Highly efficient free-space fiber coupler with 45° tilted fiber grating to access remotely placed optical fiber sensors

In this work, a 45° tilted fiber grating (TFG) is used as a waveguide coupler for the development of a portable interrogation system to access remotely placed optical fiber sensors. The TFG is directly connected to a remote fiber sensor and serves as a highly efficient light coupler between the portable interrogation unit and the sensor. Variation of strain and temperatures are measured with a standard fiber Bragg grating (FBG) sensor, which serves as a remotely placed optical sensor. A light beam from the interrogation unit is coupled into the TFG by a system of lenses, mirrors and optical collimator and acted as the input of the FBG. Reflected light from the FBG sensor is coupled back to the interrogation unit via the same TFG. The TFG is being used as a receiver and transmitter of light and constituent the key part of the system to connect "light source to the optical sensor" and "optical sensor to detector." A successful demonstration of the developed system for strain and temperature sensing applications have been presented and discussed. Signal to noise ratio of the reflected light from the sensors was greater than ∼ 40 dB.