JPH0572076A - Optical amplifier for optical pulse tester - Google Patents

Abstract

PURPOSE:To use an optical amplifier in connection with an existing optical pulse tester with a high gain while stably operating the same by providing at least one optical switch in a loop wherein forward and return light paths are arranged in parallel. CONSTITUTION:The probe pulse light signal (hereinafter referred to as a light signal) split by a light splitter 21 through a port Po and a light splitter 11 to enter a light path A is amplified by an optical amplifier 23. At this time, the light signal preliminarily split by the light splitter 11 is inputted to an optical switch driving circuit 13 and an optical ON/OFF switch 15 is set to a connection state for the passing time of the light signal. The passed light signal is incident on an optical fiber to be measured through a light splitter 22 and a port Pf. The back scattering light generated herein is split by the light splitter 22 through the port Pf to enter a light path B and passes through an optical amplifier 24 to be inputted to an optical pulse tester. Usually, when Flesnel reflection is generated and a loop gain is 1 or more, the optical amplifier becomes stable. However, the light paths A, B are closed only for the slight time required in the passage of the light signal through the switch 15 and the time required when the light goes round a loop is longer than said time and the amplifiers 23, 24 are stably operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier for an optical pulse tester, and more particularly to an optical amplifier for an optical pulse tester which expands a dynamic range for the optical pulse tester and operates stably with high gain.

[0002]

2. Description of the Related Art Optical pulse tester (Optical Time Domain
Reflectometer (OTDR) is used to search for anomalies in an optical fiber by injecting an optical pulse into the optical fiber and time-resolving the intensity of the light that is scattered backward in the optical fiber and returns to the incident end. belongs to. Recently, attempts have been made to expand the dynamic range (optical fiber loss that can be measured) of an optical pulse tester by applying an optical amplifier that has been actively researched and developed.

FIG. 12 shows an apparatus configuration for detecting an abnormal point in an optical fiber by using the optical pulse tester 120. In the figure, 130 is an optical fiber to be measured, 14
Reference numeral 0 denotes an optical amplifier, and the optical amplifier 140 is connected to the optical pulse tester 120 via the port Po and to the optical fiber under test 130 via the port Pf. The optical pulse tester 120 includes a light source 121, optical amplifiers 122 and 124, an optical directional coupler 123, and a photodetector 125.

The optical amplifier 122 is used as a power amplifier of the light source 121. The amplifier 124 is used as a preamplifier for the photodetector 125. The light from the light source 121 is amplified by the optical amplifier 122, passes through the optical directional coupler 123 and the optical amplifier 140, reaches the optical fiber 130 to be measured, is scattered backward in the optical fiber, and returns to the optical amplifier 140. The light intensity is measured at the photodetector 125 through the optical directional coupler 123 and the optical amplifier 124.

Two such amplifiers 122 and 1 are provided.
In the mode of use with 24, since the flow of the optical signal is only in one direction, by using an isolator for each of the input and output parts of the optical amplifiers 122 and 124, deterioration of the optical signal can be suppressed and high gain characteristics can be obtained. Is possible.

However, in this case, as can be seen from FIG. 12, it is necessary to incorporate the optical amplifiers 122 and 124 into the optical pulse tester 120, and the performance can be improved without modifying the existing optical pulse tester. Can not be improved. On the other hand, since the optical amplifier 140 is an in-line amplifier that is used by inserting it between the optical pulse tester 120 and the optical fiber 130 under test, the existing optical pulse tester 1 can be easily used.
The performance of 20 can be improved. Therefore, it has been attempted to improve the performance of the existing optical pulse tester 120 by using the optical amplifier 140.

[0007]

However, in order to improve the performance of the existing optical pulse tester by inserting an optical amplifier between the optical pulse tester and the optical fiber under test as described above, the bidirectional Since it is necessary to perform optical amplification, the isolator cannot be used for the input / output section of the optical amplifier, and 1) the optical amplifier oscillates due to reflection from the front and rear stages of the optical amplifier, and high gain can be obtained. 2) Amplified spontaneous emission light (Amp
Led Spontaneous emission (ASE) is incident on the detector of the optical pulse tester, which causes a significant deterioration of the SN ratio.

Therefore, the present invention solves the problems of the conventional optical amplifier for an optical pulse tester, provides a high gain, and provides an optical amplifier which can be easily connected to an existing optical pulse tester for use. The purpose is to do.

[0009]

FIG. 1 shows a principle configuration of an optical amplifier for an optical pulse tester of the present invention which achieves the above object. The optical pulse tester optical amplifier of the present invention is provided between the optical pulse tester OTDR for searching for an abnormal point of the optical fiber and the optical fiber LF to be measured,
A port Po connected to the optical pulse tester OTDR, a port Pf connected to the measured optical fiber LF, and a port Po.
And a first optical path L1 for optical signal transmission provided between the port Pf and the second optical path L2 for optical signal transmission provided in parallel with the first optical path L1 and the first and second optical paths. Optical path L1,
One-way optical amplifier LA provided in at least one of L2
And is provided on at least one of the first and second optical paths L1 and L2, or the first optical path L1 and the second optical path L2.
Of the two branch points, the optical switch SW provided at at least one branch point and the operation timing of the optical switch SW are controlled so that the light incident from the port Po passes through the first optical path L1. Light reaching the port Pf and entering from the port Pf returns to the port Po through the second optical path L2, and the loop formed by the first and second optical paths L1 and L2 is opened. And an optical switch control means CONT capable of controlling

[0010]

According to the optical amplifier for an optical pulse tester of the present invention,
A first optical path, which is a forward path, and a second optical path, which is a return path, are provided in parallel between a port Po connected to the optical pulse tester and a port Pf connected to the measured optical fiber.
Since at least one optical switch is provided in the middle of the loop consisting of the forward path and the return path, the optical signal passes through either the forward path or the return path, and the optical pulse tester and the optical fiber to be measured. Make a round trip between. As a result,
Oscillation of the optical amplifier arranged in the loop is suppressed, and the optical amplifier for the optical pulse tester operates stably.

[0011]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a diagram for explaining the configuration of the optical amplifier for optical pulse tester 20 according to the first embodiment of the present invention. In the figure, Po is a port connected to the optical pulse tester, Pf
Is a port connected to the optical fiber to be measured, and the optical pulse tester optical amplifier 20 of this embodiment has ports Po and Pf.
In the meantime, the optical branching device 11, the photodetector 12, the optical switch driving circuit 13, the optical delay circuit 14, the ON / OFF optical switch 15,
Optical filter 16, two optical splitters 21, 22 and 2
The optical amplifiers 23 and 24 having one isolator are provided. Then, two optical splitters 21 and 22 are connected in parallel to each other.
One optical path is formed and one optical path (hereinafter referred to as optical path A)
Has an optical amplifier 23 and an on / off optical switch 15,
An optical filter 16 and an optical amplifier 24 are provided on the other optical path (hereinafter referred to as optical path B), and the two optical paths A and B are switched by the optical branching devices 21 and 22.

As the optical amplifiers 23 and 24, rare earth element-doped optical fiber amplifiers such as erbium-doped optical fiber amplifiers and neodymium-doped optical fiber amplifiers, semiconductor laser optical amplifiers, Raman optical amplifiers, and Brillouin optical amplifiers can be used. Is. Further, as the on / off optical switch 15, an AO (A
cousto Optical: Optical switch (using acousto-optic effect),
Alternatively, an optical switch using a LiNbO3 crystal or the like can be used. Furthermore, an optical fiber coupler or a half mirror can be used for the optical branching devices 21 and 22.

Next, the operation of the optical pulse tester optical amplifier 20 configured as described above will be described. The probe pulse optical signal from the optical pulse tester is input from the port Po. The optical branching device 21 passes through the optical branching device 11 and the optical delay circuit 14.
The probe pulse optical signal branched to the optical path A side by
It is amplified by the optical amplifier 23. At this time, the probe pulse optical signal partially branched by the optical branching device 11 is previously received by the photodetector 12 so that the amplified probe pulse optical signal can pass through the ON / OFF optical switch 15, and the electric signal is received. It is input to the optical switch drive circuit 13, and the on / off optical switch 15 is brought into the connected state for the time during which the probe pulse passes. Since the on-off optical switch 15 is in the disconnected state for the other time, most of the amplified spontaneous emission light generated by the optical amplifier 23 is on-off optical switch 15.
Shut off by. At this time, the optical switch drive circuit 13
When the response of the on / off optical switch 15 to the signal from is slow (for example, in the case of an AO optical switch, the response time is 1 μm).
s), the ON / OFF optical switch 15 cannot be connected in synchronization with the probe pulse optical signal. Therefore, as shown in FIG. 2, the optical delay circuit 14 is inserted between the ON / OFF optical switch 15 and the branching device 11. In this way, the probe pulse optical signal that has passed through the on / off optical switch 15 passes through the optical branch 22 and is incident on the optical fiber under measurement via the port Pf.

The probe pulse optical signal incident on the optical fiber under measurement produces backscattered light in the optical fiber under measurement. The backscattered light enters from the port Pf, passes through the optical branching device 22, enters the optical path B side, and is optically amplified by the optical amplifier 24. The backscattered light that has been optically amplified includes the optical filter 16, the optical branching device 21, the optical delay circuit 14, and the optical branching device 1.
1) Passes through the port Po and is input to the optical pulse tester. The optical filter 16 is for reducing the amplified spontaneous emission light generated by the optical amplifier 24.

Fresnel reflection usually occurs at the ports Po and Pf. In such a case, the optical path A from the port Po to the port Pf via the optical branching devices 11 and 21, the optical amplifier 23, the ON / OFF optical switch 15, the optical branching device 22, and the port Pf to the optical branching device 22 and the optical amplifier. 24,
After passing through the optical filter 16 and the optical splitters 21 and 11, the port P
When the loop gain is 1 or more in the loop formed by the optical path B to reach o, the operations of the optical amplifiers 23 and 24 become unstable.

However, in this embodiment, the ON / OFF optical switch 15 is in the connected state, and the loop consisting of the optical paths A and B is closed only for a short time Tw when the probe pulse optical signal passes through the optical switch 15. Normal,
Since the time Tr for the optical signal to go around the loop consisting of the optical path A and the optical path B is longer than Tw, the optical amplifiers 23 and 24 do not oscillate and the operation does not become unstable. If Tr ≤
In the case of Tw, an optical delay circuit using an optical fiber or the like may be inserted in the loop so that Tr> Tw. Normally, the pulse width used in the optical pulse tester is about 1 μs, so that an optical fiber of 200 m may be inserted as an optical delay circuit, and this can be easily performed. In this way, the optical pulse tester optical amplifier of the present embodiment,
It is possible to realize an optical amplifier that can be used by inserting it between the optical pulse tester and the optical fiber to be measured and still operate stably.

In the above description, the optical branching devices 21 and 22 are assumed to be optical fiber couplers and half mirrors.
However, in this case, the optical signal suffers a loss of 3 dB each time it passes through the optical branching device, so that the optical signal goes and goes back and forth through the optical amplifier for the optical pulse tester of the above-described embodiment, so that two optical branching devices are provided. A total of 12 dB will be lost by 21 and 22. Therefore, it is desirable to use optical circulators for the optical branchers 21 and 22. An optical circulator is a kind of optical non-reciprocal circuit. For example, consider an optical circulator having four ports, and if the ports are ,, then the optical signal transmission is →→
→ → is performed in only one direction, and its passage loss is theoretically zero. The specific structure is described in the literature (<1> Matsumoto et al., IEICE Technical Report, OQE78-149, pp. 25-2.
8, 1979, <2> H. IWAMURA et a
l. , Electron. Lett. , 15, pp. 8
30-831, 1979, <3> M. SHIRASAK
I et al. , Trans. of IEICE J
apan, E64, pp. 30-31, 1981,
<4> Koga et al., IEICE Technical Report, CS91-9, OCS91-
9, pp. 1-6, 1991). So now,
Two optical circulators are used as the optical branching devices 21 and 22, and ports 21c and 22c of the optical branching devices 21 and 22 are made to correspond to the ports of the circulators.
1a and 22b correspond to, and ports 21b and 22a correspond to. The circulator port is not used here. Then, the loss of the optical branching devices 21 and 22 becomes zero, and a high-performance optical pulse tester optical amplifier can be realized.

FIG. 3 is a diagram for explaining the configuration of the optical amplifier for optical pulse tester 30 of the second embodiment of the present invention, which is the same as the optical amplifier 20 for optical pulse tester shown in FIG. Are given the same reference numerals. The optical pulse tester optical amplifier 30 shown in FIG. 3 is different from the optical pulse tester optical amplifier 20 shown in FIG. 2 in that the changeover optical switch 31, instead of the optical splitters 21 and 22, is provided at the connection point between the optical paths A and B. 32
Is provided, and the optical switch drive circuit 13
However, the switching optical switches 31 and 32 and the on / off optical switch 1
5 is the same as that of the first embodiment shown in FIG. 2 except that it is driven in synchronization.

The operation of this embodiment will be described with reference to the timing chart shown in FIG. FIG. 4A shows time t0.
The probe pulse optical signal from the optical pulse tester passing through the port Po is shown in FIG.
In FIG. 4B, from time t0 to t1 (= port Po,
The probe pulse optical signal arriving at the switching optical switch 31 after the optical signal propagates to the switching optical switch 31)
Changeover optical switch 31 for transmitting along the optical path A
It represents the operation of. In FIG. 4B, when the solid line is on the upper side, the terminal 31c of the changeover optical switch 31
Indicates that it is connected to the terminal 31a on the optical path A side, and when the solid line is on the lower side, the changeover optical switch 31
31c is connected to the terminal 31b on the optical path B side. As shown in FIG. 4B, the terminal 31c of the switching optical switch 31 connected to the terminal 31b side is
At time t0 + t1, the probe pulse optical signal can be transmitted along the optical path A by reconnecting to the terminal 31a for the time Tw. Furthermore, after a lapse of time t2 (= the time for the optical signal to propagate from the changeover optical switch 31 to the on / off optical switch 15), the on / off optical switch 15 is brought into the connected state for the time Tw as shown in FIG. 4 (c). The probe pulse optical signal is turned on and off by the optical switch 1.
Go through 5. At this time, since the on / off optical switch 15 is in the disconnected state at other times,
SE (spontaneous emission light) can be largely removed. Furthermore, from the state of FIG. 4C, time t3 (= on-off optical switch 1
(5) Optical signal propagation time from the changeover optical switch 32)
After the lapse of time, as shown in FIG. 4 (d), the changeover optical switch 32 connected to the terminal 32b side is moved to the terminal 3 for the time Tw.
The probe pulse optical signal can be transmitted along the optical path A to the port Pf by changing the connection to 2a. In addition, in FIG. 4D, similar to FIG.
When the solid line is on the upper side, the terminal 3 of the changeover optical switch 32
2c is connected to the terminal 32a on the optical path A side, and when the solid line is on the lower side, the changeover optical switch 3
The second terminal 32c is connected to the terminal 32b on the optical path B side. As described above, the probe pulse optical signal input from the optical pulse tester to the port Po is
The light is amplified and transmitted to the port Pf.

On the other hand, the optical signal entering the port Pf from the optical fiber to be measured is, as shown in FIG. 4 (e), the Fresnel reflected light from the port Pf and the subsequent backscatter from the optical fiber to be measured. It is composed of light (in FIG. 4 (e), the time during which the optical signal propagates between the change-over optical switch 32 and the port Pf is ignored). Since the changeover optical switch 32 operates as shown in FIG.
The signal transmitted along the optical path B after passing through 2 is shown in FIG.
As shown in, the backscattered light has only the unnecessary Fresnel reflection removed. This backscattered light is amplified by the optical amplifier 24, reaches the changeover optical switch 31 connected to the terminal 31b on the optical path B side, further passes through it, and is transmitted to the port Po connected to the optical pulse tester.

As can be seen from the above description, in this second embodiment, by using the changeover optical switches 31 and 32, the loop consisting of the optical path A and the optical path B is always open and can be closed. Absent. Therefore, the optical amplifiers 23 and 24 operate stably.

In the above description, the changeover optical switches 31, 3 are
For 2, we assumed an ideal switch with less crosstalk. Next, the two AO optical switches whose crosstalk deteriorates in a certain operating state are replaced with the switching optical switches 31, 32.
The case where it is used as

FIG. 5 shows the operating principle of the AO optical switches 31 and 32 to which the ultrasonic optical deflector is applied. An RF (high frequency) electric signal is input to a transducer attached to an ultrasonic optical deflector crystal (for example, TeO2, PbMoO4, etc.) to propagate ultrasonic waves in the crystal. At this time, since the optical signal incident on the crystal is deflected by the diffraction grating formed by the ultrasonic wave, the ultrasonic optical deflector operates as an optical switch using the RF electric signal as a control signal.

Since the terminals 31c and 31b are connected and the terminals 32c and 32b are connected,
AO optical switch 3 corresponding when the optical path B is connected
Four combinations of α to δ shown in FIG. 5 can be considered as combinations of the operation states of 1 and 32. Here, in order to make the explanation easy to understand, the components other than the AO optical switches 31 and 32 are omitted.

(1) Combination α AO changeover optical switches 31 and 32 are in a combination in which RF electric input is applied. At this time, the terminals 31c and 31b and the terminals 32c and 32b are connected by being deflected by diffraction in the AO optical switches 31 and 32. However, since the diffraction efficiencies of the AO optical switches 31 and 32 usually do not reach 100%, the terminals 31c and 31a and the terminals 32c and 32 are not connected.
The connection between a is also established. This is indicated by a broken line in FIG. Therefore, the loop consisting of the optical paths A and B is closed, and the operation of the optical amplifiers 23 and 24 provided in the middle of the optical paths A and B becomes unstable.

(2) Combination β In this state, since the RF electric signal is not input to the AO optical switch 32, the optical signal is the terminal 32c and the terminal 32.
It only goes straight between b, and the terminals 32c and 32a
Is not connected between. Therefore, the loop is open. However, when an RF electric signal is applied to the AO optical switch 32 in the state shown in the combination β, the state shifts to a state where the terminals 32c and 32a are connected to each other, and the loop is closed like the combination α. Become.

(3) Combination γ In this state, since the RF electric signal is not input to the AO optical switch 31, the optical signal is the terminal 31c and the terminal 31.
It only goes straight between the terminals b and the terminals 31c and 31a.
Is not connected between. Therefore, the loop is open. However, when an RF electric signal is applied to the AO optical switch 31 in the state shown in the combination γ, the state shifts to a state in which the terminal 31c and the terminal 31a are connected, and the state similar to the combination α is closed. Become.

(4) Combination δ In this state, since no RF electric signal is input to the AO optical switches 31 and 32, the optical signal is output to the terminal 31c.
It only goes straight between the terminal 31b and the terminal 32b and between the terminal 32c and the terminal 32b, and there is no connection between the terminal 31c and the terminal 31a and between the terminal 32c and the terminal 32a.
Therefore, the loop is open. From this state, the loop is closed because the RF electric signal is applied to both of the AO optical switches 31 and 32, so that the terminals 31c and 31a are connected and the terminals 32c and 32a are connected.
Only when a is connected. However, this condition is
It does not exist as shown in the time chart of FIG. Therefore, as shown in the combination δ, the AO optical switches 31, 3 are
By connecting and operating 2, the optical amplifier can be stably operated even if the crosstalk characteristics of the AO optical switches 31 and 32 are insufficient.

On the other hand, considering the case where the delay time t2 + t3 is very short in the time chart of FIG. 4, at this time, in the state shown in the combination δ, A0
There is a state where the terminals 31c and 31a and the terminals 32c and 32a are connected by applying an RF electric input to the optical switches 31 and 32. At this time, as described above, the loop consisting of the optical path A and the optical path B is closed, and the operation of the optical amplifier becomes unstable. Therefore, the connection and operation of the AO optical switches 31 and 32 shown in the combination δ cannot be adopted. In this case, the combination β or the combination γ is adopted, and the AO optical switch 31 is used.
6 and 32 may be operated in phase with each other as shown in FIG. Actually, at this time, either one of the AO optical switches 31 and 32 is always in the state where the optical path A or the optical path B is separated, so that the loop formed by the optical paths A and B is always in the open state.

In the above description, the on / off optical switch 15 is used.
Was used only for the purpose of removing ASE. The operation of the changeover optical switches (AO optical switches) 31 and 32 kept the loop consisting of the optical path A and the optical path B open. However, in the same manner, it is obvious that the loop can be always opened by the operation of the combination of the switching optical switch 31 and the on / off optical switch 15 or the combination of the switching optical switch 32 and the on / off optical switch 15. Is. Further, even when an optical switch such as an AO optical switch whose crosstalk characteristic is deteriorated in a certain operating state is used as this optical switch, the loop is always opened by taking the same measures as described above. You can see that it can be put into a state.

7 and 8 show the case where the loop can always be opened by the operation of combining the AO switching optical switch 31 and the AO on / off optical switch 15. 7 and 8, the AO optical switch 31 and the AO
Parts other than the on / off optical switch 15 are omitted.

FIG. 7 shows a case where the AO optical switch 31 and the AO on / off optical switch 15 do not connect the optical path A at the same time, as shown in the timing chart of FIG. Figure 7
In FIG. 3, α indicates the operating state when the probe pulse optical signal from the optical pulse tester passes through the AO optical switch 31. β indicates the operating state when the probe pulse optical signal passes through the AO on / off optical switch 15. γ indicates an operating state when the backscattered light from the optical fiber under measurement is transmitted from the port Pf to the port Po. It can be seen that in any of the operating states, at least one of the AO optical switches is completely off, and the loop formed by the optical paths A and B is open.

FIG. 8 shows a case where the AO optical switch 31 and the AO on / off optical switch 15 may connect the optical path A at the same time. At this time, both optical switches are operated in phase with each other. In FIG. 8, α indicates the operating state when the probe pulse optical signal from the optical pulse tester passes through the optical path A. Further, β represents the operating state when the backscattered light from the optical fiber under measurement passes through the optical path B. As in the case of FIG. 7, one of the AO optical switches is completely in the off state and the loop including the optical path A and the optical path B is in the open state in any operation state. I understand.

FIG. 9 is a diagram for explaining the configuration of the optical amplifier 40 for an optical pulse tester according to the third embodiment of the present invention.
Reference numeral 7 is an optical circulator. This embodiment is an optical amplifier for optical pulse tester 2 of the first embodiment of the present invention shown in FIG.
0, the optical splitters 21 and 22 are replaced with only the optical circulator 16 and the optical amplifier in the optical path B is omitted. Since the passage loss of the optical circulator is zero in principle as described above, a high performance optical amplifier for an optical pulse tester can be realized.

FIG. 10 is a diagram for explaining the configuration of the optical amplifier for optical pulse tester 50 according to the fourth embodiment of the present invention. In this embodiment, in the optical pulse tester optical amplifier 20 of the first embodiment of the present invention shown in FIG. 2, the optical branching device 21 is a switching optical switch 31, and the optical branching device 22 is an optical circulator 17. This corresponds to the case of replacement. Since the passage loss between the switching optical switch 31 and the optical circulator 17 is zero in principle, a high-performance optical amplifier for an optical pulse tester can be realized.

The time Tw in which the on / off optical switch 15 is in the connected state is only a short time during which the probe pulse optical signal from the optical pulse tester passes through the on / off optical switch 15. Therefore, as described in the first embodiment, normally, the time Tr during which an optical signal propagates through the loop composed of the optical path A and the optical path B is longer than Tw. It is possible to easily satisfy Tr> Tw by inserting it inside. Therefore, the optical amplifiers 23 and 24 do not oscillate and operate stably with high gain.

Further, as described in the second embodiment, by timing the operation of the changeover optical switch 31 and the on / off optical switch 15, the loop consisting of the optical path A and the optical path B is always opened, and the optical amplifier It is also possible to perform high gain stable operation.

FIG. 11 is a diagram for explaining the configuration of the optical amplifier for optical pulse tester 60 according to the fifth embodiment of the present invention. In this embodiment, in the optical pulse tester optical amplifier 20 of the first embodiment of the present invention shown in FIG. 2, the optical branching device 22 is a switching optical switch 32, and the optical branching device 21 is an optical circulator 17. This corresponds to the case of replacement. By adopting such a configuration, a high performance optical amplifier for an optical pulse tester can be realized as in the fourth embodiment.

In the first, second, fourth, and fifth embodiments described above, the optical filter 16 is used after the optical amplifier 24 in the optical path B. When the line width of the light source used in the optical pulse tester is narrow, the ASE of the optical amplifier 24 can be effectively removed by narrowing the transmission wavelength width of the optical filter 16. However, when the line width of the light source used in the optical pulse tester is wide, the effect is small. In the latter case, the optical amplifier 24 and the optical filter 16 in the optical path B can be obtained from the first, second, fourth and fifth embodiments of the present invention.
Obviously, the operation of the present invention does not change even if the omission is omitted.

Further, in FIGS. 5, 7 and 8, a transducer is attached to the upper side of the ultrasonic optical deflector crystal,
Although an RF electrical signal is input, this transducer may be on the lower side. In this case, the positive and negative shift amounts of the frequency of the optical signal that is incident on the ultrasonic optical deflector and is diffracted differ depending on the difference between the attachment positions on the upper side and the lower side of the transducer, but the operation of the present invention does not change. Absent.

[0042]

As described above, the optical amplifier for an optical pulse tester of the present invention has the following effects.

(1) Since the optical path from the optical pulse tester to the optical fiber under test and the optical path from the optical fiber under test to the optical pulse tester are provided separately, a one-way optical amplifier can be used for each optical path. A stable and high-gain optical amplifier can be realized.

(2) Since the optical switch for opening the loop consisting of two optical paths is provided, the optical amplifier operates stably.

(3) It is possible to provide an optical amplifier for an optical pulse tester capable of expanding the dynamic range of the optical pulse tester by simply inserting it between the optical pulse tester and the optical fiber under test.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of an optical amplifier for an optical pulse tester of the present invention.

FIG. 2 is a diagram showing a configuration of an optical amplifier for an optical pulse tester according to a first embodiment of the present invention.

FIG. 3 is a diagram showing the configuration of an optical amplifier for an optical pulse tester according to a second embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the optical switch.

FIG. 5 is a diagram for explaining a connection state between the optical paths A and B and an AO optical switch and its operation.

FIG. 6 is a timing chart for explaining the operation of the AO optical switch.

FIG. 7 is a diagram for explaining the operation of the AO optical switch.

FIG. 8 is a diagram for explaining the operation of the AO optical switch.

FIG. 9 is a diagram showing the configuration of an optical amplifier for an optical pulse tester according to a third embodiment of the present invention.

FIG. 10 is a diagram showing a configuration of an optical amplifier for an optical pulse tester according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a configuration of an optical amplifier for an optical pulse tester according to a fifth embodiment of the present invention.

FIG. 12 is a diagram for explaining a mode in which a conventional optical amplifier is applied to an optical pulse tester.

[Explanation of symbols]

11, 21 and 22 Optical branching device 12 Photodetector 13 Optical switch driving circuit 14 Optical delay circuit 15 Optical switch 16 ON / OFF optical switch 16 Optical filter 17 Optical circulator 31, 32 Switching optical switch 31a, 31b, 31c, 32a, 32b, 32c Terminal 120 Optical pulse tester 121 Light source 122,124,140 Optical amplifier 123 Optical directional coupler 125 Photodetector 130 Optical fiber under test Po, Pf port

Claims (1)

[Claims] 1. An optical pulse tester (OTDR) and an optical fiber under test (LF) for searching for an abnormal point in an optical fiber.
An optical amplifier for an optical pulse tester provided between the optical pulse tester (OTDR) and a port (P
o) and a port (P) connected to the measured optical fiber (LF)
f), the first optical path (L1) for optical signal transmission provided between the port (Po) and the port (Pf), and the light provided in parallel with the first optical path (L1). A second optical path (L2) for signal transmission, a one-way optical amplifier (LA) provided in at least one of the first and second optical paths (L1, L2), and the first and second optical paths Light provided on at least one of (L1, L2), or light provided on at least one branch point of the two branch points of the first optical path (L1) and the second optical path (L2). The operation timing of the switch (SW) and the optical switch (SW) is controlled so that the light incident from the port (Po) reaches the port (Pf) through the first optical path (L1). ,And,
The light incident from the port (Pf) returns to the port (Po) through the second optical path (L2), and
And an optical switch control means (CONT) capable of opening a loop formed by the second optical paths (L1, L2), and an optical amplifier for an optical pulse tester.