JPS63249945A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain high reliability with low cost, by reflecting an incident beam of light from a semiconductor laser and introducing it to an information recording medium by a non-polarizing beam splitter. CONSTITUTION:A beam of light emitted from the semiconductor laser 1 is changed to a parallel ray by a collimator lens 2, and is reflected on the non- polarizing beam splitter 3, and is image-formed on the layer 52 of the information recording medium by an objective lens 4 as a micro spot. Reflected light from the layer 52 of the information recording medium of a disk 5 is changed to the parallel ray again by the objective lens 4. And it transmits the non- polarizing beam splitter 3, and passes through a condenser lens 6, and arrives at an optical detector 7. In such a way, since the detection of an RF signal, focus control, and tracking control, etc., can be performed, it is possible to obtain an optical pickup with the low cost and the high reliability.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention has a semiconductor laser as a light source, and records and reproduces information by irradiating an information recording medium with a light beam from the semiconductor laser as a minute spot. This invention relates to an optical pickup that performs either or both of the following.

[Conventional technology]

Conventionally, optical pickups used to accurately reproduce information recorded on information recording media, such as compact discs, emit a beam of light from a semiconductor laser as a light source toward the information recording medium, and a light beam that is reflected by the information recording medium and is detected by a photodetector. In order to separate the light beams directed to the beam, an isolator was constructed using a polarizing beam splitter and a local wavelength plate.

On the other hand, optical cards, which have been attracting attention in recent years, have a card-like shape and are attracting attention for their ease of carrying. However, if an optical card is carried or stored under stress for a long time, polycarbonate (PC), which is used as the material for the protective layer of the optical card, may
may cause locally different birefringence within it. If such an optical card is reproduced using an optical pickup having the above-mentioned isolator configuration, the amount of light reaching the photodetector will be affected by the unevenness of the birefringent state, and as a result, the amount of light will fluctuate depending on the original information. It is difficult to distinguish whether the change is caused by the presence of birefringence or by the presence of birefringence, resulting in misreading.

In order to eliminate this drawback, a system has been proposed in which the optical path is separated using a half mirror (non-polarizing beam splitter) instead of a polarizing beam splitter without using a local wavelength plate.

First, the configuration of a conventional optical pickup using a non-polarizing beam splitter will be explained with reference to FIG. In FIG. 8, 1 is a semiconductor laser 3, 2 is a collimator lens, and 3 is a non-polarizing beam splitter.

4 is an objective lens, 5 is a disk, 51 is a transparent protective layer of the disk 5, 52 is an information recording medium layer of the disk 5, 53 is a supporting substrate of the disk 5, 6 is a condenser lens, and 7 is a photodetector.

The light beam emitted from the semiconductor laser 1 is made into a parallel light beam by a collimator lens 2, and is then converted into a parallel light beam by a non-polarizing beam splitter 3.
The information recording medium layer 5 of the disk 5 is transmitted through the objective lens 4.
2 is imaged as a minute spot.

The reflected light from the information recording medium layer 52 of the disk 5 is turned into a parallel light beam by the objective lens 4 again.

The light is then reflected by the non-polarizing beam splitter 3, passes through the condenser lens 6, and reaches the photodetector 7. Thereby, RF signal detection, focus control, tracking control, etc. are performed using known methods. Furthermore, information is also recorded and erased using this system.

Further, FIG. 9 shows a schematic cross-sectional view of the non-polarizing beam splitter 3. In FIG. 9, 31.degree. 32 is a prism, and on the oblique side of the prism 31, a dielectric thin film 3, a silver film 34, . A dielectric thin film 35 is deposited and bonded to the prism 32 with an adhesive 36.

Such conventional optical pickups have the following drawbacks.

When the light beam from the semiconductor laser 1 passes through the non-polarizing beam splitter 3, a portion of the light beam is reflected in the direction of the arrow in the figure, so that the amount of light reaching the disk 5 is reduced. In order to prevent this phenomenon, it is possible to increase the transmittance by reducing the thickness of the silver film 34 of the non-polarizing beam splitter 3. However, if an attempt is made to deposit the silver film 34 thinly, the silver film 34 becomes macroscopic. From a physical perspective, the film is deposited in islands, making it extremely difficult to obtain uniform film characteristics. Therefore, it is necessary to improve the sensitivity of the information recording medium layer 52 of the disc 5, but this also has its limits. Alternatively, it becomes necessary to perform recording for a sufficient amount of time, resulting in a decrease in the recording speed. Furthermore, although it is possible to use a semiconductor laser with a higher output power, this would lead to a higher cost of the device.

[Summary of the invention]

An object of the present invention is to eliminate the drawbacks of the optical pickup having the above configuration and to provide a highly reliable optical pickup at low cost.

The above-mentioned object of the present invention is to provide a semiconductor laser that emits a light flux that is irradiated onto an information recording medium, and a semiconductor laser that is disposed in an optical path from the semiconductor laser to the information recording medium, and that emits a light flux reflected from the information recording medium that is incident on the semiconductor laser. In an optical pickup comprising a non-polarizing beam splitter having a surface that separates the light beam, and means for detecting the separated reflected light beam, the non-polarizing beam splitter reflects the incident light beam from the semiconductor laser to detect the information. This is accomplished by directing the information to a recording medium.

(Embodiment) FIG. 1 is a schematic diagram showing an embodiment in which the present invention is applied to an optical disk device. In the figure, the same members as in FIG. The resulting light beam is made into a parallel light beam by the collimator lens 2, reflected by the non-polarizing beam splitter 3, and imaged by the objective lens 4 as a minute spot on the information recording medium layer 52 of the disk 5.

The reflected light from the information recording medium layer 52 of the disk 5 is turned into a parallel light beam by the objective lens 4 again.

The light then passes through the non-polarizing beam splitter 3, passes through the condensing lens 6, and reaches the photodetector 7. Thereby, RF multiplied signal detection, focus control, tracking control, etc. are performed using known methods. Furthermore, information is also recorded and erased using this system.

In addition, FIG. 2 shows a cross section 4 of the non-polarizing beam splitter 3.
Shows Mo-style diagram. In FIG. 2, 3.

32 is a prism, and dielectric thin films 33 . Silver +1! ! 34. A dielectric thin film 35 is deposited and bonded to the prism 32 with an adhesive 36.

Figure 3 shows a semiconductor laser 1 with a non-polarizing beam splitter 3.
FIG. 3 is a schematic diagram showing the relationship between the amount of light incident on the disk 5, the amount of light incident on the photodetector 7, and the reflectance of the non-polarizing beam splitter 30 when the light beam emitted from the optical fiber is guided onto the disk 5. Here, RA represents the average value of the S component and the P component of the reflectance.

Considering the preferable reflectance characteristics of the non-polarizing beam splitter 30, in order to properly record and reproduce information on the disk 5, the light beam emitted from the semiconductor laser 1 must be efficiently reflected by the non-polarizing beam splitter 3. It is necessary to guide it to the disk 5. Therefore, the following conditions must be satisfied.

RA≧50% (1) Of course, the recording state of the disk 5 is not determined only by the reflectance characteristics of the non-polarizing beam splitter 3;
It is clear that parameters such as the output of the semiconductor laser 1, the rotational speed of the disk 5, the size of the beam spot formed on the information recording medium layer 52 of the disk 5, and the sensitivity of the information recording medium layer 52 have an effect. However, when considering providing a highly reliable optical pickup at a reasonably low cost overall, it is desirable to use a non-polarizing beam splitter 3 with a reflectance RA of 50% or more.

Further, in order to properly reproduce and record information from the disc 5, it is necessary to efficiently transmit the reflected light from the disc 5 through the non-polarizing beam splitter 3 and guide it to the photodetector 7. Therefore, the following conditions must be satisfied.

RA≦80% (2) Of course, the detection state of the photodetector 7 is not determined only by the reflectance characteristics of the non-polarizing beam splitter 3, but also depends on the sensitivity of the photodetector 7, the photodetector It is clear that the parameters of the electrical circuit connected to 7 have an effect, but if we consider providing a highly reliable optical pickup at a reasonable and low cost overall, the reflectance RA should be 8.
It is desirable to use a non-polarizing beam splitter 3 with a polarization ratio of 0% or less.

Next, two examples of actual film configurations of the non-polarizing beam splitter 3 will be shown. Optical thickness 245n for dielectric thin film 33.35
m of zirconium oxide, the geometric thickness of the silver film 34 is 24
FIG. 4 shows a spectral characteristic diagram of the wavelength of nm. In FIG. 4, Rs.

R,,T,,T,indicate the reflectance of the S component, the reflectance of the P component, the transmittance of the S component, and the transmittance of the P component, and RA,
TA represents the average value of the S component and P component of reflectance and transmittance, respectively. FIG. 5 shows a spectral characteristic diagram of a dielectric thin film 11u33.3s with zirconium oxide having an optical thickness of 245 nm and a silver film 34 having a geometric thickness of 34 nm. Explanations of the symbols used in the figures have been described above and will therefore be omitted here.

The present invention is not limited to the above-described embodiments, and can be applied in various ways. For example, as shown in Fig. 6, a non-polarizing beam splitter 3
The surface 3. of the non-polarizing beam splitter 3 is designed to prevent ghost light generated by the beam from entering the photodetector 7. A non-polarizing beam splitter 3 as shown in Figure 7.
It is conceivable to have a beam shaping function for the light beam emitted from the semiconductor laser 1.

Similar effects can be obtained even when the present invention is applied to an optical pick-up used in other optical recording and reproducing devices such as an optical cart recording and reproducing device, a digital audio disc device, and a video disc device.

〔Effect of the invention〕

As explained above, in conventional optical pickups, non-polarizing beam splitters reflect the incident light beam from the semiconductor laser and guide it to the information recording medium, thereby providing a highly reliable optical pickup at low cost. be.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams explaining one embodiment of the optical pickup of the present invention, and Figure 3 is the relationship between the amount of light incident on the disk, the amount of light incident on the photodetector, and the reflectance of the non-polarizing beam splitter. FIGS. 4 and 5 are spectral characteristic diagrams of a non-polarizing beam splitter used in the optical pickup of the present invention, and FIGS. 6 and 7 show other embodiments of the optical pickup of the present invention. 8 and 9 are diagrams explaining a conventional optical pickup. 1... Semiconductor laser, 2... Collimator lens, 3... Non-polarizing beam splitter,

Claims (2)

[Claims] (1) A semiconductor laser that emits a light beam that is irradiated onto an information recording medium; and a semiconductor laser that is arranged in an optical path from the semiconductor laser to the information recording medium, and that separates the reflected light beam from the information recording medium from the incident light beam from the semiconductor laser. In an optical pickup comprising a non-polarizing beam splitter having a surface and means for detecting the separated reflected light beam, the non-polarizing beam splitter reflects the incident light beam from the semiconductor laser and guides it to the information recording medium. An optical pickup characterized by: (2) The non-polarizing beam splitter has an average value R_A of the S component and P component of the reflectance of 50% or more, and 80% or more.
% or less. % or less.