JPH08261877A - Otdr apparatus - Google Patents

Abstract

PURPOSE: To provide an OTDR apparatus which is suitable for measuring the characteristic of an optical fiber at a specific wavelength, which has a small number of components and a simple constitution. CONSTITUTION: An inspection light source 110 which is provided in an OTDR apparatus 100 is provided with a current excitation-type semiconductor light- emitting element 10 which comprises a light radiant face 12 and a light reflecting face 11 facing the light radiant face and an optical waveguide 30 in which a diffraction grating 35 has been formed in a core. Radiant light from the semiconductor light-emitting element 10 is reflected by the diffraction grating 35 and the light reflecting face 11, and inspection laser light is output. By using the inspection light, an optical fiber to be measured is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OTDR (Optical Time-Domain Reflectomet) for measuring characteristics of an optical fiber such as loss at any position along the optical axis of the optical fiber.
ry) device.

[0002]

2. Description of the Related Art Conventionally, OTDR devices have been widely used for optical fiber loss measurement and the like. The OTDR device inputs pulse inspection light emitted from a light source from one end of the measured fiber through an optical coupler or the like, detects Rayleigh scattering at each point of the optical fiber, and detects backscattered light emitted from the measured fiber. The electrical characteristics of the measured fiber are measured by collecting the electric signal data obtained every time.

A semiconductor laser light source having a multi-longitudinal mode is used as an inspection light source of a commonly used OTDR device. However, since the longitudinal multimode semiconductor laser light source has a wide oscillation wavelength width of 20 nm or more, there is a limit in measuring the characteristics of the optical fiber at a specific wavelength using the conventional OTDR device.

On the other hand, as an OTDR device suitable for measuring the characteristics of an optical fiber at a specific wavelength, the one disclosed in JP-A-6-13688 is known. This is to use an optical fiber laser as a light source for inspection light and to use an inspection light having a narrow wavelength width of several nm or less to satisfactorily measure the characteristics of an optical fiber at a specific wavelength.

[0005]

However, the inspection light source of the optical fiber laser is composed of a large number of optical components such as an erbium-doped fiber (EDF), an optical isolator, a polarization modulator, and a polarization filter. Is. Therefore, the OTDR device using the optical fiber laser as the inspection light source is not easy to manufacture because the design of the optical system and the arrangement of the optical components are complicated, and it is difficult to achieve the downsizing of the device. Further, it is difficult to reduce the manufacturing cost, which is not suitable for mass production due to the difficulty of manufacturing.

The present invention has been made in view of the above problems, and provides an OTDR device suitable for measuring the characteristics of an optical fiber at a specific wavelength and having a simple structure with a small number of parts. The purpose is to do.

[0007]

In order to solve the above problems, an OTDR device of the present invention comprises a current excitation type semiconductor light emitting device having a light emitting surface and a light reflecting surface facing the light emitting surface. An inspection light source having an optical waveguide in which a diffraction grating is formed in a core, the laser light being emitted from the semiconductor light-emitting element is reflected by the diffraction grating and a light reflecting surface to perform laser oscillation. It has a feature.

The inspection light source may further include a stress applying means for applying a stress to the portion including the diffraction grating in the optical waveguide along the optical axis direction.

The inspection light source may further include a temperature adjusting means for changing the temperature around the portion of the optical waveguide including the diffraction grating.

[0010]

When an operating current is applied to the semiconductor light emitting element of the inspection light source of the OTDR device of the present invention, spontaneous emission light and stimulated emission light are generated, and light having a relatively wide wavelength width is emitted from the light emission surface. It When this emitted light enters the optical waveguide and reaches the diffraction grating formed in the core, only light with a wavelength width narrower than the output wavelength width of the semiconductor light emitting element with the reflection wavelength (Bragg wavelength) of this diffraction grating as the center Is reflected with sufficient reflectance. The reflected light enters the semiconductor light emitting element from the light emission surface and causes stimulated emission to reach the light reflection surface, where it is reflected and travels in the opposite direction. This reflected light travels in the light emitting device while causing stimulated emission,
The light is emitted from the light emitting surface. This emitted light is reflected again by the diffraction grating. By repeating the above phenomenon, light is amplified and finally laser oscillation is performed. Therefore, in the semiconductor light emitting device, since only the wavelength of the light that travels back and forth is amplified, the emission level of light of other wavelengths becomes extremely small, and laser oscillation occurs only in a narrow wavelength width. The laser light thus obtained is emitted from the optical waveguide. This laser light is the inspection light output from the inspection light source.

As described above, since the inspection light source of the OTDR device of the present invention performs laser oscillation by using the diffraction grating formed in the core of the optical waveguide and the light reflecting surface of the semiconductor light emitting element as a reflector, A laser beam having a sufficiently narrow wavelength width corresponding to the reflection spectrum width of the diffraction grating is output.
According to the OTDR device of the present invention, the laser light having the narrow wavelength width is used as the inspection light, and as a result, the characteristics of the optical fiber at the specific wavelength can be measured well.

The inspection light source is composed of a semiconductor light emitting element and an optical waveguide, and the number of parts is significantly smaller than that of a conventional OTDR device using an optical fiber laser as a light source. Therefore, in the OTDR device of the present invention, the design of the optical system and the arrangement of the optical components are easy, the manufacture is easy, and the downsizing is easy.

In the OTDR apparatus of the present invention, in which the inspection light source has the stress applying means, stress is applied to a portion of the optical waveguide including the diffraction grating, so that the period of the diffraction grating or the like changes, and in response thereto. As a result, the reflection wavelength of the diffraction grating also changes. The reflection wavelength of the diffraction grating is adjusted by adjusting the stress applied by the stress applying means. Since the output wavelength of the inspection light source also changes according to the reflection wavelength of the diffraction grating, the wavelength of the inspection light is adjusted by adjusting the stress applied by the stress applying means.

In the OTDR device of the present invention, the inspection light source has the temperature adjusting means, and the temperature around the portion of the optical waveguide including the diffraction grating is changed to expand or contract the portion. As a result, the period of the diffraction grating changes and the reflection wavelength of the diffraction grating changes accordingly. The reflection wavelength of the diffraction grating is adjusted by controlling the temperature adjusting means and adjusting the temperature around the portion including the diffraction grating. Since the output wavelength of the inspection light source also changes according to the reflection wavelength of the diffraction grating, the wavelength of the inspection light is adjusted by controlling the temperature adjusting means.

[0015]

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.

Embodiment 1 FIG. 1 is a schematic diagram showing the configuration of an OTDR device 100 of this embodiment. The OTDR device 100 includes an inspection light source 1
10, an optical coupler 40, and a measuring unit 50.

The inspection light source 110 oscillates a laser beam as inspection light in a pulsed manner, and comprises a Fabry-Perot type semiconductor laser 10, a lens 20 and an optical fiber 30. This is one in which an optical fiber 30 is optically connected via a lens 20 to a Fabry-Perot type semiconductor laser 10 which has been conventionally used as an inspection light source of an OTDR device. The inspection light source 110 is
D. M. Bird et al. (Electron. Lett., Vol, No. 1
3, pp1115-1116, 1994).

The Fabry-Perot type semiconductor laser 10 has an I
It is a semiconductor light emitting device composed of a heterostructure of nGaAsP / InP, and is excited by application of an operating current and outputs 1550 nm band pulsed light. A light reflecting surface 11 and a light emitting surface 12 are provided at both ends of the heterostructure. These planes face each other and form a Fabry-Perot type laser resonator. Light reflection surface 11
Has a high reflectance (about 80% in this embodiment), and the light emitting surface 12 has a low reflectance (about 5% in this embodiment).
%)have. As is the case with most Fabry-Perot type semiconductor lasers, the semiconductor laser 10 is a longitudinal multimode laser, and exhibits an oscillation spectrum in which the output increases corresponding to the wavelength of each mode.

The lens 20 converges the light emitted from the semiconductor laser 10 and makes it enter the optical fiber 30 to couple the optical power from the semiconductor laser 10 to the optical fiber 30. As the lens 20, it is possible to use an ordinary lens for optical coupling as used in optical communication.

Instead of interposing the lens 20 between the semiconductor laser 10 and the optical fiber 30 as in this embodiment, an optical fiber 30 having a lens action by processing the tip by melting or cutting is used. You can also

The optical fiber 30 is an ordinary single mode optical fiber in which a diffraction grating 35 is formed in a part of the core. The diffraction grating 35 is one region of the core, and its refractive index periodically changes between the minimum refractive index and the maximum refractive index according to the position along the optical axis.
The period of this refractive index fluctuation is the period of the diffraction grating.

It is generally known that the diffraction grating 35 can be formed by generating interference fringes of ultraviolet light by a _two- beam interference method and irradiating the optical fiber having GeO ₂ added to the core with the interference fringes. Has been. This forming method is described in Japanese Patent Application Publication No. 62-500052. According to this method, the effective refractive index of the core increases in accordance with the light intensity distribution of the interference fringes, and as a result, there is a region where the refractive index fluctuates between the original effective refractive index of the core and the increased effective refractive index. It is formed. This is the diffraction grating 35.

The diffraction grating 35 has a predetermined reflection wavelength λ _R.
Reflects light over a narrow wavelength band centered on. This reflection wavelength λ _R is expressed as λ _R = 2 · n · Λ (1) n: minimum refractive index of diffraction grating 35 Λ: period of diffraction grating 35.

The optical coupler 40 is a kind of four-terminal optical directional coupler, and has first to third terminals 41 to 43 and a non-reflection terminal 44. The first terminal 41 is the optical fiber 30.
The inspection light from the inspection light source 100 is incident on the optical coupler 40. Second terminal 4
An optical fiber 60 to be measured is connected to 2.

When the inspection light enters the optical coupler 40, it is branched into two. One of the branched lights enters the optical fiber 60 to be measured. Of the incident inspection light, the backscattered light that travels in the opposite direction due to Rayleigh scattering at each point of the optical fiber enters the optical coupler 40 and is branched into two. One of the branched lights is incident on the measurement unit 50.

As with the conventional OTDR device, it is possible to use an optical directional coupler such as an optical circulator other than the optical coupler 40.

The measuring section 50 measures the backscattered light of the optical fiber 60 to be measured, and is connected to the third terminal 43 of the optical coupler 40. This measuring unit 50 is a normal O
It is similar to the one used in the TDR device, and includes a photodetector that detects backscattered light and converts it into an electrical signal, an amplifier that amplifies the electrical signal output from the photodetector, and an amplifier output signal
A signal processing unit that performs D / D conversion and further performs averaging processing, a CRT device connected to the signal processing unit, and the like are provided. CR
The T device displays the scattered light power of the measured optical fiber 60 with respect to the distance from a predetermined reference point to the measured point in the measured optical fiber 60 based on the output signal of the signal processing unit. By observing the displayed waveform, the loss between any two points of the optical fiber can be obtained.

The inspection light source 110 outputs laser pulse light having a wavelength width narrower than the output wavelength width of the semiconductor laser 10. Hereinafter, this principle will be described.

When an operating current is passed through the Fabry-Perot type semiconductor laser 10, spontaneous emission light is generated. This is repeatedly reflected between the light reflecting surface 11 and the light emitting surface 12 while causing stimulated emission, whereby the light is amplified and finally laser oscillation occurs. Thus, the light is reflected by the light emitting surface 12. The light contributes to the laser oscillation of the semiconductor laser 10.

However, since the light emitting surface 12 has a low reflectance of 5%, most of the spontaneous emission light and the stimulated emission light generated by the semiconductor laser 10 pass through the light emitting surface 12. Figure 2
FIG. 4 is a diagram showing a wavelength spectrum of light emitted from the light emitting surface 12. Emitting light is about 1540 nm to about 1560 nm
Has a wavelength range of about 20 nm.
Is.

The light emitted through the light emitting surface 12 passes through the lens 20, enters the optical fiber 30, and reaches the diffraction grating 35. FIG. 3 is a diagram showing a reflection spectrum of the diffraction grating 35. As shown in this figure, the reflection wavelength λ _R of the diffraction grating 35 is about 1553.3 nm,
It exhibits a relatively high reflectance over a narrow wavelength band centered on this wavelength. The reflectance for the reflection wavelength is about 47.
%.

The light reflected by the diffraction grating 35 is reflected by the lens 2
The light enters the semiconductor laser 10 from the light emitting surface 12 via 0 and reaches the light reflecting surface 11 while causing stimulated emission. The light reflected by the light reflecting surface 11 proceeds while causing stimulated emission, exits from the light emitting surface 12, and enters the optical fiber 30 again. This incident light reaches the diffraction grating 35 and is reflected again. In this way, the light is amplified by the repeated reflection between the diffraction grating 35 and the light reflecting surface 11, and finally laser oscillation occurs. This allows
Laser light is emitted from the end face of the optical fiber 30 on the optical coupler 40 side. This is the inspection laser light output from the inspection light source 110.

The light that causes the laser resonance between the diffraction grating 35 and the light reflecting surface 11 is limited to the light having a wavelength reflected by the diffraction grating 35 with a relatively high reflectance. As shown in Figure 2,
The light transmitted through the light emitting surface 12 and incident on the optical fiber 30 covers a wavelength range of about 1540 nm to about 1560 nm, but the diffraction grating 35 has a wavelength of about 1553.
Since only light having a wavelength width of about 0.3 nm centered on 3 nm is reflected with sufficient reflectance, light having a narrower wavelength width than the semiconductor laser 10 alone causes laser resonance. Since the reflectance of the diffraction grating 35 with respect to the reflection wavelength is sufficiently larger than the reflectance of the light reflecting surface 11, the laser light output due to the laser resonance between the diffraction grating 35 and the light reflecting surface 11 is generated by the semiconductor laser 10. The output of the laser beam is sufficiently higher than that of the laser beam. As a result, the inspection light source 11
The laser light output from 0 has a narrower wavelength width than the output laser light of the semiconductor laser 10.

FIG. 4 is a diagram showing an oscillation spectrum of the inspection light source 110. As shown in this figure, the inspection light source 110 performs laser oscillation in a single longitudinal mode. Since only the light reflected by the diffraction grating 35 having a relatively high reflectance satisfies the oscillation condition, the line width (half-value width) of the oscillation spectrum is about 0.1 nm. It is even narrower than the line width of the reflection spectrum.

The output wavelength width of the inspection light source 110 is 2
If it is less than or equal to nm, the characteristics of the optical fiber at a sufficiently suitable specific wavelength can be measured sufficiently suitably. Inspection light source 110
The output wavelength width of can be adjusted by appropriately setting the line width of the reflection spectrum of the diffraction grating 35.

The inspection light source 110 of this embodiment is a semiconductor laser which has been conventionally used as an inspection light source, and the lens 20 and the optical fiber 30 are added to the semiconductor laser. Resonance occurs between the light reflection surface 11 and the light reflection surface 11, and the semiconductor laser 10
In the above, laser resonance also occurs between the light reflecting surface 11 and the light emitting surface. However, the diffraction grating 35 and the light reflection surface 11
In practice, laser resonance in the semiconductor laser 10 is not always necessary because laser light having a narrow wavelength width can be obtained if laser resonance occurs between and. Therefore, the light reflecting surface 11
It is also possible to make the reflectance of the light emitting surface 12 lower than that of the embodiment without changing the reflectance of the above. By doing this, the light exit surface 1
Since the power of the light emitted from 2 increases, the diffraction grating 35
The reflectance may be lower than that in the example.

The OTDR device 100 of this embodiment is equipped with the above-mentioned inspection light source 110 and uses laser light having a sufficiently narrow wavelength width as inspection light.
The characteristic at a specific wavelength of 0 can be suitably measured.

Further, the inspection light source 110 is a simple one composed of the semiconductor laser 10 and the optical fiber 30, and the lens 20 for optically coupling the two, and the conventional OTDR device using the optical fiber laser as the light source. Compared to
The number of parts is remarkably small. Therefore, the OT of this embodiment
The DR device 100 has the advantages that it is easy to design an optical system and install optical components, is easy to manufacture, and is easy to downsize. The fact that the number of parts is small and the manufacturing is easy leads to a reduction in manufacturing cost. Therefore, the OT of this embodiment is
The DR device is also suitable for mass production.

Embodiment 2 The OTDR device of this embodiment is the inspection light source 10 of the first embodiment.
In addition to the configuration of 0, an inspection light source further including a stress applying device 70 for applying stress to the optical fiber 30 is provided, which is different from the first embodiment.

FIG. 5 is a diagram showing the structure of the stress applying device 70. The stress applying device 70 includes arms 71 and 72 for holding the optical fiber 30 at two points of the optical fiber 30 that sandwich the diffraction grating 35, and the arms 71 and 72.
And a piezo element 73 to which is attached.
A variable voltage source (not shown) is connected to the piezo element 73, and the piezoelectric element 73 expands and contracts when a drive voltage is applied from the variable voltage source. The direction of expansion and contraction is substantially parallel to the optical axis direction of the optical fiber 30.

When the piezo element 73 is expanded or contracted, stress (tension or pressure) is applied to the optical fiber 30 via the arms 71 and 72 in the optical axis direction. Thereby, the diffraction grating 3
The period of 5 and the effective refractive index of the core change. As shown in the above equation (1), the reflection wavelength of the diffraction grating 35 depends on the period of the diffraction grating 35 and the effective refractive index of the core, and accordingly, the reflection wavelength of the diffraction grating 35 also changes. .
When the reflection wavelength changes, the output wavelength of the inspection light source also changes. Therefore, if the expansion and contraction of the piezo element 73 is controlled by adjusting the magnitude and positive / negative of the driving voltage of the piezo element 73, the output wavelength of the inspection light source can be arbitrarily set. You can switch. In this example, it was possible to realize an output wavelength change of 10 nm / kg.

As described above, the OTDR device of this embodiment is
Since the inspection light source having a variable wavelength is provided, it is possible to select a wavelength from a predetermined wavelength variable region and measure the characteristic of the measured optical fiber at this wavelength. This inspection light source is the optical fiber 3 in the inspection light source 100 of the first embodiment.
Although the stress applying device 70 is attached to No. 0, it is not a structure in which a new optical component is added. Therefore, the OTDR device of the present embodiment also has an advantage that the design of the optical system and the installation of the optical parts are easy and the manufacture is easy, as in the first embodiment. Further, even if the stress applying device 70 is added, the number of parts is still small, and since the stress applying device 70 is a small device using a piezo element, it is possible to sufficiently reduce the size of the entire OTDR device.

Example 3 The OTDR device of this example also differs from the inspection light source 100 of Example 1 in the structure of the inspection light source. That is, the inspection light source of the OTDR device according to the present embodiment further includes a temperature control tank accommodating the portion including the diffraction grating 35 of the optical fiber 30 in addition to the components of the inspection light light source 100 according to the first embodiment. There is. This temperature control tank is for arbitrarily changing the temperature in the tank within a predetermined temperature range.

Further, in this embodiment, as shown in FIG.
The optical fiber 30 is embedded in the V groove 91 of the fixed plate 90, and a metal plate (aluminum plate) 8 is provided in a portion including the diffraction grating 35.
0 is attached. The aluminum plate 80 is adhered to the optical fiber 30 with an adhesive 81 at two places sandwiching the diffraction grating 35.

When the temperature inside the temperature control tank is changed, stress is applied to the optical fiber 30 in accordance with the difference in thermal expansion coefficient between the aluminum plate 80 and the optical fiber 30. As a result, the portion including the diffraction grating 35 expands or contracts along the optical axis direction, so that the period of the diffraction grating 35 changes and the reflection wavelength changes. Therefore, if the temperature in the temperature control tank is adjusted, the output wavelength of the inspection light source can be arbitrarily switched. In this embodiment, an output wavelength change of 0.05 nm / ° C can be realized.

If the temperature in the temperature control tank changes,
Since the optical fiber 30 itself expands or contracts, the reflection wavelength of the diffraction grating 35 changes without the aluminum plate 80. However, by attaching the aluminum plate 80, the change of the reflection wavelength with respect to the temperature change becomes large. This is preferable since the output wavelength can be switched over a wider wavelength range. Further, the controllability of the output wavelength is better when the aluminum plate 80 is attached.

The OTDR device of this embodiment is also the same as that of the second embodiment.
As with the TDR device, since a wavelength tunable inspection light source is provided, it is possible to select a wavelength from a predetermined wavelength variable region and measure the characteristics of the measured optical fiber at this wavelength. In addition, this inspection light source does not add a new optical component to the configuration of the inspection light source of the first embodiment, and therefore has an advantage that the design of the optical system and the installation of the optical component are easy and easy to manufacture. are doing.

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, in the embodiment, the inspection light source is configured by using a diffraction grating formed on the core of an optical fiber, but it is also possible to use a diffraction grating formed on the core of another optical waveguide such as a thin film waveguide. It is possible to obtain the same effect as that of the embodiment.

[0049]

As described above in detail, the O of the present invention
The TDR device is composed of a semiconductor light emitting element and an optical fiber in which a diffraction grating is formed in the core, and is equipped with an inspection light source that outputs inspection light with a narrow wavelength width, so that the characteristics of the optical fiber at a specific wavelength can be improved. Can be measured,
It has a small number of parts and has a simple structure, and the design of the optical system and the arrangement of the optical parts are easy and easy to manufacture, and the miniaturization can be easily realized.

In the OTDR device of the present invention, the inspection light source having the stress applying means allows the wavelength of the inspection light to be adjusted by adjusting the stress applied by the stress applying means, and therefore the characteristics of the optical fiber at a plurality of wavelengths. Can be measured. Therefore, in this OTDR device, the design of the optical system and the arrangement of the optical components are easy and the manufacture is easy, and more suitable measurement can be performed.

The same applies to the OTDR device of the present invention in which the inspection light source has the temperature adjusting means. The wavelength of the inspection light can be adjusted by controlling the temperature adjusting means, and the characteristics of the optical fiber at a plurality of wavelengths can be measured. I can, so this OT
The DR device is also easy to design because the optical system and the arrangement of the optical components are easy to manufacture, and more suitable measurement can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an OTDR device according to a first embodiment.

FIG. 2 is a diagram showing a wavelength spectrum of emitted light of a semiconductor laser 10.

FIG. 3 is a diagram showing a reflection spectrum of a diffraction grating 35.

FIG. 4 is a diagram showing an oscillation spectrum of the inspection light source 100.

5 is a diagram showing a configuration of a stress applying device 70. FIG.

FIG. 6 is an aluminum plate 80 attached to the optical fiber 30.
FIG.

[Explanation of symbols]

10 ... Fabry-Perot type semiconductor laser, 11 ... Light reflecting surface, 12 ... Light emitting surface, 20 ... Lens, 30 ... Optical fiber, 35 ... Diffraction grating, 40 ... Optical coupler, 50 ... Measuring part,
60 ... Optical fiber to be measured, 100 ... OTDR device, 11
0 ... Inspection light source.

Claims (3)

[Claims] 1. An inspection light source, comprising: a current-excited 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, An OTDR device comprising: a device that oscillates laser light when light emitted from the semiconductor light emitting element is reflected by the diffraction grating and the light reflecting surface. 2. The inspection light source further comprises stress applying means for applying a stress to a portion of the optical waveguide including the diffraction grating along an optical axis direction thereof. OTDR device. 3. The OTDR device according to claim 1, wherein the inspection light source further includes temperature adjusting means for changing a temperature around a portion of the optical waveguide including the diffraction grating.