JP3236661B2 - Optical pulse tester - Google Patents

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, and more particularly to an optical pulse tester for testing characteristics such as optical loss of an optical fiber and an optical fiber line as a transmission medium of an optical signal.

[0002]

2. Description of the Related Art Conventionally, in order to realize a highly reliable and economical optical communication system, it is important to construct a highly reliable and economical optical fiber line. Must be measured and tested over a short distance using a highly reliable tester.

An optical pulse tester (hereinafter referred to as OTDR (Optica)
l Time Domain Reflectometer) sends an optical pulse to the optical fiber under test, receives reflected light and backscattered light from the optical fiber, analyzes it, and displays characteristics such as light loss on a CRT or the like. This is a very useful tester because it can be tested by inputting and outputting light from one end of an optical fiber. For this reason, research and development for increasing the OTDR measurable distance (this is called a dynamic range) has been conventionally performed.

In order to expand the dynamic range, a method of increasing the intensity of a pulse transmitted to the optical fiber under test and a method of improving the sensitivity of receiving backscattered light or the like are mainly employed. As one method for improving reception sensitivity, application of a coherent detection technique such as heterodyne or homodyne reception is being studied.

Conventional OT using coherent detection technology
DR will be described with reference to FIG. OTD shown in FIG.
In R, the test signal light and the local signal light are generated by the same light source. In the drawing, reference numeral 1 denotes a light source unit that generates light having a narrow line width spectrum, 2 denotes a first multiplexer / demultiplexer that splits light emitted from the light source unit 1 into a test signal light a and a local signal light b, and 3 denotes a branch. A first acousto-optic switch (hereinafter, referred to as an AO switch) that pulse-forms the test signal light at a constant period and modulates the optical frequency of the test signal light. The second guides the reflected light and the backscattered light c from the fiber 5 into the tester.
It is a branching device.

Reference numeral 6 denotes a third multiplexer / demultiplexer for multiplexing the reflected light and backscattered light c guided into the tester with the local signal light b, and 7 denotes a multiplexed reflected light and rear light. A photodetector 8 for optically / electrically converting the beat signal light d between the scattered light and the local signal light. A signal 8 converts the beat signal output from the photodetector 7 to a baseband signal, and then performs A / D conversion and further square conversion. It is a converter. Here, in the case of the homodyne detection method in which the beat signal from the light receiver 7 is directly obtained as a baseband signal, the process proceeds to the next A / D conversion process without performing this conversion.

Reference numeral 9 denotes an addition processor for adding a signal of a fixed period squared by the signal converter 8 to improve the SN ratio, 10 denotes a logarithmic converter for subtracting an offset power value from the added signal and performing logarithmic conversion, Reference numeral 11 denotes a longitudinal distribution of the intensity of each of the reflected light and the backscattered light c (hereinafter, OTD).
A CRT 12 for displaying an R waveform) is a timing generator for pulsing the test signal light a at a constant period or performing an addition process. The above-described signal converter 8, addition processor 9, logarithmic converter 10, and CRT 11 constitute an electric signal processing means 13.

An OTDR using such a coherent detection technique (hereinafter referred to as a coherent detection OTDR)
In order to perform coherent detection, the light source unit 1 that generates light having a narrow line width spectrum of several KHz is indispensable. In order to realize this, a distributed feedback semiconductor laser (hereinafter referred to as a DFB-LD) 14 is used. Length 1 at output end of
The optical fiber 15 of about km is fusion spliced, and the optical fiber 1
Narrowing the line width using the backscattered light from No. 5 is performed. FIG. 2 shows this example.
-An LD 14 and the like, an optical fiber 15 for narrowing the line width, and an optical isolator 19.

In the coherent detection OTDR, a beat signal light d obtained by combining a local signal light b having a relatively large intensity with a weak backscattered light c is received and detected. Assuming that the backscattered light intensity is Ac and the local signal light intensity is Ab, the intensity Ad of the beat signal light is the local signal light intensity Ab
And the backscattered light intensity Ac is proportional to the square root. Therefore,
By making the local signal light intensity Ab relatively large, even weaker backscattered light can be received,
The dynamic range as the OTDR can be expanded.

However, in the above-mentioned conventional optical pulse tester (OTDR), the dynamic range can be expanded by using the coherent detection technique. However, since the light source unit 1 having a narrow line width spectrum is used, the fading on the OTDR waveform is performed. There has been a drawback of generating noise called noise.

FIG. 3 shows an example of an OTDR waveform observed by the above-described coherent detection OTDR. OT shown in FIG.
The DR waveform is an OTD when an optical pulse having a wavelength of 1.55 μm, a pulse width of 1 μs, a pulse period of 1 ms, and a peak intensity of −10 dBm is incident on an optical fiber 5 having a length of 10 km.
This is an R waveform. The number of additions for improving the SN ratio of the OTDR waveform is 2.6 × 10 ⁵ . The addition processing time at this time was about 260 seconds.

The OTDR waveform of the observation result should be almost straight, but due to the fading noise ±
A fluctuation of about 0.2 dB is observed. Due to this noise, it was difficult to determine a step due to a change in the connection portion or loss in the optical fiber 5 under test. For example, 0.1 dB
A level difference cannot be determined as a level difference at all. Therefore, it is necessary to reduce fading noise of the coherent detection OTDR.

The fading noise is caused by interference between scattered lights scattered in a minute section corresponding to the light pulse width in the optical fiber, and the polarization dependence of the backscattered light changes in the longitudinal direction of the optical fiber 5 to be tested. Due to doing so. The magnitude of the fluctuation on the OTDR waveform due to the fading noise is proportional to the reciprocal of the square root of the number of statistically independent backscattering waveforms. Therefore, the number of independent backscattering waveforms can be reduced by performing addition processing.

Therefore, conventionally, the optical frequency of the light source unit 1 for generating the test signal light a and the local signal light b is changed, and the polarization state of the multiplexed test signal light or local signal light is controlled. By doing so, a method of increasing the number of independent backscattered waveforms and reducing fluctuation due to fading noise of the coherent detection OTDR has been taken.

FIG. 4 is a block diagram showing a conventional example when this fading noise reduction method is used. In the figure, reference numeral 14 denotes a semiconductor laser such as a DFB-LD capable of controlling an optical frequency, and 16 denotes an optical frequency control unit, which includes a light source unit 22 having an optical frequency variable together with an optical fiber 15 for narrowing a line width and an optical isolator 19. Make up. 17 is a polarization state controller,
Reference numeral 18 denotes a main control unit that controls the optical frequency control unit 16, the polarization state controller 17, and the timing generator 12.

The temperature of the semiconductor laser 14 is increased from 15 ° C. to 2
When the temperature is changed between 8 ° C., the intensity of the emitted light hardly changes, and the optical frequency of the light source unit 22 can be changed by about 140 GHz. The polarization state on the test signal light side can be controlled by inserting a polarization state controller 17 using elements such as a rotating phase plate, a rotating fiber rank, an electro-optic crystal, and a Faraday rotator. I have.
Here, as the polarization state controller 17, a rotary phase plate type in which two phase plates of a (1/4) wavelength plate and a (1/2) wavelength plate are connected in series is used.

Light emitted from the light source unit 22 whose optical frequency can be controlled can have its optical frequency changed while its light output is kept almost constant by the optical frequency control unit 16. The spectral line width of the emitted light is reduced by the optical fiber 15 for narrowing the line width.
It has a sufficient line width to perform coherent detection. The emitted light is split by the first splitter 2 into a test signal light a and a local signal light b. Test signal light a branched
The polarization state of the optical fiber under test 5 is controlled by a polarization state controller 17, pulsed at a constant period by an AO switch 3 and optically frequency-modulated, and passed through a second multiplexer / demultiplexer 4. Is incident on.

The reflected light and the backscattered light c from the optical fiber under test 5 are guided to the third coupler 6 via the second coupler 4. In the third multiplexer / demultiplexer 6, the local signal light b is combined with the reflected light and the backscattered light c. The multiplexed beat signal light b is optically / electrically converted by the photodetector 7. The beat signal is converted into a baseband signal by the signal converter 8, A / D-converted and square-converted, and then added by the addition processor 9 to improve the SN ratio. Thereafter, the logarithmic converter 10 subtracts the offset power, performs logarithmic conversion, and displays the CRT 11 as an OTDR waveform. The timing generator 12 supplies a signal for pulsing the test signal light to the drive unit of the AO switch 3 and supplies an addition processing timing signal to the signal converter 8 and the addition processor 9.

The main control unit 18 controls the operations of the optical frequency control unit 16, the polarization state controller 17, and the timing generator 12, and finally determines the timing of the optical pulse to be transmitted to the optical fiber 5 under test. The optical frequency is changed in accordance with the condition (1) to control the state of polarization. Therefore, the number of independent backscattering waveforms returning from the optical fiber under test 5 increases, and the fluctuation due to fading noise on the OTDR waveform is reduced by the addition processing. FIG. 5 shows the second
OTD measured by conventional coherent detection OTDR
An example of an R waveform is shown. The OTDR waveform shown in FIG.
In the long optical fiber under test 5, a wavelength of 1.55 μm, a pulse width of 1 μs, a pulse period of 1 ms, and a peak intensity of −10 dBm
This is when the light pulse is incident. The number of additions for improving the SN ratio of the OTDR waveform was 2.6 × 10 ⁵ times. The addition time at this time was about 260 seconds.

The change in optical frequency is ±± from the center optical frequency.
Reciprocated 70 GHz. One round trip time is about 130 seconds. The polarization state was changed in four ways every 0.65 × 10 ⁵ additions. As a result, the fluctuation on the OTDR waveform due to fading noise is as small as ± 0.1 dB as compared with the OTDR waveform in the first conventional example shown in FIG.

[0021]

However, in the above-mentioned second conventional example, it is difficult to determine a step of 0.1 dB. Therefore, it is necessary to further reduce the fluctuation due to the fading noise.

The reason that this fluctuation cannot be sufficiently reduced in a short time is due to the response of the optical frequency change of a single optical frequency semiconductor laser such as a DFB-LD used for the light source unit 22 that generates light having a narrow line width spectrum. caused by. When the optical frequency of the semiconductor laser is changed at high speed, the amount of change in the optical frequency is small, so that a sufficiently large independent backscattering waveform cannot be obtained,
It is difficult to reduce fluctuation on the OTDR waveform due to fading noise. When the optical frequency is changed by temperature control, the response of the optical frequency becomes slow. For this reason,
In order to reduce the fluctuation on the OTDR waveform due to fading noise, it is necessary to increase the number of independent backscattering waveforms by increasing the repetition period of the signal light pulse.
In this case, there is a problem that the addition processing time, that is, the measurement time becomes long, and is not suitable for practical use as an optical line test technique.

In view of the above problems, an object of the present invention is to provide an OTDR using a coherent detection system,
An object of the present invention is to provide an optical pulse tester in which fluctuation due to fading noise on a waveform is small and measurement time is short.

[0024]

In order to achieve the above object, according to the present invention, there is provided a signal light generating means for generating a test signal light and a local signal light, and pulsing the test signal light. Optical pulse generation means for repeatedly sending out to the optical fiber under test every predetermined period; and optically multiplexing the reflected light and the backscattered light returning from the optical fiber under test with the local signal light to beat. Optical multiplexing means for obtaining signal light, opto-electric conversion means for receiving the beat signal light and converting it to an electric signal, electric signal processing means for processing the electric signal, and based on the result of the electric signal processing, in OTDR and display means for displaying a waveform of the reflected light and backscattered light, the signal light generating means simultaneously generates a plurality of optical frequencies of the optical frequency spacing of about 200 GHz, before Optical pulse generating means to propose an optical pulse tester sends simultaneously the tested optical fiber of the plurality of optical frequency as the test signal light.

According to the second aspect, the test signal light and the low
Signal light generating means for generating a cull signal light, and the test signal
The light is pulsed and repeated to the optical fiber under test at predetermined intervals.
Optical pulse generating means for returning and transmitting the optical pulse;
Reflected light and backscattered light repeatedly returning from fiber
Optically multiplexing the local signal light with a beat signal light
Optical multiplexing means for receiving the beat signal light and
Opto-electrical conversion means for converting to a signal, and processing this electric signal
Electrical signal processing means for performing the
Display for displaying the waveforms of the reflected light and the backscattered light
Means, the signal light generating means includes a PLC (Planar Lightwave Cir) to which at least one or more rare earth elements are added.
circuit) ring laser (hereinafter, rare earth element added PLC)
Optical frequency f1 adjacent to each other consisting of say a ring laser)
The interval from (λ1) to fn (λn) is at least the signal reception band.
Multiple optical loops at predetermined optical frequency intervals separated by more than twice the frequency range
Generating a wave number at the same time, the light pulse generating means said test
The plurality of optical frequencies are simultaneously used as the signal light.
We propose an optical pulse tester for sending to fiber .

According to a third aspect of the present invention, in the optical pulse tester according to the second aspect, the rare earth element- added PLC ring laser has a temperature control unit for controlling a temperature of a part or the whole of a ring resonator. Suggest a tester.

In a fourth aspect of the present invention, in the optical pulse tester according to the second or third aspect, the rare earth element- added PLC is preferably used.
An optical pulse tester in which a ring laser, the first optical multiplexing means, and the photoelectric conversion means are arranged on the same plane substrate is proposed.

[0028]

According to the first aspect of the present invention, the signal light generating means includes:
A test signal light and a local signal light having a plurality of optical frequencies at optical frequency intervals of about 200 GHz are generated. The test signal light is pulsed by the optical pulse generation means, and is repeatedly transmitted to the optical fiber under test at predetermined intervals. Also,
The reflected light and the backscattered light that are repeatedly returned from the optical fiber under test are multiplexed with the local signal light by the optical multiplexing means to be beat signal light. The interference characteristics of the reflected light, the backscattered light, the local signal light, and the beat signal light differ depending on the optical frequencies of the test signal light and the local signal light. Therefore, an independent backscattering waveform is obtained for each optical frequency. Since the signal light generating means has a plurality of optical frequencies, a backscattering waveform obtained by adding and averaging independent backscattering waveforms of only the optical frequencies of the signal light generating means can be obtained in one measurement. Further, the display means displays the waveforms of the reflected light and the backscattered light.

According to the second aspect, the signal light generating means is constituted by a PLC ring laser doped with at least one or more rare earth elements.

According to the third aspect, the temperature of a part or the whole of the rare earth element- added PLC ring laser is controlled by a temperature control unit.

According to the fourth aspect, the signal light generating means, the optical multiplexing means, and the photoelectric conversion means are arranged on the same planar waveguide substrate.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention aims to reduce fluctuations on an OTDR waveform due to fading noise by using signal light generating means for simultaneously generating a plurality of optical frequencies at predetermined optical frequency intervals. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a first embodiment of the present invention. In the figure, the same components as those of the above-described second conventional example are denoted by the same reference numerals, and description thereof will be omitted. The difference between the second conventional example and the first embodiment is as follows.
Instead of the light source unit 22, a light source unit 20 that simultaneously generates a plurality of optical frequencies at an optical frequency interval of about 200 GHz is used.

That is, the light source unit 20 is, for example, an MQW-LD (MultiQuantum Well Laser) having four different optical frequencies.
Diodes 20a are arranged in an array, and each light output is multiplexed by a 4-to-1 coupler 20b. Each MQ
The spectral line width of the W-LD 20a at the optical frequencies f1 (.lambda.1) to f4 (.lambda.4) is several tens KHz or less.
The interval between (λ1) and f4 (λ4) is about 200 GHz. Also,
Each of the MQW-LDs 20a is mounted on a temperature controller 16 composed of a Peltier element, so that the temperature of the MQW-LD 20a is kept at 15 ° C. to 28 ° C. while the DFB-LD drive current is kept constant as shown in FIG. When the optical frequency f1 (λ
1) -f4 (λ4) could be changed by about 140 GHz.

Reference numeral 17 denotes a polarization state controller, (1/1).
4) A rotary phase plate system in which two phase plates, a wave plate and a (1/2) wave plate, are connected in series. Reference numeral 18 denotes a main control unit that controls the temperature control unit 16, the polarization state controller 17, and the timing generator 12.

Next, the configuration and operation of the coherent detection OTDR of the first embodiment will be described. The output light from the light source unit 20 is split by the first splitter 2 into a test signal light a and a local signal light b. The split test signal light a is controlled in its polarization state by a polarization state controller 17, is further pulsed by an AO switch 3 at a constant period, and is optically frequency-modulated. Then, the light enters the optical fiber under test 5. The reflected light and the backscattered light c from the optical fiber under test 5 are guided to the third coupler 6 via the second coupler 4.

The local signal light b and the reflected light and the backscattered light c are multiplexed by the third multiplexer / demultiplexer 6.
The multiplexed beat signal light d is optically / electrically converted by the optical receiver 7, and the beat signal converted into an electric signal is converted by the signal converter 8.
Are converted to baseband signals, A / D converted, and further squared, and then added by an adder 9 to improve the SN ratio. Thereafter, the logarithmic converter 10
After subtracting the offset power at
1 is displayed as an OTDR waveform. The timing generator 12 supplies a signal for pulsing the test signal light to the drive unit of the AO switch 3 and supplies an addition processing timing signal to the signal converter 8 and the addition processor 9.

The main control unit 18 controls the temperature control unit 16, the polarization state controller 17, and the timing generator 12, and finally determines the optical frequency in accordance with the timing of the optical pulse transmitted to the optical fiber 5 under test. To control the state of polarization.

As described above, the light source unit 20 is approximately 200 G
And generating a test signal light a and a local signal light b having a plurality of optical frequencies at an optical frequency interval of 1 Hz.
Is pulsed by an optical pulse generator comprising an AO switch 3 and is repeatedly transmitted to the optical fiber under test 5 at predetermined intervals. The reflected light and the backscattered light c repeatedly returned from the optical fiber under test 5 are multiplexed with the local signal light b to form a beat signal light d.

Accordingly, the interference characteristics of the reflected light, the backscattered light c, the local signal light b, and the beat signal light d are determined by the optical frequency f1 (λ) of the test signal light a and the local signal light b.
1) to f4 (λ4), and each optical frequency f1
An independent backscattering waveform is obtained for each of (λ1) to f4 (λ4). As a result, in one measurement, a backscattering waveform obtained by averaging independent backscattering waveforms by the number of optical frequencies f1 (λ1) to f4 (λ4) of the light source unit 20 is obtained, and the OTDR due to fading noise is obtained. Waveform fluctuation is reduced.

The result of experimentally confirming the effect of the present invention will be described. Coherent detection OTDR shown in FIG.
FIG. 7 shows an OTDR waveform obtained by measuring the optical fiber under test 5 having a length of 10 km. The light pulse transmitted to the optical fiber under test 5 has a wavelength of 1.55 μm and a pulse width of 1 μm.
s, pulse period 1 ms, peak intensity -10 dB,
The local signal light intensity input to the third coupler 6 is approximately 0 dBdm. 2.6 × 10 ⁵ additions for improving the SN ratio of the backscattered waveform were performed. Addition time is about 26
0 seconds. The polarization state was changed in four ways every 0.65 × 10 ⁵ additions. The above measurement conditions are based on the second
Are the same as the measurement conditions in the conventional example. The temperature of the semiconductor laser 14 was changed between 15 ° C. and 28 ° C., and the optical frequencies f1 (λ1) to f4 (λ4) of the light source unit 20 were reciprocated ± 70 GHz from the center optical frequency. One round trip time is about 130 seconds. Four different optical frequencies f1 (λ1) to f4
(.lambda.4), an independent backscattering waveform is obtained about four times more than the second conventional example, and the fluctuation on the OTDR waveform due to fading noise is about 1 / l of the conventional example shown in FIG. 2, which can be reduced to ± 0.05 dB, and the waveform is almost straight, which confirms the effectiveness of the present invention.

Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is the same as the configuration of the above-described first embodiment. The difference between the first embodiment and the second embodiment is that the light source unit 20 is replaced with the light source unit 20 as shown in FIG. That is, the light source unit 21 is used. However, the control of the optical frequency by the temperature control unit 16 is not performed.

The light source unit 21 is an erbium-doped PLC ring laser, has a pump light source 21a and a ring resonator 21b of about 15 cm, and allows the temperature control unit 16 to variably control the length of the ring resonator 21b. Has become. Wavelength of this erbium-doped PLC ring laser
Is 1.53 μm to 1.57 μm, and is about 40 nm
Multimode oscillation occurs at an optical frequency interval of about 2 GHz in the (3.3 THz) band. The spectral line width at each of the optical frequencies f1 (λ1) to f4 (λ4) is several tens KHz.

However, adjacent optical frequencies f1 (λ1) to fn (
The interval of λn) needs to be at least twice as long as the signal receiving band (the reciprocal of the signal light pulse width).

The light source section 21 has a structure of 3.3 as described above.
Since the multi-mode oscillation occurs at an optical frequency interval of about 2 GHz in the THz band, the measurement was practically performed simultaneously at an optical frequency of about 1600. Thus, the fluctuation on the OTDR waveform due to fading noise could be reduced to about 1/40 of the second conventional example shown in FIG. Therefore, the number of additions necessary to reduce the fluctuation on the OTDR waveform due to fading noise to ± 0.05 dB, which is the same level as in the first embodiment, may be 1/10, and the addition time is about 1/10. It can be reduced to about 26 seconds. As a result, a result similar to that of FIG. 7 was obtained in a short time, and the effectiveness of the present invention was confirmed.

Next, a third embodiment of the present invention will be described. In the third embodiment, the temperature of the light source unit 21 is controlled by the temperature control 16 with the same configuration as that of the second embodiment. As a result, the addition time for reducing the fluctuation on the OTDR waveform due to fading noise to ± 0.05 dB, which is the same level as in the first embodiment, could be reduced to about 1/20, that is, about 13 seconds. Also in this configuration, the effectiveness of the present invention was confirmed.

For example, as shown in FIG.
The same effect was obtained when the first, third and third couplers 2 and 6 and the light receiver 7 were arranged on the same plane substrate 30. Furthermore, compact integration of the optical pulse tester was realized.

[0047]

As described above, according to the first aspect of the present invention, the fluctuation on the OTDR waveform due to fading noise is achieved by using the signal light generating means for simultaneously generating the optical frequencies at the optical frequency intervals of about 200 GHz. Can be reduced in a short time. Therefore, by using the optical pulse tester of the present invention, OTDR due to fading noise, which was the biggest problem of OTDR using coherent detection technology, was
Fluctuations in the waveform are reduced in a short time, and a connection point in the middle of the optical fiber under test and a step due to a change in loss can be determined. Further, downsizing of the optical pulse tester can be realized. Thus, the coherent detection OTDR can be put to practical use as a tester for constructing a highly reliable optical line.

According to the second aspect, adjacent optical frequencies
The interval between the numbers f1 (λ1) to fn (λn) is at least a signal.
It is possible to easily generate test signal light and local signal light having a plurality of optical frequencies at a predetermined optical frequency interval separated by at least twice the reception band .

According to the third aspect, in addition to the above effects, by changing the temperature of the rare earth-doped PLC ring laser, the optical frequencies f1 (λ1) to fn (λ
n) are separated by at least twice the signal reception band
Predetermined distance of each optical frequency of the test signal light and the local signal light having a plurality of optical frequencies of the predetermined optical frequency intervals are can be easily changed while maintaining the.

According to the fourth aspect of the present invention, in addition to the above effects, the signal light generating means, the optical multiplexing means and the photoelectric conversion means can be integrated on the same planar waveguide substrate. This is a very excellent effect that the shape can be formed small.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a first conventional coherent detection OTDR;

FIG. 3 is a diagram showing a backscattered waveform in the first conventional example.

FIG. 4 is a configuration diagram showing a coherent detection OTDR of a second conventional example.

FIG. 5 is a diagram showing a backscattering waveform in the second conventional example.

FIG. 6 is a diagram illustrating a relationship between an optical frequency and a temperature in the light source unit according to the first embodiment.

FIG. 7 is a diagram showing a backscattering waveform in the first embodiment.

FIG. 8 is a configuration diagram showing a second embodiment.

FIG. 9 illustrates an example of integration.

[Explanation of symbols]

Reference numeral 1 denotes a light source unit for generating light having a narrow line width spectrum;
3 ... AO switch, 4 ... second combiner,
Reference Signs List 5: optical fiber under test, 6: third multiplexer / demultiplexer, 7: photodetector, 8: signal converter, 9: addition processor, 10: logarithmic converter, 11: CRT, 12: timing generator, 13 ... Electrical processing system, 14 ... DFB-LD, 15 ... Optical fiber for narrowing line width, 16 ... Temperature controller, 17 ... Polarization state controller, 1
8: Main control unit, 19: Optical isolator, 20, 21: Light source unit, 20a: MQW-LD, 20b: Coupler, 21a
... a pump light source, 21b ... a ring resonator.

Continuing from the front page (72) Izumi Mikawa 1-6-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Fumihiko Yamamoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Stocks In-company (56) References JP-A-62-52426 (JP, A) JP-A-4-72540 (JP, A) JP-A-4-132293 (JP, A) JP-A-2-252279 (JP, A) JP-A-53-75956 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 11/00-11/08 H01S 3/00-3/30

Claims (4)

(57) [Claims] A signal light generating means for generating a test signal light and a local signal light; an optical pulse generating means for pulsating the test signal light and repeatedly transmitting the test signal light to an optical fiber under test at predetermined intervals; Optical multiplexing means for optically multiplexing the reflected light and the backscattered light returning from the test optical fiber and the local signal light to obtain a beat signal light; and receiving the beat signal light and converting it into an electric signal An optical-to-electrical conversion unit, an electrical signal processing unit for processing the electrical signal, and a display unit for displaying the waveforms of the reflected light and the backscattered light based on the result of the electrical signal processing. in the signal light generating means simultaneously generates a plurality of optical frequencies of the optical frequency spacing of about 200 GHz, simultaneously a plurality of optical frequencies the light pulse generating means as said test signal light OTDR, characterized by delivering to the tested optical fiber. 2. A test signal light and a local signal light are generated.
Signal light generating means for pulsing the test signal light
Light transmitted repeatedly to the optical fiber under test at regular intervals
Pulse generating means and repeating from the optical fiber under test
Returning reflected and backscattered light and the local signal light
Multiplexing means for optically multiplexing the signals to obtain beat signal light
And the light that receives this beat signal light and converts it into an electrical signal
Electric conversion means and electric signal processing for processing the electric signal
Means and the reflected light based on the result of the electrical signal processing.
And display means for displaying a waveform of backscattered light
In the pulse tester, the signal light generating means includes a PLC (Planer Lightwa) to which at least one or more rare earth elements are added.
ve the Circuit) ring laser (hereinafter, adjacent consists say rare earth element-doped PLC ring laser) light
The interval between the frequencies f1 (λ1) to fn (λn) is at least
Of a predetermined optical frequency interval that is more than twice the signal reception band
A plurality of high frequencies are generated at the same time, and the optical pulse generation means generates the plurality of high frequencies as the test signal light.
Wherein the optical frequency at the same time this to be sent to be tested optical fiber
And an optical pulse tester. 3. The optical pulse tester according to claim 2, wherein the rare-earth element-added PLC ring laser has a temperature control unit for controlling the temperature of a part or the whole of the ring resonator. 4. An optical pulse tester according to claim 2, wherein said rare earth element-added PLC ring laser, said optical multiplexing means and said photoelectric conversion means are arranged on the same plane substrate.