Abstract: A device includes an input coupling grating having a first grating structure characterized by a first set of grating parameters. The input coupling grating is configured to receive light from a light source. The device also includes an expansion grating having a second grating structure characterized by a second set of grating parameters varying in at least two dimensions. The second grating structure is configured to receive light from the input coupling grating. The device further includes an output coupling grating having a third grating structure characterized by a third set of grating parameters. The output coupling grating is configured to receive light from the expansion grating and to output light to a viewer.

Abstract: A device includes an input coupling grating having a first grating structure characterized by a first set of grating parameters. The input coupling grating is configured to receive light from a light source. The device also includes an expansion grating having a second grating structure characterized by a second set of grating parameters varying in at least two dimensions. The second grating structure is configured to receive light from the input coupling grating. The device further includes an output coupling grating having a third grating structure characterized by a third set of grating parameters. The output coupling grating is configured to receive light from the expansion grating and to output light to a viewer.

Abstract: A method and apparatus are described for using a series of signals that create an illusion of a continuous ascending or descending series of pitches as call waiting or call progress or process progress signals. In a preferred embodiment, a condition appropriate for representation by a call waiting or call progress or process progress signal is detected and, in response thereto, a series of signals is generated that creates an illusion of a continuous ascending or descending series of pitches. Preferably, the series of signals is Shepard's tones and the tones are generated by generating a plurality of tones, or partials, at octave intervals, amplitude filtering the partials to produce an amplitude envelope that peaks near the centermost partial or partials, and shifting the partials upwards (or downwards) through the octave in steps that are a fraction of an octave and preferably are a semitone.