Back light unit, fabricating method thereof and display device

A back light unit comprising a composite layer, wherein the composite layer comprises:

• a light guide layer and a first substrate opposite to each other, wherein the light guide layer comprises a light exit surface facing the first substrate;
• a plurality of first microprisms on the light exit surface of the light guide layer, wherein each first microprism of the plurality of first microprisms extends in a first direction parallel to the light exit surface of the light guide layer, wherein the plurality of first microprisms are sequentially arranged in a second direction parallel to the light exit surface of the light guide layer, and wherein the second direction and the first direction cross each other;
• and
• a plurality of second microprisms on a surface of the first substrate facing the light guide layer, wherein each second microprism of the plurality of second microprisms extends parallel to the second direction, and wherein the plurality of second microprisms are sequentially arranged in the first direction,
• wherein the first microprisms are connected to the second microprisms, and
• wherein the composite layer further comprises:
• one or more grooves at positions where the plurality of first microprisms and the plurality of second microprisms are in contact with each other,
• wherein each groove is in one first microprism of the plurality of first microprisms and configured to receive a portion of a corresponding second microprism of the plurality of second microprisms, or each groove is in one second microprism of the plurality of second microprisms and configured to receive a portion of a corresponding first microprism.