Ergonomic head mounted display device and optical system

A freeform waveguide comprising at least three physical surfaces, at least one of which contains a plurality of reflective and refractive freeform optical surfaces disposed thereon, where an interior space defined by the physical surfaces is filled by a refractive medium having an index (n) greater than 1, where the plurality of reflective and refractive surfaces folds and extends an optical path length so that the waveguide can be fit to an eyeglass shape, which enables an image display unit to be placed at a side of a head, and which enables a wide see-through field of view of up to 90° relative to a straight ahead view in temple directions, and up to 60° in a nasal direction, and up to 60° above and below relative to a straight ahead view, where inner and outer surfaces thereof are designed, within a constraint of fitting an eyeglass form factor and a maximum thickness, so that the plurality of freeform reflective and refractive optical surfaces guide light towards a pupil of a user without distorting the image, the physical and optical surfaces comprising:

• (a) a physical inner surface 115, disposed towards the pupil of the user, where the physical inner surface is constrained to approximate a pre-designated curved surface for an eyeglass form factor, where the inner surface is configured to reflect an image to an eyeball of the user with a minimum amount of distortion;
• (b) a physical outer surface 125, disposed towards an external scene, where the physical outer surface is configured to reflect an image to the pupil of the user with a minimum amount of distortion, where the physical outer surface is within a maximum distance of the inner surface at all points, where the physical outer surface contains at least one refractive surface to allow light from the external scene to pass through the waveguide and reach the eyeball of the user;
• (c) a physical edge surface 120, which optionally contains a refractive surface for light from an image display unit to enter the waveguide;
• (d) a refractive input surface 130, disposed on one of the physical surfaces, that allows light from an image display unit to enter the waveguide;
• (e) a refractive output surface 135 that allows light to exit the waveguide, disposed upon the physical inner surface, near the pupil of the user;
• and
• (f) a plurality of three (3) or more freeform reflective surfaces, disposed upon the physical inner and outer surfaces, where each reflection is produced by either satisfying a Total Internal Reflection criterion, or by application of a semi-transparent, partially reflective coating to the surface of the waveguide;
• where these reflections are optimized to guide the light along the interior of the waveguide with a minimum of distortion, where a plurality of reflections extends the optical path length such that the waveguide enables a wide see-through field of view, and a size suitable to fitting to a human head;
• whereupon light 140 from an image display unit 105 enters the waveguide, through the refractive input surface 130;
• whereupon the light 140 follows a path 145 along the waveguide that comprises the plurality of reflections upon the plurality of reflective and refractive surfaces, from the refractive input surface 130 to the refractive output surface 135, where each reflection is produced either by satisfying conditions of Total Internal Reflection, or by a semi-transparent coating applied to the surface;
• whereupon light 140 passes through the refractive output surface 135 beyond which the user places the pupil 150 to view the image;
• whereupon light 198 from the external scene is refracted through the physical outer surface 125 of the waveguide 100 and the physical inner surface 115 of the waveguide before reaching the pupil 150, where the see-through field of view through the waveguide is up to 90° in the temple directions, up to 60° in the nasal direction, and up to 60° above and below a straight ahead view.