JPS58121141A - Focus detector of optical pickup - Google Patents

Abstract

PURPOSE:To increase the detecting sensitivity, by forming a reflecting surface of a critical angle reflecting prism to which a reflected light is made incident from a recording surface with two slanted surfaces. CONSTITUTION:The light emitted from a light source 1 of a laser, etc. is turned into a circular polarized beam through a mask 2, a condenser lens 3, a polarizing prism 4 and lambda/4 plate 5 and then condensed on a disk surface 12 through an objective lens 6. The reflected light travels backward to be reflected by the prism 4 and is made incident at a critical angle to surfaces 8 and 9 of a focus detecting prism 15 which are inclined slightly to each other. This reflected light is made incident to photosensors 10 and 11 to obtain a focusing signal. The incident luminous fluxes to the surfaces 8 and 9 are not parallel to each other, and therefore the intensity of one of surfaces 8 and 9 decreases if the intensity of the other side increases owing to an out-of-focus state. As a result, the detecting intensity is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is recorded in the '7) 11f report track on the disc.
The present invention relates to focus detection fc1111 in an optical pickup for optically receiving fC information.

Information is recorded on the upstream track of the disc, which is also known as a video disc, electronic file, etc., and the recorded information is transferred from a light source such as a laser to the information track using an objective lens. An optical pickup that detects light modulated by recorded information is used as a reproducing device. In optical pickup, in order to accurately transfer the information recorded at high density to the VC, a focusing sub-leg is used to displace the VC in the optical axis direction so that the objective lens is always in focus with respect to the track. However, this'7)rd'IJ # r=No.'f is superior7)
A focus detection device is incorporated.

As this υ focus detection device, a linear lens is introduced on the modulated light detection side, and a focus with astigmatism υ is established.
However, in this method, the optical path length is large because the focus must be focused in order to detect the focus υ. As the optical system becomes larger and the focus is placed on the cylindrical lens mentioned above, there is no astigmatism and the focus detection becomes Komachi-no, so the range in which the control signal can be obtained is narrow. was there.

In order to eliminate the above-mentioned drawbacks, an optical member such as a prism is placed on the quality control light detection side so that the fvj4 light is reflected at almost the critical angle at the convergence point. '7) Utilizing the fact that the 1st side is incident at #X oblique [, opposite to the other side, depending on the state of defocus, the incident angle of the 7) @D beam becomes small, and the beam exits the prism due to refraction. A method has been proposed to detect leakage and reduction of coercion. (Special issue! F4 No. 7246/1983) However, in the first trick method, the prism υ reflection surface must be disposed at approximately the critical angle when focusing, so the light D incident on the prism must be a parallel beam of light. For this reason, in an optical system that serves as both a beam projection lens and a beam projection lens, the projected light must also be parallel light, and the O distance from the objective lens to the disk becomes long, making it difficult to make the optical system compact. 11, and there was a duck left that I thought was a good detection because there was only one reflective surface.

The present invention provides the above-mentioned O
It's the same without the flaws.

This will be explained in detail below with reference to FIG. 1111.

FIG. 1 is a υ optical path diagram when the optical pickup of the present invention is in focus. It becomes hm light after passing through the
The fruit is dyed onto la12. In the case of VC2, -, it is necessary to calculate the luminous flux υ emitted from the condenser lens 3 by the sum of Vi + line. 1) As shown in Fig. 1, condenser lens 37) output f
-If the I beam is a convergent beam, it will be reflected and changed by the υ emotion track on the disk (3)! Originally, the reflected light beam picked up by the objective lens 6 becomes a divergent light beam. At the end of the process, the incident light and polarized light 1 pass through the 174 wavelength plate 5 and become 9 (J[different direct/MIM lights), are reflected by the polarizing prism 4, and enter the focus detection prism 15.This 7) focus detection Prism 157) Reflection 1j0
8.9 is composed of surfaces that are tilted to the same degree on both sides of the point 7v on the optical axis, each of which forms a nearly critical angle with respect to the light beam incident on the surface. It is arranged like this. What is the reflected light from the reflecting surface 8.9?
1 enters the optical sensor 1O111, and a focus signal is emitted.

Figure 2 shows the objective lens 6 and the disk ml 3L7'').
The aperture is shorter than the focal point 1i112, and the light beam incident on the focus detection prism 15 is larger than the older ML,
In the figure, the upper O luminous flux is reflected by the reflecting surface 8 (7) and enters the center flu, but the lower tilllj V luminous flux increases in the part where the O incident M on the reflecting surface 9 is smaller than the critical angle, and is not lost to the outside of the prism due to refraction. The part that is covered increases by 1.

Conversely, as shown in Figure 3, the objective lens 6 and the disk (
3) When the distance between 14 and Q is reached, O to the focus detection prism 15
The incident light emission IeL angle becomes small, the O incident angle to the reflecting surface 8 becomes small, and the O incident angle to the reflecting surface 9 becomes large. Ofc
The O reflected light flux becomes weaker at the reflecting surface 8, and the reflected light flux at the 1 reflecting surface 9 becomes stronger. Then, depending on the state of FIGS. 2 and 3'7), the output of the 7ys1O111 becomes unbalanced, and the objective lens 60 outputs the inertia.

The present invention has a reflective surface 8.
Since 9 is composed of two 0 faces, the i-complement Grism 4
It is not necessary that the incident light is a parallel light flux, but if this light flux is the east end light and there is a leakage of 1, it will be 7
) The distance can be reduced, and a compact pickup optical system can be achieved.

Reflection u1] 8.9 When the incident light flux is not a parallel light flux υ,
There is a total reflection part and a part that is refracted and escapes, but
From the off-set point vtl, the ratio will change. Therefore sensor 10. ll'7) The output is not such that one level is υ level when focused and the other υ level is below, but the relationship is such that one rises and the other falls, producing the effect that the detection feeling lf increases.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the optical path of the present invention 7) Original pickup'7) Focus detection device'D when the device is in focus, and FIGS. 2 and 3 are diagrams of the optical path when the device is out of focus. l: Light source 2: Mask 3: Condenser 4: IM source prism 5: 1/4 wavelength plate 6: Objective lens 8.9
: Reflective surface lo, ll: Sensor 12: Disc surface when in focus

Claims (1)

[Claims] The light from the light source is focused on the information recording surface by an objective lens, the variable-pigeon light is picked up by the objective lens, and at least a part of the picked-up light is arranged so that the light flux is incident at approximately a critical angle. enter the optical member,
Due to changes in the light sensitivity distribution of 0 reflected light and refracted light on the reflective surface,
MU object lens 7) In a focus detection VC position that receives a focusing signal for the information recording surface, light whose special feature is that the reflecting surfaces are formed from two mutually inclined circles #Ie. Pickup focus detection device