Method and system for beam expansion in a display device

A method of improving color uniformity in an exit beam in an optical device, the optical device having

• an input surface section to admit a light beam, the light beam comprising at least a first wavelength component and a second wavelength component;
• and
• an exit surface section for allowing the exit beam to exit the optical device through the exit surface, said method comprising:
• providing at least a first layer and second layer in the optical device;
• providing a first diffractive element and a second diffractive element on the first layer;
• providing a first diffractive element and a second diffractive element on the second layer, such that
• at least a part of the admitted light beam is diffracted in the first diffractive element in the first layer for providing a first diffracted portion;
• at least a part of the admitted light beam is diffracted in the first diffractive element in the second layer for providing a second diffracted portion;
• at least a part of the first diffracted portion is further diffracted in the second diffractive element in the first layer, thereby forming a first part of an exit beam exiting through the exit surface section;
• and
• at least a part of the second diffracted portion is further diffracted in the second diffractive element in the second layer, thereby forming a second part of the exit beam exiting through the exit surface section, wherein
• the amount of the first wavelength component in the first part of the exit beam is greater than the amount of the second wavelength component in the first part of the exit beam, and
• the amount of the second wavelength component in the second part of the exit beam is greater than the amount of the first wavelength component in the second part of the exit beam.

A display module, comprising:

• an optical engine for receiving image data;
• a display device operatively connected to the optical engine for forming an image based on the image data;
• and
• an exit pupil extender, comprising:
• an exit surface section;
• an input surface section to admit a light beam, the light beam comprising at least a first wavelength component and a second wavelength component;
• and
• at least a first layer, a second layer and a third layer, each of the first, second and third layers comprises a first diffractive element and a second diffractive element, such that
• at least a part of the admitted light beam is diffracted in the first diffractive element in the first layer for providing a first diffracted portion;
• at least a part of the admitted light beam is diffracted in the first diffractive element in the second layer for providing a second diffracted portion;
• at least a part of the admitted light beam is diffracted in the first diffractive element in the third layer for providing a third diffracted portion;
• at least a part of the first diffracted portion is further diffracted in the second diffractive element in the first layer, thereby forming a first part of an exit beam exiting through the exit surface section;
• at least a part of the second diffracted portion is further diffracted in the second diffractive element in the second layer, thereby forming a second part of the exit beam exiting through the exit surface section;
• and
• at least a part of the third diffractive portion is further diffracted in the third diffractive element in the third layer, thereby forming a third part of the exit beam exiting through the exit surface section.

An electronic device comprising:

• a data processing unit;
• an optical engine operatively connected to the data processing unit for receiving image data from the data processing unit;
• a display device operatively connected to the optical engine for forming an image based on the image data;
• and
• an exit pupil extender, comprising:
• an exit surface section;
• an input surface section to admit a light beam, the light beam comprising at least a first wavelength component and a second wavelength component;
• and
• at least a first layer, a second layer and a third layer, each of the first, second and third layers comprising a first diffractive element and a second diffractive element, such that
• at least a part of the admitted light beam is diffracted in the first diffractive element in the first layer for providing a first diffracted portion;
• at least a part of the admitted light beam is diffracted in the first diffractive element in the second layer for providing a second diffracted portion;
• at least a part of the admitted light beam is diffracted in the first diffractive element in the third layer for providing a third diffracted portion;
• at least a part of the first diffracted portion is further diffracted in the second diffractive element in the first layer, thereby forming a first part of an exit beam exiting through the exit surface section;
• at least a part of the second diffracted portion is further diffracted in the second diffractive element in the second layer, thereby forming a second part of the exit beam exiting through the exit surface section;
• and
• at least a part of the third diffractive portion is further diffracted in the third diffractive element in the third layer, thereby forming a third part of the exit beam exiting through the exit surface section.