Abstract

A multiwavelength half adder was recently proposed and demonstrated¹. In this paper, we propose a multiwavelength full adder to avoid the repeat of the SUM and CARRY operations. Similar to the half adder, discrete wavelengths are used to represent specific bits in a binary word. Bits are ‘1’ if power at their wavelength is present, or ‘0’ if not. To simultaneously compute the SUM, which is achieved using a Mach-Zahnder interferometer XOR gate, it is necessary to determine all the carries in advance. One way to achieve this carry look-ahead is to first obtain the original carries as in the case of the half adder. A given original carry will then propagate through the next higher bit if either number is ‘ 1 ’ at that bit, and such propagation continues until both input bits are ‘0’.² Using these original carries and the input beams from (A+B) as the two writing beam sets into a second crystal, the propagation of these carries can be achieved. In a second approach, all the carries can be generated in a single crystal by appropriately re-injecting the original carries back into the crystal. The pathlengths of the writing beams and reinjected beams are carefully arranged so that interference can be only achieved between the desired beam pairs.

© 1993 Optical Society of America