HFCL itself is in process. It joined a Department of Telecommunications-funded consortium led by IIT Delhi to develop hollow core fiber.
Source:
But STL Tech has more lead in this than HFCL. They launched India’s first hollow-core fiber cable just few days back. They are specifically targeting AI Data Centers, hyperscalers, and high-frequency trading setups.
You can read this thread it is very well covered by @HIMSHAH @saurabhsharmaa2020