Low-refractive-index ultraviolet-transmitting optical glasses, their preparation methods and applications

Abstract

This invention relates to a low-refractive-index ultraviolet-transmitting optical glass, its preparation method, and its applications. The low-refractive-index ultraviolet-transmitting optical glass, by mass percentage, comprises: 37-41% SiO2, 4-7% B2O3, 16-26% BeF2, 5-9% NaF, 5-10% KF, 5-10% P2O5, 3-4% K2O, 2-4% Na2O, 2-5% Li2O, 2-5% Al2O3, and 0.2-0.7% other components. The low-refractive-index ultraviolet-transmitting optical glass of this invention is used as the cladding optical glass for optical fibers, possessing a low refractive index and high ultraviolet transmission performance. During the grating etching process, the cladding portion of the optical fiber exhibits high ultraviolet transmission performance, ensuring that the fiber core absorbs most of the ultraviolet light, thereby improving the efficiency of ultraviolet grating etching.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, specifically to low-refractive-index ultraviolet-transmitting optical glass, its preparation method, and its applications. Background Technology

[0002] In fiber optic sensing applications, the refractive index of the fiber core changes periodically under the influence of technologies such as ultraviolet laser irradiation or femtosecond laser irradiation, forming a grating that reflects light of a specific wavelength. This grating can be used to measure physical quantities such as acceleration, pressure, strain, and temperature. To allow sufficient light to enter the fiber, enhance the intensity of the reflected light signal, and improve sensing accuracy, the fiber must have a high light-gathering capacity to more accurately measure physical parameters.

[0003] In optical fibers, numerical aperture describes the cone angle of light entering and exiting the fiber. It is a parameter that measures the light-receiving capability of the fiber end face. The formula for calculating numerical aperture is as follows:

[0004]

[0005] In the formula, n1 represents the core refractive index, n2 represents the cladding refractive index, and α represents the critical angle. Light exceeding the critical angle refracts upon entering the fiber and eventually escapes, a phenomenon known as cladding leakage light, causing optical signal loss. This is particularly problematic when light reflected from the grating is transmitted through the fiber, easily leading to sensor signal loss and hindering sensing measurements. Large numerical aperture fibers can couple most of the light while preventing leakage of reflected light signals, effectively avoiding this problem. Furthermore, during fiber grating writing, the cladding glass easily absorbs ultraviolet light, reducing writing efficiency. Therefore, increasing the numerical aperture of the fiber and improving ultraviolet writing efficiency are pressing technical issues that need to be addressed. Summary of the Invention

[0006] The main objective of this invention is to provide a low-refractive-index ultraviolet-transmitting optical glass that reduces the refractive index of the optical glass and improves its ultraviolet transmission performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A low-refractive-index ultraviolet-transmitting optical glass, comprising, by mass percentage: 37–41% SiO2, 4–7% B2O3, 16–26% BeF2, 5–9% NaF, 5–10% KF, 5–10% P2O5, 3–4% K2O, 2–4% Na2O, 2–5% Li2O, 2–5% Al2O3, and ≤0.7% other components.

[0009] Furthermore, it also includes Sb2O3 and / or As2O3; the sum of the contents of Sb2O3 and As2O is 0.2-0.7%.

[0010] The low-refractive-index ultraviolet-transmitting optical glass has a refractive index of 1.430–1.453; an ultraviolet transmittance of 80–95% in the 200–300 nm wavelength band; an average dispersion coefficient of 60–65; and a coefficient of linear expansion of 80 × 10⁻⁶. -7 / ℃~90×10 -7 / ℃; glass transition temperature is 600~700℃; glass sag temperature is 700~750℃; glass softening point is 750~800℃; elastic modulus E is 61~64GPa.

[0011] The present invention also provides a method for preparing the aforementioned low-refractive-index ultraviolet-transmitting optical glass, which includes the following steps:

[0012] 1) Weigh the raw materials according to the formula ratio, mix them evenly to obtain a mixture; the raw materials include: 37-41% SiO2, 4-7% B2O3, 16-26% BeF2, 5-9% NaF, 5-10% KF, 5-10% P2O5, 3-4% K2O, 2-4% Na2O, 2-5% Li2O, 2-5% Al2O3, ≤0.7% other components;

[0013] 2) Add the mixture to a crucible, melt it at 1000-1300℃, clarify it, and pour it to obtain low-refractive-index optical glass that transmits ultraviolet light.

[0014] The present invention further provides an optical fiber comprising the aforementioned low-refractive-index ultraviolet-transmitting optical glass, comprising:

[0015] The clad glass tube is made of the aforementioned low-refractive-index ultraviolet-transmitting optical glass; the clad glass tube has a spectral transmittance of 80-95% in the 200-300 nm wavelength range; and,

[0016] The fiber-core glass rod is made of optical glass with high photosensitivity and low elastic modulus, with a refractive index of 1.515–1.550 and a photosensitivity of 5 × 10⁻⁶. -3 ~10×10 -3 Its elastic modulus is 60–70 GPa, its transmittance in the 200–300 nm spectrum is ≤20%, its average dispersion coefficient is 60–65, and its coefficient of linear expansion is 80 × 10⁻⁶. -7 / ℃~90×10 -7 / ℃; glass transition temperature is 550~700℃; glass sag temperature is 750~800℃; glass softening point is 800~850℃.

[0017] The present invention further provides a method for preparing the optical fiber, comprising the following steps:

[0018] 1) A cladding glass tube is prepared using the aforementioned low-refractive-index ultraviolet-transmitting optical glass, and a fiber core glass rod is prepared using high-photosensitivity, low-elastic-modulus optical glass.

[0019] 2) The cladding glass tube and the fiber core glass rod are vertically immersed in anhydrous ethanol with a mass concentration of 99% at a temperature of 50-70°C, and cleaned three times with ultrasonic waves at 20kHz.

[0020] 3) The cladding glass tube is inserted into the fiber core glass rod to assemble it into an optical fiber preform, which is then drawn at 700-800℃ to obtain an optical fiber.

[0021] The optical fiber has a numerical aperture of 0.5 to 0.6 and an optical fiber loss of 0.4 to 0.8 dB / m.

[0022] The present invention also provides a method for fabricating fiber gratings using the optical fiber, comprising the following steps:

[0023] 1) Place the mask above the optical fiber;

[0024] 2) Irradiate the optical fiber with an ultraviolet laser or a femtosecond laser, wherein the laser passes through the cladding glass tube and irradiates the core glass rod, causing the refractive index of the core glass rod to change periodically, thereby obtaining a fiber grating.

[0025] The present invention further provides an application of the aforementioned low-refractive-index ultraviolet-transmitting optical glass in the fields of fiber optic sensing, fiber optic lasers, fiber optic communication, and fiber optic imaging.

[0026] In the above-described technical solution of this invention, SiO2 is the main component forming the glass framework and plays a major role in the glass framework. By mass percentage, the SiO2 content is 37-41%, which is beneficial for reducing the coefficient of thermal expansion of the glass and improving its thermal stability, chemical stability, softening temperature, heat resistance, hardness, and mechanical strength. However, when the SiO2 content is higher than 41%, its refractive index is too high, failing to meet the requirement of a low refractive index. This invention strictly limits the SiO2 content to 37-41%.

[0027] B2O3 is a glass-forming oxide and a component of the glass framework, as well as a flux that reduces the viscosity of glass melt. In this invention, B2O3 also plays a key role in reducing dispersion and refractive index. Boron-oxygen trihedrons [BO3] and boron-oxygen tetrahedrons [BO4] are structural components. Under different conditions, boron may exist as trihedrons [BO3] or boron-oxygen tetrahedrons [BO4]. Under high-temperature melting conditions, it is generally difficult to form boron-oxygen tetrahedrons, and it can only exist as trihedrons. However, under ultraviolet irradiation, structural changes are easily made. Under low-temperature melting conditions, under certain conditions, B2O3... 3+ B₂O₃ tends to capture free oxygen to form tetrahedral structures, resulting in a compact structure and increased low-temperature viscosity. Simultaneously, it is less prone to structural changes under ultraviolet irradiation. To reduce glass dispersion and improve chemical and thermal stability, strict requirements are placed on the form in which B₂O₃ exists in the glass. Experimental studies have shown that, by mass percentage, this invention strictly limits the B₂O₃ content to 4–7% during the melting process of low-refractive-index ultraviolet-transmitting optical glass.

[0028] The roles of BeF2, NaF, and KF in glass are to reduce the refractive index, thus enabling the preparation of low-refractive-index glass. BeF2 exists in the form of tetrahedral [BeF2] molecules within the glass network structure, similar to the spatial arrangement of SiO2, forming the glass network structure together with SiO2 in silicate glass. NaF and KF mainly fill the voids in the glass network structure as small molecules, improving the glass's strength while simultaneously reducing the refractive index and dispersion coefficient. Experimental studies have shown that, by mass percentage, this invention strictly limits the content of BeF2 to 16-26%, NaF to 5-9%, and KF to 5-10% during the melting process of low-refractive-index ultraviolet-transmitting optical glass.

[0029] The ultraviolet (UV) transmittance of glass is related to the excitation of photons by the outer electrons of oxygen ions. The ability of electrons to absorb photons is related to the characteristics of the chemical bonds between oxygen ions and cations. To improve the UV transmittance of glass, the composition is adjusted to change the chemical bonds and reduce this absorption. In the aforementioned glasses, the number of bridging oxygen bonds in the structure is the main factor affecting the UV transmittance of the sample. Since silicate glasses have low UV transmittance, studies have shown that introducing R2O into phosphate glasses can repair the fracture points of [PO4] and [BO3], transforming the triangular layered structure of [BO3] into a tetrahedral structure of [BO4]. This strengthens the network connection, increases the number of bridging oxygen bonds, and reduces the number of non-bridging oxygen bonds. The intrinsic UV absorption of the glass shifts towards shorter wavelengths, thus improving UV transmittance. Therefore, introducing P2O5 into the silicate glass system, together with SiO2, constitutes the network structure of the glass, forming more bridging oxygen bonds, thereby improving UV transmittance. Experimental studies have found that, by mass percentage, the P2O5 content strictly limited in this invention is 5-10%.

[0030] K₂O and Na₂O are both alkali metal oxides. They exist as network components in the glass structure, causing the glass structure to relax and reducing the elastic modulus. Furthermore, alkali metal oxides play an important role in regulating thermal properties such as glass transition temperature, coefficient of thermal expansion, and softening temperature. Experimental studies have shown that glass containing 3–4% K₂O and 2–4% Na₂O can achieve the various properties described in the embodiments of this invention.

[0031] Li₂O exists in glass as a network exosphere. + Its main function is accumulation; its introduction is primarily to improve the chemical stability and surface tension of the glass. Experimental studies have shown that, by mass percentage, the content of Li₂O in this invention is strictly limited to 2-5%.

[0032] Al₂O₃ plays a unique role in silicate phosphate glasses. Introducing a certain amount of Al₂O₃, existing as AlPO₄ groups in the glass system, improves the chemical stability of the glass by maintaining a layered framework structure of the phosphate. It also facilitates the filling of alkali metal ions, increasing the strength of the glass material and reducing the elastic modulus. Experimental studies have shown that, by mass percentage, this invention strictly limits the Al₂O₃ content to 2–5%.

[0033] By employing the above technical solution, the present invention has at least the following advantages:

[0034] To improve the numerical aperture of optical fibers, one approach is to increase the refractive index of the fiber core, and another is to decrease the refractive index of the cladding. Considering that the fiber core material is closely related to parameters such as photosensitivity and Young's modulus, and that the range of refractive index adjustment is limited, this invention primarily employs the method of decreasing the refractive index of the cladding to increase the numerical aperture. Furthermore, during the grating etching process, the cladding portion of the fiber exhibits high ultraviolet transmission performance, ensuring that the core absorbs most of the ultraviolet light, thereby improving the efficiency of ultraviolet grating etching. The optical glass used as the cladding in this invention has a low refractive index and high ultraviolet transmission performance.

[0035] Optical glass with high photosensitivity and low elastic modulus is used as the core glass. By increasing the ultraviolet transmittance of the core glass, corresponding to the improvement of grating efficiency, ultraviolet light passes through the cladding glass and is efficiently absorbed by the core glass, thereby improving the ultraviolet grating efficiency.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0037] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific implementation methods, structures, features, and effects of the present invention are described in detail below with reference to preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0038] This invention proposes a low-refractive-index ultraviolet-transmitting optical glass, which, by mass percentage, comprises: 37-41% SiO2, 4-7% B2O3, 16-26% BeF2, 5-9% NaF, 5-10% KF, 5-10% P2O5, 3-4% K2O, 2-4% Na2O, 2-5% Li2O, 2-5% Al2O3, and 0.2-0.7% other components.

[0039] The optical glass may also contain antimony trioxide and / or arsenic trioxide in a total amount not exceeding 0.7% by mass percentage. These are mainly introduced into the glass system as clarifying agents, which help to remove bubbles during the glass melting process, reducing defects such as bubbles and streaks generated during glass melting and improving the internal quality of the optical glass. Preferably, the content of Sb₂O₃ is 0–0.5% and the content of As₂O₃ is 0–0.4%.

[0040] This invention also proposes a method for preparing low-refractive-index ultraviolet-transmitting optical glass. First, the raw materials are weighed according to the formula ratio; the formula of the raw materials is as described above for low-refractive-index ultraviolet-transmitting optical glass; the raw materials are mixed evenly; then the mixture is added to a crucible, stirred in an oxygen atmosphere, melted at 1000-1300℃, clarified, and finally cast to obtain low-refractive-index ultraviolet-transmitting optical glass.

[0041] The low-refractive-index ultraviolet-transmitting optical glass prepared by the method described above has a low refractive index and high ultraviolet transmission performance.

[0042] This invention evaluates various properties of optical glass using the following method:

[0043] According to GB / T 7962.1~2010, the refractive index of low-refractive-index ultraviolet-transmitting optical glass is tested, and its refractive index (n) d The value ranges from 1.430 to 1.453.

[0044] According to GB / T 7962.12~2010, the spectral transmittance of a 3mm thick glass slide was tested using a spectrophotometer. The transmittance in the 200~300nm band was greater than 80%. This result indicates that the optical glass, as the cladding of the photosensitive fiber, has extremely high transmittance in the ultraviolet band (i.e., the band in which ultraviolet lasers are used to write fiber gratings), which is beneficial to improving the grating efficiency of the photosensitive fiber.

[0045] According to GB / T 7962.6~2010, the elastic modulus is obtained by measuring the propagation speed of elastic waves in a glass sample using the ultrasonic pulse echo method. The elastic modulus E is 61~64 GPa.

[0046] According to GB / T 7962.1~2010, the Abbe number (mean dispersion coefficient) is tested, and its mean dispersion coefficient (Abbe number υ) is... d The value is 60-65.

[0047] According to GB / T 7962.16~2010, the coefficient of thermal expansion, transition temperature, softening temperature, and softening point were tested, and its linear expansion coefficient was 80×10⁻⁶. -7 / ℃~90×10 -7 / ℃; Glass transition temperature (Tg) is 600~700℃; Glass sag temperature (Ts) is 700~750℃; Glass softening point (viscosity is 10) 7.6 The temperature corresponding to Pa·s is 750–800℃.

[0048] Preferably, by mass percentage, the optical glass comprises: 37-41% SiO2, 4-7% B2O3, 16-26% BeF2, 5-9% NaF, 5-10% KF, 5-10% P2O5, 3-4% K2O, 2-4% Na2O, 2-5% Li2O, 2-5% Al2O3, and 0.2-0.7% other components. The optical glass has a refractive index of 1.430 and an ultraviolet transmittance greater than 80% in the 200-300 nm wavelength range, as in Example 1.

[0049] This invention also proposes an optical fiber comprising the aforementioned low-refractive-index ultraviolet-transmitting optical glass; the optical fiber consists of a cladding and a core; the cladding is made of a low-refractive-index ultraviolet-transmitting optical glass material; the core is made of a high-photosensitivity, low-elastic-modulus optical glass, with the following main properties: refractive index of 1.515–1.550, and photosensitivity of 5 × 10⁻⁶. -3 ~10×10 -3 Its elastic modulus is 60-70 GPa, and its transmittance in the 200-300 nm spectrum is ≤20%.

[0050] The optical fiber can be single-mode or multimode, and there are no restrictions on the cladding diameter and core diameter.

[0051] The optical fiber is not limited to a single-core optical fiber; it can also be a multi-core optical fiber, a hollow-core optical fiber, etc., and no specific limitation is made in this invention.

[0052] This invention also proposes a method for fabricating optical fibers, specifically as follows: The physical dimensions of the core glass rod and cladding glass tube are designed according to the optical fiber specifications (core diameter d1 and cladding diameter d2), wherein the diameter of the core glass rod is D1, the outer diameter of the cladding glass tube is D2, and the inner diameter is D1 + ΔD. Theoretically, d1 and d2, and D1 and D2 are proportional, but in the actual process of drawing fibers using the tube-rod method, there is a certain gap between the core glass rod and the cladding glass tube. When the core rod and the cladding glass tube are in close contact, they are proportional. This invention preferably uses ΔD of 0.1 to 0.5. mm, which ensures smooth assembly of the core glass rod and the cladding glass tube while minimizing the gap between them; preferably D2 / D1=d2 / d1; then, the cladding glass tube is made using the aforementioned low-refractive-index ultraviolet-transmitting optical glass; the raw materials are weighed according to the formula; the weighed raw materials are mixed evenly; the mixture is melted into optical glass according to the aforementioned optical glass preparation method, and processed into a cladding glass tube with an outer diameter of D2 and an inner diameter of D1+ΔD; the inner and outer walls of the glass tube are polished by mechanical, flame, or other methods, and the surface is polished.

[0053] A cladding glass tube with an inner diameter of D1+ΔD and an outer diameter of D2 is prepared using a low-refractive-index ultraviolet-transmitting optical glass material. The cladding glass tube and the core glass rod are vertically immersed in 99% anhydrous ethanol at 50-70℃ and cleaned three times with a 20kHz ultrasonic cleaner to thoroughly remove organic impurities such as polishing fluid, coolant, and oil, reducing core-cladding interface loss. The cladding glass tube is then fitted onto the core glass rod to assemble an optical fiber preform. The optical fiber preform is fixed directly above the heating furnace of the optical fiber drawing tower. When the furnace temperature reaches the drawing requirement, the end of the optical fiber preform is lowered to the highest point of the furnace temperature. The preferred drawing temperature for the optical fiber is 700-800℃. The end of the optical fiber preform softens and falls off at high temperature, and the optical fiber is uniformly drawn under traction force.

[0054] Since the refractive index of the cladding glass is 1.430-1.453 and the refractive index of the core glass is 1.515-1.550, the numerical aperture of this optical fiber can be controlled within the range of 0.5-0.6, which can couple light at a large angle, improve the optical signal intensity, and meet the application requirements of different numerical apertures.

[0055] The fiber core material, high photosensitivity and low elastic modulus optical glass, can undergo a permanent change in refractive index under ultraviolet light, and also exhibits significant deformation under a unit force, making it suitable as a high-precision and high-sensitivity fiber grating.

[0056] The cladding of the optical fiber is made of low-refractive-index ultraviolet-transmitting optical glass. When the optical fiber is irradiated with ultraviolet laser or femtosecond laser, the low-refractive-index ultraviolet-transmitting optical glass cladding absorbs less energy, which can improve the efficiency of writing gratings.

[0057] This invention also proposes a fiber grating and its fabrication method, wherein the cladding material is made of the aforementioned low-refractive-index ultraviolet-transmitting optical glass, which has low refractive index and high ultraviolet transmittance; the fabrication method of the fiber grating includes the following steps: 1) covering the aforementioned optical fiber with a mask; 2) irradiating the fiber core with an ultraviolet laser or femtosecond laser through the cladding, causing its refractive index to change periodically, thereby obtaining the fiber grating.

[0058] The fiber grating is used in fields such as fiber optic sensing, fiber lasers, and fiber optic communication.

[0059] The optical fiber has a loss of 0.4 to 0.8 dB / m, exhibiting low loss and making it suitable for applications such as high-sensitivity, high-precision optical fiber sensors, high-power optical fiber lasers, and medical imaging.

[0060] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0061] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0062] Examples 1 to 5

[0063] Examples 1 to 5 of the present invention respectively prepare optical glasses with high and low refractive indices that transmit ultraviolet light. The composition of the glass is shown in Table 1 below by mass percentage.

[0064] Table 1

[0065]

[0066]

[0067] Weigh the raw materials according to the components shown in Table 1 above, mix them evenly, and add them to a crucible. Examples 1 and 2 were melted and clarified at 1200°C, Examples 3 and 4 were melted and clarified at 1000°C, and Example 5 was melted and clarified at 1300°C. After clarification, the molten glass was poured into optical glass, and then the main performance tests of the optical glass were carried out. The test results are shown in Table 2.

[0068] Table 2

[0069]

[0070] Examples 6 to 10

[0071] Using the low-refractive-index ultraviolet-transmitting optical glass prepared in Examples 1 to 5 of this invention as the cladding glass material, an optical fiber is prepared respectively, specifically including the following steps:

[0072] 1) Prepare cladding glass tubes using low-refractive-index ultraviolet-transmitting optical glass, and prepare fiber-core glass rods using high-photosensitivity, low-elastic-modulus optical glass.

[0073] 2) The cladding glass tube and the fiber core glass rod are vertically immersed in anhydrous ethanol with a mass concentration of 99% at a temperature of 50-70°C, and cleaned three times with ultrasonic waves at 20kHz.

[0074] 3) The cladding glass tube is inserted into the fiber core glass rod to assemble it into an optical fiber preform, which is then drawn at 700-800℃ to obtain an optical fiber.

[0075] A method for fabricating a fiber Bragg grating includes the following steps:

[0076] 1) Place the mask above the prepared optical fiber;

[0077] 2) Irradiate the optical fiber with an ultraviolet laser or a femtosecond laser, wherein the laser passes through the cladding glass and irradiates the core glass rod, causing the refractive index of the core glass rod to change periodically, thereby obtaining a fiber grating.

[0078] The performance parameters of the fiber core material of the optical fiber of the present invention are shown in Table 3 below.

[0079] Table 3

[0080]

[0081] The core material, by mass percentage, comprises: 50–60% SiO2, 5–10% B2O3, 0–8% Ge2O3, 4–7% Al2O3, 5–14% PbO, 5–10% BaO, 5–6% K2O, 4–6% Na2O, and also includes Sb2O3 and / or As2O3, with the sum of Sb2O3 and As2O content ≤0.8%.

[0082] The specific composition of the fiber core material is shown in Table 4 below:

[0083] Table 4

[0084]

[0085]

[0086] The cladding material, fiber parameters, and fabrication process parameters of the optical fiber of this invention are shown in Table 5 below.

[0087] Table 5

[0088] optical fiber Example 6 Example 7 Example 8 Example 9 Example 10 Cladding material Example 1 Example 2 Example 3 Example 4 Example 5 Core material Photosensitive glass 1 Photosensitive glass 2 Photosensitive glass 3 Photosensitive glass 4 Photosensitive glass 5 Core diameter / μm 9.5 9.5 9.8 9.6 10.1 Cladding diameter / μm 400 400 400 400 400 Immersion temperature / ℃ 60 50 70 65 55 Wire drawing temperature / ℃ 720 740 760 800 780 Numerical Aperture (NA) 0.5 0.51 0.55 0.54 0.54 Loss (dB / m) 0.72 0.40 0.80 0.47 0.55

[0089] As can be seen from the data in Tables 1 to 3, the optical glass of the present invention has the characteristics of low refractive index and high ultraviolet transmittance, and can be used in the cladding part of high photosensitivity Young's modulus optical fiber. After being irradiated by a mask and ultraviolet laser or femtosecond laser, it can efficiently write gratings, and then be applied to the fields of fiber optic sensing, fiber laser, and fiber optic communication.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A low-refractive-index optical glass that transmits ultraviolet light, characterized in that: By mass percentage, it includes: 37~41% SiO2, 4~7% B2O3, 16~26% BeF2, 5-9% NaF, 5-10% KF, 5-10% P2O5, 3~4% K2O, 2~4% Na2O, 2-5% Li2O, 2~5% Al2O3, and ≤0.7% other components; The other components include Sb2O3 and / or As2O3; the sum of the contents of Sb2O3 and As2O is 0.2-0.7%.

2. The low-refractive-index ultraviolet-transmitting optical glass according to claim 1, characterized in that, The low-refractive-index ultraviolet-transmitting optical glass has a refractive index of 1.430~1.453; an ultraviolet transmittance of 80~95% in the 200-300nm wavelength band; an average dispersion coefficient of 60~65; and a coefficient of linear expansion of 80×10⁻⁶. -7 / ℃~90×10 -7 / ℃; glass transition temperature is 600~700℃; glass sag temperature is 700~750℃; glass softening point is 750~800℃; elastic modulus E is 61~64GPa.

3. A method for preparing a low-refractive-index ultraviolet-transmitting optical glass as described in claim 1 or 2, characterized in that, It includes the following steps: 1) Weigh the raw materials according to the formula ratio, mix them evenly to obtain a mixture; the raw materials include: 37~41% SiO2, 4~7% B2O3, 16~26% BeF2, 5-9% NaF, 5-10% KF, 5-10% P2O5, 3~4% K2O, 2~4% Na2O, 2-5% Li2O, 2~5% Al2O3, 0.2-0.7% other components; 2) Add the mixture to a crucible, melt it at 1000~1300℃, clarify it, and pour it to obtain low refractive index ultraviolet-transmitting optical glass.

4. An optical fiber comprising the low-refractive-index ultraviolet-transmitting optical glass as described in claim 1 or 2, characterized in that, It includes: The cladding glass tube is made of the aforementioned low-refractive-index ultraviolet-transmitting optical glass; the cladding glass tube has a spectral transmittance of 80-95% in the 200-300nm wavelength range. and, The fiber-core glass rod is made of optical glass with high photosensitivity and low elastic modulus, with a refractive index of 1.515~1.550 and a photosensitivity of 5×10⁻⁶. -3 ~10×10 -3 Its elastic modulus is 60~70 GPa, its spectral transmittance at 200~300 nm is ≤20%, its average dispersion coefficient is 60~65, and its coefficient of linear expansion is 80×10⁻⁶. -7 / ℃~90×10 -7 / ℃; glass transition temperature is 550~700℃; glass sag temperature is 750~800℃; glass softening point is 800~850℃.

5. A method for fabricating an optical fiber according to claim 4, characterized in that, Includes the following steps: 1) A cladding glass tube is prepared using the aforementioned low-refractive-index ultraviolet-transmitting optical glass, and a fiber core glass rod is prepared using high-photosensitivity, low-elastic-modulus optical glass. 2) The cladding glass tube and the fiber core glass rod are vertically immersed in anhydrous ethanol with a mass concentration of 99% at a temperature of 50~70℃, and cleaned three times with ultrasonic waves at 20kHz. 3) The cladding glass tube is inserted into the fiber core glass rod to assemble it into an optical fiber preform, which is then drawn at 700-800℃ to obtain an optical fiber.

6. The preparation method according to claim 5, characterized in that, The optical fiber has a numerical aperture of 0.5 to 0.6 and an optical fiber loss of 0.4 to 0.8 dB / m.

7. A method for fabricating a fiber grating using the optical fiber of claim 4, characterized in that, It includes the following steps: 1) Place the mask above the optical fiber; 2) Irradiate the optical fiber with an ultraviolet laser or a femtosecond laser, wherein the laser passes through the cladding glass tube and irradiates the core glass rod, causing the refractive index of the core glass rod to change periodically, thereby obtaining a fiber grating.

8. The application of the low-refractive-index ultraviolet-transmitting optical glass as described in claim 1 or 2 in the fields of fiber optic sensing, fiber optic lasers, fiber optic communication, and fiber optic imaging.

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