JPS63127127A - Light power measuring device - Google Patents

Abstract

PURPOSE:To measure the light power of laser at a low power level with high accuracy without using an auxiliary wavelength measuring means, by using a specific formula on the basis of the respective output signals of two light receivers. CONSTITUTION:A part of the light emitted from a light source 1 to be measured passes through an aperture 2 at first and impinges against a pervious diffusion plate 3 to be diffused. A part of the diffused light passes through a glass filter 4 to reach a silicon photodiode 6 and the other part of the diffused light passes through a glass filter 5 to reach a silicon photodiode 7. The photocurrents generated in the photodiodes 6, 7 are amplified by operational amplifiers 9, 10. Next, a microcomputer 13 controls an analogue switch 11 and an A/D converter 12 to calculate the output signal Sa of a light receiver 6 of which the absolute spectral sensitivity Ra(lambda) is shown by a formula Ra(lambda)=alambda+b and the output signal Sb of a light receiver 7 of which the absolute spectral sensitivity Rb(lambda) is shown by a formula Rb(lambda)=clambda+d and, from the respective signals Sa, Sb, the sum total of incident powers can be calculated. In the formulae, a-d are coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a measuring device for measuring the optical radiation power of lasers, LEDs, various light sources for illumination, and the like.

BACKGROUND OF THE INVENTION Conventional optical power measuring instruments use thermal detectors with no wavelength selectivity in sensitivity as standard equipment.

In addition, as a practical measuring instrument, a quantum detector, such as a silicon photodiode or PbS, which is wavelength selective but has higher sensitivity, is used to limit the wavelength to be measured to a narrow range and to obtain a practical radiation power. are being measured.

Problems to be Solved by the Invention As mentioned above, thermal detectors without wavelength selectivity have low sensitivity, require a chopper for AC operation, and require a lock-in amplifier when measuring low-level radiation. It is difficult to handle and is used as a calibration standard in the laboratory or for measuring high power density light such as lasers, but it is extremely difficult to measure light sources with low optical power. On the other hand, highly sensitive quantum photodetectors such as silicon photodiodes have great wavelength selectivity in their sensitivity, so when the target is an emission line spectrum with a known wavelength, such as a laser beam, measurement is performed based on the value of that wavelength. Relatively high accuracy can be obtained by correcting the values. However, there are LEDs and light sources for lighting that have a wide emission spectrum, and ffl#J whose wavelength cannot be determined! There is no way to correct the measured value of spectral radiation other than by measuring its spectral distribution, and it has been difficult to perform highly accurate measurements for such light sources.

Another method is to flatten the relative spectral sensitivity by applying an optical filter to the quantum photodetector, but it is extremely difficult to obtain a highly accurate flat spectral sensitivity, and it is difficult to obtain a highly accurate flat spectral sensitivity over a wide wavelength range. There was no practical way to measure the low radiated power of.

Means for Solving the Problems The present invention solves the above problems, and uses a quantum photodetector whose spectral sensitivity is not flat but has high sensitivity. The purpose of the present invention is to provide an optical power measuring device that can measure the radiation power or the power of a laser beam that is a mixture of several emission lines with high precision and at a low optical power level without the need for auxiliary wavelength measurement means. do.

The present invention uses two light receivers whose spectral responsivity changes linearly with wavelength by a combination of a highly sensitive light receiving element such as a silicon photodiode and an optical filter, and whose spectral responsivity is assigned a value of absolute spectral responsivity. and an arithmetic unit that performs the following operations.

Hereinafter, a method of measuring the radiation power of a light source having a continuous spectral distribution using two light receivers having the above-mentioned characteristics will be described. Since radiation from a light source with a continuous spectral distribution can be considered as a collection of many emission lines, first consider the case of finding the total power of two ya lines whose wavelengths are unknown.

Now, if these two light receivers are called light receiver A and light receiver B, the absolute spectral responsivity of each light receiver Ra (λ), R
b(λ) is Ra(λ)=aλ+b・・・・・・・・・・・・・・・
(1) Rb(λ)=cλ+d (a-#e)...
...It is expressed as (2). Next, as shown in Figure 3,
The wavelength is λ1. λ2, two v with radiation power Pl and P2
When the I-line beam is received by receiver A and receiver B, the output signals Sa and Sb of each receiver are as follows: Sa = pt Ra (λ1) + P2 Ra (λ2) ・
・(3) Sb = PI Rb (λ+) + P 2 R
b(λ2)...(4) is expressed. Also, Ra(λ)?
Since Rb(λ) is a straight line, P between input and input is
There is a barycenter wavelength λX expressed by the following equation depending on the ratio of l and P2.

λX2 λ1+P2 (λ2-λ1)/(P1+22)...
(5) Expanding and rearranging equations (3) and (4), we get (5)
What are λ1 and λ2 from the relationship in the formula? Sa = (P1 + P2) (aλx + b) - (8) Sb
==(P1+P2)(Cλ×10d)・・・・・・(7
) is obtained. Equations (6) and (7) can be calculated from the total amount of incident power p, +p2 from the output signal Sa or sb if λX is known.
It shows that this is required. However, λ1,
Since each of λ2, PL, and P2 is unknown, λX cannot be determined using equation (5). Therefore, take the ratio k of the photoreceiver output SaX Sb, k=5a/Sb ・・・・・・・・・・・・・・・・・・
...If defined as (8), then from equations (6) and (7), k
= (aλx + b) / (Cλx + d) ... (9)
So, by transforming this formula, λx=(kd-b)/(a-kc)...(1
0) is obtained, and λX can be derived from the ratio k of the photoreceiver outputs. Once λX is found, using equation (6), P1+P
2=Ba/{aλx +b)=Sa/(a(d-3
a/5b-b) (ac-5a/Sb) persimmon) (11)
is obtained, and the total incident power can be determined from the readings of the output signals Sa and Sb of each photoreceiver without having to know the individual values of Pl, P2, λ1, and λ2.

According to the above calculation, two bright lines with wavelengths λ2 and λ2 can be replaced with one bright line with a center-of-gravity wavelength X, without changing the total power and the output current of each photoreceiver. If another emission line λ3 is added to this convergence, the same calculation can be performed to replace it with one emission line without changing the total power and output current of the receiver, and the center of gravity wavelength λ ×° corresponds to the centroid wavelength determined from the ratio of output currents when the bright lines of λ1, λ2, and input 3 are incident on each photoreceiver. Therefore, even when there are many bright lines, the center wavelength λ
= is replaced by one bright line, and the incident power can be determined. Furthermore, since a light source with a continuously changing spectral distribution can be considered as a collection of many bright lines, the power of the incident light can be determined using the same principle.

As described above, by using two photoreceivers whose spectral sensitivity changes linearly with respect to wavelength and whose absolute spectral sensitivity values are assigned, the radiation of incident light can be determined from the reading of the output signal of each photoreceiver. A method for determining the total amount of power can be realized.

The present invention measures the spectral distribution of the incident light and the wavelength of the emission line from the reading of the output of each receiver by sequentially performing measurements using two receivers that combine a highly sensitive quantum photodetector and an optical filter. The absolute value of incident power can be easily and accurately measured without needing to know it.

Embodiment FIG. 1 shows the configuration of an optical system of an optical power measuring instrument in an embodiment of the present invention, in which 1 is a light source to be measured, 2 is an aperture, 3 is a transmission diffusion plate, 4 and 5 are glass filters,
6 and 7 are silicon photodiodes. It is assumed that the light source 1 to be measured is a light source such as an illumination lamp or a laser, and has an emission spectrum in the range of λ1 to λ2.

FIG. 2 shows the configuration of the circuit portion of the embodiment of the present invention, in which 6 and 7 are silicon photodiodes, 9 and 10 are operational amplifiers, 11 is an analog switch, and 12 is an analog switch.
/D converter, 13 is a microcomputer.

FIG. 4 shows a schematic flowchart of the program of the microcomputer 13.

In FIG. 1, a portion of light emitted from a light source to be measured 1 first passes through an aperture 2, hits a transmission diffusion plate 3, and is then diffused. A part of the diffused light passes through the glass filter 4 and reaches the silicon photodiode 6, and another part of the diffused light passes through the glass filter 5 and reaches the silicon photodiode 7. Therefore, a fixed proportion of the light flux that has passed through the aperture 2 always enters the front surfaces of the glass filters 4 and 5, respectively. That is, the aperture 2, the transmission diffusion plate 3, the glass filter 4, and the silicon photodiode 6 form the light receiver A, and the aperture 2, the transmission diffusion plate 3, the glass filter 5, and the silicon photodiode 7 form the light receiver B. There is.

When the glass filter 4 is combined with the silicon photodiode 6, the transmittance is adjusted so that the spectral sensitivity changes linearly in the range from λ1 to λ2. This adjustment is performed by combining several glass filters, but since the spectral sensitivity curve of a silicon photodiode is originally close to a straight line, it can be achieved relatively easily. Similarly, the transmittance of the glass filter 5 is adjusted so that the spectral sensitivity varies linearly in the range from λ1 to λ2. However, the glass filter 5 is selected so that the slope of the straight line of spectral sensitivity differs from that of the glass filter 4 as much as possible. Adjustment of the transmittance of the filter in this case is also much easier than in the case of flattening the spectral sensitivity, since an appropriate slope of the straight line can be selected.

Once the filter has been decided, a standard light bulb is placed in place of the light source 1 to be measured while it is fixed in a predetermined position and turned on, and the absolute sensitivity (A/ W), and the coefficient a in equations 1 and 2.

Find b, c, and d.

Next, in FIG. 2, the silicon photodiode 6
The photocurrent generated at and 7 is converted into a current voltage by an operational amplifier 9.10. The microcomputer 13 is
The analog switch 11 and the A/D converter 12 are controlled to output the output signal S as shown in the flowchart shown in FIG.
Take in a, 5b (3 formulas, 4 formulas), and calculate the ratio k of the receiver output.
The barycenter wavelength λx (formula 10) is obtained from (formula 8), and the incident power (formula 11) is calculated from the value of Sa and λX and displayed.

If the light source 1 to be measured has a beam narrower than the aperture 2, such as a laser beam, P represents the power of the incident light beam itself. If the light source 1 to be measured is a type of light source that diffuses and emits light, such as a light bulb, then P divided by the area of the aperture 2 represents the irradiance (W/m2).

Effects of the Invention The optical power measuring device of the present invention uses a photodetector such as a silicon photodiode that is highly sensitive but has wavelength selectivity, and can measure a wide wavelength range without the need to know the spectral distribution of the incident light. The present invention provides an optical power measuring instrument that can easily measure the power of optical radiation in the area, has high sensitivity, high measurement accuracy, and a wide range of uses, and its practicality is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical system of an optical power measuring device in an embodiment of the present invention, and FIG. 2 is a configuration diagram of a circuit portion of the same measuring device.
FIG. 3 is a spectral sensitivity characteristic diagram of two light receivers used in the present invention, and FIG. 4 is a flowchart of a program of the microcomputer of the same measuring instrument. 1... Light source to be measured 2... Aperture 3...
・Transmission diffuser plate 4.5...Glass filter 6.7
... Silicon photodiode 9.10 ... Operational amplifier 11 ... Analog switch 12 ... A/D converter 13 ... Microcomputer Name of agent Patent attorney Toshio Nakao Idiot 1 Figure 1 Figure 2 IO calculation and gambling Figure 3 C A2 No 3 Figure 4

Claims (1)

[Claims] Absolute spectral sensitivity Ra(λ) is approximately Ra(λ)=aλ+
The photoreceiver A is expressed by the formula b, and the absolute spectral sensitivity Rb(λ
) is approximately defined by the formula Rb(λ)=cλ+d, and the output signal Sa of each of the photodetectors A and B,
From Sb, P=Ba/{a(d・Sa/Sb−b)/(a
-c.Sa/Sb)+b}; and an arithmetic unit that calculates the incident radiation power P using the formula: -c.Sa/Sb)+b}.