SANTA CLARA, California, March 11 (Reuters) - Celestial

AI, one of several Silicon Valley chip startups aiming to crack

a key speed constraint in artificial intelligence, said on

Tuesday it has raised an additional $250 million in venture

capital, bringing its total raised to date to $515 million.

Celestial AI is tapping photonics - a technology that uses

light, rather than electrical signals - to create speedy links

between AI computing chips and memory chips.

The speed of that connection, a measure called memory bandwidth,

has become so central to advancing AI systems that it is one of

the factors that determine whether a chip is subject to U.S.

government export controls such as those designed to limit

China's AI advances.

At present, Nvidia ( NVDA ) reigns supreme in memory bandwidth

with proprietary technologies called NVLink and NVSwitch. That

has set off a technology race among startups and a flurry of

funding to find alternatives that can be used by other chip

firms. Celestial AI rivals Lightmatter and Ayar Labs have raised

$850 million and $370 million, respectively.

Celestial AI, which is backed by the venture arm of Nvidia ( NVDA )

rival Advanced Micro Devices ( AMD ), is developing a technology

that can sit like a bridge between two or more chips and uses a

different kind of photonics technology than its rivals.

The goal of this "photonic fabric," Celestial AI CEO Dave

Lazovsky told Reuters, is to provide speed while saving space

and power, the two things that are at a premium in every chip's

design.

"There are no good answers right outside of Nvidia ( NVDA ),"

Lazovsky said in an interview at the firm's Santa Clara,

California headquarters. "What we had created with the photonic

fabric does the same thing, but at a different level of energy

efficiency and of latency."

Celestial AI said the new round of funding was led by

Fidelity Management & Research and joined by BlackRock ( BLK ),

Maverick Capital, Tiger Global Management and Lip-Bu Tan, the

former CEO of chip design software firm Cadence Design Systems.

Also joining were existing investors AMD Ventures, Koch

Disruptive Technologies, Singapore state investor Temasek,

Temasek's wholly-owned subsidiary Xora Innovation, Porsche

Automobil Holding and The Engine Ventures.