JPH0998119A - Optical pulse tester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exactly grasp a zone loss or a connection loss in the optical fiber to be tested of a communication signal with very high-level distance resolution without affecting communication by generating an optical pulse for which the test light and dummy light of different wavelengths are multiplexed in time sharing manner. SOLUTION: For measurement having the very high-level resolution, a pulse driver 28-1 generates the pulse of sufficiently narrow pulse width T1. A pulse driver 28-2 generates the dummy light for time sharing multiplex on a test signal pulse. Then, a synthetic pulse is generated by time sharing multiplexing the test light and that pulse is sent out to an optical fiber 4 to be tested. Even when the fiber 4 is tested by an optical pulse tester 20 while the communication signal of high frequency is transmitted to it, the S/N of the communication signal at a receiver 7 is not degraded. Besides, only the signal light of narrow pulse width having a wavelength λm is extracted by a wavelength depending optical fiber 29 and can be tested from the reflected light and rear dispersed light of a time sharing multiplexed optical signal returned to the tester 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pulse tester for remotely and accurately testing optical loss and other characteristics of an optical fiber which is a transmission medium for optical signals.

[0002]

2. Description of the Related Art In order to realize a highly reliable and economical optical communication system, the reliability and economical efficiency of an optical fiber line as an optical transmission line are important issues. for that reason,
It is necessary to accurately measure the section loss, splice loss, and return loss of the optical fiber without affecting communication.

An optical pulse tester which meets such requirements sends an optical pulse to an optical fiber under test, receives reflected light and backscattered light from the optical fiber under test, analyzes the received light and analyzes the backscattered light. This is a device for displaying the optical loss and other characteristics of an optical fiber on a screen. Conventionally, the method shown in FIG. 11 has been used in order to perform an optical line monitoring test without affecting communication signals (Japanese Patent Application No. 6-127678).

In FIG. 11, an optical transmitter 1 and an optical receiver 2 are connected to both ends of an optical fiber 4 under test. A communication signal from the optical transmitter 1 is sent to the optical receiver 2 through the optical fiber 4 under test, converted into an electric signal, and then passed through the bandpass filter 6 to be input to the receiver 7. The optical pulse sent from the optical pulse tester 40 for testing the optical fiber under test 4 is incident on the optical fiber under test 4 via the optical directional coupler 3. This optical pulse is incident on the optical receiver 2 together with the communication signal, and the waveform of the optical pulse is shaped so that the frequency component of the received signal of this optical pulse does not occur in the band of the communication signal.

For example, if a pulse having a wide pulse width is used, its frequency component is limited to a low frequency, so that the optical pulse of the optical pulse tester does not affect the communication signal using the high frequency band. However, the distance resolution of the optical pulse tester deteriorates in proportion to the pulse width. Therefore, it has been proposed to generate a pulse waveform in a special waveform instead of a rectangular wave (Japanese Patent Application No. 6-127678).

In this case, for example, when the pulse width of the pulse waveform is a raised cosine waveform of 100 ns, the spectrum component of the pulse signal in the frequency band of the communication signal (for example, near 100 MHz) is a rectangular pulse having the same pulse width of 100 ns. Compared to that, it is about 40 dB smaller. Therefore, by adopting such a special pulse waveform, it is possible to suppress the deterioration of the communication signal due to the optical pulse of the optical pulse tester entering the optical receiver 2.

FIG. 12 is a block diagram showing a conventional optical pulse tester 40. The reflected light and the backscattered light returning from the optical fiber under test 4 are incident on the light receiver 22 via the optical directional coupler 3, converted into an electric signal, and input to the A / D conversion circuit 23. The output of the A / D conversion circuit 23 is sequentially input to the addition processing circuit 24. The display 25 displays a waveform obtained by logarithmically converting the addition signal in the addition processing circuit 24. The timing generation circuit 26 sends a synchronization signal of a predetermined cycle to the addition processing circuit 24 and the pulse driver 42 for generating an optical pulse waveform. The pulse driver 42 for generating an optical pulse waveform receives the synchronization signal and sends a pulse to the test light source 41.

Although the conventional optical pulse tester has been described above, it is difficult to perform measurement with an ultrahigh range resolution in a test using such a conventional optical pulse tester.
The reason for this will be described below. In order to make the distance resolution of the optical pulse tester super high, it is necessary to narrow the pulse width of the transmitted optical pulse. However, if the pulse width of the pulse waveform as shown in FIG. 13 is narrowed, the frequency spectrum of the optical pulse spreads in proportion to the reciprocal of the pulse width. A frequency component of the received signal of the test light pulse is generated, which deteriorates the transmission quality.

Therefore, at the present time, when conducting a monitoring test of an optical line such as a subscriber optical line having a short wiring length and densely connecting points, communication is not affected and the inside of the optical line of the communication signal light is not affected. The development of an optical pulse tester that measures loss and other factors at a very high range resolution has become an issue.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to accurately measure the section loss, splice loss, return loss, etc. of a communication signal in an optical fiber under test with super-high distance resolution without affecting communication. It is to provide a device for grasping.

[0011]

DISCLOSURE OF THE INVENTION The present invention provides an optical pulse generating means for generating an optical pulse having a signal waveform which can be cut off by an electric frequency filter incorporated in an optical communication receiving terminal device, and a generated optical pulse. Means for sending out to the test optical fiber, means for extracting reflected light and backscattered light returning from the optical fiber under test, photoelectric conversion means for receiving the extracted reflected light and backscattered light and converting them into electric signals,
In an optical pulse tester comprising an electric signal processing means for performing processing such as addition of electric signals, and means for displaying the waveforms of the reflected light and the backscattered light of the optical pulse based on the result of processing the electric signal, The optical pulse generating means comprises means for generating an optical pulse in which test light and dummy light having different wavelengths (or optical frequencies) are time-division multiplexed, and further, an optical pulse in which the test light and dummy light are time-division multiplexed. Selective receiving means for transmitting a signal to the optical fiber under test, blocking the signal due to the dummy light and selectively receiving only the signal due to the test light among the signals due to the reflected light and the backscattered light returning from the optical fiber under test. Equipped with.

The time-division multiplexed pulse sent from the optical pulse tester according to the present invention has a wide pulse width, so that it is sufficiently removed by the band filter built in the demodulator, and the optical line is monitored without affecting the communication. It becomes possible to carry out a test. Furthermore, since the wavelength (or frequency) -dependent selective receiving means built into the optical pulse tester can extract only the test signal light with a narrow pulse width from the time division multiplexed pulse with a wide pulse width, it has an ultra-high range resolution. It becomes possible to carry out a monitoring test of the optical line.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical line monitoring test using the optical pulse tester of the present invention. In the figure, parts other than the optical pulse tester 20 of the present invention are the same as the configuration of the conventional optical line monitoring test system shown in FIG.

2 to 9 are block configuration diagrams showing an embodiment of the optical pulse tester 20 of the present invention. In the figure, the test light source 27-1 (wavelength λm) and the dummy light source 27-2 (wavelength λd
≠ λm), pulse driver for generating optical pulse waveform for test 28
-1, Dummy optical pulse waveform generation pulse driver 28-2,
The other parts except the optical coupler 21 and the wavelength-dependent filter 29 have the same configuration as that of the conventional optical pulse tester, and are denoted by the same reference numerals and will not be described. Although the wavelength dependent optical filter 29 is not used in the above-mentioned conventional example, it is a conventionally known means.

Pulse driver for generating optical pulse waveform for test
The 28-1 is designed to perform measurements with super-high range resolution.
Like the pulse 100 (shaded area) shown in Figure 10,
This is a waveform generator for generating a pulse having a sufficiently narrow pulse width T1. The dummy optical pulse waveform generating pulse driver 28-2 is a waveform generating device for generating dummy light (portions shown by 101 and 102 in FIG. 10) for time division multiplexing with the test signal pulse. FIG. 10 is a diagram showing how the test light pulse and the dummy light pulse are time-division multiplexed. T1 is the pulse width of the test light pulse of wavelength λm, and T2 is the pulse width of the dummy light pulse of T1 and wavelength λd. It is the time width including and.

The test lights generated by the two pulse drivers are time-division multiplexed to generate a composite pulse, which is sent to the optical fiber 4 under test. In the case of the optical signals shown in FIGS. 10 (a) and 10 (b), the pulse width T2 of the time division multiplexed pulse is wide, and therefore the high frequency component of the received signal is very small. Therefore, even if a test is performed by the optical pulse tester 20 while a high frequency communication signal is being transmitted to the optical fiber under test 4, the communication signal power to noise power ratio of the receiver 7 is not deteriorated. On the other hand, from the reflected light and the backscattered light of the time-division multiplexed optical signal returning to the optical pulse tester 20, only the signal light with a narrow pulse width of the wavelength λm is extracted by the wavelength-dependent optical filter 29. The optical fiber under test can be tested with a high distance resolution.

The pulse shown in FIG. 10 (a) (rectangular pulse of pulse width T2) and the pulse shown in FIG. 10 (b) (for example, raise of width T2).
d cosine waveform), both have the same pulse width T
As described above, even in the case of 2, the high-frequency component of the pulse in FIG. 10 (b) is significantly lower, and therefore, the latter is superior in performance. In FIG. 10 (a), the test light pulse of wavelength .lambda.m is shown positioned at the edge within the pulse of pulse width T2.
Needless to say, anywhere in the light pulse of

The raised cosine waveform is expressed by the following equation of c (t). c (t) = (A / 2) (1 + cos (π · B T -t)), - T2 ≦ t ≦ T2 c (t) = 0, | T2 | <t where, A is the peak value, B _T = 1 / T2, T2 is the pulse width, and t is the time.

In FIG. 10 (b), the test light pulse having the wavelength λm is positioned at the center of the light pulse of the raised cosine waveform having the pulse width T2. At this time, the power of the test light pulse having the wavelength λm is maximized, and the test accuracy is also maximized. Of course, the position of the test light pulse may be changed within this light pulse within a range where there is no problem from the viewpoint of accuracy. At this time, the shape of the test light pulse of wavelength λm is shaped so as to form a part of the raised cosine waveform. Here, the combined use of the test light pulse having the wavelength λm and the dummy light pulse having the wavelength λd in this way is called time division multiplexing.

Next, the embodiment shown in FIGS. 3 to 5 will be described.
Pulse drivers 28-1, 28-2 and external modulators 30-1, 30 of FIG.
-2, changeover optical switch 31 in FIG. 4, high-speed wavelength tunable light source in FIG.
The other parts except 32 are the same as the configuration of the optical pulse tester in FIG. 2, and are denoted by the same reference numerals and will not be described.

In the embodiment shown in FIG. 2, the light sources 27-1 and 27-2 are directly modulated, but in the embodiment shown in FIG. 3, the test signal external modulator 30-1 and the dummy signal external are externally provided. A modulator 30-2 is provided, and external modulation is performed by this to obtain a test light pulse and a dummy light pulse. In the embodiment of FIG. 4, test light and dummy light having respectively different wavelengths λm and λd are time-division-multiplexed by the switching optical switch 31 to generate continuous light, and then an optical pulse is generated from the continuous light by the external modulator 30. To do. At this time, in order to include both the test light and the dummy light in the optical pulse, the optical pulse waveform generation pulse driver 28 operates by receiving the timing signal from the timing generation circuit 26.

In the embodiment shown in FIG. 5, the high-speed wavelength variable light source 32 is used.
A continuous light whose wavelength is temporally changed is obtained (for example, DFB or DBR laser) (this is referred to as frequency shift keying), and this continuous light is emitted by the external modulator 30 in the same manner as the embodiment of FIG. Generate a pulse. 3 to 5
The other operation of the embodiment shown in FIG. 2 is the same as that of the embodiment of FIG.

Next, the embodiment shown in FIGS. 6 to 9 will be described.
A light source having good coherence is used as the light source 27-1 in FIGS. 6 to 8 and the high-speed wavelength variable light source 32 in FIG. 9, and a part of the output thereof is used as reference light. The reflected light or the backscattered light of the above is mixed and received, and the beat signal is selectively received by the electric filter, so that the signal by the dummy light is blocked and only the signal by the test light is selectively received. You can That is, the signal by the dummy light is blocked by the heterodyne detection or the homodyne detection, and only the signal by the signal light is selectively received. In this case, the wavelength dependent optical filter 29 becomes unnecessary.

Other operations of the embodiment shown in FIGS. 6, 7, 8 and 9 are the same as those of the embodiments shown in FIGS. 2, 3, 4 and 5, respectively. In the above description, the wavelength of the time-division-multiplexed light is two wavelengths of λm and λd, but it goes without saying that more wavelengths may be used.

[0025]

As described above, by using the optical pulse tester of the present invention, in conducting the monitoring test of the optical line, the optical line section loss of the communication signal and the connection can be achieved without affecting the communication. It becomes possible to accurately grasp the loss and the return loss with a high distance resolution.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical line monitoring test using an optical pulse tester of the present invention.

FIG. 2 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 3 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 4 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 5 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 6 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 7 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 8 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 9 is a block configuration diagram showing details of an example of an optical pulse tester of the present invention.

FIG. 10 is a diagram showing an example of a waveform of a pulse transmitted from the optical pulse tester of the present invention.

FIG. 11 is a block diagram showing a conventional optical line monitoring test method.

FIG. 12 is a block configuration diagram showing details of a conventional optical pulse tester.

FIG. 13 is a diagram showing an example of a waveform of a pulse transmitted from a conventional optical pulse tester.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 In-station device 2 Optical receiver 3 Optical directional coupler 4 Optical fiber under test 5 Demodulator 6 Bandpass filter 7 Receiver 20 Optical pulse tester of the present invention 21 Optical coupler 22 Photoreceiver 23 A / D conversion circuit 24 Addition processing Circuit 25 Display 26 Timing generator 27-1 Test light source 27-2 Dummy light source 28-1 Test optical pulse waveform generation pulse driver 28-2 Dummy optical pulse waveform generation pulse driver 29 Wavelength dependent optical filter 30 External Modulator 30-1 Signal Light External Modulator 30-2 Dummy Light External Modulator 31 Optical Changeover Switch 32 High-Speed Wavelength Tunable Light Source 40 Conventional Optical Pulse Tester 41 Conventional Test Light Source 42 Conventional Optical Pulse Generation Pulse driver

Claims (1)

[Claims] 1. An optical pulse generating means for generating an optical pulse having a signal waveform that can be blocked by an electric frequency filter built in an optical communication receiving terminal device, a means for transmitting the generated optical pulse to an optical fiber under test, Means for extracting reflected light and backscattered light returning from the optical fiber under test, photoelectric conversion means for receiving the extracted reflected light and backscattered light and converting them into electric signals, processing such as addition of electric signals, etc. In the optical pulse tester comprising means for displaying the waveform of the reflected light and the backscattered light of the light pulse based on the result of processing the electric signal and the electric signal processing means for performing the electric signal, the light pulse generating means, (Or optical frequency)
Means for generating an optical pulse in which the test light and the dummy light different from each other are time-division multiplexed, and further, the optical pulse in which the test light and the dummy light are time-division multiplexed is transmitted to the optical fiber under test, and the optical fiber under test is transmitted. An optical pulse tester characterized by comprising selective receiving means for blocking signals due to dummy light among signals due to reflected light and backscattered light returning from and selectively receiving only signals due to test light.