Optical device for AR glasses

A method to generate a beam combining device using a substrate comprising a first surface and a second surface, said first surface and said second surface being substantially parallel, and said beam combining device enabled to combine a first beam with a second beam of a different spectrum into a combined beam, said method comprising:

• depositing a first antireflective coating on said first surface, said first antireflective surface being antireflective to a spectrum of a first beam;
• depositing a dichroic filter coating on said first surface, said dichroic filter coating being antireflective to a spectrum of said second beam, and said dichroic filter coating being reflective to said spectrum of said first beam;
• depositing a reflective coating on said second surface, said reflective surface being reflective to said spectrum of said first beam;
• and
• depositing a second antireflective coating on said second surface, said second antireflective surface coating being antireflective to a spectrum of said combined beam, wherein:
• said spectrum of said combined beam combines said spectra of said first beam and said second beam,
• the first beam and the second beam are each incident on the first surface at substantially a same angle θ and have substantially a same width L,
• the first antireflective coating and the dichroic filter coating define non-overlapping lateral regions on the first surface, each having a coating length≥L/cos (θ),
• the substrate has a thickness h=L/(2·sin (θ)) when the first and second beams are substantially adjacent on the first surface,
• the first beam reflects from the reflective coating on the second surface toward the dichroic filter coating to combine with the second beam at the dichroic filter coating, and
• the combined beam exits the device through the second antireflective coating on the second surface.