Light travels at 299,792 km/s in a vacuum.
Inside optical fibre it slows to about 200,000 km/s.
That's already fast enough to circle Earth 5 times per second.
On July 21, 2026, researchers announced a programmable optical chip that can slow light further, on demand, and precisely control the delay.
Why engineers care:
In photonic computing and quantum networks, timing is everything.
When optical signals arrive at slightly different times, data gets scrambled.
Current systems use fixed optical delay lines, loops of fibre that add a set delay.
Fixed means inflexible. Any change in traffic pattern requires physical hardware changes.
This chip programs the delay in software.
Different signals can be slowed by different amounts, simultaneously, on the same chip.
Applications already being developed:
• Optical signal synchronisation for photonic AI accelerators
• Quantum network nodes that need to hold quantum states while other parts of the system catch up
• Radar and sensing systems where precise signal timing determines accuracy
Einstein said nothing can travel faster than light.
Engineers are now deciding exactly how much slower it goes.