Why does India still import most of the glass preform behind its own optical fibre?

Every kilometre of optical fibre that carries India's telecom traffic, its BharatNet broadband, and its defence networks begins as a single object: a glass rod called a preform. India imports between 40 and 85 per cent of the preform it consumes, a dependence estimated in 2025 across India and Southeast Asian markets. The fibre-drawing towers are here; the glass they draw from is largely not.

What it is, and why it is hard

A preform is a metre-scale cylinder of ultra-pure glass with a precisely doped core. Drawing it out produces hundreds of kilometres of hair-thin fibre. Making the preform is the hard part.

The processes that build it — Modified Chemical Vapour Deposition (MCVD), Outside Vapour Deposition (OVD), Vapour Axial Deposition (VAD), Plasma Activated CVD (PCVD) — deposit doped glass layers atom by atom from vapour. They are capital-intensive and demand cleanroom-grade purity with precise control of dopants that set the fibre's refractive-index profile. VAD alone accounts for over 55 per cent of the global market. Only six nations manufacture preform at scale: the United States, Japan, China, Italy, South Korea and India. The top three global producers — YOFC, Corning and Prysmian — hold more than 40 per cent of the market between them.

Where India stands

India's presence on that list rests heavily on one firm. Sterlite Technologies (STL) has made preform indigenously at Aurangabad since the 1990s, tracing back to an optical fibre plant built there in 1995. In 2019 it added the Gauav plant, which STL describes as one of the world's largest greenfield semiconductor-grade preform facilities. For years, industry analysis noted STL was the only Indian firm with the technology — an advantage that gave it higher margins than competitors who merely draw fibre from imported rod. Aksh Optifibre is also credited with niche preform capability, though at far smaller scale.

The country's second-largest fibre-cable maker, HFCL, still imports its preform. In 2026 its board approved roughly ₹580 crore for a greenfield preform plant of 300–310 MT capacity, described by managing director Mahendra Nahata as backward integration to cut upstream import dependence. Completion is targeted for July 2029. So the honest status is: India produces preform, but the capability is concentrated, and the second-tier is only now committing to localise — three years out.

Why the gap persists

The reason is layered beneath the preform itself. Drawing towers and standards certification are the mature parts of the chain. The upstream inputs are not. High-purity precursor and dopant chemicals — silicon tetrachloride, germanium tetrachloride, phosphorus oxychloride — are not made domestically at the required grade. Neither is the precision glass-lathe and deposition-furnace equipment, nor the specialty rare-earth dopants such as erbium and ytterbium used in amplifier and defence-grade fibre. Ultra-pure synthetic silica glass, the core feedstock, is still emerging.

Preform is where these gaps converge. A firm can install a drawing tower cheaply; building a preform line means securing purity, chemistry and capital equipment simultaneously. That is why import dependence persists even as cable capacity scales.

The direction is already visible in the industry's own moves. Globally, major cable makers in India and China are investing in captive preform production to secure supply, driven by government broadband programmes procuring fibre by the multi-million kilometre. HFCL's 2029 plant is India's example of that logic.

Closing the gap durably means building the layers under the preform: domestic precursor chemistry, precision deposition equipment, and specialty dopants, not only more deposition capacity. The external market rewards it — Indian preform exporters have begun shipping into China but hold under 2 per cent there, held back by qualification barriers. The climb is from a working foothold, not from zero.