  We propose an optical memory cell based on ultrafast wavelength switching in
coupled-cavity microlasers, featuring bistability between modes separated by
several nanometers. A numerical implementation is demonstrated by simulating a
two-dimensional photonic crystal microlaser. Switching times of less than 10
ps, switching energy around 15--30 fJ and on-off contrast of more than 40 dB
are achieved. Theoretical guidelines for optimizing the performance of the
memory cell in terms of switching time and energy are drawn.
