JPH08271375A - Optical line inspecting method and optical line inspecting system - Google Patents

Abstract

PURPOSE: To provide an optical line inspecting method using an optical filter constituted of few optical wave guide type diffraction gratings. CONSTITUTION: A luminescence section 10 outputs the inspection light having the wavelength width of about 20nm or below. Since this inspection light is used to inspect an optical line 3, the reflected wavelength width of an optical filter 60 provided at the terminal end section of the optical line 3 can be made sufficiently narrow. The number of the optical wave guide type diffraction gratings constituting the optical filter 60 can be reduced, the transmission loss of the signal light due to a mode mismatch or the absorption of the OH group is reduced, and the optical line can be inspected while the effect on the optical communication is sufficiently suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for inspecting the state of an optical line using inspection light, particularly in the field of optical fiber communication technology.

[0002]

2. Description of the Related Art Generally, in an optical line inspection system using an inspection device such as an OTDR device, an optical filter is provided at the terminal end of the optical line. This optical filter has a function of blocking the inspection light so as not to send the inspection light to the subscriber's house, and a function of reflecting the inspection light and causing the inspection device to recognize the end.

An optical waveguide type diffraction grating can be used as the optical filter. This is a region of the core of the optical waveguide, and the effective refractive index of the core periodically fluctuates along the optical axis between the minimum refractive index and the maximum refractive index. This optical waveguide type diffraction grating reflects light having a narrow wavelength width centered on a predetermined reflection wavelength (Bragg wavelength). The reflection wavelength is determined according to the period of the optical waveguide type diffraction grating.

[0004]

Conventionally, the light source for the inspection light is 30 nm like a vertical multimode semiconductor laser.
Wide oscillating wavelength range is used,
The variation of the central wavelength that represents the oscillation wavelength width is large. Therefore, the reflection wavelength width of the optical filter that reflects the light is wider than this, and preferably about 30 nm or more.

In this case, a single optical waveguide type diffraction grating has three
Since it is difficult to have a reflection wavelength width of 0 nm or more,
A method is conceivable in which an optical filter having a reflection wavelength width of 30 nm or more is realized by configuring the optical filter with a plurality of optical waveguide type diffraction gratings having slightly different reflection wavelengths.

On the other hand, in order to ensure a good function as an optical filter, the higher the reflectance of the optical waveguide type diffraction grating constituting the optical filter is, the better. Therefore, after exposing the optical waveguide to a hydrogen atmosphere, ultraviolet light is emitted. It is conceivable to use an optical waveguide type diffraction grating manufactured by irradiating optical interference fringes. However, in this method, OH groups are generated in the optical waveguide type diffraction grating upon irradiation with ultraviolet light.
A problem is that it has a property of absorbing light in the 0 nm band. That is, the optical filter provided on the optical line has a function of blocking the inspection light and passing the signal light, but when the OH group contained in the optical filter absorbs light, it is usually used in optical communication. This causes an adverse effect that the transmission loss of the signal light in the 1300 nm band becomes large.
If it is attempted to construct an optical filter having a reflection wavelength width of 30 nm or more, the number of optical waveguide type diffraction gratings increases, and the number of times of ultraviolet light irradiation for forming this increases. This means an increase in OH groups in the entire optical filter, which leads to an increase in transmission loss of signal light, and is not preferable.

Further, since the optical waveguide type diffraction grating is a region where the refractive index changes along the optical axis as described above,
A mode mismatch occurs in the signal light passing through each optical waveguide type diffraction grating, which also causes a transmission loss. 30
If the number of optical waveguide type diffraction gratings is increased in order to realize a reflection wavelength width of nm or more, mode mismatch frequently occurs, and the transmission loss due to mode mismatch also becomes so large that it cannot be ignored.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical line inspection method and an optical line inspection system using an optical filter composed of a small number of optical waveguide type diffraction gratings. .

[0009]

In order to solve the above-mentioned problems, the optical line inspection method of the present invention is an optical line to be inspected, which is provided with an optical filter at its terminal end. Is a method of inspecting the state of the optical line by detecting the inspection light reflected or scattered in each part of the optical line and the optical filter, wherein the optical filter is
It is composed of one or more optical waveguide type diffraction gratings having mutually different periods, and the wavelength width of the inspection light is about 20.
It is characterized in that it is less than or equal to nm. Here, the wavelength width of the inspection light is preferably about 5 nm or less.

Next, the optical line inspection system of the present invention is provided at a light emitting portion for outputting inspection light having a wavelength width of about 20 nm or less and for making the inspection light incident on the optical line, and at a terminal end of the optical line. Optical filter, which is composed of one or more optical waveguide type diffraction gratings having mutually different periods, and the optical line of each part of the optical line and the inspection light reflected or scattered by the optical filter. And an inspection unit for inspecting the condition. Here, it is preferable that the wavelength width of the inspection light output from the light emitting unit is about 5 nm or less.

The optical line inspection system of the present invention further comprises an optical function unit for making the inspection light incident on the optical line and for making the inspection light reflected or scattered by each part of the optical line and the optical filter enter the inspection unit. May be.

A first embodiment of the light emitting section is provided with a Fabry-Perot type semiconductor laser and a bandpass filter into which laser light emitted from this Fabry-Perot type semiconductor laser is incident. It is conceivable that the above laser light transmitted through the filter is used as the inspection light. As the bandpass filter, for example, a dielectric multilayer filter can be used.

As a second embodiment of the light emitting section, a Fabry-Perot type semiconductor laser, an optical waveguide in which a diffraction grating is formed in a core, and laser light emitted from the Fabry-Perot type semiconductor laser are made incident on this optical waveguide. An optical component that causes the laser light reflected by the diffraction grating to enter the optical line is provided, and the laser light that enters the optical line from the optical component may be used as the inspection light.

As a third embodiment of the light emitting section, it is conceivable that the distributed feedback semiconductor laser is provided and the laser light emitted from the distributed feedback semiconductor laser is used as the inspection light.

As a fourth embodiment of the light emitting portion, it is possible to provide a distributed Bragg reflector type semiconductor laser, and use laser light emitted from this distributed Bragg reflector type semiconductor laser as inspection light. .

The distributed Bragg reflector type semiconductor laser includes, for example, a current-excitation type semiconductor light emitting device having a light emitting surface and a light reflecting surface facing the light emitting surface, and an optical element having a core formed with a diffraction grating. It is possible to use a device that has a waveguide and that emits light from the semiconductor light emitting element to perform laser oscillation by being reflected by the diffraction grating and the light reflecting surface.

In the above description, the optical waveguide means a circuit or line for confining light in a certain area and transmitting it, and includes an optical fiber, a thin film waveguide and the like.

[0018]

In the optical line inspection method of the present invention, the optical line is inspected by using the inspection light having the wavelength width of about 20 nm or less, so that the number of optical waveguide type diffraction gratings constituting the optical filter can be small. As a result, the transmission loss of the signal light due to the mode mismatch and the absorption of the OH group is reduced, and the optical line is inspected while sufficiently suppressing the influence on the optical communication.

In particular, when the inspection light having a wavelength width of about 5 nm or less is used, the number of optical waveguide type diffraction gratings constituting the optical filter can be extremely small, and the influence of the inspection of the optical line on the optical communication is extremely small. .

Next, in the optical line inspection system of the present invention,
The light emitting section outputs the inspection light having a wavelength width of about 20 nm or less, and the inspection light is used to inspect the optical line, so that the reflection wavelength width of the optical filter can be sufficiently narrowed. As a result, the transmission loss of the signal light due to the mode mismatch and the absorption of the OH group is reduced, so that the optical line inspection system of the present invention can inspect the optical line while sufficiently suppressing the influence on the optical communication.

Particularly, when the wavelength width of the inspection light output from the light emitting section is about 5 nm or less, the number of optical waveguide type diffraction gratings can be extremely small, and therefore the influence of the inspection of the optical line on the optical communication is extremely small. Become.

[0022]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.
Further, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is an overall configuration diagram showing an optical line inspection system of this embodiment. First, the basic configuration of the optical communication network to which the inspection system of the embodiment is applied will be described. One or more optical lines 3 (three optical lines are shown as a representative in FIG. 1) connected to a transmission device 2 installed in a station 1 such as a subscriber communication network are optical fibers. It is bundled as a cable 4 and extends to the subscriber's home 5. As a result, the transmission device 2 and each subscriber's house 5 are connected by one optical line 3. The communication light output from the transmission device 2 propagates through the optical line 3 and is received by the terminal installed in the subscriber's house 5. In the optical communication network of this embodiment, about 1300n
Signal light having a wavelength of m is used.

Next, the structure of the inspection system of this embodiment will be described. This inspection system includes an OTDR device 100, an optical switch 40 connected to the inspection light from the OTDR device 100 via an optical fiber 22, and an optical coupler 50 installed at the end of the optical line 3 on the transmission device 2 side. , And an optical filter 60 provided at the end of each optical line 3 (end on the subscriber home 5 side).

The OTDR device 100 comprises a light emitting section 10, an optical coupler 20 connected to the light emitting section 10 via an optical fiber 21, and an inspection section 30 connected to the optical coupler 20 via an optical fiber 23. Has been done.

The light emitting section 10 pulse-oscillates the laser light as the inspection light. Full width at half maximum of wavelength spectrum of this inspection light,
That is, the wavelength width is about 20 nm or less. The central wavelength of the inspection light (the central wavelength of the half-value width) is different from the wavelength of the signal light, and is about 1550 nm.

The optical coupler 20 makes the inspection light incident through the optical fiber 21 incident on the optical switch 40 through the optical fiber 22 and is reflected or scattered by each part of the optical line 3 and the optical filter 60 to return. The inspection light received is incident on the inspection unit 30 via the optical fiber 23.

The inspection unit 30 detects the returned inspection light and inspects the state of the optical line 3. The inspection unit 30 is similar to that used in a normal OTDR device, and includes a photodetector that detects inspection light and converts it into an electric signal, an amplifier that amplifies an electric signal output from the photodetector, and an amplifier. A signal processing device for A / D converting the output signal and further performing averaging processing, a CRT device connected to the signal processing device, and the like are provided.

Next, the optical switch 40 is used in the OTDR device 1.
The optical coupler 20 in 00 and any one of the optical couplers 50 in the optical line 3 are optically switched and connected via the optical fiber 41. Since the inspection light from the OTDR device 100 is incident on the optical line 3 including the connected optical coupler 50, the optical line 40 to be inspected can be selected by operating the optical switch 40.

The optical coupler 50 makes the inspection light incident on the optical line 3 and propagates it toward the subscriber's house 5, and at the same time, returns the inspection light reflected or scattered by each part of the optical line 3 and the optical filter 60. It is incident on the optical switch 40.

As is apparent from the above, the optical coupler 20, the optical switch 40, and the optical coupler 50 allow the inspection light to be incident on the optical line 3 as a whole, and the optical line 3
The function of causing the reflected light from and the backscattered light to enter the inspection unit 30 is achieved. That is, the optical coupler 20, the optical switch 40, and the optical coupler 50 configure an optical function unit that has the above-described functions.

The optical filter 60 has a function of reflecting light over a predetermined wavelength range, and inspects the inspection light in the subscriber's house 5.
The light is shut off immediately before to prevent the inspection light from becoming noise in optical communication. In addition, the inspection unit 30 includes the optical filter 6
The end of the optical line 3 is recognized by detecting the reflected light at 0. From the viewpoint of sufficiently exerting the inspection light blocking function, the optical filter 60 preferably has a reflection wavelength width equal to or larger than the inspection light wavelength width.

FIG. 2 is a diagram schematically showing the reflection spectrum of the optical filter 60 and the wavelength spectrum of the inspection light. As shown in this figure, the optical filter 60 preferably has a reflection wavelength width (half-value width of reflection spectrum) wider than the wavelength width of the inspection light.

The optical filter 60 of this embodiment is composed of a plurality of optical waveguide type diffraction gratings provided on the optical line 3. The optical waveguide type diffraction grating is one region of the core of the optical waveguide, and the effective refractive index of the core periodically fluctuates along the optical axis between the minimum refractive index and the maximum refractive index. The optical waveguide diffraction grating reflects light having a relatively narrow wavelength width centered on a predetermined reflection wavelength (Bragg wavelength). It is generally known that an optical waveguide type diffraction grating can be manufactured by irradiating an optical waveguide with interference fringes of ultraviolet light, and this manufacturing method is disclosed in Japanese Patent Application Laid-Open No. 62-50005.
2 is also disclosed.

Each of the plurality of optical waveguide type diffraction gratings constituting the optical filter 60 has a single period, but the periods of the optical waveguide type diffraction gratings are slightly different from each other. In this way, the optical filter 60 is configured by providing a plurality of optical waveguide type diffraction gratings with slightly different periods in series in the optical line 3 to configure the optical filter 60.
Has a wide wavelength width reflection spectrum in which the reflection spectra of the diffraction gratings are slightly overlapped. The larger the number of optical waveguide type diffraction gratings, the wider the reflection wavelength width.
The optical filter having such a configuration is described in R. Kashy
ap et al., “Novel method of producing all fibr
e photoinduced chirped gratings ”(ELECTRONICS LE
TTERS 9th June 1994 Vol.30 No.12).

In order to secure a good function as an optical filter, the higher the reflectance of the optical waveguide type diffraction grating is, the more preferable it is. Therefore, the optical waveguide is exposed to a hydrogen atmosphere and then the ultraviolet light interference fringes are irradiated. The formed optical waveguide type diffraction grating was used in this example. By this method, an optical waveguide type diffraction grating having a high reflectance can be obtained, and the reflectance of the optical filter 60 also becomes high. However, OH generated during irradiation with ultraviolet light
Since the base absorbs the signal light and becomes a factor to increase the transmission loss, it is preferable that the number of optical waveguide type diffraction gratings constituting the optical filter 60 is small.

Since the optical line 3 includes an optical fiber which is an optical waveguide, the optical filter 60 can be formed directly in the optical line 3. Further, the optical filter 60 may be provided by connecting an optical fiber, a thin film waveguide, or the like, on which the optical filter 60 is formed in advance, to the optical line 3.

Next, an optical line inspection method using the inspection system of this embodiment will be described. The inspection light output from the light emitting unit 10 propagates through the optical fiber 21, enters the optical coupler 20, and is branched into two. One of the branched inspection lights reaches the non-reflection end of the optical coupler 20, while the other inspection light propagates through the optical fiber 22 and the optical switch 40.
Incident on. The inspection light enters the optical line 3 to be measured via the optical fiber 41 and the optical coupler 50, then travels through the optical line 3 toward the subscriber's house 5, and reaches the optical filter 60.

The inspection light partially returns in the direction opposite to the traveling direction due to Fresnel reflection at an obstacle (such as a broken portion) of the optical line 3 or Rayleigh scattering at each point of the optical line 3. The reflected light and the backscattered light are split into two by the optical coupler 50, and one of the split lights enters the optical switch 40. Thereafter, the reflected light and the backscattered light from the optical line 3 propagate through the optical fiber 22 and are branched into two by the optical coupler 20, and one branched light propagates through the optical fiber 23 and enters the inspection unit 30.

The inspection unit 30 includes the optical line 3 and the optical filter 6.
By detecting reflected light and backscattered light from 0 and performing signal processing on this, the power of the reflected light or the backscattered light of the optical line 3 can be changed from a predetermined reference point in the optical line 3 to the CRT device. It is displayed for the distance to the measurement point. By observing the displayed waveform, the failure point of the optical line 3 and the loss between any two points of the optical line 3 can be obtained. In this way, the inspection of the optical line 3 is executed.

In the optical line inspection system of the present embodiment, the light emitting section 10 outputs the inspection light having a narrow wavelength width of about 20 nm or less, so that the reflection wavelength width of the optical filter 60 can be narrowed accordingly. Therefore, the number of optical waveguide type diffraction gratings constituting the optical filter 60 can be reduced. In particular, if the wavelength width of the inspection light is about 5 nm or less, the number of optical waveguide type diffraction gratings can be extremely reduced, and the optical filter 60 can be composed of a single optical waveguide type diffraction grating. .

By reducing the number of optical waveguide type diffraction gratings, the number of OH groups described above can also be reduced, so that the transmission loss of signal light can be suppressed. Further, if the number of the optical waveguide type diffraction gratings is small, the mode mismatch generated when the signal light passes through the diffraction grating is also reduced, so that the transmission loss of the signal light can be suppressed also from this aspect. Thus, according to the optical line inspection method of the present embodiment,
It is possible to inspect the optical line while sufficiently suppressing the influence on the optical communication.

As the light emitting section 10, various configurations can be applied. 3 to 6 are schematic diagrams showing configuration examples 10a to 10d of the light emitting unit 10. In the following, each configuration example will be described with reference to each drawing.

First, the light emitting section 10a in FIG. 3 is composed of a Fabry-Perot type semiconductor laser 70, lenses 71 and 74, an isolator 72, and an optical filter 73. The optical filter 73 of this embodiment is a dielectric multilayer filter.

The Fabry-Perot type semiconductor laser 70 has three
It has an oscillation wavelength width of about 0 nm. The lens 71 is
The output laser light of the semiconductor laser 70 is collimated and enters the isolator 72. The isolator 72 makes the direction of the arrow in the figure the forward direction, and blocks the light traveling in the reverse direction. The laser light that has passed through the isolator 72 enters the optical filter 73.

The optical filter 73 limits the wavelength width of the laser light of the semiconductor laser 70 and has a wavelength width of about 20 nm or less centered around a predetermined wavelength of the light included in the oscillation wavelength range of the semiconductor laser 70. Allows only light to pass through. Although some of the laser light from the semiconductor laser 70 may be reflected by the optical filter 73, such reflected light is blocked by the isolator 72. The same applies to reflected light and backscattered light from the optical line. As a result, light is emitted from the semiconductor laser 7
It is possible to prevent a situation in which the light enters the resonator of 0 and disturbs the stable oscillation state.

The laser light transmitted through the optical filter 73 enters the lens 74. The lens 74 causes the parallel light beam to enter the optical fiber 21 while being converged. The laser light emitted from the lens 74 is the output inspection light of the light emitting unit 10a. Since the laser light from the semiconductor laser 70 passes through the optical filter 73 as described above, the wavelength width is about 2
Inspection light of 0 nm or less is realized.

Next, the light emitting section 10b shown in FIG. 4 comprises a Fabry-Perot type semiconductor laser 70, a lens 75, and an optical fiber 76.
And 78 and an optical circulator 77. The optical circulator 77 is connected to the optical fibers 76 and 78 and the optical fiber 21. An optical waveguide type diffraction grating 79 is provided in a part of the core of the optical fiber 78.

The semiconductor laser 70 includes a light emitting portion 10a shown in FIG.
Similarly to the above, it has an oscillation wavelength width of about 30 nm. The lens 75 converges the output laser light of the semiconductor laser 70 and makes it incident on the optical fiber 76 to couple the optical power from the semiconductor laser 70 to the optical fiber 76. The laser light that has entered the optical fiber 76 enters the optical circulator 77 and is emitted to the optical fiber 78. The laser light travels in the optical fiber 78 and reaches the optical waveguide type diffraction grating 79. The optical waveguide type diffraction grating 79 is about 20 nm of the light included in the oscillation wavelength range of the semiconductor laser 70.
Only light with the following wavelength width is reflected. This reflected light enters the optical circulator 77 and is emitted to the optical fiber 21. The light incident on the optical fiber 21 via the optical circulator 77 is the inspection light of the light emitting unit 10b.

As described above, the light emitting section 10b uses the light reflected by the optical waveguide type diffraction grating 79 as the inspection light. Therefore, if the reflection wavelength width of the diffraction grating is about 20 nm or less,
The wavelength width of the inspection light is about 20 nm or less. Since it is easy to fabricate the optical waveguide type diffraction grating 79 having a narrow reflection wavelength width, it is easy to realize inspection light having a wavelength width of 5 nm or less by the light emitting unit 10b.

It should be noted that instead of interposing the lens 75 between the semiconductor laser 70 and the optical fiber 76 as shown in FIG. 4, an optical fiber having a lens action by processing the tip by melting or cutting is used as the optical fiber 76. Used as a lens 7
It is also possible to omit 5.

Next, the light emitting section 10c shown in FIG. 5 includes a distributed feedback (DFB) type semiconductor laser 80, lenses 71 and 7.
4 and an isolator 72. The output laser light from the distributed feedback semiconductor laser 80 is reflected by the lens 71.
After being converted into a parallel light flux by the laser beam, it is incident on the isolator 72. The isolator 72 has the direction of the arrow in the drawing as the forward direction and blocks light traveling in the reverse direction. This prevents a situation where reflected light from the optical line 3 or backscattered light enters the resonator of the semiconductor laser 80 and disturbs the stable oscillation state. The laser light that has passed through the isolator 72 enters the lens 74 and enters the optical fiber 21 while being converged. The laser light emitted from the lens 74 is the output inspection light of the light emitting unit 10c.

The wavelength width of the inspection light output from the light emitting section 10c is equal to the oscillation wavelength width of the distributed feedback semiconductor laser 80. The distributed feedback semiconductor laser 80 has strong longitudinal mode selectivity and has an extremely narrow oscillation wavelength width.
Therefore, according to the light emitting unit 10c, the wavelength width of the output inspection light can be easily reduced to about 20 nm or less, and the inspection light with the wavelength width of about 5 nm or less can be easily realized.

Next, the light emitting section 10d shown in FIG. 6 includes a Fabry-Perot type semiconductor laser 88, a lens 75 and an optical fiber 8.
4. An optical waveguide type diffraction grating 85 is formed in the core of the optical fiber 84. The optical fiber 21 is connected to the optical fiber 84.

This light emitting portion 10d is a D.I. M. Bird et al. (Electron. Lett., Vol. No. 13, pp1115-1116, 199).
It is similar to that described in 4). The light emitting portion 10d can be considered as a kind of distributed Bragg reflector (DBR) type semiconductor laser.

The Fabry-Perot type semiconductor laser 88 has a light reflecting surface 86 with a high reflectance and a light emitting surface 87 with a low reflectance at both ends, and light with a wavelength width of about 30 nm is emitted from the light emitting surface 87. It The lens 75 converges the output light of the semiconductor laser 88 and makes it incident on the optical fiber 84 to couple the optical power from the semiconductor laser 88 to the optical fiber 84. The light traveling in the optical fiber 84 reaches the diffraction grating 85. The diffraction grating 85 is the semiconductor laser 8
Of the light included in the oscillation wavelength width of No. 8, only the light with a wavelength width of about 20 nm or less centered on a predetermined wavelength is reflected. The reflected light enters the semiconductor laser 70 via the lens 75. The incident light travels in the semiconductor laser 88 while causing stimulated emission, reaches the light reflecting surface 86, and is reflected. The reflected light travels in the semiconductor laser 70 while causing stimulated emission, exits from the light emitting surface 87, and is reflected by the diffraction grating 85 again. In this way,
Light is amplified by repeated reflection between the diffraction grating 85 and the light reflecting surface 86, and finally laser oscillation occurs. This is the output inspection light of the light emitting unit 10d. The inspection light passes through the diffraction grating 85 and enters the optical fiber 21.

The light that causes the laser resonance between the diffraction grating 85 and the light reflecting surface 86 is limited to the light having a wavelength reflected by the diffraction grating 85 with a relatively high reflectance. Therefore, by using the diffraction grating 85 having an appropriate reflection wavelength width,
The wavelength width of the output inspection light of 0d is about 20 nm or less.
Since it is easy to fabricate the diffraction grating 85 having a narrow reflection wavelength width, it is easy to realize the inspection light having a wavelength width of 5 nm or less by the light emitting unit 10d.

Since the light emitting section 10d outputs the inspection laser light by the laser resonance between the diffraction grating 85 and the light reflecting surface 86, the laser resonance in the semiconductor laser 88 is not always necessary in the light emitting section 10d. Absent.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments and various modifications can be made. For example, the optical waveguide type diffraction grating constituting the optical filter is not limited to the one formed in the optical fiber, and may be one formed in another optical waveguide such as a thin film waveguide.

[0060]

As described above in detail, according to the optical line inspection method of the present invention, the inspection is performed by using the inspection light having the wavelength width of about 20 nm or less, so that the optical waveguide type diffraction grating is composed of a small number. It becomes possible to use the optical filter described above, and it is possible to inspect the optical line while sufficiently suppressing the influence on the optical communication.

In particular, by using the inspection light having the wavelength width of about 5 nm or less, the number of the optical waveguide type diffraction gratings constituting the optical filter can be extremely reduced, and the optical line having an extremely small influence on the optical communication can be obtained. An inspection can be done.

Further, in the optical line inspection system of the present invention,
Since the light emitting section outputs the inspection light having a wavelength width of about 20 nm or less, and the inspection of the optical line is performed using this inspection light, it becomes possible to use the optical filter composed of a small number of optical waveguide type diffraction gratings. . Therefore, according to the optical line inspection system of the present invention, it is possible to inspect the optical line while sufficiently suppressing the influence on the optical communication.

Particularly, in the optical line inspection system in which the light emitting section outputs the inspection light having the wavelength width of about 5 nm or less, the number of the optical waveguide type diffraction gratings constituting the optical filter can be extremely reduced, so that it is suitable for optical communication. It is possible to inspect an optical line that has an extremely small influence.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall configuration of an optical line inspection system of this embodiment.

FIG. 2 is a diagram schematically showing a reflection spectrum of an optical filter and a wavelength spectrum of inspection light.

FIG. 3 is a schematic diagram showing a first configuration example of a light emitting unit 10.

FIG. 4 is a schematic diagram showing a second configuration example of the light emitting unit 10.

5 is a schematic diagram showing a third configuration example of the light emitting unit 10. FIG.

FIG. 6 is a schematic diagram showing a fourth configuration example of the light emitting unit 10.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Station building, 2 ... Transmission device, 3 ... Optical line, 4 ... Optical fiber cable, 5 ... Subscriber house, 10 ... Light emitting part, 20 ... Optical coupler, 30 ... Inspection part, 40 ... Optical switch, 50 ... Optical Coupler, 60 ... Optical filter, 100 ... OTDR device.

Claims (11)

[Claims] 1. An inspection light is made incident on an optical line to be inspected and an optical filter is provided at a terminal end of the optical line, and the inspection light reflected or scattered by each part of the optical line and the optical filter is introduced. A method of inspecting the state of the optical line by detecting, wherein the optical filter is composed of one or more optical waveguide type diffraction gratings having mutually different periods, and the wavelength width of the inspection light is The optical line inspection method is characterized by being about 20 nm or less. 2. The optical line inspection method according to claim 1, wherein the wavelength width of the inspection light is about 5 nm or less. 3. A light emitting section which outputs inspection light having a wavelength width of about 20 nm or less and makes the inspection light incident on an optical line, and an optical filter provided at a terminal end of the optical line,
Inspecting the state of the optical line by detecting an inspection light reflected or scattered by each part of the optical line and the optical filter, which comprises one or more optical waveguide type diffraction gratings having mutually different periods. An optical line inspection system including an inspection unit. 4. The optical line inspection system according to claim 3, wherein the wavelength width of the inspection light output from the light emitting unit is about 5 nm or less. 5. An optical function unit is further provided which makes the inspection light incident on the optical line and makes the inspection light reflected or scattered by each part of the optical line and the optical filter enter the inspection unit. The optical line inspection system according to claim 3, which is characterized in that. 6. The light emitting section includes a Fabry-Perot type semiconductor laser and a bandpass filter into which laser light emitted from the Fabry-Perot type semiconductor laser is incident, and the inspection light is the bandpass filter. The optical line inspection system according to claim 3, wherein the laser light is transmitted through a filter. 7. The optical line inspection system according to claim 6, wherein the bandpass filter is a dielectric multilayer filter. 8. The Fabry-Perot type semiconductor laser, an optical waveguide having a diffraction grating formed in a core, and laser light emitted from the Fabry-Perot type semiconductor laser are incident on the optical waveguide, and An optical component that causes the laser light reflected by a grating to enter the optical line, wherein the inspection light is the laser light that is incident on the optical line from the optical component. The optical line inspection system according to claim 3. 9. The light beam according to claim 3, wherein the light emitting unit includes a distributed feedback semiconductor laser, and the inspection light is laser light emitted from the distributed feedback semiconductor laser. Road inspection system. 10. The light emitting unit includes a distributed Bragg reflector semiconductor laser, and the inspection light is laser light emitted from the distributed Bragg reflector semiconductor laser. Three
The described optical line inspection system. 11. The distributed Bragg reflector type semiconductor laser comprises a current excitation type semiconductor light emitting device having a light emitting surface and a light reflecting surface facing the light emitting surface, and an optical waveguide having a diffraction grating formed in a core. 11. The optical line inspection system according to claim 10, further comprising: and radiating light emitted from the semiconductor light emitting element by the diffraction grating and the light reflecting surface to perform laser oscillation.