JPH0534735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical head in an optical information recording and reading device.
When a semiconductor laser or the like is used as a light source, the light intensity distribution in a plane perpendicular to the optical axis of the generated light beam tends to be elliptical, so polarized light can also serve as an optical means to shape this into a perfect circle. This invention relates to an optical head using a beam splitter.

[Prior art]

In optical heads for optically recording or reproducing information on optical information carriers (hereinafter referred to as disks), gas lasers such as helium-neon lasers and argon lasers have traditionally been used as light sources, but in recent years small-sized lasers have been used. Semiconductor lasers that can be directly modulated have come into use. As is well known, semiconductor lasers generally have an optical output of 15
~25mW, smaller than conventional gas lasers,
Further, the light beam is usually anisotropic in that the far-field pattern is elliptical (in other words, the cross-sectional pattern of the emitted beam from the semiconductor laser is not a perfect circle but an ellipse).

Therefore, in an optical head using a semiconductor laser as a laser light source, it is necessary to improve the light utilization efficiency of the optical system from the laser light source to the objective lens. Furthermore, in order to record information at high density on a disk, the light beam incident on the objective lens is made into an isotropic light beam (the beam is cut in the direction perpendicular to its emission direction) with equal aspect ratios. It is also necessary to shape the light beam so that its cross-sectional shape is a perfect circle.

Conventionally, in optical heads using semiconductor lasers, in order to improve light utilization efficiency, the light beam emitted from the semiconductor laser is converted into a parallel light beam by a collimating lens with a large numerical aperture, and the collimating lens and objective lens are It is customary to provide a correction means in the optical path for converting an anisotropic light beam into an isotropic light beam.
For this reason, optical heads as shown in FIGS. 1 and 2 have conventionally been used.

FIG. 1 is a perspective view of an optical head using a shaping prism as a light beam correction means. In FIG. 1, an anisotropic light beam 11 emitted radially from a semiconductor laser 1 is converted into a parallel light beam 12 by a collimating lens 2, and an incident light beam 13 that is isotropic in the vertical and horizontal directions is converted into a parallel light beam 12 by a shaping prism 3. formatted into.

The incident light 13 enters the incident surface 4a of the polarizing beam splitter 4, passes through the polarizing surface 4b, and then exits as the first output light 14 from the first output surface 4c. The first emitted light 14 passes through the quarter wavelength plate 5, is focused by the objective lens 6, and is irradiated onto the disk. The reflected light from the disk 7 passes through the objective lens 6 and quarter-wave plate 5 again, enters the first output surface 4c of the polarizing beam splitter 4, and enters the polarizing surface 4b.
The light is reflected by the light beam and exits as second outgoing light 15 from the second outgoing surface 4d. The second emitted light 15 is focused by the condenser lens 8 and passes through the cylindrical lens 9, and then is irradiated onto the detection element 10.

In the above configuration, although the first output light 14 and the second output light 15 are perpendicular to each other, the light beam 12 incident on the shaping prism 3 is
In order to intersect obliquely with the second emitted light 15, it is necessary to arrange the semiconductor laser 1 and the collimating lens 2 obliquely with respect to the other optical components shown in FIG. Therefore, there is a drawback that it is difficult to assemble each optical component with high precision.

Furthermore, although most of the incident light 13 that enters the incident surface 4a of the polarizing beam splitter 4 passes through the polarizing surface 4b and exits from the first exit surface 4c,
Since the light beam 11 emitted from the semiconductor laser 1 is not completely linearly polarized, a portion of the incident light 13 is reflected at the polarization plane 4b, further reflected at the plane 4e, and then reflected again at the polarization plane 4b. By the way,
The light is emitted from the incident surface 4a, traces the same optical axis as the incident light 13 in the opposite direction, and returns to the semiconductor laser 1. The fact that the emitted light from the laser returns to the laser again has a disadvantage, especially in semiconductor lasers, in that noise is generated in the laser light.

FIG. 2 is a plan view of a conventional optical head in which two cylindrical lenses are used as light beam shaping means instead of the shaping prism in FIG. 1. Note that optical components not shown are the same as those shown in FIG. 1.

In FIG. 2, an anisotropic light beam 11 radially emitted from a semiconductor laser 1 is converted into a parallel light beam 12 by a collimating lens 2.
The cylindrical lenses 20 and 21 shape the incident light 13 to be isotropic in the vertical and horizontal directions. The incident light 13 enters the incident surface 4a of the polarizing beam splitter 4, passes through the polarizing surface 4b, and then exits from the first output surface 4c. The reflected light from the disk that returns along the same optical axis as the first output light 14 enters the first output surface 4c of the polarization beam splitter 4 again, and the polarization surface 4b
The light is reflected by the light beam and exits as second outgoing light 15 from the second outgoing surface 4d. In the configuration shown in Figure 2,
Since the optical axis of the light beam 12 and the optical axis of the incident light 13 coincide, there is no need to arrange the semiconductor laser 1 and the collimating lens 2 obliquely with respect to other optical components constituting the optical head. However, as the number of parts increases, the amount of light decreases due to the increase in the number of boundary surfaces, and the generation of stray light increases. Furthermore, in order to accurately match the optical axes of the collimating lens 2 and the cylindrical lenses 20 and 21 and to accurately arrange their mutual positions, there is a drawback that assembly and adjustment become complicated.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the prior art described above, to correct the anisotropy of semiconductor laser light, and to adjust the optical axis of incidence to a polarizing beam splitter.
An optical system in which one of the two output optical axes orthogonal to each other is parallel to each other, stray light caused by reflected light from the polarization plane of the polarizing beam splitter does not return to the semiconductor laser, and the number of parts is small. The aim is to provide a head.

[Summary of the invention]

In order to achieve the above object, the optical head according to the present invention has a polarizing beam splitter including an incident surface, first and second exit surfaces, a polarizing surface therein, and an incident surface on the incident surface. and a reflective surface that guides the light beam to the polarization plane, and the first and second
The first and second light beams are emitted from each of the exit surfaces, the exit optical axes of which are orthogonal to each other, and the optical axes of incidence on the entrance surface are aligned with the first and second exit optical axes. The incident optical axis and the first output optical axis are located in the same plane, and the incident optical axis and the first output optical axis are perpendicular to each other. A polarizing beam splitter that has an angle sufficient to shape the beam into a polarizing beam, and in addition to the above-mentioned incident surface, reflective surface, polarization surface, first exit surface, and second exit surface, there is a A polarizing beam splitter is provided with a surface parallel to the surface and a surface perpendicular to the polarizing beam splitter, and in which the first output surface and the first output optical axis and the second output surface and the second output optical axis are oblique to each other. Using.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to embodiments shown in the drawings. FIG. 3 is a perspective view showing an embodiment of the optical head according to the present invention.

In FIG. 3, an anisotropic light beam 11 emitted radially from a semiconductor laser 1 is converted by a collimating lens 2 into an incident light beam 12 which is a parallel light beam.
By being obliquely incident on the beam a, it is shaped into a light beam 13 that is isotropic in the vertical and horizontal directions, and is reflected by the reflective surface 30b inside the polarizing beam splitter 30 to be perpendicular to the optical axis of the incident light beam 12. It becomes a light beam 16, passes through the polarization plane 30c, and is emitted from the first output surface 30d as the first output light 14 through the output surface 30.
It emits obliquely to d.

The first outgoing beam 14 passes through a quarter-wave plate 5,
The light is focused by the objective lens 6 and irradiated onto the disk 7 . The reflected light from the disk 7 passes through the objective lens 6 and quarter-wave plate 5 again, obliquely enters the first output surface 30d of the polarized beam syslitter 30, is reflected by the polarized surface 30c, and is reflected by the second polarized beam syslister 30. The second output light 15 that is orthogonal to the first output light 14 is output from the output surface 30e while intersecting the second output light 14. The second outgoing beam 15 becomes a convergent light beam 16 by the condensing lens 8, and after passing through the cylindrical lens 9, it is irradiated onto the detection element 10.

4 is a plan view of only the polarizing beam splitter 30 in FIG. 3 viewed from the direction of arrow A in FIG. 3. FIG.

In the configuration shown in FIG. 4, the optical refractive index of the polarizing beam splitter 30 at the wavelength of the semiconductor laser is n.
The magnification factor of the light beam 12 in the plane parallel to the paper surface for correcting the anisotropy of the light beam is m
Then, the illustrated angle θ ₁ in the splitter 30 is expressed by the following equation (1), and the angle θ ₂ is also expressed by the equation (2).

θ ₁ = ₁ + 45° ... (1) θ ₁ = ( ₂ - ₁ ) / 2 + 90° ... (2) However ₂ = sin ^-1 (sin ( ₁ )/n) ... (4) In the above configuration, the angle θ ₃ ≠ θ ₄ and the incident angle of the incident light 12 with respect to the incident surface 30a are ₁ , and the incident light It is assumed that the beam 12 has a cross-sectional shape that is longer in the direction perpendicular to the plane of the paper than in the direction parallel to the plane of the paper.

For example, if the refractive index of the prism is n = 1.51 and the magnification m = 2.40, then if we set θ ₁ = 116.05° and θ ₂ = 73.87°, the light beam 12 will have an anisotropy of 1:2.40 vertically: horizontally. The optical axis of incidence on the polarizing beam splitter 30 and the output optical axis 15, which is one of the two output optical axes 14 and 15 that are perpendicular to each other, are parallel to each other, and the optical beam 13 is isotropic. Obtainable.

In the polarizing beam splitter 30 configured as described above, a portion of the light beam 16 is
Although reflected at point c, the reflected light does not return to the semiconductor laser 1 because it enters the incident surface 30a at a different angle from the light beam 13.

Further, since the parallel light beam 12 and the output light beam 15 are parallel to the disk 7, it is possible to construct a thin optical head. Moreover, the number of interfaces through which the light beam passes or is reflected is one less than the equivalent functional parts of the conventional optical head shown in FIG. 1, and three fewer than the conventional optical head shown in FIG.
Since the number of lights is reduced, the problem of stray light is also alleviated, and by applying a reflective coating to the reflective surface 30b, the light utilization efficiency is also improved.

Note that in FIG. 4, the first output light 14 and the first output surface 30d do not intersect at right angles, and similarly the second output light 14 and the first output surface 30d do not intersect at right angles.
It will be recognized that the values of the angles θ ₁ , θ ₂ , θ 3 , and θ ₄ are determined such that the angles θ 1 , θ 2 , θ ₃ , and θ 4 are not orthogonal to each other.

With the above configuration, even if there is light reflected by the first output surface 30d of the light beam 16, the reflected light will not trace the same optical axis as the light beam 16 in the opposite direction. Moreover, the above matters also apply to the second exit surface 30e.

〔Effect of the invention〕

As explained above, in conventional optical heads, the reflected light from the polarization plane of the polarization beam splitter returns to the semiconductor laser, generating noise, and a prism is used to correct the anisotropic light beam. If the light beam is corrected with two cylindrical lenses, the incident optical axis and the output optical axis will intersect obliquely, making it difficult to assemble optical components with high precision. Although the optical heads are perpendicular or parallel, the number of optical components increases and higher precision is required for assembling each optical component.However, in the optical head according to the present invention, anisotropic A new polarizing beam splitter is created by integrating a prism for correcting a light beam and a polarizing beam splitter, and a reflecting surface is used to guide the light beam corrected by the prism part to the splitter part (Fig. 4, 30b). At the same time, by appropriately obliquely intersecting the incident optical axis and the incident plane, one of the two output optical axes orthogonal to the incident optical axis is perpendicular to the other, and the other is parallel to the incident optical axis. Since the reflected light does not return to the semiconductor laser, the above-described drawbacks of the prior art can be solved. Furthermore, by integrating the correction prism and the splitter, the number of interfaces through which the light beam passes is reduced, improving light utilization efficiency.
Another advantage is that the optical head portion can be made thinner.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a conventional example of an optical head, FIG. 2 is an explanatory view showing another conventional example, FIG. 3 is a perspective view showing an embodiment of an optical head according to the present invention, and FIG. 4 is a plan view of the polarizing beam splitter 30 in FIG. 3 viewed from the direction of arrow A. FIG. Description of symbols, 1...Semiconductor laser, 2...Collimating lens, 5...1/4 wavelength plate, 6...Objective lens, 7...Disc, 8...Condensing lens, 9...
Cylindrical lens, 10...detection element, 30...polarized beam splitter.

Claims (1)

[Scope of Claims] 1. A semiconductor laser light source, an objective lens for condensing laser light emitted from the semiconductor laser onto an optical information carrier, and an optical path for guiding light reflected from the optical information carrier from the semiconductor laser to the objective lens. an optical head comprising at least a polarizing beam splitter for separating the reflected light from the polarizing beam splitter; and a detection means for detecting the reflected light separated by the polarizing beam splitter; Each of the second exit surfaces has a polarizing surface therein, and a reflecting surface that guides the light beam incident on the incident surface to the polarizing surface, and the second exit surface has a polarizing surface therein, and a reflecting surface that guides the light beam incident on the incident surface to the polarizing surface. First and second light beams are emitted from each of the first and second exit surfaces, and their exit optical axes are orthogonal to each other, and the incident optical axes of the first and second light beams on the input surface are aligned with each other. The output optical axis is located in the same plane, and the input optical axis and the first
a polarizing beam splitter, which is orthogonal to the output optical axis of the input optical axis, and has an oblique angle of the input optical axis with respect to the incident surface sufficient to reshape the input optical beam from an anisotropic beam to an isotropic beam; In addition to the above-mentioned incident surface, reflective surface, polarization surface, first exit surface, and second exit surface, it is provided with a surface parallel to the incident optical axis and a surface perpendicular to the incident optical axis, and also has the above-mentioned surfaces. An optical head characterized in that it uses a polarizing beam splitter in which a first output surface and a first output optical axis and a second output surface and a second output optical axis are oblique to each other.