Implementation of All Optical Arithmetic and Logic Unit based on Nonlinear Properties of Semiconductor Optical Amplifiers

Abstract

Optical communication systems operating at gigabits per second are commercially available and the data rates are achieved above 10 Tb/s in research laboratories. In order to achieve such data rates, all-optical computing should be realized using digital optical devices. These days, ultra-fast and all-optical processes are required in the high-capacity photonic networks to avoid optoelectronics conversions. The key components for these all-optical networks amongst others are all-optical regenerators, wavelength converters, packet switches and all optical memory. All optical gates, optical arithmetic and logic circuits and flip-flops form important subsystems of these components. An all-optical arithmetic and logic unit is the integral part of optical computing and data processing. So, there is a need of all optical digital devices which provide better performance (in terms of simple structure, operation at multi Gbs-1 speeds, photonic integration etc.) for future all optical networks. With the advances in the optical semiconductor device design and fabrication techniques, the semiconductor optical amplifiers (SOAs) have become a preferred choice for use in future optical communication networks for in line amplification and optical switching. This thesis mainly designs, characterizes and investigates all optical arithmetic and logical devices using on nonlinear properties of semiconductor optical amplifiers. The all optical digital devices are implemented considering various important design aspects such as data rate; simple structure; potential for integration etc. Initially an optical gate architecture is proposed to perform AND, OR and NOT logic gates using a single SOA. All optical logic operations are simple and reconfigurable and are implemented using RZ modulated signals at 40 Gb/s operational speed. Contrast ratio and extinction ratio values have also been analyzed for the above mentioned logic gates. Maximum extinction ratio and contrast ratio achieved are 19dB and 17.2 dB respectively. Simple structure and potential for integration makes the proposed architecture an interesting approach in photonic computing and optical signal processing. Next we investigated SOA-based all-optical flip flops, binary counter and registers. First, a simple and new scheme for all-optical SR and D flip-flop employing XGM effect in two wideband SOAs is proposed. The simulation results exhibit contrast ratio of 13 dB and an amplitude modulation of less than 2.5 dB. Flip-flop operation has been verified for several set-reset pulse signals confirming successful operation at 10Gb/s. Secondly, we investigated the operation of a circular shift register for a 10-bit input sequence at the sequence bit rate fb = 2.5 Gb/s and fb = 10 Gb/s respectively. The all-optical circular shift register is realized using a fiber-loop based optical buffer (OB) and an optical AND gate. BER = 10-9 is achieved at an OSNR of 16dB at the output of the shift register. The dependence of the output quality factor (Q-factor) on SOA parameters is also investigated and discussed. Finally, an all optical binary counter is presented employing two stages of optical T flip-flop and an optical NOT Gate. The TFF consists of a SOA based Mach–Zehnder interferometer and an external feedback loop. The proposed counter is implemented using the minimum number of active components and with only a single control signal as input. Principle of operation is numerically evaluated for the proposed counter at 5 GHz. The switching times are less than 80 ps. Simple structure implies low power consumption and reduced footprint making it ideal for photonic integration.