Photonic Sensing: Principles and Applications for Safety and Security Monitoring

Chapter 7

Optical Coherence Tomography for Document Security and Biometrics

Shoude Chang, Youxin Mao, Costel Flueraru

Institute for Microstructural Sciences, National Research Council Canada, Ottawa, ON, Canada

7.1 Introduction

Optical coherence tomography (OCT) is an emerging technology for high resolution cross-sectional imaging of 3D structures. The first OCT system was reported by Huang et al. [1] in 1991, and since then the OCT technology has been attracting the attention of researchers all around the world. Some good survey books and review articles are listed in References 2–5.

OCT relies on the interferometric measurement of coherent backscattering variation to sense the internal interface structures of test samples such as biological tissues or internal layered materials. It is analogous to ultrasound B mode imaging, except that it uses infrared light source rather than ultrasound [6, 6, 8]. OCT takes advantage of the short temporal coherence length of the broadband light source that is used in the system to achieve precise optical sectioning in the depth dimension.

Advantages of OCT over other volume-sensing systems are as follows:

1. High Resolution. Compared to other systems: OCT, 5–20 μm; ultrasound, 150 μm; High resolution CT, 300 μm; MRI, 1000 μm. This feature enables greater visualization of details.

2. Noninvasive and Noncontact. This feature increases the safety and ease of use and extends the possibility for in situ and in vivo applications, which is important ...