JPH06236574A - Optical power meter - Google Patents

Abstract

PURPOSE:To improve the measuring precision of a semiconductor laser output by head positioning the diferential outputs of two pieces each of quadripartite photodetectors while watching a spot position by an oscilloscope. CONSTITUTION:The photodetector 2 is quartered to A-D, and the outputs of the divided parts A, C are inputted to a differential circuit 7 and the outputs of the divided parts B, D are inputted to the differential circuit 8. The output differences (A-C) and (B-D) of respective divided parts are outputted from the circuits 7, 8, to be inputted to the X, Y axes of the oscilloscope. Then, the center of an incident luminous flux on the photodetector 2 is detected by making to coincide the spot with the intersected point of both axes. Thus, the photodetector 2 is positioned precisely for the luminous flux by moving a head and making to coincide it with the intersected point of both axes while watching the spot position on the oscilloscope, and the output of the semiconductor laser being a pickup light source is measured at the position. The output is displayed on an output display part as the sum of the outputs of the quadripartite A-D of the photodetector 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical power meter for measuring the optical output of a semiconductor laser light source used as a light source for a pickup of an optical disk device.

[0002]

2. Description of the Related Art FIG. 6 is a front view showing an example of a conventional optical power meter, and FIG. 7 is a front view for explaining the operation of the example of FIG.

A conventional optical power meter for measuring the optical output of a semiconductor laser light source used as a light source of a pickup of an optical disk device is driven by a lens driving device 38 provided in a pickup 37, as shown in FIG. The light receiving element 32 of the head 31 is arranged above the objective lens 39, and the head 31 is connected to the main body 33 having the output display section 34 via the cable 36.

A light beam emitted from the semiconductor laser 40, which is the light source of the pickup 37, is emitted as the measurement light 35 from the objective lens 39 and is captured by the light receiving element 32, and its output value is measured. The output signal of the light receiving element 32 is transmitted to the main body 33 via the cable 36 and displayed on the output display section 34.

[0005]

The conventional optical power meter as described above has the following problems.

That is, as shown in FIG. 7A, all the measurement light 35 emitted from the objective lens 39 must be captured and measured by the light receiving element 32, but the light emitted from the semiconductor laser 40 is infrared. Since the light has a wavelength in the range, it cannot be visually confirmed. Therefore, the output value of the pickup 37 must be measured by moving the head 31 in an appropriate direction while observing the display on the output display unit 34 to search for a position where the display on the output display unit 34 shows the maximum value. The operation of searching for the position where the display of the output display unit 34 shows the maximum value is not only a difficult operation, but also the accuracy is low. Therefore, as shown in FIG. 7B, the measurement emitted from the objective lens 39. Even when not all the light 35 is captured by the light receiving element 32, the position is picked up as the maximum light receiving point.
The output value of may be measured.

[0007]

SUMMARY OF THE INVENTION An optical power meter of the present invention differentially divides an output from a four-divided light receiving element for capturing an optical output from a semiconductor laser light source and two opposing divided portions of the light receiving element. A head having two differential amplifying circuits for amplifying, a two-channel oscilloscope for respectively inputting signals from the two differential amplifying circuits, and a signal from the four-divided light receiving element for inputting them. And a main body having an output display unit for displaying the sum, and further, an automatic gain control circuit is added to the differential amplifier circuit.

[0008]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a front view showing the first embodiment of the present invention, FIG. 2 is a bottom view showing the operation of the light receiving element of the embodiment of FIG.
3 is a schematic diagram for explaining the beam position detecting method in the embodiment of FIG. 1, and FIG. 4 is a front view showing an oscilloscope of the embodiment of FIG.

In FIG. 1, a head 1 having a light receiving element 2 is provided with output cables 4 and 2 via three cables 6.
It is connected to a main body 3 having a channel oscilloscope 5.

The light receiving element 2 is arranged above the objective lens of the pickup (see FIG. 6), and as shown in FIG. 2, is divided into four parts (portions A to D). The outputs of the parts A and C are input to the differential circuit 7 incorporated in the head 1, and the outputs of the parts B and D are input to the differential circuit 8 incorporated in the head 1. Therefore, a differential output (AC) corresponding to (output of section A-output of section C) is output from the differential circuit 7, and (output of section B-from the differential circuit 8).
A differential output (BD) corresponding to the output of the D section) is output.

The differential output (A-C) and the differential output (B-D) are input to one of the two channels of the oscilloscope 5, and the bright spot on the cathode-ray tube 10 of the oscilloscope 5 is set to the X-axis. And move in the Y-axis direction.
Therefore, the center of the light beam incident on the light receiving element 2 can be detected by matching the bright point with the center point on the cathode ray tube 10.

That is, when the light beam 9 is evenly incident on the four parts A to D of the light receiving element 2, FIG.
As shown in (a), the cathode ray tube 1 of the oscilloscope 5
The bright point 11 appearing on 0 is displayed at the intersection of the X axis line 18 and the Y axis line 19.

When the light beam 9 incident on the light receiving element 2 is deviated and both the differential output (AC) and the differential output (BD) are positive, as shown in FIG. The bright spot 11 is
Appears in the first quadrant on the cathode ray tube 10. When both the differential output (AC) and the differential output (BD) are negative, the bright spot 11 appears in the third quadrant on the cathode ray tube 10 as shown in FIG. .

Therefore, the head 1 is moved while observing the position of the bright spot 11 on the cathode ray tube 10, and the bright spot 11 is moved to the X-axis line 18
And the Y-axis 19 make it possible to accurately position the light receiving element 2 with respect to the light beam 9, and measure the output of the semiconductor laser of the light source of the pickup at that position. The output is displayed on the output display section 4 of the main body 3 as the sum of the outputs of the A section to the D section of the light receiving element 2.

However, when the light beam 9 incident on the light receiving element 2 is 4
In some cases, it is not necessary that the light is evenly incident on the divided parts A to D. That is, when all the incident light flux 9 is received by the light receiving element 2, there is no problem in measuring the output of the semiconductor laser even if the light flux is not evenly incident on the portions A to D.

Therefore, as shown in FIG.
A circle 20 centering on the intersection of the X-axis line 18 and the Y-axis line 19 is provided on 0, and when the bright spot 11 is in this circle 20, it is acceptable. The circle 20 has a bright spot 1 when the output of the light beam 9 is constant and its value is known in advance, for example, when the deviation of the center of the light beam 9 is 50 microns.
The range of the oscilloscope 5 and the gains of the differential circuit 7 and the differential circuit 8 are adjusted so that 1 is on the circumference of the circle 20. By doing so, the head 1 can be positioned so that the deviation of the center of the light beam 9 from the center of the light receiving element 2 is within 50 microns.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

The present embodiment is effective when the output value of the semiconductor laser of the pickup to be measured is unknown, and the differential circuit 7 and the differential circuit 8 of the embodiment of FIG. (AGC circuit) is added.

That is, the light beam captured by the photodetector 21 is divided into two paths. The first path is the differential circuit section 22, the AGC circuit section 23, and the oscilloscope 25.
The first route is a route including the light output measuring unit 26 and the light output display unit 24.

In the second path, as in the embodiment of FIG. 1, the light output measuring unit 26 obtains the sum of the outputs of the four-division light receiving elements of the light detecting unit 21 and displays it on the light output display unit 26. To do. In the first path, as in the embodiment of FIG. 1, two differential circuits of the differential circuit section 22 output differential outputs, which are input to the AGC circuit section 23. Even if the output value of the semiconductor laser of the pickup to be measured is unknown, the AGC circuit section 23 causes the circle on the cathode ray tube of the oscilloscope 25 (see FIG. 4) to
The amplification value of the differential output is automatically adjusted and input to the oscilloscope 25 so that the deviation of the center of the light flux from the center of the light receiving element is displayed as 50 microns. Therefore, regardless of the output value of the semiconductor laser of the pickup to be measured, the output value of the semiconductor laser can be measured without switching the measurement range of the oscilloscope 25.

[0022]

As described above, the optical power meter of the present invention uses the light receiving elements divided into four as the light receiving elements of the head, and the differential output of each two is used as the X axis and the Y axis of the 2-channel oscilloscope. By inputting to the axis and enabling to position the head while observing the position of the bright spot appearing on the cathode ray tube of the oscilloscope,
There is an effect that the center of the light flux from the semiconductor laser of the pickup incident on the light receiving element can be accurately aligned with the center of the light receiving element, thus improving the measurement accuracy of the output of the semiconductor laser and facilitating the operation. The effect is that you can.

[Brief description of drawings]

FIG. 1 is a front view showing a first embodiment of the present invention.

FIG. 2 is a bottom view showing the operation of the light receiving element of the embodiment of FIG.

FIG. 3 is a schematic diagram for explaining a beam position detecting method in the embodiment of FIG.

FIG. 4 is a front view showing the oscilloscope of the embodiment of FIG.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIG. 6 is a front view showing an example of a conventional optical power meter.

FIG. 7 is a front view for operating the operation of the example of FIG.

[Explanation of symbols]

 1/31 head 2/32 light receiving element 3/33 body 4/24/34 output display 5.25 oscilloscope 6/36 cable 7.8 differential circuit 9 luminous flux 10 cathode ray tube 11 bright spot 18 X-axis 19 Y-axis 20 circle 21 photodetector section 22 differential circuit section 23 AGC circuit section 26 optical output measuring section 35 measuring light 37 pickup 38 lens driving device 39 objective lens 40 semiconductor laser

Claims (2)

[Claims] 1. A head having a four-divided light receiving element for capturing an optical output from a semiconductor laser light source and two differential amplifier circuits for differentially amplifying outputs from two facing divided portions of the light receiving element. And a main body having a two-channel oscilloscope for inputting signals from the two differential amplifier circuits and an output display section for inputting signals from the four-divided light receiving elements and displaying the sum thereof. An optical power meter, comprising: 2. The optical power meter according to claim 1, wherein an automatic gain control circuit is added to the differential amplifier circuit.