Wavelength-selective planar holograms.

Planar gratings and holograms are normally readout-wavelength insensitive. We show, however, that a binary phase surface-relief hologram can be transparent at one wavelength (lambda) yet diffract efficiently at another (lambda'), provided that the phase delay is an integer number of waves (e.g., 3) at lambda and a half-integer number of waves (e.g., 2.5) at lambda'. We fabricated a 7.9-microm-deep binary phase grating in BK7 glass that separates the standard telecommunications wavelengths, 1.3 and 1.55 microm, with 80% efficiency (neglecting Fresnel losses) and greater than 30:1 contrast.