Optical fiber probing (OFP) is a very useful and practical technique for investigating and monitoring multiphase systems, and it is particularly suitable for simultaneously measuring a bubble's/droplet's chord length, velocity and number density in an industrial-scale apparatus, as well as a laboratory-scale setup. Here, we outline the principles of OFP and propose several types of optical fiber probes that meet the requirements for particular purposes of the multiphase systems in chemical engineering processes. We describe measurement methods that use an optical fiber probe suitably tuned for liquid film and foam, as well as for bubble measurement. The basic measurement principle of OFP is very simple: the probe tip's detection of changes in the refraction indices from a gas phase to a liquid phase or vice versa. For example, to precisely measure a bubble's properties such as the chord length and velocity, it is necessary to determine the precise relationship between the process of the optical fiber probe's penetration into the bubble and the optical signal. Since the probing signal provides a variety of information due to the complicated interaction of the laser beams, optical fiber and gas-liquid interfaces, it is necessary to use both experimental and computational approaches in order to extract the physical meanings of the probe's signals. Using our own fully-3D ray-tracing simulator and well-arranged high-speed visualization setups, we discuss how to improve the measurement accuracy of OFP. We first computationally analyze the OFP signals under several penetration conditions, and we explain our recommendations regarding how to improve the accuracy of a single-tip optical fiber probe used for measurement in multiphase systems. On the basis of our present findings and the improvement in measurement accuracy, we then propose several applications of OFP to chemical engineering processes.