The reciprocal linear effect, a new optical effect of the Sagnac type

The Sagnac effect can be demonstrated with light propagating either along a circular contour or, as done by Wang et al., back and forth along a linear contour. In the linear Sagnac effect, the emitter-receiver device is in motion relative to the contour where light propagates. In the reciprocal linear Sagnac effect (RLSE), the device is stationary and the contour is in motion. When the contour changes direction of motion, some special features of the linear Sagnac effect are not fully reciprocal to the RLSE, which foresees variations of the first order in v/c in the round-trip time taken by a light signal to cover the contour. The RLSE can be tested with present technology and, if confirmed experimentally, it might have interesting technological applications. Presently, it can be important for testing light-speed invariance, simultaneity, and the relativity principle.