Integrated optical wavelength division multiplexing devices

An optical device, comprising:

• an optical chip having an input/output portion, a waveguide portion and a retroreflecting portion having a plurality of reflecting surfaces;
• a first optical fiber at the input/output portion;
• a second optical fiber at the input/output portion;
• a third optical fiber at the input/output portion;
• a first waveguided optical path through the optical chip between the first optical fiber and the second optical fiber for light at a first wavelength;
• a second waveguided optical path through the optical chip between the first optical fiber and the third optical fiber for light at a second wavelength different from the first wavelength;
• a first wavelength selective filter disposed to receive light from the first optical fiber, one of the first and second waveguided optical paths including transmission through the first wavelength selective filter and the other of the first and second waveguided optical paths including reflection at the first wavelength selective filter;
• wherein at least one of the first and second waveguided optical paths passes through the retroreflecting portion.