A fuel injector has an actuator which is situated in an actuator housing connected by force-locking to a valve member at an end on the valve-needle side. The light-emitting element is driven continuously in one of the operating modes, for quick sensing of the object, and is pulsed in another of the operating modes, to reduce power dissipation by the sensor system. The opening spans an arc length of about 90 degrees with respect to the circumference of the scaffold or balloon.