For measuring the angle of rotation of flat objects using projected fringes, the method of point-of-light triangulation and the method of line-of-light triangulation will breakdown when the grating lies on the axis of rotation. Therefore, a grating other than a point or linear lines is preferred. In this paper, a simple Michelson interferometer-based method for the generation and projection of circular gratings is described. The basic optical element in a Michelson interferometer is a beam- splitting cube. With this Michelson interferometer, a circular grating is observed when the screen is placed normal to the line containing the two point-light sources produced by the beam splitter. By placing an expander between the beam-splitter and the laser source, and by carefully adjusting the two mirrors beside the beam- splitting cube, the frequency of the circular grating can be adjusted. This paper also describes the use of the generated circular optical grating for measuring the amount of rotation of flat surfaced that are either diffuse or specularly reflective - the method is based on relating the distortion of the circular grating to the angular rotation of the surface.
In recent years, optical fringe-projection and other optical interferometric techniques for surface profiling have received much attention because they are whole-field and non-contacting; very high data processing speeds can be achieved using computer image-processing techniques. These advantages over many other mechanical probe-based techniques are particularly useful for the measurement of large surfaces as well as for micro-systems at the sub-micron level. In the fringe-projection technique, a reference optical grating is first generated and then projected onto the surface of interest. For a given optical set-up, the distribution of the reference grating is perturbed in accordance with the profile of the test surface, thereby enabling direct derivation of surface profiles from measurements of the perturbed fringe distribution. The reference gratings are readily generated with a Michelson interferometer, which uses a beam-splitting cube and mirrors - these optical elements are readily available in all laboratories. A major drawback of this technique is the need for good vibration isolation, as otherwise unstable fringes will be generated. Alternatively, beam-splitting cubes with coated reflective surfaces can be used, but this would not allow adjustment of the frequency of the generated fringes. This paper describes a very simple method of generating and projecting optical grating for surface profiling. The working principle is based on the reflection-refraction of a commercial beam-splitting cube. By carefully adjusting the orientation of the laser beam, the frequency of the grating can be varied. A distinct advantage of this method over the Michelson interferometer lies in its ability to generate stable carrier fringes under lax vibration isolation conditions.
As a premier school, Raffles Institution (RI) seeks relevant and forward-looking educational initiatives. Bringing emerging technologies into the school encourages the students to cultivate skills and attitudes that will empower them to ride the present and future waves of information and technology most meaningfully and innovatively. Photonics has diverse applications in the modern technological world, and Singapore aims to become a center of excellence for optics and photonics in the region. However, a serious study of photonics begins only at the college level (K - 11/12). Entrusted with Singapore's brightest young minds, RI pioneered the development of a Photonics Exploratory Laboratory (X-LAB), being the first among secondary (K-7 to K- 10) schools in Singapore and possibly in the region. Young RI students are learning photonics fundamentals and recognizing photonics as a potentially rewarding field of study. With the expertise of lecturers from tertiary institutions, selected RI students are instructed in basic theory and trained in fundamental experiments. These students progress to embark on projects and in-depth studies under the wing of tertiary institutions and universities. Studies on Haidinger Fringes, Laser Doppler Anemometry and Optical Gratings have thus been successfully completed. Furthermore, the X-LAB acts as a focal point for students to experiment with Holography and Laser Animation.