JPS6043569B2 - Optical recording and reproducing device using a semiconductor laser as a light source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In general, a semiconductor laser can directly modulate its output light with an electrical signal without using an optical modulator;
It is characterized by its small size compared to other lasers, and is increasingly being used as a light source for various devices.

For example, research is being conducted on how to utilize the above characteristics as a light source for optical communications. Practical use is also being considered as a light source for playback of known optical video discs. The present invention focuses the light of a semiconductor laser into a light beam with a minute diameter (approximately 1 μm in diameter) and irradiates it onto a disk coated with an optical recording material, as in the case of the above-mentioned video disc, to record information such as images and audio. The present invention provides an optical device using a semiconductor laser that can be applied to a device for optically recording and reproducing information at high density, or a device for reproducing already recorded information.

Generally, when a semiconductor laser is used as a light source in the above-mentioned optical recording/reproducing device, it is required to generate light with a certain high output power corresponding to one sensitivity of the optical recording material. For example, when using a silver halide film that requires development and fixing after irradiation with light as an optical recording material, such output power is not required, but real-time recording materials that do not require development and fixing, such as metal thin film 100 to 100 on the recording material.
A recording energy of 0rT1J/Clt is required, and the output power of the light source is also required to be several tens of n1W or more. Also,
In order to satisfy the above recording energy on a recording material, it is necessary to make the light transmission efficiency as high as possible in an optical system that narrows the output light of the semiconductor laser to a minute diameter. Since the output light of a semiconductor laser is essentially spread light, special consideration is required in this respect. Furthermore, the beam diameter of the light irradiated onto the optical recording material needs to be narrowed down to the smallest possible beam diameter in order to satisfy the above-mentioned recording energy condition and to record and reproduce signals as densely as possible.

In general, the cross-sectional shape of the light beam at the light emitting surface of a high-power semiconductor laser is flat, with a thickness of 1 to 2 μm in the thickness direction of the bonded surface and approximately 10 pm in the direction parallel to the bonded surface, in relation to the bonded surface. ing.

In addition, the light beam emitted from it has a fairly large spread angle, for example, ±15 ~ in the direction perpendicular to the joint surface.
25, and has a spread of ±50 to 105 in the direction parallel to the bonding surface, requiring significantly different handling compared to a general He-Ne gas laser. One of the conventional optical systems that uses a semiconductor laser having the above-mentioned properties as a light source for reproducing optical video disks is "JP JHee".
msKerkAPPLIED, OPTICS. Vol.
l7JUIy, l978, p2OOr' 2001. The main parts of this example, shown on page 5, are shown in FIG.

In FIG. 1, 1 indicates a semiconductor laser, and the angle ψ indicates the divergence angle of the semiconductor laser at a portion where the energy is half the value, for example.

2 is the objective lens of the microscope.

It is a condensing lens with a short focal length that is used. In this conventional example, an objective lens with a small numerical aperture (N, A2) is used as the condensing lens 2 to collect only the light at the center of the semiconductor laser light. That is, the condenser lens 2
By reducing the NA, the condenser lens 2 is also made to function as a slit. In the figure, 0 indicates the spread angle of light that can be collected by the condenser lens 2, and Sinθ/2=NA2
have the following relationship. In the above example, a condensing lens with NA2=0.07 is used, so θ/2=Si′1(0.0
7)=4, and light within a spread of approximately ±4 is collected. The semiconductor laser 1 is placed slightly outside the focal point of the condenser lens 2, and forms an image of a portion of the light source at point Q on the optical axis (Z). Reference numeral 3 denotes an aperture lens which, like the condensing lens 2 described above, is composed of an objective lens of a microscope or the like.

A large numerical aperture (NA3) of this aperture lens 3 is used in order to improve the aperture performance. In the above example, an aperture lens with NA=0.65 is used. As a result, the image at point Q is formed at point R as an image with a minute diameter. The information recording surface of the video disc is placed at this point R. The optical system shown in FIG. 1 attempts to collect and narrow down only the light at the center of the emitted light from the semiconductor laser 1 having the flat light emitting surface using a condensing lens.The optical system shown in FIG. The rate at which power is transmitted to point R) is extremely low, only a few percent.
become.

In addition, in order to increase the transmission efficiency, the numerical aperture (
If an objective lens with a large NA2) is used, there is a conflicting factor in that the aperture diameter of the light at point R cannot be made small.
In order to fully demonstrate the lens performance, a sufficiently long optical path length is required, and although the aperture diameter of the light becomes small, the optical path length becomes large and the entire optical system becomes large. Furthermore, in order to always irradiate the information recording surface of the video disk with a minute aperture beam of a constant size, it is necessary to keep the distance between the objective lens 3 and the disk surface constant.

So-called focus control, in which the objective lens 3 is provided movably in the optical axis direction and is moved in accordance with the disk surface deflection, is well known as a publicly known technique.

Generally, the focus control signal is generated by receiving reflected light from the disk surface with a photoelectric conversion element and using the output signal thereof. FIG. 1 shows an optical system for obtaining a typical focus control signal.

After the reflected light from the disk surface passes through the objective lens 3, it is separated from the incident light by a half mirror 4, and guided to a photoelectric conversion element 6 divided into, for example, four parts, via a cylindrical lens 5.
When the distance between the objective lens 3 and the disk surface changes, the shape of the reflected beam on the photoelectric conversion element 6 changes.

Information corresponding to this change is included in the output signal of each element of the four-divided photoelectric conversion element 6, and this output signal is processed in a known manner and then moved in the optical axis direction of the objective lens 3. Provided as a focus control signal. It is also well known that the output signal of the photoelectric conversion element 6 can be provided as an information signal or a tracking control signal. Since the optical path length of the aperture optical system shown in FIG. 1 is large as described above, a half mirror 4 is provided in the optical path to separate the light emitted from the semiconductor laser and incident on the aperture lens from the light reflected from the disk. There is no need to further increase the optical path length of the diaphragm optical system.

The present invention relates to an optical recording/reproducing apparatus constructed with a smaller aperture optical system that has better light transmission efficiency than the aperture optical system shown in FIG.

More specifically, although a beam splitter such as a half mirror for separating the incident light and reflected light is provided in the optical path, the optical recording/reproducing device is configured without increasing the optical path length of the small aperture optical system. It provides:

The present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the optical recording/reproducing apparatus of the present invention. The optical system in FIG. 2 shows a cross section of light emitted in a direction parallel to the junction surface of a semiconductor laser, and is partially shown in a perspective view.

A semiconductor laser 11 has a flat light emitting surface as described above.

Reference numeral 12 denotes a semiconductor laser dynamic circuit that modulates the output light of the semiconductor laser and controls the optical output of recording light and reproduction light.

13 is a condensing lens and a semiconductor layer having a widening. ser 11
The emitted light is focused into a parallel beam of light.

Reference numeral 14 indicates a concave cylindrical lens, and 15 indicates a convex cylindrical lens, which are arranged so as to have a maximum curvature in a direction parallel to the cemented surface.

16 is installed in the optical path between the cylindrical lenses 14 and 15. It is a multi-digit beam splitter.

Reference numeral 17 denotes a tracking mirror for changing the optical path, and is configured to perform tracking control using a known technique.

18 indicates an aperture lens.

Reference numeral 19 denotes a disk, which has a disk structure coated with the optical recording material.

The disk 19 is configured to rotate around a rotating shaft 21 connected to a motor 20 and move in its radial direction (not shown). Reference numeral 22 denotes a known voice coil structure, which drives the aperture lens 18 in a direction perpendicular to the surface of the disk 19 in response to disc surface wobbling, and maintains a constant distance between the disk 19 and the aperture lens 18. .

23 is a convex cylindrical lens whose direction of maximum curvature is different from the direction of the convex cylindrical lens 15 by 90 degrees around the optical axis.

24 is a photoelectric conversion element divided into four parts.

Here, in order to explain the optical system shown in FIG. 2 in more detail, the explanation will be made based on FIG. 3, which shows only the diaphragm optical system.

Items that are the same as in Figure 2 are given the same numbers. FIG. 3a shows a cross section of the semiconductor laser 11 taken along the optical axis in the direction perpendicular to the bonding surface (L direction), and FIG. 3b shows a cross section taken along the optical axis in the direction parallel to the bonding surface (/direction). A cross section is shown.

First, the operation in the direction perpendicular to the joint surface shown in FIG. 3a will be explained.

The size of the light emitting surface perpendicular to the junction surface of the semiconductor laser is 2μ
m1 The spread angle in that direction is set to ψ1 = 15 degrees at the point where the energy is half the value. When the focal length of the condensing lens 13 is set as Fl3 and the light emitting surface of the semiconductor laser 11 is placed at the focal point of the condensing lens 13, the output light of the condensing lens 13 is a parallel light beam with a beam width φ1 shown in FIG. 3a. Obtainable. Now, if the numerical aperture (NAl3) of the condensing lens 13 is 0.5, this lens 13 will condense all the light having a spread of 2φ1=300 and generate a parallel light beam, so the condensing lens will be Almost all of the light in the direction perpendicular to the bonding surface can be transmitted without loss due to vignetting. And the luminous flux width φ1 of the parallel luminous flux is approximately 2×Fl3
It is given by ×Tanψ1. This parallel light flux is on the optical axis (Z)
It is stopped by the aperture lens 18 placed at the upper point t,
A minute diameter image is formed at point u on the optical axis. Therefore,
If the entrance aperture of the diaphragm lens 18 is made larger than φ1, almost all of the light will be transmitted to the point u without any loss due to eclipse caused by the optical element. If the focal length of the diaphragm lens 18 is Fl8, the size of the image in the direction perpendicular to the cemented surface of the semiconductor laser formed at point U, I is, in terms of geometric optics, I × 2 μm... (1) Given. Next, Figure 3b
An optical system parallel to the cemented surface will be explained.

The size of the light emitting surface in this direction is 8 μm, and the spread angle of light is
Assume that ψ2=5 at the half-value point of energy. When the light emitting surface of the semiconductor laser 11 is placed at the focal point of the condenser lens 13, parallel light with a beam width φ2 is obtained. And φ2'-2×Fl3
×Tan5, as mentioned above, numerical aperture (NA13) =
If a 0.5 condensing lens is used, most of the light in this direction can be condensed without being rejected by the condensing lens and loss.

However, φ2 has a much smaller luminous flux width than φ1 in FIG. 3a. When this φ2 is stopped directly using the diaphragm lens 18 in the same manner as shown in Fig. 3a, the point u on the optical axis is I±''=length×8 μm.
As a result, a short shelf-shaped light similar to 2 μm x 8 μm is formed at point u. Therefore, the concave and convex cylindrical lenses 14 and 15 change the magnification of the light in the direction parallel to the cemented surface, and adjust the beam width φ3 of the parallel beam entering the aperture lens to form a substantially circular shape at point u. It forms an image. In Fig. 3b, if the focal length of the concave cylindrical lens 14 is Fl4, the concave cylindrical lens has a luminous flux width φ2
A virtual image is created at point l by receiving a parallel beam of light. Positive distance between point l and position r of concave cylindrical lens 14 = Fl4
becomes. Therefore, light that spreads from one point is generated from the concave cylindrical lens 14 and enters the convex cylindrical lens 15 (focal length Fl5). 1, where s is the position of this convex cylindrical lens 15 on the optical axis Z.
If a convex cylindrical lens is placed at a position where the distance between and s = Fl5, a parallel beam with a beam width φ3 is generated as shown in FIG. 3b. The relationship between φ3 and φ2 is φ3/φ2=earth=? ...(2).

1rf1,1 This parallel light beam φ3 is passed through the objective lens 1
8 to generate an image at point u on the optical axis.

If the size of the geometric optical image in this direction is I/, then 1
18 statues! 14 1/=F. ．． ．． ．． , 4-X8μm... (3) Therefore, from equations (1) and (3), = ↓...
...If the focal length of each concave and convex cylindrical lens is selected so as to obtain (4), it will become φ1''.φ3, and I±''. at point u in Fig. 3. It is possible to obtain a substantially circular image or a substantially positive image having a ratio of 1/2.

In FIG. 3b, point l is the concave cylindrical lens 1
4 and the convex cylindrical lens 1
5, by arranging each cylindrical lens, parallel light with a beam width φ2 is converted into a beam width φ
This converts the light into three parallel beams.

Therefore, the mutual distance between the concave and convex cylindrical lenses 14 and 15? These lenses have the feature of being able to be placed at any position between the condenser lens 13 and the diaphragm lens 18 as long as they are kept constant. It can be taken. In addition, in FIG. 3, the distance π between the condenser lens 13 and the concave cylindrical lens 14 and the distance I between the convex cylindrical lens 15 and the aperture lens 18 are such that the light beam between them is parallel light.
It can be made to any length. Therefore, the Buddha i
By shortening the optical system, the optical system can be made significantly smaller. Now, as a value that satisfies equation (4), F
l3=20W! M,fl4=80Ts! What if t? =
The optical system has a very short optical path length. Since the aperture optical system is configured as described above, when the optical recording material surface of the disk 19 is at the above-mentioned image position of I'-1/ (desired position of the disk), the reflected light from the disk 19 is After being converted into a parallel beam by the aperture lens 18,
The optical path is changed by a tracking mirror 17.

Then, this parallel reflected light is subjected to a lens action by the convex cylindrical lens 15, where only the light in the direction perpendicular to the cemented surface is subjected to a lens action. Thereafter, the reflected light is separated from the incident light by the beam splitter 16 and reaches the convex cylindrical lens 23. The reflected light is subjected to an optical lens action in a direction parallel to the cemented surface by the convex cylindrical lens 23, and the photoelectric conversion element 2 is divided into four parts.
The light is received at 4. The convex cylindrical lens 23 is provided to the convex cylindrical lens 15 so that the reflected light does not converge on the same plane as shown in FIG. 2 after passing through the convex cylindrical lens 23.

The output signal of each element of the 4-divided photoelectric conversion element 24 is subjected to appropriate signal processing and then used to drive the voice coil structure 22, which consists of an aperture lens, two cylindrical lenses, and a 4-divided photoelectric conversion element. This is a well-known method similar to the method of obtaining a focus control signal using an element.

Since the present invention is configured as described above, it has the following effects. (1) Beam splitter 16 and condensing lens 13
The space between the concave and convex cylindrical lenses 14 and 15, which is necessary to convert the parallel light beam from the beam into a parallel light beam with a different cross-sectional shape, is used and is provided between them, so there is no need to increase the optical path length in order to provide a beam splitter. It is a small optical system that depends only on the optical path length of the diaphragm optical system, and as shown in Figure 1, there is no vignetting of light due to the lens, so the reduction rate is 40% to 50% or more, depending on the selection of optical components. An optical recording/reproducing device with high light transmission efficiency can be obtained.

(2) As mentioned above, when using a cylindrical lens to obtain a focus control signal from the reflected light from the disk, the reflected light passes through the convex cylindrical lens 15 and is separated by the beam splitter, so the convex cylindrical lens 15 is apertured. It can be used commonly as one optical component constituting an optical system or as one optical component of an optical system that obtains a focus control signal.

Although the cylindrical lens 14 is described as being concave in FIGS. 2 and 3, the same structure can be achieved by using a convex cylindrical lens. An example of this case is shown in FIG.
Components that are the same as those in FIGS. 2 and 3 are given the same numbers. In Figure 4, the focal length of the convex cylindrical lens 14'' is Fl.
4, by setting 1=Fl4 and ■=Fl5, it is possible to obtain a parallel light beam φ3 such that φ3=blue light φ2. however,? =Fl4''+Fl5, so ? is longer than in the configuration shown in Fig. 3, and the aperture optical system becomes larger, but it is sufficiently smaller than the aperture optical system shown in Fig. 1. The optical path length of the optical system can be further shortened by shortening the focal length of the cylindrical lens, but
In this case, in order to eliminate lens aberrations, it is preferable to configure a plurality of assembled lenses, for example, the cylindrical lens 14.

Furthermore, in the embodiment shown in FIG. 2, the beam splitter 16 may be constructed of something like a half mirror, but in this case, as shown in FIG. It shifts.

In this respect, if a cubic beam splitter as shown in FIG. 5B is used, the optical axis will not be deviated due to the thickness t or refractive index.

In this case, not only is it easier to align the optical axes, but also it is easier to attach the cylindrical lenses 14 and 15 to the integral lens barrel.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional semiconductor laser light aperture device, FIG. 2 is a configuration diagram showing an embodiment of the present invention, and FIG. 3A
, b are diagrams for explaining the operation of the embodiment, respectively;
FIG. 4 is a diagram showing the main part configuration of another embodiment of the present invention, and FIG.
Figures A and b are diagrams showing beam splitters, respectively.

Claims (1)

[Scope of Claims] 1 A semiconductor laser is used as a light source, comprising an optical system that irradiates light emitted from a semiconductor laser onto a recording medium with a minute beam aperture and receives reflected light from the recording medium with a photoelectric conversion element. In the optical recording/reproducing device, a first beam condenses the light emitted from the semiconductor laser to generate parallel light.
a second optical means for converting the parallel light in a direction parallel to the junction surface of the semiconductor laser into parallel light having different cross-sectional shapes using at least two cylindrical lenses; a third optical means for focusing the parallel light generated by the second optical means into a minute light beam, and a beam splitter for separating the reflected light from the recording medium, the beam splitter An optical recording/reproducing apparatus using a semiconductor laser as a light source, characterized in that the second optical means is provided in an optical path between at least two cylindrical lenses. 2. The beam splitter is configured such that the optical axis of the light after the light emitted from the semiconductor laser passes through the beam splitter and the optical axis of the light before the light passes through the beam splitter are in a straight line. An optical recording/reproducing device using the semiconductor laser described in 1 as a light source.