Optical sensing systems

A flexible optical construction configured to be incorporated in a window, the flexible optical construction comprising an optical film bonded to, and substantially coextensive in length and width with, a first bonding layer configured to bond to a first substrate of the window, the optical film comprising a plurality of alternating different polymeric first and second layers numbering at least 20 in total, each of the first and second layers having an average thickness of less than about 500 nm,

• the first and second layers have respective indices of refraction nx1 and nx2 along a same in-plane first direction, ny1 and ny2 along an in-plane second direction orthogonal to the first direction, and nz1 and nz2 along a third direction orthogonal to the first and second directions, such that for a first infrared wavelength between about 800 nm and about 2000 nm, nx1−nx2>0.1, and nz1 and nz2 are within about 20% of each other,
• such that for an incident light incident in an air and having the first infrared wavelength and for each of mutually orthogonal first and second polarization states:
• for the first infrared wavelength, the optical film reflects at least 60% of the incident light at a first incident angle of less than about 5 degrees, and transmits at least 40% of the incident light at a second incident angle of greater than about 30 degrees, and the first bonding layer has an optical transmittance of greater than about 80% for each of the first and second incident angles;
• and
• for a visible wavelength range between about 420 nm and about 680 nm, each of the optical film and the first bonding layer has an average optical transmittance of greater than about 70%, such that the flexible optical construction is configured to bend at a radius of less than about 10 cm with no or little damage to the flexible optical construction.