  The ring interferometer with zero optical path difference known as Sagnac one
is offered with a diffraction splitting of the entering light beam. As the
beamsplitter, a transmission holographic Bragg grating is used. Conditions of
normal operation of this interferometer achieve under the equal intensity of
beam copies and the adjustable phase shift between them in its two
interferometer shoulders. These conditions are met with the holographic
grating, which provides the phase shift 180^0 on the central Bragg wavelength.
Experimental approbation of the modified interferometer validates the expected
results.
