JPS6258106A - Optical apparatus for detecting physical quantity - Google Patents

Abstract

PURPOSE:To inexpensively detect stable physical quantity, by calculating the change quantity and position of physical change from the beam intensity ratio and delay time of two pulse beam. CONSTITUTION:Polarizing plane maintaining fibers 1 different in a refractive index and having two optical axes crossing at a right angle to each other are arranged in a region where physical quantity is detected. At first, the pulse beam emitted from a beam source 4 transmits through a polarizing prism 2 to be converted to the linear polarized beam coinciding with the optical axis of one fiber 1 to be incident to the fiber 1. At this time, when physical change is generated at the certain area 10 of the fiber 1, the above mentioned pulse beam is leaked to the optical axis of the other fiber 1 at the area 10 to generate crosstalk. Then, the original pulse beam and crosstalk pule beam are emitted from the fiber 1 and respectively received by beam receivers 6, 7 through the polarizing prism 3 and the intensity signals thereof are inputted to an operator 8. Because two optical axes of the fibers 1 have different refractive indices, two pulse beams generate different delay times. Subsequently, the physical quantity and position of the area 10 are calculated from a beam intensity ratio and the delay times by the operator 8.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical physical detection device using an optical fiber as a sensor element, and in particular, the present invention relates to an optical physical detection device that uses an optical fiber as a sensor element. The present invention relates to an optical physical quantity detection device that detects a physical quantity by utilizing the fact that crosstalk (light leakage) occurs between two propagation paths having different rates.

[Prior art] A conventional physical ω detection device using an optical fiber involves inputting light emitted from a light source into a conversion element such as an optical crystal through an optical fiber, and detecting a physical quantity from changes in the transmitted light and reflected light. There is a method to detect it.

In addition, the optical fiber itself is used as a sensor element (X).The physical quantity detection device uses a phase difference (interferometer) to measure optical path length changes based on changes in refractive index and expansion/contraction caused by the physical environment (temperature, pressure, etc.) of the optical fiber. There is also a method of detection based on changes in transmitted light intensity, etc.

[Problems to be Solved by the Invention] However, in the above-mentioned method using a conversion element such as an optical crystal, the structure of the sensor section becomes complicated and the coupling state between the optical fiber and the conversion element remains for a long period of time. There are problems in that the detection device may change or the detection device becomes complicated. Furthermore, since physical information can only be obtained as point information from the sensor section, many sensors must be installed when examining the average or physical distribution of physical quantities over a wide area.

In addition, with the method described above that uses the optical fiber itself as a sensor element, it is possible to detect physical quantities as line information along the optical fiber, but it is difficult to determine the position where a physical change has occurred, and it is difficult to measure. There was a problem in that it was easily susceptible to disturbances other than physical quantities, making stable measurements impossible.

[Object of the Invention] This invention was devised to solve the problems of the above-mentioned prior art, and an object of the invention is to simultaneously and easily detect the location and amount of physical change.
Stable physics lies in providing a physical quantity detection device that can perform detection at low cost.

[Summary of the Invention] In order to achieve the above object, the present invention provides an optical fiber having two propagation paths with different refractive indexes, and a transmitter for injecting pulsed light into one propagation path of the optical fiber. A system, a pulsed light propagating through one of the propagation paths, and a pulsed light which crosstalks to the other propagation path due to physical changes imparted to the optical fiber and propagates through the other propagation path. and a receiving system for detecting the light intensity ratio of both pulsed lights and the delay time, and detects whether there is a physical change and before the physical quantity changes from the light intensity ratio of both pulsed lights. At the same time, the position where the physical change has occurred is determined from the delay time of both pulsed lights.

[Examples] Examples of the present invention will be described in detail below with reference to the accompanying drawings.

In Fig. 1, 1 is 2 orthogonal to each other with different refractive indices.
The polarization maintaining fiber 1 is a polarization maintaining fiber having two optical axes, and the polarization maintaining fiber 1 is disposed within a region where a physical quantity (temperature, etc.) is to be detected. Polarizing prisms 2.3 are provided at the input and output ends of the polarization-maintaining fiber 1 as polarizers and analyzers. The transmitted polarization direction and the reverse polarization direction of the polarizing prism 2.3 are arranged to coincide with the two optical axes of the polarization maintaining fiber 1. A light source 4 is provided on the transmission side of the polarizing prism 2 with respect to the input end of the polarization maintaining fiber 1. The light source 4 is configured to emit pulsed light having a short pulse width in response to a pulse signal from the pulse generating circuit 5. Furthermore, light receivers 6 and 7 are provided on the transmission side and the reflection side of the polarizing prism 3 relative to the output end of the polarization-maintaining fiber 1, respectively. The light intensity signal detected by the light receiver 6.7 is input to the calculator 8. Further, a display 9 is connected to the calculator 8 to display the results of the calculation. - The pulsed light emitted from the light source 4 is transmitted through the polarizing prism 2, converted into linearly polarized waves that coincide with one optical axis of the polarization-maintaining fiber 1, and input into the polarization-maintaining fiber 1. At this time, if there is no change in the physical state of the polarization-maintaining fiber 1, the linearly polarized pulsed light incident on one optical axis of the polarization-maintaining fiber 1 will leak to the other optical axis. Therefore, only pulsed light aligned with one optical axis is propagated. Therefore, the light emitted from the polarization-maintaining fiber 1 is linearly polarized pulsed light that coincides with one optical axis, and all of this pulsed light passes through the polarizing prism 3, is detected by the light receiver 6, and is sent to the arithmetic unit 8. is input. Arithmetic unit 8
Since there is no input from the optical receiver 7, it is determined that there is no change in the physical quantity in the measurement area along the polarization-maintaining fiber 1, and the result is displayed on the display 9.

If a physical change occurs at a certain point or portion 10 of the polarization preserving fiber 1, linearly polarized pulsed light incident on one optical axis of the polarization preserving fiber 1 will be
At the site 10 where a physical change has occurred, the light leaks to the other optical axis and crosstalk occurs. After the part 10, the original pulsed light incident on one optical axis of the polarization maintaining fiber 1 and the crosstalk pulsed light leaked from the original pulsed light to the other optical axis are transmitted through two propagation paths. are propagated, respectively, and both pulsed lights are emitted from the output end of the polarization-maintaining fiber 1. The original pulsed light of this emitted light passes through the polarizing prism 3 and is received by the light receiver 6.
Further, the crosstalk pulse light is reflected by the polarizing prism 3 and received by the light receiver 7. Intensity signals of these pulsed lights detected by the light receivers 6 and 7 are input to a calculator 8. Since both propagation paths of the polarization maintaining fiber 1 have different refractive indices, the original pulse light a input to the calculator 8 and the cross, -
As shown in FIG. 2, a delay time occurs in the optical pulse. In this example, the refractive index of the propagation path that transmits the linearly polarized original pulse light a that coincides with one optical axis is smaller than the refractive index of the other propagation path that transmits the crosstalk pulse light.

The greater the amount of physical change in the part 10, the more the front of the crosstalk pulse light beam, that is, the light intensity, increases. The physical quantity of the part 10 is calculated from the intensity ratio. Furthermore, in the arithmetic unit 8, since the delay time t between the original pulsed light a and the crosstalk pulsed light is proportional to the fiber length from the part 10 where a physical change has occurred to the output end of the polarization-maintaining fiber 1, The position of the region 10 where the physical change has occurred is calculated from the delay time t of both pulsed lights.

Next, the relationship between the amount of physical change and the amount of crosstalk will be described using a temperature change as an example of a physical change.

Polarization-maintaining fibers reduce the amount of crosstalk between the two propagation paths by slightly changing the refractive index of the propagation paths corresponding to the two optical axes; the closer the refractive indices of both propagation paths are, the more , the amount of crosstalk increases. Therefore, by setting the temperature coefficients of the refractive indexes of the two propagation paths to different values, the amount of crosstalk changes depending on the temperature, and conversely, the temperature can be detected by detecting the amount of crosstalk.

Regarding other physical quantities, if distortion is added to the polarization-maintaining fiber due to changes in the physical quantities, and the difference in refractive index between both propagation paths of the polarization-maintaining fiber is changed by this distortion, the above-mentioned result can be achieved. It can be measured in the same way as the example of yA degree detection.

In the above example, the polarization maintaining fiber 1 was used as the optical fiber, and the physical quantity was detected using the crosstalk of the linearly polarized waves in the two optical axis directions. The same measurement as in the above embodiment is also possible by using a twin-core fiber having two cores with different values and utilizing crosstalk between the two cores (propagation paths).

[Effects of the Invention 1 In summary, the present invention provides the following excellent effects.

(1) The optical fiber itself is a sensor and does not require an optical conversion element such as an optical crystal. Therefore, the device configuration can be simplified, handling is easy, and the device can be provided at low cost.

(b) The location where a physical change has occurred and the location of the change can be simultaneously detected simply and with high accuracy.

(3) Average physical ω and physical quantity distribution along the optical fiber can be measured.

(4) There are no loss-causing factors due to intervening elements or coupling conditions, and it is less susceptible to external disturbances, allowing stable, low-loss, long-distance sensing.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of an optical physical quantity detection device according to the present invention, and FIG. 2 is a diagram showing an example of pulsed light emitted from an optical fiber (polarization maintaining fiber) of the device. . In the figure, 1 is a polarization maintaining fiber, 2 and 3 are polarizing prisms, 4 is a light source, 5 is a pulse generation circuit, 6.7 is a light receiver,
8 is an arithmetic unit, 9 is a display, 10 is a part where a physical change has occurred, a is an original pulsed light, b is a crosstalk pulsed light, and [ is a delay time. Agent: Patent Attorney Fujio Sato Figure 1 Figure 2 Makoto

Claims (3)

[Claims] (1) An optical fiber having two propagation paths with different refractive indexes, a transmission system for inputting pulsed light into one of the propagation paths of the optical fiber, and the pulsed light propagating through one of the propagation paths and the transmission system. A receiving system for receiving pulsed light that crosstalks with a pulsed light propagating through the other propagation path due to physical changes imparted to an optical fiber, and detecting the light intensity ratio and delay time of both pulsed lights. An optical physical quantity detection device comprising: (2) The optical fiber is a polarization-maintaining fiber having mutually orthogonal optical axes with different refractive indexes, and linearly polarized pulsed light is input from the transmission system to one optical axis of the polarization-maintaining fiber. An optical physical quantity detecting device according to claim 1, characterized in that the optical physical quantity detecting device is configured as follows. (3) The optical physical quantity detection device according to claim 1, wherein the optical fiber is a twin-core fiber consisting of two cores having different refractive indexes and one cladding layer surrounding them.