Light modulation by frustration of total internal reflection

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) a support member disposed adjacent the prismatic surface so as to leave a plurality of channels between the prismatic surface and the support member;
• (c) an electrophoretic medium contacting the prismatic surface and disposed between the prismatic surface and the support member;
• (d) a plurality of particles suspended in the electrophoretic medium;
• and
• (e) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the electrophoretic medium and the plurality of particles are contained within a plurality of capsules disposed within the plurality of channels.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the electrophoretic medium comprises a viscosity modifier.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the particles comprise carbon black bearing a polymer coating.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the volume fraction of the particles in the electrophoretic medium is at least about 50 percent.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein at least some of the plurality of particles are attached to the reflective sheet by flexible filaments.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the plurality of particles vary in electrophoretic mobility, at least one of the particles having an electrophoretic mobility which is at least twice that of another of the particles.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the plurality of particles are selected from substantially spherical particles having diameters in the range of about 200 to about 300 nm, oblate ellipsoids and spheroids, and flat plates and prisms having an aspect ratio of at least about 3:1.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface,
• wherein the prismatic surface is provided with an electrode and a layer of a substantially insulating material having a low refractive index covering the electrode.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet;
• (e) a rear support disposed on the opposed side of the electrophoretic medium from the reflective sheet;
• and
• (f) a plurality of cross-walls extending from the reflective sheet to the rear support and separating the electrophoretic medium into a plurality of cells isolated from one another by the cross-walls,
• the electrophoretic medium having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface to frustrate total internal reflection at the prismatic surface of light rays passing through the reflective sheet,
• the electrophoretic medium comprising first and second phases, the first phase wetting the prismatic surface while the second does not, whereby a layer of the first phase is formed covering and substantially conforming to the prismatic surface, the first phase having an index of refraction sufficiently smaller than the index of refraction of the reflective sheet that most of the light passing through the reflective sheet undergoes total internal reflection at the prismatic surface when the particles are not closely adjacent the prismatic surface.

An image display device comprising:

• (a) a reflective sheet having a prismatic inward surface and an opposed outward surface;
• (b) an electrophoretic medium contacting the prismatic surface;
• (c) a plurality of particles suspended in the electrophoretic medium;
• and
• (d) means for applying a voltage across the electrophoretic medium to selectively move the particles closely adjacent the prismatic surface,
• wherein the particles comprise at least one light-scattering or light-absorptive center disposed within a light transmissive matrix, whereby, when the particles are disposed closely adjacent the prismatic surface, most of the light passing through the reflective sheet passes into the particles and is scattered or absorbed by the light-scattering or light-absorptive center.