Non‐touch detection of rhodamine B concentration in distilled water using fiber coupler and concave mirror (CM) successfully demonstrated. Based on displacement sensor, the concentration of rhodamine B is detected through the peak voltage value which is resulted from the displacement profile. Using the He‐Ne (543 nm) laser as the source, the fiber coupler as the sensor probe and CM with the curvature radius of 12 mm as the reflector as well as the sample container, the rhodamine B concentration can be detected in the range 0‐20 ppm and the resolution of 0.26 ppm.