JP2001183552A - Method and apparatus for detecting light in optical fiber - Google Patents

Abstract

(57) [Summary] [Problem] Without forcibly bending an optical fiber,
Provided are a method and a device for detecting light in an optical fiber that can be easily miniaturized. SOLUTION: Leakage light is detected through a concave portion 13 formed by deleting an arbitrary portion of a clad 12.
At the boundary between the core and the cladding, 10-20% of the optical power is present, and the optical power distribution from this boundary to the clat is expressed by an attenuation function. The light can be detected through the concave portion 13 formed by the above. The leaked light obtained from the optical fiber 1 is incident on the light guide plate 21 provided with the reflection film 211, and after the light is converged by the condenser lens 22, the O / E converter 2
The photodetector is configured by performing current or voltage conversion in 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method and an apparatus for detecting light in an optical fiber.

[0002]

2. Description of the Related Art An optical fiber usually has a round pencil-like structure. The part corresponding to the lead of the pencil is called a "core", and the part corresponding to the spindle surrounding the lead is called a "cladding". Optical fiber communications, the core has a main component quartz cladding both, by adding an appropriate impurity, such as G _e O _2, the refractive index of the core portion is higher than the refractive index of the cladding portion.

[0003] Conventionally, bending has been applied to an optical fiber to leak a part of an optical signal propagating through the optical fiber to the outside, and the leaked optical signal has been detected. Specifically, as shown in FIG. 6, the conventional light detection device detects an optical fiber 62 by sandwiching an optical fiber 62 in a block 61 having an uneven portion and obtaining leakage light from a bent portion. This block 61 can give a fixed curvature to the optical fiber, and the optical signal in the core can be taken out to the cladding part by the bending of the optical fiber and leaked out of the optical fiber. In the figure, 63 is a condenser lens, 64 is O / E
It is a sensor consisting of a converter. This is disclosed in detail in, for example, JP-A-60-244907.

[0004]

As described above, conventionally, in the optical detection in an optical fiber, a bend is given in the middle of the optical fiber, and leaked light is detected through the bent portion. In addition, if the radius of curvature is reduced, there is a risk of fiber breakage, so that the curvature is inevitably increased, and the block becomes large. Further, in order to forcibly bend the optical fiber and leak the signal light, there have been problems of polarization dependency, loss due to waveform dispersion, and reduction of BER (Bit Error Rate) during detection.

The present invention has been made in view of the above circumstances, and by removing an arbitrary portion of a clad portion, a refractive index difference is provided between the removed portion and an air layer, and a clad portion near a corresponding core portion is provided. By obtaining light propagating through the part as leak light, without forcibly bending the optical fiber,
It is an object of the present invention to provide a method and an apparatus for detecting light in an optical fiber that can be easily miniaturized.

[0006]

According to a first aspect of the present invention, there is provided a method for detecting light in an optical fiber, comprising the steps of: providing a concave portion at an arbitrary portion of a cladding of an optical fiber; By providing a difference in the rate, light propagating in the clad near the core is detected as leaked light through the concave portion. Thereby, a refractive index difference is provided by forming tens of μm of the clad as a concave portion, and light propagating through the clad near the core is obtained as leaked light. 10-2 at core / cladding boundary
Since there is 0% optical power and the optical power distribution from this boundary surface to the clat portion is expressed by an attenuation function, light can be detected through the concave portion.

According to a second aspect of the present invention, there is provided a method for detecting light in an optical fiber, wherein the concave portion is formed by removing a clad positioned corresponding to the core. I decided that. Light detection becomes possible by removing several tens of μm from the cladding part, and since the signal is not detected from inside the core where the signal is detected, there is no influence on polarization dependency, waveform dispersion, and BER.

Further, in the method for detecting light in an optical fiber according to claim 3, in the method according to claim 1, light leaked from the concave portion is guided to a light guide plate covered with a reflective film. Thus, the leaked light obtained from the optical fiber is incident on the light guide plate covered with the reflective film, so that the leaked light having different emission directions can be efficiently incident on the light detection system.

According to a fourth aspect of the present invention, there is provided a method for detecting light in an optical fiber according to the first aspect, wherein the light exiting surface of the leaked light directs an optical path of light propagating through the clad toward the light guide plate. It was refracted. Further, the method for detecting light in an optical fiber according to claim 5 is the method according to claim 1, wherein the light emitted from the concave portion is:
The light is reflected toward the light guide plate by a surface having an angle with respect to a surface positioned substantially parallel to the light propagating through the core.

[0010] For example, as shown in FIG. 3, the concave portion has a surface B located substantially parallel to the light propagating through the core,
The surface A and the surface C are positioned parallel to the vertical direction, and the surface A has an angle so that the leaked light is refracted by the light guide plate provided near the concave portion. Further, the concave portion has a surface B positioned substantially parallel to the light propagating through the core, and a surface A and a surface C positioned parallel to the surface B in a direction perpendicular thereto.
And the surface C has an angle so that the leaked light is reflected by the light guide plate provided near the concave portion. Thus, the light leaked to the clad is repeatedly reflected between the surfaces A and C, and is refracted in the direction of the light guide plate so as not to be absorbed by the clad before reaching the light guide plate. A may have an angle α, or the surface C may be reflected in the direction of the light guide plate.
Has an angle β, the light can be efficiently collected by the photodetection system.

According to another aspect of the present invention, there is provided a photodetector for an optical fiber, comprising: an optical fiber having a concave portion provided at an arbitrary position of a cladding surrounding a core; a condenser lens; An optical-to-electrical converter for converting the leaked light into an electric signal after converging the leaked light through a lens is provided. With the above configuration, leaked light obtained from an optical fiber in which several tens of μm of the clad portion has been deleted is incident on the light guide plate, and after converging the light with a condenser lens, the O / O
Current or voltage conversion is performed by the E converter. As a result, it is possible to reduce the size of the photodetector without the need for a block that is conventionally required to forcibly bend the optical fiber.

The optical fiber light detecting device according to claim 7 is provided in the same device as in claim 6, provided near the concave portion of the clad, and based on a difference in refractive index between the concave portion and the air layer. A light guide plate covered with a reflective film is provided to collect light leaked from the core through the concave portion of the clad to the condenser lens. This allows the leaked light obtained from the optical fiber to be incident on the light guide plate covered with the reflective film, so that the leaked light having different emission directions can be efficiently incident on the light detection system.

Further, an optical fiber light detecting device according to claim 8 is the light detecting device according to claim 6, wherein the light detecting device comprises a concave portion of the clad, a light guide plate, a condenser lens, and a photoelectric converter. A substrate for fixing the optical fiber is further provided so that the positional relationship of the system does not change.
Thereby, the above-mentioned positional relationship is fixed, and the mechanical strength of the concave portion of the optical fiber can be compensated,
Further, by providing a reflective film on the substrate, a derivative effect of receiving light power on the substrate side can be obtained.

According to a ninth aspect of the present invention, there is provided an optical fiber light detecting device according to the eighth aspect, wherein the optical fiber having the concave portion formed in the cladding and the light detecting system are fixed at an angle. did. As a result, the light leaked to the cladding is repeatedly reflected between the surfaces A and C of the concave portion of the cladding, and is not absorbed by the cladding before reaching the light guide plate. Can be collected.

[0015]

FIG. 1 is a view showing a structure of an optical fiber cable 1 to which the present invention is applied. As shown in the figure, a concave portion 13 is provided at an arbitrary portion of the clad portion 12, and here, by removing several tens of μm, a refractive index difference is provided between the portion and the air layer, and the core portion 11 is formed. Light propagating in the nearby clad (recess 13) can be detected as leaked light.

FIG. 2 is a graph showing the optical signal distribution in the fiber. Optical power (in percentage) on the vertical axis, XY on the horizontal axis
The axis (the radius of the optical fiber cable 1 shown in FIG. 1) is shown.
As can be seen from the figure, about 10 to 20% of optical power is present at the core-cladding interface (in the circle in the figure). The optical power distribution from the boundary surface toward the cladding is expressed by an attenuation function. Therefore, light can be detected by eliminating several tens of μm in the clad portion. Here, since the detection is not performed from the core portion where the signal is transmitted, there is no influence on the polarization dependency, the waveform dispersion, and the BER.

Light travels while being reflected in the optical fiber cable 1, and this reflection occurs at the boundary surface due to the difference in the refractive index between the core 11 and the clad 12. Therefore, optical power also exists at the interface. On the actual interface, not all of the light is reflected, and there is also optical power that passes through the interface and leaks to the clad portion 12. This depends on the reflection angle at the interface, and can be understood from the fact that light is leaked by bending the optical fiber.

[0018]

(Equation 1) (Equation 1) is an equation for calculating the distribution of light power when light propagates through the waveguide. A power distribution can be obtained by inputting the refractive index of the core / cladding of a general silica-based optical fiber. The above-mentioned 10 to 20% is calculated by this formula,
This is a value obtained by normalization. E ₀ is the optical power, n
c is the cladding refractive index, nf is the core refractive index, and k0 is 2π /
λ and N are transmission refractive indices and are represented by N = nf · sin θ. E is the light intensity (W) passing through the optical fiber.

FIG. 3 exemplifies a deformation of a clad provided with a concave portion. (A) is an optical fiber cable 1
(B), (c) and (d) show the sectional structure of the concave portion. In the figure, the concave portion 13 is composed of a surface B located substantially parallel to the light propagating through the core 11 (in the direction of the arrow in the figure), and surfaces A and C located parallel to the surface B in a direction perpendicular thereto. This will be described below.

Core 1 provided on optical fiber cable 1
Since the refractive index difference between 1 and the cladding 12 is around 0.3%, the critical angle is not changed to 2 / π. Light propagating in the core 11 is totally reflected after entering at an angle exceeding the critical angle between the core 11 and the clad 12. For this reason, light leaked from the core 11 to the clad 12 enters the boundary at an angle smaller than the critical angle due to deformation of the optical fiber 1 or the like. Furthermore,
Since the light leaking to the clad 12 is refracted toward the core 11 at the boundary surface, it is considered that the traveling direction of the light propagating through the clad 12 has a component substantially parallel to the light propagating through the core 11. Therefore, the light detected from the surface A is the largest, the light detected from the surface B is small, and the light detected from the surface C is scarce.

When the surfaces A and C are provided in parallel and both surfaces are smoothed, the light leaked to the clad 12 is repeatedly reflected between the surfaces A and C as shown in FIG. As described above, all the light is absorbed by the cladding 12 before reaching the light guide plate located near the concave portion. Therefore, as described later, in the light detection device, light leaked from the surface A is irregularly reflected and reaches the light guide plate. Therefore, as shown in (c), the surface A has an angle α so that the light leaked to the clad 12 is refracted in the direction in which the light guide plate is located,
As shown in (d), a modification is conceivable in which the surface B has an angle β so that the light leaked to the clad 12 is reflected in the direction in which the light guide plate is located.

As will be described later, the same effect can be obtained even if the optical fiber or the light detection system itself has an angle in order to efficiently collect light to a light detection system such as a light sensor.

FIG. 4 is a diagram showing an embodiment of the photodetector of the present invention. The light detection device 2 includes a light guide plate 21 with a reflective film,
Condenser lens 22, O / E converter 23, light emitting element (LE
D: Light Emitting Diode and drive circuit) 24,
And a substrate 25. In the figure, broken lines indicate the paths of leaked light.

In the figure, the leaked light obtained from the optical fiber cable 1 from which several tens of μm of the cladding 12 has been removed is made incident on the light guide plate 21 whose both ends are covered with the reflection film 211. Here, the reason why the light guide plate 21 is covered with the reflection film 211 is that light leaks out from the portion (the concave portion 13) where the clad 12 is removed, but the light is emitted in different directions, and the leaked light is efficiently collected. This is a consideration for collecting the light on the optical lens 22 and making the light enter the O / E converter 23.

The leaked light incident on the light guide plate 21 is converged by the condenser lens 22 and is, for example, a photoelectric (O / E) converter 23 composed of a PD (Photediode) or a solar cell.
The optical signal is converted into a current and a voltage via the optical signal, and light detection is performed by these light detection systems. Note that a substrate 25 is provided below the optical fiber cable 1. The substrate 25 includes a clad recess 13 of an optical fiber, a light guide plate 21, and a condenser lens 2.
2. An optical fiber cable 1 is mounted on the substrate 25 so that the positional relationship with the light detection system including the O / E converter 23 does not change.
It is installed for the purpose of fixing. Further, the above-described clad recess 13 has no mechanical strength and can be reinforced by the substrate 25. Further, when a reflection film is provided on the substrate 25, the optical power on the substrate 25 side can also be received.

In the embodiment of the present invention described above, the cladding 1
2, a concave portion 13 is provided at an arbitrary position, and a difference in refractive index occurs between the deleted portion and the air layer, for example, when the portion is deleted. Light that propagates in the clad portion 12 near the corresponding core portion 11 is obtained as leakage light. As described above, substantially the same effect can be obtained even when the concave portion is not deleted even when the concave portion is formed, for example, by reducing the thickness of the clad portion. Accordingly, the present invention provides a method and an apparatus for detecting light in an optical fiber that can be easily miniaturized without forcibly bending the optical fiber.

[0027]

As described above, according to the first aspect of the present invention, a refractive index difference is provided by forming a few tens of μm of the clad as a concave portion, and light propagating in the clad near the core leaks. Can be obtained as light. According to the second aspect of the present invention, it is possible to detect leaked light through a concave portion formed by removing an arbitrary portion of the clad. At the boundary between the core and the cladding, 10-20% of the optical power is present, and the optical power distribution from this boundary to the clat is expressed by an attenuation function. In this case, light detection is possible through the concave portion formed by the above. In this case, since the signal is not detected from inside the core portion where the signal is detected, there is no influence on polarization dependency, waveform dispersion, and BER.

According to the third aspect of the present invention, the leaked light obtained from the optical fiber is incident on the light guide plate covered with the reflection film, so that the leaked light having a different emission direction can be efficiently converted into light. It can be incident on the detection system. Further, according to the invention described in claim 4 or 5, light leaked to the clad is
The surface A is angled so that it is refracted in the direction of the light guide plate or the direction of the light guide plate so that the light is repeatedly reflected between the surfaces A and C and is not absorbed by the cladding before reaching the light guide plate. Since the surface C has an angle so as to reflect the light, the light can be efficiently collected by the light detection system.

According to the sixth aspect of the present invention, the leaked light obtained from the optical fiber in which several tens of μm of the cladding is removed (recessed) enters the light guide plate and is converged by the condenser lens. After that, since the photodetector is configured by performing current or voltage conversion by the O / E converter, the photodetection device does not require a block which was conventionally required to forcibly bend the optical fiber. The size of the device can be reduced.

According to the seventh aspect of the present invention, the leaked light obtained from the optical fiber is made incident on the light guide plate covered with the reflection film, so that the leaked light having different emission directions can be efficiently converted into light. It can be incident on the detection system. Further, according to the invention of claim 8, the positional relationship is fixed, and the mechanical strength of the concave portion of the optical fiber can be compensated,
Further, by providing a reflective film on the substrate, a derivative effect of receiving light power on the substrate side can be obtained. According to the ninth aspect of the present invention, the light leaked to the clad is repeatedly reflected between the surfaces A and C of the concave portion of the clad and is not absorbed by the clad before reaching the light guide plate. Thus, the leaked light can be efficiently collected on the light guide plate.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an optical fiber to which the present invention is applied.

FIG. 2 is a graph showing an optical signal distribution in a fiber.

FIG. 3 is a diagram illustrating a deformation of a clad provided with a concave portion;

FIG. 4 is a diagram showing an embodiment of the photodetector of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional photodetector in an optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber cable 2 Photodetector 11 Core part 12 Cladding part 13 Cladding concave part 21 Light guide plate 22 Condensing lens 23 O / E converter 24 LED 25 Substrate 211 Reflective film

Claims (9)

[Claims] 1. A concave portion is provided at an arbitrary portion of a clad in an optical fiber, and a difference in refractive index between the concave portion and an air layer is provided, so that light propagating in the clad near the core is detected as leaked light through the concave portion. A method for detecting light in an optical fiber. 2. The method according to claim 1, wherein the concave portion is formed by removing a clad located corresponding to the core. 3. The method for detecting light in an optical fiber according to claim 1, wherein the light leaking from the concave portion is guided to a light guide plate covered with a reflection film. 4. The method for detecting light in an optical fiber according to claim 1, wherein an optical path of light propagating through the clad is refracted toward the light guide plate by an exit surface of the leaked light. . 5. A light guide plate, wherein light emitted from the concave portion is reflected toward the light guide plate by a surface having an angle with respect to a surface substantially parallel to light propagating through the core. The method for detecting light in an optical fiber according to claim 1. 6. An optical fiber provided with a concave portion at an arbitrary position of a clad surrounding a core, a condenser lens, and light for converting the leaked light to an electric signal after converging the leaked light via the condenser lens. A photodetector in an optical fiber, comprising: an electric converter. 7. A reflection film provided near the concave portion of the clad, for collecting leaked light obtained from the core through the concave portion of the clad on the condensing lens based on a difference in refractive index between the concave portion and the air layer. The photodetector for an optical fiber according to claim 6, further comprising a light guide plate covered with a light guide plate. 8. A substrate for fixing the optical fiber so that the positional relationship between the concave portion of the clad and a light detection system including a light guide plate, a condenser lens, and an optical / electrical converter does not change. The optical detection device for an optical fiber according to claim 6. 9. The optical fiber optical detection device according to claim 8, wherein the optical fiber having a concave portion formed in the clad and the optical detection system are fixed at an angle.