JPH0754823Y2 - Light intensity measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention relates to a light intensity measuring device suitable for measuring the light intensity, particularly the average intensity of pulse-modulated light, by an optical power meter, an optical spectrum analyzer or the like.

“Prior Art” A conventional light intensity measuring device is provided with a light receiving element 11 as shown in FIG.
The light incident on is converted into a current, the current is converted into a voltage by the current-voltage converter 12, and the converted voltage is amplified by a variable gain amplifier, so-called ranging amplifier 13,
The amplified output is converted into a digital signal by the AD converter 14,
The digital signal is input to the controller 15 composed of a CPU,
It is displayed on the display 16 via the controller 15. In this case, the output of the variable gain amplifier 13 is within a predetermined range, that is, the AD converter.
The controller 15 controls the gain of the variable gain amplifier 13, so-called range, or the conversion of the current-voltage converter 12 so that 14 does not saturate and its converted digital signal falls within the display range of the display 16. Change control gain. In this way, control is performed so that the maximum range (gain) is achieved in a range that does not saturate according to the intensity of incident light.

When the input light is an optical pulse, for example, the output of the variable gain amplifier 13 corresponds to the input pulse light as shown in FIG.
As shown in FIG. B, and when the sampling in the AD converter 14 for this is as shown in FIG. 7C, when the sampling coincides with the incidence of the optical pulse, the digital signal corresponding to the optical power is changed. Although it is obtained as shown in FIG. 7D, at the time of sampling which does not coincide with the incident pulse, the output becomes zero and a dropout occurs. Also, the converted digital signal based on the sampling that does not match this optical pulse is the controller.
When it is input to 15, the controller 15 determines that the intensity of the input light is small and operates to increase the gain of the variable gain amplifier 13. Therefore, when the input pulsed light and the sampling match, the variable gain amplifier 13 and the AD converter 14 may be saturated by the input pulsed light. In any case, the measured value varies depending on whether the input light pulse and the sampling match or not, and the gain (range) switching of the variable gain amplifier 13 may not converge forever.

In order to solve these problems, in the past, as shown in FIG. 8, a low pass wave filter 17 was inserted in series between the variable gain amplifier 13 and the AD converter 14. The time constant of the low pass wave filter 17 is set sufficiently longer than the sampling interval of the AD converter 14. In this way, the AD converter 14
Does not occur, and the problem of non-convergence of range switching does not occur. However, when the duty ratio of the input optical pulse is small, the output level of the low pass wave filter 17 becomes small even if the peak value of the optical pulse is large, and as shown in FIG. The controller 15 operates so as to increase the gain of the variable gain amplifier 13, and even in the extreme case, even if it is set to the maximum gain, the output of the low pass wave filter 17 does not reach the overrange threshold value. In this case, the output pulse of the variable gain amplifier (ranging amplifier) 13 is saturated due to the optical pulse, and the output pulse is assumed to be saturated in the variable gain amplifier 13 as shown in FIG. 9B. The level is too low to measure correctly.

[Means for Solving the Problem] According to this invention, the output current of the light receiving element is first integrated by the integrator, and the integrated output is amplified by the variable gain amplifier. The amplified output is periodically converted into a digital signal by the AD converter. In synchronization with this conversion cycle, the output of the integrator is discharged immediately after the conversion. The controller switches the gain of the variable gain amplifier according to the magnitude of the output digital signal of the AD converter so that the digital signal falls within a predetermined range.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 6 are designated by the same reference numerals. In this invention, the output current of the light receiving element 11 is first integrated by the integrator 18, the integrated output is amplified by the variable gain amplifier 13, and the amplified output is periodically converted into a digital signal by the AD converter 14. According to the magnitude of the digital signal, the controller 15 controls the variable gain amplifier.
Gain of 13 is controlled. The integrated output of the integrator 18 is discharged in synchronization with the conversion cycle of the AD converter 14. That is, the integrator 18 is discharged immediately after conversion into a digital signal. Therefore, the controller 15 issues a conversion command to the AD converter 14, and the integrator 18
Issue a discharge control signal. Alternatively, when the AD converter 14 itself is performing conversion periodically, a signal indicating the conversion time point (sampling time point) is given to the controller 15, and based on this, the discharge controller signal is output To do. Further, in this example, the gain of the integrator 18 can be changed, and the gain can be changed by the controller 15 as necessary.

Such an integrator 18 is constructed, for example, as shown in FIG. That is, the light receiving element 11 is connected to the inverting input terminal of the operational amplifier 19.
The one end of the connection, the non-inverting input of the operational amplifier 19 is grounded, and each one end of the capacitor C ₁ -C _n is connected to the inverting input terminal, the other end of the capacitor C ₁ -C _n switches 21 Is switched and connected to the output terminal of the operational amplifier 19. In addition, a reset switch is provided between the inverting input terminal and the output terminal of the operational amplifier 19.
22 is connected. The switch 21 is switch-controlled by a range switching signal. The amount of charge charged in the capacitor to which the switch 21 is connected by one input light pulse is determined by the peak value and width and the conversion efficiency of the light receiving element 11, so that the output digital signal of the AD converter 14 is predetermined, for example. If the value is less than the value, the switch 21 is switched and connected to a capacitor having a smaller capacity than the currently connected capacitor to increase the integrated output voltage, that is, the gain. The reset switch 22 is turned on by the discharge control signal and the capacitor C ₁ ~
Discharge the charge of C _n .

According to this configuration, for example, when an optical pulse is input as shown in FIG. 3A, the integrated voltage proportional to the peak value and the width of each optical pulse increases as shown in FIG. 3B. This integrated output is amplified by the variable gain amplifier 13, and the amplified output is periodically converted into a digital signal by the AD converter 14 at the timing shown in FIG. 3C, and the controller 15 according to the magnitude of the digital signal. Indicates that the digital signal has a predetermined range, that is, the displayable range on the display 16, the AD converter 14
Variable gain amplifier to enter the smaller conversion range
The gain of 13 or the gain of the integrator 18, the integration time T ₁ of the integrator 18, or a plurality of these are controlled simultaneously. AD
Immediately after the conversion in the converter 14, a discharge control signal is issued as shown in FIG. 3D, and the integrated output of the integrator 18 is discharged to zero.

As described above, in the present invention, the output of the light receiving element 11 is immediately averaged and supplied to the variable gain amplifier 13, so that there is no problem that the variable gain amplifier 13 is saturated at the peak of the pulse, and the optical pulse with a small duty ratio is eliminated. But it can be measured correctly.

The output of the AD converter 14 may be directly supplied to the display 16.
As shown in FIG. 4, _one of the capacitors C _{1 to} C _n is switched between the inverting input terminal and the output terminal of the operational amplifier 19 by the switch 21, or the switch R 21 connects the resistors R _{1 to} R _m. When the input light is continuous light, the switch 21 is connected to any _one of the resistors R _{1 to} R _m and the integrator 18 is used as a current-voltage converter. It may be used. The continuous light may be measured by connecting the switch 21 to any of the capacitors C _{1 to} C _m . Integrator
18 is not limited to the feedback type shown in FIG. 2, but may be the voltage amplification type shown in FIG. 5, for example. The integrator 18 may have a fixed gain.

[Advantage of Device] As described above, according to this device, since the output of the light receiving element is immediately integrated, when an optical pulse is input, it is immediately averaged, and the averaged output is sent to the variable gain amplifier 13. Since it is supplied, it is possible to correctly measure even an optical pulse having a small duty ratio.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a connection diagram showing a concrete example of the integrator 18, FIG. 3 is a time chart showing an operation example of FIG. 1, and FIG. FIG. 5 is a connection diagram showing an example in which the integrator 18 can also be used as a current-voltage converter, FIG. 5 is a connection diagram showing another example of the integrator 18, and FIG. 6 is a block diagram showing a conventional light intensity measuring device. , FIG. 7 shows the sixth
FIG. 8 is a time chart for explaining problems in measuring an optical pulse with the device shown in FIG. 8, FIG. 8 is a block diagram showing a conventional device which solves the problem of the device shown in FIG. 6, and FIG. 9 is FIG. 3 is a time chart for explaining a problem of the device of FIG.

Claims (1)

[Scope of utility model registration request] 1. A light-receiving element that converts input light into a current, an integrator that integrates the output current of the light-receiving element, the integrated output is periodically discharged, and the integrated output of the integrator is amplified, A variable gain amplifier that can change its gain, an AD converter that converts the output of the variable gain amplifier into a digital signal immediately before each discharge, and the output digital signal of the AD converter is input, A light intensity measurement comprising: a controller that controls the gain of the variable gain amplifier according to the magnitude so that the digital signal falls within a predetermined range; and a display that displays the output of the AD converter. apparatus.