<p>A backup waveguide (16) for introducing backup light, is intersected obliquely to the main waveguides (15A-15O) that guide light from a main source. A set of mirrors (17A-17D) are insertable and retractable by a driver, so that when inserted, the mirrors block main light and reflect backup light towards the multiplexer. Independent claims are also included for the following: (1) light emitter switching method; (2) light receiver switching method; (3) multiplexer; (4) demultiplexer; and (5) optical communication system.</p>
