JPH0862092A - Light circuit for optical fiber analyzer - Google Patents

Abstract

PURPOSE: To provide an optical fiber analyzer which perform an equivalent operation with one optical isolator by reducing the light loss of the light circuit of an optical fiber analyzer for increasing the distance to be monitored of the optical fiber cable by the optical fiber analyzer. CONSTITUTION: An optical connector cord 503 for taking out the light output of a semiconductor laser 501 which is a light generation element of an optical fiber analyzer is connected to an optical connector cord 505 of a first light input edge of a four-terminal optical circulator 504, an input/output optical connector code 510 of a reflection-type optical fiber amplifier 511 is connected to an in/out optical connector cord 506 of a second light input/output terminal, the terminal of an optical fiber cable to be monitored is connected to an optical connector cord 507 of a third light input/output terminal, and an avalanche photodiode 51 as a photoelectric conversion element is connected to an optical connector cord 508 of a fourth light input/output terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit for an optical fiber analyzer which is an apparatus for measuring an optical loss for monitoring an optical fiber cable or searching for a position of a fault point, and has a large inspectable distance. The present invention relates to an optical circuit for an optical fiber analyzer capable of performing an inspection while performing optical communication.

[0002]

2. Description of the Related Art An outline of the configuration of an optical circuit of a conventional typical optical fiber analyzer is as shown in FIG. Reference numeral 101 denotes a semiconductor laser having an emission wavelength in the vicinity of 1.55 μm (hereinafter referred to as μm), 102 denotes an optical connector code for extracting an optical output from the semiconductor laser, and 103 denotes for inputting an electric signal to the semiconductor laser. An electric cable, 104 is an avalanche photodiode (hereinafter referred to as APD) that converts an optical signal into an electric signal,
Reference numeral 105 denotes an optical connector code for inputting an optical signal to the APD, reference numeral 106 denotes an electric cable for extracting an electric signal of the APD, reference numeral 107 denotes an optical switch body, and reference numeral 108 denotes an optical connector code at a common end of the optical switch. The optical connector cord to which the measuring optical fiber is connected, 109 is one of the switching ends of the optical switch, and the optical connector cord is connected to 102. 110 is the other switching end of the optical switch and is connected to 105. The optical connector cord 111 is an electric cable for inputting an electric signal for driving the optical switch.

The operation of the optical circuit of FIG. 1 will be described below. A semiconductor laser 101 generates an optical pulse proportional to the electrical pulse applied through 103. The time width and pulse interval of the optical pulse depend on the length of the optical fiber cable to be measured and the light intensity of the semiconductor laser, but when measuring the optical loss of an optical fiber cable of 80 km, for example,
The pulse time width is 1 microsecond (hereinafter referred to as μs), and the pulse interval is 1.25 milliseconds (hereinafter m
s).

The optical pulse propagates through 102 and 109 and is input to the optical switch body 107. The control signal applied to 111 causes 107 to be conductive between 109 and 108 while the optical pulse emitted from 101 is transmitted through 108, and the next optical pulse is transmitted immediately after one optical pulse passes. Until it is emitted, 110 and 108 operate to conduct. Immediately after the optical pulse passes through 108, Rayleigh scattered light generated in the optical fiber to be measured propagates through 108 and is input to 107. At this time, since 108 and 110 are in conduction, Rayleigh scattered light passes through the AP through 105.
It is input to D104.

The Rayleigh scattered light intensity weakens as the light pulse moves away from 108. Such a time change of the Rayleigh scattered light intensity is converted into a time change of the current by the APD 104. Although not shown in FIG. 1, the optical fiber analyzer performs a numerical operation on an electric signal generated by the APD by a signal processing circuit connected to 106 to calculate the optical loss of the optical fiber.

In FIG. 1, a method of using a three-terminal optical isolator instead of the optical switch 107 is also known.
FIG. 2 is a diagram for explaining the operation of the three-terminal optical isolator.
02 is an optical connector code of a first optical input / output end, 203 is an optical connector code of a second optical input / output end, and 204 is an optical connector code of a third optical input / output end. The light input from 202 is output from 203, and the light input from 203 is 2
Since the light output from 04 and the light input from 204 are output from 205, 201 can be used instead of 107 in FIG. The optical isolator is more expensive than the optical switch, but has an excellent advantage that a control signal is unnecessary and insertion loss is small.

Referring to FIG. 1, an optical circuit in which the emission wavelength of the semiconductor laser 101 is around 1.65 μm has been developed. In optical communication using an optical fiber cable, the wavelength of signal light is 1.3 μm or 1.55 μm, so that 1.65
An optical fiber analyzer with a μm semiconductor laser
It has a feature that it is possible to measure the optical loss of the optical fiber while continuing the optical communication.

An easily conceivable method for increasing the searchable optical fiber length of an optical fiber analyzer is shown in FIG.
Is to insert an optical amplifier between 102 and 109. Erbium-doped optical fiber (hereinafter referred to as ED
F) as an active medium (hereinafter referred to as E).
DFA) can be used.

An outline of the structure of a generally known EDFA is shown in FIG. Reference numeral 301 denotes an optical connector code for inputting light to be amplified (hereinafter, referred to as amplified light);
Is an excitation light source, 303 is an optical multiplexer that combines the amplified light and the excitation light, 304 is an optical isolator that allows light to pass only in the direction of the arrow, 305 is an EDF, 306 is an optical isolator, and 307 is amplified light. This is an optical connector code for taking out the optical connector.

An outline of the structure of an EDFA called a reflection type is shown in FIG. 401 is a three-terminal optical isolator body, 40
2 is an input optical connector code for inputting amplified light, 403
Is an excitation light source, 404 is an optical multiplexer for multiplexing the amplified light and the excitation light, 405 is an EDF, 406 is a light reflector, and 407 is an optical connector code for extracting the amplified light. The outline of this EDFA operation is as follows.

The pump light output from 403 passes through 404 and is input to the EDF 405 to contribute to amplification. The amplified light is input from 402, and by the action of 401,
04 and is amplified while passing through the 405 EDF. The amplified light is reflected by the reflection plate 406 and re-
Although it passes through 5, it is also amplified during this period and input to 401. Due to the action of 401, the amplified light is output from 407. Since the reflection type EDFA effectively uses the excitation light, it has a characteristic of high efficiency.

However, when the optical fiber analyzer of FIG. 1 and the reflection type optical fiber amplifier of FIG. 4 are combined, two expensive optical isolators are required, which is economically disadvantageous. Further, the wavelength of the excitation light source is usually 1.48 μm or 0.
98 μm, wavelength is from 1.53 μm to 1.56 μm
Amplifies the light. Therefore, such an EDFA is
It cannot be applied to the above-mentioned optical fiber analyzer having a wavelength of 1.65 μm. A method utilizing stimulated Raman scattering is known as a method for amplifying light having a wavelength of 1.65 μm, but a high gain cannot be easily obtained.

[0013]

In order to increase the monitorable distance of the optical fiber cable by the optical fiber analyzer, the optical loss of the optical circuit of the optical fiber analyzer is reduced, and when an optical amplifier is used, two isolator units are used. Was necessary and was uneconomical. In order to measure the optical loss of an optical fiber while continuing optical communication, it is appropriate to use an optical fiber analyzer having a light source with a longer wavelength than the signal light. There was no appropriate means for amplifying light having a wavelength of 1.65 μm.

In the present invention, an optical isolator required for an optical fiber amplifier and an optical isolator for separating the output of the optical fiber analyzer from the scattered light can be shared by one optical isolator. It is another object of the present invention to find a wavelength of an optical fiber analyzer which can provide optical amplification at a longer wavelength than signal light.

[0015]

In order to solve the above problems, a 4-terminal isolator is used, and
The optical fiber amplifier is of a reflection type in which light input and output are performed by a common optical fiber. An optical connector code for extracting an optical output of a semiconductor laser, which is a light generating element of an optical fiber analyzer, is connected to an optical connector code at a first optical input end of the four-terminal optical circulator. Connect the input / output optical connector cord of the reflection type optical fiber amplifier to the input / output optical connector cord,
The terminal of the monitored optical fiber cable is connected to the optical connector cord at the third optical input / output end of the four-terminal optical circulator, and the optical connector cord at the fourth optical input / output end of the four-terminal optical circulator is APD which is a kind of conversion element
Connect. The wavelength of the optical fiber analyzer is set to 1.
The wavelength is 59 μm or more and 1.62 μm or less.

[0016]

With this structure, the optical circulator required for the optical fiber amplifier and the optical isolator required for the optical fiber analyzer can be completed by one optical isolator. Also, with the above-mentioned wavelength, a large optical output can be easily obtained by the optical fiber amplifier, and the optical line can be monitored without interrupting the optical communication performed at 1.55 μm.

[0017]

FIG. 5 is a schematic diagram showing the configuration of an embodiment of the present invention. Reference numeral 501 denotes a semiconductor laser which is a light emitting element of an optical fiber analyzer; 502, an electric cable for supplying a current to 501; 503, an optical connector cord for extracting light from the semiconductor laser; 504, a main body of a four-terminal optical circulator; 504 is an optical connector code which is a first optical input / output terminal of 504, 506 is an optical connector code which is a second optical input / output terminal of 504, 507 is an optical connector code which is a third input / output terminal of 504, and 508 is An optical connector code 504 is a fourth optical input / output terminal, 509 is an optical multiplexer for multiplexing the excitation light and the amplified light, 510 is an optical connector code for inputting the amplified light, 511 is an EDF, 512 513 is an excitation light source, 513 is an APD for converting an optical signal into an electric signal, and 516 is an electric cable for extracting an electric signal.

Next, the operation of this optical circuit will be described. 501
Generates light in proportion to the electric signal input from 502. If this light is called supervisory signal light, the supervisory signal light is 50
3 and 505 and input to the optical circulator 504. Due to the action of the optical circulator on the monitoring signal light, 5
It is output from 06 and input to 510. The monitoring signal light is combined with the pump light at 509 and input to the EDF 511. The supervisory signal light amplified in 511 is reflected by 512, propagates through 511 again, and is amplified. The amplified supervisory signal light passes through 510 and is input to 506 to 504. The amplified signal light is output to 507 by the operation of the optical circulator body 504. A monitored optical fiber cable is connected to 507. Rayleigh scattered light is generated in the monitored optical fiber cable and propagates in a direction opposite to the propagation of the monitoring signal light.

Therefore, the Rayleigh scattered light is input to the optical circulator main body 504 through 507. Rayleigh scattered light is output from 508 by the action of 504,
5 and is input to the photoelectric conversion element 514. The electrical signal is extracted from 516 and input to a signal processing circuit following 516.

All commercially available products, including the four-terminal optical circulator, can be applied to the components shown in FIG. For the connection between 503 and 505 and the connection between 506 and 510, fusion loss of the optical fiber can reduce the connection loss. The light reflecting plate 512 may be a mirror, and in that case, the optical fiber axis may be perpendicular to the mirror and brought into contact with the mirror. However, when a light reflection film is deposited on the end face of the optical fiber, a more complete reflector is obtained.

When the wavelength of the pumping light source of the optical fiber amplifier is set to 1.48 μm or 0.98 μm in the configuration of FIG.
It is well known that light of 53 μm to 1.57 μm can be amplified. However, since this wavelength range is a wavelength used for optical communication, it is impossible to send the supervisory signal light while the optical communication is being executed.

In the present invention, the excitation light source has an emission wavelength of 1.5.
The semiconductor laser is in a wavelength range of 9 μm to 1.62 μm. It is known that when the wavelength of the pump light is 1.55 μm, light amplification in this wavelength range is possible.

FIG. 6 shows the measurement result of the gain characteristic of the reflection type optical fiber amplifier of FIG. The horizontal axis represents the input optical power and the unit is DBM (dBm). The vertical axis indicates the gain, and the unit is davy (dB). The light wavelength is 1.60 μm. The EDF has an erbium concentration of 1000 ppm and a length of 100 m. The pump light input is 180 mW. From FIG. 6, the gain is about 24 dB when the signal input is -30 dBm.
It can be seen that it is. The average value of the output of the optical pulse used in the optical fiber analyzer is -40 dBm, and the gain of the optical fiber amplifier is determined by the average value.
It becomes more than dB.

Therefore, if the maximum power of the pulse of the semiconductor laser emitting the monitoring signal light is 1 mW, the output of the reflection type optical fiber amplifier can be 240 mW or more.

FIG. 7 shows an optical fiber analyzer equipped with an optical circuit for an optical fiber analyzer according to the present invention.
It is an observation result of Rayleigh scattered light intensity of an optical fiber of km. Although the maximum power of the light pulse was 140 mW,
The reflection from the end face of km is clearly shown.

[0026]

As described above, according to the optical circuit for an optical fiber analyzer of the present invention, an optical fiber analyzer with a large output can be economically provided by one 4-terminal optical circulator and one reflective optical fiber amplifier. There is an effect that can be built. Furthermore, if the wavelength of the semiconductor laser of the optical circuit for the optical fiber analyzer is set to a value in the range of 1.59 μm to 1.62 μm, it is possible to monitor a long-distance optical line without interrupting optical communication. is there.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a configuration of an optical circuit of a conventional typical optical fiber analyzer.

FIG. 2 is a schematic diagram for explaining the operation of a three-terminal optical isolator.

FIG. 3 is a schematic diagram of a configuration of a generally known EDFA;

FIG. 4 is a schematic diagram of a configuration of a reflection type optical fiber amplifier.

FIG. 5 is a schematic diagram of a configuration of an embodiment of the present invention.

6 is a measurement result diagram of a gain characteristic of the reflection type optical fiber amplifier of FIG.

FIG. 7 is an observation result diagram of the Rayleigh scattered light intensity of an optical fiber having a length of 80 km measured by an optical fiber analyzer equipped with an optical circuit for an optical fiber analyzer of the present invention.

[Explanation of symbols]

501 semiconductor laser 502 electric cable 503, 505, 506, 507, 508, 510, 5
15 Optical connector code 504 Four-terminal optical circulator body 509 Optical multiplexer 511 Erbium-doped optical fiber 512 Light reflector 513 Excitation light source 514 Avalanche photodiode 516 Electric cable

Claims (2)

[Claims] 1. A light input from a first light input end is supplied to a second light input end.
The light input from the second light input / output terminal is output from the third light input / output terminal, and the light input from the third light input / output terminal is output from the fourth light input / output terminal. An optical circuit including a four-terminal optical circulator output from the optical output end of the optical fiber, a semiconductor laser, an avalanche photodiode, and a reflective optical fiber amplifier having the same input / output end and output end. An optical output terminal of the semiconductor laser is connected to a first optical input terminal of the four-terminal circulator, and an optical input / output terminal of the reflection type optical amplifier and a second optical input terminal of the optical circulator.
Is connected to the optical input / output end of the four-terminal optical isolator and the optical input end of the avalanche photodiode.
An optical output terminal of the optical fiber analyzer. 2. The optical fiber according to claim 1, wherein the semiconductor laser according to claim 1 is a semiconductor laser having an emission wavelength of 1.59 μm or more and 1.62 μm or less. Optical circuit for analyzer.