It is shown that the interface linear graded DBR has the minimum roughness and better surface morphology, which can be used in the fabrication of vertical cavity surface emitting lasers.

Graded materials may also be used with a gradient from a 100% concentration of ceramic at one surface, and gradually changing into a 100% metal at the other surface, would be advantageous.

The raisin has different size and complicated surface, so it couldn't be graded well only by color and naked eyes.