Optical waveguide tube

Abstract: In an optical waveguide tube comprising a tubular cladding filled with a solid core having a higher refractive index than the cladding, a ferrule surrounding the outer periphery of the cladding at each end is fastened for securing the cladding to the core at each end for preventing the core from projecting out of the cladding. The ferrule may have a collar disposed in abutment with the core end face.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an optical waveguide tube comprising a tubular cladding filled with a solid core having a higher refractive index than the cladding. Prior Art Optical waveguide tubes comprising a transparent core and a tubular cladding around the core having a lower refractive index than the core have been used in a variety of optical transmission applications. It is a routine to increase the diameter of the core to 3 mm or greater in order to effectively transmit a larger amount of light. Both solid and liquid cores are known in the art. The solid cores, especially plastic single cores are advantageous because of ease of handling, for example, ease of cutting to a desired length. Optical waveguide tubes of this type receive light from a light source at one end face of the solid core, transmit light therethrough, and emit light from an opposite end face of the core. Since the one end face of the core is given by cutting, it contains minute irregularities so that entrance efficiency is low. Even if the one end face is worked to a smooth surface by polishing, dust and debris deposit thereon from the outside. When light from a light source directly reaches the one end face, part of light is absorbed by such contaminants and converted into heat. This means that all the light incident on the one end face of the core is not transmitted by the core so that the efficiency of light transmission may be reduced. Additionally, since the incident light has relatively high energy, the one end face is heated to a relatively high temperature so that the core may be thermally expanded or deteriorated and even burnt at the one end face, leading to a risk of fire. The core end face can be clouded white in the presence of moisture, also leading to a loss of transmittance. There is a demand for overcoming these problems. When the core undergoes thermal expansion due to direct exposure to light and changes in the ambient atmosphere, the core can project out of the cladding because of the difference in coefficient of thermal expansion between the core and the cladding, especially when the cladding is made of a fluoro resin. The position of light incidence then changes to alter the quantity of incident light. Also the end face of the core and the outer periphery of its projecting portion can be deformed to alter transmission capability. These undesirably change the efficiency of light incidence. Particularly when the core is formed of flexible plastic materials such as acrylic resins, the core is more likely to project out of the cladding. Such core projection leads to losses of light incidence efficiency and light quantity transmitted. Once the core projects out of the cladding, the tube does not always resume the original state when the temperature is restored. The tube can be fixed with the core projected. This is undesirable especially at the incident side. WO 94 11768 A relates to a fibre termination comprising a protective tubular member surrounding the end portion of an optical fibre which fibre comprises a glass filament and a protective sheath surrounding said filament wherein the end portion of said filament is exposed to facilitate optical connection thereto. WO 82 02604 A relates to an optical fiber assembly comprising an elongated optical fiber having ends, a sheath surrounding said optical fibrer, and a window within said sheath. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide tube of the solid single core type which prevents the core end face from being directly heated upon exposure to light, and which prevents the core from projecting out of the cladding. Broadly stated, the present invention is directed to an optical waveguide tube comprising a tubular cladding filled with a solid core having a higher refractive index than the cladding. The tube and hence, the core has axially opposed end faces on light incident and emergent sides. The object of the invention is achieved by an optical waveguide tube according to claim 1. The close contact between the window member and the core is preferably attained by bonding the window member to the core end face with an adhesive. The optical waveguide tube of the invention becomes more advantageous when the core is formed of a flexible plastic material and the window member is formed of an inorganic glass material. The optical waveguide tube of the invention is of the solid single core type wherein light from a light source directly reaches the core for light entry. In such application, various inconvenient problems arose with conventional waveguide tubes. In the optical waveguide tube of the invention wherein a light transmissive window member is disposed in close contact with at least the incident end face of the core, light from a light source reaches the window member and enters the core through the window member. This prevents heat generation by direct entry of incident light to the core end face due to light absorption by fine irregularities and deposits on the core end face, and thus prevents the core from being directly heated by light irradiation. This, in turn, prevents the core from thermal expansion and deterioration and eliminates the risk that the core end face is heated by high energy light to a temperature high enough to burn to cause a fire. Also the window member prevents dust and contaminants from depositing on the core end face and shuts off moisture from the ambient atmosphere so that the core may experience a minimal loss of transmittance. Ultraviolet radiation which otherwise enters the core is absorbed by the window member so that only a reduced quantity of ultraviolet radiation enters the core, minimizing deterioration of the core by direct incidence of ultraviolet radiation on the core end face. These advantages become more prominent when the window member is made of inorganic glass. The present invention is very effective to optical waveguide tubes wherein the core is made of a flexible plastic material which is relatively less resistant to heat, has a high efficient of thermal expansion, and is likely to undergo thermal deterioration. In an optical waveguide tube according to the invention, a securing means is disposed around the cladding and the window member for securing the window member to the cladding. The securing means is a tape wrapped around the cladding and the window member or a sleeve and a ferrule surrounding the cladding and the window member,wherein the tape or the sleeve is disposed between the ferrule and the cladding. The tape may be wrapped on the outer periphery of the cladding and the window member with an adhesive, typically pressure-sensitive adhesive intervening therebetween. This is simply accomplished by using a pressure-sensitive adhesive tape. The sleeve may be a heat shrinkable sleeve which is heat shrunk to cover the outer periphery of the cladding and the window member. It is also possible that the heat shrunk sleeve surrounds the cladding via the tape wrapping. It is also effective to adhesively bond the ferrule to the cladding. In addition to the advantages described above, the optical waveguide tube of the invention has the advantage that if the window member is secured to the cladding by wrapping a pressure-sensitive adhesive tape or fitting a heat shrinkable sleeve each together with a ferrule, the window member restricts axial motion of the core within the cladding, eliminating the inconvenience that the core might project out of the cladding due to thermal expansion when the ambient atmosphere is hot. Even in the optical waveguide tube wherein the window member is in close contact with the core end face for protection, if the core can project out of the cladding, then dust and contaminants will deposit on the outer periphery of the projecting core portion, the core will absorb moisture through the projecting portion, and light and heat will directly act on the projecting core portion. The embodiment of the invention wherein the core is firmly secured to the cladding is effective for preventing the core from projecting out of the cladding, eliminating the inconvenient problems described just above. This ensures that the core is protected by the window member. Preferably, a light transmissive window member of inorganic glass is disposed in close contact with at least the end face on a light incident side by adhesive or other bonding means. When the ferrule is fastened to the cladding, a tape or sleeve of flexible plastic material is interposed between the ferrule and the cladding. Particularly when the window member is in close fit with the core end face, a tape may be continuously wrapped on the cladding and the window member with an adhesive, typically pressure-sensitive adhesive intervening therebetween, or a heat shrinkable sleeve is fitted over the cladding and the window member and heat shrunk thereto, or a heat shrinkable sleeve is fitted over the tape wrapping and heat shrunk thereto, for the purpose of securing the window member to the cladding. In these cases, the ferrule is fitted over the tape wrapping or the sleeve and fastened to the cladding. The optical waveguide tube of the invention is of the solid single core type. Since the solid core is firmly secured to the cladding by fastening the ferrule thereover, the invention prevents the core from projecting out of the cladding due to thermal expansion, eliminating the above-mentioned problems including reduced efficiency of light incidence and deformation of the projecting core end. Even when the core end is heated, the metallic ferrule characterized by effective heat transfer and heat dissipation is effective for quickly dissipating the heat to the outside. In this regard, the ferrule minimizes thermal influence on the core end. Where a light transmissive window member is disposed in close contact with at least the incident end face of the core, it prevents heat generation by direct entry of incident light to the core end face and thus prevents the core from thermal expansion. In an optical waveguide tube according to the invention, the ferrule may be a tubular member which is secured to the cladding at each end for surrounding the outer periphery thereof. The member can have at one end a radially inwardly extending collar which is abutted against the core end face. The tubular member may be a metallic ferrule having a radially inwardly extending collar at one end. In this case, by fastening or crimping the ferrule, the ferrule is secured to the cladding for securing the core to the cladding. A tape or sleeve of plastic material is interposed between the ferrule and the cladding. Also, a light transmissive window member of inorganic glass is disposed in close contact with at least the end face on a light incident side by adhesive or other bonding means. In a preferred embodiment, the collar of the tubular member is abutted against the outer surface of the window member. Where the tubular member is a ferrule which is fastened to the cladding, a tape or sleeve of flexible plastic material is interposed between the ferrule and the cladding. Particularly when the window member is in close fit with the core end face, a tape is continuously wrapped on the cladding and the window member with an adhesive, typically pressure-sensitive adhesive intervening therebetween, or a heat shrinkable sleeve is fitted over the cladding and the window member and heat shrunk thereto, or a heat shrinkable sleeve is fitted over the tape wrapping and heat shrunk thereto, for the purpose of securing the window member to the cladding. In these cases, the ferrule is fitted over the tape wrapping or the sleeve and fastened to the cladding. The optical waveguide tube of the invention is of the solid single core type. If the annular collar of the tubular member at the inner surface abuts the end face of the core or the outer surface of the window member where the window member is in close fit with the core end face, the invention prevents the core from projecting out of the cladding due to thermal expansion, eliminating the above-mentioned problems including reduced efficiency of light incidence and deformation of the projecting core end. Where the tubular member is a metallic ferrule which is fastened to the cladding, the core is firmly secured to the cladding so that projection of the core from the cladding is more effectively prevented. Even when the core end is heated, the metallic ferrule characterized by effective heat transfer and heat dissipation is effective for quickly dissipating the heat to the outside and hence, minimizing thermal influence on the core end. Where the light transmissive window member is disposed in close contact with at least the incident end face of the core, it prevents heat generation by direct entry of incident light to the core end face and thus prevents the core from thermal expansion. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmental cross-sectional view of an optical waveguide tube according to a Reference embodiment. FIG. 2 is a fragmental cross-sectional view of another optical waveguide tube according to a Reference embodiment. FIG. 3 is a fragmental cross-sectional view of an optical waveguide tube according to a Reference embodiment. FIG. 4 is a fragmental cross-sectional view of another optical waveguide tube according to a Reference embodiment. FIG. 5 is a fragmental cross-sectional view of a further optical waveguide tube according to a Reference embodiment. FIG. 6 is a fragmental cross-sectional view of a still further optical waveguide tube according to a Reference embodiment. FIG. 7 is a fragmental cross-sectional view of one exemplary optical waveguide tube according to the invention. FIG. 8 is a fragmental cross-sectional view of another exemplary optical waveguide tube showing the light exit side. FIG. 9 is a fragmental cross-sectional view of one exemplary optical waveguide tube showing another light exit side. FIG. 10 is a fragmental cross-sectional view of another exemplary optical waveguide tube according to the invention. FIG. 11 is a fragmental cross-sectional view of a further exemplary optical waveguide tube FIG. 12 is an enlarged front view of the tube of FIG. 11. BEST MODE FOR CARRYING OUT THE INVENTION Various embodiments of the present invention as well as Reference embodiments are described below in conjunction with the figures. Optical waveguide tubes have the same basic structure throughout the figures. That is, an optical waveguide tube generally designated at 1 is illustrated as comprising a tubular transparent cladding 2 which is filled with a solid core 3 having a higher refractive index than the cladding 2. The tube 1 and hence, the core 3 has axially opposed end faces on light incident and emergent sides although only the light incident side is shown in the figures. In a Reference embodiment, as shown in FIG. 1, the optical waveguide tube 1 further includes a light transmissive window member 4 disposed in close contact with at least the end face of the core on the light incident side, preferably with each of the end faces of the core. The window member 4 is in close fit with the core end face over its entire surface. In the illustrated Reference embodiment, the close contact is attained by bonding the window member 4 to the core 3 end face with an adhesive 5. The window member 4 may be closely contacted or bonded to either only the end face of the core 3 as shown in FIG. 1 or both the end faces of the core 3 and the cladding 2 as shown in FIG. 2 although the latter is preferred. The window member and the core are in close contact so that no air layer intervenes therebetween, thereby increasing the efficiency of light incidence from the window member to the core. The adhesive bonding of the window member to the core, preferably to both the core and the cladding at the end face thereof minimizes projection or retraction of the core relative to the cladding even when the core is thermally expanded or contracted as a result of a temperature variation of the service atmosphere and the presence or absence of light irradiation. The hollow tubular cladding is preferably made of plastic and elastomeric materials which are flexible, moldable into tubing, and have a relatively low refractive index. Exemplary cladding materials include polyethylene, polypropylene, polyamide, polystyrene, ABS resins, polymethyl methacrylate, polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, ethylene-vinyl alcohol copolymers, fluoro-resins, silicone resins, natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymers, butyl rubber, halogenated butyl rubber, chloroprene rubber, acryl rubber, EPDM, acrylonitrile-butadiene copolymers, fluoro-rubber, and silicone rubber. Preferred among others are silicone polymers and fluorinated polymers having a low refractive index. Examples include silicone polymers such as polydimethylsiloxane polymers, polymethylphenylsiloxane polymers, and fluorosilicone polymers; polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), tetrafluoroethylene-perfluoroalkoxy ethylene copolymers (PFE), polychlorotrifluoroethylene (PCTFE), ethylene tetrafluoride-ethylene copolymer (ETFE), polyvinylidene fluoride, polyvinyl fluoride, vinylidene fluoride-trifluorochloroethylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymers, tetrafluoroethylene-propylene rubber, and fluorinated thermoplastic elastomers. These materials may be used alone or in admixture of two or more. The solid material of which the core is formed may be selected from various materials which have a higher refractive index than the cladding. Flexible plastic materials are preferred in the practice of the invention. More particularly, homopolymer and copolymer resins of (meth)acrylic monomers are preferably used. More preferred are copolymers of at least one monomer selected from Groups A and B shown below and homopolymers and copolymers of a monomer selected from Group B. Group A: Esters of (meth)acrylic acid with lower alcohols having 1 to 5 carbon atoms. Group B: Monomers of general formulae (1) and (2) shown below. In formula (1), R 1 is a hydrogen atom or methyl group, R 2 is an alkyl group having 8 to 20 carbon atoms. In formula (2), R 3 is a hydrogen atom or methyl group, R 4 is an alkyl or aryl group, letter n is an integer of 1 to 10, and m is an integer of 1 to 10. The light transmissive material of which the window member is formed includes inorganic glass materials such as quartz glass, Pyrex® glass, multicomponent glass, sapphire, and rock crystal, and organic glass and plastic transparent materials such as polyethylene, polypropylene, ABS resins, acrylonitrile-styrene copolymers, styrene-butadiene copolymers, acrylonitrile-EPDM-styrene terpolymers, styrene-methyl methacrylate copolymers, (meth)acrylic resins, epoxy resins, polymethylpentene, allyl diglycol carbonate resins, spiran resins, amorphous polyolefins, polycarbonates, polyamides, polyarylates, polysulfones, polyallylsulfones, polyether sulfones, polyether imides, polyimides, polyethylene terephthalate, diallyl phthalate, fluoro-resins, polyester carbonates, and silicone resins. Among these, inorganic glass materials such as quartz glass, Pyrex® glass, and multicomponent glass offer superior performance since they are not only highly transparent, but also heat resistant and chemically stable. Where the window member is adhesively bonded to the core, the adhesive may be selected from transparent adhesives, for example, adhesives based on acrylic resins, epoxy resins, phenolic resins, cyanoacrylate resins, silicone resins, and chloroprene rubber. In the practice of the invention, the window member is preferably formed as a disc having an axial thickness of 0.1 to 5 cm, especially 0.3 to 2 cm. The incident end face of the window member is preferably finished to a smooth surface for increasing the efficiency of light incidence on that end face. Although the optical waveguide tube of the invention favors to use an adhesive as means for providing close contact between the window member and the core, it is acceptable, for example, to interpose grease between the core and the window member and securing the window member to the cladding by suitable coupling means. In either case, it is preferred that the window member and the core are in close contact so that no air layer intervenes therebetween. Heat fusing is also acceptable. Owing to the window member attached to the end face of the core, the optical waveguide tube prevents heat generation by direct entry of incident light to the core end face, thereby minimizing thermal expansion and deterioration by such heat generation and eliminating the risk of the core burning and catching fire. It also prevents deterioration of the core end face by deposition of contaminants from the ambient atmosphere and penetration of moisture. The tube thus maintains a superior light transmitting function. In an embodiment of the invention, the optical waveguide tube having a light transmissive window member disposed in close contact with at least the end face of the core on the light incident side over its entire surface further includes securing means disposed around the cladding and the window member for securing the window member to the cladding. The securing means may be a tape continuously wrapped around the cladding and the window member or a sleeve each together with a ferrule surrounding the cladding and the window member. In one Reference example, as illustrated in FIG. 3, a heat shrinkable sleeve or tubing 6 is fitted so that it may cover the outer periphery of an end portion of the cladding 2 and the entire outer periphery of the window member 4 whereupon the sleeve 6 is heat shrunk to tightly fit on the cladding 2 and the window member 4 for firmly securing the window member 4 to the cladding 2. In another Reference example, as illustrated in FIG. 4, a pressure-sensitive adhesive tape 7 is tightly wound on the outer periphery of an end portion of the cladding 2 and the entire outer periphery of the window member 4 for firmly securing the window member 4 to the cladding 2. In a further Reference example, as illustrated in FIG. 5, a pressure-sensitive adhesive tape 7 is wound on the cladding 2 and the window member 4 as in the Reference embodiment of FIG. 4 and a heat shrinkable sleeve 6 is fitted over the tape wrapping 7 and heat shrunk for tight fit. The pressure-sensitive adhesive tape used herein may be selected from those adhesive tapes prepared by coating substrates such as fabric, nonwoven fabric, plastic films and metal films with pressure-sensitive adhesives of acrylic, butyl rubber, natural rubber, hot melt, and silicone systems, for example. The substrates include films of polyamide resins, polyethylene terephthalate resins, fluoro-resins, polypropylene resins, polyethylene resins, polyimide resins (e.g., Kapton®), glass fibers, brass, aluminum, copper, and stainless steel as well as metallized plastic films. The heat shrinkable sleeve used herein may be selected from tubes of Teflon®, PFA, FEP, dual TFE/FEP, synthetic rubber, polyethylene, silicone rubber, and polyvinyl chloride systems. In the invention, the way of wrapping a tape or fitting a sleeve is not limited to the illustrated examples. For example, a plastic tape or sleeve may be bonded to the outer periphery of the cladding and the window member while separately applying an adhesive. An adhesive may be coated to the outer periphery of the cladding and the window member before a heat shrinkable sleeve is heat shrunk thereto. FIG. 6 shows a further Reference example of the optical waveguide tube. A ferrule 8 is bonded to an end portion of the cladding 2 and the window member 4 with an adhesive 5' so as to surround the outer periphery of the cladding end portion and the entire outer periphery of the window member 4. This Reference example has the same function and results as the above-mentioned Reference examples. Upon adhesive bonding of the ferrule 8 to the cladding 2, preferably the cladding at its outer periphery is previously subject to surface treatment for improving adhesion, for example, surface treatment with sodium-based agents and plasma treatment. The adhesive 5' used herein may be the same as that used in bonding the window member to the core end face. The ferrule 8 may be either metallic or plastic. The metallic ferrule which is improved in heat transfer has the function of quickly dissipating heat even when the core end is heated. The metallic ferrule may be made of stainless steel, aluminum, copper, brass, iron and plated such metals. In addition to the advantages mentioned above the optical waveguide tube according to the embodiment of the invention has the advantage of eliminating the inconvenience that the core projects out of the cladding when the core undergoes thermal expansion. Referring to FIG. 7, the embodiment of the invention is described. In the example as shown in FIG. 7, the optical waveguide tube comprising a tubular transparent cladding 2 and a solid core 3 encased therein having a higher refractive index than the cladding further includes a ferrule 9 surrounding the outer periphery of the cladding at each end. The ferrule 9 is fastened at 10 for securing the cladding 2 to the core 3 at each end. A light transmissive window member 4 as previously described is disposed in close contact with at least the end face of the core 3 on the light incident side, preferably with each of the end faces of the core 3. In the illustrated embodiment, the close contact is attained by bonding the window member 4 to the core 3 end face with an adhesive 5. The window member 4 may be closely contacted or bonded to either only the end face of the core 3 or both the end faces of the core 3 and the cladding 2 although the latter is preferred. Further an intermediate layer 11 in the form of a sleeve or tape is interposed between the cladding 2 and the ferrule 9. The ferrule 9 may be provided at its rear end with an annular collar extending radially inwardly therefrom for tip protection. The ferrule 9 may be made of stainless steel, aluminum, copper, brass, iron and plated such metals. The ferrule 9 is preferably fastened to a crimping rate of 10 to 90%, especially 20 to 60%. With a too low crimping rate, the ferrule would be less effective for preventing the core from projecting out of the cladding. Fastening the ferrule to a too high crimping rate would cause an increased optical loss of the core. The fastening method is not critical. The ferrule may be fastened in a three ring pattern as shown in FIGS. 7 and 8 or a four ring pattern by any desired caulking means. Zone fastening is also acceptable. The crimping rate used herein is a percent deformation of the entire optical waveguide tube including the intermediate layer (tape or sleeve) if any. It is empirically determined according to the following equation (see FIG. 8). Crimping rate (%) = D 3- tƒ D 1+ tc + ti x 100 tc: a gage of the cladding ti: a gage of the intermediate layer tf: a gage of the ferrule D1: an outer diameter of the core D2: an outer diameter of the cladding D3: a diameter of a crimped groove Before the ferrule 9 is fastened to firmly secure the core 3 to the cladding 2, a plastic tape or sleeve 11 is interposed between the ferrule 9 and the cladding 2 as shown in FIG. 7. Particularly when the window member 4 is disposed in close contact with the core end face, better results are obtained by using a pressure-sensitive adhesive tape as the intermediate layer 11 and wrapping the tape around the cladding 2 and the window member 4 so as to cover the outer periphery of an end portion of the cladding 2 and the entire outer periphery of the window member 4 for coupling the window member 4 to the cladding 2. By coupling the window member 4 to the cladding 2, the core 3 is also restricted by the window member 4 so that projection of the core 3 from the cladding 2 is more positively prevented. A heat shrinkable sleeve may be used as the intermediate layer 11 instead of the adhesive tape. The heat shrinkable sleeve 11 is fitted around the cladding 2 and the window member 4 so as to cover the outer periphery of an end portion of the cladding 2 and the entire outer periphery of the window member 4. The heat shrinkable sleeve 11 is heat shrunk for coupling the window member 4 to the cladding 2. The ferrule 9 is fastened over the tape or sleeve 11 to provide tighter anchoring effect. It is also possible to wrap a tape on the cladding and the window member, fit a heat shrinkable sleeve on the tape wrapping, and heat shrink the sleeve before a ferrule is fitted and fastened in place. The type and wrapping of a pressure-sensitive adhesive tape, the type of a heat shrinkable sleeve and the like are the same as previously described. Preferably the intermediate layer 11 is made of a material having a lower modulus than the core and the cladding, low creep, and high frictional resistance with respect to the cladding and the ferrule for the purposes of minimizing deformation of the core to reduce optical losses and preventing removal of the sleeve. Referring to FIGS. 10, a further embodiment of the invention is described. In an optical waveguide tube according to this embodiment, a light transmissive window member 4 is disposed in close contact with at least the end face on the light incident side, preferably with each of the end faces on the light incident and emergent sides. In this case, the collar 13 of the tubular member 12 is abutted against the outer surface of the window member 4. The close contact of the window member 4 is typically achieved by bonding the window member 4 to the end face of the core 3 with an adhesive 5. The tubular member 12 may be either metallic or plastic. The tubular member 12 is secured to the cladding 2 by any desired means, for example, adhesive bonding and mechanical fastening. Preferably the tubular member 12 is a metallic ferrule having a radially inwardly extending collar at one end. In this case, the ferrule may be secured to the cladding with the aid of an adhesive as mentioned above, but preferably by mechanically fastening the ferrule. At the same time as the ferrule is secured to the cladding, the core is secured to the cladding. The ferrule may be made of stainless steel, aluminum, copper, brass, iron and plated such metals. The ferrule is preferably fastened to a crimping rate of 10 to 90%, especially 20 to 60%. The crimping rate used herein is as defined above. With a too low crimping rate, the ferrule would be less effective for securing the core to the cladding. Fastening the ferrule to a too high crimping rate would cause an increased optical loss of the core. The fastening method is not critical. The ferrule may be fastened in a three ring pattern as shown in FIG. 10 or a four ring pattern by any desired caulking means. In the example shown in FIG. 10, the ferrule 12 is fastened at 14 to the cladding 2 through an intermediate layer 15 in the form of a tape or sleeve. The intermediate layer 15 is the same as the intermediate layer 11 previously described in conjunction with FIG. 7. The shape of the collar of the tubular member 12 is not limited to the annular one 13 shown in FIGS. 10. The collar may be discontinuous, that is, consist of a plurality of spaced-apart tabs 16 extending from the inner surface of the tubular member 12 as shown in FIG. 12. The collar is only required to engage the core 3 or window member 4 for retaining it. The collar 13 of the tubular member 12 defines the opening 13a which may have a diameter as small as about 1 mm if the light source is a beam light source such as a laser. However, the opening 13 preferably has a larger diameter so that light may enter the core without obstruction. The optical waveguide tubes of the embodiments of the invention prevent projection of the core from the cladding due to thermal expansion of the core, thereby eliminating inconvenient problems such as a reduced efficiency of light incidence and deformation of a projecting end portion of the core. The provision of the metallic ferrule improves heat dissipation at the core end, suppressing thermal expansion and deterioration of the core. Where the light transmissive window member is in close contact with the end face of the core on the light incident side, the window member prevents heat generation at the core end face by direct irradiation of light from a light source to the core end face, thereby minimizing thermal expansion and deterioration and eliminating the risk of the core giving rise to combustion and fire. The window member also prevents deterioration of the core by deposition of contaminants on the core end face from the surrounding atmosphere and penetration of moisture, helping the core maintain a stable light transmitting function. As the window member is secured to the cladding, the above-mentioned projection of the core from the cladding is more effectively prevented. The securing ensures that the core is protected by the window member. EXAMPLE Reference Examples and Examples of the present invention are given below by way of illustration and not by way of limitation. Reference Example 1 An optical waveguide tube having a diameter of 10 mm was prepared using a FEP tube with a gage of 0.6 mm as the cladding and a 4/6 copolymer of Acrylate M and Acrylate SL (manufactured by Mitsubishi Rayon K.K.) as the core. As shown in FIG. 2, a window disc of quartz having a thickness of 1 cm was bonded to one end face of the tube on an incident side using an acrylic adhesive (Photobond 300, Meisei Sunrise K.K.). A similar optical waveguide tube without a window disc was prepared as a control. Both the optical waveguide tubes were coupled to 150-W focus halogen lamps for fiber optics (manufactured by Hayashi Watch K.K.) whereupon a continuous lighting test of burning the lamp for 8 hours a day was carried out for several days. The tube with a window disc remained intact. In contrast, the control tube without a window disc started smoking on the fifth day. At the end of the test, the incident end face of the control tube was observed to find a carbonized area of about 2 mm in diameter. Reference Example 2 An optical waveguide tube having a diameter of 13.6 mm was prepared using a FEP tube with a gage of 0.6 mm as the cladding and a 4/6 copolymer of Acrylate M and Acrylate SL (manufactured by Mitsubishi Rayon K.K.) as the core. As shown in FIG. 5, a window disc of quartz having a thickness of 1 cm was bonded to each end face of the tube using an acrylic adhesive (Photobond 300, Meisei Sunrise K.K.). A pressure-sensitive adhesive tape in the form of a Teflon film of 2 cm wide having an acrylic adhesive coated thereon was wrapped around the tube end and the window disc. A heat shrinkable PFA sleeve of 4 cm long was fitted over the wrapped tape. On the optical waveguide tube having the tape and sleeve mounted thereon, a thermal cycling test consisting of cooling at -30°C for 1 hour and heating at 80°C for 1 hour was continuously carried out for 7 days. Projection of the core from the cladding was not observed during the test. Another optical waveguide tube was similarly prepared as shown in FIG. 6 by treating the outer peripheral surface portion of the cladding on which a ferrule was to be fitted with Tetra-Etch (sodium based surface treating agent by Junko K.K.), then fitting a ferrule on the outer periphery of the cladding and the window disc and bonding the ferrule thereto with an epoxy resin adhesive. From this tube, equivalent results were obtained in the thermal cycling test. Example 1 An optical waveguide tube having a diameter of 13.6 mm was prepared using a FEP tube with a gage of 0.6 mm as the cladding and a 4/6 copolymer of Acrylate M and Acrylate SL (manufactured by Mitsubishi Rayon K.K.) as the core. As shown in FIG. 7, a window disc of Pyrex® having a thickness of 0.5 cm was bonded to each end face of the tube using an acrylic adhesive (Photobond 300, Meisei Sunrise K.K.). A heat shrinkable FEP sleeve with a gage of 0.3 mm was fitted over the cladding end and the window disc to cover the outer periphery thereof. A generally cylindrical stainless steel ferrule having an outer diameter of 16.0 mm, an inner diameter of 14.3 mm and a length of 30 mm was fitted over the sleeve. The ferrule was externally fastened in a triple-ring pattern to a crimping rate of about 40%. On the optical waveguide tube, a thermal cycling test consisting of cooling at -30°C for 1 hour and heating at 80°C for 1 hour was continuously carried out for 7 days. Projection of the core from the cladding was not observed during the test. Example 2 An optical waveguide tube having a diameter of 13.6 mm was prepared using a FEP tube with a gage of 0.6 mm as the cladding and a 4/6 copolymer of Acrylate M and Acrylate SL (manufactured by Mitsubishi Rayon K.K.) as the core. As shown in FIG. 10, a window disc of Pyrex® having a diameter of 13.5 mm and a thickness of 5 mm was bonded to each end face of the tube using an acrylic adhesive (Photobond 300, Meisei Sunrise K.K.). A heat resistant, pressure-sensitive adhesive tape in the form of a Kapton film with a gage of 0.3 mm having a silicone adhesive coated thereon was wrapped around the cladding end and the window disc to cover the outer periphery thereof. A generally cylindrical stainless steel ferrule with an outer diameter of 16.0 mm, an inner diameter of 14.3 mm and a length of 30 mm and having an annular collar with a width of 0.5 mm at a rear end was fitted over the wrapped tape until the collar on the inside surface abutted against the window disc. The ferrule was externally fastened in a triple-ring pattern to a crimping rate of about 40%. On the optical waveguide tube, a thermal cycling test consisting of cooling at -30°C for 1 hour and heating at 80°C for 1 hour was continuously carried out for 7 days. Projection of the core from the cladding was not observed during the test. Although some preferred embodiments have been described, many modifications and variations may be made thereto in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims: An optical waveguide tube having opposed ends and comprising a tubular cladding (2), a solid core (3) within the cladding (2) having a higher refractive index than the cladding (2), wherein the core (3) has opposed end faces, and a ferrule (9) surrounding the outer periphery of the cladding (2) at each end, said ferrule (9) being fastened for securing the cladding (2) to the core (3) at each end, the tube further comprising a light transmissive window member (4) disposed in close contact with at least the end face on a light incident side, characterized in that a tape or a sleeve (11) covering the outer periphery of an end portion of the cladding (2) and the outer periphery of the window member (4) is disposed between said ferrule (9) and said cladding (2), for securing said window member to said cladding. The optical waveguide tube of claim 1 wherein said window member (4) is adhesivley bonded to the core end face. The optical waveguide tube of claim 1 wherein the core (3) is formed of a flexible plastic material and the window member (4) is formed of an inorganic glass material. The optical waveguide tube of claim 1, wherein a tape (11) is wrapped around said cladding (2), and said window member (4), with an adhesive intervening therebetween, for securing said window member (4) to said cladding (2), and the ferrule (9) is fitted over the tape wrapping (11) and fastened to said cladding (2). The optical waveguide tube of claim 1, wherein a heat shrinkable sleeve (11) is fitted over said cladding (2) and said window member (4) and heat shrunk for securing said window member (4) to said cladding (2) and the ferrule (9) is fitted over the sleeve (11) and fastened to said cladding (2). The optical waveguide tube of claim 1, wherein a tape (11) is wrapped around said cladding (2) and said window mem-ber (4) with an adhesive intervening therebetween, and a heat shrinkable sleeve (11) is fitted over said tape wrapping and heat shrunk for securing said window member (4) to said cladding (2), the ferrule (9) being fitted over the sleeve (11) and fastened to said cladding (2). An optical waveguide tube according to any one of claims 1 to 6 wherein the ferrule (9) is a tubular member secured to said cladding (2) at each end for surrounding the outer periphery thereof, said member having a radially inwardly extending collar which is abutted against the core end face or against the outer surface of said window member (4). The optical waveguide tube of claim 7 wherein said tubular member is a metallic ferrule (9) which is fastened to said cladding (2). The optical waveguide tube of claim 7 wherein said tubular member is a metallic ferrule (9) which is fastened to said cladding (2) and said window member (4).

Inventors: HASHIMOTO TORAO, HOTTA ATSUSHI, ISHIHARADA MINORU, SUGIMACHI MASATO, SUGIYAMA HIDEO, TANUMA ITSUO, HASHIMOTO, TORAO, HOTTA, ATSUSHI, ISHIHARADA, MINORU, SUGIMACHI, MASATO, SUGIYAMA, HIDEO, TANUMA, ITSUO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1996
Main classification: G02B6
IPC codes: G02B6