JPH04106732A - Focus error detector - Google Patents

Abstract

PURPOSE:To make the device simple and high sensible by providing a bisected type photodetector for receiving a light beam from a knife edge for intercepting one part of the light beam, provided in a reimaging position of reflected light from an optical system. CONSTITUTION:An emitted beam from a laser beam source 1 is passed through a beam splitter 4 to form a minute spot on a medium 3 by a condenser lens 2, and a reflected beam from the medium 3 is splitted by the splitter 4 to be imaged again. The knife edge 5 is set up at an imaging point, and approximate half of the beam is intercepted. The bisected type photodetector 6 is set up on a far field surface in the rear of the edge 5. Under the focusing state, a distribution on the photodetector 6 becomes uniform, and since the edge 5 becomes the far field surface when a medium surface is close to or remote from the edge, a shadow of the edge 5 appears as it is in a beam pattern on the detector 6 as shown in the figure. By this method, positional accuracy is promoted by the edge 5, whereas the edge is a simple part, and the detector 6 is set low, and is easily and stably fixed up.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to a focus for an optical disc device, a laser printer device, etc., which uses light from a laser light source by condensing it into a minute spot. This relates to an error detection optical system.

[Prior Art] In an optical head for an optical disk device, a minute spot is focused on a recording medium. Therefore, it is essential to detect errors in the focal position.

FIG. 4 shows an example of the configuration of an optical system for detecting such a focus error. The light emitted from the laser light source 41 forms a minute spot on the medium 43 by the condenser lens 42 . The reflected light from the medium 43 is separated by a beam splitter 44 and imaged again. A knife 45 is installed on the way to the re-imaging point, and approximately half of the light beam is blocked. A two-part photodetector 46 is installed at the imaging point. In this method, when the position of the medium 43 changes in the optical axis direction, the spot shape on the photodetector 46 changes to the fifth position.
Changes as shown in the figure. In other words, when the spot shape is as shown in FIG. 5(a), the medium 43 is too close and the spot shape as shown in FIG.
), it is a focused state. Further, if the spot shape is as shown in FIG. 5(C), the medium 43 is moving too fast.

Since the spot shape on the photodetector 46 changes in this way, a focus error signal can be obtained by taking the difference between the outputs of the two photodetectors.

[Problem to be solved by the invention]

Such an optical system for detecting a focus error can be composed of only a knife and a two-split photodetector, and can obtain a simple signal with high sensitivity. However, in order to obtain a good signal, the dividing line of the photodetector must be precisely aligned with the imaged spot position, and the precision required is on the order of micrometers. Furthermore, since it is necessary to lead out an electrical signal line from the photodetector, it is necessary to fix it stably and firmly, which has the disadvantage of complicating the structure around the photodetector.

An object of the present invention is to provide a simple and sensitive optical device for detecting focus errors without causing the above-mentioned problems.

[Means to solve the problem]

The present invention provides a focus error detection device that focuses emitted light from a laser light source on a reflective surface as a minute spot using a condenser lens, and detects reflected light from the reflective surface that is received by the condenser lens, comprising: an optical system that re-forms an image of the condensed spot; a knife installed at a re-imaging position of the reflected light from the optical system to block a part of the light beam; and a knife that receives the light beam from the knife. It is characterized by having a split type photodetector.

The present invention also provides a focus error detection device that focuses emitted light from a laser light source on a reflective surface as a minute spot using a condenser lens, and detects reflected light from the reflective surface that is received by the condenser lens. an optical system that re-forms an image of a condensed spot of the reflected light; an optical element installed at a re-imaging position of the reflected light from the optical system that spatially separates the light beam into two traveling directions; It is characterized by having two split-type photodetectors that receive the light beam from the element.

[Effect]

In the present invention, since the knife is installed at the reimaging point of the reflected light and the photodetector is installed at the far field position, low positional accuracy is sufficient.

On the other hand, the knife requires high positional accuracy, but since it is a simple component, stable fixation can be easily achieved.

Furthermore, by installing a prism or the like instead of the knife to divide the optical path of the light beam into two and detecting it with a two-split photodetector, the error signal can be detected without loss of light quantity.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram showing an example of a focus error detection device according to the present invention. The focus error detection device shown in FIG.
An optical device that condenses light emitted from a laser light source 1 into a minute spot on a reflective surface of a medium 3 using a condenser lens 2, and detects reflected light from the reflective surface that is received by the condenser lens 2. an optical system consisting of a lens 2 and a beam splitter 4, which re-forms an image of the focused spot; a knife 5, which is installed at the re-imaging position and blocks part of the light beam; and a knife 5, which is installed behind the knife 5. and a two-segment photodetector 6 that receives a light beam.

Next, the operation of this embodiment will be explained.

The emitted light from the laser light source 1 passes through a beam splinter 4 and forms a minute spot on a medium 3 by a condenser lens 2 . The reflected light from the medium 3 is separated by a beam splitter 4 and imaged again. A knife 5 is installed at the imaging point, and approximately half of the light beam is blocked. A two-part photodetector 6 is installed on the far field surface behind the knife 5. That is, the two-split photodetector 6 is installed at a position behind the knife 5 and away from the imaging point. FIG. 2 shows changes in the shape of the light beam on the photodetector 6. FIG. In the case of Fig. 2(a), medium 3
is too close, and in the case of FIG. 2(b), it is in a focused state. In addition, when the light beam shape is as shown in FIG. 2(C), the medium 3
is too far away.

In this way, in the focused state shown in FIG. 2('b), the knife 5 is almost at the focal position, so the distribution on the photodetector 6 becomes uniform. Also, when the media surface is close or far,
Since the knife position is on the far field plane, the beam pattern on the photodetector 6 is as shown in Fig. 2 (ah (C
), the shadow of Naifetsuji appears as it is.

This embodiment is an optical device in which light emitted from a laser light source is focused on a reflective surface as a minute spot by a condensing lens, and the reflected light from the reflective surface received by the condensing lens is detected by a photodetector. , an optical system that re-forms an image of the focused spot, a knife installed at the re-imaging position to block part of the light beam, and a two-part photodetector installed behind the knife to receive the light beam. Consists of.

In such a configuration, low positional accuracy is sufficient since the photodetector is located at a far field position. On the other hand, the knife requires high positional accuracy, but since it is a simple component, stable fixation can be easily achieved.

FIG. 3 is a configuration diagram showing another example of the focus error detection device according to the present invention. The focus error detection device shown in FIG. 3 focuses the emitted light from a laser light source 31 on a reflective surface of a medium 33 as a minute spot using a condensing lens 32, and collects the light reflected from the reflective surface received by the condensing lens 32. an optical system for detecting light, which is composed of a condensing lens 32 and a beam splitter 34, and re-forming an image of the condensed spot;
A prism 37, which is an optical element installed at the re-imaging position and spatially separates the light beam into two traveling directions, and two optical elements installed behind the prism 37 to receive the light beam.
A split type photodetector 36 is provided.

In this focus error detection device, a prism 37 is installed in place of the knife in the focus error detection device of FIG. 1, and divides the traveling direction of the light beam into two. Since a two-split type photodetector 36 is installed in each light beam, a signal can be obtained without loss of light quantity. For example, a diffraction grating may be used instead of the prism 37.

This embodiment is an optical device in which light emitted from a laser light source is condensed onto a reflective surface by a condensing lens as a minute spont, and the reflected light from the reflective surface received by the condensing lens is detected by a photodetector. , an optical system that re-forms an image of the focused spot, an optical element installed at the re-imaging position to spatially separate the light beam into two traveling directions, and an optical element installed behind the optical element to receive the light beam. It consists of two two-part photodetectors.

With such a configuration, by dividing the optical path of the reflected light into two and detecting each with a two-split photodetector, it is possible to detect an error signal without loss of light amount.

〔Effect of the invention〕

As described above, according to the present invention, a highly stable focus error signal detection device can be easily obtained.

[Brief explanation of the drawing]

1 and 3 are block diagrams showing an example of a focus error detection device according to the present invention, FIG. 2 is a diagram showing a spot shape of the focus error detection device of FIG. 1, and FIG. 4 is a diagram showing a conventional focus error detection device. FIG. 5 is a diagram showing a spot shape of the focus error detection device of FIG. 4. FIG. 1... Laser light source, condensing lens, medium, beam splitter, knife, photodetector

Claims (2)

[Claims] (1) In a focus error detection device that focuses emitted light from a laser light source on a reflective surface as a minute spot using a condensing lens, and detects reflected light from the reflective surface received by the condensing lens, an optical system that re-forms an image of the condensed spot; a knife edge installed at a re-imaging position of the reflected light from the optical system to block a portion of the light beam; and a knife edge that receives the light beam from the knife edge. 1. A focus error detection device comprising a two-segment photodetector. (2) In a focus error detection device that focuses emitted light from a laser light source on a reflective surface as a minute spot using a condensing lens, and detects reflected light from the reflective surface received by the condensing lens, the reflected light an optical system that re-forms an image of the condensed spot of the optical system; an optical element installed at a re-imaging position of the reflected light from the optical system that spatially separates the light beam into two traveling directions; and an optical element that spatially separates the light beam into two traveling directions. 1. A focus error detection device comprising two two-part photodetectors that receive a light beam.