**3.1 Optical fiber sensor geometry**

The validation of drawn fiber sensor geometry such as tapered fiber, MZI etc. can be done by using scanning electron microscopy (SEM). SEM is a kind of electron microscopy which employs a focused beam of the electron to analyze the surface of optical fibers. The SEM image of a tapered optical fiber probe is illustrated in **Figure 9**. In **Figure 9**, there are two SEM images where the first one is representing an image of tapered optical fiber sensor and another image such as **Figure 9(b)** is representing the distribution of nanoparticles coated over the sensing region of fiber structure. In some other cases, the diameter analysis of tapered optical fiber sensor structure was measured directly by using the fabricating machine, but the accuracy of the measured diameter was not up to the mark, and illustrated in **Figure 10** [55].
