Abstract: A heating apparatus of an induction furnace used for stretching large-diameter preformed rods of optical fibers, said heating apparatus of the induction furnace comprising a furnace casing, a graphite exothermic sleeve, an insulating layer and an induction coil. At the upper end of the graphite exothermic sleeve is provided a floating seal gland, the inner bore thereof being adapted to the upper end of the graphite exothermic sleeve, and the outer periphery of the floating seal gland being adapted to the top cover plate furnace hole of the furnace casing. The use of the floating seal gland increases furnace stability and prolongs furnace life.

Abstract: A low attenuation single mode optical fiber includes a core layer and claddings. The core layer has the relative refractive index difference (RRID) ?1 ranging from ?0.1% to +0.1% and the radius R1 ranging from 4.0 ?m to 6.0 ?m. The claddings have three claddings layers surrounding the core layer. The RRID of the first cladding layer ?2 ranges from ?0.2% to ?0.6%, and the radius R2 thereof ranges from 10 ?m to 22 ?m. The RRID of the second cladding layer ?3 is less than ?2. The RRID and radius of the first cladding layer and the RRID and radius of the second cladding layer satisfy the relationship of: V=(?2??3)×(R3?R2), and the value of V ranges from 0.15% ?m to 0.8% ?m. The third cladding layer is all the layers that closely surround the second cladding layer, and the RRID of each layer is greater than ?3.

Abstract: A low attenuation single mode optical fiber includes a core layer and claddings. The core layer has the relative refractive index difference (RRID) ?1 ranging from ?0.1% to +0.1% and the radius R1 ranging from 4.0 ?m to 6.0 ?m. The claddings have three claddings layers surrounding the core layer. The RRID of the first cladding layer ?2 ranges from ?0.2% to ?0.6%, and the radius R2 thereof ranges from 10 ?m to 22 ?m. The RRID of the second cladding layer ?3 is less than ?2. The RRID and radius of the first cladding layer and the RRID and radius of the second cladding layer satisfy the relationship of: V=(?2??3)×(R3?R2), and the value of V ranges from 0.15% ?m to 0.8% ?m. The third cladding layer is all the layers that closely surround the second cladding layer, and the RRID of each layer is greater than ?3.

Abstract: A plasma microwave resonant cavity used for a plasma chemical vapor deposition (PCVD) apparatus comprises a resonant cavity housing and a waveguide device connected with the cavity housing. Two ends of the cavity housing are provided with coaxial through-holes along the axial direction of the cavity. A glass inner liner is arranged through the through-holes at the two ends, and runs through a cavity body and the through holes at the two ends. The glass inner liner comprises a glass cylinder and glass stop rings arranged at the two ends of the glass cylinder. One or two ends of the glass cylinder are provided with external threads. The glass stop rings are connected with the ends of the glass cylinder by screw holes formed on the glass stop rings.

Abstract: A plasma microwave resonant cavity used for a plasma chemical vapor deposition (PCVD) apparatus comprises a resonant cavity housing and a waveguide device connected with the cavity housing. Two ends of the cavity housing are provided with coaxial through-holes along the axial direction of the cavity. A glass inner liner is arranged through the through-holes at the two ends, and runs through a cavity body and the through holes at the two ends. The glass inner liner comprises a glass cylinder and glass stop rings arranged at the two ends of the glass cylinder. One or two ends of the glass cylinder are provided with external threads. The glass stop rings are connected with the ends of the glass cylinder (1) by screw holes formed on the glass stop rings.

Abstract: A bending-resistant large core diameter high numerical aperture multimode fiber includes a core and a cladding surrounding the core. The core has a radius R1 in a range of 28 to 50 microns, a refractive index profile of a parabola shape with ? being in a range of 1.9 to 2.2, and a maximum relative refractive index difference ?1% max being in a range of 1.9% to 2.5%. The cladding includes an inner cladding and/or a trench cladding, and an outer cladding disposed from the inner to the outer in sequence. The radius R2 of the inner cladding is in a range of 28 to 55 microns, and the relative refractive index difference ?2% is ?0.1% to 0.1%. The radius R3 of the trench cladding is in a range of 28 to 60 microns, and the relative refractive index difference ?3% is in a range of ?0.15% to ?0.8%.