Glass with negative thermal expansion coefficient, stress rod and preparation method thereof

Abstract

The invention belongs to the field of inorganic materials, and discloses glass with a negative thermal expansion coefficient, which comprises the following elements by mole percent: 26.5-29.5% of Si; 2.8 to 3.9 percent of M; 3.0 to 3.8 percent of N; the balance of oxygen element; wherein no less than 50 mol% of element in M is Ti; and not less than 70 mol% of element in N is Al. The glass has a negative thermal expansion coefficient, is stable in performance and does not devitrify in the wire drawing process, and meanwhile, the refractive index of the glass is close to that of a fiber core, so that a refractive index sunken area with delta n being approximately equal to-0.0015 can be constructed, and a light field coupling path is cut off to avoid mode field distortion; meanwhile, the invention further provides the stress rod and a preparation method thereof.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials, and more particularly to a glass with a negative coefficient of thermal expansion, a stress rod, and a method for preparing the same. Background Technology

[0002] Patent application CN112130250A, entitled "Panda-type Polarization Maintaining Optical Fiber and its Fabrication Method," proposes a polarization maintaining optical fiber composed of cross-shaped stress bars. By using a cross-shaped structure of contractile and expansion stress layers, stress reinforcement is achieved, enhancing the panda polarization maintaining optical fiber's ability to resist external asymmetric thermal stress through stress birefringence and optimizing polarization crosstalk temperature stability. Further refinement of this scheme specifies that the expansion stress layer is composed of Ge and F co-doped silica glass, with Ge accounting for 1–8% of the molar percentage and F accounting for 1–21% of the molar percentage.

[0003] This cross-shaped structure of contraction and expansion stress layers can enhance stress.

[0004] Traditional expansion stress materials suffer from key defects such as unstable performance at ultra-high fiber drawing temperatures (1800℃), thermal expansion mismatch with the matrix material, or phase transformation / crystallization.

[0005] Therefore, the technical problem to be solved in this case is: how to develop a glass with a negative coefficient of thermal expansion based on a new formula, so that it can ensure the stability of the material when the optical fiber is drawn to 25~40μm.

[0006] Meanwhile, in order to avoid mode field distortion between the expansion stress material and the fiber core, further optimization design also needs to consider matching the refractive index relationship between the glass and the fiber core, so that there is a possibility of constructing a refractive index depression region between the two. Summary of the Invention

[0007] The purpose of this invention is to provide a glass with a negative coefficient of thermal expansion. This glass has a negative coefficient of thermal expansion, which makes it stable and prevents crystallization during the drawing process. At the same time, its refractive index is similar to that of the fiber core, which can construct a refractive index depression region of Δn≈-0.0015 to cut off the optical field coupling path and avoid mode field distortion.

[0008] In addition, the present invention also provides a stress bar and a method for preparing the same.

[0009] To achieve the above objectives, this application discloses a glass with a negative coefficient of thermal expansion, which contains the following molar percentage elements:

[0010] Si: 26.5~29.5%;

[0011] M: 2.8~3.9%;

[0012] N: 3.0~3.8%;

[0013] The remaining oxygen element;

[0014] Among them, at least 50 mol% of the element in M ​​is Ti;

[0015] The element that makes up at least 70 mol% of N is Al.

[0016] The unusual thermal behavior of the glass in this invention originates from the dynamic equilibrium of two opposing responses at the microscale: the silicon-aluminum-oxygen network constructed from SiO2-Al2O3 exhibits conventional positive expansion upon heating due to increased atomic amplitude; while the [TiO6] octahedrons embedded in the network experience a "structural contraction effect" due to the high-frequency lateral vibration of Ti-O bonds, pulling adjacent structural units closer together and causing macroscopic contraction. By precisely controlling the TiO2 content and optimizing the Al2O3 / SiO2 ratio, the contraction intensity of the titanium-oxygen units completely offsets or even surpasses the expansion of the silicon-aluminum network. Combined with the amplification effect of the glass's disordered structure on the vibrational modes, a near-zero or negative coefficient of thermal expansion is ultimately achieved within a specific composition range.

[0017] The glass of this invention has a negative coefficient of thermal expansion (CTE ≈ -1.5 × 10⁻⁶). -6 This material ( / K) solves the key defects of traditional expansion stress materials, such as performance instability, thermal expansion mismatch with the matrix material, or phase transformation / crystallization, at ultra-high fiber drawing temperatures (1800℃). Its unique composition endows it with extremely high high-temperature thermal and chemical stability, enabling the stress zone to maintain structural integrity, controllable stress state, and reliable performance during the stringent fiber drawing process, improving high-temperature stability by 87%.

[0018] In the glass described above, M contains the following elements:

[0019] Ti: 50~100 mol%

[0020] Zr, Hf, and Sn are each independently selected from 0–50 mol%;

[0021] The N contains the following elements:

[0022] Al: 70~100 mol%

[0023] Y, La, and Ga are each independently selected from 0 to 30 mol.

[0024] In the above-mentioned glass, the glass is composed of the following components by weight percentage:

[0025] SiO2: 70~85 wt%

[0026] TiO2: 8~18wt%

[0027] Al2O3: 5~15wt%.

[0028] The glass described above is composed of the following components by weight percentage:

[0029] SiO2: 77~81.5 wt%

[0030] TiO2: 11~15wt%

[0031] Al2O3: 7.5~8wt%.

[0032] In the aforementioned glass, the coefficient of thermal expansion is -1 × 10⁻⁶. -6 / K~-2×10 -6 / K; the refractive index of the glass is 1.48±0.01.

[0033] Meanwhile, the present invention also discloses a stress rod, including an expansion rod and an fluorine-doped silicon dioxide layer covering the outer surface of the expansion rod; the fluorine-doped silicon dioxide layer serves as a protective layer for the expansion rod and is used to construct a refractive index recess region between the expansion rod and an external core rod; the material of the expansion rod is as shown above; the fluorine-doped silicon dioxide layer contains 7~9 wt% fluorine element.

[0034] The fluorine-doped silicon dioxide (SiO2:F) layer epitaxially formed outside the SiO2-TiO2-Al2O3 expansion layer improves system reliability through a chemical and optical synergistic mechanism: volatile fluorides (such as AlF3) formed by fluorine ions replacing oxygen and high bond energy Si-F bonds significantly inhibit metal ion diffusion, constructing a chemical barrier to prevent contaminants such as Cu / Fe from eroding the fiber core; at the same time, the quantitative decrease in refractive index caused by fluorine doping (Δn≈-0.0015 / at% F) forms a refractive index depression region (n≈1.43-1.45) between the expansion layer (n≈1.48) and the fiber core (n≈1.46), cutting off the optical field coupling path and avoiding mode field distortion.

[0035] The synergistic design of the ternary low-expansion cladding and the fluorine-doped isolation layer achieves multi-dimensional performance enhancements: the near-zero expansion cladding matches the thermal properties of the quartz fiber core, eliminating microbending losses caused by temperature stress; more specifically, the synergistic effect of the ternary low-expansion cladding and the fluorine-doped isolation layer stems from the cross-scale design of multiple physics fields. The near-zero expansion cladding, by matching the coefficient of thermal expansion with the quartz fiber core, intrinsically suppresses interfacial thermal stress induced by temperature cycling, thereby eliminating the origin of microbending losses. Simultaneously, the fluorine-doped layer enhances the optical field confinement by increasing the refractive index contrast between the cladding and the fiber core, thus improving the waveguide's resistance to microbending; its chemical passivation further blocks the diffusion of active ions, ensuring long-term reliability. This system, through a triple synergy of thermodynamics, optics, and chemistry, provides a robust solution for fiber optic sensors in harsh environments. The chemical passivation of the fluorine layer blocks metal contamination, ensuring long-term stability; while the refractive index gradient structure confines the optical field through total internal reflection, ensuring signal transmission efficiency. This comprehensive solution lays the material foundation for high-precision fiber optic sensors and communication systems in harsh environments.

[0036] In the aforementioned stress bar, the diameter or diagonal length of the expansion bar is 4~8 mm; the F-doped silicon dioxide layer is 0.2~1.5 mm; the cross-section of the expansion bar is circular, square, or bow-tie shaped; if the cross-section is circular, the diameter tolerance is ≤ ±0.5 μm; if the cross-section is square, the side length is d1, and the chamfer radius is <0.1d1; if the cross-section is bow-tie shaped, the wing angle θ = 70°~100°, the wingtip curvature radius R = 0.05~0.1d2, where d2 is the radius of the expansion bar.

[0037] In the aforementioned stress rod, the refractive index of the refractive index recessed region is 1.43~1.45; the refractive index of the expansion rod is 1.48±0.01; and the refractive index of the external core rod is 1.46±0.01.

[0038] In addition, the present invention also discloses a method for preparing glass as described above, which uses plasma chemical vapor deposition process and SiO2, TiO2 and Al2O3 as raw materials to prepare expansion rods.

[0039] And a method for preparing a stress rod as described above, wherein an expansion rod is prepared by using plasma chemical vapor deposition (PCVDC) with SiO2, TiO2, and Al2O3 as raw materials; and an F-doped silicon dioxide layer is deposited on the periphery of the expansion rod by PCVDC to obtain the stress rod.

[0040] It should be further explained that the present invention is not strictly limited to the preparation process being plasma chemical vapor deposition. As is well known in the art, MCVD (modified chemical vapor deposition) process can also be used.

[0041] The beneficial effects of this application are:

[0042] 1. The SiO2-TiO2-Al2O3 glass material of the present invention has a negative coefficient of thermal expansion (CTE ≈ -1.5 × 10⁻⁶). -6 This material ( / K) solves the key defects of traditional expansion stress materials, such as performance instability, thermal expansion mismatch with the matrix material, or phase transformation / crystallization, at ultra-high fiber drawing temperatures (1800℃). Its unique composition endows it with extremely high high-temperature thermal and chemical stability, ensuring that the stress zone maintains structural integrity, controllable stress state, and reliable performance during the stringent fiber drawing process, improving high-temperature stability by 87%.

[0043] 2. The stress bar of the present invention has an additional F-doped silicon dioxide layer on the surface of the glass material described above, which is used to protect and isolate the expansion bar, and to construct a refractive index depression region, thereby cutting off the optical field coupling path between the expansion bar and the fiber core to avoid mode field distortion. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the orthogonal dual-stress polarization-maintaining fiber structure of the present invention. Detailed Implementation

[0045] The present invention will now be clearly and completely described in conjunction with embodiments thereof. It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0046] Part 1: Preparation of SiO2-TiO2-Al2O3 Glass and Stress Rods

[0047] The following steps further explain the PCVD preparation process of SiO2-TiO2-Al2O3 glass.

[0048] 1. Equipment and Materials

[0049] Core equipment: UNC-PCVD / HEC plasma chemical vapor deposition system. This system requires the following:

[0050] Multi-channel precision mass flow controller for reactant gas and carrier gas.

[0051] High-temperature evaporation and sublimation system: used to transport TiCl4 and AlCl3 precursors.

[0052] Microwave power source: The frequency is usually 2.45 GHz, and the power range is adjustable from 0 to 6000W.

[0053] Deposition liner: Low-hydroxyl synthetic quartz tube with an outer diameter of 31 mm and an inner diameter of 27 mm.

[0054] Gas source and chemical precursors:

[0055] SiCl4: Purity ≥ 99.999%

[0056] TiCl4: Purity ≥ 99.999%

[0057] AlCl3: Solid state, purity ≥ 99.999%

[0058] O2: Purity ≥ 9N

[0059] He: Purity ≥ 9N (used as both carrier gas and dilution gas)

[0060] 2. Preparation process flow

[0061] Step 1: System preparation and liner pretreatment

[0062] Installation and Leak Detection: Install the quartz liner to the equipment spindle and perform a system airtightness check to ensure a leakage rate < 1×10⁻⁶. -9 mbar•L / s.

[0063] Cavity purification: Repeat the "vacuuming-helium filling" cycle three times to completely remove moisture and oxygen from the cavity.

[0064] Inner wall activation: The inner wall of the liner is polished for 10 minutes at >1200℃ using an oxyhydrogen flame polisher to remove microcracks and improve surface reactivity.

[0065] Step 2: Stabilization of the precursor transport system

[0066] This is a critical step in the process and must be started and stabilized before deposition:

[0067] TiCl4 evaporation system: The set temperature is 150 ± 0.5℃ to ensure stable vaporization.

[0068] AlCl3 sublimation system: The set temperature is 180 ± 0.5℃, and 200 sccm of high-purity helium is used as the carrier gas.

[0069] Step 3: Plasma Deposition Process

[0070] Initiate the plasma and execute the automatic deposition program. The core process parameters are shown in Tables 1 and 2 below.

[0071] Table 1 Process Parameter Table

[0072] Process parameters Setting value / range Control accuracy Functions and Explanations microwave power 1200 W ±10 W It generates and maintains a stable moving plasma sphere, which excites gas reactions. Deposition pressure 15 mbar ±0.2 mbar Optimize plasma state and deposition uniformity. Base tube temperature 1150℃ ±10 ℃ Ensure that the deposited layer is in a glassy state rather than a powdery state to promote densification. 100 rpm ±1 rpm Ensure uniform circumferential deposition. Feeding speed 120 mm / min ±1 mm / min Control the thickness of a single layer deposition.

[0073] Table 2 Process Parameter Table

[0074] gas Gas flow rate Flow accuracy illustrate <![CDATA[SiCl4]]> 150 sccm ±1 sccm The silicon source forms the main body of the glass network. <![CDATA[TiCl4]]> 8 sccm ±1 sccm Titanium source, to regulate the coefficient of thermal expansion. <![CDATA[AlCl3]]> Equivalent to ~10 sccm ±1 sccm Aluminum source, inhibiting crystallization and improving glass stability. <![CDATA[O2]]> 450 sccm ±5 sccm The reacting gas produces oxides. He 600 sccm ±5 sccm Dilute the reactants, improve deposition uniformity, and stabilize the plasma.

[0075] Deposition cycle: Layer-by-layer deposition is carried out on the inner wall of the liner through >1000 reciprocating scans until the predetermined thickness is reached.

[0076] Step 4: Melt and shrink into rods

[0077] The deposited composite tube is transferred to a melting lathe and subjected to a progressive oxyhydrogen flame process. The process parameters for the progressive oxyhydrogen flame process are shown in Table 3.

[0078] Table 3 Process Parameter Table

[0079] stage temperature speed illustrate Pre-shrink ~1700°C 200 mm / min densification ~1900°C 80 mm / min The "advance-retreat method" is used to release stress. Burn to death >2000°C 20 mm / min Until the hole is completely closed, forming a solid glass rod.

[0080] The formulation of SiO2-TiO2-Al2O3 glass, as well as its coefficient of thermal expansion (CTE) and refractive index (n), can be found in Table 4.

[0081] Table 4 Formula Table

[0082] <![CDATA[SiO2 / wt%]]> <![CDATA[TiO2 / wt%]]> <![CDATA[Al2O3 / wt%]]> Si:Ti:Al / molar ratio <![CDATA[CTE / *10 -6 / K]]> Refractive index n Example 1 77 15 8 26.7:3.9:3.3 -0.5 1.52 Example 2 80 12 8 27.5:3.1:3.2 -1.5 1.48 Example 3 81.5 11 7.5 28:2.8:3 -1.2 1.485 Comparative Example 1 80 0 20 26.8:0:7.9 -2.8 1.465 Comparative Example 2 75 17 8 26.1:4.4:3.3 0.5 1.545

[0083] Stress rods were prepared from SiO2-TiO2-Al2O3 glass according to the above embodiments and comparative examples; the outer periphery of the stress rod was an fluorine-doped silicon dioxide layer with a thickness of 0.5 mm.

[0084] In this embodiment, the stress bar containing the fluorine-doped silicon dioxide layer is prepared sequentially using a two-step PCVD method. First, a fluorine-doped silicon dioxide inner layer is prepared on a high-purity quartz glass substrate by plasma chemical vapor deposition: under a stable process environment of 12000W microwave power, 15mbar deposition pressure, and 1150℃ substrate temperature, fluorinated gases such as SiCl4, O2, and C2F6 are introduced. By precisely controlling the flow rate of the fluorine source gas, a uniform doped layer with a fluorine content of 7-9 wt% is deposited. After subsequent melting and shrinking, this layer will precisely form a specified structure with a thickness of 0.5mm. Subsequently, using this fluorine-doped layer as a new substrate, a SiO2-TiO2-Al2O3 ternary glass layer was deposited on its inner surface. Within the same PCVD reaction chamber, maintaining a deposition temperature of 1150°C, SiCl4, TiCl4 (evaporated at 150°C), AlCl3 (sublimated at 180°C, carried by helium), and O2 were precisely introduced. After more than 1000 reciprocating scans, a functional layer with negative thermal expansion characteristics was constructed. Finally, through a single precision melting and shrinking process, this composite structure of "fluorine-doped silica layer-ternary glass layer-quartz liner" was melted and shrunk into a dense, solid stress bar. This sequence ensures that the fluorine-doped layer, acting as an optical isolation and chemical barrier layer, is located between the ternary functional layer and the outer layer, ultimately forming a structure from the inside out (from the fiber core side) of "high refractive index ternary glass layer → low refractive index fluorine-doped layer," effectively constructing the required refractive index depression region and achieving excellent thermal stress matching and optical field confinement.

[0085] The relevant formulation parameters for each stress bar can be found in Table 5;

[0086] Table 5. Stress bar formulation

[0087]

[0088] The refractive index of the fluorine-doped silicon dioxide layer was approximately n≈1.44.

[0089] The aforementioned diameter includes the F-doped silicon dioxide layer.

[0090] The stress bar obtained above was then used for the second part of the test.

[0091] Part Two: Efficacy Demonstration

[0092] Fabrication of Orthogonal Dual-Stress Polarization-Maintaining Fiber

[0093] Application Example 1

[0094] Fabrication of 40-micron dual-stress polarization-maintaining fiber

[0095] The structure of the 40-micron dual-stress polarization-maintaining fiber can be referenced. Figure 1It mainly includes a core layer 101, an inner cladding layer 102, an outer cladding layer 103, and a coating layer 106 arranged sequentially from the inside out; the shrinkage stress zone 104 and the expansion stress zone 105 are arranged in a cross shape on the outer cladding layer.

[0096] Before drawing, the core layer 101, the inner cladding layer 102, and the outer cladding layer 103 constitute the substrate of the Φ50mm×500mm synthetic quartz rod; the substrate is prepared by conventional external spray deposition method.

[0097] After drawing, the dimensions and specifications of the core layer 101, inner cladding layer 102, outer cladding layer 103, shrinkage stress zone 104, expansion stress zone 105, and coating layer 106 are shown in Table 6.

[0098] Table 6 Specifications

[0099] mark Component Name Material composition (wt%) Functions and parameters Diameter (μm) 101 Core layer <![CDATA[SiO2- 6wt% GeO2]]> Light guide core (NA=0.16) 4 102 Inner cladding <![CDATA[SiO2- 10wt% F]]> <![CDATA[Transfer stress transition layer (CTE = +3.2×10 -6 / K)]]> 6 103 Outer layer Low-hydroxyl quartz Mechanical protection 40 104 Contraction stress zone <![CDATA[SiO2- 20wt% B2O3]]> <![CDATA[Apply tensile stress (CTE = +25×10 -6 / K)]]> 7.5 105 Expansion stress zone Refer to Table 5 <![CDATA[Apply compressive stress (CTE = -1.5×10 -6 / K)]]> 5 106 Coating layer acrylic resin outer protective layer 90

[0100] Its preparation process is as follows:

[0101] S1: Deep hole machining:

[0102] In the deep hole machining stage, a Φ50mm×500mm synthetic quartz rod is used as the substrate. A deep hole drilling machine equipped with a diamond-coated die (5μm grit) is used to machine a shrinkage stress rod hole (diameter Φ9.2mm) and an expansion stress rod hole (diameter Φ6.2mm), respectively, to achieve a precision deep hole structure with a depth-to-diameter ratio of 41:1 (depth 500mm). After machining, the hole wall is subjected to hydrofluoric acid pickling and drying treatment to strictly control the surface roughness to Ra<0.05μm, providing an ultra-smooth interface for stress rod assembly and eliminating the risk of stress concentration in the subsequent wire drawing process.

[0103] S2: Stress bar preparation

[0104] During the stress bar fabrication stage, differentiated process paths were implemented for shrinkage stress bars and expansion stress bars. Shrinkage stress bars were fabricated using plasma-enhanced chemical vapor deposition (PCVD) to deposit a SiO2-B2O3 glass layer (B2O3 doping concentration 20%), followed by melting and shrinking on a melting lathe, and finally ultra-precision grinding to a cylinder with a diameter of Φ9mm. Expansion stress bars, on the other hand, were fabricated using PCVD to deposit a SiO2-TiO2-Al2O3 ternary composite glass, with a fluorine-doped SiO2 protective layer on the outer layer to suppress the volatilization of high-temperature components; they were then shaped to a standard Φ6mm size using the same ultra-precision grinding process. The core design logic of this process is that the shrinkage bar relies on high borosilicate glass (CTE=+25×10⁻⁶). -6 / K) to achieve directional thermal expansion, and the expansion rod utilizes a titanium-aluminum-silicon composite system (CTE=-1.5×10) -6 / K) generates a negative expansion effect; the risk of material deformation is blocked by the dual technology of nitrogen protection (shrinkage rod) and fluorination coating (expansion rod), and the stress field matching of subsequent orthogonal assembly is ensured by geometric precision control.

[0105] S3: Assembly

[0106] During assembly, the polarization-maintaining master rod (50mm in diameter) undergoes ultrasonic cleaning, hydrofluoric acid (HF) etching, and drying to ensure that the deviation of the central angle of its orthogonal holes is ≤0.02°. The simultaneously implanted boron-doped quartz tensile stress rod (9mm in diameter) and titanium-aluminum-silicon glass compressive stress rod (6mm in diameter) are both surface activated through fine grinding, HF etching, and drying to strictly eliminate the risk of interface bubbles. The high-precision assembly of the three components, through coordinated control of diameter tolerances (master rod ±0.1mm / stress rod ±0.2mm) and surface energy optimization, ensures the geometric orthogonality of the stress zone and zero-defect bonding at the interface, establishing a high-precision stress field foundation for the subsequent wire drawing process.

[0107] S4: Graphite Induction Drawing

[0108] In the graphite induction drawing stage, a graphite induction furnace is used as the core equipment, and fiber forming is achieved through multi-level precision control: the furnace temperature gradient is stabilized at 2000℃ by PID control of the graphite heating element, providing a uniform thermal field for the molten preform; the drawing speed is set at 500 m / min, and the servo motor system achieves a speed accuracy of ±0.1%; the cooling stage uses helium vortex tube technology for forced rapid cooling, enabling the fiber surface cooling rate to exceed ≥100 K / s, quickly locking the residual stress field; the fiber diameter is monitored in real time by a dual laser interferometer and dynamically fed back to the traction system, strictly controlling the final diameter within a tolerance range of 40±0.1 μm. This process, through the synergistic effect of precise thermal field control, uniform speed traction, and ultrafast cooling, solidifies the thermodynamic configuration of the orthogonal stress region at the molecular scale, laying the foundation for the optical anisotropy and mechanical reliability of polarization-maintaining fibers.

[0109] The expansion stress rods used in S2 above are stress rod 1, stress rod 2, stress rod 3, stress rod 5, stress rod 6, stress rod 7 and stress rod 8 as shown in Table 2;

[0110] The dual-stress polarization-maintaining fibers prepared in this way are numbered as fiber 1, fiber 2, fiber 3, fiber 5, fiber 6, fiber 7, and fiber 8, respectively.

[0111] Application Example 2

[0112] Fabrication of 25-micron dual-stress polarization-maintaining fiber

[0113] The application is largely the same as in Example 1, and its specifications are shown in Table 7.

[0114] Table 7 Specifications

[0115] mark Component Name Material composition (wt%) Functions and parameters Diameter (μm) 101 Core layer <![CDATA[SiO2- 6wt% GeO2]]> Light guide core (NA=0.16) 4 102 Inner cladding <![CDATA[SiO2- 10wt% F]]> <![CDATA[Transfer stress transition layer (CTE = +3.2×10 -6 / K)]]> 5.5 103 Outer layer Low-hydroxyl quartz Mechanical protection 25 104 Contraction stress zone <![CDATA[SiO2- 20wt% B2O3]]> <![CDATA[Apply tensile stress (CTE = +25×10 -6 / K)]]> 5 105 Expansion stress zone Stress rod 4 <![CDATA[Apply compressive stress (CTE = -1.5×10 -6 / K)]]> 3.5 106 Coating layer acrylic resin outer protective layer 60

[0116] In this embodiment, a 50 mm synthetic quartz rod is used as the matrix material. Orthogonally distributed double circular holes (central angle deviation ≤ 0.02°) are precisely machined using a deep hole drilling machine, and shrinkage stress rods and expansion stress rods are implanted in them respectively. The shrinkage stress rods are made of SiO2-20wt% B2O3 glass (10.0 mm in diameter), and the expansion stress rods are made of SiO2-12wt% TiO2-8wt% Al2O3 ternary composite glass (atomic ratio Si:Ti:Al = 27.5:3.1:3.2, diameter 7.0 mm), with a diameter ratio d1 / d2 = 1.5. The expansion rod surface is coated with a 0.5 mm fluorine-doped SiO2 protective layer, forming a 90° orthogonal double stress zone structure. The structure is subjected to a high temperature of 1900℃ and a stress range of 10... -3 High-speed fiber drawing is performed under a vacuum environment of Pa, and the residual stress field is locked by helium quenching technology (cooling rate of 100 K / s). The fiber diameter accuracy (25±0.1μm) is controlled in real time by a dual laser interferometer.

[0117] Optical fiber 4 is obtained through the above process.

[0118] Meanwhile, as a comparison, this invention also provides a conventional panda fiber (40 μm), whose core layer is Ge-doped quartz, the stress region consists of two symmetrical B2O3-SiO2 circular regions, and the cladding is pure quartz. This sample is named conventional panda fiber (40 μm).

[0119] Performance testing:

[0120] Test conditions:

[0121] Fiber optic sample length: 100 m

[0122] Environmental testing standard: GB / T 9771.3-2020 "Optical fibers for communication - Part 3: Characteristics of wavelength-band extended non-dispersion-shifted single-mode optical fibers";

[0123] Test items: birefringence Δn, temperature stability (zero deviation drift, -65~85℃, ° / h), minimum bending radius, tensile strength;

[0124] The test results are shown in Tables 8 and 9;

[0125] Table 8 Test Results

[0126] Performance indicators Traditional Panda fiber (40μm) Fiber 2 Fiber 4 Test methods Birefringence Δn <![CDATA[1.8×10 -4 ]]> <![CDATA[4.05×10 -4 ]]> <![CDATA[6.22×10 -4 ]]> Sagnac Intervention Temperature stability (zero offset drift, -65~85℃, ° / h) >0.01 0.005 0.002 Zero Deviation Drift Measuring Instrument Minimum bending radius 3 mm 2 mm 1 mm GB / T 15972.47-2021 tensile strength 100 kpsi 240 kpsi 310 kpsi GB / T 15972.31-2021

[0127] Table 9 Test Results

[0128] Performance indicators Fiber 1 Fiber 3 Fiber 5 Fiber 6 Fiber 7 Fiber 8 <![CDATA[Birefringence Δn (*10 -4 )]]> 3.82 4.8 4.1 4 2.1 4.95 Temperature stability (zero offset drift, -65~85℃, ° / h) 0.007 0 0.005 0.005 0.015 0.006 Minimum bending radius (mm) 2.2 1.8 2 2.1 2.8 2.3 Tensile strength (kpsi) 220 260 235 230 180 210

[0129] Results analysis:

[0130] As can be seen from the results in Table 5, the SiO2-TiO2-Al2O3 glass material of the present invention, when applied to polarization-maintaining optical fibers, has the following advantages:

[0131] (1) Birefringence performance: The measured birefringence Δn of the 40μm dual-stress region polarization-maintaining fiber of this invention reaches 4.05×10 -4 Compared to traditional Panda fiber (1.8×10), -4 The gain is 125%. This breakthrough gain stems from the synergistic effect of the orthogonal dual stress zones: the contraction stress bar (20wt% B2O3) achieves a high positive thermal expansion coefficient (CTE = +25 × 10⁻⁶). -6 / K) applies directional tensile stress to the fiber core, while the expansion stress bar (12wt% TiO2-8wt% Al2O3) utilizes negative thermal expansion characteristics (CTE=-1.5×10) -6 / K) generates reverse compressive stress, and the two together form a strong asymmetric stress field in the core region. Although the stress zone spacing of the 40 μm structure is slightly larger than that of the 25 μm version (resulting in Δn = 6.22 × 10), -4 However, it still achieves birefringence multiplication of traditional structures through material composition optimization.

[0132] (2) Temperature stability performance: Under harsh temperature cycling conditions of -65~85℃, the zero-bias drift of the new 40μm optical fiber is only 0.004° / h, which is 60% lower than that of the traditional structure (>0.01° / h). This advantage is supported by the following three technologies: the negative expansion stress zone (SiO2-TiO2-Al2O3) utilizes the "structural contraction effect" of the titanium oxide octahedron (high-frequency transverse vibration-induced structural contraction) to effectively offset the thermal expansion of the matrix; the fluorine-doped inner cladding (SiO2-10wt% F) acts as a thermal stress buffer layer to block the transmission of temperature deformation to the fiber core; and the inner cladding and fiber core are designed with a matching coefficient of thermal expansion (CTE) of +3.2×10 -6 / K), precisely suppressing thermally induced birefringence drift.

[0133] (3) Enhanced mechanical reliability: The negative expansion characteristics (CTE=-1.5×10) of titanium aluminum silicon glass (SiO2-TiO2-Al2O3) -6 / K) During the fiber cooling process, radial compressive stress (approximately -85 MPa) is applied to the quartz matrix. This residual stress field, together with the low-hydroxyl quartz cladding, enhances reliability: when bent, the compressive layer preferentially offsets the surface tensile stress, reducing the minimum bending radius to 2 mm (33% improvement over the traditional 3 mm fiber); at the same time, combined with the fiber drawing rapid cooling process (≥100 K / s) and deep hole acid etching technology (Ra<0.05 μm), a gradient compressive stress structure that resists crack propagation is formed on the surface, driving the tensile strength to jump to 540 kpsi (an increase of 116%), achieving a generational breakthrough in mechanical properties.

[0134] (4) Enhancement Mechanism Essence: Titanium aluminum silicon glass significantly improves the overall performance of optical fiber through thermo-mechanical coupling effect: its "structural contraction effect" effectively counteracts the positive thermal expansion of the quartz matrix during temperature cycling, suppressing the thermally induced deformation of the fiber core to ≤0.02μm / 100℃, thereby greatly reducing polarization crosstalk (ΔCT optimization range reaches 52%); the synchronously established residual compressive stress field (-85 MPa) forms a mechanical synergy with the outer cladding, preferentially resisting surface tensile stress during bending, achieving a minimum bending radius of 2mm, and simultaneously sealing the propagation path of microcracks. Combined with the rapid cooling process to lock in the high-density structure, a dual breakthrough in temperature stability and mechanical reliability is achieved.

[0135] As can be seen from the results in Table 6, the SiO2-TiO2-Al2O3 glass material of the present invention has the following advantages when applied to polarization-maintaining optical fibers:

[0136] By systematically analyzing the performance data of fibers 1 to 8, the regular influence of material composition and structural parameters on fiber characteristics can be clearly observed. Regarding material composition optimization, fibers 1 to 3 demonstrate the significant effect of fine-tuning the composition in the SiO2-TiO2-Al2O3 system: as the TiO2 content was optimized from 15wt% to 12wt% and then to 11wt%, the birefringence coefficient increased from 3.82 × 10⁻⁶. -4 4.05×10 -4 Up to 4.80×10 -4 The stable improvement in birefringence, coupled with a corresponding improvement in temperature stability (0.007→0.005→0.004° / h), confirms that there exists an optimal ratio of titanium and aluminum elements within the 11-15wt% content range, enabling an ideal thermal compensation mechanism through the "structural shrinkage effect." Structural parameter studies show that fiber 4, by increasing the diameter of the expansion rod to 7mm while maintaining the same fluorine-doped layer parameters, successfully increased the birefringence to 6.22×10⁻⁶. -4 The peak value and tensile strength reached 310 kpsi, and the minimum bending radius was optimized to 1.0 mm, proving that moderately increasing the size of the stress zone helps to form a more uniform stress distribution, thereby achieving a simultaneous breakthrough in optical and mechanical properties.

[0137] Experiments on the fluorine-doped layer (fibers 5-6) revealed the precise window requirement for fluorine content: when the fluorine content was adjusted from the baseline of 8 wt% to 7 wt%, the birefringence remained at 4.10 × 10⁻⁶. -4 The birefringence remained at a relatively high level, with temperature stability maintained at 0.005° / h; however, when the fluorine content increased to 9wt%, the birefringence decreased slightly to 4.00×10⁻⁶. -4 This indicates that excessive fluorine doping may weaken the interfacial bonding strength, and this phenomenon determines that 7-9 wt% is the optimal doping range for fluorine. Of particular note is the experimental confirmation of the crucial role of titanium in the material system through the study of comparative groups of fibers 7-8: the titanium-deficient sample (fiber 7) exhibits severe performance degradation, with birefringence plummeting to 2.10 × 10⁻⁶. -4 The temperature stability deteriorated to 0.015° / h; while the titanium-excess sample (fiber 8) maintained a high birefringence (4.95 × 10⁻⁶). -4 However, its temperature stability (0.006° / h) and mechanical properties (210kpsi) were significantly lower than those of the optimized group. This result verifies from both positive and negative perspectives the necessity of titanium content in the range of 2.8-3.9 mol% for maintaining negative thermal expansion characteristics.

[0138] This study established the application criteria of the SiO2-TiO2-Al2O3 material system in polarization-maintaining optical fibers through eight sets of systematic experiments: In terms of material composition, an optimal ratio window exists between 11-15 wt% TiO2 and 7.5-8 wt% Al2O3; in terms of structural design, a 6-7 mm stress bar diameter combined with a 0.5 mm fluorine-doped layer (7-9 wt% F) achieves the best performance balance; and in terms of elemental control, a titanium content below 2.8 mol% cannot form an effective negative expansion effect, while a content above 3.9 mol% introduces the risk of crystallization. These principles collectively constitute the theoretical basis for the design of high-performance polarization-maintaining optical fibers, providing a scientific basis for the development of next-generation fiber optic sensors.

[0139] This study ultimately constructed a multi-layered material synergy mechanism: In a thermodynamic dimension, a stable asymmetric stress field is formed in the fiber core region through the negative expansion of SiO2-TiO2-Al2O3 and the positive expansion of B2O3-SiO2; in an optical dimension, effective optical field confinement is achieved through the refractive index gradient constructed by the fluorine-doped layer (n=1.43-1.45) and the stress region (n=1.48); and in a mechanical dimension, dynamic mechanical equilibrium is formed by the compressive field of the negative expansion stress region and the tension of the cladding. This multi-layered synergistic design lays a solid material foundation for next-generation high-precision fiber optic sensors and space communication systems, marking a significant paradigm shift in special fiber optic materials from empirical optimization to rational design.

Claims

1. A type of glass with a negative coefficient of thermal expansion, characterized in that, It contains the following molar percentage elements: Si: 26.5~29.5%; M：2.8~3.9%； N：3.0~3.8%； The remaining oxygen element; Among them, at least 50 mol% of the element in M ​​is Ti; The element that makes up at least 70 mol% of N is Al.

2. The glass according to claim 1, characterized in that, M contains the following elements: Ti: 50~100 mol% Zr, Hf, and Sn are each independently selected from 0–50 mol%; The N contains the following elements: Al: 70~100 mol% Y, La, and Ga are each independently selected from 0 to 30 mol.

3. The glass according to claim 1, characterized in that, The glass is composed of the following components by weight percentage: SiO2: 70~85 wt% TiO2: 8~18wt% Al2O3: 5~15wt%.

4. The glass with a negative coefficient of thermal expansion according to claim 3, characterized in that, It consists of the following components by weight percentage: SiO2: 77~81.5 wt% TiO2: 11~15wt% Al2O3: 7.5~8wt%.

5. The glass with a negative coefficient of thermal expansion according to any one of claims 1 to 4, characterized in that, The coefficient of thermal expansion of the glass is -1×10⁻⁶. -6 / K~-2×10 -6 / K; the refractive index of the glass is 1.48±0.

01.

6. A stress bar, characterized in that, The invention includes an expansion rod and an fluorine-doped silica layer covering the outer surface of the expansion rod; the fluorine-doped silica layer serves as a protective layer for the expansion rod and is used to create a refractive index depression between the expansion rod and an external core rod; the material of the expansion rod is as described in any one of claims 1 to 5; the fluorine-doped silica layer contains 7 to 9 wt% fluorine.

7. The stress bar according to claim 6, characterized in that, The diameter or diagonal length of the expansion rod is 4~8mm; the F-doped silicon dioxide layer is 0.2~1.5mm; the cross-section of the expansion rod is circular, square, or bowtie-shaped; if the cross-section is circular, the diameter tolerance is ≤±0.5 μm; if the cross-section is square, the side length is d1, and the chamfer radius is <0.1d1; if the cross-section is bowtie-shaped, the wing opening angle θ = 70°~100°, the wingtip curvature radius R = 0.05~0.1d2, where d2 is the radius of the expansion rod.

8. The stress bar according to claim 6, characterized in that, The refractive index of the refractive index depression region is 1.43~1.45; the refractive index of the expansion rod is 1.48±0.01; and the refractive index of the external core rod is 1.46±0.

01.

9. A method for preparing glass as described in any one of claims 1 to 5, characterized in that, Expanded rods were prepared using plasma chemical vapor deposition (PCVDC) with SiO2, TiO2, and Al2O3 as raw materials.

10. A method for preparing a stress rod as described in any one of claims 6 to 8, characterized in that, An expansion rod was prepared using plasma chemical vapor deposition (PCVDC) with SiO2, TiO2, and Al2O3 as raw materials. A stress rod was then obtained by depositing an F-doped silicon dioxide layer on the periphery of the expansion rod using PCVDC.

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