JPS6229762B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an incident optical transmission line used in measuring the characteristics of an optical fiber, and more particularly to an incident optical transmission line that can be used for both transmission loss measurement and transmission band measurement. Measuring and knowing the transmission loss and transmission band of an optical fiber is an important matter for designing optical communication systems and other matters. Conventionally, such measurement methods include the cutback method (destructive measurement method), in which a break point is created at a predetermined position on the optical fiber to be measured, and the transmission loss is determined from the relative relationship between this break point and the measurement point, and the cutback method (destructive measurement method), which involves setting the above break point. There is an insertion method (non-destructive measurement method) that does not require a breaking point, and the insertion method is said to be more convenient than the cutback method because it does not require a breaking point. One of the above-mentioned insertion methods, the one shown in FIG. 1, which has already been implemented, has the following structure. In the figure, 1 is a transmitter, 2 is a laser diode, 3 is a light emitting diode, 4 ₁ and 4 ₂ are optical switches, 5 is an incident optical transmission line, 6 ₁ and 6 ₂ are V-groove type simple connectors, and 7 is the optical fiber to be measured, 8 is the AP
(avalanche photo) diode, 9 is a receiver, 10 is an optical power meter, 11 ₁ , 11 ₂ is an optical code, 12 ₁ , 12 ₂ , 12 ₃ is the optical code 1
This optical cord has a larger core diameter than those of No. 1 ₁ and No. 11 ₂ , and these are optically connected as shown. When measuring the transmission loss and transmission band of the optical fiber 7 to be measured using the measuring means shown in FIG. The flowchart of the flow of optical pulses during band measurement and loss measurement using the symbols in Figure 1 is as follows:
For band measurement, 1, 2 → 11 ₁ → 4 ₁ → 5 →
7 → 12 ₁ → 4 ₂ → 12 ₂ → 8, 9, and the transmission band of the optical fiber 7 to be measured is detected via the AP diode 8 and the receiver 9. On the other hand, when measuring the loss, 3 → 11 ₂ → 4 ₁ →
5 → 7 → 12 ₁ → 4 ₂ → 12 ₃ → 10, and the transmission loss of the optical fiber 7 to be measured is detected by the optical power meter 10. By the way, in the case of the above-mentioned incident optical transmission line 5, if it is used for band measurement, a configuration is required to make the incident conditions (excitation conditions) to the optical fiber 7 to be measured appropriate when using this for band measurement. Similarly, a configuration for adjusting the incident conditions for loss measurement is also required. For example, the incident light transmission line 5 for band measurement must satisfy temporal or spatial coherence, such that the incident light is a continuous wave with a single frequency, the lights are randomly overlapped, or the wavefront is distorted. On the other hand, in the case of the incident optical transmission line 5 for loss measurement, it is required to emit multimode light with uneven wavelength phases. Traditionally, dedicated input optical transmission lines have already been provided for bandwidth measurement, loss measurement, etc., and include step index type (SI type) optical fiber and graded index type (GI type) optical fiber. The above two types of conventional examples consisting of a combination of the above have also obtained satisfactory results as dedicated types. These conventional examples will be briefly explained below with reference to FIGS. 2A and 2B. Figure 2A shows the incident optical transmission line 5A for loss measurement, and Figure 2B shows the incident optical transmission line 5B for band measurement. , SI type optical fiber 22, GI type optical fiber 23, and also GI type optical fiber 2
4 are fused and spliced in the longitudinal direction,
The other incident optical transmission line 5B is an SI type optical fiber 3.
1. A GI type optical fiber 32 and an SI type optical fiber 33 are fused and spliced in the longitudinal direction. Table 1 shows the specifications of the incident light transmission lines 5A and 5B.

[Table] In addition, the incident light transmission lines 5A and 5B in Figure 2 A and B
, the exit NA (50%) is 0.1±0.03,
Spot size (50%) is 30±3 μm. In the above, one input optical transmission line 5A is used by the known cutback method, and the other input optical transmission line 5B is connected between the optical switch ₄₁ and the simple connector ₆₁ in FIG. 1 (insertion method). The optical fibers to be measured were each measured. The results are shown in Table 2.

[Table] The length of the optical fibers No. 1 to 5 to be measured is 1 km.
It is an optical fiber core wire, and the core diameter/cladding diameter is
50μm/125±3μm, relative refractive index difference (△) is 1.0±
It is 0.15%. Further, when measuring loss using the incident optical transmission line 5A and measuring bandwidth using the incident optical transmission line 5B, the wavelengths used by the light emitting diode (LED) and the laser diode (LD) are each 0.85 μm. The measurement results shown in Table 2 above are extremely reliable values, and therefore, conventionally, the incident optical transmission line 5
A and 5B are used to perform loss measurements and band measurements individually. However, loss measurement and band measurement must be performed separately, which is time-consuming. Of course, even if a device for loss measurement is used for band measurement, or conversely, a device for band measurement is used for loss measurement, as will be clear from the comparison with the present invention described later, reliable values cannot be obtained. . In view of the above, the present invention improves the input optical transmission path so that even if the input conditions are different for loss measurement and band measurement, the input optical transmission path can obtain input conditions suitable for both measurements. The effects will be explained based on drawings and experimental results. FIG. 3 shows an incident light transmission line 5C according to the present invention, in which 41 is an SI type optical fiber, 42 is a GI type optical fiber, and 43 is an SI type optical fiber. Each optical fiber 41, 42, 43 in the above
As shown in the figure, they are fused and spliced in the longitudinal direction in an SI type-GI type-SI type arrangement, and their specifications are as shown in Table 3.

[Table] In the case of the incident light transmission line 5C in the present invention, the output NA (50%) is 0.1±0.03 and the spot size (50%) is 26±3 μm. Next, the incident optical transmission line 5C of the present invention was set between the optical switch ₄₁ and the simple connector 61 shown in FIG. ₁ , and the transmission loss and transmission band of the optical fiber under test were measured in the same manner as above. The results will be explained using Tables 4 and 5. Incidentally, the incident light transmission line 5C at this time includes a 1-2 m optical fiber 41, a 1-m optical fiber 42, and 1-2 m optical fibers.
m optical fiber 43 is used, and on the other hand,
The optical fibers (No. 1 to 5) to be measured were those shown in Table 2 above. In addition, in Table 4 showing the measurement results of transmission loss,
The transmission loss measurement values in Table 2 were used as a standard, and Table 5, which shows the transmission band measurement results, was based on the transmission band measurement values in Table 2.

【table】

[Table] As is clear from Table 4, the incident light transmission line 5 of the present invention
The loss measurement results using C were almost close to the reference values and showed reliable values, but the incident optical transmission line 5B, which is dedicated to band measurement (Figure 2 B), did not show satisfactory values. On the other hand, even in the band measurement results shown in Table 5, there is almost no difference between the band measurement results of the present invention and the reference values, whereas the incident optical transmission line 5A for loss measurement (Fig. 2 A)
However, the values fluctuate considerably above and below the standard value, with large variations. Next, the reproducibility during the above transmission band measurement will be explained with reference to Table 6. In Table 6, the No. 1 optical fiber to be measured is the measurement target, and each incident optical transmission line 5A, 5B, 5C
Each was set in the apparatus shown in FIG. 1, and the applied band was measured five times.

[Table] As is clear from Table 6, the input optical transmission line 5A used exclusively for loss measurement (Figure 2 A) is compared with the reference input optical transmission line 5B for band measurement (Figure 2 B). Although the deviation value is greatly exceeded and the deviation value is also large, the incident light transmission line 5 of the present invention
The measured value of C is similar to that of FIG. 2B, and the deviation value is small, indicating good reproducibility. Next, regarding transmission loss, Table 7 shows the results summarized from the comparison between the insertion method and the cutback method and the relationship with connection loss. In this case, the incident optical transmission line 5C of the present invention collects data by the insertion method shown in FIG.
The incident light transmission line 5A in Figure A shows data obtained by the cutback method described above. The optical fibers to be measured (Nos. 1 to 5) are the same as those described above.

[Table] As is clear from Table 7, the measured transmission loss of the incident optical transmission line 5A in Figure 2A varies by more than ±0.1 dB, and the connection loss also varies between the maximum and minimum values.
Although there is a difference of 0.12 dB, the incident optical transmission line 5 of the present invention
In case C, the measured values of transmission loss match within 0.1 dB, and the difference in connection loss also falls within 0.05 dB. In addition, in the case of the incident light transmission line 5C according to the present invention,
The length of each optical fiber 41, 42, 43 is 0.1 to 10
If it is within the range of m, almost the same results as described above can be obtained, but in practice
1 is preferably about 1 to 2 m, the optical fiber 42 is about 1 m, and the optical fiber 43 is about 1 to 2 m. As explained above, the input optical transmission line of the present invention has step index type (SI) optical fibers at both ends and a graded index type (GI type) optical fiber in the middle. Optical fibers are connected in the longitudinal direction, and each optical fiber has a length of 0.1 to 10 m, a core diameter of 30 ± 5 μm,
It is characterized by a relative refractive index difference of 0.8 ± 0.1%, and can be used to measure both transmission loss and transmission band using one incident optical transmission path, so unlike conventional methods, it is possible to measure both transmission loss and transmission band. This eliminates the trouble of preparing two types of transmission lines or using them to investigate the characteristics of each separately.Of course, the measured values are also highly reliable and have sufficient reproducibility. Since reliable measurement values can be obtained not by the cutback method, which requires cut-off points, but by the insertion method, which is simpler than this method, convenient measurement conditions can be ensured overall.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing a measurement means using the insertion method, FIGS. 2A and 2B are front views schematically showing a conventional incident light transmission path, and FIG. 3 is a schematic diagram of an incident light transmission path according to the present invention. FIG. 3 is a schematic front view. 5C...Incoming light transmission line, 41...Step index type optical fiber, 42...Graded index type optical fiber, 43...Step index type optical fiber.

Claims (1)

[Claims] 1. A step index type optical fiber is arranged at both ends and a graded index type optical fiber is arranged in the middle, and these three optical fibers are connected in the longitudinal direction. The optical fiber has a length of 0.1 to 10 m, a core diameter of 30 ± 5 μm, and a relative refractive index difference of 0.8 ± 0.1%. It is an incident light transmission line for measuring transmission loss and transmission band. 2. An incident light transmission line for measuring transmission loss and transmission band of an optical fiber according to claim 1, wherein each optical fiber has a length of 1 to 2 m.