JP2567908Y2 - Light sensor - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the amount of light, such as an optical power meter, and more particularly to a light amount sensor capable of measuring a high dynamic range from weak light to large light.

[0002]

2. Description of the Related Art There are two types of conventional light quantity sensors, a high sensitivity type capable of measuring weak light and a low sensitivity type capable of measuring large light quantity. The former high-sensitivity type includes photon counting (hereinafter simply referred to as PC).
Type photomultiplier tube, avalanche photodiode, and the like. The latter low-sensitivity type includes P
There are an IN photodiode and an analog photometry type photomultiplier tube.

[0003] Among the high sensitivity types, the PC method measures a photon (photon) one by one, and therefore has a higher S than that of the analog photometry method in the ultra-low light range.
/ N ratio can be measured. In the PC method, in general light quantity measurement, many photons fall on the photocathode at once, and the output pulses of the photomultiplier tube overlap and become a fluctuating DC. As the light incident on the photomultiplier tube is reduced, the intervals between the output pulses increase, and finally the output pulses become discrete pulses. In such a state, counting the number of pulses enables more advantageous light quantity measurement in terms of S / N and stability than performing current measurement by averaging discrete pulses. The light quantity measurement by this pulse count is a PC method. On the other hand, the low-sensitivity type has a good S / N ratio when measuring a large amount of light because the output signal is measured by an analog value.

[0004]

However, the PC system has a drawback that the output is saturated when the amount of light is large because of high sensitivity. In addition, the analog photometry method has a problem that the S / N ratio in a weak light range is not as good as that of the PC method.

The present invention has been made in view of the above-mentioned problems of the prior art. By combining a light amount sensor suitable for a large light amount and a light amount sensor suitable for a weak light region, a wide range from a weak light amount to a large light amount is obtained. It is an object of the present invention to provide a light quantity sensor capable of measuring an area with good S / N.

In particular, as this combination method, the amount of light is obtained by calculating the output of both the analog photometry system and the weak photometry (PC) system.

[0007]

In order to solve the above-mentioned problems, a light quantity sensor according to the present invention has one or more light receiving elements, a PC signal processing circuit for processing an output signal from the light receiving elements, and an analog signal. A photometric signal processing circuit, two correction circuits for correcting the outputs of the two signal processing circuits, two weight calculation circuits for multiplying the outputs of the two correction circuits by weights, and the outputs of the two weight calculation circuits, respectively. And a signal operation circuit comprising an addition circuit for addition.

[0008]

Since two photometric methods, the PC method and the analog photometric method, can be used, the light quantity can be measured with good S / N from the weak light area to the large light quantity area.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the light quantity sensor of the present invention. In FIG. 1, reference numeral 1 denotes a light receiving element that receives a signal light and converts the signal light into an electric signal, 2 denotes a PC signal processing circuit that processes an output signal from the light receiving element 1, and 3 similarly processes an output signal from the light receiving element 1. Analog photometric signal processing circuit. 4
Is a signal arithmetic circuit to which the outputs of the PC signal processing circuit 2 and the analog photometric signal processing circuit 3 are input to determine the light quantity;
The configuration includes correction circuits 41 a and 41 for correcting the outputs of the PC signal processing circuit 2 and the analog photometric signal processing circuit 3.
b, weight calculation circuits 42a and 42b for multiplying outputs of the correction circuits 41a and 41b by weight, and weight calculation circuits 42a and 42b
And an addition circuit 43 for adding the outputs of Note that the weights of the weight calculation circuits 42a and 42b are controlled by the magnitude of the output of the analog photometric signal processing circuit 3.

Here, as described above, the PC method is a method of measuring the number of discrete pulses corresponding to each photon. Therefore, when measuring extremely weak light, the S / N is good. on the other hand,
When the light intensity increases, the pulses overlap each other,
Since it becomes a superimposed pulse, it becomes impossible to measure each pulse individually, so that it is possible to measure the output DC component with better S / N than the PC method. This relationship is shown in FIG.
(A) and (b).

In such a configuration, returning to FIG. 1, upon receiving the signal light, the light receiving element 1 outputs a discrete pulse in the case of weak light and a superimposed pulse in the case of a large amount of light. The output of the light receiving element 1 is input to a PC signal processing circuit 2 and an analog photometric signal processing circuit 3,
Outputs a pulse count number, and the analog photometric signal processing circuit 3 outputs a DC component of the light receiving element 1. The output-incident light amount and output-S / N characteristics at this time are shown in FIG.
The relationship shown in (a) and (b) is obtained.

Next, both outputs are input to the signal operation circuit 4. The correction circuits 41a and 41b in the signal operation circuit 4
PC signal processing circuit 2 and analog photometric signal processing circuit 3
If the characteristics opposite to the light amount-output characteristics are provided, the outputs of the correction circuits 41a and 41b become linear with respect to the incident light amount. In this case, there is no change in the light amount-S / N ratio characteristics.

When the output of the analog photometric signal processing circuit 3 is input to the control terminals of the weight calculation circuits 42a and 42b and a value larger than a threshold value is input to the weight calculation circuits 42a and 42b, the weight calculation circuit 42b Is set to 1 and
Otherwise, it is set to 0. Also, the weight calculation circuit 42
a is 1 when the value is smaller than the threshold value, and 0 otherwise.
The output will be as shown in Fig. 3,
The output (output-light quantity characteristic) of the addition circuit 43 is linear, and the S / N is good at any light quantity.

As described above, according to the above-described embodiment, the light amount is obtained by calculating the outputs of both the analog light metering system which is a light amount sensor suitable for a large light amount and the PC system which is a light amount sensor for a weak light region. Thus, a wide range from weak light to large light can be measured with good S / N.

In the above embodiment, the light receiving elements of the PC method and the analog photometry method are shared. However, as shown in FIG. 4, the PC method and the analog photometry method have separate light receiving elements.
The distribution of light to both may be performed by a light distributor 5 such as a beam splitter or a half mirror. However, in this case, it is assumed that the wavelength dependence and the polarization dependence of the distribution ratio of the beam splitter, the half mirror, and the like are known, and the optical distributor can be removed. The optical path to the light receiving element of the PC method and the optical path to the light receiving element of the analog photometry method may be switched by a mirror (the switching time interval is variable). Further, the light receiving element may have a plurality of light receiving elements of the PC method and a plurality of light receiving elements of the analog photometry method, both of which may be randomly arranged on the same plane. Further, a configuration having a plurality of correction functions of the PC signal processing circuit 2 may be employed. However, the correction function is switched according to the magnitude of the output of the analog photometric signal processing circuit. Furthermore, the weights generated by the weight calculation circuits 42a and 42b may be of a function type that continuously changes with respect to the output of the analog photometric signal processing circuit. In any of the configurations, a wide area from weak light to large light quantity is obtained. S / N
Can measure well.

[0016]

As described above in detail with the embodiments, according to the present invention, both the PC method and the analog photometry method can be used. A light amount sensor capable of measuring a light amount in a high dynamic range can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a light quantity sensor of the present invention.

FIG. 2 is a diagram showing a relationship between incident light quantity-output and incident light quantity-S / N ratio.

FIG. 3 is a diagram showing an input / output relationship of a signal calculation circuit of the light quantity sensor according to the present invention.

FIG. 4 is a configuration diagram showing another embodiment of the light amount sensor of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light receiving element 2 photon counting (PC) signal processing circuit 3 analog photometric signal processing circuit 4 signal calculation circuit 41 a, 41 b correction circuit 42 a, 42 b weight calculation circuit 43 addition circuit

Claims (1)

(57) [Scope of request for utility model registration] 1. One or a plurality of light receiving elements, a photon counting signal processing circuit and an analog photometric signal processing circuit for processing an output signal from the light receiving element, and correcting the outputs of these two signal processing circuits, respectively.
A signal operation circuit including two correction circuits, two weight operation circuits for multiplying the outputs of the two correction circuits by respective weights, and an addition circuit for adding the outputs of the two weight operation circuits. Characteristic light intensity sensor.