JPH0264928A - Optical head - Google Patents

Abstract

PURPOSE:To prevent an unnecessary optical beam from feeding back to a light source or a detecting optical system by obtaining an oblique angle which is enough to shape an incident beam from an anisotropic beam to an isotropic beam in an incident optical axis to an incident surface, providing a third outgoing surface with extending the incident surface and fetching a reflected light from a dividing reflection surface to the external part of a beam splitter. CONSTITUTION:For an incident angle alpha of an incident light on the incident surface of a beam splitter 3 which has beam shaping operation, the light refractive index of the beam slitter 3 is selected near a Brewster angle so that the reflection loss of the incident beam can be reduced. Since a condition for the incident angle alpha to be the Brewster angle is alpha=tan<-1>n, such a condition is achieved by using the material of the light refractive index with which the condition of m n can be obtained for beam shaping magnification (m) and optical diffraction factor (n) of the beam splitter 3. Since the same effect as this operation can be obtained even to the optical beam from the third outgoing surface provided by extending the incident angle, the reflection loss is eliminated on the outgoing surface and almost all the optical beams can be taken out to the external part of the beam splitter 3. Thus, a stray light can be extremely lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an optical head for optically recording and reproducing information, and particularly to an optical head having a beam splitter.

(Prior Art) A semiconductor laser is used as a light source for the purpose of downsizing an optical head in an optical information recording/reproducing device. However, the output of semiconductor lasers is low, and the far-field pattern of the emitted beam is usually an anisotropic one, which is an ellipse. In order to focus the light as an isotropic microspot on the surface, it is necessary to shape the emitted light from the semiconductor laser into an isotropic beam. Stray light was a problem. As a means to solve this problem, it has been proposed to use a composite beam splitter. (Refer to Japanese Unexamined Patent Publication No. 59-188852.) The structure of this optical head is shown in FIG. The beam splitter used in this system is a polarizing beam splitter (TP=
100%, R8=100%), in FIG.
An anisotropic light beam 11 emitted radially from a semiconductor laser 1 is converted into a parallel light beam 1 by a collimating lens 2.
2, the incident surface 17 of the polarizing beam splitter 17
a, the light beam 13 is shaped into a vertically and horizontally isotropic light beam 13, which is reflected by the reflective surface L7b inside the polarizing beam splitter 17 to form the incident light beam 12.
The light beam becomes perpendicular to the optical axis of the light beam and passes through the polarization plane 17c.

The first outgoing light 14 is emitted vertically from the first outgoing surface 17d.

The first emitted light 14 passes through the quarter wavelength plate 18, is focused by the objective lens 4, and is irradiated onto the disk 5. The reflected light from the disk 5 passes through the objective lens 4 and the quarter-wave plate 18 again, enters the first exit surface 17d of the polarization beam splitter 17 perpendicularly, is reflected by the polarization surface 17c, and enters the second exit surface 17e. The light is emitted horizontally as second emitted light 15. The second emitted light 15 becomes a focused light beam by the condensing lens 7, passes through the cylindrical lens 19, and then is irradiated onto the photodetector 20.

FIG. 5 is a plan view of only the polarizing beam splitter 17 in FIG. 4 viewed from the direction of the arrow. parallel light beam 12
is P with respect to the incident surface 17a of the polarizing beam splitter 17.
Enter as polarized light. Therefore, although the reflection loss at the incident surface 17a is small, it is necessary to provide a reflective film on the reflective surface 17b. Furthermore, all of the light beam 13 is transmitted through the polarization plane 17c and becomes the first emitted light 14. The first emitted light 14 is 4
Since it passes through the 1/1 wavelength plate 18 on the outward and return trips,
The polarized light is converted into S-polarized light and returned to the polarization beam splitter 17. Therefore, all of the light reflected by the disk 5 is reflected from the polarizing surface 17c and is emitted as second emitted light 15 from the second emitting surface 17e.

A composite beam splitter with such a configuration is effective against stray light when it is a polarizing beam splitter, but when the information recording medium is a magneto-optical recording film, it is effective against stray light that is incident on the magneto-optical recording film. In order to detect the rotation of the polarization plane of the light beam and reproduce information, the beam splitter becomes a splitting reflective surface that splits the light beam for the P-polarized incident light, and the reflective surface 1
A large amount of reflected light occurs at beam splitter surface 17f at 7c.
Since the reflected light enters the detection optical system and significantly deteriorates the detection characteristics, it has been impossible to use the polarizing beam splitter in its conventional shape as a normal beam splitter.

(Problems to be Solved by the Invention) As described above, if a conventionally shaped polarizing beam splitter is used as a normal beam splitter, the detection characteristics will be significantly deteriorated.

Therefore, the present invention aims to solve the unnecessary light beam with extremely high intensity that is generated when a conventional composite polarizing beam splitter is used as a beam splitter with the same shape.
It is an object of the present invention to provide an optical head having a beam splitter with a novel shape that can prevent stray light from being guided to the outside of the beam splitter and returning to a light source or a detection optical system.

[Structure of the invention]

(Means for Solving the Problems) The present invention has an entrance surface, first and second exit surfaces, and
It has a dividing reflection surface that splits the light beam inside, and a total reflection surface that guides the incident light beam to the division reflection surface, and the incident optical axis with respect to the input surface changes the incident beam from an anisotropic beam to an isotropic beam. an optical head having a beam splitter having an oblique angle sufficient to shape the beam into a normal beam, and having a configuration in which an incident surface is extended to provide a third exit surface and the reflected light from the one-divided reflecting surface is extracted to the outside of the beam splitter. It provides:

(Function) The optical refractive index of the beam splitter is selected to be near the Brewster angle so that the incident angle α of the incident light on the incident surface of the beam splitter that has a beam shaping effect is such that the reflection loss of the incident beam is small. Since the condition for the incident angle α to be the Brewster's angle is α=tan-''n, this can be achieved by using a material with an optical refractive index such that the beam shaping magnification m and the optical refractive index n of the beam splitter are man.

The same effect as described above can be obtained for the light beam from the third exit surface provided by extending the entrance surface, so the reflection loss at the exit surface is reduced and almost all of the light beam is sent to the beam splitter. It can be taken out to the outside and stray light can be significantly reduced.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an optical head using a beam splitter as an embodiment of the present invention. In FIG. 1, a light beam 11 radially emitted from a semiconductor laser 1 is converted into parallel light by a collimating lens 2. The light beam 12 with an anisotropic intensity distribution, which has been turned into parallel light by the collimating lens 2, is obliquely incident on the incident surface 3a of the beam splitter 3, and is transformed into a light beam 1 having isotropy in the vertical and horizontal directions.
3, is totally reflected by the reflecting surface 3b of the beam splitter 3, and enters the dividing reflecting surface 3c. The divided reflective surface 3c is.

Intensity transmittance (Tp) is 70% for P-polarized incident light,
The intensity reflectance (Rs) is 100 for S-polarized incident light.
A reflective film with characteristics of % is deposited. The light beam 13 is incident on the split reflecting surface 3c as P polarized light, and has a polarization of 70
% of the light is emitted as the first emitted light 14 from the first emitting surface 3d.

The first emitted light 14 is focused by the objective lens 4 and irradiated onto the disk 5 . The disk 5 is a rewritable disk provided with a magneto-optical recording medium. In order to record and erase information, it is necessary to apply a bias magnetic field to a position facing the objective lens 4 across the disk 5, but this is not shown since it is generally known.

The reflected light from the disk 5 passes through the objective lens 4 again, enters the first exit surface 3d of the beam splitter 3, is reflected by the split reflection surface 3c, and is reflected from the second exit surface 3e to the second exit surface 3d.
It is emitted as emitted light 15. The plane of polarization of the second emitted light 15 is rotated by 45 degrees by a half-wave plate 6, and then split into two beams by a polarizing beam splitter 8, which are irradiated onto each of the photodetectors 9 and 10 for recording. Information is reproduced and focus errors and tracking errors are detected.

On the other hand, a part of the light beam 13 is reflected by the split reflecting surface 3c, and a third exit surface 3f (incidence surface 3
a and the third output surface 3f are the same surface), the output light 1
6 and enters the photodetector 21.

The output of the photodetector 21 is converted by a current-voltage converter 22 into a voltage value proportional to the intensity of light incident on the photodetector 21. The output of the current-voltage converter 22 is compared with a reference voltage corresponding to the reference light intensity and is sent to the drive device 23 via the amplifier 23.
is controlled so that the intensity of the light emitted from the semiconductor laser 1 becomes the reference intensity.

FIG. 2 is a plan view of only the beam splitter in FIG. 1, viewed from the direction of the arrow. If the optical refractive index of the beam splitter 3 at the wavelength of the semiconductor laser 1 is n, and the shaping magnification in a plane parallel to the paper for correcting the anisotropy of the light beam 12 is m, then the illustrated angle θ at the beam splitter is .

α and β are expressed by the following equations.

The incident angle α of the light beam 12 on the incident surface 3a is determined by the Brewster angle (α=tan
-1n) is used nearby, that is, a material in which the shaping magnification m and the optical refractive index n of the beam splitter 3 are approximately equal is used, so
The output light 16 from the third output surface 3f can also reduce reflection loss and stray light can be significantly reduced.

In addition, in the above configuration, the divided reflective surface 3c and the reflective surface 3
b are mutually orthogonal surfaces, and the prism formed by the divided reflective surface 3c, the first output surface 3d, and the second output surface 3e is an isosceles right-angled prism with the divided reflective surface 3c as the hypotenuse.

Under this configuration, the light beam 1 incident on the reflecting surface 3b
3 satisfies the total reflection condition, so there is no need to provide a reflective film on the reflective surface 3b, and the light 16 emitted from the third output surface 3f, which is provided by extending the incident surface 3a, and the incident light 12 do not interact with each other. The optical axes can be parallel, and the semiconductor laser 1. Collimator lens 2 and photodetector 21 can be efficiently arranged.

Furthermore, the present invention is not limited to the beam splitter shown in FIG. 2; for example, as shown in FIG. A method may also be adopted in which the output light 16 is configured to have an angle and is guided to the photodetector 21.

In this case, the size including the photodetector 21 can be reduced somewhat.

As explained above, in an optical head using an element that integrates a conventional prism for shaping an anisotropic light beam and a polarizing beam splitter to create a new polarizing beam splitter, In order to use the polarizing beam splitter as an optical head, the light beam incident from the light source is split and reflected by changing the polarizing beam splitter to a normal beam splitter, that is, the reflecting surface that separates the beams from the polarizing reflecting surface to the splitting reflecting surface. However, in the optical head using the beam splitter according to the present invention, the split reflecting surface Since the reflected light from the beam splitter is guided to the outside of the beam splitter, it is prevented from returning to the detection optical system or the light source as stray light. In addition, since the reflective surface provided to guide the light beam shaped by the incident surface of the beam splitter to the split reflective surface satisfies the conditions for total reflection, there is no need to provide a reflective film, so the beam splitter can be used at a lower cost. Can be provided.

Furthermore, there is also the effect that the intensity of the light beam guided outside the beam splitter can be monitored and the light output of the light source can be controlled.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an optical head that guides unnecessary light beams to the outside of the beam splitter so that they do not become stray light and does not return to the light source or the detection optical system.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an optical head according to an embodiment of the present invention, FIG. 2 is a plan view of the beam splitter (an embodiment of the present invention) in FIG. 1, viewed from the direction of the arrow, and FIG. FIG. 4 is a plan view showing a beam splitter according to another embodiment of the present invention, FIG. 4 is a perspective view showing a conventional example of an optical head, and FIG. 5 shows the polarizing beam splitter 17 (conventional example) in FIG. This is a plan view. 1... Semiconductor laser 2... Collimator lens 3
...Beam splitter 4...Objective lens 5...
・Disk 6...1/2 wavelength plate 7...Condensing lens 8...Polarizing beam splitter 9.10.21
...Photodetector agent Patent attorney Nori Ken Chika Yudo Mitsuyuki Matsuyama Figure 1 Figure 2 θ Figure Figure Figure Figure

Claims (1)

[Claims] The light emitted from the light source is made into parallel light, the parallel light is guided to the objective lens by a beam splitter, and is converged and irradiated onto the recording surface of the recording medium, and the reflected light from the recording medium of the irradiated light is reflected by the beam splitter. In the optical head that leads to the detection optical system, the beam splitter has an entrance surface into which the parallel light enters, first and second exit surfaces, a split reflection surface that splits the light beam into the interior, and It is equipped with a total reflection surface for guiding the beam to the split reflection surface and a third exit surface extending from the entrance surface, and the incident optical axis with respect to the entrance surface changes the incident beam from an anisotropic beam to an isotropic beam. An optical head characterized by having an oblique angle for shaping a beam.