Optical seat belt tension sensor

A belt tension sensor includes an armature that is displaced in relation to belt tension and an optical sensing mechanism that detects armature displacement as a measure of belt tension. In a first mechanization, a lens element is mounted on the armature for movement therewith, and light emitted by a light source passes through the lens element before impinging on a light responsive element; the lens element variably diffuses the emitted light in relation to the belt tension, and the light impinging on the light responsive element provides a measure of the belt tension. In a second mechanization, the armature includes a protuberance that abuts and variably collapses a compressible optical waveguide to vary its optical transmissivity in relation to the armature displacement, and the optical transmissivity of the optical waveguide provides a measure of the belt tension.