JPH03266232A - Optical head - Google Patents

Abstract

PURPOSE:To minimize the error of a focus detection signal and a track detection signal by providing a condensing member in such a manner that the laser light emitted from a light source to a spacing between the light source can a spectral means can be condensed onto a spectral means. CONSTITUTION:A condenser member 8 is so provided that the laser beam from the light source 1 to the spacing between the light source 1 and the spectral means, i.e. flat plate beam splitter is condensed onto the flat plate beam splitter 2. The laser beam emitted from the light source 1 is condensed onto the flat plate beam splitter 2 by the condenser member 8 and is then changed in the optical path. The laser beam subjected to the optical path change is collimated by a collimating lens 3 to collimated beams of light which are condensed by an objective lens 4 to an optical disk 5. The reflected light from the optical disk 5 transmits the objective lens 4, the collimating lens 3 and the flat plate beam splitter 2 and is then condensed by a condenser lens 6 to a signal detector 7. The errors of the focus detection signal and the track detection signal is extremely minimized even if the spectral means, such as flat plate beam splitter 2 is inclined by a change with lapse of time or temp. change, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical head, and particularly to an optical head suitable for an optical disk device.

[Conventional technology]

An example of a conventional optical head is shown in FIG. 4. In FIG. 4, a laser beam emitted from a light source is converted into an optical path by a flat plate beam splitter 2, which is a spectroscopic means, and is made into parallel light by a collimating lens 3.
1. : The light is further focused and reaches point A of the optical disc 5. The reflected light from the optical disk 5 is transmitted through the objective lens 4. The light passes through the collimator lens 3 and the flat beam splitter 2, passes through the condenser lens 6, and reaches point B of the signal detector 7.

[Problem to be Solved by the Invention] However, in the conventional optical head as described in 2 above, the focus detection signal and track There was a problem that a large error occurred in the detection signal.

That is, in FIG. 4, when the flat beam splitter 2 is tilted at an angle θ to become the flat beam splitter 2', the laser beam is converted into an optical path by the flat beam splitter 2', made into parallel light by the collimating lens 3, and then passed through the objective lens. 4 and reaches point A' of the optical disk 5. The reflected light from the optical disk 5 is transmitted through the objective lens 4. Collimator lens 3
The light then passes through the flat beam splitter 2', passes through the condenser lens 6, and reaches point B' of the signal detector 7. At this time, the distance between point B and point B' is do. This amount of deviation dO is approximately expressed as dO=f tanθ (1), where f is the focal length of the condensing lens 6. This shift amount dO causes an error in the focus detection signal and the tracking error signal in the signal detector.

The present invention was devised in view of these points, and is capable of minimizing errors in focus detection signals and track detection signals even if a spectroscopic means such as a flat beam splitter is tilted due to changes over time or temperature. The objective is to provide an optical head that can

[Means to solve the problem]

In the optical head according to the present invention, a condensing member is provided between the light source and the spectroscopic means so that the laser beam emitted from the light source can be focused onto the spectroscopic means.

[Effect]

Since the optical head according to the present invention has the above structure, even if the spectroscopic means such as a flat beam splitter is tilted due to changes over time or temperature, errors in the focus detection signal and the track detection signal can be kept extremely small.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings. FIG. 1 is an explanatory diagram showing a first embodiment of the present invention.

The optical head shown in FIG. 1 is different from the conventional one shown in FIG.
The difference is that a light condensing member 8 is provided so that the light is condensed upward.

In FIG. 1, the same parts as in FIG. 5 are given the same reference numerals. That is, 1 is a light source, 2 is a flat beam splitter as a spectroscopic means, 3 is a collimating lens,
4 is an objective lens, 5 is an optical disk, 6 is a condensing lens, 7
8 indicates a signal detector and 8 indicates a condensing lens as a condensing member.

A laser beam emitted from a light source 1 is focused onto a flat beam splitter 2 by a focusing member 8, and then its optical path is changed. The laser beam whose optical path has been changed is made into parallel light by a collimating lens 3 and focused onto an optical disk 5 by an objective lens 4 . The reflected light from the optical disk 5 is transmitted through the objective lens 4.
After passing through the collimator lens 3 and the flat beam splitter 2, the light is focused on the signal detector 7 by the condenser lens 6.

Now, let us consider the amount of spot shift at the signal detector that occurs when the flat beam splitter 2 is tilted at an angle θ as shown in FIG. The magnification of the optical lens 6 is assumed to be m.

When the flat beam splitter 2 rotates around a point C that is a distance α from the point where the light is focused by the condensing lens 8 and tilts at an angle θ, the spot deviation ido' is approximately expressed as do' = mC1tanθ (2) .

Here, when comparing the above do' and the deviation ldo in the conventional example shown in Fig. 4, generally (1) and (2)
), since mα<f, do<d.

In addition, when the flat beam splitter 2 rotates around the point where the light is focused by the condenser lens 8 and tilts at an angle θ, that is, when α=0 in equation (2), the spot shift ld
O″ is do″=0.

Therefore, the optical head according to the present invention can suppress errors in the focus detection signal and the track detection signal to an extremely small level even if the spectroscopic means such as the flat beam splitter 2 is tilted due to aging, temperature change, or the like.

FIG. 3 is an explanatory diagram showing a second embodiment of the present invention.

In this embodiment, a cubic beam splitter 9 is used in place of the flat beam splitter 2 in FIG. 1 showing the first embodiment of the present invention, and a configuration is shown in which errors in the focus detection signal are detected by the Knifezi method.

Here, the cubic beam splitter 9 has a knife 1110 whose knife end is in contact with the optical path changing surface.

Due to the same effect as described in the first embodiment, even if the cubic beam splitter 9 is tilted, the error in the focus detection signal can be kept extremely small.

〔Effect of the invention〕

As explained above, according to the present invention, a condensing member is provided between the light source and the spectroscopic means so that the laser beam emitted from the light source can be condensed onto the spectroscopic means. Accordingly, even if the spectroscopic means is tilted, errors in the focus detection signal and the tracking error signal can be suppressed to an extremely small value, so that a remarkable effect can be obtained in that an optical head that can stably detect information signals can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the first embodiment of the present invention, FIG. 2 is an explanatory diagram showing the spot shift on the signal detector 7 when the flat beam splitter 2 is tilted, and FIG. FIG. 4 is an explanatory diagram of a conventional optical head. 1. Light source, 2. Flat beam splitter, 3 collimating lenses, 4. Scoop. Body lens, 5... Optical disk, 6... Condensing lens, 7... Signal detector, 8.
... Condensing lens, 9 ... Cubic beam splitter, 1
0... Naifetsuji layer. Mata 2 Figure 3 Figure 1

Claims (1)

[Claims] a light source that emits a laser beam; a spectrometer that converts the optical path of the laser beam; a collimating lens that converts the laser beam with the optical path converted into parallel light; and an objective lens that focuses the parallel light onto an optical disk. In an optical head comprising the objective lens and a signal detector that takes in reflected light from the optical disk that has passed through the collimating lens and the spectroscopic means, the laser beam is separated into the spectrometer between the light source and the spectroscopic means. An optical head characterized in that a condensing member is provided to condense light onto the means.