JPS6344141A - Light emitting characteristic measuring system for light emitting element - Google Patents

Abstract

PURPOSE:To measure emission characteristic accurately, by measuring time to be taken until an image signal left in a solid image sensor of a video camera lowers to a saturation level of the solid image sensor to compute a light receiving level with the correction thereof based on time. CONSTITUTION:When a measurement start command is provided to a processor 6, the device 6 sends a shot signal to a synchronous signal generator 5. The generator 5 sends out a drive pulse transmission timing signal to a drive pulse generator 4, which outputs a drive pulse. An emission light of a light emitting element 1 generated by this drive pulse is taken with a video camera 2 and an image signal outputted from the camera 2 is converted 3 into a digital signal to be inputted into the device 6. With the inputting of the image signal thereinto, the device 6 determines whether the light receiving level of the emission light of the element 1 inputted into the camera 2 reaches a saturation level of a solid image sensor or not from the level of the image signal. When it exceeds the saturation level, the device measures time to be taken until it comes down to the saturation level to compute light emitting characteristic with the correction based on time and the, outputs an emission characteristic pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to the use of a solid-state imaging device such as a CCD type or MOS type video camera to capture light emitted from a light emitting element that emits light at a high level of intensity, such as a laser diode. The light emission is imaged by the video camera used and the light emission of the light emitting element: fj is measured, and the measurement method t'ζ is concerned.

[Technical background of the invention]

For example, a light emitting element such as a laser diode used as a light source for various measurements or various information reading signals is required to have good light emission characteristics.

The light emission of a light emitting element is expressed by a contour line pattern connecting the same level points of the light emitting surface or the projected image of light emission.
As a measurement device for obtaining such light emission characteristics, there is a device that uses a video camera to image the light emission of a light emitting element to be measured, analyzes it, and draws a light emission pattern.

The inventor of the present invention uses a camera (CCD type or MOS type video camera) that uses a solid-state image sensor as a video camera, and captures the image taken by the instantaneous light emission of the light-emitting element to be measured by the afterimage characteristics of the solid-state imaging element. It is best to hold it for a while at
Therefore, since no thermal stress remains in the light emitting element,
In another patent application, we proposed a measuring device that can measure the luminescence percentage at the chip stage (before the casing in the manufacturing process, that is, before the heat sink is applied).

[Problem that the invention seeks to solve]

In the measurement device proposed above, when a solid-state image sensor used in a video camera captures a light emission image of a light-emitting element with a strong emission intensity, such as a laser diode, the light reception level of the solid-state image sensor reaches a saturation region, and the image is captured. The output level of the signal is clipped at the saturation level, and a correct imaging signal proportional to the incident light cannot be obtained.

In order to solve the above problems, for example, the aperture mechanism of the video camera can be narrowed down, but since the light emitting time of the light emitting element for beam measurement in the 6111 measurement device is a short time of about l Q Q n5ec, It is difficult to artificially set an appropriate aperture value, and it is also difficult to correct the light emission characteristics using the aperture value pc.

The present invention is proposed to solve the above-mentioned problems, and is a measuring device for measuring custom-made luminescence using a video camera having a solid-state image sensor, which has a strong level of imaging capability exceeding that of the video camera. The purpose of this study is to obtain a measurement method that can accurately measure the light emission of a light-emitting element that emits light.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a method for capturing an image of the solid-state image sensor when the light reception level of the solid-state image sensor reaches the saturation region of the solid-state image sensor when the instantaneous light emission of the σill constant light emitting element is imaged with a video camera. Measure the time until the image afterimage level of the element leaves the saturation level, and calculate the light emission level of the light emitting element to be measured from this time (when the degree to which the received light level exceeds the saturation level is low), or Estimate the light emitting level of the light emitting element to be measured from the time, calculate an aperture value that will not saturate the solid-state image sensor at that light emitting level, set the aperture mechanism of the video camera to the above aperture value, and then turn the light emitting element to be measured again. A special order for light emission can be obtained by emitting light instantaneously and capturing an image with the video camera (when the above-mentioned light receiving level exceeds the saturation level).

[Configuration of Example]

FIG. 1 is a block diagram showing the configuration of a top 1j fixing device according to an embodiment of the present invention.

As shown in FIG. 1, the measuring device according to the present invention measures the emitted light of a light-emitting element to be measured (hereinafter referred to as a light-emitting element) 1 that emits light at a high level, such as a laser diode.
A video camera 2 that captures an image, a V converter 3 that converts the image signal from the video camera 2 into A/Df, a drive pulse generator 4 that supplies a drive pulse with an extremely short duration (approximately 100 n5ec) to the light emitting element IK, The above video camera 2 and A/
A synchronization signal generator 5 that sends a synchronization signal to the D converter 3 and a drive pulse sending timing signal to the drive pulse generator 4, and a synchronization signal generator 5 that collectively performs various controls and the A/D converter 3. A processing bag f (so-called CP
U) Consists of 6.

The light receiving part of the video camera 2 is provided with an electric aperture mechanism 21 controlled by the processing bag [f6, and the image sensor of the video camera 2 is a solid-state image sensor such as a CCD type or MO8 type image sensor. It is used.

[Effect of the embodiment]

2 is a time chart showing the operation of the embodiment shown in FIG. 1, FIG. 3 is a flowchart showing control by the processing device 6, and FIGS. FIG.

First, the characteristics of the solid-state image sensor will be explained with reference to FIGS. 4 and 5 (B).

The solid-state image sensor is charged with an amount corresponding to the amount of incident light, and outputs an image signal based on the amount of charge on each part of the light-receiving surface. The amount of charge on each part of the light-receiving surface gradually discharges naturally after receiving light, and as long as the charge remains, an image signal can be extracted even if no light is incident. In other words, it has a custom-made afterimage.

By the way, the amount of charge accumulated by a solid-state image sensing device has a limit at which it can be output as an image signal and a limit at which it can no longer be accumulated as a charge. Here, the former is referred to as the saturation level, and the latter is referred to as the charging limit level (see FIG. 5).

If the level of light received by the solid-state image sensor due to light emission from the light-emitting element 1 is equal to or higher than the saturation level, the image signal from the solid-state image sensor is clipped at the saturation level, as shown by the solid line in FIG. An image signal corresponding to the level of light received by light emitted from the element 10 cannot be obtained. However, the level of light received by the video camera 2 can be determined from the discharge characteristics of the charges in the solid-state image sensor, the time until the image signal level exits the saturation region, and K. That is, as shown in FIG. 4, the light reception level t due to light emission from the light emitting element 1 can be determined from the time T taken until the image signal level reaches the point PK, which is indicated by the solid line, at which it leaves the saturation level.

Furthermore, as shown in Figure 5^, when the level of light incident on the solid-state image sensor is above the saturation level but below the charging limit level, the image is output after some time has passed after the solid-state image sensor receives the light. The signal is output while maintaining a constant relationship with the light emission level pattern (shown by the broken line) of the light emitting element 1, as shown by the dashed line. However, as shown in FIG. 5(B), when the level of light incident on the solid-state image sensor is higher than the charging limit level, the image signal outputted after a certain period of time after the solid-state image sensor receives the light is as follows. As shown by the dashed line, a clipped output pattern remains for the S portion that exceeds the charge limit level above Egami, so the emission level pattern (
(indicated by a broken line). however,
The above incident light level is load,! Even if the charge level exceeds the charge limit level, the entire light-receiving surface of the solid-state image sensor will not receive light at a charge charge limit level or above, so the time T shown in FIG.
It is possible to estimate the light emission level of the light emitting element 1 (the level of light incident on the solid-state image sensor) because it changes depending on the magnitude of the light emission level of the light emitting element 1.

In the embodiment of the present invention, the case shown in @5 above and the case shown in Figure 5
The processing method is different from the case shown in ) in the figure.

Next, the operation will be explained with reference to FIGS. 2 and 3.

Note that A to F in FIG. 2 indicate signals output to points with the same symbols in FIG. 1 (C).

As shown in FIG. 2A, the synchronization signal generator 5 sends a synchronization signal to the video camera 2, the A/D converter 3, and the processing device 6 at a set period t. repeats the imaging operation, and the A/D converter 3 synchronizes with the imaging operation of the video camera 2, and the digital signals 4 and 7 send converted image signals to the processing device 6. Further, the camera synchronization signal input to the processing device 6 is used when measuring the change time of the image signal level, which will be described later.

When a measurement start command is input to the processing device 6, the processing device 6 clears the counter as shown in FIG. 3(A) and outputs the shot signals of FIG. The signal is sent to the synchronization signal generator 5.

The above-mentioned counter is a counter (so-called soft counter) according to a program set in the processing device f6 to count camera synchronization signals. The synchronization signal generator 5 sends a drive pulse sending timing signal shown in FIG. 4 outputs a driving pulse with a pulse width t as shown in the second diagram. The pulse width of the driving pulse is 10 Q n
The time is set to be extremely short, about 5 ec, and the light emitting element 1 emits light instantaneously as shown in FIG. 2EK.

The light emitted from the light emitting element 1 is imaged by a video camera 2 as shown in FIG. 3(c). Although the light emitted from the light emitting element 1 is instantaneous, the video camera 2 temporarily retains the captured image by customizing the afterimage of the solid-state image sensor, and the image signal output from the video camera 2 is thereby transmitted to the A/D converter 3. It is converted into a digital signal and input to the processing bag f6.

The processing device 6 processes the image II! When a signal is input, as shown in FIG. to judge.

When the light reception level of the emitted light is at a level that does not reach the saturation level of the solid-state image sensor of the video camera 2, the second
Since the image signal remains in the solid-state imaging probe at a level corresponding to the received light level as shown by the dashed line in FIG. Processes the signal, calculates the luminescence characteristics, and outputs a custom-made luminescence pattern.

When the light receiving level of the emitted light is higher than the saturation level of the solid-state image sensor of the video camera 'f)2, that is, the level shown by the broken line in FIG. Since this is a signal clipped at the saturation level, it is not possible to immediately calculate the light emission characteristics from this image signal. Therefore, the processing device 16 measures the time it takes for the level of the image signal to drop to the saturation level K due to the discharge of the charge caused by the light reception of the solid-state image sensor, that is, the time T explained in FIG. 4, as follows. . That is, as shown in FIG. 3(G), after the video camera 2 receives the light emitted from the light emitting element 1, the camera synchronization signal output from the synchronization signal generator 5 is used to control the counter set in the processing device 6. As shown in Figure 3 (a), the level of the image remaining on the solid-state image sensor is 12!
It is detected whether or not the image level has decreased to the sum level, and this operation is repeated while incrementing the counter until the image level reaches the saturation level.

As a result, if the value of the counter becomes 'n' as shown in Figure 2A, then the time T becomes 'n-
tl".

Next, the processing device 6 determines whether the value n of the counter is greater than or equal to the set value m as shown in FIG. This value is used to determine whether the received light level is equal to or higher than the charging limit level. In other words, if the received light level is high, it takes a long time for the image level to drop to the saturation level, so it can be determined from this time whether the received light level is equal to or higher than the charging limit level. , = mt
, J (see Figure 2A for t).
Just set the value of .

When the value n of the counter is smaller than the set value m, the light receiving state at the solid-state image sensor is as shown in Figure 5, and as described above, the light receiving level is calculated from the image signal remaining in the solid-state image sensor. It can be found by That is, as shown in the partially enlarged view of FIG. 2F, the image signal level t1 at the time of sending the n-th camera synchronization signal is calculated by calculation since the attenuation characteristics of the image signal level maintain a constant relationship. and this image signal level t
The light reception level can be determined from 1 and the counter value n. Based on the above, the processing device 6 corrects the image signal using the counter value n as shown in FIG. and outputs a light emission characteristic pattern.

When the value n of the counter mentioned above is larger than the set value m, the light receiving state K at the solid-state image sensor is the state shown in FIG. It is not possible to calculate the received light level. Therefore, the processing device 6 clears the residual image signal of the solid-state image sensor as shown in FIG. A desired aperture value is calculated, and a signal indicating the aperture value calculated above is sent to the electric aperture mechanism 21 of the video camera 2 as shown in FIG. 2G, as shown in FIG. 3 (B). The electric aperture 81 structure 21 is set to the aperture υ value as described above. After that, Figure 3 (A) explained above
, (0), and H. In the process shown in FIG. 3), the received light level is below the saturation level as shown by FKf in FIG. Proceeding to step (e), the light emission characteristics are calculated and a custom light emission pattern is output. Note that the above-mentioned correction based on the aperture value of the aperture mechanism 21 is added to the calculation of the light emission characteristics at this point.

In the above operation, it is also possible to omit the processing in FIG. The comparison mechanism 21 may be controlled to control the amount of light incident on the solid-state image sensor to be below the saturation level.

Further, in the above embodiments, time measurement was performed based on the camera synchronization signal, but the present invention can also be implemented based on the clock signal of the processing device.

〔Effect of the invention〕

As explained in detail above, the present invention measures the time for the image signal remaining in the solid-state image sensor of a video camera to drop to the saturation level of the solid-state image sensor, and makes corrections based on the time to adjust the received light level. or by setting the aperture value calculated from the time in the aperture mechanism of the video camera to cause the light emitting element to be measured to emit light again to obtain a light emission characteristic pattern. Even if a light-emitting element emits light at a strong level that exceeds its ability, the light emission can be accurately measured, and the application time of the light-emitting power applied to the light-emitting element to be measured can be set to a short time, and the number of times it can be applied is also maximized. The present invention has extremely significant effects, such as the fact that thermal stress does not occur on the light emitting element because it only needs to be applied twice.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a measuring device according to an embodiment of the present invention;
Fig. 2 is an operation time chart of the embodiment shown in Fig. 1, Fig. 3 is a flowchart showing control of the embodiment shown in Fig. 1, Figs. 4 and 5, and a1+) are images of the solid-state image sensor. FIG. 3 is a diagram illustrating custom-made signals. (Main symbols) 1...Light emitting element to be measured 2...Video camera 21
...Electric aperture mechanism 6...Processing device.

Claims (1)

[Scope of Claims] 1. In a measuring device that images the light emission of a light emitting element to be measured using a video camera to obtain the light emitting characteristics of the light emitting element to be measured, a camera having a solid-state imaging device is used as the video camera. When the light emission intensity of the light emitting element to be measured is at a level high enough to saturate the light reception level of the solid-state image sensor within its charge limit, the solid-state image sensor captures an image by instantaneous light emission of the light-emitting element to be measured. A method for measuring light emitting characteristics of a light emitting element, in which the time required for the afterimage level of the image to escape the saturation level is measured, and the light emitting level of the light emitting element to be measured is calculated from this time to obtain the light emitting characteristics. 2. Measurement of the light emitting characteristics of the light emitting element according to claim 1, wherein the time until the afterimage level of the solid-state image sensor leaves the saturation region is measured by counting the imaging synchronization signal of the video camera. method. 3. In a measurement device that uses a video camera to image the light emitted from a light emitting element to be measured to obtain the luminescence characteristics of the light emitting element to be measured, a camera having a solid-state image sensor is used as the video camera, and the light emitting element to be measured is When the light emission intensity of is at a high level that saturates the light reception level of the solid-state image sensor, until the afterimage level of the image of the solid-state image sensor captured by the instantaneous light emission of the device under test exceeds the saturation level. estimating the light emission level of the light emitting element to be measured from this time, calculating an aperture value at which the solid-state image sensor is not saturated at the light emission level, and setting the aperture mechanism of the video camera to the aperture value. A custom light emitting measurement method for a light emitting element in which the light emitting element to be measured is then momentarily caused to emit light again and the light emitting characteristics are obtained by capturing an image with the video camera. 4. Measurement of the light emitting characteristics of the light emitting device according to claim 3, wherein the time until the afterimage level of the solid-state image pickup device exits the saturation region is measured by counting the imaging synchronization signal of the video camera. method.