JPH071208B2 - Optical fiber pressure sensor - Google Patents

Description

The present invention relates to a pressure sensor using a polarization-maintaining optical fiber.

[Prior Art] Polarization-maintaining optical fibers include an elliptic clad type optical fiber having an elliptical clad 10 as shown in FIG.
As shown in FIG. 3 (b), there is a stress applying type having a stress applying portion 11. These are the components of the incident light that are polarized components in the direction of arrow A in the figure and in the direction of arrow B at right angles to arrow A, respectively, and propagate without energy exchange. Suitable to use fiber.

[Problems to be solved by the invention]

However, since the polarization-preserving optical fiber has different propagation speeds of light in the polarization direction of the arrow A and the polarization direction of the arrow B, the phases of the light in the two polarization directions are not constant. Normally, a polarization-maintaining optical fiber has a phase difference of two polarization directions for one wavelength in several mm. Assuming that a phase difference of 1 wavelength occurs at 2 mm for light with a wavelength of 0.85 μm, a difference of 10,000 wavelengths (that is, a distance difference of 8.5 mm in vacuum) for a 20 m optical fiber. Will occur.
If the coherency of the used light is poor, this difference causes deterioration of interference efficiency when utilizing interference. In addition, since this phase difference varies depending on the ambient temperature, the temperature characteristic of the characteristics is deteriorated.

[Means and Actions for Solving Problems]

The present invention is an optical fiber pressure sensor using a polarization-maintaining optical fiber, comprising at least two optical fibers connected in series, and at this connection point, the polarization direction of the optical fibers is The two different axes are connected to each other, and the two axes with the connection point therebetween are configured to apply a pressure from the outside via a pressure receiving plate, and different until the incident light is emitted. It is characterized in that the two axes are configured to propagate the same length.

〔Example〕

FIG. 1 shows an embodiment of the present invention and shows an example of a pressure sensor. Polarization-maintaining optical fibers 1 and 2 of the same length are
As shown in FIG. 2, the optical fiber 1 and the optical fiber 2 are connected at the connection point 3 so that they are rotated 90 ° with respect to each other so that the direction of the arrow A of the optical fiber 1 and the direction of the arrow B of the optical fiber 2 coincide with each other. The pressure from the outside to be detected is applied to the optical fibers 1 and 2 with the connection point 3 interposed therebetween via the pressure receiving plates 4 and 5. At this time, the orientation of the optical fiber is set so that the optical fiber 1 is applied in the direction of arrow A and the optical fiber 2 is applied in the direction of arrow B.

The light from the light source 6 is polarized, and as shown by E in FIG. 2, 45 ° to the optical fiber 1 with respect to the directions of arrow A and arrow B.
Incident at an inclined angle. In this case, the polarization component C in the direction of arrow A and the polarization component D in the direction of arrow B have the same light amount.

The optical fiber 1 and the optical fiber 2 have the same length and are connected so that the direction of the arrow A of the optical fiber 1 and the direction of the arrow B of the optical fiber 2 coincide with each other. Therefore, the phases of the polarization component C and the polarization component D at the emitting portion of the optical fiber 2 become equal. At this time, if the optical fiber 1 and the optical fiber 2 have the same temperature even if the temperature changes, the polarization component C and the polarization component D
Are equal in phase.

On the other hand, the pressure is applied from the outside in the direction of the polarization component C in both the optical fiber 1 and the optical fiber 2. Therefore, the ratio of the influence of the phase change on both polarized lights due to the pressure from the outside is equal in both the optical fiber 1 and the optical fiber 2. Therefore, the polarization component C,
When the applied pressure is measured by measuring the phase difference between D, the fluctuation of the phase difference due to temperature is reduced, and the measurement with less influence of the coherency of the light source is possible.

The phase difference can be detected by aligning the polarization direction of the polarizer 7 with the light emitting portion of the optical fiber 2 at an angle of 45 ° with respect to the arrow A and the arrow B, and detecting the output with the photodetector 8 results in the polarization component C. , An output corresponding to the phase difference of D is obtained.

In the embodiment, the case where there is one connection point has been described. However, even when a plurality of connection points are provided, that is, when a plurality of optical fibers are connected in series, the polarization component C,
The same effect can be expected if D is set so as to propagate in the direction of arrow A and the direction of arrow B by the same length.

〔The invention's effect〕

As described above, in the optical fiber pressure sensor using the polarization maintaining optical fiber, the light incident in one of the two polarization directions of the polarization maintaining optical fiber is the optical fiber pressure sensor. Providing an optical fiber pressure sensor with good temperature stability by configuring two polarization directions of the polarization maintaining optical fiber to propagate the same length before exiting the polarization maintaining optical fiber be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. FIG. 1 (a) is an overall view, FIG. 1 (b) is a sectional view taken along the line AA 'in FIG. 1 (a), and FIG. Is a diagram for explaining the method of connecting the optical fibers of FIG. 1, FIG. 3 is a diagram showing an example of a polarization maintaining fiber, FIG. 3 (a) is an elliptical clad type, and FIG. ) Indicates a stress imparting type. 1,2: polarization-maintaining optical fiber, 4,5: pressure plate, 6: light source, 7: polarizer, 8: photodetector.

Claims (1)

[Claims] 1. An optical fiber pressure sensor using a polarization-maintaining optical fiber, comprising at least two optical fibers connected in series, and at this connection point, the polarization direction of the optical fibers. The two different axes are connected to each other, and pressure is applied from the outside to the two axes with the connecting point in between, through which the incident light is emitted. An optical fiber pressure sensor characterized in that two different axes are propagated by the same length.