JPS59146013A - Optical device - Google Patents

Abstract

PURPOSE:To correct the astimatism of a semiconductor laser easily by providing parallel plane glass having specific plate thickness so that its normal vector slants at a specific angle to an optical axis in the semiconductor junction plane of the semiconductor laser. CONSTITUTION:One sheet of parallel plane glass 5 of specific plate thickness (t) where luminous flux is transmitted is provided in the window W of the gap of the semiconductor laser 1 where divergent luminous flux is transmitted between the semiconductor laser 1 and a collimator lens 4. In this case, the normal vector of the parallel plane glass 5 slants at the specific angle Up to the optical axis in the semiconductor junction surface (X-Y) of the semiconductor laser 1. The plate thickness (t) and inclination angle Up are selected to generate the astigmatism which is as large as and opposite in sign to the astigmatism DELTAZ generated by the semiconductor 1. Thus, the astigmatism generated by the semiconductor laser 1 is corrected easily.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to optical pickups, for example, in which the light source is a semiconductor laser, which has astigmatism due to the difference in the convergence point of the oscillated light beam within the semiconductor junction plane and in the plane perpendicular thereto. Regarding optical devices such as
In particular, the light beam of an optical disc player for audio, video, etc. is configured to refract the light beam derived from the semiconductor laser, form an image on the reading surface of the optical disc, and read information recorded on the reading surface. It is most suitable for use in pickups.

BACKGROUND TECHNOLOGY AND PROBLEMS For example, a gain guiding type semiconductor laser, which is a type of double heterojunction semiconductor laser, uses the return light beam from the reading surface, etc., which is often seen in the same type of index guiding type semiconductor laser. There is no increase in noise level due to self-coupling effects. For this reason, especially high S
Its value is being reconsidered as a light source for the optical pickup of video optical disk players, which require a high IN ratio. This is because gain-guiding type semiconductor lasers oscillate in longitudinal multi-mode, compared to semiconductor lasers with longitudinal single mode oscillation such as index-guiding type semiconductor lasers.
This is due to the essential property that the oscillation due to the returned light beam is not easily disturbed. However, from the viewpoint of optical characteristics, as shown in Figures 1 (a) and (b), the mode waist of the oscillation light flux of the gain guiding type semiconductor laser (1) is half), Body joint surface (X - Y Q
1+ plane) and in mi (X-ZM plane) perpendicular to this plane. In other words, the flight plane (X −Z 'j
In the ai1 plane), point A coincides with the mirror surface (2), whereas in the junction plane (: ) becomes point B, which is deeper inside the resonator. However, in the semiconductor laser (X-Y axis plane) and in the plane perpendicular to this (X-Z axis plane), the convergence point of the oscillation light beam is the stomach, which is what is called the front center in optical terms. The astigmatic 1F difference (ΔZ) is obtained.

If this li semiconductor ti-the is used as a source of the optical disc brake in )1-pink-up)'(,), it will be refracted with a lens etc. and an image will be formed on the reading section of the optical disc. The reading spot is distorted due to point aberration, resulting in a flat vertical spot and a horizontally long spot.

Therefore, due to straddling adjacent tracks, etc., the required optical system OT F (0, ptial Transfer
Point 9a occurs during which the characteristic (r Function ) is no longer obtained.

Conventionally, the following measures have been taken to solve this problem. One of them is (,)Y of divergent deafness derived from semiconductor laser.
This is a means of extracting only the narrow angularly changing part near the center of the two wheels and using it for reading, thereby reducing the disturbance of the wavefront due to astigmatism. With this method, the practical problem is that the influence of astigmatism differs depending on the collimator lens of which culmosity and numerical aperture is used to guide the objective lens (this luminous flux). If you take out only the narrow angle part of
Although the efficiency of light use decreases, the disturbance of the wavefront becomes smaller. Therefore, digital audio optical disc (DA
I)) If it does not require a high SIN ratio like Breyer's optical big amplifier, the required OT F% +! :
1) is done.

In other words, as a pick amp for a DAD player,
The self-strength (required in order to avoid hearing a high S/N ratio) is not so necessary.For this reason, the ratio is very small, for example 0
．． Since a 13 NA collimator lens with an aperture of 11 is sufficient, even if a semiconductor laser with an astigmatism of 25 μNor 1 is used as a light source, the wavefront disturbance will be 0.056 [:λ] in RMS value.
] is well within the diffraction limit and there is no particular problem.

However, for applications that require a high S/N ratio, such as the optical pickup of a video optical disk player, this method has poor utilization efficiency of the luminous flux derived from the semiconductor laser, so the laser output must be increased by 19%. This results in the drawback of shortening the life of the semiconductor laser.

Otherwise, in order to use a light source such as an optical pink amplifier for a video optical disk player that requires a high S/N ratio,
This is because, considering the divergence angle of the light beam emitted from current semiconductor lasers, it is necessary to form an image using a collimator lens with an open number of, for example, 0.2 NA or more. However, in this case, the wavefront disturbance due to the astigmatism of 25 μm has an RMS value of 0.13 [λ], which significantly deteriorates the 0TFe property and makes it impossible to obtain the required OTF characteristic.

Incidentally, the RM of wavefront disturbance allowed within the diffraction limit
The S value is 0.07λ (Marecbal Cr1ter
ion). Conversely, the lens astigmatism required to satisfy this requirement is determined by setting the numerical aperture of the collimator lens to 0.
The deviation from 2NA is 'I, 3 pm. It should be noted that the current gain-based guiding type semiconductors are -
Considering the astigmatism of "()", it is about 25 ti ry+. Therefore, when a high S/N ratio, that is, a strong light intensity is required, such as in an optical pickup of a video optical disk player, , some kind of astigmatism must be corrected.

Alternatively, (b) the +war (
Means for correcting astigmatism using optical elements having different coupling powers is used. However, in this case, since the power of the optical element is made to vary depending on the direction, the optical element surface, that is, the lens surface, becomes a deformed curved surface instead of a spherical surface. Therefore, the disadvantage is that it is extremely difficult to form the surface. In addition, since there is power and the power differs depending on the direction, the angular position f(11) of the optical element with respect to the optical axis, and the position f66 in the optical axis direction
However, the position of the directionality of the power with respect to astigmatism must be carefully determined, and there is also the disadvantage that it is difficult to adjust the position of the optical system.

Purpose of the Invention The present invention was invented in view of the above-mentioned circumstances, and its purpose is to use a single semiconductor laser with various astigmatisms, even if it has a high S/N1 ( Even in cases where optical elements are required and require high light intensity, the optical element is easy to form and the position can be easily adjusted. Optical device that can be obtained without increasing output by +7
It is about providing.

Summary of the Invention The optical device according to the present invention is the same as that described at the beginning.
A window of a cap that covers the semiconductor laser through which the light flux derived from the semiconductor laser passes (this is a transparent plate of a predetermined thickness; At least one light beam is provided so as to be inclined at a predetermined angle within the semiconductor joint plane of the semiconductor integrated laser with respect to the axis, and is configured to correct astigmatism of the guided light beam. .

This makes surface formation easy, position adjustment easy, and the plane-parallel plate that is the central optical element, and since the plane-parallel plate is provided in the window of the semiconductor laser camp, it can be easily incorporated into the device with high precision. , the required OTF characteristics are obtained without increasing the laser power.

EXAMPLE Hereinafter, an example in which the present invention is applied to an optical big amplifier will be explained with reference to the drawings, with only the aperture optical system thereof being taken out.

FIG. 2 shows a cross section of the semiconductor laser along the optical axis within the semiconductor junction surface, and FIG. 3 shows a cross section of the semiconductor laser along the optical axis within a plane perpendicular to the semiconductor junction surface. Note that the coordinate axes shown in the figure are the same as those in FIG.

The semiconductor laser (1) that is the light source is a gain guiding type of double heterojunction semiconductor laser. As mentioned above, in this semiconductor laser (1), the convergence point of the oscillation light beam is in the Q plane (
2) Enter the resonator a little further back and perpendicular to it (x
-z! (lh plane), it coincides with the mirror surface (2) and causes astigmatism.

On the optical axis of the optical path of the light flux emitted from this semiconductor laser (1), in order to refract the emitted light flux so that it becomes a parallel light flux, the focus is set on the mirror surface of the semiconductor laser (1).
2) with the required numerical aperture (4).
) is provided. Therefore, in the optical path of the divergent light beam between the semiconductor laser (1) and the collimator lens (4), there is a gap (CA) that covers the semiconductor laser (1).
A parallel plane glass (5) having a predetermined thickness t and capable of transmitting the light beam is provided in the window (2) through which the light beam derived from the semiconductor laser (1) of P) passes. Then, this parallel plane glass (5) (as shown in the figure, its normal vector is at a predetermined angle [Up tilt) within the semiconductor junction surface (X-Y axis plane) of the semiconductor laser (1) with respect to the optical axis. <.This corrects the astigmatism of the luminous flux derived from the semiconductor laser (1). (Note that the plate ff
t, angle Ul, etc. will be described later. )Also,
In order to receive the parallel light beam from the collimator lens (4) and refract it so as to form an image on the reading surface (6) of a video optical disc, etc., an objective lens (with a force It is provided on the optical axis.By this image formation, what is recorded on the reading surface (6) is read.

Next, the reason why astigmatism is corrected using the plane-parallel glass (5) will be explained based on FIG. 4.

The same applies to the case of the divergent state, but for example, as shown in the figure, the optical path of the light beam in the convergent state (numerical aperture NA = sinU)
Assume that a parallel plane glass (5Y (plate +yt', refractive index N) is positioned inside with a tilt Up' with respect to the light ff11+.

The astigmatism difference (astigmatism) that occurs at this time is, for example, W
, J, Sm1th ; Modern 0ptical
F': ngineering (M, C.

GraW-Kawa 11 N, Y, 1966) According to Iko, Njin no Yoo IC becomes.

Note that lt' is the PfW darkness to the convergence point in the plane (meridian plane) including the sacrilege/optical axis, and r' is the distance to the convergence point in the plane orthogonal to this (the spherical plane).

On the other hand, the spherical aberration is It is.

According to equations (1) and (2) above, the required numerical aperture, for example N
By selecting the plate thickness t' and the inclination angle Up' at A = sinU = 0.2, the semiconductor laser fl)
It can be seen that it is possible to generate astigmatism of the opposite sign to the astigmatism caused by rotation, and to suppress the coma aberration that occurs at the same time to a sufficiently low level. That is, any U
, ' to D, the astigmatism difference amount (astigmatism) is A, : i, '-1t'< rl.

Therefore, if the meridian plane is taken as the semiconductor junction surface of the semiconductor laser (1), the astigmatism of the semiconductor laser (1) can be corrected.

For example, t'=o, i bar, Up'=45°, N=1
．． 5, the amount of astigmatism (astigmatism) is As:ls'-lt'=-0,025(ml)-m-2
It becomes 5 μm. Since the astigmatism of the current gain-guiding type semiconductor laser (1) is about 25 μm as described above, it is clear that the astigmatism and aberration can be sufficiently corrected. Moreover, the comatic aberration that occurs at this time is 1? , MS value is approximately 11.02 (
λ] can be sufficiently ignored.

Note that both astigmatism and coma aberration are caused by parallel flat plate glass (
5) Since the astigmatism is proportional to the plate thickness t', and the astigmatism is approximately square for the inclination angle U,', and the coma is proportional to the plate thickness t', 17", which produces a constant astigmatism, is Flat glass (!5Y
It is possible to suppress the coma aberration that occurs at the same time by making corrections by making the plate t' smaller and increasing the tilt angle LT, /.

As a result of the above, the normal vector is increased at a predetermined angle within the semiconductor laser (X-Y axis plane) of the semiconductor laser (1) with respect to the optical axis.
A predetermined plate Vy, t of tilted plane glass (5
), it can be seen that the astigmatism of the semiconductor laser (1) is corrected.

Therefore, the reading spot that is focused on the reading surface (6) from the objective lens (7) is the parallel plane glass (5).
Astigmatism is corrected by , so that the shape becomes almost circular, and the required OTF/% is obtained without extending over adjacent tracks.

In this example, astigmatism is corrected using a parallel plane glass (!”
i), but it may be made of sapphire or the like and may be a flat parallel plate, as long as it is a flat parallel plate through which the light beam from the semiconductor laser (1) can pass.

Further, in this embodiment, a single piece of parallel glass (5) is used, but astigmatism can be corrected if there is a plate thickness t required to correct a certain astigmatism. Therefore, dividing this plate thickness t,
Two or three parallel plane glasses (5) may be used.

Furthermore, in this embodiment, the semiconductor laser (1) is a double heterojunction semiconductor laser of the gain guide type Jniji, but the convergence point of the emitted light beam is different in the semiconductor junction plane and in the plane perpendicular to this. It goes without saying that the present invention can be applied to any semiconductor laser that exhibits astigmatism.

In addition, the normal vector of the parallel plane glass (5) is tilted 45 degrees (=Up) with respect to the optical axis, and the surface opposite to the semiconductor laser (1) is coated with a vapor-deposited film, so that the beam beam can be used as a half-dove mirror. It is also possible to use Kokichi as a printer.

Application Examples The present invention can be applied to distance measuring devices, object movement measuring devices, information recording devices (optical audio and video disk master manufacturing devices, etc.), information transmission devices, etc.

Effect of the invention The present invention has the following advantages.

By providing the parallel plane plate so that its normal vector is inclined at a predetermined angle within the semiconductor junction surface of the semiconductor laser with respect to the optical axis, even if a semiconductor laser with astigmatism is used, a high S/N ratio can be achieved. Even if it is required and requires light intensity,
The required OTF characteristics are obtained without increasing the laser power.

Since the optical element for correcting astigmatism is a plane-parallel plate, its surface can be formed extremely easily. In addition, since it has no power (coupling force), it is possible to adjust the angular position by tilting the normal vector to the optical axis l within the semiconductor junction surface of the semiconductor laser, as described above, or to easily position it. Can be adjusted.

Moreover, since the parallel plane plate is provided in the gap window of the semiconductor laser, it can be easily and accurately inserted into the device without the need to provide a support part or the like to the device. be able to.

[Brief explanation of drawings]

Figures 1 (a) and (b) are diagrams explaining astigmatism of a gain guiding type semiconductor laser, and Figure 2 is a semiconductor junction of a semiconductor laser in an aperture optical system of an optical pickup to which the present invention is applied. Cross-sectional view in the plane along the optical axis, No. 6
This figure is a cross-sectional view of the semiconductor laser shown in FIG. 2 taken along the optical axis in a plane perpendicular to the semiconductor laser, and FIG. 4 is a diagram illustrating correction of astigmatism using parallel plane glass. In addition, in the symbols used in the drawings, (1)
・ ・Semiconductor・-The (5)・・Parallel plane glass. Agent Katsutsune
Yoshio Sugiura Shuny (t i"rit'i /! f', :4

Claims (1)

[Claims] In an optical device using a semiconductor laser as a light source, the convergence point of the oscillated light beam differs between the semiconductor junction plane and the plane perpendicular to it, resulting in astigmatism. At least one transparent or semi-transparent parallel plane plate having a predetermined thickness is provided in the window through which the light beam passes, so that its normal vector is inclined at a predetermined angle within the semiconductor bonding surface of the semiconductor laser with respect to the optical axis; An optical device configured to correct astigmatism of the derived light beam.