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In this work we present an optical refractive index sensor based on the spectral analysis of anomalies in the optical response from the diamond like carbon film (DLC) diffraction grating employing polarized polychromatic light. The sensor consists of holographic diffraction grating formed in a thin (110 nm) SiOx doped DLC film synthesized by direct ion beam deposition from the mixture of the hexamethyldisiloxane vapor with hydrogen as a feed gas on the fused silica substrate. The diffraction grating (period 435 nm) in DLC was formed employing HeCd laser beam interference lithography in positive tone photoresist and plasma chemical etching in CF4/O2 gas mixture. Use of DLC as a grating material ensures chemical inertness of the system preserving the spectral range and sensitivity necessary for the measurement. [ABSTRACT FROM AUTHOR]