Multi-layer coating structure to minimize phase shifts, method of manufacture, waveguide and head mount display

1 . An apparatus comprising:

a waveguide; and

a plurality of partially reflective surfaces disposed at an angle relative to side-wall surfaces of the waveguide,

wherein each of the partially reflective surfaces comprises a multi-layer coating structure,

wherein a first portion of the multi-layer coating structure comprises one or more first layers configured for optical characteristics causing light that traverses through the one or more first layers at a second incident angle to have an overall phase shift relative to light that traverses through the one or more first layers at a first incident angle, and

wherein a second portion of the multi-layer coating structure comprises one or more second layers configured for optical characteristics selected to decrease the overall phase shift.

2 . The apparatus according to claim 1 ,

wherein the one or more second layers comprise a single second layer with a single refractive index.

3 . The apparatus according to claim 2 ,

wherein the single second layer interfaces with the first portion and an ambient material of the waveguide.

4 . The apparatus according to claim 2 ,

wherein a thickness of the single second layer is greater than a thickness of any of the one or more first layers.

5 . The apparatus according to claim 2 ,

wherein a thickness of the single second layer is based on a central or dominant wavelength to be propagated through the waveguide.

6 . The apparatus according to claim 2 ,

wherein a thickness of the single second layer is based on a central field of view.

7 . The apparatus according to claim 2 ,

wherein a thickness of the single second layer is selected based on a weighted mean of wavelengths to be propagated through the waveguide.

8 . The apparatus according to claim 7 ,

wherein a weighting of the weighted mean is based on a sensitivity of a human eye.

9 . The apparatus according to claim 3 ,

wherein the single refractive index corresponds to a refractive index of the ambient material.

10 . The apparatus according to claim 3 ,

wherein a thickness of the single second layer is selected based on the overall phase shift, a central or dominant wavelength, an incident angle, a refractive index of the ambient material, and a refractive index of the single second layer.

11 . The apparatus according to claim 1 ,

wherein the one or more second layers comprise a plurality of second layers with respective refractive indexes.

12 . The apparatus according to claim 11 ,

wherein the plurality of second layers are configured to have 95% or greater transmittance.

13 . The apparatus according to claim 11 ,

wherein the plurality of second layers comprises at least three refractive indexes.

14 . The apparatus according claim 11 ,

wherein the plurality of second layers comprises an even number of layers.

15 . The apparatus according to claim 1 ,

wherein the one or more first layers are interleaved with the one or more second layers.

16 . An apparatus comprising:

a waveguide; and

a plurality of partially reflective surfaces disposed at an angle relative to side-wall surfaces of the waveguide,

wherein each of the partially reflective surfaces comprises a multi-layer coating structure, and

wherein one or more layers of the multi-layer coating structure is selected to limit an overall phase shift of light that traverses through the multi-layer coating structure at a second incident angle, relative to light that traverses through the multi-layer coating structure at a first incident angle, to below a predetermined threshold.

17 . The apparatus according to claim 16 ,

wherein one or more other layers of the multi-layer coating structure are selected to satisfy a plurality of optical properties other than phase shift.

18 . The apparatus according to claim 17 ,

wherein the plurality of optical properties other than phase shift include limiting an overall phase shift of light propagating through a distance in the multi-layer coating structure relative to the distance in an ambient material of the waveguide.

19 . The apparatus according to claim 16 ,

wherein the one or more layers comprises a single layer with a thickness based on a central or dominant wavelength to be propagated through the waveguide.

20 . The apparatus according to claim 16 ,

wherein the one or more layers comprises a single layer with a thickness based on a weighted mean of wavelengths to be propagated through the waveguide.

21 . The apparatus according to claim 20 ,

wherein a weighting of the weighted mean is based on a sensitivity of a human eye.