LAUSR

An adaptive optical fiber sensor/demodulator of an optical phase modulation with a Sagnac interferometer configuration is reported. The dynamic population grating recorded in ytterbium-doped fiber (YDF) at a wavelength of 1064 nm enables adaptive properties of this configuration with a high-pass transfer function and with the cut-off frequency of about 260 Hz at ∼10mW cw recording power. A linear response with nearly 100% modulation depth is ensured by effective formation of the nonshifted phase dynamic grating with the amplitude one order of magnitude greater than can be expected from the saturation of the YDF absorption at the recording wavelength. This is associated with the photoinduced changes in the UV optical absorption of the YDF and enables minimal detected amplitude of the phase modulation ≈0.7∗10-7Hz in our experimental configuration. We believe that, in general, this mechanism of the phase grating formation can ensure the sensor resolution limited by the photonic noise of the utilized light power only.