JPS6073334A - Method and apparatus for measuring transmission characteristic of optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method and apparatus for measuring the transmission band of an optical fiber with high precision.

(Prior Art and its Problems) The transmission band of an optical fiber is an important characteristic that governs its performance as a communication path, and it is extremely important to accurately measure this.

Conventionally, transmission band measurement of optical fibers has been carried out using a dummy fiber that excites the output light from a light source 1 that has been modulated by a signal generator 2 with an appropriate signal waveform (pulse or sine wave), as shown in Figure 1. 3 to the optical fiber to be measured 5 and received by the photodetector 6 at the output end of the optical fiber to be measured, the optical signal is processed by the signal processing unit 7 to measure the transmission band.

Here, the excitation dummy fiber 3 and the optical fiber to be measured 5
The connections were made by butting using V-grooves or by fusion splicing. However, the transmission band of an optical fiber has a property that it largely depends on the excitation conditions at the input end of the optical fiber to be measured. For this reason, there is a drawback that the measured value of the transmission band tends to change depending on the connection state between the excitation dummy fiber and the optical fiber to be measured. this is,
This is particularly noticeable when the core portion of the optical fiber to be measured is eccentric.

As a method to improve the deterioration of reproducibility due to such causes, the conventional method is to connect one side of the excitation dummy fiber 3 and the optical fiber under test 5 at the connection point, as shown in FIG. The optical fiber end is fixed to a finely movable alignment device 8, and the axis of the optical fiber is aligned at the connection point while being monitored by an output level monitor 9 so that the light output received at the light receiving section is maximized. be. However, the light source for transmission band measurement, such as a semiconductor laser, generally has poor output stability, and in addition, output fluctuations called mode noise inevitably occur in the optical output transmitted through the optical fiber to be measured. Therefore, as described above, it is extremely difficult to align the axis with high precision so that the light output is maximized in the light receiving section.

(Contents of the Invention) The present invention eliminates such drawbacks and provides a method and apparatus for measuring the transmission band of an optical fiber with good reproducibility by always realizing constant excitation conditions.

Therefore, in the method according to the present invention, output light from both light sources, a transmission band measurement light source and a highly stable reference light source, is incident on one end of an excitation optical fiber, and the other end of the excitation optical fiber is adjusted. The optical fiber to be measured is connected to the optical fiber to be measured via a core device, the output end of the optical fiber to be measured is coupled to a light receiving section, the optical signals from the two light sources are separated in the light receiving section, and the separated reference The signal from the optical source is used as a reference signal to fully control the alignment device in order to optimize the connection between the excitation optical fiber and the optical fiber under test, and the signal from the other separated light source is used to measure the entire transmission band. It is assumed that it is used as a signal for use.

Further, the device according to the present invention includes a transmission band measurement light source, a reference light source with a highly stable output, an excitation optical fiber into which the output light from both light sources is input at one end, and the other end of the excitation source fiber. It includes an iN, lI constant optical fiber connected to the optical fiber through an alignment device, and a light receiving section coupled to the output end of the optical fiber to be measured; The device has a separation means for separating the signal from the reference light source, and monitors the connection state of the excitation optical fiber and the optical fiber to be measured, which receives a signal from the reference light source separated by the signal separation means in the light receiving section. It is characterized in that the output level monitor is connected to a signal processing section for measuring the transmission band of the signal from the other light source.

Hereinafter, the content of the present invention will be explained with reference to the embodiment shown in the attached figure 1.

FIG. 3 shows an example of the configuration of an apparatus for carrying out the method of the present invention, and in this figure, the same reference numerals as in FIG. 1.2 indicate the same components.

In this device, in addition to the transmission band measurement light source 1, a highly stabilized 4t light source (for example, L
ED light source), and its output light is introduced into the excitation fin 3 via an optical multiplexer. In the light receiving section, the optical signals from these two light sources are separated, and while referring to the output of only the reference light, the axis alignment of the connection part is performed while monitoring with the output level monitor 9 so that the output becomes maximum. For example, high-quality alignment can be achieved.

As a method of separating only the reference light output in the light receiving section, as shown in Fig. 3 (,z), the wavelengths of the transmission band measurement light source and the reference light source should be set apart by 0.05 in this case.
(It is sufficient if the separation is at least μm), the outputs of both parties must be separated by a wavelength-selective demultiplexer 12 in the light receiving section, or a third
As shown in Figure (1)), a modulated sound is applied to the reference light source with a continuous waveform of a constant frequency different from the frequency of the constant-angle signal (a), and the signal is detected from the electrical signal output of the photodetector 6 at the light receiving section. There are alternatives, such as separating only the 1 auspicious frequency component in the nausea circuit 13, but both are effective.

In this way, it is necessary to align the excitation fiber 3 and the optical fiber to be measured 5 with a high degree of coherence using the reference light stabilized at the foot of the mountain. is highly controlled so that it remains constant, making stable and highly accurate transmission band measurement possible.

(Effect of the invention) In order to investigate the axis alignment ability sound of the connection part in the present invention, the third
In the configuration shown in figure (α), the amount of axis misalignment at the connection point (
(The relationship between the light output and output power was measured. The constant results are shown in Figure 4. The core diameter of the optical fiber used was 50 μm. Also, the time fluctuation of the reference light output was measured, and the results were shown in Figure 4. The maximum variation width was less than 0.01 dB.

Here, an LEDt is used as a reference light source. From the results shown in FIG. 4, it can be seen that according to the method of the present invention, it is possible to align the axis to the container with an accuracy of within 1 μm. On the other hand, the temporal variation of the optical output for band measurement (a semiconductor laser was used as the light source) reached a maximum variation of 1 layer within 1 minute of 0.8 dB. From FIG. 4, it can be seen that the conventional device can only align with an accuracy of about 5 Am.

From the above results, it is clear that according to the present invention, the excitation conditions for the optical fiber to be 1j can be set to a high degree of uniformity, thereby making it possible to perform stable and highly accurate transmission band measurements. Further, in the present invention, since a very specific reference signal can be obtained, it is extremely easy to add a complete device that automatically aligns the connecting portion using this reference signal.

[Brief explanation of the drawing]

FIGS. 1 and 2 are configuration diagrams of a conventional apparatus. Figure 3 (cLl (bl) is a configuration diagram of the device based on the present invention. Figure 4 is a graph showing the results of measuring the relationship between the amount of axis deviation at the connection point and the reference light output using the method of the present invention. In the drawing, 1 is a light source for transmission band measurement, 2 (is a signal generator, 3 is an excitation fiber, 4 is a connection point, 5 is an 'e1. measurement optical fiber, 6.6' is a photodetector, and 7 is a signal processing section,
8 (is the tip alignment mechanism, 9 is the output level monitor, 10 is the
is a reference light source, 11 is an optical multiplexer, 12 is an optical demultiplexer, 13
shows all the old separation circuits. (4 other people)

Claims (4)

[Claims] (1) The output light from both the transmission band measurement light source and the reference light source with highly stable output is input into one end of an excitation optical fiber, and the other end of the excitation optical fiber is connected via an alignment device. Connect it to the optical fiber to be measured, couple the output end of the constant optical fiber to the light receiving part, separate the optical signals from the two light sources in the light receiving part, and collect all the signals from the separated reference light source. In order to optimize the connection state between the excitation optical fiber and the target tt1+ constant optical fiber, the alignment device tf is used as a reference signal for fullil, and the signal from the other separated light source is used as a signal for both transmission and transmission bands. A method for measuring transmission characteristics of an optical fiber. (2) Transmission band z11] The wavelength of the regular light source and the wavelength of the reference light source are separated by 0.05 μm or more, and the optical signals from both light sources are separated by an optical demultiplexer Qτ with wavelength selectivity in the light receiving section. A method according to claim 1, characterized in that: (3) The reference light source is modulated with a constant frequency different from the frequency of the transmission band measurement signal, and the signal component of the frequency is separated by an electric circuit in the light receiving section. The method described in section. (4) A transmission band measurement light source, a reference light source with highly stable output, an excitation optical fiber into which the output light from both light sources is input at one end, and an alignment device at the other end of the excitation optical fiber. and a light receiving section coupled to the output end of the optical fiber to be measured, the light receiving section having a signal separating means for separating the optical signals from the two light sources. and an output level monitor for monitoring the connection state between the excitation optical fiber and the optical fiber to be measured, which receives a signal from the reference light source separated by the signal separation means, and receives a signal from the other light source. An optical fiber transmission characteristic measurement device connected to a signal processing section for transmission band measurement.