JPS60140778A - Measuring device for astigmatism of semiconductor laser - Google Patents

Abstract

PURPOSE:To measure the astigmatism of a semiconductor laser with high accuracy by cutting the enlarged image of a light-emitting section for the semiconductor laser from two directions of the joining surface of the semiconductor laser and the direction rectangular to the joining surface at the same time. CONSTITUTION:Knife edges 15a, 15b capable of moving in the direction x of the joining surface and the y direction of the direction orthogonal to the joining surface of a semiconductor laser 1 progress toward an optical axis, and luminous flux is interrupted in succession by the edges. When the knife blades of these edges 15a, 15b are moved and cross optical beams, the total amount of light reception of a light-amount measuring section 16 is kept constant where beams are not interrupted at all, and slowly reduces with the interruption of beams, and the amount of light is brought to 0 where more separate from a position where beams are interrupted completely. An output from the measuring section 16 is differentiated by a differentiating circuit 19 and light intensity is obtained becuase light intensity is in proportion to the change of the amount of light in the case when the edges 15a, 15b are moved by an extremely slight fixed amount, that is, it takes the differentiating value of the amount of light received. When astigmatism is measured actually, positional difference in the direction of a Z axis at the maximum intensity point in the x and y directions is obtaind, and the difference is divided by the square of the longitudinal magnification of an objective 14, thus acquiring astigmatism.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to astigmatism measurement of semiconductor lasers used for recording, reproducing, and transmitting optical information.

Conventional Structure and Problems The optical information recording and reproducing method has the advantage that the recording density is much higher than other methods.

This is due to the fact that the minimum recording unit of the optical recording method can be made small. Incidentally, the size of the minimum recording unit is approximately 3 μm2. In order to perform recording and reproduction in such small units, the light source used in this optical system is also required to have high performance. Conventionally, a HeNe gas laser has been used as a light source, but in recent years attempts to use a semiconductor laser, which is advantageous for downsizing the device, have been abandoned in many places. However, semiconductor lasers have specific problems compared to HeNe gas lasers, and the case where semiconductor lasers are used will be described in detail below.

Figure 1 shows the emission characteristics of a semiconductor laser. 1 is a semiconductor laser, and 2 is a junction surface. Since the emission angle of the semiconductor laser is different in the in-plane X direction of the bonded surface and in the Y direction perpendicular thereto, the emission pattern becomes an ellipse. Furthermore, the semiconductor laser 1 has different light emitting points in equal numbers in the in-plane direction and in the orthogonal direction. This is shown as Px and Py in FIG. This discrepancy between the light emitting points is called astigmatism of the semiconductor laser, and it has a serious effect on the aperture characteristics of the optical system, which will be explained next.

FIG. 2 shows an example of an actual optical system. FIG. 2(a) shows the trajectory of a light ray within the outer surface perpendicular to the cemented surface, and FIG. 2(b) shows the trajectory of the light ray within the cemented surface.

1 is a semiconductor laser, and 3 is a collimator lens, which functions to collimate the light emitted from the semiconductor laser 1. 4 and 6 are cylindrical openings and convex lenses, which expand parallel rays within the cemented surface into parallel rays with a wide beam width.

However, no changes are made to the light rays within the bonded surface. In this way, the concave and convex cylindrical lenses 4 and 5 are used to expand the light rays within the cemented surface with a small emission angle, thereby making the elliptical emission pattern circular. Reference numeral 6 denotes an aperture lens, which has the function of narrowing parallel light to form a spot on the recording medium 7, and the thermal energy condensed in this spot causes the medium to evaporate or undergo a phase change, thereby recording information.

There is a direct relationship between the recording and reproducing characteristics and the aperture beam diameter, and the smaller the aperture beam diameter, the better the recording and reproducing characteristics. Therefore, it is necessary to always focus on the medium, and although not shown in the figure, this adjustment is performed by moving the aperture lens 6 in the optical axis direction. Furthermore, when the semiconductor laser 1 has astigmatism, it also affects the aperture beam diameter. In Fig. 2, if there is a deviation in the optical axis direction, that is, astigmatism, between the light-emitting point PX in the cemented surface and the light-emitting point Py in the plane perpendicular to this, then the light that exits Px enters the lens 6 in parallel. When the optical system is adjusted so that the light emitted from Py does not enter the lens 6 in parallel, as shown by the dotted line in the figure. Therefore, since the imaging position gun a by the lens 6 is not located on the medium 7, the diameter of the aperture beam increases, leading to deterioration of recording and reproducing characteristics. Therefore, it is important to minimize the astigmatism of the semiconductor laser. Furthermore, it is necessary to inspect and select the semiconductor lasers to be mounted in the device, and it is desired to develop an accurate and quick method for measuring astigmatism.

Next, a conventional semiconductor laser astigmatism measuring method will be explained. FIG. 3 shows the lens imaging characteristics when the light source has astigmatism. Assuming that Px, Py are the equal number of light sources of light rays in the plane
The images Px' and Py' also have deviations in the optical axis direction. In terms of geometrical optics, the image at p, / is a straight line 11 in the X-axis direction, and the image at Py' is a straight line I5 in the y-axis direction, OP.
The intermediate image between x' and Py' changes continuously from an ellipse long in the X-axis direction to an ellipse long in the y-axis direction as it approaches Py' from p/. Distance a' between Px' and Py' and Px and P
The astigmatism a of the semiconductor laser with respect to a′
By measuring , it can be known using equation (1). Since the distance a' is the distance between the line image 11 in the X direction and the line image I5 in the y direction shown in FIG. 3, by sequentially moving the image observation position in the optical axis direction and observing changes in the shape of the image, Semiconductor laser astigmatism can be measured. A concrete example of this is shown in FIG. 1 is a semiconductor laser, 8 is a lens, 9 is a television camera, and 10Id is a television monitor. An image 11 of the light emitting part of the semiconductor laser 1 is displayed as an image 1 on the television monitor 10.
By sequentially moving the television camera 9 in the optical axis direction Z, the observation position of the image 11 of the light emitting section is changed, and changes in the image 12 on the television monitor 9 are observed. The distance a' in FIG. 3 is x, y of the image 12 on the TV monitor 9.
It is known as the amount of positional change in the optical axis Z direction of the television camera when the widths Wx and Wy of the directions are respectively minimum. Divide by the square of the square.

Conventionally, this method of directly observing the shape of the image was used, but since the image actually obtained here does not have a clear outline as shown by geometric optics, the TV monitor shown in Figure 4 was used. The minimum widths WX and Wy of the image 12 of No. 9 cannot be measured accurately. In addition, the astigmatism a required for the semiconductor laser 1 is very small, 5 μm or less, and with this level of astigmatism a, the minimum states of W, , and Wy actually occur almost simultaneously. This had the disadvantage that it could not be measured separately.

OBJECTS OF THE INVENTION An object of the present invention is to provide a semiconductor laser astigmatism measuring device that can easily measure the astigmatism of a semiconductor laser with an accuracy of several μm.

Structure of the Invention The present invention includes an objective lens that forms an enlarged image of a semiconductor laser emitting part, and an objective lens that moves in the vicinity of the enlarged image in a plane perpendicular to the optical axis, one in the direction of the semiconductor laser junction surface and the other in the direction perpendicular to the junction surface. It is composed of two knives that sequentially block the optical path, a transfer section that moves the knives in the optical axis direction, a light amount measuring section that is arranged behind the optical path with respect to the knife, and a calculation section that differentiates the measured light amount.

DESCRIPTION OF EMBODIMENTS FIG. 5 shows a configuration diagram of a semiconductor laser astigmatism measuring apparatus according to an embodiment of the present invention. 1 is a semiconductor laser, 14 is an objective lens that magnifies the light emitting part 13 of the semiconductor laser 1, 15
Reference numerals a and 15b designate knives movable on the mounting table 17 perpendicular to the optical axis Z in the direction of the bonded surface of the semiconductor laser 1 in the X direction and in the direction orthogonal to the bonded surface in the y direction. The light flux is sequentially blocked by Reference numeral 16 denotes a light amount measuring section installed approximately on the optical axis behind the optical path of the knives 15a and 15b, and the light not blocked by the knives is received here. Reference numeral 19 is a differential circuit for the output of the light amount measuring section 16, and reference numeral 20 is a transfer section for sending the knives 15a and 15b in two directions of the optical axis. Naifetsuji 16a
, 16b and the light quantity measuring section 16 measure the shape of the aperture beam, which will be explained below.

When the cutting edges of the knives 15a and 15b move in the right direction of the arrow from dl to d6 and cross the light beam 21 in FIG. The light intensity is constant to the left of the position d2 that does not block the light, gradually decreases as you move to the right of the position d2, and becomes 0 to the right of the position d5 that completely blocks the light. It is proportional to the change in light intensity when moving by a very small fixed amount, that is, it is a differential value of the amount of received light, so by differentiating the curve in Fig. 6 (b), Fig. 6 (C) is obtained, and this is the light intensity. The differentiating circuit 19 shown in Fig. 5 is used for this purpose.When measuring astigmatism, as shown in the conventional example Fig. 3, the light beam width W in the direction of the cemented surface and the direction perpendicular to the cemented surface of the semiconductor laser is used.
We must measure the mechanical strength and Wy. Therefore, as shown in FIG. 6, two knives 15a and 15b that move in two orthogonal directions are provided, and FIG. 7 shows a V-shaped knife that performs the same function. The V-shaped knife 23 reciprocates in the vertical direction in FIG. 7, and the knife tips 22a, 22b are provided at an angle of 45° with respect to the vertical feeding direction. When the V-shaped knife 23 moves up and down, the knife tip 22a.

22b cuts the light beam in the Y and X directions perpendicular to the knife tip, respectively, as shown by dotted lines.

By adopting the V-shaped knife in this way,
The structure is simplified and at the same time two knife tips 22
It becomes possible to set the cutting planes of a, 22b on the same plane.

By the method described above, it is possible to measure the intensity distribution of an enlarged image of the semiconductor laser light emitting section 13 in the direction of the junction surface of the semiconductor laser and in the direction perpendicular thereto. The light beam intensity can be measured by sequentially moving the mounting table 17 in the optical axis Z direction and measuring the minimum width W and Wy shown in FIG. Instead of determining the W work 9wy, a method of determining the maximum strength point is adopted. This is because the distribution width of the light beam and the maximum intensity are inversely proportional to each other.

Actual measurement of astigmatism is performed as follows.

As shown in Fig. 8, the light beam is cut while sending a knife in the direction of the optical axis, and the light intensity distribution is measured.
1. Astigmatism of the semiconductor laser is reduced by taking the positional difference in the Z-axis direction of max2 (distance 8 mm shown in FIG. 3) and dividing this by the square of the vertical magnification of the objective lens.

In this embodiment, since the light intensity distribution itself can be measured in this way, the minimum widths w, , 'wy mentioned above are measured, so that the accuracy is improved in this respect as well. Additionally, in this embodiment, since the intensity distribution of an enlarged image of the semiconductor laser light emitting section is measured, errors in setting the cutting position of the knife can be suppressed. As a result, an astigmatism measurement accuracy of 2 μm can be obtained.

Effects of the Invention The present invention reduces the astigmatism of the semiconductor laser to 2 μm by simultaneously cutting the 5-magnified image of the semiconductor laser light emitting part from two directions: the semiconductor laser bonding surface and the direction perpendicular to the bonding surface using a 7-shaped knife. It is possible to measure with high accuracy, and it is also easy to automate and high-speed measurement, and its effects are outstanding.

[Brief explanation of the drawing]

Figure 1 is a diagram of the emission characteristics of a semiconductor laser, Figure 2 is a diagram of the configuration of the optical system of an optical information recording/reproducing device, Figure 3 is a diagram of lens imaging characteristics when there is astigmatism, and Figure 4 is a diagram of conventional FIG. 5 is a block diagram of a semiconductor laser astigmatism measuring device according to an embodiment of the present invention, FIG. 6 is a diagram relating to light intensity measurement using the same knife, and FIG. is a configuration diagram of the same V-shaped knife, and FIG. 8 is a diagram of the same light intensity distribution. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 13... Light emitting part, 14... Objective lens, 15a, 15b...
... Naifetsuji, 16 ... Light amount measuring section, 1
9...differentiation circuit, 20...transfer section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (1) (1)) Figure 3 Figure I' 4 [1ii1 /? 10 Figure 5 I Porridge Figure 6 Figure 7? 2α

Claims (1)

[Claims] An objective lens that forms an enlarged image of the semiconductor laser light-emitting part, and in the vicinity of this enlarged image, one moves in the direction of the semiconductor laser junction surface and the other moves in the direction perpendicular to the junction surface in a plane perpendicular to the optical axis to sequentially block the optical path. Semiconductor laser astigmatism comprising two knives, a transfer section for moving the knife in the optical axis direction, a light amount measuring section disposed on the optical axis behind the optical path with respect to the knife, and a calculation section for differentiating the measured light amount. measuring device.