Fiber Optic Quartz at the Core of Every Optical Fiber

In fiber manufacturing, the preform components are not passive hardware — defects and impurities introduced at the preform stage are copied into every metre of fiber drawn from it. Six factors make fiber optic quartz selection more consequential than in almost any other application.

Ultra-Low Hydroxyl (OH)

OH groups create the 1383 nm water peak that raises fiber loss. Low-water-peak fiber needs low-OH fused silica throughout the cladding, including the substrate tube.

Metallic Purity

Sub-ppb iron, chromium, copper or nickel create absorption centres. Tube glass must be high-purity so contamination cannot diffuse into the deposited core layers.

Wall-Thickness Uniformity

Substrate-tube eccentricity becomes core ellipticity and polarisation mode dispersion in the fiber. Tight wall control protects high-speed transmission margin.

Thermal & Chemical Stability

Deposition, collapse, dehydration and sintering all run hot and use halide and chlorine chemistry. Fused silica survives these without contaminating the preform.

Dimensional Reproducibility

OD, ID, bow and surface finish must repeat lot-to-lot across millions of metres of fiber. Consistent quartz preform tubes keep fiber performance in spec.

Index Control via Doping

Fluorine-doped tubes depress the index for the cladding; germanium-doped layers raise it for the core. Controlled dopant grades set numerical aperture and cut-off.

FGQuartz supplies high-purity fused silica across the entire optical fiber preform chain — from the substrate tube on the glass lathe to the final jacketing assembly before draw. Custom dimensions matched to specific lathe platforms and OEM process specs are produced from the same facility.

The MCVD substrate tube is the most geometrically critical component in inside-deposition preform manufacturing. It rotates on the glass lathe while the torch traverses, depositing the layers that become the cladding and core. Wall-thickness eccentricity translates directly into core ellipticity and PMD, so FGQuartz controls OD, ID, wall uniformity and bow to lathe-chuck specs, in low-OH grade.

SMF / MMF / DSF · Matched to lathe OD · Low-OH grade

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After the core-cladding rod is deposited, a large-diameter quartz preform tube with a precise inner bore is sleeved over it and fused in a jacketing furnace to build the outer diameter up to draw size. Because the jacket fuses into the fiber cladding, its purity and bore quality matter as much as the rod. FGQuartz supplies overclad and jacketing tubes in a range of bores for standard preform rod diameters.

Overclad · Jacketing · Large-bore precision · Low-OH

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In VAD, flame-hydrolysis burners grow a porous soot preform axially at the tip of a rotating starting rod. The reaction tube around the deposition zone gives a controlled atmosphere, and the starting rod — the seed for the core — must be low-OH fused silica free of trace metals. FGQuartz supplies VAD reaction tube assemblies, deposition-zone liners and low-OH starting rods for telecom-grade fused silica preform growth.

Reaction chambers · Low-OH starting rods · Zone liners

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In outside vapour deposition, a rotating mandrel is coated with successive soot layers, then removed after sintering to leave a hollow soot preform. The mandrel must survive deposition while staying removable without damaging the preform. FGQuartz produces fused silica OVD mandrels in solid and hollow-tube forms, plus deposition enclosure tubes, burner-housing parts and soot-handling fixtures.

Removable mandrels · Enclosure tubes · Handling fixtures

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Single-mode and many specialty designs need a cladding index below pure silica, achieved by doping the glass with fluorine. F-doped quartz tubes serve as inner cladding in MCVD and as surrounding cladding in rod-in-tube assembly. Dopant concentration sets the index depression — and so the numerical aperture and cut-off wavelength. FGQuartz supplies F-doped fused silica tubes for SMF, dispersion-shifted and PM designs.

F-doped SiO₂ · Depressed-cladding · NA control · PM-compatible

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Specialty fibers — PM, photonic crystal, large-mode-area, rare-earth-doped, hollow-core and multi-core — need preform parts well beyond standard telecom geometry. FGQuartz makes PCF capillary tubes and matching solid rods, PM jacket tubes with CNC-drilled SAP holes, large preform cylinders, lathe chuck fittings and draw-tower hardware — to exact drawing, from single-piece prototypes to production volume.

PCF capillaries · PM jackets · Lathe fittings · DXF / STEP / IGES

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Each preform process uses a different set of quartz components. Here is what FGQuartz supplies into each, and why each part must be fused silica.

A quartz substrate tube is mounted on a glass lathe; an oxy-hydrogen torch traverses outside while halide vapours (SiCl₄, GeCl₄, POCl₃) flow inside and oxidise into glass layers — cladding first, then high-index core. The tube is then collapsed into a solid preform. The substrate tube becomes the outermost cladding, so its purity must match the deposited glass. FGQuartz supplies MCVD substrate tubes, lathe chuck inserts, tail-stock couplings and fluorine-doped cladding tubes.

Flame-hydrolysis burners grow a porous soot preform axially on a rotating seed rod, producing a graded index naturally through deposition-zone geometry. The soot preform is then dehydrated with chlorine and consolidated into clear glass in a sintering furnace. The reaction tube, deposition-zone liner, starting rod and sintering muffle tube must all be high-purity fused silica. FGQuartz supplies starting rods, reaction tubes, zone liners, sintering muffle tubes and chlorine-treatment tubes.

A traversing burner deposits soot onto a rotating mandrel — cladding outward first, then the doped core. The soot cylinder is removed from the mandrel, consolidated and drawn. For specialty fiber, fused silica mandrels are preferred over alumina to avoid particle contamination at the preform inner surface. FGQuartz produces fused silica OVD mandrels (solid and hollow), deposition enclosure tubes, exhaust-handling parts and sintering furnace liners.

A core-cladding rod is inserted into a fused silica jacketing tube and fused by zone heating into a larger preform ready for draw — used when the deposited preform is too small or needs more cladding glass. The jacket becomes part of the fiber cladding, so its purity and inner-bore quality matter. FGQuartz supplies jacketing and overclad tubes, large-bore precision tubes, fluorine-doped cladding and jacketing furnace liners.

Polarisation-maintaining fiber embeds borosilicate stress-applying parts (SAPs) in a fused silica cladding to create birefringence (PANDA, bow-tie). Photonic crystal fiber stacks thin-walled quartz capillaries and solid rods into a precise array drawn down to fiber. Both demand high dimensional uniformity. FGQuartz supplies PM jacket tubes with CNC-drilled SAP holes, overclad tubes, PCF capillary tubes, solid cladding rods and hollow-core elements.

The draw tower heats the preform tip to the softening point and pulls fiber at controlled speed and diameter. While the furnace uses graphite or induction heating, quartz components sit throughout: preform feed collets, neck-zone baffles and heat shields, gas-purge tubes, and UV-transparent windows for the coating-cure zone. FGQuartz supplies preform chuck inserts, neck-zone baffles, atmosphere-control tubes and UV curing windows for production and research draw towers.

FGQuartz fiber optic quartz components are used to make optical fiber across the full range of types — from high-volume telecom fiber to small-batch specialty fiber for research, sensing and high-power lasers.

The backbone of global telecom. ITU-T G.652, G.654 and G.657 fibers are drawn in huge volumes from MCVD, VAD and OVD preforms. Substrate and jacketing tubes must hold quality across lots of millions of metres. FGQuartz supplies these to SMF-line specs with tight lot-to-lot consistency.

Graded-index MMF carries 10G/25G/100G links in data centres and LANs. Preforms come mainly from MCVD and VAD with precise radial index control. Substrate tubes must be dimensioned to yield 50 µm or 62.5 µm cores on collapse. FGQuartz supplies tubes for both core sizes.

PM fiber is essential for coherent comms, fiber-optic gyroscopes and interferometric sensors. PANDA, bow-tie and elliptical-clad types need SAPs embedded in fused silica jackets. FGQuartz supplies jacket and overclad tubes with the precision needed for correct SAP positioning relative to the core.

Erbium-doped amplifiers (EDFAs) and ytterbium fiber lasers drive telecom and kilowatt industrial lasers. The rare-earth core is doped during MCVD, and the cladding geometry must allow efficient pump coupling. FGQuartz supplies large-mode-area jacketing and overclad components for high-power fiber laser preforms.

PCF enables endlessly single-mode guidance, hollow-core guidance and high nonlinearity for supercontinuum generation — assembled from capillary and rod stacks. FGQuartz produces the high-uniformity PCF capillary tubes and matching solid rods for stack-and-draw preforms, including hollow-core and anti-resonant designs.

Distributed temperature, acoustic and strain sensing (DTS/DAS) use fiber as a continuous sensor over tens of kilometres. In harsh settings — downhole, subsea, high-voltage — fiber must also survive heat and aggressive chemistry. FGQuartz supplies the specialty substrate and jacketing tubes used for sensing and hermetically coated fiber.

Quartz selection and quality control at the preform stage is more consequential than in almost any other application — defects introduced there are present in every metre of fiber drawn from that preform.

OH groups in fused silica create IR absorption — the fundamental peak at 2.73 µm with overtones at 1383 nm (the water peak), 1.24 µm and 0.95 µm, all in the telecom bands. Low-water-peak fiber (G.652.D) reaches below 0.4 dB/km at 1383 nm using ultra-low-OH glass throughout the cladding, including the substrate tube. High-OH grade — good for deep-UV optics — is unsuitable as a low-water-peak substrate tube.

The substrate tube is a precision optical component, not a passive container. Wall-thickness eccentricity sets the roundness of the deposited cross-section and hence core ellipticity — which causes polarisation mode dispersion (PMD), a limit on high-speed long-haul links. Tube bow affects deposition uniformity along the length and can cause chromatic-dispersion variation in the drawn fiber. This is why OD, ID, wall and bow are measured along the full tube length.

Even with dry precursors, residual OH is incorporated during deposition. To reach the sub-0.4 dB/km water peak of G.652.D, the soot preform is treated with chlorine before consolidation — Cl₂ reacts with OH to form HCl, which diffuses out. The treatment tube must be high-purity fused silica compatible with hot chlorine chemistry and must not reintroduce OH. The mix of high temperature, halide chemistry and strict purity rules out lower quartz grades.

Optical fiber is among the purest glass made at scale — core glass holds transition metals at parts-per-trillion, because sub-ppb iron, chromium, copper or nickel add absorption above the Rayleigh limit. Although the tube glass ends up in the outer cladding, contamination can diffuse into the deposited layers during hot deposition and collapse. So substrate and jacketing tubes must be high-purity grade fused silica, even though the tube is nominally outside the optical core.

Tell us your preform process, lathe platform, substrate-tube dimensions and fiber type. The FGQuartz engineering team will respond with the right specification and a detailed quote within 24 hours.