JPH037253B2 - - Google Patents

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 is performed by using a dummy fiber 3 for excitation with output light from a light source 1 modulated by a signal generator 2 with an appropriate signal waveform (pulse or sine wave), as shown in FIG. Through,
The transmission band is measured by processing an optical signal inputted into the optical fiber 5 to be measured and received by the photodetector 6 at the output end of the optical fiber to be measured in the signal processing unit 7.

Here, the excitation dummy fiber 3 and the optical fiber 5 to be measured are connected by butting with a V-groove, fusion splicing, or the like. 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 of the excitation dummy fibers 3 and the optical fiber 5 to be measured at the connection point, as shown in FIG. In this method, the end of the optical fiber is fixed to a finely movable alignment device 8, and the axis of the optical fiber is aligned at the connection part while being monitored by an output level monitor 9 so that the light output received by the light receiving part is maximized. . 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 has been 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 these 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 semiconductor laser as a light source for transmission band measurement and a light emitting diode as a reference light source, is incident on one end of an excitation optical fiber, and the other end of the excitation optical fiber is The end is connected to an optical fiber to be measured via an alignment 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 optical signals from the two light sources are separated. The signal from the separated reference light source is used as a reference signal for controlling the alignment device to optimize the connection state between the excitation optical fiber and the optical fiber to be measured, and the signal from the other separated light source is transmitted. It is characterized in that it is a signal for band measurement.

Further, the device according to the present invention includes a semiconductor laser as a light source for transmission band measurement, a light emitting diode as a reference light source, an excitation optical fiber into which the output light from both light sources is input at one end, and the excitation optical fiber. The optical fiber to be measured includes an optical fiber to be measured connected to the other end via an alignment device, and a light receiving section coupled to the output end of the optical fiber to be measured, and the optical signals from the two light sources are received in the light receiving section. an output level monitor which has a signal separation means for separating, and monitors the connection state of the excitation optical fiber and the optical fiber to be measured, the light receiving section receiving a signal from the reference light source separated by the signal separation means; The device is characterized in that it is connected to a transmission band measurement signal processing section that receives signals from the light source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be described below with reference to embodiments shown in the accompanying drawings.

FIG. 3 shows an example of the configuration of an apparatus for carrying out the method of the present invention, in which the same reference numerals as in FIGS. 1 and 2 indicate the same components.

In this device, in addition to the transmission band measurement light source (semiconductor laser) 1, a highly stabilized light source (LED light source, such as a surface-emitting diode or an edge-emitting diode) is used as a reference light source 10.
The output light is introduced into the excitation fiber 3 via the optical multiplexer 11. 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 adjusted while monitoring with the output level monitor 9 so that the output is maximized. If you do this, you can achieve highly accurate alignment.

As shown in Figure 3a, the method of separating only the reference light output in the light receiving section is to set the wavelengths of the transmission band measurement light source and the reference light source apart (in this case, a separation of 0.05 μm or more is sufficient). ), the two optical outputs are separated by a wavelength-selective demultiplexer 12 in the light receiving section, or the reference light source is set to a constant frequency different from the frequency of the transmission band measurement signal, as shown in Figure 3b. There are methods such as applying modulation with a continuous waveform of , and separating only the signal component of the frequency from the electrical signal output of the photodetector 6 in the light receiving section using the electrical circuit 13, but any of these methods are effective.

In this way, the excitation optical fiber 3 and the optical fiber to be measured 5 are connected using the highly stabilized reference light.
By performing highly accurate axis alignment with the optical fiber, the excitation conditions of the optical fiber to be measured are highly controlled to be constant, making it possible to perform stable and highly accurate transmission band measurements.

(Effects of the Invention) In order to examine the axial alignment ability of the connection portion in the present invention, the relationship between the amount of axial deviation at the connection point and the reference light output was measured using the configuration shown in FIG. 3a. The measurement results are shown in the fourth
As shown in the figure. The core diameter of the optical fiber used was 50 μm.
It is. In addition, when the time fluctuation of the reference light output was measured, the maximum fluctuation axis within one minute was 0.01 dB or less. Here, an LED 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, axis alignment can be easily achieved with an accuracy of within 1 μm. On the other hand, the temporal fluctuation of the optical output for band measurement (using a semiconductor laser as the light source) reached a maximum fluctuation of 0.3 dB within one minute. From FIG. 4, it can be seen that the conventional device can only align with an accuracy of about 5 μm.

From the above results, it is clear that according to the present invention, the excitation conditions of the optical fiber to be measured can be highly controlled, thereby enabling stable and highly accurate transmission band measurement. Further, in the present invention, since an extremely stable reference signal is obtained, it is extremely easy to add a device that automatically aligns the connection portion using this reference signal.

[Brief explanation of the drawing]

FIGS. 1 and 2 are configuration diagrams of a conventional apparatus. Figures 3a and 3b are block diagrams of an apparatus according to the invention. FIG. 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 according to the method of the present invention. In the drawing, 1 is a transmission band measurement light source, 2 is a signal generator, 3 is an excitation fiber, 4 is a connection point, 5 is an optical fiber to be measured, 6 and 6' are photodetectors, 7 is a signal processing section, and 8 is a Connection centering mechanism, 9 is an output level monitor, 10 is a reference light source, 11 is an optical multiplexer, 1
2 represents an optical demultiplexer, and 13 represents a signal separation circuit.

Claims (1)

[Claims] 1. Injecting output light from both light sources, a semiconductor laser as a light source for transmission band measurement and a light emitting diode as a reference light source, into one end of an excitation optical fiber,
The other end of the excitation optical fiber is connected to the optical fiber to be measured via an alignment device, the output end of the optical fiber to be measured is coupled to a light receiving section, and the optical signals from the two light sources are received within the light receiving section. and the signal from the separated reference light source is used as a reference number for controlling the alignment device to optimize the connection state between the excitation optical fiber and the optical fiber to be measured, and the separated other A method for measuring transmission characteristics of an optical fiber, characterized in that a signal from a light source is used as a signal for measuring a transmission band. 2 The wavelength of the light source for transmission band measurement 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 a wavelength-selective optical demultiplexer in the light receiving section. A method according to claim 1. 3. According to claim 1, 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 of. 4 A semiconductor laser as a light source for transmission band measurement, a light emitting diode as a reference light source, an excitation optical fiber into which the output light from both light sources is input at one end, and a laser beam aligned to the other end of the excitation optical fiber. A signal separation means that includes an optical fiber to be measured connected through the device and a light receiving section coupled to the output end of the fiber for the light to be measured, and separates the optical signals from the two light sources in the light receiving section. and an output level monitor for monitoring the connection state between the excitation optical fiber and the optical fiber to be measured, which receive signals from the reference light source separated by the signal separation means in the light receiving section, and signals from the other light source. An optical fiber transmission characteristic measuring device connected to a signal processing section for measuring the transmission band.