Reducing optical loss in reflective optical gratings

An optical device, comprising:

• a light-transmitting medium positioned on a base, the light-transmitting medium at least partially defining waveguides and a free propagation region through which light signals travel, the waveguide including an input waveguide and output waveguides;
• and
• a reflective grating positioned such that light signals guided by the input waveguide can travel through the free propagation region and be received by the optical grating, the optical grating being configured to reflect the light signal back into the free propagation region such that the light signals are received at the output waveguides, the optical grating reflecting the light signals such that the light signals associated with different wavelengths are received at different output waveguides,
• a portion of the light transmitting medium that defines the free propagation region having a facet through which the light signals are transmitted,
• the grating including a reflecting layer configured to reflect the light signals received by the grating, an upper portion of the reflecting layer being on a top of the light transmitting medium and the facet extends from the top of the light transmitting medium toward the base, and
• a buffer layer being between the upper portion of the reflecting layer and the free propagation region of the light-transmitting medium.