JPS59185045A - Optical pickup device - Google Patents

Abstract

PURPOSE:To prevent a reflected light from being returned to a semiconductor laser by making a ray reflected on a recording face incident to a reflected face of a prism in an angle approximate to a critical angle or larger and further making a ray from a light source incident to the reflecting face of the prism at the critical angle or below. CONSTITUTION:The ray from the semiconductor laser 10 is made incident to the reflecting face 12 of the prism 11 at an angle causing less reflection. The ray transmitted through the prism 11 and an objective lens 13 and reflected on the recording face 14 passes again through the objective lens 13 and is made incident to the prism 11. This ray is set so as to be made incident to the reflecting face 12 in the vicinity of the critical angle. The light reflected from the replecting face 12 of the prism 11 is made incident to a photodetector 15. The emitted light from a semiconductor laser 10 is made incident to the reflecting face 12 of the prism 11 at a critical angle or little smaller, and the reflected light from the recording face 14 is prevented from being returned to the semiconductor laser 10 and a focus error signal is obtained at the same time by means of the critical angle method by making the irradiated light of the semiconductor laser 10 incident to the reflecting face 12 of the prism 11 at an angle slightly smaller than the critical angle and making the reflected light from the recording face 14 to the reflecting face 12 of the prism 11 at the critical angle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for optically reading information from a recording medium, such as an optical disc, on which information is recorded by optical structural changes.

A conventional device of this type will be described with reference to FIG.

In FIG. 1, a light beam emitted from a semiconductor laser l passes through a collimator lens 2, is reflected by a beam splitter 3, and is reflected by a quarter-wave plate 4. The light passes through the objective lens 5, is reflected by the recording surface 6, passes again through the objective lens 5° and the quarter-wave plate 4, further passes through the beam splitter 3, and is reflected by the critical angle prism 70 and the reflecting surface 8. incident on the detector. Tsumufu,
The conventional optical pickup device has the disadvantage that a quarter wavelength plate 4 and a beam splitter 3 are required to prevent the reflected light from the recording surface 6 from returning to the semiconductor laser, which increases the number of optical components. Therefore, the cost is high, the overall quality of the optical pickup is poor, and it is susceptible to external disturbances.
Another disadvantage is that it is difficult to access at high speed, and there are many adjustments to be made when assembling the optical pickup. An object of the present invention is to provide an optical system configuration in which reflected light does not return to the semiconductor laser without using the quarter-wave plate 4 and the beam splitter 3.

FIG. 2 is an explanatory diagram showing an embodiment of the present invention. The light beam from the semiconductor laser 10 is made to be incident on the reflective surface 12 of the prism 11 at an angle with little reflection.

The recording surface 1 passes through the prism 11 and the objective lens 13.
The light beam reflected by the lens 4 passes through the objective lens 13 again and enters the prism 11. This ray is reflected by the reflective surface 1 of the prism 11.
It is set so that the incident angle is near the critical angle with respect to 2. The light reflected from the reflective surface 12 of the prism l enters the photodetector 15. In the conventional optical pickup device, in order to prevent the reflected light from the recording surface from returning to the semiconductor laser 1,
A half-wave plate 4 and a beam splitter 3 were used, but
In the present invention, the emitted light from the semiconductor laser IO is incident on the reflective surface 12 of the prism II at an angle slightly smaller than the critical angle, and the reflected light from the recording surface 14 is incident on the reflective surface 12 of the prism 11.
By making it incident at a critical angle with respect to 2, 4
It is possible to simultaneously prevent the reflected light from the recording surface 14 from returning to the semiconductor laser 1 () without using the half-wave plate 4 and the beam splitter 3, and to obtain the focus error signal using the critical angle method. be.

FIG. 3 is an explanatory diagram showing another embodiment of the present invention. By setting the setting so that the reflected light from the recording surface always returns to the reflective surface 18 of the prism 17 by a critical angle or more, even if a focus shift occurs, the semiconductor laser 16 will not be able to reach the recording surface 18.
The reflected light from 0 can be prevented from returning. When using the present invention in such a method, a separate device for obtaining a focus error signal is required. FIG. 3 shows a case where a critical angle method is used using a critical angle prism 21 which is set so that a light beam is incident on a reflecting surface 22 at a critical angle.

As mentioned above, the optical pickup device based on the present 1% laser beam eliminates the need for two optical components, the quarter-wave plate 4 and the beam splitter 3, which were required in the past, and reduces the cost of the optical pickup device. This makes it possible to reduce the mass of the entire optical pickup device. Moreover, since the mass is small, it is resistant to external disturbances, high-speed access is facilitated, and the number of optical components is reduced, making it easier to assemble and adjust the optical pickup device.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional optical pickup device, FIG. 2 is an explanatory diagram of an embodiment of the optical pickup device of the present invention, and FIG.
The figure is an explanatory diagram of another embodiment of the optical pickup device of the present invention. 1.Hl.16.-Semiconductor laser 2..Collimator lens 3 r @beam fritter 4--1/4
Wave plate 5, 13, 19・φ Objective lens 6°13
, 19... Recording surface 7, 21... Critical angle prism 8
, 12 , 18 , 22-・Reflecting surface, 11 , 17 ・・
9 prisms, 23...photodetector. Applicant Daini Seikosha Co., Ltd. Agent Patent Attorney Mogami Figure 1 Figure 2 Figure 3 (2)

Claims (1)

[Claims] a light source, a prism through which the light beam from the light source passes, a lens through which the light beam that has passed through the prism is irradiated onto a recording surface, and a photodetector through which the light beam reflected by the recording surface, passed through the lens, and reflected by the prism is incident. In the optical pickup device, a light beam reflected from the recording surface is incident on the reflective surface of the prism at an angle near or above a critical angle, and a light beam from the light source is incident on the reflective surface of the prism at an angle less than or equal to the critical angle. An optical pickup device characterized by: