**2. Typical applications of OI in science and engineering**

Interferometry resulting from electromagnetic waves has been used in many routine applications. One of the most popular methods in OI involves the superposition of Doppler-shifted laser beams. For simplicity and convenience of discussion, applications of interferometry could be divided into three major areas of science and engineering research. Historically physics and astronomy have used interferometry in many ways and could be taken as the first major application area. The second group of applications could be grouped under the engineering and applied science header. Finally, applications focused on research problems related to biology makes the third major area. Of course, this oversimplified classification is insensitive to some nuances of interdisciplinary works and serves only an ad hoc purpose.

These techniques found extensive relevance in investigations where probing small displacements, refractive index changes, surface irregularities, and remote analysis of optical signals are needed [11]. The progress of technology has played a critical role in shaping the advancement of these techniques. Even the "successful" demonstration of the famous negative result in physics from the 19th century, named after Michelson and Morley, found extraordinary level of precision with the help of modern technologies [12]. Interferometers have typically been used in the scientific industry for manufacturing and characterization of surfaces, integrated circuits, multiplexing methods needed for applications in telecommunications, in navigation systems, and to aid spectroscopy for materials characterization [13].

Extremely active and rapidly progressing, the typical applications provide the foundations for many interdisciplinary applications of OI techniques. These examples, noted in Section 3, are the most awe-inspiring results of modern-day scientific research.
