JP2548733Y2 - Optical power measurement device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical power measuring device for measuring optical power of laser light or the like.
The present invention relates to an optical power measuring apparatus for preventing output fluctuation caused by atmospheric pressure fluctuation when measuring laser power of about several tens of μW.

[0002]

2. Description of the Related Art FIG.
Is known. In the drawing, reference numeral 1 denotes a photoreceptor, and a cylindrical body 3 having an inner surface coated with a light absorbing paint 2.
And a heat transfer plate 1a in which a heater 4 is embedded.
5, 5a are temperature difference detecting elements, 7 is a thermoelectric cooling element, and these elements are formed by Peltier elements having equivalent performance.
It is fixed while being sandwiched between the heat transfer plate 1a and the temperature reference jacket 10. 8 is a temperature difference detecting element 5, 5a and heater 4
Feedback amplifier connected to the
11 and a main amplifier 12 having a PID control function. 9 is a constant current source connected to the thermoelectric cooling element.

FIG. 8 is a sectional view of a jacket for accommodating the optical power measuring device 15 shown in FIG. 7, in which a second jacket 22 and a temperature reference jacket 10 are arranged inside a first jacket 21 via an air layer. ing. The heat capacity of the heat transfer plate 1a including the cylindrical body 3 and the heat capacity of the temperature reference jacket 10 are, for example, about 1: 1000, and are larger in the temperature reference jacket. Reference numeral 23 denotes an optical path for guiding the laser light La from the outside to the photoreceptor 1 of the optical power measuring device.

In the above configuration, the temperature reference jacket 10 is at room temperature, and the thermoelectric cooling element 7 cools the heat transfer plate 1a side by the output from the constant current source 9. In this case, the temperature reference jacket 10 is heated, but the heat capacity of the temperature reference jacket 10 is large, and the heating amount of the heat transfer cooling element 7 is small, so that the temperature of the temperature reference jacket 10 is increased. Does not reach. Therefore, in this state, the temperature on the temperature reference jacket 10 side is high and the temperature on the light receiving body 1 side is low. The temperature difference detecting elements 5 and 5a detect this temperature difference and heat the heater 4 via the feedback amplifier 8. As a result, the temperature of the photoreceptor 1 is always maintained at the temperature of the temperature reference jacket 10, and the feedback amplifier 8 always outputs a predetermined electric signal (PHi).

Next, when the laser beam La to be measured enters from the upper part of the cylinder 3, the photoreceptor 1 absorbs the light, and its light power
The temperature rises accordingly. The heat is conducted to the heat transfer plate 1a,
A temperature difference occurs between the heat transfer plate 1a and the temperature reference jacket 10. The temperature difference is detected by the temperature difference detecting elements 5 and 5a, and the feedback amplifier 8 controls the electric signal sent to the heater in the negative direction to lower the temperature of the heater and to conduct heat transfer. Board
1a and the temperature of the temperature reference jacket 10 are controlled to be constant. Assuming that the electric signal at this time is PHf, the change in the output of the feedback amplifier 8 before and after the light irradiation is (PHi−PH
f) When the laser light power and the replacement ratio of the change are E, the laser light optical power Pa becomes Pa = E (PHi
−PHf).

Here, in the above-mentioned optical power measuring device, when the pressure of the atmosphere fluctuates, the pressure in the temperature reference jacket 10 also fluctuates via the optical path 23. As a result, the air in the reference jacket is compressed or expanded, and the temperature inside it rises or falls.
To 0.3 mm H ₂ has O about changes, temperature changes from 0.01 to temperature references the jacket based on the change in atmospheric pressure 0.0
It is considered to be around 01 ° C). Incidentally, as described above, the heat capacity of the heat transfer plate 1a including the cylindrical body 3 and the temperature reference jacket 10a
Has a large difference in heat capacity, the degree of change following the temperature change is different. That is, the temperature change (ΔT) of the heat transfer plate 1a is large and the temperature change (Δt) of the temperature reference jacket 10 is small. This causes a decrease in accuracy in an optical power measuring device that measures optical power from a change in an electric signal supplied to a heater after maintaining a temperature balance.

Therefore, it is conceivable to solve the above-mentioned problem caused by the fluctuation of the atmospheric pressure by adopting the configuration shown in FIG. FIG. 9 will be described. In FIG. 9, the light-receiving absorber 30 includes the cylindrical body 3 described in FIG. 7, the heat transfer plate 1a,
This is a portion composed of the temperature difference detecting elements 5 and 5a, the thermoelectric cooling element 7, and the temperature reference jacket 10. The light-receiving absorber 30 is irradiated with a laser beam to be measured. This figure 9
The device has a configuration in which a compensation absorber 31 is newly provided in addition to the configuration described with reference to FIGS. This compensating absorber 31
Has the same configuration as the above-described light-receiving absorber 30, but the compensation absorber 31 is not irradiated with laser light.
The temperature difference detecting element 5 provided in the compensating absorber 31
9 and the outputs of the temperature difference detecting elements 5 and 5a provided in the light-receiving absorber 30 are differentially extracted as shown in FIG. 9, and based on this differential signal, feedback is performed in the same manner as in FIG. It is intended to be applied. Here, assuming that the atmospheric pressure is in a constant state, the temperature reference jacket 10, the light receiving absorber 30, and the compensating absorber 31 are maintained at room temperature.

Prior to the measurement, a current is applied from the constant current source to the cooling element 7 of the light-receiving absorber 30 in a state where laser light is not incident, thereby cooling the heat transfer plate 1a, and the temperature difference from the temperature reference jacket 10. Set the initial balance state by supplying current to the heater so that no error occurs. At this time, the outputs from the temperature difference detectors 5 'and 5a' of the compensating absorber 31 are 0 (because it is assumed that there is no change in the atmospheric pressure). Next, when the laser beam La to be measured is incident on the light-receiving absorber 30, a temperature difference is generated between the heat transfer plate 1a and the temperature reference jacket 10 as described above. This temperature difference is detected by the temperature difference detecting elements 5 and 5a of the light-receiving absorber 30, and the temperature difference detecting elements 5 'and 5a' of the compensating absorber 31, and based on the electric signals, the feedback amplifier 8 The electric signal sent to the heater is controlled in the negative direction to lower the heater temperature, and the temperature of the heat transfer plate 1a and the temperature reference jacket 10 is controlled to be constant.

Then, when the pressure fluctuation occurs, the compensating absorber
If there is no 31, temperature-based jacket based on atmospheric pressure fluctuation
As described above, the output of the preamplifier 11 fluctuates due to a temperature change in the output 10, but the output of the preamplifier 11 does not fluctuate in FIG. The reason will be described. In FIG.
In the vicinity of the light receiving absorber 30, a compensating absorber 31 equivalent to the absorber 30 is provided, and the temperature difference detecting element is provided.
The polarities of 5 'and 5a' are connected in series with the polarities of the temperature difference detecting elements 5 and 5a of the light-receiving absorber 30 in the opposite direction. Since the compensating absorber 31 has the same shape as the light receiving absorber 30,
The temperature fluctuation of the same value as that of the light-receiving absorber 30 based on the atmospheric pressure fluctuation also occurs in the compensating absorber 31, and the temperature difference detecting elements 5 ′, 5 a ′ output signals of substantially the same fluctuation values as 5, 5 a. Is done. Since the temperature difference detecting elements 5, 5a and 5 ', 5a' are differentially connected, the preamplifier 11
A signal is output in which the fluctuation of the output signal caused by the atmospheric pressure fluctuation generated in 30 and 31 is canceled.

That is, assuming that the output of the isothermal control for the laser beam in the light-receiving absorber 30 is Vt and the fluctuation due to the atmospheric pressure fluctuation is Vd1, the temperature difference detecting element 5 of the light-receiving absorber 30
The output VT1 of 5a is VT1 = Vt + Vd1. Further, assuming that the output fluctuation due to the atmospheric pressure fluctuation in the compensating absorber 31 is Vd2, the output VT2 of the temperature difference detecting elements 5 ', 5a' of the compensating absorber 31 is VT2 = Vd2. Therefore, the input V _in to the pre-amplifier is the _{V in = VT1-VT2 = Vt} + (Vd1-Vd2). Here compensating absorber 31 are the same shape as the light receiving absorber 30, it is possible to prevent V _in = Vt becomes so can be regarded as Vd1-Vd2 = 0, the output variation due to pressure variation.

[0011]

However, in the apparatus shown in FIG. 9, the structures of the light-receiving absorber 30 and the compensating absorber 31 are the same, so that the following problem arises. If there is a fluctuation in the atmospheric pressure, in order to make the sensitivity of the pressure fluctuation of the compensation absorber 31 the same as that of the light absorber 30,
Both have the same shape. In other words, the compensating absorber 31 is also provided with a thermoelectric cooling element. However, the thermoelectric cooling element provided in the compensating absorber 31 does not perform the original cooling function at all, and is merely provided, thereby lowering the price efficiency as a product. The light-receiving absorber 30 must have a large shape to cope with a laser beam having a large power. Therefore, in this case, the shape of the compensating absorber 31 also becomes large. However, it is difficult to store two large absorbers in the temperature reference jacket 10 (see FIG. 8).

An object of the present invention is to provide an optical power measuring apparatus which can obtain a compensating effect (not affected by atmospheric pressure fluctuation) equivalent to that of the apparatus in FIG. 9 even if the compensating absorber is made smaller than the light receiving absorber. To provide.

[0013]

SUMMARY OF THE INVENTION According to the present invention, a cooling element and a first cooling element are connected to a temperature reference jacket disposed inside a heat insulating device.
A light-receiving absorber, which is mounted with a temperature difference detecting element interposed therebetween and receives the measuring light, a heating element for heating the light-receiving body, and a second light-receiving absorber to the temperature reference jacket;
A compensating absorber having a second photoreceptor mounted with the temperature difference detecting element interposed therebetween, wherein a difference signal between an output signal of the first temperature difference detecting element and an output signal of the second temperature difference detecting element is provided. In equipment that removes the effects of atmospheric pressure fluctuations by using
The compensation absorber is a member smaller than the shape of the light-receiving absorber, and a thermal time constant of the compensation absorber determined by a heat capacity of the second light-receiving body and a thermal resistance of the second temperature difference detection element; First
The thermal time constant of the light-receiving absorber, which is determined by the heat capacity of the light-receiving element and the thermal resistance of the cooling element and the first temperature difference detecting element, is the same, and (PB / PA). (VB / VA) = 1 is set. Where PA is the power sensitivity of the light receiving absorber, PB is the power sensitivity of the compensating absorber, VA is the internal volume of the first photoreceptor, and VB is the internal volume of the second photoreceptor.

[0014]

Since the thermal time constant of the absorber for absorption and the thermal time constant of the absorber for light reception are the same, even if the thermal fluctuation occurs in the heat insulating device due to the fluctuation of the atmospheric pressure, the temperature change of the absorber for compensation. And the rate of temperature change of the light-receiving absorber are the same. In addition, the applicant has determined from the experimental data that (PB / PA). (VB /
It was confirmed that when the relationship of VA) = 1 was set, the pressure fluctuation sensitivity of the two absorbers (the light receiving absorber and the compensating absorber) became equal. Therefore, even if the shape of the compensating absorber is smaller than the shape of the light receiving absorber, the differential operation can cancel the influence of the pressure fluctuation.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG.
FIGS. 2 and 4 show examples of dimensions of the photoreceptor, FIGS. 3 and 4 show measurement data in the case of the photoreceptor of FIG. 2, and FIGS. It is measurement data in the case of a photoreceptor.

The device of FIG. 1 differs from the device of FIG. 9 in the structure of the compensating absorber 33 (other structures are the same). That is, the point is that the shape of the compensating absorber 33 is smaller than that of the light receiving absorber 30. Then, instead of simply reducing the shape, the thermal time constant determined by the heat capacity of the light receiving body (the cylinder 41 and the heat transfer plate 40) of the compensating absorber 33 and the thermal resistance of the temperature difference detecting element 42, The heat capacity of the light receiving body (the cylinder and the heat transfer plate) of the absorber 30 and the thermal time constant determined by the thermal resistance of the cooling element 7 and the thermal resistance of the temperature difference detecting elements 5 and 5a are the same, and (PB / PA) · (VB / VA) = 1. The applicant has experimentally confirmed that the pressure fluctuation sensitivity of the two absorbers (the light-receiving absorber and the compensating absorber) becomes equal when configured and set in this manner. Therefore, even if the shape of the compensating absorber is smaller than the shape of the light receiving absorber, the differential operation can cancel the influence of the pressure fluctuation. In addition, the thermoelectric cooling element 7 'in FIG. 9 was removed, and the size of the thermo module was reduced. Hereinafter, the present application will be described in detail focusing on points different from FIG.

(A) First, the pressure characteristics of the two absorbers when the shapes are merely similar (not the present invention) will be described based on the experimental data in FIGS. In FIG. 2, (a) is an absorber having a cylinder length of 15 mm and a diameter of 5φ, and (b) is an absorber having a cylinder length of 22.5 mm and a diameter of 7.5φ. That is, the dimensional ratios are in a relationship of 2: 3.

Although not shown in FIG. 2, the absorber shown in FIGS. 2A and 2B is provided with a thermo module (a large number of thermoelectric cooling elements 7 and temperature difference detecting elements 5 and 5a shown in FIG. 9). Peltier element).
(A) In the absorber shown in the figure, the total number of thermo-module elements added is 48, and among them, the number of modules used for the temperature difference detecting element is 32. This ratio is commonly referred to as the log ratio. Therefore, the logarithmic ratio of the absorber in FIG.
32/48 = 2/3. The logarithmic ratio is a numerical value indicating the temperature detection sensitivity, that is, the optical power detection sensitivity. on the other hand,
(b) The total number of thermomodule elements of the absorber in the figure is 96, of which 64 modules are used for the temperature difference detection element. In other words, the logarithmic ratio of the absorber shown in FIG.
/ 96 = 2/3, and was selected in the same manner as the absorber of (a).

When the logarithmic ratio is determined in this manner, the power sensitivity (detection sensitivity of optical power) is determined as described above. In other words, the power sensitivity of the absorber shown in (a) is 0.26 V / w. That is, when a light power of 1 watt is irradiated, a voltage of 0.26 V is output from the thermocouple. On the other hand, the power sensitivity of the absorber shown in Fig. (B) is 0.28 V / w. That is, since the logarithmic ratios are equal, the power sensitivity of the absorber in FIG.

Next, the thermal time constant will be described. The thermal time constant of the absorber is determined by multiplying the heat capacity of the cylinder and the heat transfer plate by the thermal resistance of the temperature difference detecting element connected thereto. In the example of FIG. 2, the thermal time constant of the absorber shown in FIG.
The thermal time constant of the absorber in the figure is 22 sec, and the value of this thermal time constant is also set to a substantially equal value. Therefore, even if heat fluctuation occurs in the heat insulating device, the rate of temperature change of the two absorbers in FIGS. (A) and (b) is the same.

As described above, pressure fluctuations are applied to two different absorbers having the same characteristics of logarithmic ratio, power sensitivity, and thermal time constant and having similar shapes as shown in FIG. 2, and the output of the thermocouple at that time is applied. 3 (that is, the output of the temperature difference detecting element) is the data shown in FIG. In FIG. 3, the horizontal axis is time (sec). The upper data (a) in FIG. 3 shows the applied pressure fluctuation value (one scale is 2 Pa / 1 V), and the lower data is the output of the thermocouple. The solid line is the data of the absorber (5φ) in FIG.
The scale is read at 250 nV) and the dotted line is the absorber (7.5 φ) of (b)
And read on the right vertical axis (500 nV per division). As can be seen from the data in FIG. 3, the pressure fluctuation value of the absorber in FIG. 2 (a) is about 33 nV / Pa, and the pressure fluctuation value of the absorber in FIG. 2 (b) is about 120 nV / Pa. . That is, in the case of the configuration examples shown in FIGS. 2A and 2B, the ratio of the pressure fluctuation value is 33/120 = 0.275.

Although the pressure sensitivities of the absorbers shown in FIGS. 2A and 2B are greatly different from each other, this ratio (0.275) is equal to the ratio of the inner volumes (the cube of the diameter) of the two absorbers. Almost equal. That is, 5 ³ /7.5 ³ = 0.275 This is because the absorber detects the work amount or the temperature difference caused by the pressure fluctuation, and the sensitivity is determined by the surface area of the absorber (the square of the diameter of the absorber). ) Or internal volume (3
Power).

(B) Absorber Having Configuration According to the Present Invention The relationship between the two absorbers according to the present invention will be described with reference to FIGS. In FIG. 4, (a) is a light-receiving absorber 30.
For example, the length of the cylindrical body is 15 mm, and the diameter is 7.5 φ. (B) shows a compensating absorber 33, for example, having a cylindrical body length of 12 mm and a diameter of 6φ. This numerical value is an example of a dimension, and the present invention is not limited to this numerical value.

In the case of using a thermo module of the same material, the power sensitivity is determined by a logarithmic ratio. Therefore, in the present invention, the logarithmic ratio of the light-receiving absorber in FIG. 4 (a) is set to 32/64 = 1/2.
And that of the compensating absorber of FIG. 4 (b) is 32/32 = 1/1.
And Therefore, the power sensitivity PA of the light-receiving absorber is PA
= 0.2 V / w, the power sensitivity PB of the compensating absorber is PB = 0.
4 V / w (◆ 0.26 × 3/2) (◆ means near equal). In addition, if the thermal response of the two absorbers is not the same, a temperature difference occurs in the transient state, so the two absorbers need to have the same thermal time constant. For that purpose, the thermal resistance ratio in the thermo module is (1/2) / (1/1) =
Since the ratio is 1/2, the ratio of the heat capacity of the photoreceptor of the absorber for light reception to the heat capacity of the photoreceptor of the absorber for compensation may be set to 2/1. The heat capacity can be easily determined by selecting the constituent materials and dimensions of the absorber.

The sensitivity of the absorber due to pressure fluctuation is
Based on the measurement data described in the above section (A), it was estimated that it was determined by the internal volume. That is, assuming that the inner volume of the photoreceptor (FIG. 4 (a)) of the light receiving absorber is VA and the inner volume of the photoreceptor (FIG. 4 (b)) of the compensating absorber is VB, (PB / PA). If (VB / VA) = 1, it can be expected that the pressure sensitivity of the two absorbers will be the same. Accordingly, FIG. 4 (a), when dimensioned shown in (b), a ^{VA = 7.5 3, VB = 6} 3. Then, as described above, PA = 0.2 V / w, PB = 0.4 V / w,
Therefore, substituting into the left side of the above equation gives (0.4 / 0.2)
The value of (6 ³ / 7.5 ³⁾ is about 1.

FIGS. 5 and 6 show measurement data when the two absorbers shown in FIG. 4 are used. FIG. 5 is (a) of FIG.
The output characteristics obtained from the light-receiving absorber (solid line data) and the compensation absorber (dotted line data) when such pressure fluctuations are applied are shown. FIG. 6 is (a) of FIG.
The data (b) shows the differential output between the output of the absorber for light reception and the output of the absorber for compensation when the same pressure fluctuation is applied. As can be seen by comparing the data of FIGS. 6 and 5, when a differential connection is made to a single output, the pressure fluctuation is reduced by 1 /
It becomes 3.

Further, since the thermoelectric cooling element 7 'in FIG. 9 is removed and the thermo-module portion is made smaller, the optical power measuring device can be manufactured at a lower cost as compared with the configuration of FIG.
Since the thermoelectric cooling element 7 'in FIG. 9 does not originally perform the original cooling operation, its performance does not decrease even if it is removed.

[0028]

As described above, according to the present invention, the thermoelectric cooling element of the compensating absorber, which has hardly functioned in the past, can be omitted, and the compensating absorber can be downsized. A low-cost optical power measuring device can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a main part of the present invention.

FIG. 2 is a diagram showing an example of dimensions of a photoreceptor;

FIG. 3 shows measurement data for the photoreceptor of FIG.

FIG. 4 is a diagram showing an example of dimensions of the photoreceptor according to the present invention;

FIG. 5 shows measurement data for the photoreceptor of FIG.

FIG. 6 shows measurement data for the photoreceptor of FIG.

FIG. 7 is a diagram showing a configuration example of a conventional optical power measurement device.

FIG. 8 is a diagram showing a configuration example of a conventional optical power measurement device.

FIG. 9 is a diagram showing a configuration example of a conventional optical power measurement device.

[Explanation of symbols]

 1a, 40 Heat transfer plate 41 Cylinder 42 Temperature difference detecting element 30 Absorber for light reception 33 Absorber for compensation

Claims (1)

(57) [Scope of request for utility model registration] 1. A first photoreceptor which is attached to a temperature reference jacket disposed inside a heat insulating device with a cooling element and a first temperature difference detecting element interposed therebetween and receives measurement light, and heats the photoreceptor. And a compensating absorber having a second photoreceptor attached to the temperature reference jacket with a second temperature difference detecting element interposed therebetween.
In an apparatus for removing the influence of atmospheric pressure fluctuation by using a difference signal between an output signal of a first temperature difference detection element and an output signal of a second temperature difference detection element, the compensating absorber has a shape smaller than that of a light receiving absorber. A small member, the thermal time constant of the compensating absorber determined by the heat capacity of the second photoreceptor and the thermal resistance of the second temperature difference detecting element, the heat capacity of the first photoreceptor, the cooling element, and the first temperature The optical power, wherein the thermal time constant of the light-receiving absorber determined by the thermal resistance of the difference detection element is the same, and (PB / PA). (VB / VA) = 1. measuring device. In addition,
PA is the power sensitivity of the light receiving absorber, PB is the power sensitivity of the compensating absorber, VA is the internal volume of the first photoreceptor, and VB is the internal volume of the second photoreceptor.