All-Optical Wavelength-Selective Switch by Intensity Control in Cascaded Interferometers

Wavelength-division-multiplexing (WDM) technology has been developing in broadband optical networks. The wavelength range used in fiber transmission systems has been increasing by employing various kinds of fiber amplifiers. In order to make it possible to handle signals of multiple wavelengths efficiently in network nodes, wavelength-selective processing in switching, routing and buffering systems will be required. In such processing systems, integrated-optic switches become one of fundamental key devices. In particular, high-speed wavelength-selective switches are required for WDM packet processing. Wavelength-selective switches are classified from viewpoint of control method into electrically controlled devices and optically controlled ones. The former includes collinear acoustooptic (AO) devices (Goto & Miyazaki, 1990). Although multiple signals at different wavelengths can be independently switched with a single AO switch, it provides a response time only at an order of micro seconds. Optical circuits consisting of arrayed waveguide gratings (AWGs) and wavelength-insensitive switches are also regarded as a device in this class (Goh et al., 2008). The switching response depends on the control mechanizm of the wavelength-insensitive switches. The response time in thermo-optic switches is an order of milli seconds (Suzuki et al., 1998). On the other hand, optically controlled switches include devices using phase shift induced by optical nonlinear Kerr effect (Doran & Wood, 1988) and phase shift in semiconductor optical amplifiers (SOAs) (Nakamura et al., 2000) and in quantum dots (Kitagawa et al., 2009). These switches using phase shifting, in general, cannot provide wavelength-selectivity. Therefore, to realize wavelength-selective switching of the latter class, combination with multiplexers and demultiplexers such as AWGs is required. As a switch of the latter class, the authors have proposed a new type of wavelength-selective switch where optical amplitudes in waveguide arms of interferometers are controlled by Raman amplifiers (Kishikawa & Goto, 2005; Kishikawa & Goto, 2006; Kishikawa & Goto, 2007a; Kishikawa & Goto, 2007b). In this article, the operation principle of wavelengthselective switching with the proposed devices is described. Computer simulation by finitedifference beam-propagation-method (FD-BPM) is performed to verify the switching operation.