JP6402482B2 - Optical fiber cut-off wavelength measurement method - Google Patents

Description

  The present invention relates to a method for measuring a cutoff wavelength of an optical fiber.

  As a method for measuring the cutoff wavelength of an optical fiber, a bending method and a multimode reference method (multimode excitation method) are known (see, for example, Patent Documents 1 and 2).

JP 2008-8710 A JP 2012-220511 A

In the above bending method, the transmitted light power is measured when a circular optical fiber having a diameter of 60 mm is applied to an optical fiber to be measured having a length of 2 m, and the circular optical fiber having a diameter of 280 mm is applied to the optical fiber to be measured. The measurement is performed twice with the measurement of the transmitted light power when bending is applied. Then, the longest wavelength is determined as the cut-off wavelength λc among the wavelengths at which the ratio of the transmitted light power obtained by two measurements with respect to the optical fiber to be measured is 0.1 dB.
On the other hand, in the above multimode reference method, the transmitted light power of a reference multimode fiber (reference optical fiber, a short multimode fiber of about 2 m) and the optical fiber to be measured are multimode excited and bent with a diameter of 280 mm. The cutoff wavelength λc is determined from the ratio to the transmitted light power when. That is, the multimode reference method is a method for obtaining the cutoff wavelength λc by utilizing a phenomenon that the transmitted light power of the optical fiber to be measured changes greatly at the stage of transition from the multimode to the single mode.

  When the bending method and the multi-mode reference method are compared, the multi-mode reference method can reuse the reference, so that a result can be obtained in one measurement for the optical fiber under measurement (measurement time). Is a short time). However, since the wavelength spectrum of the transmitted light power in the multimode fiber is used as a reference, there is a problem that the fluctuation is larger than the wavelength spectrum in the single mode fiber and the measurement reproducibility is poor.

  Accordingly, an object of the present invention is to provide an optical fiber cut-off wavelength measurement method capable of stabilizing the cut-off wavelength measurement reproducibility by the multimode reference method.

The optical fiber cut-off wavelength measurement method of the present invention that can solve the above-mentioned problem is a reference measurement step of measuring a wavelength characteristic of transmitted light power by applying a slight bend to a reference multimode optical fiber;
A measurement optical fiber measurement step for measuring the wavelength characteristic of the transmitted light power of the measurement optical fiber;
A cut for calculating a cutoff wavelength of the optical fiber to be measured based on a wavelength characteristic of a ratio between a wavelength characteristic of the transmitted light power of the reference multimode optical fiber and a wavelength characteristic of the transmitted optical power of the optical fiber to be measured Off-wavelength calculation step;
Have

  According to the present invention, the measurement reproducibility of the cutoff wavelength by the multimode reference method can be stabilized.

It is a figure explaining the method of calculating a cut-off wavelength from the wavelength spectrum of transmitted light power ratio by a multimode reference method. It is a schematic diagram explaining the cutoff wavelength measuring method of the optical fiber which concerns on embodiment of this invention. In the optical fiber cut-off wavelength measurement method according to the embodiment of the present invention, when the transmitted light power is measured with the reference multimode optical fiber, a measurement result obtained when a minute bend having a diameter of 20 mm is added as a minute bend. It is a figure which shows an example. In the optical fiber cut-off wavelength measurement method according to the embodiment of the present invention, when the transmitted light power is measured with the reference multimode optical fiber, the measurement result obtained when a minute bend having a diameter of 10 mm is added as a minute bend. It is a figure which shows an example.

[Description of Embodiment of Present Invention]
The optical fiber cutoff wavelength measuring method according to the embodiment of the present invention is:
(1) A reference measurement process for measuring a wavelength characteristic of transmitted light power by applying a slight bend to a reference multimode optical fiber;
A measurement optical fiber measurement step for measuring the wavelength characteristic of the transmitted light power of the measurement optical fiber;
A cut for calculating a cutoff wavelength of the optical fiber to be measured based on a wavelength characteristic of a ratio between a wavelength characteristic of the transmitted light power of the reference multimode optical fiber and a wavelength characteristic of the transmitted optical power of the optical fiber to be measured Off-wavelength calculation step;
Have
According to the method (1), by measuring a reference multimode optical fiber with a slight bend, a higher mode is removed from the transmitted light power of the reference multimode optical fiber, and the multimode reference The measurement reproducibility by the method can be stabilized.

(2) The diameter of the minute bend in the reference measurement step is made smaller than 20 mm.
According to the method (2), since the bending diameter applied to the reference multimode optical fiber in the reference measurement step is smaller than 20 mm, the wavelength from which the higher-order mode has escaped from the transmitted light power of the reference multimode optical fiber. The waveform in the band becomes flatter, and the measurement reproducibility by the multimode reference method can be further stabilized.

[Details of the embodiment of the present invention]
A specific example of an optical fiber cutoff wavelength measuring method according to an embodiment of the present invention will be described below with reference to the drawings.
In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

The optical fiber cutoff wavelength measuring method according to the present embodiment is based on the multimode reference method.
First, a calculation method of the cutoff wavelength λc by the multimode reference method will be described. FIG. 1 is a diagram for explaining a method for calculating a cutoff wavelength from a wavelength spectrum of a transmitted light power ratio.
In the multimode reference method, the wavelength characteristic of the transmitted light power Pr (λ) of the reference multimode optical fiber serving as a reference, and the optical fiber to be measured are subjected to multimode excitation and bending with a diameter of 280 mm (typical use). Measure the wavelength characteristics of the transmitted light power Ps (λ) when adding to simulate the form). And these transmitted light power ratio A ((lambda)) is calculated | required by following Formula (1).
A (λ) = 10 × log ₁₀ (Ps (λ) / Pr (λ)) (1)
Since the transmitted light power Ps (λ) of the optical fiber to be measured changes greatly at the stage of transition from the multimode to the single mode, the wavelength spectrum of the transmitted light power ratio A (λ) also extends from the multimode region to the single mode region. As shown in FIG.
Then, a straight line approximated to the long wavelength side of the single mode region of the wavelength spectrum of A (λ) shown in FIG. A straight line L2 obtained by shifting the base line L1 upward by 0.1 db is drawn, and the wavelength of the intersection with the wavelength spectrum of A (λ) is determined as the cutoff wavelength λc.

Next, a method for measuring the cutoff wavelength of an optical fiber according to this embodiment will be described. FIG. 2 is a diagram for explaining a method for measuring a cutoff wavelength of an optical fiber according to the present embodiment.
(Reference measurement process)
In this embodiment, as shown in FIG. 2A, in the reference measurement step, a minute bend 2 is applied to the reference multimode optical fiber 1 (for example, wound around a mandrel having a diameter of about 10 mm to 30 mm). Then, the light output from the light source unit 3 is propagated to the reference multimode optical fiber 1, the light transmitted through the minute bend 2 is received by the light receiving unit 4, and the wavelength characteristic of the transmitted light power is measured. . At this time, since the minute bending 2 is added, the high-order mode is removed from the transmitted light power (but not the single mode).

(Measurement optical fiber measurement process)
Next, as shown in FIG. 2B, the light output from the light source unit 3 is propagated to the measured optical fiber 5 with respect to the measured optical fiber 5, and the transmitted light is received by the light receiving unit 4. The light is received and the wavelength characteristic of the transmitted light power is measured. In order to simulate a typical usage pattern of the optical fiber 5 to be measured, the measurement optical fiber 5 is measured with a bend 6 having a diameter of 280 mm (for example, wound around a mandrel having a diameter of 280 mm).

(Cutoff wavelength calculation process)
The wavelength characteristics of the transmitted light power Ps (λ) of the reference multimode optical fiber 1 measured in the reference measurement process, and the transmitted light power Pr (λ of the measured optical fiber 5 measured in the measured optical fiber measurement process. ) And the transmitted light power ratio A (λ) with the wavelength characteristic is calculated from the above-described equation (1). Then, the cutoff wavelength λc is determined from the calculated wavelength spectrum of the transmitted light power ratio A (λ) in accordance with the standard of the multimode reference method described above.

  As described above, according to the present embodiment, in the reference measurement process, a high-order mode is removed from the transmitted light power of the reference multimode optical fiber 1 by applying a minute bend 2 to the reference multimode optical fiber 1. Thus, the measurement reproducibility by the multi-mode reference method can be stabilized.

Next, the wavelength spectrum of the transmitted light power ratio A (λ) obtained by the optical fiber cutoff wavelength measuring method of the present embodiment and the wavelength spectrum of the transmitted light power ratio measured by the bending method for comparison are shown. In contrast, the accuracy of the cutoff wavelength obtained in this embodiment will be described.
FIG. 3 shows an optical fiber cut-off wavelength measurement method according to an embodiment of the present invention, in which a small bend 2 having a diameter of 20 mm is added as a small bend 2 when measuring the transmitted light power in the reference multimode optical fiber 1. FIG. 4 is a diagram showing an example of the measurement result when a minute bending with a diameter of 10 mm is applied.

In FIG. 3 and FIG. 4, in order to verify the accuracy of the measurement results, the measurement results of the cut-off wavelength by the bending method are superimposed.
As shown in the examples of FIGS. 3 and 4, the cut-off wavelength λc1 by the cut-off wavelength measurement method of the optical fiber according to the present embodiment and the cut-off by the bending method, which is another cut-off wavelength measurement method with little variation. The difference from the wavelength λc0 is small.
On the other hand, in the cut-off wavelength measurement method of the optical fiber that does not add the minute bend 2, the difference between the obtained cut-off wavelength λc2 and the cut-off wavelength λc0 obtained by the bending method is a fine bend of 20 mm in diameter. It becomes larger than the example of FIG.
That is, by measuring a reference multimode optical fiber 1 with a minute bend 2, the higher-order mode is removed from the measured transmitted light power, and the measurement reproducibility by the multimode reference method is stabilized. Can do.
Further, in the present embodiment, by using the measurement result of the reference multimode optical fiber 1 for the bending method that requires two measurements for the optical fiber 5 to be measured, the optical fiber 5 to be measured is used. On the other hand, since the cut-off wavelength can be obtained by only one measurement, the measurement time can be shortened compared to the bending method.

3 is added (for example, when the diameter is 10 mm in FIG. 4), the transmitted light power of the optical fiber 5 to be measured and the transmitted light of the multimode optical fiber 1 for reference are used. In the wavelength spectrum of the ratio to the power, the fluctuation of the measured value in the region where the baseline L1 after the change of the transmitted light power changing from the multimode to the single mode should be determined is smaller than in the case of FIG.
As described above, when the microbending 2 having a diameter of less than 20 mm is added, the fluctuation of the base line L1 becomes smaller. Therefore, the transmitted light power of the measured optical fiber 5 and the transmitted light of the reference multimode optical fiber 1 are reduced. The cut-off wavelength can be calculated more accurately based on the wavelength spectrum of the ratio to the power.

[Example]
In the reference measurement process of the present embodiment, when measuring the transmitted light power of the reference multimode optical fiber 1, measurement was performed by adding one turn of each of the diameters 10 mm, 15 mm, 20 mm, and 30 mm as the minute bend 2. .
On the other hand, in the measurement optical fiber measurement step of the present embodiment, the transmitted light power was measured for 27 optical fibers to be measured.
Then, in the cutoff wavelength calculation step of the present embodiment, the wavelength characteristic of the transmitted light power of the reference multimode optical fiber 1 and the transmitted light power of the measured optical fiber 5 measured in the measured optical fiber measurement step The transmitted light power ratio A (λ) with respect to the wavelength characteristics of the optical fiber is calculated, the cut-off wavelengths of the 27 optical fibers to be measured are calculated, and the microbending 2 of the reference multimode optical fiber 1 is 10 mm, 15 mm in diameter, It calculated | required in each case of 20 mm and 30 mm.
Also, when the 27 optical fibers 5 to be measured are bent by the bending method, the transmitted light power when the circumferential minimum bending of 60 mm in diameter is applied and the minimum bending of the circumference of 280 mm in diameter are applied. And the cut-off wavelength was determined.
For the 27 optical fibers 5 to be measured, the cut-off wavelength obtained in each of the cases where the microbending 2 of the reference multi-mode optical fiber 1 has a diameter of 10 mm, 15 mm, 20 mm, and 30 mm and the bending method are used. The difference from the calculated cutoff wavelength was determined. Table 1 shows the number of optical fibers whose difference from the measurement result by the bending method is ± 5 nm or more and ± 7 nm or more, and the standard deviation of the difference from the measurement result by the bending method.

  As shown in Table 1, when the diameter of the minute bend 2 applied to the reference multimode optical fiber 1 in the reference measurement process of the present embodiment is particularly smaller than 20 mm, the difference from the bend method is small and the variation (standard) On the other hand, in the case of 20 mm or more, the difference from the bending method is large and the variation is large. This is presumably because the smaller the bending diameter, the flatter the wavelength spectrum in the wavelength band from which the higher-order mode has escaped, and the more stable the measurement reproducibility by the multimode reference method.

DESCRIPTION OF SYMBOLS 1 Multimode optical fiber for reference 2 Minute bending 3 Light source part 4 Light receiving part 5 Optical fiber to be measured 6 Bending with a diameter of 280 mm

Claims (2)

A reference measurement process for measuring the wavelength characteristic of transmitted light power by applying a slight bend to the multimode optical fiber for reference,
A measurement optical fiber measurement step for measuring the wavelength characteristic of the transmitted light power of the measurement optical fiber;
A cut for calculating a cutoff wavelength of the optical fiber to be measured based on a wavelength characteristic of a ratio between a wavelength characteristic of the transmitted light power of the reference multimode optical fiber and a wavelength characteristic of the transmitted optical power of the optical fiber to be measured Off-wavelength calculation step;
A method for measuring the cutoff wavelength of an optical fiber having   The cut-off wavelength measurement method for an optical fiber according to claim 1, wherein a diameter of the minute bend in the reference measurement step is made smaller than 20 mm.

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