JP2011174713A - Method and device for detection of water surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for detection of a water surface, capable of detecting a turbulent water surface. <P>SOLUTION: The water surface detection method for the water surface detection device 301 includes: outputting a light pulse toward a water surface 7 from a distal end 6 of an optical fiber 8 connected to an OTDR 1, receiving the light pulse reflected by the water surface 7 at the distal end 6, and detecting the distance from the distal end 6 to the water surface 7 by measuring a propagation time from the output of the light pulse at the distal end 6 to the reception at the distal end 6. At least part of the distal end 6 of the optical fiber 8 is a dual-mode fiber. The light pulse is output from an inner core of the dual-mode fiber in a gravity direction. The light pulse reflected by the water surface 7 is received by an outer core of the dual-mode fiber. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a water surface detection method and a water surface detection device that measure a distance from a far end of a fiber connected to a water surface using an OTDR (Optical Time Domain Reflectometer).

  FIG. 1 is a diagram for explaining a conventional water surface detection method. In the conventional water surface detection method, a laser pulse light of 1550 nm emitted from OTDR is collimated by a lens from the emission end (far end) of a single mode fiber (SMF), and vertically irradiated to the water surface at a distant position. The distance to the water surface was measured by measuring the delay of the light pulse reflected from the surface. FIG. 2 shows the result of water surface detection performed by a conventional water surface detection method. As shown in FIG. 2, the spatial distance from the far end of the fiber to the water surface can be obtained by multiplying the difference L (m) between the reflection at the far end of the fiber and the reflection from the water surface by the fiber refractive index. This is because the commercially available OTDR distance display is converted to the fiber length, so that this is returned to the spatial distance (see, for example, Non-Patent Document 1).

Okukuo and Yoshiaki Yamabayashi, “Laser Surface Detection and Proximity Altimeter”, “The 39th Lightwave Sensing Technology Research Conference Proceedings”, no. LST39-23, pp. 143-148, June 2007. Hiromasa Tanobe (NTT), Masaru Kobayashi (NTT-AT), Ryo Nagase, Yoshihisa Kai (NTT), IEICE Tech. 107, no. 190, OCS 2007-37, pp. 27-32, August 2007

  Usually, the water surface is often rippled (swaying), and it is necessary to be able to detect the shaking water surface. However, the conventional water surface detection method uses a single mode fiber for the fiber wiring from the OTDR to the far end, and the probability that an optical pulse reflected by the shaken water surface returns to the far end core is low, and the water surface is detected. There was a problem that it was difficult.

  On the other hand, the OTDR emits several thousand light pulses as a probe, averages the light intensity of the reflected and returned light, removes noise components, and pairs of signals having an OTDR waveform composed of the light intensity of the returned light with respect to the distance. An averaging process for improving the noise ratio (SNR) can be performed. However, when there are many light pulses that are reflected by the oscillating water surface and do not return to the far end core, the signal components of the light pulses that have returned to the far end are almost eliminated by averaging. For this reason, even if it performed the averaging process by OTDR, the conventional water surface detection method had the subject that it was difficult to detect a water surface.

  Then, in order to solve the said subject, an object of this invention is to provide the water surface detection method and water surface detection apparatus which can detect the fluctuating water surface.

  In order to achieve the above object, the water surface detection method and the water surface detection device according to the present invention employ a means for returning most of the light pulses reflected by the swaying water surface to the far end.

  Specifically, the first water surface detection method according to the present invention outputs an optical pulse from the far end of an optical fiber connected to an OTDR (Optical Time Domain Reflectometer) toward the water surface, The light pulse reflected at the water surface is received at the far end, and the distance from the far end to the water surface is measured by measuring the propagation time until the light pulse is output from the far end and received at the far end. The optical fiber in at least the far end portion is a dual mode fiber, and the optical pulse is output from the inner core of the dual mode fiber in the direction of gravity and reflected by the water surface. The optical pulse is received by the outer core of the dual mode fiber.

  Further, the first water surface detection device according to the present invention includes: an optical fiber that outputs a light pulse from the far end toward the water surface, and that receives the light pulse reflected by the water surface at the far end; and The optical pulse is input to the opposite end of the far end, and the propagation time from the far end to the water surface is measured by measuring the propagation time until the optical pulse is output from the far end and received at the far end. OTDR for detecting a distance, wherein the optical fiber is a dual mode fiber at least at the far end, and outputs the optical pulse from the inner core of the dual mode fiber in the direction of gravity. The optical pulse reflected by the water surface is received by the outer core of the dual mode fiber.

  The water surface detection method and the water surface detection device use a dual mode fiber (DMF) at the far end. As shown in FIG. 3, the dual mode fiber has a single mode core formed at the center of the multimode core. A single fiber can support both single mode and multimode optical transmission systems. In addition, the single-mode has a double-clad structure and a small bending loss (see, for example, Non-Patent Document 2).

  By using the dual mode fiber at the far end portion, the core portion expands, and the optical pulse that has not returned to the core portion of the single mode fiber can also return to the multimode core portion of the dual mode fiber. For this reason, the distance to the water surface which is shaken by OTDR can be measured. In addition, since the probability that the optical pulse returns to the core portion at the far end is increased and the amount of received optical pulses increases, the averaging process can be performed by OTDR.

  Therefore, the present invention can provide a water surface detection method and a water surface detection device that can detect a swaying water surface.

  The second water surface detection method according to the present invention outputs a light pulse from the far end of an optical fiber connected to the OTDR toward the water surface, receives the light pulse reflected by the water surface at the far end, and A water surface detection method for detecting a distance from the far end to the water surface by measuring a propagation time until an optical pulse is output from the far end and received by the far end. A corner cube array is arranged around the edge, and the light pulse is output in the direction of gravity from the far end, the light pulse reflected by the water surface is reflected by the corner cube array, and the corner is turned from the far end. The optical pulse is coupled to the far end in the same optical path to the cube.

  The second water surface detection device according to the present invention outputs an optical pulse from the far end toward the water surface, receives the light pulse reflected at the water surface at the far end, and the optical fiber. The optical pulse is input to the opposite end of the far end, and the propagation time from the far end to the water surface is measured by measuring the propagation time until the optical pulse is output from the far end and received at the far end. An OTDR for detecting a distance, further comprising: a corner cube array disposed around the far end of the optical fiber, wherein the optical fiber gravitates the light pulse from the far end. The corner cube array reflects the light pulse reflected by the water surface, and connects the light pulse to the far end through the same optical path from the far end to the corner cube array. Characterized in that it.

  In the water surface detection method and the water surface detection device, a corner cube array facing the water surface is arranged around the far end. As shown in FIG. 4, the corner cube array performs retroreflection used in a reflector such as a bicycle. As shown in FIG. 4, the retroreflection is a reflection having a property of reflecting incident light once at each mirror surface and returning the incident light in the incident direction regardless of the incident angle.

  By placing the corner cube array around the far end, the light pulse irregularly reflected on the water surface can be reversed using retroreflection and refocused on the core portion at the far end. For this reason, even when the inclination of the water surface is too large or light is scattered by the water surface, the distance to the water surface can be measured by OTDR. In addition, since the amount of light pulses reflected on the water surface increases, the averaging process can be performed by OTDR.

  Therefore, the present invention can provide a water surface detection method and a water surface detection device that can detect a swaying water surface.

  The third water surface detection method according to the present invention outputs a light pulse from the far end of the optical fiber connected to the OTDR toward the water surface, receives the light pulse reflected by the water surface at the far end, and A water surface detection method for detecting a distance from the far end to the water surface by measuring a propagation time until an optical pulse is output from the far end and received by the far end. A corner cube array is arranged at a position different from the end, and the light pulse is output in a direction inclined in the direction of the corner cube array with respect to the direction of gravity from the far end, and the light pulse reflected on the water surface is output. The optical pulse is reflected by the corner cube array, and the optical pulse is coupled to the far end through the same optical path from the far end to the corner cube array.

  The third water surface detection device according to the present invention includes: an optical fiber that outputs a light pulse from the far end toward the water surface, and that receives the light pulse reflected at the water surface at the far end; and The optical pulse is input to the opposite end of the far end, and the propagation time from the far end to the water surface is measured by measuring the propagation time until the optical pulse is output from the far end and received at the far end. An OTDR for detecting a distance, further comprising a corner cube array disposed at a position different from the far end of the optical fiber, the optical fiber receiving the optical pulse from the far end. The light is output in a direction inclined from the direction of gravity to the direction of the corner cube array, the corner cube array reflects the light pulse reflected on the water surface, and the corner cube is reflected from the far end. Characterized by coupling said light pulses to the far end of the same optical path as the optical path to the ray.

  In the water surface detection method and the water surface detection device, a corner cube array directed to the water surface is disposed at a location separated from the far end by a certain distance. Then, the light pulse is tilted from the direction of gravity and irradiated on the water surface so as to be inclined. The light pulse reflected from the water surface reaches the corner cube array. This light pulse can be reversed using the retroreflection of the corner cube array and refocused on the core portion at the far end. For this reason, even when light is scattered by the water surface, the distance to the water surface can be measured by OTDR. In addition, since the amount of light pulses reflected on the water surface increases, the averaging process can be performed by OTDR.

  Therefore, the present invention can provide a water surface detection method and a water surface detection device that can detect a swaying water surface.

  The fourth water surface detection method according to the present invention outputs a light pulse in the direction of gravity from the far end of the optical fiber connected to the OTDR toward the corner cube array that is arranged on the water surface and fluctuates according to the water surface. The light pulse reflected by the corner cube array is received at the far end, and the propagation time until the light pulse is output from the far end and received at the far end is measured from the far end. It is characterized by detecting the distance to the water surface.

  In this water surface detection method, a corner cube array facing the far end is arranged on the water surface. This corner cube array oscillates in accordance with the sway of the water surface, but since it is retroreflected, it can reverse the light pulse and refocus it on the core portion at the far end. For this reason, even when the inclination of the water surface is too large or light is scattered by the water surface, the distance to the water surface can be measured by OTDR. In addition, since the amount of light pulses reflected on the water surface increases, the averaging process can be performed by OTDR.

  Therefore, the present invention can provide a water surface detection method and a water surface detection device that can detect a swaying water surface.

  In the second to fourth water surface detection methods and the second to third water surface detection devices according to the present invention, at least the optical fiber in the far end portion is a dual mode fiber, and the optical pulse is sent to an inner core of the dual mode fiber. Alternatively, light is received by the outer core. By using the dual mode fiber at the far end portion, the core portion expands, and the optical pulse that has not returned to the core portion of the single mode fiber can also return to the multimode core portion of the dual mode fiber. For this reason, the distance to the water surface which is shaken by OTDR can be measured. In addition, since the probability that the optical pulse returns to the core portion at the far end is increased and the amount of received optical pulses increases, the averaging process can be performed by OTDR.

  The present invention can provide a water surface detection method and a water surface detection device that can detect a swaying water surface.

It is a figure explaining the conventional water surface detection method. It is the result of having performed water surface detection by the conventional water surface detection method. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining a taper fiber. It is a figure explaining OTDR. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention. It is a figure explaining the water surface detection method and water surface detection apparatus which concern on this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 8 is a diagram illustrating the water surface detection device 301 of the present embodiment. The water surface detection device 301 outputs an optical pulse from the far end 6 toward the water surface 7, and receives the optical pulse reflected by the water surface 7 at the far end 6 and an end opposite to the far end 6. OTDR 1 that detects the distance from the far end 6 to the water surface 7 by inputting the light pulse to the optical fiber 8 and measuring the propagation time until the light pulse is output from the far end 6 and received by the far end 6. And comprising.

  The optical fiber 8 is a dual mode fiber at least at the far end 6, outputs the optical pulse from the inner core of the dual mode fiber in the direction of gravity, and reflects the optical pulse reflected by the water surface 7 to the outside of the dual mode fiber. Light is received by the core.

  The water surface detection method of the water surface detection device 301 is to output a light pulse from the far end 6 of the optical fiber 8 connected to the OTDR 1 toward the water surface 7 and receive the light pulse reflected by the water surface 7 at the far end 6. A water surface detection method for detecting a distance from the far end 6 to the water surface 7 by measuring a propagation time until the optical pulse is output from the far end 6 and received by the far end 6, and at least the far end The six-part optical fiber 8 is a dual-mode fiber, the optical pulse is output in the direction of gravity from the inner core of the dual-mode fiber, and the optical pulse reflected by the water surface 7 is transmitted by the outer core of the dual-mode fiber. It is characterized by receiving light.

  FIG. 7 is a diagram illustrating OTDR1. The OTDR 1 includes a laser diode (LD) 21, a photodiode (PD) 22, an LD output fiber 23, a PD input fiber 24, an input / output fiber 25, and an optical multiplexer / demultiplexer 27. The LD 21 outputs an optical pulse. This optical pulse is output to the outside via the LD output fiber 23, the optical multiplexer / demultiplexer 27, and the input / output fiber 25. On the other hand, the input / output fiber 25 receives an optical pulse from the outside. The optical multiplexer / demultiplexer 27 couples this optical pulse to the PD input fiber 24. The PD 22 receives an optical pulse that propagates through the PD input fiber 24.

  The LD output fiber 23 is a single mode fiber, the PD input fiber 24 is a multimode fiber, and the input / output fiber 25 through which the output optical pulse and the received optical pulse propagate is a dual mode fiber that can support both a single mode fiber and a multimode fiber. It is. By setting it as such a structure, all the optical fibers 8 between OTDR1 and the far end 6 can be made into a dual mode fiber.

  The optical fiber 8 outputs a light pulse in the direction of gravity from the inner core of the far end 6 which is a dual mode fiber. The lens 3 irradiates the water surface 7 with a light pulse from the far end 6 as parallel light. The irradiated pulse is reflected by the water surface 7. Here, as shown in FIG. 3, the water surface 7 is shaken, and the reflected light pulse travels to the far end 6 along an optical path different from the light pulse directed to the water surface 7 due to the inclination of the water surface 7. Thus, the reflected light pulse cannot return to the inner core for single mode operation of the dual mode fiber, but can return to the outer core for multimode operation.

  Optical fiber 8 couples the received reflected light pulses to OTDR1. OTDR1 multiplies the difference between the distance from the optical pulse reflected from the far end 6 to the far end 6 and the distance from the optical pulse reflected from the water surface 7 to the water surface 7 by the fiber refractive index. The spatial distance from the far end 6 to the water surface 7 can be calculated.

(Embodiment 2)
FIG. 5 is a diagram illustrating a water surface detection device 302 in which the optical fiber 8 is in another form. OTDR1 of the water surface detection apparatus 302 of FIG. 5 is for multimode fibers. The optical fiber 8 includes a tapered fiber 15, a circulator 16, an erbium-doped optical fiber amplifier (EDFA) 17, a dual mode fiber 11, and a single mode fiber 2. As shown in FIG. 6, the taper fiber 15 is formed by connecting a core of a single mode fiber and a core of a multimode fiber with a taper 19. The tapered fiber 15 converts the spot size of the optical pulse for multimode fiber emitted from the OTDR 1 and couples it to the single mode fiber 2 with high efficiency.

  The optical pulse converted for single mode by the taper fiber 15 is amplified by the EDFA 17 and coupled to the dual mode fiber 11. The behavior of the light pulse output from the far end 6 is the same as described with reference to FIG. The light pulse reflected by the water surface 7 is received at the far end 6 as described in FIG. 8, and is bypassed by the circulator 16 by the EDFA 17 and coupled to the OTDR 1. Similarly to the water surface detection device 301, the water surface detection device 302 can obtain a spatial distance from the far end 6 to the water surface 7. Since the water surface detection device 302 amplifies the optical pulse with the EDFA 17, the SNR of the OTDR waveform is improved and the measurement accuracy is improved.

(Embodiment 3)
FIG. 11 is a diagram illustrating the water surface detection device 303 of the present embodiment. The water surface detection device 303 outputs an optical pulse from the far end 6 toward the water surface 7 and receives the optical pulse reflected by the water surface 7 at the far end 6, and the opposite of the far end 6 of the optical fiber 8. OTDR1 detects the distance from the far end 6 to the water surface 7 by measuring the propagation time from the far end 6 to the optical pulse being input to the side end and the optical pulse being output from the far end 6 and received by the far end 6 And comprising.

  A difference from the water surface detection device 301 of FIG. 8 is that a corner cube array 13 is further provided around the far end 6 of the optical fiber 8. The corner cube array 13 reflects the light pulse reflected by the water surface 7 and couples the light pulse to the far end 6 in the same optical path from the far end 6 to the corner cube array 13.

  The water surface detection method of the water surface detection device 303 is to output a light pulse from the far end 6 of the optical fiber 8 connected to the OTDR 1 toward the water surface 7 and receive the light pulse reflected by the water surface 7 at the far end 6. A water surface detection method for detecting a distance from a far end 6 to a water surface 7 by measuring a propagation time until an optical pulse is output from a far end 6 and received by the far end 6. A corner cube array 13 is arranged around the edge 6, the light pulse is output in the direction of gravity from the far end 6, the light pulse reflected by the water surface 7 is reflected by the corner cube array 13, and the corner from the far end 6 The optical pulse is coupled to the far end 6 through the same optical path as that up to the cube array 13.

  As shown in FIG. 4, the corner cube array 13 reflects incident light once at each mirror surface, and performs retroreflection to return the light to the direction of incident light regardless of the incident angle. The corner cube array 13 arranged around the far end 6 can recursively reflect the light pulse that has been diffusely reflected with a large inclination of the oscillating water surface 7 and can be reflected again by the water surface 7 and coupled to the far end 6.

  The OTDR 1 can calculate the spatial distance from the far end 6 to the water surface 7 as described with reference to FIG. It should be noted that the far end 6 of the water surface detection device 303 includes a light pulse that reciprocates only between the water surface 7 and the far end 6 (this is referred to as “direct bounce light pulse”), the water surface 7, and the corner cube array 13. And a light pulse (which will be referred to as a “retro-reflected light pulse”) that travels back and forth between the light and the light. Therefore, the water surface detection device 303 determines whether the light pulse received by the far end 6 is a bounce light pulse or a retroreflected light pulse, and calculates the spatial distance from the far end 6 to the water surface 7. . Specifically, since three optical pulse waveforms are observed in the OTDR waveform, the water surface detection device 303 uses the light pulse reflected at the far end 6 as the waveform generated at the shortest distance, and the waveform generated at the farthest distance. Is a retroreflected light pulse, and the waveform generated between them is a direct light pulse. And if it is a waveform of a direct light return pulse, the water surface detection apparatus 303 will calculate the spatial distance from the far end 6 to the water surface 7 as demonstrated in Embodiment 1. FIG. In the case of the waveform of the retroreflected light pulse, not only the distance from the far end 6 to the water surface 7 but also the distance from the water surface 7 to the corner cube array 13 is included. The spatial distance from the far end 6 to the water surface 7 is calculated by multiplying the difference in distance and the distance obtained from the waveform of the retroreflected light pulse by the fiber refractive index and halving it.

If the distance from the water surface 7 to the far end 6 is different from the distance from the water surface 7 to the corner cube array 13 as shown in FIG. 9, the distance L _c in the gravity direction from the far end 6 to the corner cube array 13 is acquired in advance. It is necessary to keep it. Then, the distance L _c is added to the distance obtained from the waveform of the retroreflected light pulse, and is halved to calculate the spatial distance L _w from the far end 6 to the water surface 7.

  Further, the water surface detection device 303 can use a single mode fiber for the optical fiber 8, but at least the optical fiber 8 at the far end 6 portion is a dual mode fiber, and the optical pulse is transmitted to the inner core or the outer side of the dual mode fiber. It is desirable to receive light at the core. Since the probability of receiving a light pulse at the far end 6 increases, the measurement accuracy of the spatial distance from the far end 6 to the water surface 7 is improved.

  Further, the water surface detection device 303 may be the optical fiber 8 described in the second embodiment. Since the water surface detection device 303 amplifies the optical pulse with the EDFA 17, the SNR of the OTDR waveform is improved and the measurement accuracy is improved.

(Embodiment 4)
FIG. 12 is a diagram illustrating the water surface detection device 304 of the present embodiment. The water surface detection device 304 outputs an optical pulse from the far end 6 toward the water surface 7 and receives the optical pulse reflected by the water surface 7 at the far end 6, and the opposite of the far end 6 of the optical fiber 8. OTDR1 detects the distance from the far end 6 to the water surface 7 by measuring the propagation time from the far end 6 to the optical pulse being input to the side end and the optical pulse being output from the far end 6 and received by the far end 6 And comprising.

  The difference between the water surface detection device 304 and the water surface detection device 303 in FIG. 11 is the position of the corner cube array 13 and the direction of the light pulse output from the far end 6. That is, the water surface detection device 304 further includes the corner cube array 13 disposed at a position different from the far end 6 of the optical fiber 8. The optical fiber 8 outputs the light pulse from the far end 6 in a direction inclined from the direction of gravity toward the corner cube array 13. The corner cube array 13 reflects the light pulse reflected by the water surface 7 and couples the light pulse to the far end 6 in the same optical path from the far end 6 to the corner cube array 13.

  The water surface detection method of the water surface detection device 304 outputs a light pulse from the far end 6 of the optical fiber 8 connected to the OTDR 1 toward the water surface 7, and receives the light pulse reflected by the water surface 7 at the far end 6, A water surface detection method for detecting a distance from the far end 6 to the water surface 7 by measuring a propagation time until the light pulse is output from the far end 6 and received by the far end 6. The corner cube array 13 is disposed at a position different from the end 6, and the light pulse is output from the far end 6 in a direction inclined in the direction of the corner cube array 13 with respect to the direction of gravity, and the light reflected by the water surface 7 The pulse is reflected by the corner cube array 13, and the optical pulse is coupled to the far end 6 by the same optical path from the far end 6 to the corner cube array 13.

  The far end 6 outputs a light pulse in a direction inclined by θ with respect to the direction of gravity. The corner cube array 13 is arranged in a direction in which this light pulse is reflected by the water surface 7 where there is no shaking. The light pulse output from the far end 6 is reflected by the water surface 7 and reaches the corner cube array 13. The corner cube array 13 can recursively reflect the light pulse reflected by the turbulent water surface 7 having a large inclination and reflected again on the water surface 7 and coupled to the far end 6.

Unlike the water surface detection device 303 in FIG. 11, the water surface detection device 304 receives only the retroreflected light pulse at the far end 6. For this reason, the OTDR 1 is a distance obtained by multiplying the difference between the distance to the far end 6 and the distance obtained from the waveform of the retroreflected light pulse by the fiber refractive index, that is, the corner cube array 13 via the water surface 7 from the far end 6. The round-trip spatial distance L _p is measured. Water sensing unit 304 calculates the spatial distance L _w between the distal end 6 and the water surface 7 from the space distance L by the following equation.
(Formula 1)
L _w = (L _p / 2) · cos θ

If the distance from the water surface 7 to the far end 6 is different from the distance from the water surface 7 to the corner cube array 13 as shown in FIG. 13, the distance L _c in the gravitational direction from the far end 6 to the corner cube array 13 is acquired in advance. It is necessary to keep it. In this case, the water surface detection device 304 calculates the spatial distance _Lw by the following equation.
(Formula 2)
L _w = {(L _p + L _c ) / 2} · cos θ

  In addition, the water level detection device 304 can use a single mode fiber for the optical fiber 8 similarly to the water level detection device 303, but it is desirable to use a dual mode fiber.

  Furthermore, the water surface detection device 304 may be the optical fiber 8 described in the second embodiment. Since the water surface detection device 304 amplifies the optical pulse with the EDFA 17, the SNR of the OTDR waveform is improved and the measurement accuracy is improved.

(Embodiment 5)
FIG. 10 is a diagram illustrating the water surface detection method of the present embodiment. This water surface detection method outputs light pulses in the direction of gravity from the far end 6 of the optical fiber 8 connected to the OTDR 1 toward the corner cube array 13 that is arranged on the water surface 7 and fluctuates according to the water surface 7. The light pulse reflected by the cube array 13 is received at the far end 6, and the propagation time from when the light pulse is output from the far end 6 to when it is received at the far end 6 is measured. Detect the distance.

  This water surface detection method is performed using the water surface detection apparatus described in FIGS. 1, 5, 8, and 11. Further, in this water surface detection method, the corner cube array 13 is floated on the water surface 7 toward the far end 6 as shown in FIG. For example, it is tied to the column 35 with a string or a cylindrical net so as not to be washed away by water.

  If a light pulse is output in the direction of gravity from the far end 6 of the water surface detector, the corner cube array 13 retroreflects this light pulse, so that even if the water surface 7 is shaken, the reflected light pulse is reflected at the far end 6. Can be combined. The OTDR 1 calculates the spatial distance from the far end 6 to the corner cube array 13 as described with reference to FIG. 8, so that the water surface detection device can obtain the spatial distance from the far end 6 to the water surface 7.

  The water surface detection method and the water surface detection device according to the present invention can be applied to a disaster prevention system for detecting the water surface of a river or a lake, a liquid level monitoring in a factory, or the like.

1: OTDR
2: Single mode fiber 3: Lens 4: Liquid 5: Container 6: Far end 7: Water surface 8: Optical fiber 9: Inner core 10: Outer core 11: Dual mode fiber 13: Corner cube array 15: Tapered fiber 16: Circulator 17: EDFA
19: Taper 21: LD
22: PD
23: LD output fiber 24: PD input fiber 25: Input / output fiber 27: Optical multiplexer / demultiplexer 35: Support columns 300, 301, 302, 303, 304: Water surface detection device

Claims (9)

An optical pulse is output from the far end of an optical fiber connected to an OTDR (Optical Time Domain Reflectometer) toward the water surface, the light pulse reflected by the water surface is received at the far end, and the light is received. A water surface detection method for detecting a distance from the far end to the water surface by measuring a propagation time until a pulse is output from the far end and received at the far end,
At least the optical fiber in the far end portion is a dual mode fiber;
The light pulse is output in the direction of gravity from the inner core of the dual mode fiber;
A method of detecting a water surface, wherein the light pulse reflected by the water surface is received by an outer core of the dual mode fiber. An optical pulse is output from the far end of the optical fiber connected to the OTDR toward the water surface, the light pulse reflected by the water surface is received at the far end, and the light pulse is output from the far end and the far end A water surface detection method for detecting a distance from the far end to the water surface by measuring a propagation time until the light is received at
A corner cube array is disposed around the far end of the optical fiber;
The light pulse is output in the direction of gravity from the far end;
A method of detecting a water surface, comprising: reflecting the light pulse reflected on the water surface by the corner cube array; and coupling the light pulse to the far end along the same optical path from the far end to the corner cube. . An optical pulse is output from the far end of the optical fiber connected to the OTDR toward the water surface, the light pulse reflected by the water surface is received at the far end, and the light pulse is output from the far end and the far end A water surface detection method for detecting a distance from the far end to the water surface by measuring a propagation time until the light is received at
A corner cube array is disposed at a position different from the far end of the optical fiber,
The light pulse is output in a direction inclined in the direction of the corner cube array with respect to the direction of gravity from the far end,
Water surface detection characterized in that the light pulse reflected by the water surface is reflected by the corner cube array, and the light pulse is coupled to the far end in the same optical path from the far end to the corner cube array. Method.   From the far end of the optical fiber connected to the OTDR, an optical pulse is output in the direction of gravity toward the corner cube array that is arranged on the water surface and fluctuates in accordance with the water surface, and the optical pulse reflected by the corner cube array is output. Light is received at the far end, and a distance from the far end to the water surface is detected by measuring a propagation time until the light pulse is output from the far end and received at the far end. Water surface detection method.   5. The water surface according to claim 2, wherein at least the optical fiber in the far end portion is a dual mode fiber, and the optical pulse is received by an inner core or an outer core of the dual mode fiber. Detection method. An optical fiber that outputs a light pulse from the far end toward the water surface and receives the light pulse reflected by the water surface at the far end;
The optical pulse is input to the end opposite to the far end of the optical fiber, and the propagation time until the optical pulse is output from the far end and received at the far end is measured. OTDR for detecting the distance to the water surface;
A water surface detection device comprising:
At least the far end portion of the optical fiber is a dual mode fiber, the optical pulse is output from the inner core of the dual mode fiber in the direction of gravity, and the optical pulse reflected by the water surface is output to the outside of the dual mode fiber. A water surface detection device characterized by receiving light at a core. An optical fiber that outputs a light pulse from the far end toward the water surface and receives the light pulse reflected by the water surface at the far end;
The optical pulse is input to the end opposite to the far end of the optical fiber, and the propagation time until the optical pulse is output from the far end and received at the far end is measured. OTDR for detecting the distance to the water surface;
A water surface detection device comprising:
Further comprising a corner cube array disposed around the far end of the optical fiber;
The optical fiber outputs the light pulse from the far end in the direction of gravity,
The corner cube array reflects the light pulse reflected from the water surface, and couples the light pulse to the far end in the same optical path from the far end to the corner cube array. Detection device. An optical fiber that outputs a light pulse from the far end toward the water surface and receives the light pulse reflected by the water surface at the far end;
The optical pulse is input to the end opposite to the far end of the optical fiber, and the propagation time until the optical pulse is output from the far end and received at the far end is measured. OTDR for detecting the distance to the water surface;
A water surface detection device comprising:
A corner cube array disposed at a position different from the far end of the optical fiber,
The optical fiber outputs the light pulse from the far end in a direction inclined from the direction of gravity toward the corner cube array,
The corner cube array reflects the light pulse reflected from the water surface, and couples the light pulse to the far end in the same optical path from the far end to the corner cube array. Detection device.   The water level detection device according to claim 7 or 8, wherein at least the optical fiber in the far end portion is a dual mode fiber, and the optical pulse is received by an inner core or an outer core of the dual mode fiber.

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