Double diffraction grating planar lightwave circuit

A planar lightwave circuit wavelength division multiplexer/demultiplexer device comprising:

• a slab waveguide defining first and second slab regions connected by a gap;
• first and second face to face concave reflective diffraction gratings on either end of the slab waveguide;
• a first waveguide extending to the first slab region;
• a second waveguide extending to the first slab region;
• and
• a third waveguide extending to the second slab region;
• wherein the first and second reflective gratings and the ends of the first, second and third waveguides are positioned, whereby light of a wavelength in a first range of wavelengths will pass between the first and second waveguides via the first grating, and whereby light of a wavelength in a second range of wavelengths, higher or lower than the first range of wavelengths, will pass between the first and third waveguides via the first and the second grating.