JP6036345B2 - Measuring method of cutoff wavelength of optical fiber - Google Patents

Description

  The present invention relates to a method for measuring a cutoff wavelength of an optical fiber, and more particularly to a method for measuring a cutoff wavelength of a single mode optical fiber by a bending method.

  As a method of measuring the cutoff wavelength in a single mode optical fiber, the following bending method is recommended by International Telecomunication Union-T (ITU-T). For example, the measurement method of the cut-off wavelength by the bending method described above uses a first mandrel having a diameter of 280 mm and a second mandrel having a diameter of 60 mm, and an optical fiber having a predetermined length has a circumferential minimum bending diameter of 60 mm. Is measured, and the transmitted light power P2 is measured when the optical fiber is subjected to a circumferential minimum bend of 280 mm in diameter, and the power ratio between these transmitted light powers P1 and P2 is measured. Is the longest wavelength at which the wavelength becomes 0.1 dB (see Patent Document 1).

Japanese Patent Laid-Open No. 9-22981

  In the measurement method of the cut-off wavelength by the bending method, a predetermined wavelength range is obtained when a circumferential minimum bend of 280 mm in diameter is added to the optical fiber and when a minimum bend of a circumference of 60 mm in diameter is added. In (Patent Document 1, in the range from 800 nm to 1400 nm), the transmitted light power is measured. In order to obtain the cut-off wavelength with certainty, it is necessary to widen the wavelength range to be measured to some extent in the measurement with each minimum bend, but the longer the wavelength range, the longer the measurement time.

  Therefore, an object of the present invention is to provide a method for measuring the cutoff wavelength of an optical fiber that can shorten the measurement time while accurately measuring.

In order to achieve the above object, the present invention adds a transmitted light power P1 when a minimum bend of about 280 mm in diameter is applied to an optical fiber having a sample length of about 2 m, and a minimum bend of about 60 mm in diameter to the optical fiber. In the measurement method of the cutoff wavelength of the optical fiber, in which the longest wavelength at which the power ratio with the transmitted light power P2 is about 0.1 dB is the cutoff wavelength,
Using either measurement data of the transmitted light power P1 or P2, the other measurement wavelength range of the transmitted light power P1 or P2 is determined.

  Further, in the method for measuring the cut-off wavelength of the optical fiber, the wavelength at which the transmitted light power of either the transmitted light power P1 or P2 is maximized is used as a reference and is longer than the wavelength at which the transmitted light power is maximized. A range up to a predetermined wavelength on at least one side of the wavelength side and the short wavelength side may be set as the other measurement wavelength range of the transmitted light powers P2 and P1.

  According to the present invention, even when the measurement wavelength range of transmitted light power is narrowed, an accurate cut-off wavelength can be obtained, so that the measurement time of the cut-off wavelength of the optical fiber can be shortened.

It is the schematic of the measuring apparatus which implements the measuring method of the cutoff wavelength of the optical fiber which concerns on one Embodiment of this invention. FIG. 2 is a schematic waveform diagram for explaining a measurement result by the measuring apparatus of FIG. 4 is a graph showing the wavelength measurement results of Example 1. It is a graph which shows the wavelength measurement result of Example 2.

  Hereinafter, a method for measuring a cutoff wavelength of an optical fiber according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic view of a measuring apparatus for carrying out a method for measuring a cutoff wavelength of an optical fiber by a bending method.
The measuring apparatus for performing the method for measuring the cutoff wavelength of the optical fiber shown in FIG. 1 includes a pair of holding parts 4 and 5 that hold both ends of the optical fiber 1 so as not to be loosened, and one holding part 4. A light source 6 for allowing measurement light to enter the end of the optical fiber held by the optical fiber, and a light receiving unit 7 for detecting the transmitted light power emitted from the end of the optical fiber held by the other holding unit 5.

  In addition, this measuring apparatus provides a first mandrel 2 with a diameter of 280 mm (diameter 280 mm) and a second mandrel 3 with a diameter of 60 mm (diameter 60 mm) by winding the optical fiber around the outer periphery. It has.

  As shown in FIG. 1 (a), by winding the optical fiber 1 around the outer periphery of the first mandrel 2, a circumferential minimum bend of φ280 mm (diameter 280 mm) can be imparted.

  Further, as shown in FIG. 1B, the optical fiber 1 is wound around the outer periphery of the second mandrel 3, or both the outer periphery of the first mandrel 2 and the outer periphery of the second mandrel 3. 1 can prevent high-order mode light from passing therethrough.

Next, a method for measuring the cutoff wavelength of the optical fiber according to the present embodiment will be described with reference to FIGS.
FIG. 2 is a schematic waveform diagram for explaining a measurement result by the measurement apparatus of FIG.
FIG. 2A is a schematic waveform diagram showing the transmitted light power P1 measured by the measuring apparatus of FIG. 1A and the transmitted light power P2 measured by the measuring apparatus of FIG. .
FIG. 2B is a schematic waveform diagram showing the power ratio (difference) between the transmitted light powers P1 and P2.

First, the optical fiber 1 having a sample length of 2 m is wound around the first mandrel 2 having a diameter of 280 mm, and the transmitted light power P1 is measured in the state shown in FIG.
In the state of FIG. 1A, the light source 6 emits light, and measurement light having a predetermined wavelength enters the optical fiber 1 from the end of the optical fiber held by the holding unit 4. This incident light passes through the portion wound around the first mandrel 2 and exits from the end of the optical fiber held by the holding unit 5. This emitted light is detected by the light receiving unit 7, and the transmitted light power P1 is thereby measured. The measurement of the transmitted light power P1 is performed for each changed wavelength by changing the wavelength by a predetermined unit (for example, 10 nm) in a predetermined wavelength range (for example, a range from 1000 nm to 1500 nm). Thereby, each transmitted light power P1 in the predetermined wavelength range is measured.

  Each measured numerical value of the transmitted light power P1 in the predetermined wavelength range thus obtained is plotted on a graph as shown in FIG. 2A, and the wavelength at which the numerical value of the transmitted light power P1 is maximized from this graph. A wavelength λmax is obtained.

  Since the cutoff wavelength λc is a wavelength on the long wavelength side near the wavelength λmax where the transmitted light power is maximum, it is possible to estimate to some extent how much the cutoff wavelength λc will be based on this measurement result. . Depending on the type and manufacturing method of the optical fiber, how far the cutoff wavelength is from λmax differs, but the actual measurement may be within the specified range for each optical fiber type and manufacturing method. I know from experience.

  Then, λmax + λa obtained by adding a predetermined numerical value λa to the wavelength λmax and λmax−λb obtained by subtracting the predetermined numerical value λb from the wavelength λmax are measured, and the transmitted light power P2 described below is measured.

  Next, the optical fiber 1 is wound around the first mandrel 2 having a diameter of 280 mm and the second mandrel 3 having a diameter of 60 mm, respectively, so that the state shown in FIG. The transmitted light power P2 is measured.

  In the state of FIG. 1B, the light source 6 emits light and measurement light having a predetermined wavelength is incident on the optical fiber 1 from the end of the optical fiber held by the holding unit 4. The incident light passes through the portion wound around the first mandrel 2 and the portion wound around the second mandrel 3 and exits from the end of the optical fiber held by the holding unit 5. This emitted light is detected by the light receiving unit 7, and the transmitted light power P2 is thereby measured. The range of the measurement wavelength in this measurement is a range from λmax−λb to λmax + λa from the value of λmax obtained by the previous measurement of the transmitted light power P1. In this wavelength range, the wavelength is changed by a predetermined unit (for example, 10 nm), and the transmitted light power is measured for each changed wavelength. Thereby, each transmitted light power P2 in the wavelength range from λmax−λb to λmax + λa is measured. Then, the transmitted light power P2 thus obtained is plotted on a graph of the transmitted light power P1 (see FIG. 2A).

  Next, when the transmitted light power ratio, which is the measured power ratio between the transmitted light powers P1 and P2 (here, the numerical value of P1-P2) is plotted on a graph, it is as shown in FIG. Then, as shown in FIG. 2B, the longest wavelength at which the transmitted light power ratio is 0.1 dB is defined as a cutoff wavelength λc.

  According to the method of measuring the cutoff wavelength λc of the optical fiber 1 according to the present embodiment, each transmitted light power P1 is measured in a predetermined wavelength range, and the wavelength λmax at which the measured transmitted light power P1 is maximized is obtained. Λmax + λa obtained by adding a predetermined numerical value λa to the wavelength λmax and λmax−λb obtained by subtracting the predetermined numerical value λb from the wavelength λmax are obtained, and the transmitted light power P2 is measured in a wavelength range from λmax−λb to λmax + λa. To obtain the cutoff wavelength λc. That is, the measurement wavelength range of the transmitted light power P2 is determined using the measurement data of the transmitted light power P1 and the wavelength λmax as a reference. Thereby, even if the measurement wavelength range of the transmitted light power P2 is narrowed, the cutoff wavelength λc can be obtained, and the measurement time of the cutoff wavelength λc of the optical fiber 1 can be shortened.

  As described above, the method for measuring the cutoff wavelength of the optical fiber according to the present invention has been described based on the embodiment. However, the above embodiment is for facilitating the understanding of the present invention and limits the present invention. is not. The present invention can be changed and improved without departing from the gist thereof, and the present invention naturally includes equivalents thereof.

  For example, the transmitted light power P2 is measured by wrapping an optical fiber only around the second mandrel 3 with a diameter of 60 mm, without using the first mandrel 2 with a diameter of 280 mm shown in FIG. Also good.

  Further, in the above embodiment, the measurement wavelength range of the transmitted light power P2 is determined by measuring the transmitted light power P1 with the measurement apparatus of FIG. 1A, and then the measurement apparatus of FIG. Although the transmitted light power P2 is measured, for example, the measured wavelength range of the transmitted light power P1 is determined by measuring the transmitted light power P2 with the measurement device of FIG. You may make it measure the transmitted light power P1 with the measuring apparatus of (a). That is, the measurement wavelength range of the transmitted light power P1 may be determined using the measured data of the transmitted light power P2.

  In addition, the predetermined numerical values λa and λb in the embodiment may be set according to the type of optical fiber. One or both of λa and λb may be changed based on the value of the wavelength λmax at which the measured transmitted light power P1 or P2 is maximum.

In the above embodiment, the measurement wavelength range of the transmitted light power P2 is from λmax−λb to λmax + λa, but the measurement start wavelength on the short wavelength side is not changed, and the predetermined wavelength (λmax + λa) on the long wavelength side of the wavelength λmax is changed. The range up to may be the measurement wavelength range. For example, even if the range of the measurement wavelength with respect to the transmitted light power P2 is up to λmax + λa, the cutoff wavelength λc, which is the longest wavelength at which the transmitted light power ratio is 0.1 dB, can be measured, and the cutoff wavelength λc of the optical fiber 1 can be measured. Time can be shortened.
Conversely, the measurement may be started from (λmax−λb) without changing the measurement end wavelength on the long wavelength side.

Next, an embodiment actually measured using an optical fiber will be described.
The measurement apparatus of FIG. 1 was used, and measurement was performed on the optical fiber A in Example 1 and the optical fiber B in Example 2.

Example 1
The optical fiber A having a sample length of 2 m is set in the state of FIG. 1A, and the transmitted light power P1 is measured by changing the wavelength of the measurement light emitted from the light source 6 by 10 nm in the wavelength range of 1000 nm to 1500 nm. It was. The measurement result is shown in the line graph of the transmitted light power P1 in FIG. From the line graph of the transmitted light power P1, it is found that the wavelength λmax at which the transmitted light power P1 is maximum is 1160 nm.

  Next, before measuring the transmitted light power P2, λa was set to 140 nm and λb was set to 40 nm, and the wavelength ranges for measuring the transmitted light power P2 were set to λmax−λb = 1120 nm and λmax + λa = 1300 nm. Then, in the state shown in FIG. 1B, the transmitted light power P2 was measured by changing the wavelength of the measurement light emitted from the light source 6 by 10 nm in the wavelength range of 1120 nm to 1300 nm.

  The measurement result is shown in the line graph of the transmitted light power P2 in FIG. Further, FIG. 3 shows a numerical value of P1-P2 as a line graph of the transmitted light power ratio based on P1 and P2. From the graph of the transmitted light power ratio in FIG. 3, it was found that the cut-off wavelength λc of the optical fiber A was 1230 nm when the longest wavelength at which the transmitted light power ratio was 0.1 dB was examined.

(Example 2)
The optical fiber B having a sample length of 2 m was set in the state shown in FIG. 1A, and the transmitted light power P1 was measured by the same method as in Example 1. The measurement results are shown in the line graph of the transmitted light power P1 in FIG. From the line graph of the transmitted light power P1, it is found that the wavelength λmax at which the transmitted light power P1 is maximum is 1190 nm.

  Next, before measuring the transmitted light power P2, λa was set to 140 nm and λb was set to 40 nm, and the wavelength ranges for measuring the transmitted light power P2 were set to λmax−λb = 1150 nm and λmax + λa = 1330 nm. Then, in the state of FIG. 1B, the transmitted light power P2 was measured by changing the wavelength of the measurement light emitted from the light source 6 by 10 nm in the wavelength range of 1150 nm to 1330 nm.

The measurement result is shown in the line graph of the transmitted light power P2 in FIG. Further, FIG. 4 shows a numerical value of P1-P2 as a line graph of the transmitted light power ratio based on P1 and P2. From the graph of the transmitted light power ratio in FIG. 4, it was found that the cut-off wavelength λc of the optical fiber B was 1290 nm when the longest wavelength at which the transmitted light power ratio was 0.1 dB was examined.
Note that the values of λa and λb described above are examples, and are not limited to the above values. Further, since the waveform of the transmitted light power is roughly determined by the type and manufacturing method of the optical fiber, the values of λa and λb may be determined in advance for each type and manufacturing method of each optical fiber.

  In the first and second embodiments described above, the measurement of the transmitted light power P1 is reduced by narrowing the wavelength range for measuring the transmitted light power P2 that does not include the higher-order mode in the measurement in FIG. Compared to the conventional measurement method in which measurement was performed in the same wavelength range, the measurement time could be shortened by about 20%.

  1: optical fiber, 2: first mandrel, 3: second mandrel, 4, 5: holding unit, 6: light source, 7: light receiving unit

Claims (2)

The power ratio between the transmitted light power P1 when a minimum bend of approximately 280 mm in diameter is applied to an optical fiber having a sample length of approximately 2 m and the transmitted light power P2 when a minimum bend of approximately 60 mm in diameter is applied to the optical fiber is approximately In the measuring method of the cutoff wavelength of the optical fiber in which the longest wavelength of 0.1 dB is the cutoff wavelength,
A method for measuring a cutoff wavelength of an optical fiber, wherein either one of the transmitted light powers P1 or P2 is used to determine a measurement wavelength range of the other transmitted light power P1 or P2. .   With reference to the wavelength at which the transmitted light power of either one of the transmitted light powers P1 or P2 is maximized, up to a predetermined wavelength on at least one side of the long wavelength side and the short wavelength side from the wavelength at which the transmitted light power is maximized 2. The method of measuring an optical fiber cut-off wavelength according to claim 1, wherein the range is set to the measurement wavelength range of the other of the transmitted light powers P2 and P1.

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