JPH0737268A - Optical pickup - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to contrive a low cost by making the shaping plane of a beam shaping prism have the function of an optical path separation plane to an optical detecting system and making the beam shaping plane to be a non-vapor-deposited plane. CONSTITUTION:A light beam emitted from a laser diode 1 is made incident on the non-vapor-deposited plane 3p of the beam shaping prism 3a via a coupling lens 2. The light beam is almost passed through the plane 3p since a P polarization transmissivity in the plane 3p is >=90% and the cross-sectional from of the beam is made to be a complete to be made incident on a 1/4 frequency plate 4. Then, the beam becomes to be a circular polarized light and irradiates a media 7 via a deflection prism 5. The reflected light from the media 7 is made incident on the 1/4 frequency plate 4 to be converted to an S polarized light and is made incident on the prism 3a. At this time, the light more than 15% of the incident S polarized light is reflected at the plane 3p and is made incident on a magneto-optical signal detecting system 9 via an objective lens 8 and then signals corresponding to information are detected. Thus, the constitution of a device is made simple and the low cost is contrived because the prism 3a is served as a beam splitter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical disk drive, and more particularly to the structure of an optical pickup having a reduced number of optical components.

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing the basic structure of a conventional magneto-optical disk pickup, in which a beam emitted from a laser diode 61 is converted into parallel light by passing through a coupling lens 62. Then, the beam shaping prism 63 at the next stage makes the cross-sectional shape of the beam into a perfect circle and outputs the beam to the beam splitter 64. The light beam emitted from the beam splitter 64 forms a minute spot on the medium 67 via the deflection prism 65 and the objective lens 66, and the information recorded on the medium 67, that is,
The reflected light depending on the presence or absence of the pit enters the beam splitter 64 via the objective lens 66 and the deflection prism 65.

A light beam incident on the beam splitter 64 is reflected by a joint surface of a polarizing film or a prism, is guided to a detection system 70 through a λ / 2 plate 68 and a detection lens 69, and a magneto-optical signal servo signal is obtained. The detection system 70 may have various forms, but since it is not directly related to the present invention, it is simply referred to as “detection system”. The beam splitter 64 and the λ / 2 plate 68 are used to enhance the magneto-optical detection sensitivity.
No. 4 has P-polarized light transmittance of about 70% and S-polarized light reflectance of 100%
It is also possible to remove the λ / 2 plate 68 by tilting the entire detection system.

FIG. 7 shows a general structure of an optical pickup which corresponds to a phase change (PC) or the like in which media information is regarded as a variation in the amount of reflected light. In FIG. 7, the same parts as those in FIG. Attach. Since the optical pickup that detects the fluctuation of the light quantity of the reflected light does not need to detect the magneto-optical signal, the polarization beam splitter 71 is used instead of the beam splitter, and the light beam emitted from the polarization beam splitter 71 passes through the λ / 4 plate 72. The isolator optical system is formed so as to transmit the light to enhance the light utilization efficiency. The above-mentioned magneto-optical pickup is reflected by the polarization beam splitter 71, and the amount of light reaching the detection system 70 is only about 30% of the reflected light from the medium, but the optical pickup for phase change or the like constitutes an isolator optical system. Therefore, 100% reflected light can be guided to the detection system.

Since the above-mentioned magneto-optical pickup and optical pickup for phase change use the beam splitter 64 or the polarization beam splitter 71 in any case, it is inevitably expensive and it is difficult to reduce the cost. There is a problem that there is, and in order to solve this problem,
As disclosed in Japanese Patent Application Laid-Open No. 58-166543, there is a method in which a beam shaping surface of a beam shaping prism is provided with a polarizing film and an optical pickup is configured without using a beam splitter or a polarizing beam splitter. In order to construct an optical pickup using the above, the beam shaping prism must be provided with a polarizing film, and there is still a problem that expensive optical parts are still required.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional problems, and an object of the present invention is to reduce the number of optical components and to construct an optical pickup with inexpensive components.

[0007]

To achieve this object, an optical pickup according to the present invention is an optical pickup mounted on a drive for detecting the presence or absence of recording pits on a medium as a change in the amount of reflected light, and at least P-polarized light is used. A laser diode that emits light, a coupling lens that makes the light beam emitted from the laser diode enter, a beam shaping prism that makes the beam cross-sectional shape of the light beam emitted from the coupling lens a perfect circle, and the light is emitted from the beam shaping prism. A λ / 4 plate for injecting a light ray, an objective lens for irradiating the light ray on the medium, and an incident light reflected by the medium,
And a light detection system for detecting the presence or absence of a recording pit, wherein the beam shaping surface of the beam shaping prism is a non-deposited surface, and an optical path for reflecting the reflected light from the medium on the beam shaping surface. It is characterized by having the function of a separation surface.

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a diagram showing a basic configuration of an optical pickup according to the present invention, in which 1 is a laser diode as a light source, 2 is a coupling lens for converting a light beam emitted from the laser diode 1 into parallel light, and 3a is A beam shaping prism that circularizes the beam cross-sectional shape of the parallel light emitted from the coupling lens, 4 is a λ / 4 plate, 5 is a deflection prism, 6 is an objective lens, 7 is a medium such as a magneto-optical disk, and 8 is an objective. The lens 9 is a magneto-optical signal detection system, the incident light surface 3p of the beam shaping prism 3a is a non-evaporated surface, and its P-polarized transmittance has a characteristic as shown in FIG.

That is, the figure shows SF11 (refractive index n = 1.7).
8, θB = 60.678 °) and BK7
The P-polarized light transmittance, the S-polarized light reflectance, and the beam shaping magnification when (refractive index n = 1.51, θB = 56.485 °) are used are shown. Whichever beam shaping prism is used, it is possible to secure a P-polarization transmittance of 90% or more at a practical beam shaping magnification of 1.5 times to 3.0 times. The reflectance of S-polarized light, which is the reflected light of, can be obtained at 15% or more.

In the optical pickup thus constructed, the light beam emitted from the laser diode 1 which is the light source enters the coupling lens 2, is converted into parallel light, and enters the emergency contact surface 3p of the beam shaping prism 3a. Since the P-polarized transmittance on the emergency plane 3p of the beam shaping prism is 90% or more, most of the light beam emitted from the laser diode 1 is transmitted, and at that time, the cross-sectional shape of the beam becomes a perfect circle, When it enters the λ / 4 plate 4 provided in the above, it becomes circularly polarized light and is irradiated onto the medium 7 such as a magneto-optical disk through the deflection prism 5 and the objective lens 6.

On the other hand, the reflected light from the medium 7 enters the λ / 4 plate 4 through the objective lens 6 and the deflecting prism 5, is converted into S polarized light, and enters the beam shaping prism 3a. At this time, since 15% or more of the incident S-polarized light is reflected by the emergency surface 3p of the beam shaping prism 3a, the reflected light enters the magneto-optical signal detection system 9 through the objective lens 8,
A signal corresponding to the information written in the pit of the medium 7 is detected. The amount of light required to decode the information written on the medium 7 in the magneto-optical signal detection system is R
Although the f signal and the servo signal must be sufficiently obtained, in the case of a magneto-optical disk, the Rf signal has a magneto-optical component ratio of about 7% in the total amount of reflected light. If the S-polarized reflectance of is 30%, the signal component is 0.3 (beam splitter reflectance) × 0.07 = 0.0
However, since the signal component in media such as phase change (PC) is about 30%, the S-polarized reflectance is 15%.
It can be seen that a signal component of 0.15 × 0.3 = 0.045 can be obtained even if it is about the level, and a signal twice or more that of the magneto-optical medium can be obtained.

On the other hand, regarding the servo signal, assuming that the configuration of the detection system is the same, since the magneto-optical medium and the phase change medium have almost the same reflectance, the S-polarized reflectance is 30%.
In contrast, in the case of S-polarized reflectance of 15%, it is simply 1
/ 2. That is, although it is considered that the reflectance of the beam splitter directly becomes the light amount ratio of the detection system, this reduction of the servo signal does not affect the servo signal detection accuracy, and the light amount is sufficient to obtain the servo signal. Therefore, even if the beam shaping prism having the S-polarized reflectance of 15% is used, the function of the optical pickup is not hindered.

The beam shaping magnification is a value that should be determined by the FFP (far field pattern) of the laser diode 1, but is generally set between 1.5 times and 3.0 times. When the beam shaping prism as described above is used, the beam shaping surface can be used as an optical path separation surface, and the beam shaping can be performed by making it extremely adhering. As is clear from FIG. 2, the S-polarized reflectance increases as the beam shaping magnification increases, and the S-polarized reflectance of the prism material having a high refractive index is higher. When SF11 (refractive index n = 1.78) is used and the beam shaping magnification is set to 2 times, the forward (P-polarized) transmittance is 99% or more, and the backward (S-polarized) reflectance is 30% or more. be able to.

FIG. 3 is a diagram showing another embodiment of the optical pickup according to the present invention, in which the construction of the basic optical parts is the same as that of the optical pickup shown in FIG. The difference between the embodiment shown in the figure and the above embodiment is that the incident angle of the light beam emitted from the laser diode 1 and transmitted through the coupling lens 2 to the beam shaping prism 3b is set to the Brewster angle. So, because of that, beam shaping surface 3
The angle formed by the optical axis of the light beam incident on p and the optical axis of the light beam reflected by the beam shaping surface 3p is a right angle, and the light utilization efficiency of the outward path is 100%.

FIG. 4 is a diagram showing another embodiment of the present invention, in which the beam shaping prism 3c in this embodiment sets its beam shaping surface 3p at Brewster's angle, and
The difference from the above-described embodiment is that the prism 10 in which the beam shaping surface 3p and the exit surface of the light beam to the photodetection system 9 are parallel is used. By configuring the optical system in this way,
The optical axis of the light beam emitted from the beam shaping prism 3c and the optical axis of the light beam emitted to the photodetection system 9 via the prism 10 are perpendicular to each other, which facilitates the arrangement of the optical pickup.

Although the beam shaping prisms 3a to 3c and the λ / 4 plate 4 are independently arranged in the above-mentioned three embodiments, they are described, but as shown in FIGS. 5 (a) to 5 (c). In addition, the λ / 4 plate 4 may be integrated with the beam exit surfaces of the beam shaping prisms 3a to 3c on the medium side to form an optical system. In these cases, the configuration of the optical system can be further simplified. It is obvious that the miniaturization of the optical pickup device and the assembling property of the device are improved.

[0017]

Since the present invention is constructed and functions as described above, the shaped beam prism can also function as a beam splitter, and since it can be made emergency-attached, an optical pickup can be obtained. The configuration can be simplified and the cost can be reduced, and by setting the beam shaping surface to be in the vicinity of the Brewster angle, almost 100% of the light beam emitted from the laser diode can be used. Furthermore, since the optical axis of the light beam emitted from the beam shaping prism and the optical axis of the light beam incident on the photodetection system can be made orthogonal to each other, the arrangement of the optical pickup can be facilitated and the beam shaping prism and the λ / 4 plate can be arranged. By integrally configuring and, the configuration can be further simplified, and the device can be downsized and the assembling property can be improved.

[0018]

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an optical pickup according to the present invention.

FIG. 2 is a diagram showing P-polarized light transmittance, S-polarized light reflectance and beam shaping magnification of a prism according to the present invention.

FIG. 3 is a diagram showing another embodiment of the optical pickup according to the present invention.

FIG. 4 is a diagram showing another embodiment of the optical pickup according to the present invention.

5A, 5B and 5C are views showing another embodiment of the prism according to the present invention.

FIG. 6 is a diagram showing a basic configuration of a conventional magneto-optical disk pickup.

FIG. 7 is a diagram showing a general configuration of an optical pickup corresponding to a phase change in which media information is captured as a change in the amount of reflected light.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser diode, 2 ... Coupling lens, 3a-3c ... Beam shaping prism, 4
... λ / 4 plate, 5 ... Deflection prism, 6, 8 ...
..Objective lens, 7 ... Media, 9 ... Photodetection system, 10 ... Prism

Claims (5)

[Claims] 1. An optical pickup mounted on a drive for detecting the presence or absence of a recording pit on a medium as a change in the amount of reflected light, wherein a beam shaping prism and λ /
An optical pickup comprising four plates, wherein the beam shaping surface of the beam shaping prism also has a function of an optical path separating surface to a photodetection system, and the beam shaping surface is a non-deposited surface. 2. The optical pickup according to claim 1, wherein an incident angle of the beam on the beam shaping surface of the beam shaping prism is set in the vicinity of Brewster's angle. 3. The optical pickup according to claim 1, wherein an angle of incidence of the beam on the beam shaping surface of the beam shaping prism is a Brewster angle, and the beam shaping prism uses a parallel plate as a refraction angle. An optical pickup that is a prism with a shape cut at the same angle. 4. The optical pickup according to claim 1, wherein the beam shaping prism has a λ / 4 plate integrally formed on a beam exit surface of the medium side thereof. 5. An optical pickup mounted on a drive for detecting the presence or absence of a recording pit on a medium as a variation in the amount of reflected light, wherein a laser diode emitting at least P-polarized light and a light beam emitted from the laser diode are incident. A coupling lens, a beam shaping prism that circularizes the beam cross-sectional shape of the light beam emitted from the coupling lens, a λ / 4 plate that makes the light beam emitted from the beam shaping prism enter, and a light beam is irradiated onto the medium. In which the beam shaping surface of the beam shaping prism is a non-evaporated surface, and the beam shaping surface of the beam shaping prism is a non-deposited surface. An optical pick having the function of an optical path separating surface for reflecting the reflected light from the medium on the shaping surface. up.