The Rheo-Optics is an experimental method that the optical measurement method or the flow observation is synchronously carried out with the rheological measurement. There are several methods to detect the structure change during the flow. The macroscopic and microscopic flow observation can visualize the phenomenon in the scale of the micrometer to the millimeter order. The small angle light scattering can observe the sub-micrometer to the micrometer size structures. The optical anisotropy, the birefringence and dichroism, can estimate the molecule orientation in the intrinsic effect and the sub-micrometer size structure change in the form effect. These optical methods can detect the specific scale size, but the results of these measurements can be directly compared by using the rheological data as a key data. Therefore, the Rheo-Optics can apply to understand the multiscale phenomena. The basis of the optical measurement techniques and the instruments are summarized. Moreover, the recent topic about the new technology that can detect the two-dimensional optical anisotropy distribution is reviewed.

We briefly introduce some applications of the rheo-optics based on birefringence measurements in order to discuss future challenges of the method. In these applications, the stress-optical rule, which is the proportionality of birefringence and stress, is modified to apply to complex systems having multiple stress origins. We show that the modified rule is very effective to clarify the microscopic origin of stress. The examples are semiflexible polymer solutions, reinforcement effect of silica particles filled rubber, and flow induced structure of wormlike micellar solutions.

This article describes an application of flow birefringence techniques, using the modulated polarization laser beam and the 2D high speed polarization camera for a local flow around a tiny bubble under-pressure oscillating field. Complex local flow is observed around the bubble surface because the bubble shape deforms repeatedly at 20 Hz and 100 Hz. These rheooptic methods can be used to measure the retardation distribution, which is related to the stress field around the bubble. In addition, different retardation distributions were observed during the contraction and expansion phases.

In the past 80 years, high-speed image sensors have been applying to various applications such as microscopy, strain measurement, and spectroscopic temperature measurement. On the other hand, by classifying those applications according to a three-element of the light, polarization has hardly been used until now. In the polarization measurement field, since polarization modulation techniques featuring a rotating polarizer, a photoelastic modulator and a liquid crystal enabled the quantification, they have successfully applied to a thickness measurement system, a shape measurement system and a birefringence measurement system. On the other hand, because currently established systems have employed time modulation, it is difficult to apply them to dynamic phenomena. In order to overcome this problem, a high-speed polarization imaging method has been developed that can measure two-dimensional polarization by single photo-detection. An element technology of High-speed Polarization Image Sensor (HSPIS) has been designed and fabricated. It is composed of a pixelated polarizer array and parallel read out circuits with a multi-channel analog to digital converters. Parallel read out pixels have been connected directly with each polarizer in order to achieve higher sampling rate of two-dimensional polarization detection. In this paper, the basic principle of the HSPIS and its application are introduced.