Optical coherent tomography (OCT) is a newly developed optical imaging technology that permits high-resolution cross-sectional imaging of an object. Most of the OCT imaging systems is developed for the biomedical applications, such as diagnostics of ophthalmology, dermatology, dentistry and cardiology. The technique behind these applications is the point scanning of laser beam penetrating into an object to obtain the internal features of the object. In this paper, we study a full-field OCT imaging system for acquiring information from a multi-layer information chip. This new system can be used in document security, identification and industrial inspection.
Differing from the biology related samples, the information chip consists of a number of thin layers with information coded on their surfaces. The surfaces of the layers are flat and specular with moderate reflectance. The information on one layer is retrieved through demodulating interference image of that layer. To obtain the tomography image of all the layers, the images in each layer are acquired and separated. The axial resolution of the system, usually defined by coherent length of light source, determines how close the separation of the two vicinal layers can be resolved. In this paper we explore a new approach to enhance the axial resolution of the OCT system. The method is based on a three-step phase shift algorithm to solve the tomography images from fused interference patterns. Theoretic study and simulation indicate that the method improves the system resolution and quality of retrieved tomography images for the multilayer information chip. Experiment results are also given in support of the proposed method.