Multipole light switch or multiplexer using rotator and interferometer

A two-way light amplitude divider includes a light rotator (18) with first (181), second (182) and third (183) ports. The second port is coupled to a port of a controllable Fabry-Perot etalon (22). The etalon can take on a state in which a particular lambda of light is passed, and others are reflected. Light at lambda 1 applied to the first port (181) of the rotator (18) passes through the etalon (22) to a port (222) when the etalon (22) is in its first state, and the light is reflected by the etalon (22) in its second state, and flows to the third port (183) of the rotator (18). Thus, the arrangement (10) acts as a single-pole, double throw switch, depending upon the state of the etalon. The arrangement can be cascaded in a manner which operates as a multiplexer (700) or demultiplexer (600).