New Approach to Ultra-Fast All-Optical Signal Processing Based on Quantum Dot Devices

Abstract

Fiber-optic technology is characterized by enormous potential capabilities: huge bandwidth up to nearly 50Tb/s due to a high frequency of an optical carrier, low signal attenuation of about 0.2dB/km, low signal distortion, low power requirement, low material usage, small space requirement, and low cost Agrawal (2002), Mukherjee (2001). However, the realization of these capabilities requires very high-bandwidth transport network facilities which cannot be provided by existing networks consisting of electronic components of the transmitters and receivers, electronic switches and routers Agrawal (2002). Most current networks employ electronic signal processing and use optical fiber as a transmission medium. Switching and signal processing are realized by an optical signal down-conversion to an electronic signal, and the speed of electronics cannot match the optical fiber bandwidth Ramamurthy (2001). For instance, a single-mode fiber (SMF) bandwidth is nearly 50Tb/s, which is nearly four orders of magnitude higher than electronic data rates of a few Gb/s Mukherjee (2001). Typically, the maximum rate at which a gateway that interfaces with lower-speed subnetworks can access the network is limited by an electronic component speed up to a few tens of Gb/s. These limitations may be overcome by the replacement of electronic components with ultra-fast all-optical signal processing components such as fiber gratings, fiber couplers, fiber interferometers Agrawal (2001), semiconductor optical amplifiers (SOAs) Dong (2008), Hamie (2002), SOA and quantum dot SOA (QD-SOA) based monolithic Mach-Zehnder interferometers (MZIs) Joergensen (1996), Wang (2004), Sun (2005), Kanellos (2007), Wada (2007), Ben-Ezra (2008), Ben-Ezra (2009), all-optical switches based on multilayer system with enhanced nonlinearity and carbon nanotubes Wada (2007). SOAs are among the most promising candidates for all-optical processing devices due to their high-speed capability up to 160Gb/s , low switching energy, compactness, and optical integration compatibility Dong (2008). Their performance may be substantially improved by using QD-SOAs characterized by a low threshold current density, high saturation power, broad gain bandwidth, and a weak temperature dependence as compared to bulk and multi-quantum well (MQW) devices Bimberg (1999), Sugawara (2004), Ustinov (2003). High-speed wavelength conversion, logic gate operations, and signal regeneration are important operations of the all-optical signal processing where SOAs are widely used Agrawal (2002), Ramamurthy (2001), Dong (2008). A wavelength converter (WC) changes the input wavelength to a new wavelength without modifying the data content of a signal Agrawal (2002). Wavelength conversion is essential for optical wavelength division multiplexing (WDM) network operation Ramamurthy (2001). 18