JP2014066923A - Endoscope and endoscope light guide fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an endoscope 1 that makes a concave lens unnecessary in an illumination optical system.SOLUTION: An endoscope 1 comprises: an insertion part 31 through which a light guide 6 having a plurality of optical fibers 10 composed of a core made of glass with a refractive index n1 being more than 1.61 and less than 1.74 and a clad made of a plastic with a refractive index n2 being more than 1.33 and less than 1.44, in which an outer diameter of the core is more than 90% of the clad and less than 99.6% thereof and a numerical aperture NA is more than 0.899 and less than 0.997, is inserted and which emits light guided by the light guide 6 from a tip end via plane-shape cover glass 30 instead of the concave lens; an operation part 37 that is arranged at an edge of the insertion part 31; and a universal code 38 which extends from the operation part 37 and in which a light guide connector 34 connecting the light guide 6 to a light source device 24 is arranged.

Description

  Embodiments described herein relate generally to an endoscope light guide fiber that is a plastic clad optical fiber including a glass core and a plastic clad, and an endoscope including the endoscope light guide fiber.

  As shown in FIG. 1, the optical fiber 10 includes a core 11 that transmits light, and a cladding 12 that is provided on the outer peripheral surface of the core 11 and reflects the light so that the light does not leak out from the side of the core. Yes. In the plastic clad optical fiber, the core 11 is made of glass, and the clad 12 is made of plastic having a refractive index lower than that of the core 11. The ratio (D1 / D2) of the outer diameter D1 of the core 11 to the outer diameter D2 of the cladding 12 (optical fiber 10) varies greatly depending on the application.

  Japanese Patent Application Laid-Open No. 7-218734 discloses a communication optical fiber having quartz as a core and a resin having a fluoroalkyl group as a clad. This optical fiber had a core refractive index n1 = 1.49, a clad refractive index n2 = 1.37, and a numerical aperture NA = 0.51. In the communication optical fiber, for example, when the core outer diameter D1 is 15 μm, the cladding outer diameter D2 is 125 μm, and D1 / D2 = 12%.

  On the other hand, unlike an optical fiber for communication, an endoscope light guide fiber has a large D1 / D2 so as to guide a large amount of light. The endoscope uses an imaging optical system having a wide angle of view, for example, an angle of view θ1 of 140 degrees to 170 degrees in order to observe a wide range of nearby subjects. For this reason, the light guided by the light guide is widened by a concave lens.

  However, the diameter of the concave lens for widening the angle of view is 10 to 20% larger than the diameter of the light guide. For example, when the diameter of the light guide is 1 mm, the diameter of the concave lens is 1.1 to 1.2 mm. For this reason, there existed a possibility of becoming a hindrance to the diameter reduction of an endoscope. Moreover, not only the cost of the concave lens but also the operations such as alignment adjustment may hinder the production cost. Further, the concave lens is designed in consideration of chromatic aberration and the like, but there is a possibility that the influence of the chromatic aberration becomes remarkable particularly in the outer peripheral portion of the irradiation range.

  Therefore, there has been a demand for an endoscope that does not require a concave lens in an endoscope light guide fiber and an illumination optical system having a high numerical aperture (NA).

  As shown in FIG. 2, hundreds or more of optical fibers 10 are bundled and filled in, for example, a silicone tube 6 </ b> A and used as the light guide 6.

JP-A-7-218734

  An object of the present invention is to provide an endoscope that does not require a concave lens in an illumination optical system and a light guide fiber for an endoscope with a high numerical aperture.

  An endoscope according to an embodiment of the present invention includes a core made of glass having a refractive index n1 of 1.61 to 1.74, and a clad made of plastic having a refractive index n2 of 1.33 to 1.44. A light guide having a plurality of optical fibers each having an outer diameter of the core of 90% to 99.6% of an outer diameter of the clad and a numerical aperture NA of 0.899 to 0.997. The light guide guided by the light guide is inserted from a distal end portion through a flat cover glass instead of a concave lens, an operation portion disposed at the base end of the insertion portion, and an operation portion. And a universal cord provided with a light guide connector for connecting the light guide to the light source device.

  Moreover, the light guide fiber for endoscopes of another embodiment has a core made of glass having a refractive index n1 of 1.61 to 1.74, and a refractive index n2 of 1.33 to 1.44. A clad made of plastic, and a numerical aperture NA of 0.899 or more and 0.997 or less.

  According to the present invention, it is possible to provide an endoscope that does not require a concave lens in the illumination optical system and an endoscope light guide fiber having a high numerical aperture.

It is a schematic diagram of the structure of an optical fiber. It is a schematic diagram of the light guide for endoscopes. It is a lineblock diagram of an endoscope system containing an endoscope of an embodiment. It is the graph which showed the range of the refractive index of the core glass of the optical fiber of embodiment, and the refractive index of clad glass.

First, the endoscope 1 according to the embodiment will be briefly described with reference to FIG.
As shown in FIG. 3, a medical endoscope system 20 including an endoscope 1 includes a processor 21 that processes an image signal, a monitor 22 that displays an endoscopic image, a user's usage conditions, and the like. The input unit 23 for setting the light source and the light source device 24 are provided.

  The endoscope 1 includes an insertion unit 31 in which an imaging unit 33 that captures an endoscope image is disposed at the distal end portion 32 and the light guide 6 is inserted, and an operation unit 37 that is disposed at the proximal end of the insertion unit 31. And a universal cord 38 extending from the operation unit 37 and provided with a light guide connector 34 and an electronic connector 36.

  When the light guide connector 34 is connected to the light source device 24, the light generated by the light source device 24 is guided by the light guide 6 and emitted from the tip end portion 32 through the flat cover glass 30. That is, in the endoscope 1, the illumination light is not increased in angle of view by the concave lens.

  An imaging signal from the imaging unit 33 such as a CCD is transmitted to the processor 21 via the electronic connector 36.

  The insertion portion 31 has, for example, a flex and gabion made of SUS304 having a thickness of 0.2 mm on the outer peripheral portion in order to keep the bendability appropriately, and the outer diameter is 15 mm. It is important to reduce the diameter of the insertion portion 31 for minimally invasiveness. For this reason, the diameter of the light guide 6 is also reduced to, for example, a diameter of 1.8 mm.

  In the endoscope light guide fiber (optical fiber) 10 of the light guide 6, the outer diameter D1 of the core 11 is 90% or more and 99.6% or less of the outer diameter D2 of the clad 12. If it is in the said range, a large amount of irradiation light can be guided efficiently.

  The distal end portion 32 of the endoscope 2 is provided with a cover glass 30 from which light guided by the light guide 6 is emitted, and a concave lens 35 of an imaging optical system that forms a subject image on the imaging unit 33. It is installed. The angle of view θ2 of the illumination light is determined in consideration of the angle of view θ1 of the imaging optical system. However, since the optical fiber 10 of the light guide 6 has a high NA, it is not necessary to widen the angle of view with a concave lens.

  Here, the angle of view θ2 is related to the numerical aperture NA and (Equation 1).

    NA = sinθ2 (Formula 1)

  That is, even if the concave lens is not used, if the numerical aperture NA of the optical fiber 10 is 0.899 or more, 128 degrees can be obtained as the field angle θ2 of the illumination light. Here, θ2 = 128 degrees is smaller than the angle of view θ1 = 140 degrees of the imaging optical system with a wide angle of view, but is a practically allowable lower limit.

  Further, if the numerical aperture NA of the optical fiber 10 is 0.940, it is preferable because θ2 = 140 degrees. If the numerical aperture NA is 0.996, θ2 = 170 degrees. On the other hand, when NA> 0.997, θ2> 170 degrees, which is not preferable because a component that is reflected by the side surface of the cover glass 30 and is not irradiated forward is generated.

  That is, the numerical aperture NA of the optical fiber 10 is 0.899 or more and 0.996 or less, preferably 0.940 or more and 0.996 or less.

  The numerical aperture NA is expressed by (Equation 2) from the refractive index n1 of the glass of the core 11 and the refractive index n2 of the plastic of the cladding 12. The refractive indexes n1 and n2 are values at the e-line.

NA = (n1 ² −n2 ² ) ^1/2 (Formula 2)

  As the plastic used for the clad 12, it is preferable to use an amorphous fluororesin or FEP (tetrafluoroethylene / hexafluoropropylene copolymer) in consideration of the refractive index n2 and the coating treatment on the core glass. The plastic is not limited to amorphous fluororesin and FEP (tetrafluoroethylene / hexafluoropropylene copolymer) alone, but may be a mixture of a plurality of plastics as long as the refractive index is within the limits.

  The following trial manufacture was performed using CYTOP (made by Asahi Glass Co., Ltd.) having a refractive index of n2 = 1.34 as an amorphous fluororesin, and plastic having a refractive index of n2 = 1.43 as FEP.

  The material used for the clad 12 is not limited to Cytop or the like, and a plastic having a refractive index n2 of 1.33 or more and 1.44 or less that is relatively easy to obtain can be used.

  On the other hand, the refractive index n1 of the glass of the core 11 that guides light (core glass) is set so that the numerical aperture NA of the optical fiber 10 is within the above range and the specification of the endoscope 1 is satisfied. It must be 1.61 or more and 1.74 or less, preferably 1.64 or more and 1.74 or less. That is, lead-free glass having a refractive index n1 of 1.64 or more is particularly suitable for the endoscope 1 as will be described later.

  In the range of “A” shown in FIG. 4, NA satisfies the range of 0.899 to 0.996, and the refractive index n1 is 1.61 to 1.74. On the other hand, the range of “B” satisfies the range of NA from 0.899 to 0.996, and the refractive index n1 is from 1.64 to 1.74.

  The optical fiber 10 has a high numerical aperture (NA) and does not need to be widened by a concave lens. Therefore, although the endoscope 1 does not have a concave lens for widening the angle of view, the endoscope 1 can irradiate illumination light having an angle of view θ2 of 128 degrees or more and 170 degrees or less.

  The endoscope 1 can be easily reduced in diameter, has a low manufacturing cost, and does not cause chromatic aberration due to the lens.

  In the endoscope 1, the cover glass 30 preferably has a light scattering function. This is because the endoscope 1 does not use a concave lens in the illumination optical system, so that each optical fiber 10 becomes a point light source and prevents unevenness in the irradiated light. In order to provide the flat cover glass 30 with a light scattering function, it is made into ground glass or fine particles are dispersed. Note that it is preferable that the cover glass 30 has a scattering surface only on the inner surface on the light guide 6 side and a mirror surface on the outer surface from the viewpoint of preventing the adhesion of dirt. Further, as shown in FIG. 3, it is preferable for preventing reflection that the cover glass 30 and the light guide 6 are joined together with an adhesive 30A having a high refractive index so that no air layer is interposed therebetween.

  Here, lead glass is known as a high refractive index glass satisfying the above refractive index n1, but glass containing no lead (lead-free glass) is required in order to cope with the environment.

  Furthermore, the medical endoscope is used while being irradiated with X-rays in order to confirm the position of the distal end portion of the endoscope after being inserted into the body of the subject. Glass is colored by X-ray exposure, with some chemical bonds being broken or distorted. High X-ray resistance is required for the light guide fiber glass of a medical endoscope. However, the known lead-free glass has not been sufficiently studied for X-ray resistance compared to lead-containing glass.

  In medical endoscopes, not only normal light observation using white light but also various special light observations using the wavelength characteristics of irradiation light are performed. For example, narrow band imaging (NBI) is performed by illuminating light in a first wavelength band of 390 nm to 445 nm and two wavelengths that are easily absorbed by hemoglobin in blood, for example, 530 nm to 550 nm. It is a method of easily distinguishing tumor tissue by irradiating light in the second wavelength band and highlighting the capillaries and mucous fine patterns on the mucosal surface layer, and the image information of the blue light region is very important.

  For this reason, lead-free glass for light guide fibers of medical endoscopes is easy to be fiberized, that is, spinnable, and has a refractive index n1 in the above range, as well as X-ray resistance and blue light. Considering the transmittance, it is preferable to satisfy the following conditional expression. “˜” means “above and below”.

(A) (SiO ₂ + B ₂ O ₃ ): 20 to 55 wt%
_(B) SiO 2: 20~55wt%
(C) B ₂ O ₃ : 0 to 10 wt%
(D) X: (BaO + SrO + La ₂ O ₃ + Lu ₂ O ₃ + Ta ₂ O ₅ + Gd ₂ O ₃ + WO ₃ + Nb ₂ O ₅ + Y ₂ O ₃
): 25-72 wt%
(E) ZnO: 0 to 30 wt%
_{(F) Al 2 O 3:} 0~10wt%
(G) ZrO ₂ : 0 to 8 wt%
(H) (Na ₂ O + K ₂ O): 0 to 10 wt%
_{(I) Sb 2 O 3:} 0~0.35wt%
Hereinafter, the above conditions will be described.

(A) (SiO ₂ + B ₂ O ₃ ): 20 to 55 wt%
_(B) SiO 2: 20~55wt%
(C) B ₂ O ₃ : 0 to 10 wt%

Conditions (A) to (C) limit the glass network former component. The reason why SiO ₂ is ₂₀ to 55 wt% is to obtain a stable glass. The amount of B ₂ O ₃ is more preferably 0 to ₂ wt%. B ₂ O ₃ is effective in preventing crystallization of glass and improving X-ray resistance.

(D) X: (BaO + SrO + La ₂ O ₃ + Lu ₂ O ₃ + Ta ₂ O ₅ + Gd ₂ O ₃ + WO ₃ + Nb ₂ O ₅ + Y ₂ O ₃ ): 25 to 72 wt%

Condition (D) includes at least one of BaO, SrO, La ₂ O ₃ , Lu ₂ O ₃ , Ta ₂ O ₅ , Gd ₂ O _3, WO _3, Nb ₂ O _5, or Y ₂ O ₃ , It shows that the total amount is 25 to 72 wt%. Condition (D) is a condition for achieving a refractive index n1 of 1.61 to 1.74. In order to make the refractive index n1 1.61 or more, (BaO + SrO + La ₂ O ₃ + Lu ₂ O ₃ + Ta ₂ O ₅ + Gd ₂ O ₃ + WO ₃ + Nb ₂ O ₅ + Y ₂ O ₃ ) is 39 to 46 wt%. Is preferred.

  BaO is an essential component for obtaining a high refractive index and a high transmittance in the blue region, has an effect on meltability and stability, has an effect, and does not exhibit an adverse effect (hereinafter simply referred to as “effective”). ) Of (D1) BaO: 15 to 35 wt%, preferably 25 to 30 wt%. (D2) The content of SrO is 0 to 15 wt%, and preferably does not exceed the content of BaO.

Here, 26.87wt% of BaO, _La 2 _{O 3} to 9.27wt%, _Ta 2 _{O 5} of 3.00 wt%, i.e. _{(BaO + SrO + La 2 O} 3 + Lu 2 O 3 + Ta 2 O 5 + Gd 2 O 3 + WO 3 The relationship with the amount of B ₂ O ₃ will be described using a La—Ba—Si—B glass having (Nb ₂ O ₅ + Y ₂ O ₃ ) of 39.14 wt% as an example. If La ₂ O ₃ / B ₂ O ₃ is 1 or more in terms of mol%, boron (B) in the glass has a 3-coordination and is slightly colored by X-ray irradiation, but recovery is also fast. When La ₂ O ₃ / B ₂ O ₃ is less than 1 in terms of mol%, boron (B) in the glass has a 4-coordinate structure, and thus it is strongly colored by X-ray irradiation and recovery is slow.

That is, although there is a deep relationship with the content of B ₂ O _3, the content of (D3) La ₂ O ₃ does not gradually increase the possibility of crystallization, so that it is 12.0 wt% or less (3.6 mol% ) Or less, more preferably (D4) 9.3 wt% (2.8 mol%) or less.

(E) ZnO: 0 to 30 wt%
_{(F) Al 2 O 3:} 0~10wt%
(G) ZrO ₂ : 0 to 8 wt%

Conditions (E) to (G) are conditions for achieving high transmittance. When melting with a platinum crucible, in order to reduce the amount of Pt mixed as an impurity, it is necessary to melt at a relatively low temperature (for example, 1000 to 1300 ° C.) and for a short time (for example, 6 hours). Since Al ₂ O ₃ and ZrO ₂ are difficult-to-melt components with high melting points, they are not sufficiently homogeneous when melted at a low temperature for a short time, and remain in the glass as fine particles of several tens to several hundreds of μm. Sometimes. These particles do not pose a problem for lenses having a normal optical path length of several mm to several tens of mm. However, when the particles have a length of several meters such as medical endoscopes, the blue light transmittance is greatly reduced. Becomes a problem.

In addition, even in the case of quartz crucible melting, at a high temperature, the quartz crucible is eroded and SiO ₂ melts into the glass, causing striae and distortion, resulting in poor yield, such as glass cracking, and a desired refractive index. It may not be obtained. For this reason, even in the case of quartz crucible melting, it is necessary to lower the melting temperature. For this reason, it is particularly preferable to satisfy the following conditions (F1) and (F2).

(F1) Al ₂ O ₃ : 0 wt%
(G1) ZrO ₂ : 0 wt%

  In addition, although ZnO of the condition (E) is an optional component, in order to obtain a high refractive index and a high transmittance in the blue region, it has an effect on meltability and stability. Therefore, (E1) 4 to 16 wt% is contained. It is more preferable.

(H) (Na ₂ O + K ₂ O): 0 to 10 wt%
The condition (H) (Na ₂ O + K ₂ O) means at least one of Na ₂ O and K ₂ O, in order to suppress crystallization of the glass and to adjust the viscosity. If Na ₂ O and K ₂ O are too much to reduce the refractive index, the desired refractive index may not be obtained. For this reason, (H1) 4-10 wt% is more preferable.

_{(I) Sb 2 O 3:} 0~0.35wt%
Condition (I) is a condition for high blue light transmittance. Sb ₂ O ₃ is added in an amount of 0.3 to 0.5 wt% in a general optical glass in order to promote homogenization of glass (melting of glass raw materials and clarification to remove bubbles). However, at the added amount, Sb ₂ O ₃ inherently absorbs blue light, so that coloring is remarkable, and the X-ray resistance is also adversely affected, so that characteristics satisfying the specifications of the core glass cannot be obtained.

Sb ₂ O ₃ absorbs light in the blue region. Furthermore, because of the effect of promoting the dissolution of platinum from a platinum crucible, Sb ₂ O ₃ doped glass is likely to increase the absorption in the blue region. For this reason, it is desirable that the amount of Sb ₂ O ₃ added is small from the viewpoint of blue light transmittance. However, glass that does not contain Sb ₂ O ₃ is not preferred to be added in an amount of 0 wt% because it tends to generate heterogeneity and striae due to insufficient stirring during production and absorption due to partial oxygen defects. Sb ₂ O ₃ is more preferably (I1): 0 to 0.050 wt%.

(J) (Na ₂ SO ₄ + K ₂ SO ₄ ): 0.26 to 1.63 wt%.
Condition (J) indicates that a predetermined amount of at least one of Na ₂ SO _{4 and} K ₂ SO ₄ is included, and is an essential condition for realizing homogenization under condition (I). That is, since the amount of Sb ₂ O ₃ in condition (I) is less than the content of general optical glass, the ability to melt the raw material is insufficient, and in order to prevent inhomogeneity (residual residue), High temperature and long melting time is required.

Na ₂ SO ₄ or K ₂ SO ₄ decomposes during melting (for example, 890 ° C.) to generate SO ₂ gas and oxygen gas, so that melting of the raw material is promoted by physical bubbling. If the amount of Na ₂ SO ₄ or K ₂ SO ₄ added to the glass raw material is less than the above range, the melting of the raw material will be insufficiently promoted, and if it exceeds the above range, melting proceeds but excessive SO ₂ gas is scum. Since a foam-like solid containing an element having a relatively low specific gravity such as SiO ₂ or alkali metal is generated, it causes inhomogeneity.

  Next, the glass raw material generally contains impurities. Since impurities of transition metals have absorption in the visible light region, they become a problem in the production of glass that requires high transmittance such as core glass, and should be minimized.

  Specifically, in the core glass, the Fe content is 3 ppm or less, the Cr content is 0.03 ppm or less, the Co content is 0.01 ppm or less, and the Ni content is 0.02 ppm or less. Is more preferable.

  Here, in order to avoid mixing impurities, a paper container or a plastic container was used for the preparation of the core glass raw material of the embodiment, instead of a metal container such as stainless steel or iron or a glass container such as a beaker. A platinum crucible to which zirconia was added or a quartz crucible was used for producing the glass melt, and stirring was performed with a sapphire rod.

  As is clear from the following composition, the composition of the core glass of the embodiment is designed such that the melting point is relatively low, so that the melting time is relatively relatively low, 1000 ° C. to 1300 ° C., and the melting time is 2 hours to 8 hours. It can be melted at a low temperature and in a short time, and even when a platinum crucible is used, mixing of impurities is suppressed. When Pt is mixed, the glass has an absorption in the blue light region, which adversely affects the transmittance and the amount of light. The amount of Pt is preferably 0.2 ppm or less.

  The composition of the core glass of the prototype optical fiber and the characteristics of the optical fiber are shown in (Table 1).

  “Vitrification” was evaluated as “◯” when the raw material was uniformly melted to form a fiber. The blue transmittance (T400) was calculated by making the transmittance of light having a wavelength of 400 nm into a glass sample having a thickness of 30 cm and a glass sample having a thickness of 1 cm (10 mm), and removing surface reflection by calculation. And blue transmittance (T400) evaluated 90% / m or more as "(circle)".

X-ray resistance (XRD) is the amount of light from 380 nm to 750 nm after the X-ray resistance test in which a recovery process of guiding light of 64 lumens / mm ² for 600 minutes after 2.5 Gy X-ray irradiation is performed before the X-ray resistance test. 68% or more of the amount of light was evaluated as “◯”.

  The main component composition was measured by EPMA, and the impurity content was measured by ICP-MS. In addition, when a composition etc. are shown, it means that the material which contains "0%" as a range of content is not an essential component but an arbitrary component. In the display of the impurity content, “less than” means that the measurement limit is not exceeded.

(Table 1)

  That is, an optical fiber including a core made of glass with a refractive index n1 of 1.61 or more and 1.74 or less and a clad made of plastic with a refractive index n2 of 1.33 or more and 1.44 or less is an aperture. Since the number NA is 0.899 or more and 0.997 or less, illumination light with a wide field angle can be irradiated without using a concave lens for an endoscope.

  For example, a fiber having a core made of glass of composition E can obtain a desired NA in combination with a CYTOP having a refractive index n2 = 1.34 or a clad made of FEP having a refractive index n2 = 1.43. However, for example, a desired NA can be obtained in combination with a clad made of plastic having a refractive index n2 = 1.40.

  In particular, an optical fiber having a core made of glass with a refractive index n1 of 1.64 or more has an NA = 0.945 and an angle of view of 142 degrees when combined with Cytop having a refractive index n2 = 1.34. Since it is possible to illuminate 140 ° which is an imaging range of an endoscope with a high angle of view, it is particularly suitable for an endoscope application. On the other hand, a fiber having a core with a refractive index n1 of more than 1.74 is difficult to vitrify and is not easy to manufacture.

  An optical fiber having a core glass composition that satisfies the conditions (A) to (I) has a necessary and sufficient blue light transmittance and X-ray resistance as a medical endoscope.

  The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Endoscope 6 ... Light guide 6A ... Silicone tube 10 ... Endoscope light guide fiber 11 ... Core 12 ... Cladding 20 ... Endoscope system 30 ... Cover glass 30A ... Adhesive

Claims (8)

A core made of glass with a refractive index n1 of 1.61 or more and 1.74 or less and a clad made of plastic with a refractive index n2 of 1.33 or more and 1.44 or less, and the outer diameter of the core is A light guide having a plurality of optical fibers having a diameter of 90% to 99.6% of the outer diameter of the cladding and a numerical aperture NA of 0.899 to 0.997 is inserted, and the light guided by the light guide An insertion part that emits light from the tip part through a flat cover glass instead of the concave lens;
An operation unit arranged at the proximal end of the insertion unit;
An endoscope comprising: a universal cord extending from an operation unit and provided with a light guide connector for connecting the light guide to a light source device.   The endoscope according to claim 1, wherein the cover glass has a light scattering function. A core made of glass having a refractive index n1 of 1.61 or more and 1.74 or less;
A clad made of plastic having a refractive index n2 of 1.33 or more and 1.44 or less,
An endoscope light guide fiber having a numerical aperture NA of 0.899 or more and 0.997 or less.   The endoscope light guide fiber according to claim 3, wherein the refractive index n1 is 1.64 or more and 1.74 or less.   The endoscope light guide fiber according to claim 4, wherein an outer diameter of the core is 90% or more and 99.6% or less of an outer diameter of the clad. The light guide fiber for an endoscope according to claim 5, wherein the glass has the following composition.
(A) (SiO ₂ + B ₂ O ₃ ): 20 to 55 wt%
_(B) SiO 2: 20~55wt%
(C) B ₂ O ₃ : 0 to 10 wt%
(D) (BaO + SrO + La ₂ O ₃ + Lu ₂ O ₃ + Ta ₂ O ₅ + Gd ₂ O ₃ + WO ₃ + Nb ₂ O ₅ + Y ₂ O ₃ ): 25 to 72 wt%
(E) ZnO: 0 to 30 wt%
_{(F) Al 2 O 3:} 0~10wt%
(G) ZrO ₂ : 0 to 8 wt%
(H) (Na ₂ O + K ₂ O): 0 to 10 wt%
_{(I) Sb 2 O 3:} 0~0.35wt% The light guide fiber for an endoscope according to claim 6, wherein the glass has the following composition.
(F1) Al ₂ O ₃ : 0 wt%
(G1) ZrO ₂ : 0 wt%
(I1) Sb ₂ O ₃ : 0 to 0.050 wt%,
(J) (Na ₂ SO ₄ + K ₂ SO ₄ ): 0.26 to 1.63 wt%.   The endoscope light guide fiber according to claim 7, wherein the plastic is an amorphous fluororesin or FEP (tetrafluoroethylene / hexafluoropropylene copolymer).

Images