JPS6031103A - Optical directional coupling device - Google Patents

Abstract

PURPOSE:To suppress a fluctuation phenomenon by a rotation of a linearly polarized light by constituting so that a circularly polarized light or an elliptically polarized light resembling the circularly polarized light, which is rotated by the number of vibration of a light is made incident to an optical fiber to be measured, and a backscatter led into a photodetector is photodetected in a state that it is rotated by the number of vibration of a light. CONSTITUTION:A polarized light maintaining fiber 10 is connected between an optical connector 11 to which an optical 5 to be measured is connected and an optical connector 8 installed to an optical directional coupler 6. A light of a linearly polarized light emitted from a laser 1 reaches a polarized light maintaining fiber 4 in its state. When it is made incident to the next polarized light maintaining fiber 10, a polarized light plane matching is executed between the polarized light maintaining fibers 4 and 10 so that an incident light of the polarized light maintaining fiber 10 becomes a circularly polarized light or an elliptically polarized light resembling the circularly polarized light from the linearly polarized light, and a light resembling the circularly polarized light is made incident to the optical fiver 5 to be measured. Accordingly, a backscattering light which returns by being reflected by the inside of the optical fiber 5 to be measured is also a circularly polarized light or an elliptically polarized light resembling the circularly polarized light, and rotated by the number of vibration of a light. Accordingly, a measured curve of the backscattering light becomes a smooth curve, and a fluctuation phenomenon is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an optical directional coupling device, particularly a polarization-maintaining fiber, to make linearly polarized light as circularly polarized as possible, and to input the circularly polarized light into an optical fiber to be measured. This invention relates to an optical directional coupling device.

Optical measuring instrument 1 For example, an optical A-lus tester, which measures an abnormality in an optical cable by injecting a light pulse into the optical cable to be measured and measuring the backscattered light that is reflected and returned within the optical cable, is conventionally shown in Fig. 1. An optical directional coupler as shown in the figure was used.

In FIG. 1, linearly polarized light emitted from a laser 1 passes through a polarizing element, for example, a polarization solism 2, enters a polarization maintaining fiber 4 via a SELFOC lens 3t, and enters the optical fiber under test A5. Was. In the same figure, reference numeral 6 denotes an optical directional coupler, and the laser 1. polarization solism 2,
The optical directional coupler 6 is composed of a Selfoclen i3, a polarization maintaining fiber 4, and a light receiver fiber 7.

Note that 8 represents an optical connector.

The nine linearly polarized light emitted from the laser beam f1 is sent to the optical directional coupler 6.
It is incident on the optical fiber 5 to be measured through the optical fiber 5. When 5 is a multimode optical fiber, the linearly polarized light incident on the optical fiber 5 to be measured is distorted in a random direction, and the reflected light that returns as backscattered light is also randomly polarized, and the light direction The vertically polarized component of the backscattered light that is split by the optical coupler 6 and introduced into the optical receiver fiber 7 is approximately constant. On the other hand, the optical fiber under test/
When is a single-mode optical fiber, the optical fiber has a property that the linearly polarized light does not easily collapse, which is different from the multi-mode optical fiber, and it is reflected back within the optical fiber 5 to be measured. The linear polarization of backscattered light does not easily collapse. However, in reality, the linearly polarized light changes to elliptically polarized light based on the length of the optical fiber 5 to be measured, the stress applied to the optical fiber 5, the elliptical deformation of the core, anisotropy, heat, etc.
As shown in the figure, a normal polarization component X of nine elliptically polarized light is split by the polarizing prism 2 of the optical directional coupler 6 and introduced into the optical receiver fiber 7. By the way, when a single mode optical fiber is used as the optical fiber 5 to be measured, the direction in which the elliptical axis of the elliptically polarized light returns is not constant, so the backscattered light received by the light receiver is As shown in FIG. 3, the light produced a jagged and oscillating phenomenon, which was an undesirable problem in measurement.

The present invention aims to solve the above-mentioned problems, and aims to connect a polarization-maintaining optical fiber between a conventional optical directional coupler and an optical fiber to be measured so that the frequency of light is transmitted to the optical fiber to be measured. By making all of the rotating circularly polarized light or elliptically polarized light close to circularly polarized light incident, and by receiving the backscattered light introduced into the receiver in a state rotated by the frequency of the light, it is possible to completely suppress the fluctuation phenomenon caused by optical rotation of the linearly polarized light. The present invention aims to provide an optical directional coupling device. The following description will be given with reference to all drawings from FIG. 4 onwards.

FIG. 4 shows the configuration of an embodiment of the optical directional coupling device according to the present invention, and FIG. 5 shows the measurement of backscattered light when measuring a single mode optical fiber using the optical directional coupling device according to the present invention. An example of a curve is shown.

In FIG. 4, 1 to 8 correspond to those in FIG. Optical connector 1 to which optical fiber 5 to be measured is connected
1 and an optical connector 8 attached to a conventional directional coupler 6, a polarization maintaining fiber 10 is connected.

Therefore, the optical directional coupler 9 according to the present invention allows light to enter the optical fiber 5 to be measured via the polarization maintaining fiber 10 into the conventional optical directional coupler 6, but does not allow light to be emitted from the polarization maintaining fiber 10. At this time, the optical fiber to be measured 5 is circularly polarized.
make it incident on the In other words, the linearly polarized light emitted from the laser 1 is transferred to the polarization preserving fiber 4t while maintaining its linear polarization.
It's coming. When entering the next polarization-preserving angle fiber A10, the polarization-maintaining fibers 4 and 10 are arranged so that the incident light on the polarization-maintaining optical fiber A10 changes from linearly polarized light to circularly polarized light or elliptically polarized light close to circularly polarized light. As described above, light close to circularly polarized light is input to the temporary measurement optical fiber 5.

Now change the optical axis of polarized Hoki fiber IO to polarization preserving fiber 40
It is assumed that the connection is made at a zero inclination to the original axis.

The linearly polarized light emitted from the polarization preserving fiber 4 is tilted by θ with respect to the polarization preserving fiber 100 axis.

When 6 is the original amplitude, the amplitude 1111 (it is considered that the orthogonal element of IJIθ and aai- is preserved in the polarization-preserving 7 eye/each 10. Then, when emitted from the polarization-maintaining fiber 10 , these are synthesized.

(where δ is the phase difference between the two components that occurs depending on the length of the polarization-maintaining fiber 10) It becomes elliptically polarized light and is emitted. To set the condition for this to be t circularly polarized light, 1 z3+1/s-/2 (2), in equation (1), θ== f/4. Required for δ='/g'. By the way, it is nearly impossible to cut the polarization preserving fiber 1 (1-) so that the phase difference between the two components caused by δ, that is, the length of the polarization-maintaining fiber 10, is 1-. This is because the storage fiber must be cut so that δ=1/2.

In the present invention, regardless of the length of the polarization maintaining fiber 10, circularly polarized or The closest thing to circularly polarized light is elliptically polarized light.

In this way, circularly polarized light or elliptically polarized light close to circularly polarized light is emitted to the optical fiber 5 to be measured via the original connector llk. The backscattered light reflected within the optical fiber 5 to be measured and returned is also circularly polarized light or elliptically polarized light close to circularly polarized light, and is rotated at the frequency of the light. This backscattered light of circularly polarized light or elliptically polarized light close to circularly polarized light is transmitted to the original connector 11. Polarization maintaining fiber lo, optical connector8. Polarization maintaining fiber 4. 9. Pass through SELFOC lens 3. The light enters the polarizing prism 2.

The backscattered light incident on the polarizing prism 2 is split into a vertically polarized component by the polarizing prism 2 with respect to the horizontally polarized wave of the laser l.
The light passes through the optical receiver phi/-77t- and is received by an optical receiver (not shown). For example, an avalanche photodiode or the like is used as the light receiver.

The electrical constant velocity of this receiver is much slower than the original frequency. The backscattered light incident on the polarizing prism 2Vc rotates in a circle or an ellipse at a period much faster than the electrical response speed of the light receiver, so from an electrical standpoint,
It can be considered that the polarization is broken into a random state. Therefore, it is considered that the vertically polarized wave component that is branched to the light receiver side by the polarizing prism 2 and the horizontally polarized wave component that goes straight to the laser 1 side are distributed approximately in a ratio of 1 to 1. Even if the optical fiber 5 to be measured rotates the light, the vertically polarized component X shown in FIG. 2 remains constant. Therefore, as shown in FIG. 5, the measurement curve of the backscattered light becomes a smooth curve, and the jagged wave phenomenon shown in FIG. 3 is suppressed.

The polarization planes of the polarization preserving 7 Aino 94 and 8 are aligned by sending a light pulse to the optical fiber 5 to be measured, measuring curve a of the backscattered light received by the light receiver + looking at the polarization preserving fiber 1.
The polarization maintaining fiber 10 is fixed at a position where the optical axis of 0 is rotated and the measurement curve of backscattered light is the smoothest. At this time, the linearly polarized light emitted from the polarization maintaining fiber 4 to the optical fiber 10 becomes circularly polarized light or elliptically polarized light close to circularly polarized light when emitted to the optical fiber 5 to be measured.

As explained above, according to the present invention, a polarization maintaining fiber is connected between a conventional optical directional coupler and an optical fiber to be measured, and the polarization plane is aligned while observing the measurement curve of backscattered light. With easy work.

An optical directional coupling device capable of suppressing shadow *' caused by optical rotation of a single mode optical fiber is realized.

[Brief explanation of the drawing]

Figure 1 is an example of the configuration of a conventional optical directional coupler, Figure 2 is an explanatory diagram to explain that a jagged fluctuation phenomenon occurs in the measurement curve of backscattered light, and Figure 3 is an example of a conventional optical directional coupler. An example of a measurement curve of backscattered light when a single mode optical fiber is measured using a coupler, FIG. 4 shows the configuration of an embodiment of the optical directional coupling device according to the present invention, and FIG. 5 shows the uA of the present invention. 3 shows an example of a measurement curve of backscattered light when a single mode optical fiber is measured using the optical directional coupling device according to the invention. In the figure, 1 is the laser, 2 is the polarizing prism, 3 is the optical lens, 4 is the polarization preserving fiber, 6 is the optical directional coupler, 7 is the receiver fiber, 8 is the original connector, 9 is the optical directional coupler, 1G represents a polarization maintaining fiber, and 11 represents an optical connector T-. Patent applicant: Anritsu Electric Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Distance certificate 19-

Claims (1)

[Claims] an optical directional coupler 6 that outputs linearly polarized light; an output of the optical directional coupler for converting the incident linearly polarized light into circularly polarized light or elliptically polarized light close to circularly polarized light and outputting the light; A polarization preserving fiber 10 connected to the end and having its optical axis positioned at a required angle with respect to the optical axis of the incident linearly polarized light; and a holding means 8 for holding the polarization preserving fiber At at the required angle. Optical directional coupling device.