Carbon Nanotube-Based Photonic Devices: Applications in Nonlinear Optics

Abstract

Carbon Nanotubes (CNTs) were first discovered by Sumio Ijima in the early 90s (Ijima et al., 1991). CNTs have since become a prominent material for an amazing breath of scientific and technological disciplines ranging from structural and material science to chemistry, biology and electronics (Dresselhaus et al., 2001). Compared to other areas of science, the study and exploitation of the optical properties of CNTs is still in its early years. In the late 1990s, various theoretical and experimental studies reported the remarkable optical properties of Carbon nanotubes (CNTs) (Kataura et al., 1999; Margulis & Sizikova, 1998). Since then, the potential applications of CNTs have been attracting increasing attention from the photonics research community. CNTs exhibit an exceptionally high third-order optical nonlinearity and nonlinear saturable absorption with ultrafast recovery time and broad bandwidth operation. Thus, CNTs are becoming a key component towards the development of fibre lasers and nonlinear photonic devices. Despite the relative late start, photonics is now one of the research fields where CNTs are making a more significant contribution towards the development of next generation devices both from an academic and an a commercial point of view. CNTs are structures from the fullerene family consisting of a honeycomb sheet of sp2 bonded carbon atoms rolled seamlessly into itself to form a cylinder. Single-walled CNT are nearly one-dimensional (1D) materials with a diameter ranging from 1nm to 3 nm, and a length that can go from 100s of nanometers to centimetres. The electronic properties of single-wall CNTs are governed by a single parameter named the chiral vector, which indicates the orientation of the tube axes with respect to the orientation of the honeycomb. Depending on this parameter, single-wall CNTs may behave as semiconductors or as metals. Those CNTs that behave as semiconductors exhibit a direct electronic bandgap which is directly proportional to the diameter of the nanotube. The optical absorption of CNT is determined by their electronic bandgap and broadband operation is a result of a large distribution of diameters formed during the CNT fabrication (Kataura et al. 1999). This discovery led to the now widespread use of CNTs in saturable absorption applications. Previous to that work, Margulis and Sizikoba had estimated theoretically that CNT presents a very high third order susceptibility χ(3) in the order of 10-8m2/W. Third order susceptibility is responsible for processes such as third harmonic generation (THG), optical Kerr effect, self-focusing and phase conjugation (Margulis and Sizikoba, 1998). Materials with a high nonlinearity combined with a fast response time are desired for roles areas such as optical