Soft Wormhole

The topology of spacetime is not flat. Going from Earth to Alpha Centauri the long way takes over 4 years at lightspeed.

Fortunately the topology of the universe is sufficiently stretched that there are shorter ways to get there without officially breaking lightspeed. These ways are hidden tunnels in the fabric of spacetime. Your warp engine does not create such tunnels. It simply makes the visible.

Of course light and gravity also transmits through these tunnels. But that is no problem.

Soft Wormhole

Soft wormholes do not require us to invent any new physics. Soft wormholes break no known laws of physics.

The topology of spacetime is not flat. It has tunnels. Going from Earth to Alpha Centauri in a straight line takes over 4 years at lightspeed. Going a wavey-gravey path might take 10 years. Going through the tunnel gets you there in weeks without officially breaking the speed of light. 

Your warp engine does not create such tunnels. It simply makes the visible.

Of course light and gravity also transmits through these tunnels. But that is no problem.