Optical substrate, mold to be used in optical substrate manufacture, and light emitting element including optical substrate

1. An optical substrate comprising:

a support substrate; and

a projection-depression structure layer on a surface of which shapes of projections and depressions are formed, the projection-depression structure layer being laminated on the support substrate,

wherein extending directions of projection portions included in the projection-depression structure layer are irregularly distributed when seen in planar view,

outlines seen in planar view of the projection portions include a plurality of sections each having a length of an average of widths of the projection portion multiplied by a factor of π, the widths being in directions approximately orthogonal to the extending directions of the projection portions seen in planar view, the plurality of sections including more straight line sections than curved line sections in a region per unit area of the projection-depression structure layer,

each curved line section is a section in which a ratio of a linear distance between both ends of the section to a length of an outline between both ends of the section is 0.75 or less,

each straight line section is a section which is not one of the curved line sections among the plurality of sections, and

a coefficient of variation of the widths of the projection portions is 0.25 or less.

2. The optical substrate according to claim 1 ,

wherein the widths of the projection portions are constant.

3. The optical substrate according to claim 1 ,

wherein in cases where an analyzed image of projections and depressions obtained through analysis of the shapes of projections and depressions formed on the surface of the projection-depression structure layer with a scanning probe microscope is subjected to two-dimensional high-speed Fourier transformation to obtain a Fourier transformed image, the Fourier transformed image shows a circular pattern or an annular pattern in which an origin having an absolute value of a wavenumber of 0 μm −1 is approximately in the center, and the circular pattern or the annular pattern is present within a region having an absolute value of a wavenumber within the range of 10 μm −1 or less.

4. The optical substrate according to claim 1 ,

wherein an average pitch of projections and depressions of the projection-depression structure layer is 100 to 1500 nm, and

a standard deviation of the depth between a projection and a depression of the projection-depression structure layer is 10 to 100 nm.

5. The optical substrate according to claim 1 , further comprising:

an optical functional layer formed on a surface of the support substrate opposite to a surface of the support substrate on which the projection-depression structure layer is formed.

6. The optical substrate according to claim 1 , further comprising:

a coating layer formed on the projection-depression structure layer.

7. A mold used in manufacturing of the optical substrate according to claim 1 , wherein the mold includes a projection-depression portion in which a projection-depression pattern corresponding to shapes of projections and depressions to be formed on the projection-depression structure layer of the optical substrate is formed.

8. A light emitting element including the optical substrate according to claim 1 ,

wherein a first electrode, an organic layer which emits light, and a second electrode are sequentially laminated on the projection-depression structure layer.