Planar front illumination system having a light guide with micro lenses formed thereon and method of manufacturing the same

A front illumination device comprising:

• a light source comprising a plurality of Light Emitting Diodes, LEDs;
• a light guide plate optically coupled with the light source, wherein the plurality of LEDs are coupled to the light guide plate along at least one edge thereof;
• an electrophoretic display disposed adjacent a first surface of the light guide plate without any substantial intervening air gaps;
• a plurality of micro lenses disposed on a second surface of the light guide plate, the second surface being opposite the first surface, wherein the plurality of micro lenses are substantially circular when viewed on the second surface, and
• wherein at least one of a spatial density, size and reflective properties of the micro lenses is varied across the second surface of the light guide plate;
• and
• a stepped index layer disposed on the second surface of the light guide plate without any substantial intervening air gaps, the stepped index layer having an index of refraction lower than an index of refraction of the light guide plate,
• wherein the light guide plate is capable of reflecting at least a portion of light injected by the light source substantially uniformly toward the electrophoretic display.

A light guide assembly for a front illumination device comprising:

• a light guide plate, the light guide plate having at least one edge for receiving light from a plurality of Light Emitting Diodes, LEDs;
• a plurality of micro lenses disposed on a first surface of the light guide plate, wherein the plurality of micro lenses are substantially circular when viewed on the first surface, and wherein at least one of a spatial density, size and reflective properties of the micro lenses is varied across the first surface of the light guide plate to be capable of reflecting at least a portion of light injected by the light source substantially uniformly from the light guide plate;
• an optically clear layer disposed on a second surface of the light guide plate without any substantial intervening air gaps, the second surface being opposite the first surface;
• and
• a stepped index layer disposed on the first surface of the light guide plate without any substantial intervening air gaps, the stepped index layer having an index of refraction lower than an index of refraction of the light guide plate.

A method for manufacturing a front illumination device, the method comprising:

• providing a light guide plate;
• forming a plurality of micro lenses on a first surface of the light guide plate, wherein the plurality of micro lenses are substantially circular when viewed on the first surface, and wherein at least one of a spatial density, size and reflective properties of the micro lenses is varied across the first surface of the light guide plate to be capable of reflecting at least a portion of light injected by the light source substantially uniformly from the light guide plate;
• forming an optically clear layer disposed on a second surface of the light guide plate without any substantial intervening air gaps, the second surface being opposite the first surface;
• forming a stepped index layer on the first surface of the light guide plate without any substantial intervening air gaps, the stepped index layer having an index of refraction lower than an index of refraction of the light guide plate;
• coupling the stepped index layer to an electrophoretic display without any substantial intervening air gaps;
• and
• coupling an edge of the light guide plate to a light source comprising a plurality of Light Emitting Diodes, LEDs.

A method for manufacturing a front illumination device, the method comprising:

• providing a light guide plate;
• forming a plurality of micro lenses on a first surface of the light guide plate, wherein the plurality of micro lenses are substantially circular when viewed on the first surface, and wherein at least one of a spatial density, size and reflective properties of the micro lenses is varied across the first surface of the light guide plate to be capable of reflecting at least a portion of light injected by the light source substantially uniformly from the light guide plate;
• forming a stepped index layer on the first surface of the light guide plate without any substantial intervening air gaps, the stepped index layer having an index of refraction lower than an index of refraction of the light guide plate;
• coupling a second surface of the light guide plate to an electrophoretic display without any substantial intervening air gaps, the second surface being opposite the first surface;
• and
• coupling an edge of the light guide plate to a light source comprising a plurality of Light Emitting Diodes, LEDs.