 Thus the rhomb functions as if it were a wideband quarter-wave plate — in contrast to a conventional birefringent (doubly-refractive) quarter-wave plate, whose phase difference is more sensitive to the frequency (color) of the light.The material of which the rhomb is made — usually glass — is specifically "not" birefringent.The Fresnel rhomb is named after its inventor, the French physicist Augustin-Jean Fresnel, who developed the device in stages between 1817 and 1823.