JPH0252210B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention accurately measures the transmission characteristics of components that transmit waves such as electromagnetic waves and elastic waves by simultaneously using two reflection coefficient measuring instruments. The present invention relates to a method for measuring wave transmission parameters.

[Prior art]

such as attenuators and transmission line connectors,
The transmission characteristics of a component that has one input and output surface (or one input and output terminal) are as shown in Figure 1, when a wave p 1 enters the component under test 3 at surface (input surface in this case) ₁ .
4 transmissions representing the relationship between the wave q ₁ that comes out of the part to be measured 3, the wave p ₂ that enters the part to be measured 3 at the surface (output surface in this case) 2, and the wave q ₂ that comes out of the part to be measured 3. It is expressed as follows using parameters a ₁₁ , a ₁₂ , a ₂₁ , and a ₂₂ .

q ₁ = a ₁₁ p ₁ + a ₁₂ p ₂ q ₂ = a ₂₁ p ₁ + a ₂₂ p ₂ However, a ₂₁ and a ₁₂ are transmission parameters that represent the amount of wave attenuation, and a ₁₁ and a ₂₂ represent the amount of reflection. .

When the waves are coherent waves such as microwaves and ultrasonic waves, generally p ₁ ,
q ₁ , p ₂ , and q ₂ are represented by amplitude and phase, and transmission parameters a ₁₁ , a ₁₂ , a ₂₁ , and a ₂₂ are complex numbers. On the other hand, if the waves are incoherent, such as white light, it is convenient to define p ₁ , q ₁ , p ₂ , and q ₂ in terms of the wave power, and the above transmission The parameters a ₁₁ , a ₁₂ , a ₂₁ , and a ₂₂ are positive real numbers.

A typical and important method of transmitting incoherent waves is optical transmission using a light emitting diode or a laser diode with a wide spectrum width as a light source.

Currently, there are methods for accurately measuring transmission parameters, such as the network analyzer method for microwaves, but these methods require changing the phase of the waves, so they are only applicable to coherent transmission. Can not. Although a special method for accurately measuring transmission parameters of incoherent transmission has not yet been developed, a direct method that can be considered is the method shown in FIGS. 2a to 2f.

That is, as shown in Fig. 2a, a non-reflection load 9 that does not reflect waves is placed on the output side of the component to be measured 3, and a reflection coefficient measurement consisting of a wave source 4, a directional coupler 5, and a reflected wave indicator 6 is performed on the input side. Place vessel 7. At this time, if the reflection coefficient measuring device 7 is ideal and the reflected wave indicator 6 accurately indicates the reflection coefficient q ₁ /p ₁ , then the indicated value q ₁ /p ₁ is the transmission parameter a will be equal to ₁₁ .

Next, as shown in Figure 2b, there is a wave source 4 with no reflection on the input side.
, and a non-reflection detector 10 for measuring transmitted waves is placed on the output side. At this time, the non-reflection detector 10
Suppose that the reflected wave indicator 8 indicates _I1 .

Thereafter, the part to be measured 3 is removed as shown in FIG. At this time, the non-reflection detector 10
Assume that the reflected wave indicator 8 indicates I′ ₁ . If the non-reflection detector 10 is ideal and indicates a value proportional to the power q ₂ of the wave entering it, then
The ratio I ₁ /I' ₁ of I ₁ and I' ₁ becomes equal to the transmission parameter a ₂₁ .

By exchanging the input side and the output side, the transmission parameter a ₂₂ can be measured according to FIG. 2d, and the transmission parameter a ₁₂ can be measured according to FIGS. 2e and f.

The drawbacks of the above measurement methods include the following.

(1) It is difficult to realize a reflection-free wave source 4 and a reflection-free detector 10.

(2) Parts to be measured 3 and measuring instruments are often attached and detached.

(3) The causes of errors increase due to (1) and (2) above.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the direct measurement method as described above, and simplifies the measurement procedure by making the reflection coefficient measuring device also function as a transmitted wave detector. Furthermore, data processing is performed so that the wave source and detector do not need to be non-reflective. This invention will be explained below.

[Embodiments of the invention]

FIGS. 3a and 3b show an embodiment of the present invention. Reference numerals 1 to 7 are the same as those shown in FIGS. 1 and 2, 11 is a wave source, 12 is a directional coupler, and 13 is a reflected wave indicator, and these constitute the reflection coefficient measuring device 14. has been done.

In this configuration, the reflection coefficient measuring devices 7 and 14 are simultaneously connected to the input and output sides of the component to be measured 3, as shown in FIG. 3a. In this state, first, the wave source 4 of the reflection coefficient measuring instrument 7 is brought into an operating state (ON state), and the wave source 11 of the reflection coefficient measuring instrument 14 is brought into a non-operating state (OFF state). In this way, the reflected wave indicator 6 of the reflection coefficient measuring device 7 indicates the reflection coefficient u ₁ when looking at the component side from the surface (input surface) 1. In addition, since the wave source 11 of the reflection coefficient measuring device 14 is in the OFF state,
It simply functions as a detector of transmitted waves. In this state, the indicated value of the reflected wave indicator 13 is set to _I2 .

Next, when the wave source 4 is turned OFF and the wave source 11 is turned ON, surface 2 becomes the input surface, surface 1 becomes the output surface, and the reflected wave indicator 13 of the reflection coefficient measuring device 14
indicates the reflection coefficient u ₂ when looking at the part to be measured 3 from the surface (input surface) 2. On the other hand, since the wave source 4 is in the OFF state, the reflection coefficient measuring device 7 functions as a detector.
At this time, the indicated value of the reflected wave indicator 6 is set to _I1 .

After recording each of the above indicated values I ₁ and I ₂ ,
Remove the part to be measured 3 and turn on the wave source 4 as shown in
When the wave source 11 is in the OFF state, 7 functions as a reflection coefficient measuring device, 14 functions as a transmitted wave detector, and the reflected wave indicator 6 functions as a reflection coefficient measuring device 14 viewed from the surface (input surface) 2. Indicate v ₂ . The indicated value of the reflected wave indicator 13 in this state is assumed to be I' ₂ .

Next, when the wave source 4 is turned OFF and the wave source 11 is turned ON, the reflected wave indicator 13 indicates the reflection coefficient v ₁ when looking at the reflection coefficient measuring device 7 from the surface (output surface) 1. The indicated value of the reflected wave indicator 6 in this state is I′ ₁
shall be.

As a result of the above, the eight data obtained are u ₁ , I ₁ ,
The following relationship exists between u ₂ , I ₂ , v ₂ , I′ ₁ , v ₁ , and I′ ₂ .

u ₁ =a ₁₁ +a ₁₂ a ₂₁ v ₂ /1−a ₂₂ v ₂ …(1) u ₂ =a ₂₂ +a ₁₂ a ₂₁ v ₁ /1−a ₁₁ v ₁ …(2) I ₂ /I′ ₂ = _a21 /(1- _{a11v1 ) ( 1} - _a22v2 ) _-a12a21v
1 v ₂ …(3) I ₁ /I' ₁ a ₁₂ / (1-a ₂₂ v ₂ ) (1-a ₁₁ v ₁ )-a ₁₂ a ₂₁ v ₁ v
₂ ...(4) That is, for the part to be measured 3, the wave sources 4, 11
Reflection coefficient measuring devices 7 and 14 that function as detectors and detectors
is not reflection-free, u ₁ , u ₂ , I ₂ /I' ₂ , I ₁ /I' ₁ are not equal to the direct transmission parameters a ₁₁ , a ₂₂ , a ₂₁ , a ₁₂ , and Equation (1) The relationship is as shown in equation (4).

However, the transmission parameters a ₁₁ , a ₁₂ , a ₂₁ , a ₂₂ are
By treating equations (1) to (4) as simultaneous equations and solving them, it can be determined as follows.

a ₂₁ =I ₂ /I' ₂ (1-u ₁ v ₁ ) (1-u ₂ v ₂ )/1-(I
₁ /I' ₁ ) (I ₂ /I' ₂ ) v ₁ v ₂ (1-u ₁ v ₁ ) (1-u ₂ v ₂ )
…(5) a ₁₂ =I ₁ /I′ ₁ (1−u ₁ v ₁ )(1−u ₂ v ₂ )/1−(I
₁ /I' ₁ ) (I ₂ /I' ₂ ) v ₁ v ₂ (1-u ₁ v ₁ ) (1-u ₂ v ₂ )
…(6) a ₁₁ =u ₁ −(I ₁ /I′ ₁ )(I ₂ /I′ ₂ )v ₂ (1−u ₁ v ₁
) ² (1−u ₂ v ₂ )/1−(I ₁ /I′ ₁ )(I ₂ /I′ ₂ )v ₁ v ₂
(1-u ₁ v ₁ ) (1-u ₂ v ₂ )...(7) a ₂₂ = u ₂ - (I ₁ /I' ₁ ) (I ₂ /I' ₂ ) v ₁ (1-u ₁ v ₁
)(1−u ₂ v ₂ ) ² /1−(I ₁ /I′ ₁ )(I ₂ /I′ ₂ )v ₁ v ₂
(1-u ₁ v ₁ ) (1-u ₂ v ₂ )...(8) The measurement method according to the present invention does not require changing the phase of the wave, so it can be applied to both coherent transmission and incoherent transmission. However, it is particularly effective for transmission systems using multimode optical fibers that currently perform incoherent transmission but for which there is no accurate measurement method for transmission parameters. Therefore, as the component to be measured 3, an optical attenuator for a multimode optical fiber will be specifically taken up. The most important characteristic of an attenuator is the amount of attenuation A=-10log a ₂₁ (in dB) when light travels from the input surface 1 to the output surface 2, so let us consider the case where we want to accurately measure A. As already mentioned, there is no source or detector that does not reflect waves at all. In the case of multimode optical fiber transmission, the source reflects approximately 10% of the optical power and the detector reflects approximately 4% of the optical power. Furthermore, the attenuator itself often has a reflection of about 6%. When these reflections exist, the amount of error that will occur if the attenuation amount A is determined using the direct method shown in Figure 2 is theoretically evaluated based on equations (1) to (8). The results are shown in Figure 4. Here, the error shows a negative value because in the direct method shown in Figure 2,
This means that the amount of attenuation is measured to be smaller than the true value (that is, the attenuation is not large), which clearly shows the problem with the direct method shown in FIG.

In a graded optical fiber transmission system with a core diameter of 50 μm and a cladding diameter of 125 μm, 0.85 μm laser diodes are used as wave sources 4 and 11, directional couplers 5 and 12 using semi-transparent mirrors, and a reflected wave indicator 6 using a silicon PIN photodiode. FIG. 5 shows the results of measurement using the method of the present invention using two reflection coefficient measuring devices 7 and 14 each having a configuration of 13.

Here, the part under test 3 changes the attenuation from 0 dB.
This is an optical variable attenuator that can be continuously varied up to 10dB and has an input loss of approximately 1.5dB at 0dB. This variable optical attenuator emits light from the end of an optical fiber into space, then attenuates the transmitted light by placing a semi-transparent mirror diagonally to the optical path and reflecting the light in different directions. It has a structure that guides light into the fiber.

Therefore, when the amount of attenuation is small, the reflected light from the output side tends to return to the input side, and the transmission parameters a ₁₁ and a ₂₂ become large (small in dB). On the other hand, as the amount of attenuation increases, it becomes difficult for the reflected light from the output side to return to the input side, so the transmission parameters a ₁₁ and a ₂₂ become smaller, but as the amount of light reflected by the semitransparent mirror increases, the amount of attenuation increases. When becomes large to a certain extent, the transmission parameters a ₁₁ and a ₂₂ remain unchanged,
Or slightly larger (dB display value is slightly smaller)
It is expected that In the experimental results shown in Figure 4,
This is confirmed.

In addition, the attenuation amount obtained by the direct method shown in Fig. 2,
The difference ΔA from the amount of attenuation measured in this invention is shown in FIG. According to FIG. 6, the results measured by the direct method of FIG. 2 are smaller in dB by about 0.02 dB to 0.035 dB. This also agrees with the theoretical prediction shown in FIG.

Note that all the above explanations have been made for parts that have one input surface and one output surface, but parts that have two or more input and output surfaces can also be
By placing a non-reflective load on all surfaces except one input surface and one output surface, and sequentially measuring the transmission parameters of the parts created in this way by changing the input and output surfaces, the transmission It is possible to determine the parameters.

〔Effect of the invention〕

As explained in detail above, the present invention connects a reflection coefficient measuring device consisting of a wave source, a directional coupler, and a reflected wave indicator to the input side and the output side of the component to be measured, and Turn on the other wave source alternately, obtain 4 data of 2 pieces from both reflected wave indicators only, then remove the part to be measured and turn on one wave source and the other wave source alternately. is turned on, 4 pieces of data are obtained 2 pieces each from both reflected wave indicators at that time, and the transmission parameters of the part under test are measured from a total of 8 pieces of data, changing the phase of the wave. Since there is no need to do this, transmission parameters of the component under test can be accurately measured for both coherent waves and incoherent waves. Therefore,
It has the following advantages.

(1) No reflection-free wave source or reflection-free detector is required.

(2) Fewer parts to be measured and measuring instruments need to be attached and detached.

(3) Due to (1) and (2) above, accurate measurement with small errors is possible.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of wave transmission parameters, Figures 2 a to f are diagrams showing conventional measurement procedures for wave transmission parameters, and Figures 3 a and b are measurements of wave transmission parameters showing an embodiment of the present invention. Diagram showing the procedure, No. 4
The figure shows the expected error in the conventional method.
FIG. 5 is a diagram showing the results of measuring transmission parameters according to the present invention, and FIG. 6 is a diagram showing the difference in measurement results between the conventional method and the method according to the present invention. In the figure, 1 and 2 are surfaces, 3 is the part to be measured, and 4, 11
is a wave source, 5 and 12 are directional couplers, 6 and 13 are reflected wave indicators, and 7 and 14 are reflection coefficient measuring devices.

Claims (1)

[Claims] 1. A reflection coefficient measuring device consisting of a wave source, a directional coupler, and a reflected wave indicator is connected to the input side and the output side of the part to be measured that transmits waves, and only the wave source of one of the reflection coefficient measuring devices is Turn ON to obtain two data from both reflected wave indicators, then turn only the wave source of the other reflection coefficient measuring device ON to obtain two data from both reflected wave indicators, and then remove the part to be measured. With the two-way couplers connected, only one of the wave sources is turned on to obtain two data from both reflected wave indicators, and furthermore, only the other wave source is turned on and two data are obtained from both reflected wave indicators. A method for measuring a wave transmission parameter, comprising obtaining data and measuring a transmission parameter of the component to be measured based on the eight pieces of data.