JPS60106038A - Optical device - Google Patents

Abstract

PURPOSE:To produce with high using efficiency a light beam given from a semiconductor laser element having no isotropic expansion angle, by using plural prisms arranged so that the incident angle of an incident light beam is set as a Brewster's angle and also the light beam is radiated vertically. CONSTITUTION:An optical device is set at the following stage of a cemented lens 2, and prisms 7 and 8 are set at Brewster's angles respectively to set the optical loss at zero on the incident surface of the prism. Both prisms expand the horizontal direction of the spread of the beam sent from a semiconductor laser element to obtain the coincidence with the vertical direction and obtains an isotropic intensity distribution for the light delivered from the prisms. These isotropic light beams are turned into isotropic spots 5 on a disk 4 by an objective 3. Thus most of the beams sent from the laser element are irradiated onto the disk. In addition, the pull-in range of automatic focus is increased since the numerical aperture of the lens 2 is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical device, and particularly to an optical device for beam shaping of a semiconductor laser.

[Background of the invention]

In recent years, development of optical information processing devices that use semiconductor laser elements as light sources in place of gas lasers has become active. Optical discs are one example. An optical disk is a device that uses a semiconductor laser element to reproduce information signals recorded on a disk (disk) or to record information on the disk at high density. That is, in order to record or reproduce information signals on a disk using a semiconductor laser, a light beam emitted from a semiconductor laser element is directed onto a disk with a diameter of 1 μm using a coupling lens and an objective lens that constitute an optical system.
It must be formed as a very small light spot.

In general, a semiconductor laser device has an anisotropic beam spread angle because its light emitting region has a different aspect ratio. The divergence angle of this semiconductor laser beam differs depending on the structure of the semiconductor laser element. That is, as shown in FIG. 1, the angles e4 in the horizontal and vertical directions of the output light distribution in the far-field image of the beam from the semiconductor laser device are each 0□.

For example, for a c, sp type semiconductor laser, θ=8', θ□=24', and θ□/θ1=3...
(1) becomes. In addition, in the BH type semiconductor laser, θ,, =16
' , θ, = 32' and θJ/θ7 = 2 (2), and in the BH type laser, the beam divergence angle ratio is 2,
It is 3 for asp type. Note that the horizontal axis in FIG. 1 is the spread angle, and the vertical axis is the light intensity. FIG. 2 shows an example of a conventional optical information processing apparatus for forming an isotropic spot with a diameter of about 1 μmφ on a disk when the beam divergence angle of the semiconductor laser device described above is not isotropic.

In FIG. 2, a beam with a non-isotropic divergence angle emitted from one end face of the semiconductor laser device 1 is transmitted to the coupling lens 2.
, a light spot 5 is formed on the disk 4 by the objective lens 3. The photodetector 6 is a detector for the output of the semiconductor laser element 1. Note that A is the optical axis. In FIG. 2, the numerical aperture NA of the coupling lens 2 has the relationship NA=sinθ−(3), where θ is the half angle of view formed by the semiconductor laser 1 and the lens 2. Regarding the beam divergence angle of the semiconductor laser device 1, as described above, e
If the sizes at -z are θ□ and 0□, in order to form an isotropic spot 5 on the disk 4 using such a semiconductor laser element, 0≦θ7〈θ1...(4 ) The numerical aperture NA of the coupling lens 2 must be selected so that In other words, by reducing the numerical aperture of the coupling lens 2, blocking off-axis rays, and using only the beam near the optical axis A<0=0>, the intensity distribution of the light emitted from the coupling lens 2 is made isotropic. It is necessary to make it a target. From the beam spread angle shown in Figure 1 and equations (1), (3), and (4), for a CSP laser, NA = 0.1 θ = 5.7° ( θ 7 θ □ ) ・・- (5), the beam after passing through the coupling lens 2 becomes almost isotropic, and therefore an isotropic spot 5 is formed on the disk 4.
is formed.

However, when such off-axis light rays are blocked, only a portion of the light rays emitted from the semiconductor laser is irradiated onto the disk, resulting in poor utilization efficiency of the light from the laser element. In particular, in the case of recording, the metal thin film provided on the disk must be melted to form holes, which requires several times the amount of light than in the case of reproduction.

Also.

When a semiconductor laser element emits a certain amount of light beyond a certain level, its lifetime becomes short. Therefore, when using a semiconductor laser element as a light source, it is absolutely necessary to increase the light utilization efficiency of the laser element and to suppress the optical output as much as possible from the viewpoint of lifespan and reliability.

Now, in the configuration shown in FIG.
When the reflected light from the disk 4 returns, the output of the semiconductor laser 1 increases or decreases depending on the strength of the reflected light from the disk, so that the information on the disk 4 can be reproduced by the output of the photodetector 6. This technique is described in Japanese Patent Application Laid-Open No. 49-69008. Normally, the disk rotates with a vertical vibration of about 1 inch, and the depth of focus of the objective lens is 2 μm.
Therefore, in order to reproduce signals from the disc, focusing is required to keep the optical spot on the disc at a diameter of about 1 μm at all times.

In order to detect the deviation of the focus of the light beam from the disk, Japanese Patent Application Laid-Open No. 53-17706 discloses a technique for detecting the deviation of the focus by slightly vibrating the light source or lens in the optical axis direction and synchronously detecting the laser output. It is proposed in the official gazette. The automatic focus control retraction range with this technique is narrow, approximately 10
μm (Electronic Materials 197
(No. 2, 1999, p. 67).

Figure 3 shows when the numerical aperture of the coupling lens 2 is NA=0.1.
It shows the change in the output from the semiconductor laser element 1 when the disk 4 is slightly moved along the optical axis direction.

As is clear from FIG. 3, when the numerical aperture NA of the coupling lens 2 is as small as 0.1, the automatic focusing range is only 10 μm. An optical information processing device that returns reflected light from a disk to a semiconductor laser element has the drawback of having a small pull-in range, as described above. Therefore, automatic focus control is difficult, and information cannot be reproduced from a disc with large vertical vibration.

[Purpose of the invention]

The present invention solves the above-mentioned problems and provides a semiconductor beam shaping optical device capable of shaping a light beam from a semiconductor laser element that does not have an isotropic divergence angle with high light utilization efficiency. purpose.

[Summary of the invention]

The present invention provides a light source in which the intensity distribution of the output light beam around the optical axis is anisotropic with respect to the optical axis; a plurality of prisms having end faces, the entrance end faces of the prisms are arranged so as to form a Brewster angle with respect to the incident light beam, and the exit end faces of the prisms are arranged perpendicular to the output light beam. It is characterized by being arranged.

[Embodiments of the invention]

As mentioned above, in order to form an isotropic spot 5 on the disk 4 using the semiconductor laser element 1 having an anisotropic divergence angle, the numerical aperture of the coupling lens 2 is set to (4) and (5).
) must be reduced as shown in the formula. However, in this case, only a portion of the light emitted from the semiconductor laser element is irradiated onto the disk, resulting in poor utilization efficiency of the light from the laser element. Moreover, the focal position of the reflected return light spot near the end face of the laser element changes greatly due to the displacement of the disk. That is, the reflected return light spot on the end face of the laser element is significantly blurred due to the focal shift, and as a result, the automatic focusing range becomes as small as 10 μm.

The inventors ignored equation (4), which is the condition of the coupling lens that the light spot 5 on the disk 4 is isotropic, and
The focusing range was experimentally determined when the numerical apertures N and A of the coupling lens 2 were increased. Figure 4 shows the numerical aperture N
The figure shows changes in the output from the semiconductor laser element when the disk 4 is slightly moved along the optical axis direction for several types of coupling lenses with different A (sin O).

As is clear from Fig. 4, the larger the numerical aperture of the coupled lens, the larger the automatic focusing range.
This means that complete automatic focusing can be achieved against vertical movement of the disc. Moreover, as the numerical aperture of the coupling lens increases, more beams from the semiconductor laser element are incident on the coupling lens, increasing the light utilization efficiency. However, if the numerical aperture NA of the coupling lens approximately satisfies the vertical spread angle θ in e-z of the far-field pattern shown in FIG. It will be injected into. Therefore, in effect,
It is sufficient to satisfy θ1<0≦O□ (6).

However, since the light beam passing through the coupling lens 2 that satisfies Equation (6) is not isotropic, the light spot 5 is also not isotropic. In the present invention, in order to solve this problem, as shown in FIG. 5, prisms 7 and 8 are arranged after the coupling lens 2 that satisfies equation (6). FIG. 5 is a diagram showing an example of an optical information processing device using the optical device of the present invention.

In Fig. 5, the prism 7.8 has its apex angle θ,
Assuming that the rectangular prism has a refractive index of N, the incident angle is θ8, and the ratio of the weight of the incident beam to the diameter of the refracted beam O (beam magnification) is m=-, these are given by the following equations.

Further, the reflectance of P-polarized light (polarized light vibrating parallel to the plane of the paper) at the incident surface of the prism is given by the following equation.

Here, when θ, +θbe=90°, R2=0 and the loss of light on the incident surface of the prism becomes zero.

(If θ, = Od, there is no effect of the prism because it is perpendicular incidence.) Here, R, = O is tan θ, which is called the Brewster angle.

It's time for 2N. At this time, equation (7) has the following relationship.

However, the beam magnification m is set depending on the structure of the semiconductor laser device used. That is, the prism extends the horizontal direction of the spread of the beam from the semiconductor laser element so that it coincides with the vertical direction, thereby making the intensity distribution of the light emitted from the prism isotropic.

Therefore, when most of the beam from the semiconductor laser element is incident on the coupling lens, in order to obtain an isotropic beam, the beam magnification m must be set to the ratio of the beam divergence angle to 0410N.
need to match. For example, when using a QSp type semiconductor laser element, the beam magnification m is set to 3 from equation (1). At this time, the shape of the prism 7.8 is the (9th)
From the formula.

Therefore, for a C8p semiconductor laser having a beam divergence angle expressed by equation (1), the prisms 7 and 8 expressed by equation (10) are replaced by the coupling lens 2 in FIG.
By inserting it directly after the prism 7.8, it is possible to convert it into an isotropic beam. This isotropic light beam makes it possible to obtain an isotropic spot 5 on the disk 4 by the objective lens 3, and almost all of the beam from the laser element is irradiated onto the disk.

Moreover, since the numerical aperture of the coupling lens 2 is increased,
The retraction range of self-control focus has been expanded.

Furthermore, since there is no loss of light due to incidence on the prism, the light utilization efficiency is excellent.

In FIG. 5, the beam from the semiconductor laser element 1 is set to be P-polarized light (the plane of polarization vibrates parallel to the plane of the paper) as indicated by the arrow in FIG.

FIG. 6 is a diagram showing the configuration of another embodiment of the present invention,
The same reference numerals as in FIG. 5 indicate the same or equivalent parts. In the embodiment shown in FIG. 6, unlike the embodiment shown in FIG. The arrangement is opposite to that of the embodiment shown in FIG. That is, the beam from the semiconductor laser element 1 is set as S-polarized light (the plane of polarization vibrates perpendicular to the plane of the paper) as shown by the black circle in FIG. 7.8. By doing so, the objective lens 3 can be made smaller.

FIG. 7 is a diagram showing the configuration of another embodiment of the present invention. In the configuration of the embodiment shown in FIG. 5, a prism 11 is disposed between the prism 8 and the objective lens 3. With this embodiment, it is possible to detect changes in the reflected light from the disk 4 from the prism 11. Note that 10 is a single wavelength plate, and 12 is a photodetector.

In addition, in the above explanation, we have described the case where a change in the amount of light reflected from the disk is detected as a change in the laser light from the other direction of the semiconductor laser. Of course, the present invention can also be applied to the case of detecting as follows.

Also, if near the point N=7 where RP=O, almost R
μtsu is 0. As a practical matter, even if the refractive index of prism 7.8 cannot be exactly J, R
, =O, RP is almost zero, so a refractive index in that vicinity can be used satisfactorily.

FIG. 8 shows the relationship between the beam magnification m and the reflectance R at the entrance surface of the prism. If it is composed of one prism, the reflectance of light is reduced and the beam magnification m = 2 to 3.
, a prism with a fairly large refractive index N is required. In the figure, BK-7 (N=1.51),
The relationship when one prism consisting of SF-11, (N=1.764) is used is shown by a dashed line and a broken line, respectively. Since the ratio of θ□ to 09 of a semiconductor laser beam is usually about 2 to 4 times, it is quite difficult to configure it with one laser. If it is composed of two pieces as in the present invention,
It becomes possible to eliminate the above-mentioned drawbacks when configuring with one piece. In the figure, the relationship when two prisms made of BK-7 are used is shown by a solid line. BK is widely known to the general public.
-7, the refractive index N=1.5 near the wavelength of 8000 people
It is 1. In this case, when m = 2.28 times R, =
It becomes O. Furthermore, the transmittance is 99.9% or more in the range of m=2.1 to 2.5.

If it is allowed up to 99%, it can be used up to 1.8 to 3 in m.

As described above, according to the present invention, it is possible to increase the beam magnification with a small reflection loss using a prism having a small refractive index N, and the range of use thereof can also be expanded. Therefore, it has the advantage of being able to perform beam shaping with excellent light utilization efficiency using ordinary optical glass.

〔Effect of the invention〕

As explained above, according to the present invention, by using a plurality of prisms arranged so that the angle of incidence of the incident light beam becomes Brewster's angle, and arranged so that the light beam exits vertically, A light beam from a semiconductor laser element that does not have an isotropic divergence angle can be shaped with high light utilization efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a far-field image of a semiconductor laser beam, FIG. 2 is a diagram for explaining a conventional optical information processing device, and FIG. 3 is a diagram for explaining a conventional autofocus pull-in range. , 4th
The figures are diagrams illustrating the automatic focusing range according to the present invention, FIGS. 5 and 6. and FIG. 7 is a diagram showing the configuration of an optical information processing device using the optical device of the present invention, and FIG. 8 is a diagram showing the relationship between the reflectance at the entrance surface of the prism and the beam magnification. 1... Semiconductor laser, 2... Coupling lens, 3...
Objective 3 Figure 1 Disk device Figure 4 Figure 5 Figure 6 Figure 11 10 Figure 8 The frame number is f7rL

Claims (1)

[Claims] 1. A light source in which the intensity of the output light beam around the optical axis is anisotropic with respect to the optical axis, an input end face into which the light beam output from the light source is incident, and an output end face from which the light beam is emitted. a plurality of prisms having a plurality of prisms, each of which is arranged such that an incident end face of the prism forms a Brewster angle with respect to the output light beam of the light source, and the outgoing end face of the prism is refracted by the prism. an optical device for shaping the intensity distribution of the output light beam from the light source, the optical device being arranged perpendicular to the output light beam;