Low-loss optical fiber for red-green-blue laser transmission and method of manufacturing the same

Abstract

The application relates to the technical field of optical fibers, in particular to a low-loss optical fiber for red-green-blue laser transmission and a preparation method thereof. The optical fiber comprises, from inside to outside, a pure quartz core, a fluorine-doped quartz cladding and a coating layer; the attenuation of the optical fiber is less than or equal to 100 dB / km at a wavelength of 320 nm and less than or equal to 10 dB / km at a wavelength of 630 nm. In the application, the internal plasma vapor deposition method is adopted in the fluorine-doped quartz cladding deposition process, and the heating temperature of the external heating source during deposition is controlled to be 1000-1200 DEG C, and the oxygen partial pressure is controlled to be less than or equal to 4 mbar, so that the penetration and diffusion of oxygen to the pure quartz core are effectively inhibited, the generation of chlorine molecules and non-bridge oxygen hole centers in the core is reduced, the transmission loss of the optical fiber in the 300-700 nm wave band is significantly reduced, and the optical fiber is suitable for high-power red-green-blue laser transmission.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a low-loss optical fiber for red, green and blue laser transmission and its fabrication method. Background Technology

[0002] Red, green, and blue lasers have broad application prospects in industrial processing, medical treatment, and scientific research. Red lasers (wavelength approximately 633nm) are technologically mature and are widely used as indicator light sources in medical and industrial equipment; green lasers (wavelength approximately 532nm) and blue lasers (wavelength approximately 450nm) also have important applications in the medical field; in addition, due to the high absorption rate of blue and green lasers by highly reflective metal materials such as copper and aluminum, blue and green lasers also show good application prospects in the field of highly reflective material processing.

[0003] With the continuous increase in laser output power, the performance requirements for optical fiber materials used to transmit lasers are becoming increasingly stringent. Quartz fiber, due to its excellent optical properties, mechanical strength, and chemical stability, has become the mainstream choice for laser transmission. However, traditional quartz fiber exhibits high inherent loss in the 300-700nm visible light band, which limits its application in high-power red, green, and blue laser transmission.

[0004] Currently, the mainstream methods for fabricating quartz optical fiber preforms are chemical vapor deposition (CVD) or external plasma vapor deposition (IPD). These processes are typically carried out at relatively high temperatures (approximately 2100°C) and under oxygen-rich conditions. Under these conditions, oxygen readily permeates and diffuses into the fiber core material. The oxygen that permeates into the core reacts with the residual Si-Cl bonds in the quartz structure at high temperatures to generate chlorine molecules (Cl2). Simultaneously, excess oxygen also interacts with the quartz network structure at high temperatures to generate non-bridging oxygen hole centers (NBOHCs). These chlorine molecules produce a broad absorption peak at approximately 320 nm, and the NBOHCs produce an absorption band at approximately 630 nm, resulting in a significant increase in background loss in the quartz optical fiber at this wavelength, making it difficult to meet the requirements of low-loss optical fibers for high-power laser transmission.

[0005] Therefore, there is an urgent need to develop a quartz optical fiber with low background loss in the red, green and blue laser bands and its fabrication method. Summary of the Invention

[0006] The purpose of this invention is to address the problem of high background loss in the 300-700nm visible light band of existing silica optical fibers due to structural defects such as chlorine molecules and non-bridged oxygen hole centers, and to provide a low-loss optical fiber for red, green, and blue laser transmission and its fabrication method. This invention employs an internal plasma vapor deposition method to fabricate a fluorine-doped silica cladding during the fabrication process, and controls the deposition temperature and oxygen partial pressure to effectively suppress oxygen penetration into the fiber core region. This reduces the generation of chlorine molecules and non-bridged oxygen hole centers in the fiber core, thereby significantly reducing the transmission loss of the optical fiber in the 300-700nm band.

[0007] To achieve the above objectives, the present invention provides a low-loss optical fiber for red, green and blue laser transmission, wherein the optical fiber comprises, from the inside out, a pure silica core, a fluorine-doped silica cladding and a coating layer; the optical fiber has an attenuation of ≤100dB / km at a wavelength of 320nm and an attenuation of ≤10dB / km at a wavelength of 630nm.

[0008] In some alternative embodiments, the diameter of the pure quartz fiber core is 50-2000 μm.

[0009] In some alternative embodiments, the ratio of the outer diameter of the fluorine-doped quartz cladding to the diameter of the pure quartz fiber core is (1.05-1.4):1.

[0010] In some alternative embodiments, the numerical aperture (NA) of the optical fiber is 0.1-0.4.

[0011] In some alternative embodiments, the coating layer is selected from polyimide coating, polyacrylic resin coating, or silicone coating.

[0012] The present invention also provides a method for fabricating the low-loss optical fiber for red, green and blue laser transmission, comprising the following steps: S1. Provide a pure quartz core rod and a quartz liner, and coaxially insert the pure quartz core rod into the quartz liner to assemble it into a deposition device; S2. A silicon source, a fluorine source, and oxygen are introduced into the annular gap between the pure quartz core rod and the quartz liner tube; simultaneously, the deposition device is heated by an external heating source, and low-pressure plasma vapor deposition is performed under the heating conditions to form a fluorine-doped quartz cladding on the outer periphery of the pure quartz core rod, thus obtaining an optical fiber preform; wherein, during the low-pressure plasma vapor deposition process, the heating temperature of the external heating source is 1000-1200℃, and the oxygen partial pressure is ≤4mbar; S3. The optical fiber preform is drawn into fibers, and a coating layer is applied during or after the drawing process to obtain a low-loss optical fiber for red, green and blue laser transmission.

[0013] In some alternative embodiments, in S2, the silicon source is selected from silicon tetrachloride; the fluorine source is selected from sulfur hexafluoride.

[0014] In some optional embodiments, in S2, the heating temperature of the external heating source is 1000-1100°C.

[0015] In some alternative implementations, in S3, the wire drawing temperature is 1800-2100°C.

[0016] In some alternative embodiments, in S2, the device to be deposited is first evacuated before low-pressure plasma vapor deposition, so that the pressure inside the quartz liner is reduced to 5-15 mbar.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention effectively suppresses the permeation and diffusion of oxygen into the pure quartz fiber core by controlling the heating temperature of the external heating source at 1000-1200℃ and the oxygen partial pressure at ≤4mbar during the deposition of the fluorine-doped quartz cladding. The reduction in oxygen content in the fiber core reduces the generation of chlorine molecules and non-bridged oxygen vacancy centers, thereby eliminating the characteristic absorption peaks in the 300-700nm band caused by these structural defects. Experimental results show that the optical fiber of this invention has an attenuation of ≤100dB / km at 320nm and an attenuation of ≤10dB / km at 630nm, which is far superior to conventional quartz optical fibers.

[0018] (2) The optical fiber of the present invention has low background loss in the red, green and blue laser bands. The efficiency of light energy to heat energy conversion during transmission is low, which effectively avoids the heating effect caused by excessive loss of ordinary quartz optical fiber and can meet the application requirements of high power laser transmission.

[0019] (3) This invention employs an internal plasma vapor deposition method, which significantly reduces the deposition temperature compared to traditional vapor deposition processes. Furthermore, by controlling the oxygen partial pressure, it effectively suppresses the formation of defects in the fiber core. The entire preparation process has highly controllable process parameters, which is conducive to achieving large-scale production.

[0020] (4) The present invention adopts a structure design of pure quartz core / fluorine-doped quartz cladding. By utilizing the characteristic of fluorine to reduce the refractive index of quartz, a good optical field confinement effect is achieved, while avoiding the additional losses that may be introduced by doping other elements in the core. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the low-loss optical fiber used for red, green and blue laser transmission in Embodiment 1 of the present invention; Figure 1 In the diagram, 1 is the pure quartz fiber core, 2 is the fluorine-doped quartz cladding, and 3 is the coating layer; Figure 2This is a refractive index profile of the optical fiber preform in Embodiment 1 of the present invention; Figure 3 This is a comparison chart of the full-band attenuation curves of the optical fiber in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention and are not limited to the described embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0023] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] Example 1 This embodiment provides a method for fabricating a low-loss optical fiber for red, green, and blue laser transmission, comprising the following steps: (1) Raw material preparation Pure Quartz Core Rod: A high-purity synthetic quartz core rod is provided. The quartz core rod has a hydroxyl (OH) content of <1ppm, a total metal impurity content of <0.1ppm, a diameter of 25mm, and a length of 500mm.

[0025] Quartz liner: A quartz glass tube is provided as the liner. The quartz glass tube has a hydroxyl (OH) content >10ppm, a total metal impurity content <1ppm, an inner diameter of 30mm, an outer diameter of 36mm, and a length that matches the mandrel.

[0026] (2) Cleaning treatment of mandrel and liner The pure quartz core rod and quartz liner were ultrasonically cleaned in deionized water for 15 minutes, then ultrasonically cleaned in anhydrous ethanol for 15 minutes, and finally ultrasonically cleaned in deionized water for 10 minutes. They were then dried with high-purity nitrogen and set aside for later use.

[0027] (3) Assemble the deposition apparatus A cleaned and dried pure quartz core rod is coaxially inserted into a quartz liner tube, creating a uniform annular gap between the core rod and the liner tube, thus assembling the deposition apparatus. The deposition apparatus is then mounted onto a plasma deposition apparatus. The plasma deposition apparatus includes a microwave plasma resonant cavity, a raw material gas supply system, a vacuum system, and a heat-preserving furnace. The microwave plasma resonant cavity has a power of 10kW.

[0028] (4) Vacuuming process Start the vacuum system to extract the air from the quartz liner, reducing the pressure inside the quartz liner to 10 mbar. Simultaneously, start the heating furnace and control the temperature to 1000℃.

[0029] (5) Deposition of fluorine-doped quartz cladding After the pressure inside the liner stabilizes at 10 mbar and the temperature stabilizes at 1000℃, silicon tetrachloride, sulfur hexafluoride, and oxygen are introduced into the annular gap between the pure quartz core rod and the quartz liner. The silicon tetrachloride is first heated and vaporized into silicon tetrachloride vapor before being introduced, and then carried in by oxygen as a carrier gas.

[0030] The microwave plasma resonant cavity is activated, and a high-frequency electromagnetic field is excited, causing the gas to ionize and form plasma. Under the action of high-energy electrons in the plasma, the gas molecules are activated and undergo a chemical reaction on the outer surface of the core rod at a deposition temperature of 1000℃, generating fluorine-doped silicon dioxide and depositing it on the surface of the core rod to form a fluorine-doped quartz cladding.

[0031] During deposition, the flow rates of each component are precisely controlled using a mass flow controller to maintain the oxygen partial pressure at 4 mbar. The deposition process continues until the thickness of the fluorine-doped quartz cladding reaches the target value. After deposition, the microwave plasma resonant cavity and raw material gas supply system are shut off, heating is stopped, and the device is allowed to cool naturally to room temperature. Then, the optical fiber preform is removed from the liner.

[0032] (6) Wire drawing The surface of the optical fiber preform is cleaned and then placed on the optical fiber drawing tower. The lower end of the preform is placed in the high-temperature zone of the drawing furnace and heated and melted at 2000℃.

[0033] After the lower end of the preform melts and forms a molten droplet, it falls under gravity to form a filament. This filament is then passed through a traction wheel and a coating device, and the traction system is activated to draw the fiber. During the drawing process, the drawing speed is controlled at 20 m / min, ensuring the preform is drawn thinner at a diameter ratio of 250:1 to achieve the desired fiber core diameter. Simultaneously, the outer diameter of the optical fiber is monitored online, and the drawing speed is controlled via feedback to ensure the uniformity of the fiber diameter.

[0034] During the fiber drawing process, a polyimide coating is applied to the drawn optical fiber. The drawn bare fiber passes through a coating mold containing liquid polyimide coating. After the fiber passes through the coating, the polyimide coating is uniformly adhered to its surface. Then, it undergoes thermal curing in a curing oven at 350℃ to completely cure the polyimide coating. After coating and curing, a finished optical fiber with a polyimide coating is obtained, which is a low-loss optical fiber used for red, green, and blue laser transmission.

[0035] A schematic diagram of the low-loss optical fiber used for red, green, and blue laser transmission in Example 1 is shown below. Figure 1 As shown; Figure 1 In the diagram, 1 represents the pure quartz fiber core, 2 represents the fluorine-doped quartz cladding, and 3 represents the coating layer. From... Figure 1 As can be seen from the diagram, the low-loss optical fiber used for red, green and blue laser transmission consists of a pure quartz core, a fluorine-doped quartz cladding, and a coating layer, from the inside out. The core diameter is 100 μm, the outer diameter of the fluorine-doped quartz cladding is 110 μm, and the outer diameter of the polyimide coating is 150 μm.

[0036] Example 2 This embodiment provides a method for fabricating a low-loss optical fiber for red, green, and blue laser transmission, which differs from Embodiment 1 in that: (1) The diameter of the pure quartz core rod is 15mm; the inner diameter of the quartz liner is 20mm and the outer diameter is 26mm.

[0037] (2) The deposition temperature is 1100℃ and the oxygen partial pressure is 3.5mbar; the power of the microwave plasma resonant cavity is 8kW.

[0038] (3) The drawing temperature is 1950℃ and the drawing speed is 15m / min. The coating layer is made of polyacrylic resin and the curing temperature is 200℃.

[0039] (4) The core diameter of the obtained optical fiber is 50 μm, the outer diameter of the fluorine-doped quartz cladding is 60 μm, and the outer diameter of the polyacrylic resin coating is 90 μm.

[0040] Example 3 This embodiment provides a method for fabricating a low-loss optical fiber for red, green, and blue laser transmission, which differs from Embodiment 1 in that: (1) The diameter of the pure quartz core rod is 50 mm and the length is 600 mm; the inner diameter of the quartz liner tube is 60 mm and the outer diameter is 70 mm, and the length matches that of the core rod.

[0041] (2) The deposition temperature is 1050℃ and the oxygen partial pressure is 3mbar; the power of the microwave plasma resonant cavity is 15kW.

[0042] (3) The drawing temperature is 2000℃ and the drawing speed is 10m / min. The coating layer is a silicone coating with a curing temperature of 200℃.

[0043] (4) The core diameter of the obtained optical fiber is 2000 μm, the outer diameter of the fluorine-doped quartz cladding is 2400 μm, and the outer diameter of the silicone coating is 2800 μm.

[0044] Comparative Example 1 This comparative example provides a conventional quartz optical fiber, which differs from Example 1 in that: it uses external plasma vapor deposition to deposit a fluorine-doped quartz layer on the surface of a quartz core rod under normal pressure using a plasma flame to prepare an optical fiber preform. The deposition temperature is 2100°C and the oxygen partial pressure is 0.6 bar.

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is that the deposition temperature is 1650°C.

[0046] Comparative Example 3 The difference between this comparative example and Example 1 is that the partial pressure of oxygen deposited is 0.5 bar.

[0047] Experimental Example 1 The refractive index profile of the optical fiber preform in Example 1 was tested using the near-field refraction (RNF) method, resulting in the refractive index profile of the optical fiber preform in Example 1, as shown below. Figure 2 As shown. From Figure 2 As can be seen, the refractive index of the core region is higher than that of the cladding region, and there is a clear step-type refractive index difference between the two, indicating that the incorporation of fluorine in the fluorine-doped quartz cladding effectively reduces the refractive index of the cladding.

[0048] Experiment Example 2 Numerical aperture (NA) measurements were performed on the optical fibers prepared in each embodiment and comparative example. The tests were conducted according to GB / T15972.43-2021. The test procedures are as follows: (1) Take the optical fiber samples prepared in each embodiment and comparative example, with a length of 2m, and cut both ends to form flat end faces; (2) Install the optical fiber sample in the numerical aperture test system, align the optical fiber input end with the light source (LED light source with a wavelength of 850nm), and connect the output end to the optical power meter. (3) Rotate the photodetector at the fiber output end with the fiber end face as the center and measure the output light power at different angles; (4) When the output light power drops to 5% of the maximum value, record the angle. The sine value of the angle is the numerical aperture NA of the optical fiber.

[0049] The NA test results are shown in Table 1.

[0050] Table 1 NA Test Results

[0051] Experimental Example 3 The low-loss optical fiber prepared in Example 1 and the conventional silica optical fiber prepared in Comparative Example 1 were subjected to spectral attenuation tests. The tests were conducted according to IEC 60793-1-40 standard using the truncation method. The test steps are as follows: (1) Take an optical fiber sample with a length of 3m and cut both ends to form flat end faces; (2) Place the fiber sample in the spectral analysis test system (the light source is a broadband white light source; the spectrometer is Ocean Optics QE65000), connect the light source and the spectrometer, and measure and record the initial output spectrum of the fiber; (3) Cut the optical fiber 2m away from the input end of the light source and measure the output spectrum of the cut optical fiber again; (4) Based on the power difference between the two measurements, according to the formula α(λ)=10 / L×log 10 [P1(λ) / P2(λ)] calculates the attenuation coefficient of the optical fiber (unit: dB / km), where L is the cut length (2m), P1 is the output power before cut, and P2 is the output power after cut; (5) Repeat the measurement 3 times and take the average value as the final result.

[0052] A comparison of the full-band attenuation curves of the optical fiber in Example 1 and Comparative Example 1 is shown below. Figure 3 As shown. From Figure 3 It can be seen that Comparative Example 1 (curve 1) has obvious absorption peaks at approximately 320 nm and 630 nm. The absorption peak at 320 nm originates from structural defects in chlorine molecules in the fiber core, and the absorption peak at 630 nm originates from structural defects in the non-bridged oxygen hole centers in the fiber core. In contrast, Example 1 (curve 2) did not observe the above-mentioned characteristic absorption peaks in the 300-700 nm band, its attenuation curve was smooth, and its overall loss level was significantly lower than that of Comparative Example 1.

[0053] In addition, the attenuation coefficients of the optical fibers prepared in other embodiments and comparative examples were tested at 320 nm and 630 nm respectively, and the attenuation coefficient test results were recorded as shown in Table 2.

[0054] Table 2 Attenuation Coefficient Test Results

[0055] The test results above show that the low-loss optical fiber prepared by controlling the deposition temperature at 1000-1200℃ and the oxygen partial pressure below 4 mbar in the embodiments of the present invention exhibits attenuation ≤100 dB / km at 320 nm and attenuation ≤10 dB / km at 630 nm, significantly better than Comparative Examples 1-3. Comparative Example 1, using external plasma vapor deposition (deposition temperature 2100℃, oxygen partial pressure 0.6 bar), showed significantly higher attenuation values ​​at 320 nm and 630 nm than the embodiments, indicating that the high-temperature, oxygen-rich conditions led to the generation of a large number of chlorine molecules and non-bridging oxygen vacancy centers in the fiber core. Comparative Example 2 also showed a relatively high attenuation value, indicating that excessively high deposition temperatures lead to increased oxygen penetration into the fiber core, thereby introducing structural defects. Comparative Example 3 also showed a significantly higher attenuation value than the embodiments, indicating that oxygen partial pressure is also a key factor affecting the formation of fiber core defects.

[0056] In summary, this invention employs an internal plasma vapor deposition method during the deposition of fluorine-doped quartz cladding, controlling the heating temperature of the external heating source at 1000-1200℃ and the oxygen partial pressure at ≤4mbar. This effectively suppresses the permeation and diffusion of oxygen into the pure quartz fiber core, reduces the generation of chlorine molecules and non-bridged oxygen vacancy centers in the fiber core, and thus significantly reduces the transmission loss of the optical fiber in the 300-700nm band. The fiber attenuation is ≤100dB / km at 320nm and ≤10dB / km at 630nm, making it suitable for high-power red, green, and blue laser transmission. Furthermore, the fabrication process of this invention is mild and controllable, facilitating large-scale production and possessing significant industrial practical value and broad market application prospects.

[0057] Finally, it should be noted that the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A low-loss optical fiber for red, green, and blue laser transmission, characterized in that, The optical fiber comprises, from the inside out, a pure quartz core, a fluorine-doped quartz cladding, and a coating layer; the optical fiber has an attenuation of ≤100dB / km at a wavelength of 320nm and an attenuation of ≤10dB / km at a wavelength of 630nm.

2. The low-loss optical fiber for red, green, and blue laser transmission according to claim 1, characterized in that, The diameter of the pure quartz fiber core is 50-2000μm.

3. The low-loss optical fiber for red, green, and blue laser transmission according to claim 1, characterized in that, The ratio of the outer diameter of the fluorine-doped quartz cladding to the diameter of the pure quartz fiber core is (1.05-1.4):

1.

4. The low-loss optical fiber for red, green, and blue laser transmission according to claim 1, characterized in that, The numerical aperture of the optical fiber is 0.1-0.

4.

5. The low-loss optical fiber for red, green, and blue laser transmission according to claim 1, characterized in that, The coating layer is selected from polyimide coating, polyacrylic resin coating or silicone coating.

6. The method for fabricating the low-loss optical fiber for red, green, and blue laser transmission according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Provide a pure quartz core rod and a quartz liner, and coaxially insert the pure quartz core rod into the quartz liner to assemble it into a deposition device; S2. A silicon source, a fluorine source, and oxygen are introduced into the annular gap between the pure quartz core rod and the quartz liner tube; simultaneously, the deposition device is heated by an external heating source, and low-pressure plasma vapor deposition is performed under the heating conditions to form a fluorine-doped quartz cladding on the outer periphery of the pure quartz core rod, thus obtaining an optical fiber preform; wherein, during the low-pressure plasma vapor deposition process, the heating temperature of the external heating source is 1000-1200℃, and the oxygen partial pressure is ≤4mbar; S3. The optical fiber preform is drawn into fibers, and a coating layer is applied during or after the drawing process to obtain a low-loss optical fiber for red, green and blue laser transmission.

7. The preparation method according to claim 6, characterized in that, In S2, the silicon source is selected from silicon tetrachloride; the fluorine source is selected from sulfur hexafluoride.

8. The preparation method according to claim 6, characterized in that, In S2, the heating temperature of the external heating source is 1000-1100℃.

9. The preparation method according to claim 6, characterized in that, In S3, the wire drawing temperature is 1800-2100℃.

10. The preparation method according to claim 6, characterized in that, In S2, before performing low-pressure plasma vapor deposition, the device to be deposited is first evacuated to reduce the pressure inside the quartz liner to 5-15 mbar.

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