Optical sensing is ubiquitous in science and technology, and is becoming prevalent in our daily lives. These sensors cover a wide range of complexity, from the simple clip-on oxygen monitoring devices in our local doctor’s office, to the miniature CCD arrays in our smart phone cameras, to the high-sensitivity optical gyroscopes navigating the planes we occupy when flying. This proliferation of optical sensors is due to the wide availability of varied optical sources and detectors, which are enabled by new materials, a better understanding of the physics of environmental optical perturbations, and the wide availability of custom designed optical fibers, as well as powerful software codes linking it all together. One advantage of optical sensors is that they can have unprecedented precision. Examples of their uncertainties are: optical clocks (10-15 second), gravitational wave detectors (10-21 strain), magnetometers (pico-Teslas), and super-resolution optical microscopy (nano-meters).