JPS5817550A - Adjusting mechanism for optical head - Google Patents

Abstract

PURPOSE:To adjust the position of light on a photodetector by providing two thin prisms in an optical system for focusing and tracking, and rotating those prisms. CONSTITUTION:Two prisms whose vertical angles are acute are arranged as shown in the figure, and their angle theta is varied from 0 deg. to 180 deg. to vary incident light optionally within a certain deflection angle range. Those two prisms are arranged in an optical system for focusing and tracking detection, thus easily adjusting the light beam striking the photodetector.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light receiving section adjustment mechanism of an optical head that reads information from an optical disc.

Conventionally, the zero point adjustment of the error signal was done only by subtly moving the center of the bisecting/quadrant photodetector with respect to the optical axis of the optical system! I was doing DIIIE.

First, the function of the deflection prism, which is made up of two thin prisms with a small apex angle α, will be explained. If the genus refractive index of a prism is n, then the angle of deflection of light that almost directly enters one prism is (n-1) (!), and the angle of deflection of light that is almost directly incident on one prism is (n-1) (!). When placed, the corner of the deflection is doubled to C2 (
n-1) a. In this state, when each prism is rotated by an angle of 0 in opposite directions, the deflection angle a changes in the plane perpendicular to the prism ridge in the initial state according to the following formula: J = x 2 (n -1) d -as# The above state is shown in Figure 1 (b).By changing the sea from 00 to iso', the angle of deflection of the incident light can be arbitrarily set within the range of g(n-1)g. It is possible to change.

The present invention will be explained in detail according to an embodiment in which the invention is applied to a tracking error signal detection section of an optical head.

An example of an optical head, as shown in Figure 2, uses semiconductor laser light as a light source to create a small light spot directly above an optical disk, and uses the presence or absence of recording dots on the optical disk as information to measure the intensity of the reflected light from the disk surface. Read from changes. In the ninth step when the optical head follows the dot sequence of the recorded sickle dots, that is, the track, the symmetry axis 3-1 of the light intensity distribution incident on the light receiving section (Fig. 3) is aligned with the optical axis 3-1 of the light receiving section optical system. 3 and placed on the optical axis so that the difference in the output of the two-split photodetector placed on the optical axis becomes zero. In particular, it is important for the tracking error signal detection to align the centers of the two-split photodetector with the axis of symmetry 3-1 of the incident light intensity distribution, the optical axis 3-3 of the condensing lens, on a straight line.

A slight deviation in the axis of symmetry of the incident light teorotic distribution occurs due to the asymmetry of the dot shape, the deflection of the disk surface, the assembly accuracy of the optical head, and the installation accuracy of the optical head, so the final adjustment is made while blocking the incident light with a polarizing prism. I take the.

Definitely p'ptyga') BK? (n = x 1.5
1 ; 830 nm), and the apex angle gs is 112°, and the focal length is 18II as the deflection prism.
If a two-part photodetector of 2■φ is placed on the axis of 151111 behind the condenser lens, the maximum deflection angle of the deflection prism will be approximately *2°, The axis of symmetry of the incident light is allowed to shift by up to 2·■.

The deflection prism according to the present invention can be used not only for rounding to balance a two-segment photodetector, but also for balancing a four-segment photodetector, thereby adjusting the zero point of the tracking and focusing error signal obtained from the four-segment photodetector. Excellent.

[Brief explanation of the drawing]

FIG. 1(a) (0) is an incident light intensity distribution and main ray diagram of the polarization prism head light receiving part optical system that characterizes the present invention. 1-1.2... Deflection prism 2-1... Semiconductor laser 2-2... Focusing/
2-3...Beam splitter-2-4...1/4
Wave plate 2-5...Objective lens 2-6...Optical disk 2-7...Condensing lens 2-8...Two-split photodetector element 2-9...
Difference signal detection circuit 3-1... Symmetry axis of incident light intensity distribution

Claims (1)

[Claims] 's? on the light receiving part of the optical head? A pair of thin prisms is provided in the optical system for focus odor sink and tracking error signal detection, and by rotating the two prisms, the direction of travel of the light is kept small, and the light is placed on the error signal detection element. An optical head adjustment mechanism that adjusts the zero point of an error signal by displacing the position of light.