Optical touchpad for touch and gesture recognition

1. An optical touchpad comprising:

a prism having a four-sided cross section including a light entry interface, a light exit interface, a touch interface and a back interface substantially parallel to and spaced apart from the touch interface;

a source of collimated light, wherein the collimated light enters the prism through the light entry interface, is reflected from the touch interface by total internal reflection, and exits the prism through the light exit interface, and wherein the source of collimated light emits light in a first wavelength range;

a first image sensor for detecting the collimated light exiting from the light exit interface;

a lens for forming an image of a hand positioned above the touch interface through the touch interface and the back interface, wherein the hand forms a gesture but does not touch the touch interface, wherein the hand is illuminated by an imaging light source different than the source of collimated light, and wherein the imaging light source emits light in a second wavelength range;

a second image sensor comprising a two-dimensional array of light-sensitive elements and optically coupled to the lens wherein the second image sensor can capture a two-dimensional image of the hand; and

a processor coupled to the second image sensor, wherein the processor can read the two-dimensional image of the hand and process the two-dimensional image to identify the gesture;

a first filter disposed between the light exit interface and the first image sensor, wherein the first filter passes the first wavelength range; and

a second filter disposed between the prism and the second image sensor, wherein the second filter passes the second wavelength range.

2. The optical touchpad of claim 1 wherein the prism has a substantially trapezoidal cross section.

3. The optical touchpad of claim 1 wherein the source of collimated light comprises:

a light source; and

a collimating lens coupled to the light source.

4. The optical touchpad of claim 1 wherein the first wavelength range is infrared light, and the second wavelength range is visible light.

5. The optical touchpad of claim 1 , further comprising a second lens that images the touch interface of the prism onto the first image sensor.

6. The optical touchpad of claim 1 , further comprising a processor coupled to the first image sensor.

7. A method for fingertip and gesture imaging, the method comprising:

directing collimated light into a prism having a four-sided cross section including a light entry interface, a light exit interface, a touch interface and a back interface substantially parallel to and spaced apart from the touch interface, wherein the collimated light has a first wavelength range and enters the prism through the light entry interface, is reflected from the touch interface by total internal reflection, and exits the prism through the light exit interface;

imaging the collimated light exiting from the light exit interface to obtain an a two-dimensional image of the touch interface wherein imaging the collimated light exiting the light exit interface comprises:

directing the collimated light through a first lens and a first filter that passes the first wavelength range onto a first image sensor, and

capturing an image of the touch interface using the first image sensor;

imaging a hand positioned above the touch interface, wherein the hand forms a gesture and is illuminated by an imaging light source different than the collimated light that emits light in a second wavelength range, and wherein imaging the hand comprises:

using a second lens to direct light from the hand through the touch interface and back interface of the prism and through a second filter that passes the second wavelength range onto a second image sensor comprising a two-dimensional array of pixels, wherein the hand is not touching the touch interface, and

capturing a two-dimensional image of the hand using the second image sensor; and

processing the two-dimensional image to identify the gesture.

8. The method of claim 7 wherein the prism has a substantially trapezoidal cross section.

9. The method of claim 7 wherein the first wavelength range is infrared light, and the second wavelength range is visible light.

10. The optical touchpad of claim 1 wherein the imaging light source is ambient light.

11. The optical touchpad of claim 7 wherein the imaging light source is ambient light.