A bidirectional optical communications system that is operable to dynamically allocate wavelengths for transmission in either direction in an optical fiber. The dynamic allocation is controlled by programmable optical devices. The programmable optical devices may be well known programmable devices such as wavelength selective switches and wavelength blockers or any other programmable optical device capable of dynamically allocating wavelengths between the two directions in the optical fiber. In addition, the programmable optical devices may be any combination of such wavelength selective switches, wavelength blockers or other programmable optical devices with other optical devices such as optical circulators, gain blocks, add/drop multiplexers, or fixed optical filters. Such a bidirectional optical communications system enables the dynamic allocation of bandwidth in an optical fiber without the need to replace components, such as fixed optical filters, and without disturbing communications on all the wavelengths transmitted in the optical fiber.