Optical film

An optical film comprising a plurality of first polymeric layers arranged sequentially adjacent to each other along a first portion of a thickness of the optical film and a plurality of second polymeric layers arranged sequentially adjacent to each other along a second portion of the thickness of the optical film, each first and second polymeric layer having an average thickness less than about 300 nm, a thickest first polymeric layer being the first polymeric layer closest to the second portion, a thinnest second polymeric layer being the second polymeric layer closest to the first portion, the first polymeric layers numbering at least 10 in total, the second polymeric layers numbering between 5 and 30 in total, the average thickness of the first polymeric layers increasing substantially linearly from the thinnest to the thickest first polymeric layers at a rate of less than about 0.25 nm per layer, the thickest second polymeric layer thicker than the thinnest second polymeric layer by at least 10%, such that:

• for substantially normally incident light having a first polarization state, an optical transmittance of the optical film comprises a band edge between about 850 nm and about 950 nm, such that a best linear fit to the band edge correlating the optical transmittance to wavelength at least across a wavelength range where the optical transmittance increases from about 10% to about 70% has a slope that is less than about 4%/nm.