JPS63269338A - Optical head - Google Patents

Abstract

PURPOSE:To facilitate the manufacture of a prism for beam arranging, by performing beam arrangement by refracting a beam of light with two planes making an angle of 90 deg. with each other without using a reflecting plane at the time of performing the beam arrangement by the prism. CONSTITUTION:A semiconductor laser 1 which outputs a laser beam, and a collimator lens 2 which changes divergent light radiated from the semiconductor laser 1 to a parallel ray are provided. The prism 3 for beam arranging applies the beam arrangement on a beam of light changed to the parallel ray, and also, is used also as a beam splitter which extracts detected light, and a first prism 31 having first and second planes making the angle of 90 deg. with each other and a second parallelogram prism 32 with a refractive index smaller than that of the first prism 31 are bonded on the prism 3. Also, a polarizing beam splitter plane P is formed on the adhesive plane of the first prism 31 and the second prism 32. The first prism 31 which performs the beam arrangement not only requires no reflecting plane, but, requires only a part having the angle of 90 deg. to refract the beam of light. In such a way, the manufacture of the prism can be performed easily.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention provides recording and recording of optical discs, etc. using a semiconductor laser.
The present invention relates to an optical head that performs reproduction and performs beam shaping on laser light.

[Technical Background of the Invention and Problems thereof] Conventionally, there is an optical head shown in FIG. 2 that uses a semiconductor laser to perform recording and reproduction on an optical disk.

In the figure, 11 is a semiconductor laser that outputs laser light;
12 is a collimator lens that converts the diverging light emitted from the semiconductor laser 11 into parallel light; 13 is a prism that shapes the beam of light that has been made into parallel light;
A polarizing beam splitter (PBS) surface P' is formed by the bonding surface between the right angle prism 13b and the right angle prism 13b.

14 is a quarter-wave plate; 15 is an objective lens that focuses the laser beam onto the disk D and also collects the reflected light from the disk D; and 16 is a detection light beam for performing focus servo using the astigmatism method. A condenser lens 17 focuses the reflected light, a cylindrical lens 17 causes astigmatism in the detection light, and a light receiving element 18.

The diverging light emitted from the semiconductor laser 11 is emitted in an elliptical cone shape as a characteristic of this semiconductor laser, so in order to effectively utilize the laser output especially in recording on an optical disk, the cross-sectional shape of the light beam is made circular. Beam shaping is performed to That is, the elliptical cone-shaped diverging light emitted from the semiconductor laser 11 is converted into parallel light with an elliptical cross section by the collimator lens 12, and this elliptical light beam is passed through the prism 1.
The beam is incident on the beam shaping section 13a of No.3. When the light beam incident on the beam shaping section 13a is refracted, the short axis direction of the ellipse is expanded and the beam is shaped into a light beam having a circular cross-sectional shape.The light beam is reflected by the reflecting surface P1' and irradiated in the direction of the disk D.

The beam-shaped parallel light passes through the PBS surface P' and the two-wavelength plate 14, is made into circularly polarized light by the quarter-wave plate 14, and is focused onto the disk D by the objective lens 15.

Incidentally, the reflected light from the disk D is condensed by the objective lens 15 and transmitted through the wavelength plate 14 as a parallel beam of light.
B 57] P', but when transmitting the above % wavelength vi4, the light flux that was first circularly polarized is linearly polarized and reflected by the PBS surface P'; The detected light extracted from the disc D is subjected to astigmatism by the condenser lens 16 and the cylindrical lens 17 as shown in the figure, for example, and is subjected to focus servo control based on the output according to the spot shape of the light receiving element 18. It is used for such things.

However, in the conventional optical head as described above, when performing beam shaping, the light beam is reflected and guided within the beam shaping section 13a, so when manufacturing such a prism, it is necessary to There was a problem in that a high degree of surface area was required.

[Purpose of the invention]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide an optical head that performs beam shaping without using a reflective surface.

[Summary of the invention]

The present invention refracts the output light of a semiconductor laser, which is made into parallel light by a collimator lens, by a first prism to shape the cross-sectional shape of the light beam, and directs this light beam through a 1/4 wavelength plate onto an optical disk using an objective lens. The reflected light from the optical disk, which is focused by the objective lens and transmitted through the two-wavelength plate, is reflected by a polarizing beam splitter formed by bonding a second prism to the first prism. An optical head adapted to extract
A first prism having two surfaces forming an angle of 90'' with each other, and bonded to the second surface of the prism to form a polarizing beam splitter and having a refractive index higher than that of the first prism. a large second prism, the parallel light from the collimator lens is incident on the first surface of the first prism and refracted, and the light beam refracted on the first surface is further refracted on the second surface. The cross-sectional shape of the light beam is shaped by refraction.

〔Example〕

FIG. 1 is a diagram showing an optical system of an optical head according to an embodiment of the present invention.

In the figure, l is a semiconductor laser that outputs laser light, and 2
is a collimator lens that converts the diverging light emitted from the semiconductor laser 1 into parallel light.

Reference numeral 3 denotes a shaping prism which performs beam shaping on the parallel light beam and also serves as a beam splitter for extracting the detection light. A first prism 31 having a second surface and a parallelogram-shaped second prism 32 having a smaller refractive index than the first prism 31 are bonded together.

Further, a polarizing beam splitter (PBS) surface P is formed at the bonding surface between the first prism 31 and the second prism 32.

4 is a 1/4 wavelength plate for causing the reflected light from the disk D to be reflected on the PBS surface P, and 5 is a quarter wavelength plate for converging the light beam onto the disk D and detecting the reflected light from the disk D. An objective lens that condenses light into parallel light.

6 is a condenser lens that converges the detection light in order to perform focus servo using the astigmatism method, 7 is a cylindrical lens for producing astigmatism, and 8 is a spot shape of the detection light with astigmatism. It is a light receiving element that outputs an output according to the
A focus error signal is obtained based on the output of this light receiving element 8.

The semiconductor laser 1 has an elliptical cone-shaped light cone in which the radiation angle in the direction parallel to the pn junction surface of the semiconductor element is the minimum and the radiation angle in the direction perpendicular to the pn junction surface is the maximum. Outputs laser light polarized in the direction perpendicular to the bonding surface.

The laser light emitted from this semiconductor laser 1 is made into parallel light by the collimator lens 2, but the cross section of the light beam has an elliptical shape with the major axis in the direction perpendicular to the plane of the paper in the figure. The first prism 3! When the ellipse enters the first surface P1 and is refracted, the short axis direction of the ellipse is expanded.

Then, the light beam with the short axis direction of this ellipse expanded is incident on the second surface, that is, the PBS surface P, and this PBS surface P
When the beam passes through the ellipse and enters the second prism 32, it is refracted in the opposite direction to that at the first surface P1, and the short axis direction of the ellipse is further expanded to form a beam.

The beam-shaped parallel light passes through the second prism 32 and is emitted, and the linearly polarized light that is polarized in a direction parallel to the plane of the drawing is circularly polarized by the 1/4 wavelength plate 4 and then polarized by the objective lens 5. It is focused on D.

The reflected light from the disk D is condensed by the objective lens 5, passes through the quarter-wave plate 4 as a parallel light beam, and enters the PBS surface P. The circularly polarized light beam becomes linearly polarized light in a direction perpendicular to the plane of the paper.

Therefore, the above luminous flux is reflected on the PBS surface P,
Further, the light is reflected by a surface formed parallel to PBS[P and enters the condenser lens 6. The light beam is focused by the condenser lens 6, and astigmatism is generated by the cylindrical lens 7, and is focused near the light-receiving surface of the light-receiving element 8. Focus servo is performed according to the output of the light-receiving element 8. .

As the first prism 31 and the second prism 32,
Each refractive index n1yn2 is n t =1.55
, using a material with nt = 1.76,
In order to cause the beam-shaped light flux to exit from the second prism 3□ at a right angle, the incident angle θ, which is incident on the first prism, may be set as follows: θ,1=i67@.

The beam shaping ratio at that time, that is, the beam width expansion rate β, is given by Given, 5in(θ1)=nt ・Sin(θ1')θ2=
90'-θ1' nl ・Sin (θ2)=n2 ・Sin (θ
2′), and β″=2.5 is obtained.

In this way, the first prism 31 that performs beam shaping not only does not require a reflective surface, but also only needs to have a portion with an angle of 90° for refracting the light beam, making the prism easy to manufacture.

〔Effect of the invention〕

As explained above, according to the present invention, beam shaping by a prism is performed by refraction by two surfaces forming an angle of 90'' with each other without using a reflective surface. An optical head that is easy to manufacture can be realized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical system according to an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional optical head. 3... Prism for shaping. Patent applicant: Pioneer Corporation Figure 2

Claims (1)

[Claims] The output light of the semiconductor laser, which has been made into parallel light by a collimator lens, is refracted by a first prism to shape the cross-sectional shape of the light flux, and this light flux is passed through a 1/4 wavelength plate to an objective lens. A polarizing beam splitter formed by bonding a second prism to the first prism to focus the reflected light from the optical disk on the optical disk, which is focused by the objective lens and transmitted through the quarter-wave plate. The optical head is configured to extract light by reflecting the light at a surface of the prism, and includes a first prism having two surfaces, a first and a second surface forming an angle of 90 degrees to each other, and a first prism attached to the second surface of the prism. a second prism forming a polarizing beam splitter and having a larger refractive index than the first prism, the parallel light from the collimator lens is incident on the first surface of the first prism and refracted; An optical head characterized in that a light beam refracted by one surface is further refracted by a second surface to shape the cross-sectional shape of the light beam.