A spectroscopic based optical fiber sensor includes a sensitive optical fiber, a probing light source, a power supply, a detector means, a signal processing means, and a display means. The sensitive optical fiber is optically affected by the presence of at least one measurand. The probing light source, adjacent to the sensitive fiber, transversely illuminates the fiber from the outside. The probing light is modified by the sensitive fiber, coupled into the optical fiber core, either as bound modes or leaky modes, as a light signal and guided to a detector means located at the terminus of the optical fiber. The detector means correlates the intensity of the light signal with an electric signal and transmits the electric signal to the signal processing means, wherein the electric signal is correlated to the quantity being measured. The correlated quantity being transmitted and displayed on the display means.