JPH03192539A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain the small-sized pickup device which has a focus-error detecting function by using an array type semiconductor laser which has >=3 light emission points and differ in the projection surface position of each light emission point in the direction of the optical axis of projection light. CONSTITUTION:The optical pickup device is equipped with the array type semiconductor 1 which has three light emission points 5-1, 5-2, and 5-3 and the respective projection point positions of the laser 1 are provided in a staircase shape in the projection direction. Projected light beams from the respective light emission points 5-1, 5-2, and 5-3 of the laser 1 are converged by a condenser lens 2 on a recording medium 3. Reflected light beams from the recording medium 3 return to the light emission points as they are. Back projection light beams of the laser 1 are detected by respective photodetectors 4-1, 4-2, and 4-3 independently. At this time, a focus error is detected from the difference signal between the outputs of the photodetectors 4-1 and 4-3 to realize focusing operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device that records or reproduces information using light.

[Conventional technology]

In optical recording, reducing the size of the optical pickup device is effective for improving access time.

A scoop method shown in FIG. 4 is known as a miniaturization method using a semiconductor laser. The light emitted from the semiconductor laser 11 is focused by the condenser lens 2 onto the optical recording medium 3 as a minute spot. The reflected light from the recording medium returns to the light emitting point as it is. The output of the semiconductor laser is configured such that the backward emitted light is monitored by a photodetector 4. When the reflectance of the storage medium changes, the amount of returned light changes, so the output of the semiconductor laser changes. Therefore, by detecting the laser output with the photodetector 4, information on the recording medium can be reproduced.

[Problem to be solved by the invention]

If an attempt is made to use the optical pickup device shown in FIG. 4 using the scoop method in an actual optical disc or the like, a function is required to detect a focus error by detecting a change in the distance between the pickup device and the recording medium. However, since this optical pickup device does not have a detection function for this purpose, a separate optical system is required, and the advantage of miniaturization is lost.

An object of the present invention is to provide a compact optical pickup device that has a function of detecting focus errors.

[Means to solve the problem]

The present invention provides an optical pink-up device that collects emitted light from a semiconductor laser as a minute spot on a recording medium, returns reflected light to the semiconductor laser, and detects a signal. The semiconductor laser is characterized in that it is an array type semiconductor laser having a light emitting point, and the light emitting points have different emission surface positions in the direction of the emission optical axis.

[Operation] The difference between the optical outputs of the two photodetectors is taken to obtain the focus 8-character characteristic. A focusing operation is realized by setting the emission position of another light emitting point near the zero cross point of this difference signal and making the difference signal zero.

〔Example〕

FIG. 1 shows an embodiment of the present invention. This optical pickup device includes an array-type semiconductor laser 1 having three light-emitting points 5-1.5-2.5-3, and focuses the emitted light from the array-type semiconductor laser on a recording medium 3 as a minute spot. A condensing lens 2 that emits light, and three photodetectors 4-1 that are arranged behind the array type semiconductor laser 1 and detect rear emitted light.
．． 4-2.4-3.

As shown in FIG. 1, the positions of the emission surfaces of the array type semiconductor laser 1 are different from each other in the direction of the emission optical axis. Therefore, if the light emitted from the central light emitting point 5-2 is set to focus on the recording medium 3, the other light emitting points 5-3 will be at the rear of the recording medium, and the other light emitting points 5-1 will be focused on the recording medium 3. The focus will be on the front of the medium.

By the way, the output of the semiconductor laser increases as shown in FIG. 2 near the focal point due to an increase in the amount of returned light. Therefore,
As shown in Fig. 3, there are two different light emitting points 5-
By taking the difference in the optical output of the photodetector 4-14-3 with respect to 1.5-3, it is possible to obtain the focus 8-character characteristic.

Therefore, by setting the emission position of the central light emitting point 5-2 near the zero loss point 6 of this difference signal, focusing operation can be realized by setting the difference signal to zero.

In the optical pickup device having the above configuration, the light emitted from each light emitting point 54.5-2.5-3 of the array type semiconductor laser 1 is focused onto the recording medium 3 by the condenser lens 2. The reflected light from the recording medium 3 returns to the light emitting point as it is. The rear emitted light of the array type semiconductor laser is transmitted to each photodetector 4-L.
4-2. Detected independently in 4-3. At this time, as described above, a focus error can be detected by the difference signal of the outputs of the photodetectors 4-1 and 4-3, and a focusing operation can be realized.

In the above embodiment, there are three light emitting points, but even if there are four or more light emitting points, a focus error signal can be obtained from the fluctuation in the light output from two light emitting points.

Further, the array type semiconductor laser may be monolithically integrated or may be a hybrid mounting of individual laser elements.

〔Effect of the invention〕

According to the present invention, the light source includes an array type semiconductor laser having three or more light emitting points, and by making the positions of the light emitting surfaces of the light emitting points different from each other in the direction of the light emitting optical axis, a compact device having a focus error detection function is provided. A pick-up device can be easily realized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the principle of the present invention, and FIG. 4 is a diagram showing a prior art. 1... Array type semiconductor laser 2... Condensing lens 3... Recording medium 4-1.4-2.4-3... Photodetector 5-1.5
-2.5-3...Emission point 6...Zero cross point 11...Semiconductor laser

Claims (1)

[Claims] (1) In an optical pickup device that focuses emitted light from a semiconductor laser as a minute spot on a recording medium and returns reflected light to the semiconductor laser to detect a signal, the semiconductor laser has three or more light emitting points. What is claimed is: 1. An optical pickup device comprising: an array-type semiconductor laser in which the emission surface positions of the respective light emitting points are different from each other in the direction of the emission optical axis.