entering the movable part 8 from the fixed part 9 is adjusted so that it is parallel to the moving direction of the movable part 8 (radial direction of the medium).

However, in reality, it is difficult to maintain a completely parallel state, and they are almost parallel. Therefore, a part of the laser beam emitted from the fixed part 9 is transmitted to the end face of the movable part 8 (window 2
0) and becomes stray light 21.

If the window 20 of the movable part 8 has a diameter R, the diameter of the laser beam received by the end face of the movable part will be larger than R (the range indicated by the dotted line in the figure).

Therefore, the laser beam enters the interior of the movable portion 8 within the range of diameter R, but in the portion larger than diameter R, it is reflected and scattered as described above, and stray light 21 is generated.

[0027] This stray light may enter the fixed part 9 again, and in such a case, signal quality may be degraded.

[0028] Therefore, it is possible to increase the diameter R of the window, but this window cannot be made very large due to problems such as the intrusion of dust.

Next, the above error signal will be explained based on FIG. 8. FIG. 8(A) shows the focus error signal FES,
FIG. 8(B) is an explanatory diagram of the track error signal TES.

[0030] Normally, in an optical disc device, the servo signal is subjected to AGC (automatic gain control). This AG
C is the total amount of light to the detector, which normalizes FES and TES.

The focus error signal FES (in the case of astigmatism) is determined as shown in FIG. 8(A). That is, the focus on the medium surface is determined by the area of the light-receiving surface of the detector.
Suppose that b, c, and d are set.

In this case, the focus is as shown in the figure.
The output of the light receiving element of the detector changes depending on defocus (out of focus) and just focus (in focus).

When this state is detected in each of the regions a, b, c, and d, the FES is given by the following equation.

[0034]

[Math 1]

Furthermore, the track error signal TES is as shown in FIG.
Decide as in (B). In this case, the areas of the detector are designated as e and f as shown in the figure.

The track error signal is also determined by receiving the reflected light from the medium with a detector, and the signal of each light receiving element is determined depending on the off-track (misaligned state), on-track (aligned state), etc. Output changes.

Using this output, the track error signal T
Determine ES using the following formula.

[0038]

[Math 2]

Here, when the above-mentioned stray light is added, and the amount of stray light component is α, the focus error signal FES is as follows.
It is given by the following formula.

[0040]

[Math 3]

Further, the track error signal TES is given by the following equation.

[0042]

[Math 4]

[0043] FES and TES when there is the above stray light component
will be explained with reference to FIG. FIG. 9(A) shows FES, and FIG. 9(B) shows TES.

In the figure, +f and -f are defocus detection levels, +t and -t are off-track detection levels, and KB is kickback (this kickback occurs once per lap of the track and is not an error). ).

As shown in the above equation, the larger the stray light component amount α, the smaller the values of FES and TES become. As a result, as shown in P1 in Fig. 9(A), for example, the defocus state occurs due to vibration, etc., but the FES value decreases due to the influence of α, and falls within the range of +f and -f. It goes in.

[0046] That is, the above P1 is + if α does not exist.
Although it exceeds the level of f, it becomes smaller than +f because of α. For this reason, detection at the defocus level becomes impossible, and the error is treated as not an error when it actually is an error. Therefore, information read/write performance is degraded.

Also, in the case of the TES shown in FIG. 9B, the signal indicated by P2, for example, falls within the range of off-track detection levels +t and -t.

That is, the above P2 is off-track due to vibrations, etc., but due to the influence of the stray light component amount α, it becomes a small value as shown in the figure. the result,
Even if it is an error, it is no longer processed as an error, which deteriorates read/write performance.

[0049]

[Problems to be Solved by the Invention] The conventional devices as described above had the following problems.

(1) Heads with separate optical systems are excellent for high-speed access, but they generate stray light and are adversely affected.

(2) When the stray light component increases, the values of the focus error signal FES and the track error signal TES become smaller, making it impossible to perform the original error detection.

[0052] For this reason, what should be an error is treated as not being an error, which degrades the signal quality.

An object of the present invention is to solve these conventional problems, reduce the influence of stray light generated in the head of a separate optical system, and prevent deterioration in signal quality.

[0054]

[Means for Solving the Problems] FIG. 1 is a diagram of the principle of the present invention, FIG. 1(A) is a diagram of the principle of the first invention, and FIG. 1(B) is a diagram of the principle of the second invention.

In the figure, the same reference numerals as in FIG. 7 indicate the same parts. Further, 22 indicates a laser beam entrance surface.

[0056] In order to achieve the above object, the present invention is constructed as follows.

(1) In an optical information recording/reproducing device equipped with a separate optical system consisting of a movable part and a fixed part, an antireflection layer for the laser beam is provided on the laser beam incident surface 22 of the movable part 8. Ta.

(2) In an optical information recording/reproducing device equipped with a separate optical system consisting of a movable part and a fixed part, the laser beam entrance surface 22 of the movable part 8 is provided obliquely, and the reflection at this surface 22 is The light is directed in a direction different from the incident light.

[0059]

[Operations] Since the present invention is constructed as described above, it has the following functions.

(1) In FIG. 1A, when the laser beam from the fixed part enters the movable part 8, it enters the interior through the window 20.

At this time, the area around the window 20 is also irradiated with the laser beam, but since the laser beam entrance surface 22 is provided with an antireflection layer, reflection is prevented.

Therefore, stray light does not occur as in the conventional case,
No deterioration in signal quality occurs.

(2) In FIG. 1(B), when the laser beam from the fixed part enters the movable part 8, it enters the inside through the window 20.

At this time, the area around the window 20 is also irradiated with the laser beam, and reflected light is generated. However, since this laser beam entrance surface 22 is formed obliquely, the reflected light is
Proceeds in a direction different from the incident light.

[0065] Therefore, it is possible to prevent the reflected light from becoming stray light and entering the fixed part again. Therefore, there is no deterioration in signal quality due to stray light, unlike in the conventional case.

[0066]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

(Description of First Embodiment) FIG. 2 is a diagram showing a first embodiment of the present invention, and in the figure, the same reference numerals as in FIG. 1 indicate the same parts.

This example is an example in which the antireflection layer shown in FIG. 1(A) is composed of an antireflection paint.

The separation type optical system is composed of a fixed part 9 and a movable part 8, and the laser beam emitted from the fixed part 9 enters the movable part 8, and is further irradiated onto the medium 2 from the objective lens 4. be.

In this case, an antireflection paint (for example, Epicoat) is applied on the laser beam entrance surface 22 of the movable part 8. That is, an antireflection paint is applied around the window 20 through which the laser beam passes to prevent reflection of the laser beam.

[0071] In this way, even if the laser beam emitted from the fixing part 9 irradiates the area around the window 20, no reflection will occur and stray light will not occur as in the conventional case.

(Description of Second Embodiment) This embodiment is shown in FIG.
This is an example corresponding to (B). In this example, the laser beam entrance surface 22 of the movable part 8 is formed obliquely. That is,
It is formed obliquely to the upper or lower surface of the movable part 8.

The laser beam emitted from the semiconductor laser in the fixed part 9 enters the interior through the window 20 of the movable part 8, exits from the objective lens 4, and irradiates the medium 2.

At this time, the laser beam from the fixed part 9
The reflected light is reflected by the laser beam entrance surface 22, but this reflected light is
As shown, the light travels in a direction different from that of the incident light.

Therefore, it is possible to prevent the reflected light from becoming stray light and entering the fixing portion 9 again.

(Description of Other Embodiments) Although the embodiments have been described above, the present invention can also be implemented as follows.

(1) As the antireflection layer, other than coating may be used. For example, an antireflection film may be applied.

(2) When the laser beam entrance surface is formed obliquely, it may be directed in either direction. In other words, the reflected light may be directed in a direction different from that of the incident light. Further, the angle of inclination may be arbitrary.

(3) In addition to optical disk devices, the present invention can also be applied to similar devices.

[0080]

[Effects of the Invention] As explained above, the present invention has the following effects.

(1) The influence of stray light can be prevented and signal quality can be prevented from deteriorating.

(2) With a simple configuration, the adverse effects of stray light can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a configuration diagram of a first embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional bulkhead.

FIG. 5 is an explanatory diagram of a separation type optical system.

FIG. 6 is a block diagram of a servo circuit.

FIG. 7 is an explanatory diagram of stray light in a separate optical system head.

FIG. 8 is an explanatory diagram of an error signal.

FIG. 9 is an explanatory diagram of FES and TES when there is a stray light component.

[Explanation of symbols]

4 Objective lens 8 Movable parts 20 Window 22 Laser beam incidence surface

Claims (2)

[Claims] Claim 1: In an optical information recording and reproducing device equipped with a separate optical system consisting of a movable part and a fixed part, a reflection prevention plate for the laser beam is provided on the laser beam entrance surface (22) of the movable part (8). An optical information recording/reproducing device characterized by providing a layer. 2. In an optical information recording and reproducing device equipped with a separate optical system consisting of a movable part and a fixed part, the laser beam entrance surface (22) of the movable part (8) is provided obliquely,
An optical information recording/reproducing device characterized in that the reflected light on this surface (22) is directed in a direction different from that of the incident light.