JPS62195542A - Detecting method for metallic impurity in optical fiber - Google Patents

Abstract

PURPOSE:To separate and detect fluorescent spectra and to facilitate detection when an optical fiber contains plural metallic impurities by varying the wavelength of light incident on the optical fiber. CONSTITUTION:The output light (wavelength: 477nm) of an argon ion laser 1 which is modulated by a chopper 2 and made homogeneous is converged by a lens 3 and incident on a fluorine fiber 4, and its projection light is guided to and diffused spectrally by a monochrometer 5; and the wavelength of a separated light component passed through a photoelectron multiplier tube 6, a preamplifier 7, and a lock-in amplifier 8 and that of a separated light component sent out by the meter 5 are recorded on an X-Y recorder 9 to measure the intensity of a fluorescent spectrum. Further, the light which has the same wavelength and is made homogeneous is made incident on an optical fiber which contains a known amount of metallic ions generating the same spectrum as said spectrum and the spectrum from its projection end is measured, thereby finding the amount of metallic impurities in the optical fiber from the intensity ratio of both fluorescent spectra.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for easily detecting metal impurities in an optical fiber without destroying the optical fiber.

(Prior art) There have been various methods for analyzing trace impurities contained in substances.Among these, atomic absorption spectrometry, emission spectrometry, and activation analysis have been used to analyze trace impurities. It is relatively commonly used as a method.

The detection concentration limits of these analytical methods may be affected by the elements in the matrix containing impurities, so they should be determined for each individual case, but in general, they are around 1ng for atomic absorption spectrometry and emission spectrometry. It is about 0.01 ng by activation analysis method.

Furthermore, during measurement, it is necessary to perform special treatment on the sample. For example, in atomic absorption spectrometry, the sample is introduced into a frame, so it is generally necessary to prepare the sample as a solution, and a solvent suitable for the sample to be measured must be selected. In addition, activation analysis is an excellent method for detecting impurities at extremely low concentrations, but for example, in neutron activation analysis, a sample must be introduced into a nuclear reactor and irradiated with neutrons.
Since it cannot be used unless there is a special environment in which nuclear reactor equipment can be used, it cannot be said to be a general measurement method.

As described above, the conventional trace impurity analysis method involves complicated procedures and cannot easily measure several types of impurities present in a fiber.

(Problems to be Solved by the Invention) The present invention provides a method for easily detecting minute amounts of metal impurities contained in an optical fiber and causing transmission loss without destroying the optical fiber. There is a particular thing.

(Means for Solving the Problems) The present invention involves inputting monochromatic light of a predetermined wavelength from one end of an optical fiber, measuring the fluorescence spectrum emitted from the other end of the optical fiber, and measuring the fluorescence spectrum emitted from the other end of the optical fiber. Monochromatic light of the same wavelength as above is input into an optical fiber containing a known amount of metal ions that produce a light spectrum, and the fluorescence spectrum from the output end is measured. From the intensity ratio of both fluorescence spectra, it is determined that the inside of the optical fiber is Find the amount of metal impurities.

In the present invention, excitation light is input into an optical fiber, and the fluorescence intensity due to metal impurities contained in the optical fiber is integrated in the longitudinal direction of the optical fiber to obtain the fluorescence intensity, so that the optical path length of the excitation light is increased. By doing so, the fluorescence intensity can be increased, and trace amounts of metal impurities can be detected compared to conventional fluorescence spectroscopy.

■ Excitation light intensity using bulk samples. When excited with light, the total fluorescence intensity I is! =2.3φI0εCd ---(1
) is given by Here, φ is the fluorescence quantum yield, ε is the molar extinction coefficient of the excitation light wavelength of the sample compound, C is the molar concentration of the fluorophore in the sample, d is the optical path length of the sample, and the absorbance (εC
d) is assumed to be 0.01 or less.

On the other hand, when excitation light with a wavelength λ1 is incident on one end of the fiber, the intensity of the fluorescent light with a wavelength λ2 emitted from the other end is given by the following equation.

Here, β. is the length of the fiber, φ is the fluorescence quantum yield, I
o is the excitation light intensity at wavelength λ, ω is the proportion of fluorescent light guided into the fiber out of the total fluorescent light, α1 is the fiber loss at wavelength λ1, ε1 is the absorption loss at wavelength λ1 by the phosphor,
α2 is the fiber loss at wavelength λ2.

FIG. 2 is a diagram showing the dependence of the fluorescence intensity given by equation (2) on the fiber length 10). However, αt = 200 dB/ 1un1CXz = 100
dll/km.

The fluorescence intensity expressed by equation (2) is the wavelength λ1, the wavelength λ2
The transmission loss in the visible range of existing fluoride optical fibers varies from 100 to 2, depending on the fiber loss at
Assuming about 00 dB/km, the maximum value of the fluorescence intensity is determined by the measurement value (measured with a commercially available fluorescence spectrophotometer given by equation 11) when the excitation light intensity and the fluorophore concentration are the same. 1 from the fluorescence intensity of 1cI11 thick bulk glass
It becomes about 00 times larger.

Therefore, as mentioned above, it is possible to detect trace amounts of metal impurities than conventional fluorescence spectroscopy.

FIG. 1 is a diagram showing an embodiment of the present invention, and shows an outline of a fiber fluorescence spectrum measurement system, in which 1 is an argon ion laser, 2 is a chopper, 3 is a lens, 4 is a fluoride fiber, and 5 is a monochromatic fiber. meter, 6 is a photomultiplier tube, 7 is a preamplifier, 8 is a lock-in amplifier, 9 is an x-y recorder,
10 is a cable, 11 is a power supply for a photomultiplier tube, 12 is a semiconductor photodetector, 13 is an optical demultiplexer, and 14 is a bandpass filter that transmits only excitation light.

The output light (wavelength: 477 nm) of the argon ion laser 1 modulated by the chopper 2 is focused by the lens 3 and input into the fluoride optical fiber 4, and the output light from the other end of the fluoride fiber 4 is guided to the monochromator 5. The photomultiplier tube 6 receives the separated light. A lock-in method is used to detect the spectroscopic light, and the output of the photomultiplier tube 6 that has passed through the preamplifier 7 and lock-in amplifier 8 and the wavelength of the spectroscopic light sent from the monochromator 5 are x- Recorded using y recorder 9.

Figure 3 shows the glass composition ZrF4-BaFz-GdF*-
The fluorescence spectrum is shown when a 2 m long fluoride fiber made of A 42 F3 is used. This is fluorescence due to ff transition of Pr'' ions, and it was confirmed that Pr3+ ions were contained in the fluoride fiber.

In order to quantify the amount of impurity Pr” ion, p r 3
+ ions each 5 p91g + 10ppm,
A fiber doped with 370 ppm was prepared and its fluorescence intensity was measured. When measuring the fluorescence intensity, the monochromator 5 shown in FIG. 4 is replaced with a 0.0.
The measurement was performed using a bandpass filter 14' that transmits 635 μm of light. By using a bandpass filter, the fluorescence intensity could be determined more easily and with better reproducibility than when using a monochromator.

As can be seen from Figure 5, the concentration of Pr'' ions is 5 to 3.
At 70 ppm, the fluorescence intensity of 0.635 μ mound and P
The r'' ion concentration is in a proportional relationship, and by comparing the fluorescence intensity in the above concentration range and the fluorescence intensity of the sample fiber,
The amount of Pr''° impurities in the sample fiber can be determined.

As a result, it was found that 2 spppb of Pr'' impurities were contained in the fluoride fiber.

In the above intensity measurement, the intensity of the light emitted from the fiber was monitored by the semiconductor detector 12, and the intensity was corrected by the loss value of the fiber at the incident light wavelength λ1 and the fluorescent light wavelength λ2.

(Effects of the Invention) As explained above, according to the detection method of the present invention, there is no need to perform any processing on the fiber that is the detection target, and even when the fiber contains multiple metal impurities. By changing the excitation wavelength, it is also possible to separate and detect each fluorescence spectrum, and trace amounts of metal impurities can be detected extremely easily.

Further, by increasing the excitation light intensity and making the fiber length longer than the 2 m length of the fiber used in the example, there is an advantage that impurity amounts of about 10 -3 PPb can be easily detected.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the present invention; Figure 2 is a diagram showing the relationship between fluorescence intensity and fiber length; Figure 3 is a diagram showing a fluorescence spectrum of an example of a fluoride fiber; Figure 4 Figure 5 shows the optical system at the fiber output end of the fluorescence intensity measurement system using a bandpass filter.
"It is a diagram showing the relationship between ions and fluorescence intensity. 1... Argon laser 2... Chopper 3...
Lens 4...Fluoride fiber 5...
Monochromator 6...Photomultiplier tube 7...Preamplifier 8...Lock-in amplifier 9...x-
y recorder 10...cable 11...power supply for photomultiplier tube 12...semiconductor photodetector 13...optical demultiplexer 14...bandpass filter 1 that transmits only excitation light
4'... Bandpass filter that transmits light with a wavelength of 0.635 μm Patent applicant Nippon Telegraph and Telephone Corporation Fig. 3 5iE&(R1fn Fig. 4 14'-480, 63'fytqnf>ltllLmt
Xt(l”/'X7tjLJIFigure 5

Claims (1)

[Claims] 1. Inject monochromatic light of a predetermined wavelength from one end of an optical fiber, measure the fluorescence spectrum emitted from the other end of the optical fiber, and measure the fluorescence spectrum that contains a known amount of metal ions that produce the fluorescence spectrum. The method is characterized by injecting monochromatic light of the same wavelength into the optical fiber, measuring the fluorescence spectrum from the output end, and determining the amount of metal impurities in the optical fiber from the intensity ratio of both fluorescence spectra. A method for detecting metal impurities in optical fibers.