JP2007333717A - Fiber anchoring method for optical sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber anchoring method for an optical sensor. <P>SOLUTION: The optical sensor imparts physical strain to an optical fiber by varying the tension applied axially to the fiber, which causes changes in the optical properties of the light transmitted through the fiber and provides a fiber holder, capable of retaining fiber under tension with almost no creep or entirely without creeps, even at high temperatures and high-humidity environment. This exemplary fiber holder provides superior retention properties over epoxy and other adhesives, while preserving the tensile strength of the original fiber. A fiber holder and a sensor that are particularly useful for monitoring ambient conditions and measuring physical properties and mechanical phenomena are also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

(Cross-reference of related applications)
This application claims the benefit of US Provisional Application No. 60 / 689,246, filed June 10, 2005. This application is incorporated herein by reference in its entirety.

  In the past few years, fiber optic based sensors have become accepted on the market as an alternative to traditional electrical sensors. In many applications, such as civil structure monitoring, oil and gas downholes, ocean and space, fiber optic sensors offer several advantages over traditional sensors. Unlike electronic sensors, fiber-based sensors are unaffected by electromagnetic interference and are suitable for electrically disturbed environments. Furthermore, fiber based sensors can be easily multiplexed, allowing multiple sensors to operate on a single fiber over long distances. Fiber-based sensors can be ultra-small and ultra-light for use in limited spaces. Fiber-based sensors can be manufactured to withstand high temperatures and corrosive environments.

  A wide range of optical sensors utilizing a variety of optical properties are available to measure the physical properties of interest. This sensor is designed to react to the physical properties to be measured by changing the amplitude, phase, polarization, or other optical properties of the light propagating in the fiber. Depending on the sensor design, one or more of these optical properties can be monitored by a signal responder and converted to the physical property of interest.

  Known inventions focus on sensor types that impart physical strain to the fiber by altering the tensile force applied axially to the fiber to change the optical properties of light propagating through the fiber. . In this type of sensor, the fiber is often mounted in a mechanical fixture, which translates the physical property to be measured into a mechanical displacement that changes the amount of strain in the fiber. . The method of attaching the fiber to a mechanical fixture is very important when it is necessary to maintain the sensor precisely over time. Any slip or creep of the fiber relative to the mechanical fixture will cause the measurement to drift.

  Fiber-based sensors use various epoxies and other adhesives to attach the fiber to a mechanical fixture. These adhesives function properly for use at moderate temperatures and low humidity, but as environmental conditions worsen, they tend to produce creep where the adhesive does not spread well. Creep is a problem in applications that require long-term durability, even under moderate conditions.

  U.S. Pat. No. 6,317,555 relates to a creep-resistant optical fiber attachment mechanism, in which the optical fiber cladding has an "external dimension change region (expand or retract)". Changing the diameter of the optical fiber cladding provides a variable region that engages a portion of the ferrule, thereby mounting the optical fiber within the ferrule. The fiber is believed to be maintained under tension against the ferrule with minimal relative motion or creep. The ferrule can be attached to a larger structure or part thereof, such as a housing. A buffer layer can be placed between the cladding and the ferrule to protect the fiber and assist in securing the fiber within the ferrule.

  US Pat. No. 6,768,825 describes an optical sensor employing the creep-resistant optical fiber attachment mechanism of US Pat. No. 6,317,555. The optical sensor includes an optical fiber having a Bragg diffraction grating in the core of the fiber for at least partially reflecting an optical signal at a characteristic wavelength. This sensor arrangement has two transition regions to allow attachment of the optical fiber, located on either side of the Bragg grating in the optical fiber cladding. The fiber attachment is attached to the pressure sensitive structure so that the characteristic wavelength can vary according to the pressure environment.

  US Pat. No. 6,726,371 relates to an apparatus for securing a coated optical fiber to an optical fiber fixture. This fixing structure includes a ferrule having one hole into which an optical fiber is inserted. The ferrule further includes an opening penetrating from the ferrule side into the optical fiber insertion hole.

  A side groove-like optical fiber fixing component having an optical fiber clamping portion is inserted into the opening and clamped onto the optical fiber to be retained in the ferrule.

  US Pat. No. 6,668,105 relates to a fiber optic sensor flat pack that has been reported to be capable of very sensitive strain measurements. This patent provides packaging and packaging methods that employ plastic materials and laminate manufacturing techniques to provide a hermetic package that is resistant to harsh environmental conditions.

  U.S. Pat. No. 5,337,387 relates to a method of making a hermetic optical fiber in a metal component. A glass hermetic seal is formed between the metal shell and the metal-coated optical fiber. Although this method is described as convenient to form a durable and airtight seal, it is a machine to metal fixture for use in sensing applications where the optical fiber is under tension. There is no teaching or suggestion that this method can be employed to form a highly durable fiber.

U.S. Pat. No. 4,357,072 relates to an apparatus for sealing an optical fiber in a light emitting diode package. A metallized fiber having a metal collar mediation is secured in the holder by melting a low melting point material such as solder provided around the fiber. The intermediary metal collar is described as convenient in positioning the fiber relative to the light emitting diode. This patent states that "relatively short non-metalized fibers can be used, in which case low melting point glass is used as the material for the annulus." However, there is no description of how to provide a collar when employing non-metallic fibers. Collars have been described as particularly beneficial to make the fibers stiffer and heavier in order to speed fiber positioning and provide strength against bending forces. The sealing method and apparatus of the present invention is said to be convenient for attaching and aligning optical fibers in relation to light emitting diodes. However, there is no teaching or suggestion that the method and apparatus employed can be employed to form a mechanically durable fiber for metal fittings used in sensing applications where the optical fiber is under tension.
US Pat. No. 6,317,555 US Pat. No. 6,768,825 US Pat. No. 6,726,371 US Pat. No. 6,668,105 US Pat. No. 5,337,387 U.S. Pat. No. 4,357,072

  Although several devices and methods for providing a seal to an optical fiber are known in the art, an alternative to eliminate or minimize creep for mounting the optical fiber in a fixture, particularly for use in sensor applications There remains a need in the art for efficient methods and apparatus.

  The present invention is an optical fiber holding device comprising a fiber holder having a bore or slot, the bore or slot extending along the longitudinal axis of the fiber holder, further comprising an optical fiber, the optical fiber comprising a fiber holder A glass or metal seal that passes through an internal bore or slot and is oriented parallel to the longitudinal axis of the fiber holder, formed between the optical fiber and the holder, and at least partially formed within the bore or slot of the fiber holder. Further prepare. The seal can be formed of glass. In certain embodiments, the optical fiber has a protective coating.

  In certain embodiments, the seal formed between the optical fiber and the fiber holder is formed over the protective coating of the fiber. In certain embodiments, the glass sealing material has a coefficient of thermal expansion that is greater than the coefficient of thermal expansion of the optical fiber. In a further embodiment, the coefficient of thermal expansion of the fiber holder material is greater than the coefficient of thermal expansion of the glass sealing material. In certain embodiments, a compression seal is formed. In another embodiment, the coefficient of thermal expansion of the fiber holder material approximately matches that of the glass sealing material. The fiber holder can be made of stainless steel, Kovar, or Invar. In certain embodiments, the fiber holder has a hermetic retaining cavity formed at least in part in the bore or slot of the holder. The fiber can have a protective coating of polyimide, carbon / polyimide, or carbon / silicon / PFA. The fiber can have a metal protective coating made of gold, copper, or aluminum. The sealing material may be a metal alloy, particularly when the protective coating is a metal. The sealing material may be a metal alloy solder comprising lead, tin, silver, indium, gold, copper.

  The optical fiber holding device further includes a second fiber holder having a bore or slot, the bore or slot extending along the longitudinal axis of the fiber holder, and the optical fiber provided with the protective coating is in the second fiber holder. The second glass holder is oriented parallel to the longitudinal axis of the second fiber holder, a second glass or metal seal is formed around the optical fiber, and at least a portion is within the bore or slot of the fiber holder. Forming a seal between the coated optical fiber and the second fiber holder, the first and second fiber holders along the optical fiber while forming two anchor points along the fiber. Are separated.

  The optical fiber holding device further comprises one or more additional fiber holders, each of the additional fiber holders having a bore or slot extending along the longitudinal axis of the fiber holder and provided with a protective coating. The fiber is directed through each bore or slot of the additional fiber holder and parallel to the longitudinal axis of each of the additional fiber holders, and for each additional fiber holder, an additional for each additional fiber holder. A glass or metal seal is formed around the optical fiber and at least partially in the bore or slot of the additional fiber holder to form a seal between the coated optical fiber and each of the additional fiber holders The fiber holder is formed on the optical fiber while forming a plurality of retaining points along the optical fiber. They are spaced apart from me.

  The optical fiber of the optical fiber holding device can be provided with a fiber grating, in particular a fiber Bragg grating, between the two anchor points. The optical fiber of the holding device can be provided with a fiber grating between one or more anchor points. The fiber grating may be a fiber Bragg grating, or more particularly a long-term grating.

  The present invention includes an optical fiber holding device of the present invention and a fixture that maintains the first and second fiber holders with their aligned axial bores, at least a portion of the fixture being along the longitudinal axis. One or more optical properties of the optical fiber that are elastic in relation to expansion, compression, or both, change when exposed to axial strain. The optical sensor of the present invention may be a device that measures strain, measures displacement, measures temperature, measures pressure, and measures acceleration.

  The present invention further provides a method for measuring strain in an optical fiber employing the optical sensor of the present invention.

  The present invention further provides a method of mounting an optical fiber having a protective coating in a fiber holder, the method comprising providing a glass or metal seal between the fiber holder and the coated optical fiber. The glass or metal seal is formed in a hermetic retention cavity that is at least partially formed in the bore or slot of the fiber holder. In certain embodiments, the optical fiber extends over the entire length of the bore or slot of the optical fiber.

  Other aspects of the invention will become apparent by consideration of the following detailed description and drawings.

  The present invention provides a method for holding an optical fiber within the optical sensor's mechanical mount in a manner that minimizes or prevents fiber slippage when a tensile force is applied to the fiber and the sensor is exposed to temperature and humidity. provide. The present invention further provides an optical fiber holding device and an optical sensor in which one or more optical fibers employing the optical fiber holding device according to the present invention are mounted in the device. The present invention still further provides an optical fiber, particularly an optical fiber mounted within the fiber holder of the present invention, which employs a seal formed of crow or metal solder to hold a protective coating mechanically coupled to the holder. provide. In general, glass sealing techniques are used to form a hermetic seal around a fiber that penetrates a hole in a metal package. In these applications, the fiber is stripped of its polymer coating and a glass seal is formed between the fiber and the metal package. In many cases, the fiber surface becomes brittle as a result of damaging the fiber surface by a stripping and sealing process.

  The approach used in the present invention preferably leaves the protective coating of the fiber in place to protect the fiber from surface damage. In some embodiments, this process uses low temperature glass to form a seal just above the fiber coating and keeps the fiber in a metal housing. The fiber coating not only prevents surface damage to the fiber surface, but also provides some strain relief to the extent that the fiber exits the glass seal. By leaving the coating intact, the fiber can retain most of its tensile force. If the fiber coating is a polymer such as polyimide, the seal will not be completely airtight, but many applications do not require complete airtightness.

Two types of glass / metal seals can be employed to keep the fiber in the metal housing, a matched seal and a compression seal. Aligned seals use sealing glass and metal holders that have a substantially matched coefficient of thermal expansion (CTE). The term “substantially matched” in this description means that the CTEs of different materials differ by up to about +/− 15% each. A material having a CTE of 7 ppm / C (μm / mK or 10 ⁻⁶ / K) is substantially matched to a material having a CTE of 7 +/− 1.05 ppm / C. Certain embodiments employ materials with a CTE difference of 10% or less, or 5% or less. An alignment seal relies on the composition of chemical bonds between the sealing glass and the oxide present on the metal surface. Two materials that differ by 15% or more in CTE are not substantially matched.

  On the other hand, a compression seal uses a CTE difference between a sealing material (eg, glass) and a holder material (eg, metal) to form a compression seal. The compression seal is designed with an alternating CTE. The low CTE fiber is surrounded by a high CTE fiber sealing glass, which is then surrounded by a higher CTE metal. For example, a fiber with a CTE of 1 ppm / ° C., a glass sealing material with a CTE of 7 ppm / ° C., and a stainless steel fiber mounting disk with a CTE of 16 ppm / ° C. provide a seal with an alternating CTE. As the assembly cools from the sealing temperature, the metal shrinks around the sealing glass and then shrinks around the fiber, creating a compressive stress around the fiber. In compression sealing, some chemical bonds also occur. The seal employed in the present invention is preferably a compression type seal that utilizes the additional holding force provided by the compressive force. The term larger (or higher) or smaller (or lower) as applied to CET value differences preferably means a difference outside the substantial alignment range. That is, the case where the difference in CET is greater than +/− 15% is shown.

  Sealing glass having a softening point of 250C to 100C is generally commercially available. Preferred sealing glasses are those having a softening point below the melting temperature of the material used for the protective coating of the optical fiber. In certain embodiments, a low temperature sealing glass (ie, having a softening point of 300 C or less) with a resin coated optical fiber (eg, typically has a value of 300 C on a continuous basis and 400 C for a short period of time). And polyimide coated fiber). Typical resin fiber coatings include polyimide, carbon / polyimide. The fiber protective coating may further be a metal coating including a copper, aluminum, gold coating. The present invention is compatible with these coatings.

  When using a metal such as copper or gold, or a metal alloy as a protective coating on an optical fiber, the alloy solder comprises lead, tin, silver, indium, gold, or to secure the fiber to the fiber holder Copper may be used as the sealing material. In the present invention, various alloy solders known in the art can be used.

  The optical fiber, the optical fiber holding device, and the fiber holder to which the optical sensor of the present invention is attached can be directly or indirectly incorporated into various devices, and these various devices include strain gauges, extensometers, temperature transducers. , Pressure transducers, accelerometers, but not limited to. There are a number of optical fiber sensor shapes that can be employed with fiber holders that are mounted with an optical fiber and an optical fiber holding device for mounting one or more optical fibers in or on the optical fiber sensor. Known in the field. Those skilled in the art, given the description herein and the facts known in the art, will adopt a device known as an optical sensor shape in this description or make the device in this description into such a sensor shape. Can be easily adapted. FIG. 3A provides an exemplary attachment of an optical fiber that provides a fiber Bragg grating into a fiber optic sensor geometry.

  Some fiber optic sensing systems include a light source, a fiber optic, a sensing element or transducer, and a detector. The principle of operation of a fiber sensor is that the transducer modulates several parameters of the optical system (intensity, wavelength, polarization, phase, etc.), so that there is a detectable change in the characteristics of the optical signal received by the detector. Arise. The fiber optic sensor can be either a native sensor where modulation occurs directly in the fiber (where the fiber itself is a transducer) or an incidental sensor where modulation is performed by some external transducer acting on the fiber. . A fiber Bragg grating introduced in an optical fiber is an illustrative transducer. Any change in fiber mode index or grating pitch caused by strain or temperature shifts the characteristic Bragg wavelength. Fiber Bragg gratings are often used in strain or temperature sensing, especially in harsh environments (eg, high EMI, high temperature, or highly corrosive environments). By further using a transducer acting on the fiber Bragg grating, it is also possible to use the fiber Bragg grating to sense other environmental parameters such as pressure chemical reactions.

  For pressure applications, an optical fiber provided with a fiber Bragg grating can be attached to a diaphragm shaped to be affected by, for example, pressure changes. Alternatively, the fiber itself can be used as a pressure transducer that produces a three-dimensional strain mode when pressure is applied to the fiber grating in the fiber.

  The magnetic and electrical regions that sense an optical fiber provided with a fiber Bragg grating can be coated with a ferromagnetic coating. When the coated fiber is in the strong magnetic region, this region expands or contracts the grating in the coated fiber. In chemical sensing, an optical fiber with a fiber Bragg grating is coated with a material that is affected by the presence of certain chemicals (chemically sensitive coatings) so that the coating is reduced to the amount of chemical present. Or strain in the fiber Bragg grating that is proportional to the reaction that produces the chemical. For example, palladium production can be used to monitor hydrogen production using a fiber Bragg grating with palladium. Palladium absorbs hydrogen and causes strain in the fiber lattice.

  Fiber optic sensor shape, operation, use, and applications of such sensors are known in the art. The following references are cited to provide details of sensor shapes that can employ fiber holders and fiber holding devices according to the present invention, as well as details of sensor operation, use, and application. Farhad Ansari (Ed.) (1993) “Applications of Fiber Sensors in Engineering Mechanics”, American Society of Civil Science.

  Eric Udd (Ed.) (1995) “Fiber Optic Smart Structures”, John Wiley & Sons Inc., Regis J. et al. Van Steenkiste and George S. Springer (1997) “Strain and Temperature with Fiber Optical Sensors”, Technological Publishing Co. (Technical Publishing Co.); And Fiber Optic Sensors for Bridges (Technical Publishing Co.); Raymond M., Fiber Optics Sensors for Construction Materials and Bridges; Measurements (2001) “Structural Monitoring with Fiber Optical Technology” (Academic Press); Jose Miguel Lopez-Higer Technology (book) “Handbook of Optical Fiber Sensing Technology”, John Wiley & Sons Inc. (“Optical Fiber Sensor Guide Funds and Optical Fiber Sensor Guide Funds”). , Micron Optics, Inc. (Micron Optics) http: // www. microoptics. com / pdfs /; et al. , “Recent Advances in Fiber Sensors for Utility Industry Applications”, Proc. SPIE vol., “Recent Advances in Fiber Grading Sensors for Utility Industries Applications”. 2594, 1995; Kashap, R .; , “Photosensitive Optical Fibers; Apparatus and Applications”, Ops. Fiber Tech. , Vol. 1, pp 17-34, 1994; Morey, W .; W. Meltz, G .; , And Glen, W .; H. , “Fiber Optic Bragg Grating Sensors”, International Optical Engineering Minutes (SPIE Proc.), Vol. 1169, pp 98-107, 1989; Meltz, “Overview of fiber-grading-based sensors”, International Optical Engineering Proceedings (Proc. SPIE), “Distributed and Multiplexed Optical Fiber Sensors VI (Distributed and Multiplexed)”. Fiber Optic Sensors Vl) "Denver, CO, vol. 2838, pp. 1-21, 1996; Patric, H. et al. J. et al. Williams, G .; M.M. Kersey, A .; D. , Pedrazaani, J. et al. R. , Vengsarkar, A .; M.M. "Hybrid fiber Bragg grating / long period fiber grating sensor for strain / temperture discriminating", American Institute of Electronics Photonics Technologies, Ltd. IEEE), Volume 8, Issue 9, Sept. 1996 page (s): 1223-1225 and More, W. et al. W. "Development of Fiber Bragg Grating Sensors for Utility Applications", US Electric Power Research Institute Report (EPRI, Report) TR-105190, September 1995.

  The following definitions apply herein.

  “Creep” means a gentle change in the relative position of two objects or a slow and gentle deformation of a material upon exposure to pressure, elevated temperature, or high humidity.

  “Elastic” means the ability of a material or object, such as a device or device component, to increase or decrease its size in relation to one or more physical dimensions. The elastic material may be expandable, compressible, or both. By elasticity is meant a characteristic of an elastic material, object, device or device component.

  “Glass seal”, “sealing glass”, and “glass seal material” mean a low temperature molten glass material commonly used to form an insulating seal around a pin that penetrates a metal-tight electrical package. Often, sealing glass is used with various binders and viscosity modifiers to improve flow and wet properties during the sealing process. Sealing glasses suitable for use in the sealing formation of the present invention may be in the form of various desired preforms that are commercially available. In certain embodiments, a glass preform having the following properties can be employed. Glass transition temperature 225 ° C., softening point 276 ° C., CTE 7.5 ppm / ° C. For example, a glass preform with OD = 0.044 inch, ID = 0.016 inch, and length = 0.03 inch can be used for the ferrule holder illustrated in FIG. 1A.

  “Optical fiber” most generally refers to any form of optical fiber having a core and cladding as is well known in the art. The method and apparatus of the present invention are effective in securing a fiber made of glass (silica) to a metal fiber holder. Optical fibers useful in sensing applications include single mode and multimode fibers. Optical fibers useful in the present invention include optical fibers having a uniform cladding diameter and optical fibers having various cladding diameters. When optical fibers having various cladding diameters are employed in the apparatus of the present invention, these variations are not the only mechanism for securing or attaching the optical fibers to the fiber holders or their interior.

  The optical fiber of the present invention is preferably a coated optical fiber having a protective coating along the outer surface of the fiber that protects the fiber from damage. The presence of the protective coating increases the operating life of the optical fiber. Typical non-metallic fiber coatings include resins, polymers, or such materials mixed with carbon, especially polyimide, carbon / polyimide, carbon / silicon / PFA (perfluoroalkoxyethylene). The protective coating further includes metal coatings such as copper, aluminum and gold. For sensor applications, the optical fiber may include one or more fiber gratings, such as a fiber Bragg grating that functions as a transducer.

  A fiber Bragg diffraction grating (FBG) is a wavelength-dependent filter / reflector formed by introducing a periodic refractive index structure in the core of an optical fiber. When a broad spectrum light beam collides with a grating, some of its energy propagates through the fiber and another part of the energy is reflected. The reflected optical signal is very narrowband and concentrates on a characteristic Bragg wavelength that is twice the periodic unit space. Conventional FBGs have a grating period of about several hundred nanometers. Further, long-term Bragg gratings (LPG, AM Vengsarkar et al., “Long-period fiber Bragg gratings as band-rejection filters, about several hundred microns, or several centimeters,” ) ", Lightwave Technology Journal (J. Lightwave Technol.) 14, 58 (1996)) can be employed in sensor applications and devices of the present invention.

  Any change in fiber mode index or grating pitch caused by strain or temperature results in a shift of the Bragg wavelength. Strain can be measured using a sensor having an optical fiber with an FBG by accurately mounting the optical fiber on or incorporating within the substrate of interest. One advantage of this technique is the fact that the detected signal is spectrally encrypted, so there is no need to worry about transmission loss in the fiber. Strain shifts the characteristic Bragg wavelength by physically expanding or contracting the grating space due to mechanical strain and refractive index changes due to strain optical effects. At axial loading, the wavelength change is typically about 1.2 pm / micro strain, or 12 nm per 1% strain.

  Further, a fiber grating having an aperiodic refractive index structure can be employed in the optical fiber and the optical sensor of the present invention. For example, a chirped fiber grating can be used. Chirped fiber gratings are of particular interest in internal grating sensing.

  By “integral body” is meant a body or object that consists of discrete components that are operatively attached to each other, made of one continuous material. The monolithic body does not include physically separated, intermittent elements. A preferred monolithic body is made from one material. However, the unitary body comprises a plurality of components connected by one or more fasteners such as welded joints, adhesives, epoxies, screws, bolts, clamps, clasps, or any known equivalent thereof. It may be.

  “Coefficient of thermal expansion” (CET) means a slight change in the length or volume of a material caused by a given temperature change. Usually expressed in terms of length / length / unit temperature (m / m / 'C).

  “Vertical to the vertical axis” means a direction defined by an axis positioned at an angle of 90 degrees with respect to the vertical axis. Similarly, “parallel to the vertical axis” means a direction defined by an axis positioned at an angle of 0 or 180 degrees with respect to the vertical axis. It will be apparent to those skilled in the art that in the apparatus and apparatus components shown herein, any deviation from vertical or parallel is permissible as long as this deviation does not significantly adversely affect the operation of the apparatus or apparatus element. I will.

  As used herein, the expression “preferred embodiment”, “alternative embodiment”, or “exemplary embodiment” refers to a particular feature, structure, or feature described in connection with an embodiment. It is meant to be included in at least one embodiment of the present invention. The expressions “preferred embodiment”, “alternative embodiment”, or “exemplary embodiment” found in various places in the specification do not necessarily refer to the same embodiment.

  Next, the present invention will be further described with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and the same reference numerals are given to two or more drawings. This refers to the element.

  FIG. 1 illustrates an exemplary embodiment of an optical fiber holding an apparatus of the present invention that can hold the optical fiber under tension with little or no creep between the fiber and the fiber holder. Show. The illustrated fiber holder (100) comprises an integral body (101). The integral body (101) has an axial bore extending along the longitudinal axis (103) formed by the cylindrical inner wall (106) of the fiber holder. An optical fiber (104) consisting of silica fibers (core and cladding) (104a) and protective coating (104b) passes along the longitudinal axis (103) through the interior of the axial bore in the fiber holder (100). It extends. The optical fiber (104) is held in a fiber holder (100) with a seal (105) formed of glass (or metal solder). During the sealing process, the glass sealing material, for example in the form of a glass preform, is heated to its melting temperature and solidified to form a seal attached around the fiber coating (104b). The seal (105) is trapped within a cavity formed between the inserted optical fiber and the axial bore (102) to form a seal between the fiber coating and the fiber holder, while the fiber coating (104b) By filling the gap between the inner walls (106) of the fiber holder, the fiber is mechanically coupled, clamped and attached to the fiber holder.

  Cavity 102 is a cavity that maintains and holds the seal-forming material and at least partially defines the shape of the seal formed between the fiber and the holder. In one illustrative embodiment, the coefficient of thermal expansion of the fiber holder (101) is greater than the coefficient of thermal expansion of the sealing material used to form the seal (105), and thus the heat of the fiber (104). Greater than expansion coefficient. As the assembly is cooled from the elevated sealing temperature, the sealing material (105) shrinks at a faster rate than the fiber (104), creating a compressive stress between the sealing glass and the fiber. At the same time, the axial bore (102) in the fiber holder (100) shrinks at a faster rate than the sealing glass (105), thereby compressing the stress between the fiber holder (100) and the glass seal (105). Occurs. In general, the protective coating on the fiber is very thin (10-20 μm) compared to the fiber (bare fiber diameter—125 μm), so the CET of the protective coating does not significantly affect the compression of the seal.

  In the particular embodiment shown in FIG. 1B, the wall (106) of the axial bore of the holder (101) includes a horizontal ledge formed by a change in the bore diameter. Due to the presence of this horizontal ledge, a lip associated therewith is created in the seal 105. The lip structure within the seal formed against the horizontal ledge in the bore provides additional mechanical strength to the seal and is parallel to the axis and downward from the lip / horizontal ledge engagement (FIG. 1B). Increase the resistance to the force applied. This structure reduces the possibility of relative motion of the bore and fiber as the fiber moves downward (see FIG. 1A).

  1C and 1D show a further shape of the fiber holder seal and bore structure. FIG. 1C shows a bore of uniform diameter (solid line 106). An alternative tapered bore is indicated by dashed line 106a. The tapered bore increases the resistance to downward movement (shown in FIG. 1B) of the fiber holder (101). FIG. 1D shows a further alternative bore structure with a recess in the bore wall. A broken line 110a indicates a bore having a curved recess, and a broken line 100b indicates a V-shaped recess. The wall forming the axial bore of the holder 101 can be recessed with one or more recessed areas, or can be provided with one or more protrusions. The term “bore” as used herein does not imply any structure of the inner wall of the holder that forms the bore. The inner wall of the holder may form a bore structure that is symmetric with respect to the longitudinal axis 103, or the wall may include a recess or protrusion that is asymmetric with respect to the axis. In a particular embodiment, the wall of the holder includes a single recess in the projection that is symmetrical about the axis 103. In another embodiment, the wall of the holder includes a plurality of indentations or protrusions that can be arranged symmetrically or asymmetrically with respect to the axis 103.

  FIG. 2A shows an alternative embodiment of the fiber holder (100). The illustrated fiber holder (200) includes an integral body (201). The unitary body (201) has a longitudinal slot (202) extending parallel to the longitudinal axis (103) and having a size and shape for receiving an optical fiber. The slot (202) is illustrated as formed by the three inner walls of the holder (ie, two side walls 206, one bottom wall 207). The slot (202) is illustrated in a rectangular shape, but may have various shapes, such as a cylindrical shape. An optical fiber (104) consisting of silica fiber (104a) and protective coating (104b) is positioned in slot (202) and extends along longitudinal axis (103). The integral body (201) has a cavity (203) that is perpendicular to the longitudinal axis (103) and is formed by recessing or expanding a portion of the side wall of the slot. . The cavity (203) forms a pocket in which sealing material can be placed to form a seal 105 between the fiber and the fiber holder. Cavity (203) includes a sealing material that preferably seals the cavity in such a manner that when melted and cooled, the walls forming cavity 203 add a compressive stress against fiber (104). To do. Cavity 203 is a cavity that maintains and holds the seal-forming material and at least partially defines the shape of the seal between the fiber and the holder. The sealing material is trapped inside the cavity (203) and fills the gap between the fiber coating (104b) and the wall forming the cavity (203).

  In an exemplary embodiment, the coefficient of thermal expansion of the fiber holder (200) is greater than the coefficient of thermal expansion of a sealing material such as, for example, a sealing glass that forms the seal (105), and thus the thermal expansion of the fiber (104). Greater than the coefficient. As the assembly cools from the elevated sealing temperature, a compressive stress is generated between the sealing materials forming the seal 105 because the sealing material in the cavity 203 shrinks at a faster rate than the fiber (104). At the same time, the wall of the hole (203) of the fiber holder (200) shrinks at a faster rate than the sealing material, thereby creating a compressive stress between the fiber holder (200) and the seal (105). FIG. 2B illustrates the seal 105 in more detail.

  FIG. 2B is a cross-sectional view of the holder of FIG. 2A at a recessed portion forming the cavity 203. This figure shows the shape of one or more walls of the slot that creates the cavity 203. The slot walls (207, 206) can include one depression (shown in FIG. 2B), one protrusion (not shown), or multiple depressions or protrusions, which are formed in the cavity 203. It forms the shape and therefore at least partially determines the shape of the seal 105.

  As shown in FIG. 2B, the seal 105 is formed between the fiber in the holder slot 202 and the wall of the slot so that the fiber and the holder are mechanically coupled.

  The seal formed in the holder of the present invention provides a durable mechanical connection between the fiber and the holder, thereby minimizing or eliminating creep (ie, relative movement of the fiber and the holder), thus It is particularly advantageous in applications.

  In the preferred embodiment shown in FIGS. 1A and 2A, the unitary body is preferably made of a material having a coefficient of thermal expansion greater than that of the glass sealing material. For example, using a stainless steel alloy that preferably has a linear thermal expansion coefficient of about 9.9 ppm / ° C. in the manufacture of an integral body with a glass sealing material having a linear thermal expansion coefficient of 7.1 ppm / ° C. Is desirable. Alternatively, Invar (TM), an iron / nickel alloy (Imphy SA Corp., Paris, France) or Kovar (TM), an iron / nickel / cobalt alloy ( The use of low expansion electronic alloys, such as CRS Holdings, Inc., Wilmington, Delaware, in the manufacture of monolithic bodies is for use with higher temperature sealing glasses having a low coefficient of thermal expansion. desirable.

  The fiber holder to which the optical fibers (100, 200) shown in FIGS. 1A and 2A are attached is an example of the fiber holding means according to the present invention. Those skilled in the art will appreciate that various fiber holder structures provide holes or cavities for receiving optical fibers and receiving sealing glass. The present invention can employ any fiber holder shape that provides a cavity through which the fiber can pass and contain the liquefied sealing material. The cavity that seals the sealing material may be of any shape that seals the sealing material as it expands during cooling and that preferably produces compressive stress to create a seal.

  FIG. 3A shows an illustrative embodiment of a strain sensor (300) that utilizes a fiber holder (101) of the type illustrated in FIG. 1A. In one preferred embodiment, two fiber holders (101) are attached to a single optical fiber separated by a distance. One or more optical properties of the length of the fiber (305) disposed between the two fiber holders (101) change when axial strain is applied to the fiber. In a preferred embodiment, the length of the fiber (305) placed between the fiber holders is subject to axial strain by shifting one or more fiber gratings, particularly the center wavelength of the reflected light spectrum. A reactive fiber Bragg grating is included. FIG. 3B schematically illustrates one or more Bragg gratings in the fiber of the sensor of FIG. 3A.

  A fiber holder (101) is attached inside the ferrule (302) for ease of handling and attachment. The protective cover tube (303) slides on the ferrule (302) to protect the optical fiber. The ferrule (302) can slide freely along the longitudinal axis (103) in the protective tube (303). In a particular embodiment, the mounting bracket (301) is secured to the ferrule (302), but it can also be bolted. In certain embodiments, the mounting bracket (301) can be secured to the ferrule (302) and bolted, welded, glued, or secured to the specimen (304) by any other suitable means. it can. To attach or secure the ferrule between the brackets, for example, each ferrule (302) can be provided with a groove (306) that engages a corresponding slot (307) in the mounting bracket 301 (groove (306). The engagement with the mounting bracket groove (307) is also shown in FIG. The specimen 304 is mechanically coupled to the bracket 301, which is then mechanically coupled to the ferrule 302 and further mechanically coupled to the holder 101, which is mechanically coupled at two locations on the optical fiber 104. is doing. The strain generated in the test object 304 can be detected when the attached optical fiber is strained.

  The protective tube (303) of the sensor of FIG. 3A is fabricated from a compliant material that stretches when strain is applied to the sensor, allowing the protective tube (303) to be directly coupled to the ferrule (302). Also good. In this configuration, the protective tube (303) does not need to slide over the ferrule (302).

  One skilled in the art will appreciate that in operation, the sensor of FIG. 3A can be optically coupled to a light source and detector, as is known in the art.

  FIG. 4 is a schematic diagram illustrating a cross-section of an exemplary ferrule shape of the sensor of FIG. 3A. FIG. 4 illustrates one exemplary method of attaching a fiber holder (100) secured to a coated optical fiber (104) via a seal (105) within a strain sensor. The ferrule 302 has an axial bore (402) that includes an inner diameter (402a) and an outer diameter (402b) of different diameters, thereby providing a shoulder (404) within the ferrule bore. ) Is formed. A small inner diameter portion (402a) of the axial bore is dimensioned to receive the coated optical fiber. The large outer diameter (402b) of the axial bore is sized and shaped to receive the fiber holder (100) (eg, the circular fiber holder of FIG. 1). The fiber holder (100) attached fiber passes through the ferrule axial bore, allowing the fiber holder to engage the shoulder 404. As shown in FIG. 3A, a second fiber holder (100) is attached to the coated optical fiber, sealed using a glass seal, and spaced from the first fiber holder by a selected fiber length. . The second fiber holder is positioned on the fiber (as shown in FIG. 3A) to engage a shoulder (404) formed in the second ferrule of the strain sensor. The fiber holders are separated such that the optical fiber between the two fiber holders is held in place in the sensor by the tensile force between the shoulders in the axial bores of the two ferrules of the sensor. Separated fiber holders sealed to optical fibers are alternately coupled to the two ferrules using a suitable adhesive so that the fibers between the two fiber holders are located between the two ferrules. can do. Alternatively, the fiber holder may be welded or soldered to the ferrule, or mechanically secured to the ferrule using a variety of fastening devices such as screws, bolts, clamps, and the like. A mechanical stop (not shown) can be installed inside the sensor assembly to prevent fiber breakage. By adjusting the space of the mounting bracket 301, the actual tension in the fiber is set.

  In one illustrative embodiment, a strain sensor having a stainless steel fiber holder, a silica fiber coated with polyimide, and a low temperature sealed glass has a wavelength drift when exposed to high temperatures and high humidity, resulting in a conventional fiber attachment method. It is significantly lower than the comparable sensor used. As shown in the graph of FIG. 5, the performance of an exemplary embodiment of the strain gauge of the present invention is compared to three strain gauges with different manufacturing methods. In all three strain gauges (V1 to V3), the fiber is attached or secured using an adhesive such as epoxy. In V1 and V3, the bare fiber is attached with an adhesive. In V2, a fiber equipped with a protective coating is attached with an adhesive. All strain gauges are exposed to 75 ° C. and 75% relative humidity while being pre-tensioned and maintained at a constant strain. Ideally, the wavelength is kept constant. The strain gauge of the present invention exhibited much improved wavelength durability compared to three strain gauges from other manufactures.

  In order to demonstrate the durability of the strain sensor of the present invention, a life cycle inspection was conducted. To perform this inspection, the sensor in FIGS. 3A and 3B was bolted to an inspection fixture having one fixed support and one moving support. The movement support unit is motor-driven, and transitions in a direction parallel to the sensor axis at a speed of 6 Hz. The moving support is adjusted to produce a strain on the sensor that varies with a micro strain of 0-200. FIG. 6 shows this life cycle inspection, where the time is periodic. The sensor was pulled over a total of 25,476,300 cycles, and showed no signs of failure and fatigue drift. The graph in FIG. 6 shows the wavelength of the sensor that oscillates between the upper and lower boundaries at 0-2000 microstrain. Due to temperature changes during the inspection, some changes occur at the upper and lower boundaries. Any slip or creep at the fiber attachment point results in a zero shift displayed as a downward trend in the data. In FIG. 6, no such zero shift was observed, which means that there was no measurable creep in the strain sensor during the inspection period.

  If a Markush group or any other group is used, all independent members in the group and all combinations and possible subcombinations of the group shall be independently included in this disclosure. . All combinations of components described or illustrated herein can be used to practice the invention unless otherwise indicated. Those skilled in the art will appreciate that methods, apparatus elements, and materials other than those specifically illustrated can be employed in practicing the present invention without resorting to undue experimentation. All functional equivalents, known in the art, of any such methods, device elements, materials are intended to be embraced by the present invention. In the present specification, when a range is given such as a temperature range, a frequency range, a time range, and a composition range, all intermediate ranges and all sub-ranges included in the given range are always used. All further independent values are intended to be encompassed by this disclosure. Any one or more independent members of the scope or group disclosed herein may be excluded from the claims of the present invention. The invention described herein by way of example can be suitably practiced without the use of any one or more elements, one or more limitations not specifically disclosed herein.

  As used herein, “comprising” is synonymous with “contains”, “contains”, or “characterized by” and is an additional, unquoted element Or encompass method steps, do not constrain them, and do not exclude them. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In particular, the description of the term “comprising” in the compositional component description or in the device element description may be replaced with “consisting essentially of” or “consisting of”.

  While the description herein includes many details, these should not be construed as limiting the scope of the invention, but merely provide an illustration of some embodiments of the invention. Should be interpreted as things. Each reference cited herein is hereby incorporated by reference in its entirety. However, in the event of any conflict between the cited references and the present disclosure, the present disclosure shall prevail. Some references provided herein are incorporated herein by reference to provide details regarding prior art prior to the filing of this application, and other references are incorporated herein by reference. References are made to provide additional or alternative instrument elements, additional or alternative materials, additional or alternative methods of analysis or use. All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which this invention pertains. The references cited herein are incorporated herein by reference in their entirety to indicate prior art prior to the filing of this application, and are identified in the prior art. In order to exclude this embodiment, this information can be employed in the present invention as needed. Those skilled in the art will understand that device elements other than those specifically illustrated, and the materials, shapes, dimensions, and methods of the device elements can be employed to practice the present invention without undue experimentation. Let's go. All functional equivalents of any such materials and methods well known in the art are intended to be encompassed by the present invention. The terms and expressions employed are used as descriptive terms, not as regulatory terms, and the use of such terms and expressions is equivalent to any equivalent or part of the features shown and described. However, it will be recognized that various modifications are possible within the scope of the claimed invention. Thus, although the present invention is specifically disclosed by means of preferred embodiments and optional features, those skilled in the art are able to use modifications and applications of the concepts disclosed herein, and It should be understood that improvements and applications are encompassed within the scope of the invention.

1 is a schematic plan view showing a fiber holder. 1B is a cross-sectional view of an embodiment of the optical fiber of FIG. 1A, in which the axial bore of the holder has two portions that differ in diameter due to the formation of a horizontal ledge. 1B is a cross-sectional view of a further embodiment of the fiber holder of FIG. 1A. FIG. In some embodiments, the axial bore of the holder is a uniform cylinder, and in another embodiment, the axial bore of the holder is tapered. 1B is a cross-sectional view of a further embodiment of the fiber holder of FIG. 1A. FIG. This figure shows two different shapes of the axial bore of the holder. Fig. 6 is a schematic plan view showing an alternative design of a fiber holder. In this case, the optical fiber is positioned within the axial slot or channel, and the slot or channel wall is shaped to form a cavity for receiving the sealing material. FIG. 2B is a cross-sectional view of an embodiment of the fiber holder of FIG. 2A. 1B is a schematic plan view showing a strain sensor employing the fiber holder of FIG. 1A. In order to see the internal elements of the device, parts of the external elements have been removed. FIG. 3B is an enlarged view of the optical fiber of the strain sensor of FIG. 3A schematically illustrating one or more Bragg grating fibers in the fiber. 3B is a schematic cross-sectional view of a portion of the strain sensor of FIG. 3A showing the position of the fiber holder within the metal ferrule. FIG. The wavelength drift as a function of time of the strain sensor of the present invention (MOI, having a polyimide-coated silica fiber and a low temperature sealed glass in a stainless steel fiber holder) is measured by three different manufactured optical fiber based strain gauges (V1, It is a graph compared with V2, V3). In all three strain gauges (V1 to V3), an adhesive such as epoxy is employed to create the fiber attachment or retention. In V1 and V3, adhesive is attached to the bare fiber. In V2, adhesive is attached to the fiber provided with the protective coating. It is a graph which shows the result of the life cycle test | inspection demonstrated below regarding the strain sensor of FIG. 3A. Time is a unit of time cycle. The sensor was tested over 25,476, 300 cycles and showed no signs of failure or drift due to fatigue.

Explanation of symbols

100, 200 Fiber holder 100b, 110a, 210 Broken line 101, 201 Integrated body 102 Axial bore 103 Vertical axis 104 Optical fiber 104a Silica fiber 104b Protective coating 105 Sealing 106 Inner wall of fiber holder 202 Vertical slot 203 Cavity 206 Side wall 207 Wall 209 Recessed wall 300 Strain sensor 302 Ferrule 303 Protective cover tube 304 Test object 305 Fiber length 306 Groove 307 Slot 402 Axial bore 402a Internal 402b External 404 Shoulder

Claims (32)

An optical fiber holding device,
A fiber holder having a bore or slot, the bore or slot extending along a longitudinal axis of the fiber holder;
Further comprising an optical fiber, the optical fiber passing through the bore or slot within the fiber holder and oriented parallel to the longitudinal axis of the fiber holder;
An optical fiber holding device further comprising a glass or metal seal formed between the optical fiber and the holder and at least partially formed within the bore or slot of the fiber holder.   The apparatus of claim 1, wherein the seal is a glass seal.   The apparatus of claim 1, wherein the optical fiber has a protective coating.   The optical fiber holder of claim 1, wherein the seal between the optical fiber and the fiber holder is formed on the protective coating of the fiber.   The optical fiber holder of claim 1, wherein the optical fiber has a protective coating that is not removed during the sealing process.   The optical fiber holding device according to claim 2, wherein the glass sealing material has a thermal expansion coefficient larger than a thermal expansion coefficient of the optical fiber.   The optical fiber holding device according to claim 2, wherein the fiber holder material has a thermal expansion coefficient larger than that of the glass sealing material.   The optical fiber holding device of claim 2, wherein a compression seal is formed.   The optical fiber holding device according to claim 2, wherein the fiber holder material has a thermal expansion coefficient that substantially matches a thermal expansion coefficient of the glass sealing material.   The optical fiber holding device according to claim 1, wherein the fiber holder is made of stainless steel, Kovar, or Invar.   The optical fiber holding device according to claim 1, wherein the fiber holder has a sealed holding cavity formed at least in part in the bore or slot of the holder.   The optical fiber holding device according to claim 1, wherein the fiber has a polyimide protective coating made of polyimide, carbon / polyimide, or carbon / silicon / PFA.   The optical fiber holding device according to claim 1, wherein the fiber has a metal protective coating made of gold, copper, or aluminum.   The optical fiber holding device according to claim 13, wherein the sealing material is a metal alloy.   The optical fiber holding device according to claim 14, wherein the sealing material is a metal alloy solder including lead, tin, silver, indium, gold, or copper. A second fiber holder having a bore or slot, the bore or slot extending along a longitudinal axis of the fiber holder;
The optical fiber provided with a protective coating passes through the bore or slot in the second fiber holder and is oriented parallel to the longitudinal axis of the second fiber holder;
A second glass or metal seal, wherein the second glass or metal seal is formed around the optical fiber, and at least a portion is formed in the bore or slot of the fiber holder; Forming a seal between the coated optical fiber and the second fiber holder;
2. The optical fiber holding device according to claim 1, wherein the first and second fiber holders are spaced along the optical fiber while forming two securing points along the fiber. One or more additional fiber holders, each of the additional fiber holders having a bore or slot extending along the longitudinal axis of the fiber holder;
An optical fiber provided with the protective coating passes through the bore or slot of each of the additional fiber holders and is oriented parallel to the longitudinal axis of each of the additional fiber holders;
For each of the additional fiber holders, an additional glass or metal seal for each of the additional fiber holders is around the optical fiber and at least partially within the bore or slot of the additional fiber holder. Forming a seal between the coated optical fiber and each of the additional fiber holders;
The optical fiber holding device according to claim 16, wherein the fiber holders are spaced along the optical fiber while forming a plurality of retaining points along the optical fiber.   The optical fiber holder of claim 16, wherein the fiber includes a Bragg grating disposed between the two anchor points.   The optical fiber holder of claim 17, wherein the fiber includes a Bragg grating between one or more anchor points.   The optical fiber holding device of claim 16, wherein the fiber includes a long-term grating between the two anchor points. An optical sensor,
An optical fiber holding device according to claim 16,
A fixture for maintaining the first fiber holder and the second fiber holder with their axial bores aligned;
At least a portion of the fixture is elastic in relation to expansion, compression, or both along the longitudinal axis, and one or more optical properties of the optical fiber change when subjected to axial strain. , Light sensor.   The optical sensor of claim 21, wherein the seal is a glass seal.   The optical sensor according to claim 21, wherein the seal is made of metal alloy solder.   The optical sensor according to claim 21, which is an apparatus for measuring strain.   The optical sensor according to claim 21, wherein the optical sensor is a device for measuring displacement.   The optical sensor according to claim 21, wherein the optical sensor is a device for measuring temperature.   The optical sensor according to claim 21, which is a device for measuring pressure.   The optical sensor according to claim 21, which is an apparatus for measuring acceleration.   A method for measuring strain in an optical fiber employing the optical sensor of claim 21.   A method of mounting an optical fiber having a protective coating in a fiber holder, the method comprising providing a glass or metal seal between the fiber holder and the coated optical fiber.   32. The method of claim 30, wherein the glass or metal seal is formed in a sealed retention cavity formed at least in part in a bore or slot in the fiber holder.   32. The method of claim 31, wherein the entire optical fiber extends over the entire length of the bore or slot of the fiber holder.

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