JPH0353141A - Method for measuring light loss of optical fiber - Google Patents

Abstract

PURPOSE:To secure measuring accuracy and to shorten a measuring time by making one of branched light beams incident on one end of an optical fiber, respectively detecting the intensity of the light beam emitted from the other end thereof and the other branched light beam at the same time and arithmetically operating based on the intensity of both light beams. CONSTITUTION:A light wave from a light source 1 is made incident on an optical fiber coupler 5. One of the branching parts of the coupler 5 is connected to one end of the optical fiber 3 to be measured and the other of the branching parts is connected to a photodetector 4b. Then, the other end of the fiber 3 is connected to the photodetector 4a. Outputs from photodetectors 4a and 4b are transmitted to a differential amplifier 6 and the output from the amplifier 6 is arithmetically operated by an arithmetic device 7 to obtain the value of light loss. by simultaneously obtaining optical outputs from the photodetectors 4a and 4b, the light loss can be measured from a difference between them, so that the measuring time is shortened. The measurement is executed without cutting the fiber 3 and does not receive the effect of the variation of the output from the light source.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical fiber optical loss measuring method for easily measuring the optical loss of an optical fiber under test in a non-destructive manner with high precision.

<Prior Art> A method widely used as a conventional optical loss measurement method is called the "cutback method", and a typical measurement method is shown in FIG. As shown in FIG. 3, in the cut-pack method, the light wave from the light a1 is transferred to the optical fiber to be measured 3 (
The light beam enters a length L [km]) via the excitation system 2, and the light output P0 is measured by the photodetector 4 at the output end of the optical fiber.

Next, the optical fiber 3 to be measured is cut at a position approximately 1 to 2 m from the input end, and the optical output P, . . . at that position is measured by the photodetector Wi4. These two optical outputs P0 and PI
From n, optical loss a is measured using the following formula.

a=1(1 0/L) l o g,0(P,/P,,
) [dB/km] Also, by using a light emitting diode or semiconductor laser as a light source, the optical loss at the emission wavelength can be reduced.
In addition, the wavelength characteristics of optical loss can be determined by dividing a white light source using a spectrometer and measuring the wavelength of the light incident on the optical fiber while changing the wavelength.

Problems to be Solved by the Invention However, in the conventional optical fiber loss measurement method described above, since the optical fiber 3 is cut, the light output received by the photodetector @ 4 changes depending on the state of the end face of the optical fiber, resulting in poor reproducibility. There were problems with measurement accuracy and reliability of loss values. Furthermore, when measuring the loss, there is also a drawback that it is difficult to obtain an accurate loss due to temporal output fluctuations of the light source 1 and the like. Furthermore, when measuring the loss of the optical fiber 3, it was difficult to measure P0 and p, . . . at the same time, as can be seen from FIG.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and it does not require cutting of the optical fiber to be measured during measurement, and provides a stable loss value even with fluctuations in the output of the light source. It is an object of the present invention to provide a non-destructive method for measuring optical loss of an optical fiber, which can secure a constant accuracy and shorten the measurement time.

Configuration of the Invention The configuration for realizing the method of the present invention includes a light source coupled to each end of the optical fiber to be measured, an excitation system, an optical fiber coupler, two photodetectors, and a differential amplifier. , and an arithmetic unit. And the light from the light source, that is, the light whose wavelength is variable,
Light with a wide wavelength spectrum or single wavelength light is split into two systems using an optical fiber coupler, one of the branched lights is input to one end of the optical fiber, and the light emitted from the other end of the optical fiber is split into two systems. The intensity and the intensity of the other branched light are simultaneously detected by photodetectors, respectively, and the optical loss is measured by comparing the two optical outputs. In this case, the optical fiber to be measured (length L [ km]
) is assumed to be P. Then, in the optical fiber coupler, the following relationship exists for the incident light wave.

P,: P2=l,k Therefore, by measuring P2, the light output of P can be evaluated. The relationship between P and P in the optical fiber coupler can be measured in advance. Therefore, since k is known, the optical loss of the optical fiber to be measured can be determined by the following equation.

a=- (1 0/L) l o g1. (P 7
(P2/k)) [dBAI1] In this measurement method, P2 and P3 can be measured simultaneously, so it is expected that the measurement time will be shortened. Also, P and P
, are measured at the same time, there is no need to correct for fluctuations in the output of the light source, and even if the light source fluctuates, it is possible to measure optical loss with high precision.

Example of implementation Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the optical loss measuring method according to the present invention, in which l is a light source, 2 is an excitation system, 5 is an optical fiber coupler, 3 is an optical fiber to be measured, 4a and 4b are photodetectors, and 6
is a differential amplifier, and 7 is an arithmetic unit.

In this measurement method, unlike the method shown in FIG. the left end), and the other branch is connected to the photodetector @4b. Further, the other end (right end) of the optical fiber 3 to be measured is coupled to the photodetector N4a. The outputs of the photodetectors 4a and 4b are sent to a differential amplifier 6, and the arithmetic unit 7 performs the calculation shown in equation (2) on the output to obtain the value of optical loss.

In this case, if a light emitting diode that outputs light with a wide wavelength spectrum width or a semiconductor laser that outputs single wavelength light is used as the light source 1, the optical loss at each emission wavelength can be measured. Furthermore, if white light separated by a spectrometer is used as the light source 1, the wavelength characteristics of optical loss can also be measured.

FIG. 2 shows the measurement results using the example.

The tuned fiber is a single mode optical fiber. Additionally, the time required for this measurement was approximately 1
It was possible to shorten the time to 72 hours. Furthermore, as a result of measuring the reproducibility of the measurement, it was confirmed that the measurement could be performed with high accuracy.

Furthermore, this measurement method can also be applied to a far-end measurement method when measuring optical loss of a laid line.

Effects of the Invention> As described above, the present invention includes a light source coupled to each end of an optical fiber to be measured, an optical fiber coupler, two photodetectors, and a calculation device, and has a wavelength Variable light, light with a wide wavelength spectrum, or single wavelength light is input into an optical fiber coupler, and one branch of the optical fiber coupler is connected to one end (input end) of the optical fiber to be measured. A photodetector then detects the optical output at the other end of the optical fiber (output end) and the optical output at the other branch of the optical fiber coupler, and the optical loss is measured by comparing the two optical outputs. This is the way to do it. As a result, the optical loss can be measured by simultaneously determining the optical outputs of the two photodetectors mentioned above and using the difference between them, reducing the measurement time, without cutting the fiber under test, and in addition to the output of the light source. It is not affected by fluctuations. Therefore, it is possible to provide a method for measuring optical loss in a destroyed optical fiber, since high measurement accuracy can be ensured and measurement time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the optical loss measuring method of the present invention, FIG. 2 is a characteristic diagram showing measurement results by the method of the present invention, and FIG. 3 is a block diagram showing the conventional optical loss measuring method. In the drawings, 1 is a light source, 2 is an excitation system, 3 is an optical fiber to be measured, 4.4a and 4b are photodetectors, 5 is an optical fiber coupler 6 is a differential amplifier, and 7 is an arithmetic unit.

Claims (1)

[Claims] The light from the light source is split into two systems by an optical fiber coupler, one of the branched lights is input to one end of the optical fiber, and the intensity of the light emitted from the other end of the optical fiber and the intensity of the other branched light are measured respectively. 1. A method for measuring optical loss in an optical fiber, characterized in that the optical loss of the optical fiber is measured by simultaneously detecting with a photodetector and calculating with a calculation device based on the detected intensities of both lights.