JP2008216577A - Monitoring fiber coupler and optical fiber type physical quantity measuring instrument using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monitoring fiber coupler capable of monitoring a light emitting element at a low cost with a simple structure. <P>SOLUTION: In the monitoring fiber coupler, a single mode optical fiber 33s and one multimode optical fiber 33m are connected to each other in the respective end faces. Further, a part of the clad in the longitudinal direction of the single mode optical fiber 33s is connected to the other multimode optical fiber 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a monitoring fiber coupler for monitoring a part of light from a multimode optical fiber, and an optical fiber type physical quantity measuring apparatus using the same.

  As a physical quantity measurement sensor using an optical fiber, there is an optical fiber temperature sensor. In this optical fiber temperature sensor, light generated by a light emitting element such as an LD (semiconductor laser) is incident on a measurement optical fiber, and St (Stokes) light and As (anti-Stokes) light from backscattered light from the measurement optical fiber. ) The wavelength of the light is separated, and the temperature along the measurement optical fiber is measured from these intensity ratios.

  The prior art document information related to the invention of this application includes the following.

JP 2005-84347 A

  Since the wavelength of light emitted from the light emitting element changes or the output fluctuates depending on the ambient temperature, it is necessary to control the drive current of the light emitting element according to the ambient temperature.

  Further, there is a demand for monitoring the light emitting element in order to determine abnormality of the light emitting element.

  However, a light-emitting element equipped with a monitoring photodiode (PD) is expensive and causes an increase in the cost of the sensor device.

  Further, in the optical fiber temperature sensor, since the excited St light and As light are weak, there is a demand that the light power from the light emitting element is not wasted at all, and a part of the light emitted from the light emitting element is used. Therefore, a configuration for monitoring the light emitting element is necessary.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a monitoring fiber coupler capable of monitoring a light emitting element with a simple configuration at low cost and a physical quantity measurement sensor using the same.

  The present invention has been devised to achieve the above object, and the invention according to claim 1 connects the end faces of a single mode optical fiber and one multimode optical fiber, and further provides the single mode optical fiber. This is a monitoring fiber coupler in which a part of the cladding in the longitudinal direction is connected to the other multimode optical fiber.

  The invention according to claim 2 is characterized in that an inclined surface is formed in a part of the clad of the single mode optical fiber, the connection side end portion where the inclined surface of the single mode optical fiber is formed, and the end surface of the multimode optical fiber. Connected monitoring fiber coupler.

  According to a third aspect of the present invention, there is provided a light source that generates a pulse signal for optically measuring a physical quantity such as temperature and strain, a measurement optical fiber through which the pulse optical signal propagates, and a rear side from the measurement optical fiber. 3. An optical fiber type physical quantity measuring apparatus comprising a light receiving device for receiving scattered light, wherein the monitoring unit for monitoring a part of the back scattered light is an optical fiber type using the monitoring fiber coupler according to claim 1 or 2. It is a physical quantity measuring device.

  According to the present invention, a part of light from a multimode optical fiber can be monitored with a simple configuration.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. First, an optical fiber temperature sensor will be described with reference to FIG. 3 as an example of an optical fiber physical quantity measuring device (optical fiber physical quantity measuring sensor) using the monitoring fiber coupler according to the present embodiment.

  As shown in FIG. 3, the optical fiber temperature sensor 31 includes a sensor body 32, an in-device optical fiber 33 provided from the LD module 36 to the optical filter module 37 having a wavelength separation function, and a measurement optical fiber for temperature measurement ( Sensor fiber) 34 and a display / control personal computer 35 as an external arithmetic processing means for controlling the control means in the sensor main body 32 to be described later and displaying the temperature of the measurement location.

  The sensor body 32 includes an LD module 36 serving as a light source that emits a pulsed light signal (hereinafter also simply referred to as light) L0 having a wavelength λ0, and an optical filter module that transmits the pulsed light signal and separates the backscattered light by wavelength. 37, three light receivers 38 for receiving Rayleigh scattered light, St light, and As light from back scattered light and converting them into electrical signals, and a signal processing circuit 39 and a control circuit 40 as control means. Composed.

  The in-device optical fiber 33 is configured by connecting a single mode optical fiber 33s and a multimode optical fiber 33m.

  Although detailed description will be given later, the monitoring fiber coupler 1 (see FIG. 1) according to the first embodiment of the present invention connects the multimode optical fiber 4 to the single mode optical fiber 33 s of the in-device optical fiber 33. Mainly composed. The monitoring fiber coupler 21 (see FIG. 2) according to the second embodiment of the present invention is mainly configured by forming an inclined surface on the single mode optical fiber 33 s of the in-device optical fiber 33.

  As the measurement optical fiber 34, a multimode optical fiber (MMF) that is easily connected is used when measuring temperature at a short distance of several kilometers. The optical filter module 37 and the light receivers 38 that receive St light and As light are also connected by MMF.

  The LD module 36 includes an LD 41 as a light emitting element and a driver 42 that drives the LD 41. Each light receiver 38 includes an APD (avalanche photodiode) 43 and a preamplifier 44 that amplifies the output of the APD 43. An A / D (analog / digital) converter 45 is connected between each light receiver 38 and the signal processing circuit 39.

  The control circuit 40 measures the St light intensity and the As light intensity scattered from the measurement optical fiber 34, and calculates the temperature along the measurement optical fiber 34 based on the St light intensity and As light intensity ratio. In addition, the control circuit 40 has a function of determining an abnormality of the LD module 36, a function of controlling the output of the LD 41, and an OTDR (Optical Time Domain Reflectometer: Detecting a failure point, a failure point, and an abnormal point of the measurement optical fiber 34. It also has a function of an optical pulse tester (for example, a detection function of loss, connection loss, side pressure state, bending state, disconnection, etc. of the measurement optical fiber 34).

  The signal processing circuit 39 is mainly for high-speed arithmetic processing of signals before being input to the control circuit 40. The control circuit 40 uses a CPU having storage means such as a memory, and the signal processing circuit 39 uses an FPGA (Field Programmable Gate Array).

  FIG. 1 is a schematic view of a monitoring fiber coupler showing a preferred first embodiment of the present invention.

  As shown in FIG. 1, the monitoring fiber coupler 1 according to the first embodiment includes an in-device optical fiber 33 as an optical fiber from the LD 41 to the optical filter module 37 (see FIG. 3), and the LD 41 side has a single mode light. The SMF 33s having the same outer diameter and the MMF 33m as one multimode optical fiber are connected so as to be a fiber (SMF) 33s.

  In the first embodiment, the end faces of the SMF 33s and the MMF 33m are brought into contact with each other so as to be fusion-bonded to form the connection portion 2 so that a part of the backscattered light from the MMF 33m is optically coupled to the cladding of the SMF 33s. Yes. When the monitoring fiber coupler 1 is used in the optical fiber temperature sensor 31 of FIG. 3, the back scattered light here is Rayleigh scattered light because the St light and As light are wavelength-separated by the optical filter module 37.

  Further, the monitoring fiber coupler 1 connects the cladding of the SMF 33 s and the monitoring MMF 4 as the other multimode optical fiber to constitute an optical coupling unit (MMF coupler) 3.

  Here, the cladding of the SMF 33s and the MMF 4 for monitoring are such that the optical coupling between the cores of the SMF 33s and the monitoring MMF 4 can be ignored (in this embodiment, the optical coupling efficiency is less than 0.1 dB). The monitoring MMF 4 is connected to the side surface of the cladding of the SMF 33 s so that the cladding is optically coupled while providing a gap between the core of the SMF 33 s and the core of the MMF 4.

  The connection between the cladding of the SMF 33 s and the monitoring MMF 4 is performed, for example, by adjoining the SMF 33 s and the monitoring MMF 4 and welding the connected portions by arc discharge. One end of the MMF 4 for monitoring is optically coupled to the first light receiver 38 (see FIG. 3), and the other end is terminated to prevent reflection.

  In this embodiment, a single mode optical fiber having a core diameter of 10 μm / cladding diameter of 125 μm is used as the SMF 33 s, and a multimode optical fiber having a core diameter of 62.5 μm / cladding diameter of 125 μm is used as the MMF 33 m or MMF4.

  The optical connection between the monitoring fiber coupler 1 and the LD 41 may be performed by forming the connection portion 2 and the optical coupling portion 3 to produce the monitoring fiber coupler 1 and then aligning the SMF 33s and the LD 41 for optical coupling.

  The monitoring fiber coupler 1 is used as a monitoring unit (portion surrounded by a dotted line in FIG. 3) for monitoring a part of the backscattered light in the optical fiber temperature sensor 31 of FIG.

  The operation of the first embodiment will be described together with the operation of the optical fiber temperature sensor 31 with reference to FIGS. 1 and 3.

  The light L0 having the wavelength λ0 emitted from the LD module 36 enters the optical filter module 37 from the SMF 33s via the MMF 33m. Further, the light L 0 passes through the optical filter module 37 and enters the measurement optical fiber 34. At this time, as shown in FIG. 1, the light L0 is incident on the connecting portion 2 from the SMF 33s having a small core diameter to the MMF 33m having a large core diameter, and thus the loss is almost zero.

  Thereafter, the backscattered light returned from each point of the measurement optical fiber 34 is wavelength-separated into Rayleigh scattered light (including strictly Brillouin scattered light), St light, and As light by the optical filter module 37.

  The Rayleigh scattered light is re-incident on the MMF 33m, and enters the SMF 33s having a small core diameter from the MMF 33m having a large core diameter at the connection portion 2. At this time, a part of the Rayleigh scattered light is optically coupled to the cladding of the SMF 33s to become the cladding mode light LM and propagates in the cladding of the SMF 33s.

  When the cladding mode light LM reaches the optical coupling unit 3, a part of the cladding mode light LM is optically coupled to the core of the MMF 4 for monitoring, propagates through the core of the MMF 4, and is the first light receiver in FIG. The light is received at 38. On the other hand, the As light and the St light are demultiplexed by the optical filter module 37 and received by the second and third light receivers 38, respectively.

  The monitor light m, As light, and St light are input to the control circuit 40 via each A / D converter 45 and the signal processing circuit 39. The control circuit 40 obtains the intensity ratio of St light and As light from each point of the measurement optical fiber 34 at each sampling time interval, and obtains the temperature of the measurement location from this intensity ratio. The sampling time interval depends on the distance resolution. The obtained temperature is displayed on the personal computer 35.

  However, since the St light and As light are very weak, the temperature measurement is repeated, and the obtained data is added to the previous data, and the temperature is calculated using the addition result to obtain the temperature result at each point. The position information is obtained from the time difference from when the light enters the measurement optical fiber 34 until the backscattered light is received.

  Further, the control circuit 40 monitors the LD 41 based on the monitor light m detected by the first light receiver 38, and feedback-controls the driver 42 to control the drive current of the LD 41.

  The control circuit 40 determines that the LD 41 is abnormal when the LD 41 does not operate in accordance with the feedback control command or the output is reduced, and sends a warning signal to the personal computer 35 to indicate that. It is displayed on the personal computer 35 or the operation of the LD 41 is stopped.

  Further, the control circuit 40 measures the transmission loss along the measurement optical fiber 34 from the monitor light m, so that the loss of the measurement optical fiber 34, the connection loss, the side pressure state, the bending state, the disconnection, and these locations ( ) Etc. are detected. Based on these detections, the control circuit 40 transmits a warning signal to the personal computer 35 and displays it on the personal computer 35 when there is a failure point, fault point, or abnormal point in the signal measuring optical fiber 34.

  As described above, the monitoring fiber coupler 1 is formed by connecting a part of the in-device optical fiber 33 mainly composed of MMF to SMF 33s and connecting the cladding of the SMF 33s and the monitoring MMF 4 to each other.

  A conventional optical fiber temperature sensor generally has a configuration in which Rayleigh scattered light returns to a light source, and does not use Rayleigh scattered light. However, in the monitoring fiber coupler 1, a part of the Rayleigh scattered light is extracted by the connection part 2 between the SMF 33 s and the MMF 33 m and is output to the light receiver 38 by the monitoring MMF 4 connected to the cladding of the SMF 33 s.

  According to the monitoring fiber coupler 1 according to the present embodiment, it is not necessary to use an expensive LD provided with a monitoring PD. Further, since Rayleigh scattered light is used, there is no need to monitor the light emitted from the LD 41. Thereby, LD41 can be monitored, without losing the optical power from LD41.

  That is, according to the monitoring fiber coupler 1, a part of light from the multimode optical fiber can be monitored with a simple configuration.

  In particular, if the optical fiber temperature sensor 31 is configured using this monitoring fiber coupler 1, the temperature along the measurement optical fiber 34 can be measured while monitoring the LD 41.

  If the monitoring fiber coupler 1 is used, an optical fiber temperature sensor 31 to which an OTDR function for detecting a failure point, a failure point, and an abnormal point of the measurement optical fiber 34 is simply added can be obtained.

  Next, a second embodiment will be described.

  As shown in FIG. 2, the monitoring fiber coupler 21 is the same as the monitoring fiber coupler 1 of FIG. 1 in that the in-device optical fiber 33 is composed of SMF 33s and MMF 33m.

  This monitoring fiber coupler 21 is formed with an inclined surface 23 serving as a reflection surface as an optical coupling portion on the cladding of the connection end portion of the SMF 33s connected to the MMF 33m, and an end surface of the SMF 33s on which the inclined surface 23 is formed. The end faces of the MMF 33m are connected to each other by an adhesive (for example, UV (ultraviolet ray) curable resin) that is transparent to the light emitted from the LD 41 to form the connection portion 22.

  In FIG. 2, the example which formed the inclined surface 23 in the lower part of the clad | crud of SMF33s was shown. The inclined surface 23 is formed so that a part of the cladding of the connection part 22 of the SMF 33s is inclined by approximately 45 ° from the connection part 22 side toward the SMF 33s side with respect to the direction orthogonal to the optical axis of the SMF 33s.

  The inclined surface 23 is formed such that a distance from one end of the inclined surface on the side close to the core of the SMF 33 s to the boundary between the core of the SMF 33 s on the inclined surface 23 side and the cladding is 10 μm or more.

  In the monitoring fiber coupler 21, a part of the Rayleigh scattered light is emitted from the MMF 33 m to the space portion at the connection portion 22, and further reflected by the inclined surface 23 (downward in FIG. 2) to be received as the monitor light m. Is output to

  The monitor light m reflected by the inclined surface 23 may be directly received by the light receiver 38. Further, depending on the structure in the sensor main body 32, the monitor light m may be optically coupled to the multimode optical fiber by a condenser lens or the like and received by a light receiver 38 provided at a desired location in the sensor main body 32. .

  Thereby, the same effect as the monitoring fiber coupler 1 can be obtained by the monitoring fiber coupler 21.

  In the above embodiment, an example in which an LD is used as a light emitting element has been described. However, an LED may be used as long as the distance is about several kilometers.

  In the above embodiment, the optical fiber temperature sensor 31 is described as an example of the physical quantity measurement sensor. However, the monitoring fiber coupler of each embodiment may be used for a strain sensor or the like.

  For example, the Rayleigh scattered light wavelength-separated from the back scattered light in the above embodiment strictly includes Brillouin scattered light shifted from the wavelength λ0 by about 10 GHz. Therefore, an optical filter for wavelength-separating the Brillouin scattered light is provided at the subsequent stage (downstream side) of each optical coupling section in FIGS. 1 and 2, and the fourth light receiver 38, A / If the D converter 45 is provided, the strain generated in the measurement optical fiber 34 can also be measured.

1 is a schematic view of a monitoring fiber coupler showing a preferred first embodiment of the present invention. It is the schematic of the fiber coupler for monitoring which shows the 2nd Embodiment of this invention. It is the schematic which shows an example of the optical fiber temperature sensor using the fiber coupler for monitoring shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fiber coupler for monitoring 2 Connection part 3 Optical coupling part 4 Multimode optical fiber for monitoring (the other multimode optical fiber)
33 In-device optical fiber 33s Single mode optical fiber 33m Multimode optical fiber (one multimode optical fiber)
41 LD (light emitting device)
LM cladding mode light m monitor light

Claims (3)

  Monitoring is characterized in that end faces of a single mode optical fiber and one multimode optical fiber are connected to each other, and a part of the longitudinal cladding of the single mode optical fiber is connected to the other multimode optical fiber. Fiber coupler.   An inclined surface is formed in a part of the clad of the single mode optical fiber, and the connection side end portion where the inclined surface of the single mode optical fiber is formed is connected to the end surface of the multimode optical fiber. Monitoring fiber coupler.   A light source that generates a pulse signal for optically measuring a physical quantity such as temperature and strain, a measurement optical fiber through which the pulse light signal propagates, and a light receiver that receives backscattered light from the measurement optical fiber An optical fiber type physical quantity measuring apparatus comprising: a monitoring fiber coupler according to claim 1 or 2 as a monitoring unit for monitoring a part of the backscattered light. apparatus.

Images