Optical stack and housing for electronic device
A housing ( 185 ) for an electronic device ( 170 ) includes an optical film ( 100 ) having an optical transmittance for substantially normally incident light having a band edge separating first and second wavelength ranges, where the first wavelength range extends from about 400 nm to about 700 nm and the second wavelength range is at least about 100 nm wide and disposed between about 800 nm and about 1100 nm. For substantially normally incident light, an average optical reflectance of the optical film is greater than about 90% in the first wavelength range, and an average optical transmittance of the optical film is greater than about 80% in the second wavelength range. For at least one frequency in a range of about 0.1 GHz to about 90 GHz and for substantially normally incident radiation, the optical film transmits at least about 95% of the incident radiation.
1 . A housing for an electronic device, the housing comprising an optical film bonded to a rigid optically transparent substrate, an optical transmittance of the optical film for substantially normally incident light and for at least one polarization state comprising a band edge separating first and second wavelength ranges, the first wavelength range extending from about 400 nm to about 700 nm, the second wavelength range being at least about 100 nm wide and disposed between about 800 nm and about 1100 nm, such that for substantially normally incident light and for the at least one polarization state:
an average optical reflectance of the optical film is greater than about 90% in the first wavelength range; and
an average optical transmittance of the optical film is greater than about 80% in the second wavelength range, wherein a best linear fit to the band edge correlating the optical transmittance of the optical film to wavelength at least across a wavelength range where the optical transmittance of the optical film increases from about 10% to about 70% has a slope that is greater than about 2%/nm, and wherein for at least one frequency in a range of about 0.1 GHz to about 90 GHz and for substantially normally incident radiation, the optical film transmits at least about 95% of the incident radiation.
2 . The housing of claim 1 , wherein for at least one frequency in a range of about 0.1 GHz to about 90 GHz, a dielectric loss tangent of the optical film is less than about 0.02.
3 . The housing of claim 1 , wherein for at least one frequency in a range of about 0.1 GHz to about 90 GHz, a real part of a dielectric constant of the optical film is no more than about 4.
4 . The housing of claim 1 , wherein the optical film comprises a plurality of polymeric layers arranged along at least a portion of a thickness of the optical film and sequentially numbered from 1 to N, N an integer greater than about 100, the plurality of polymeric layers comprising a polymeric end layer at each end thereof, a plot of an average layer thickness versus a layer number of the plurality of polymeric layers comprising a first knee region separating a left region comprising at least N 1 sequentially arranged polymeric layers, N 1 an integer greater than about 50, where the polymeric layers have lower layer numbers, from a middle region comprising at least N 2 sequentially arranged polymeric layers, N 2 an integer greater than about 10, where the polymeric layers have higher layer numbers, such that a linear fit to the at least N 1 sequentially arranged polymeric layers in the left region has a positive linear slope having a magnitude of greater than about 0.04 nm per layer number with an r-squared value of greater than about 0.8, and a linear fit to the at least N 2 sequentially arranged polymeric layers in the middle region has a negative linear slope having a magnitude of greater than about 0.05 nm per layer number with an r-squared value of greater than about 0.8.
5 . The housing of claim 1 , wherein the at least one polarization state comprises orthogonal first and second polarization states.
6 . The housing of claim 1 , wherein the at least one polarization state comprises a first polarization state and for substantially normally incident light having a second polarization state orthogonal to the first polarization state, an average optical transmittance of the optical film is greater than about 80% in each of the first and second wavelength ranges.
7 . The housing of claim 1 , wherein the at least one frequency in a range of about 0.1 GHz to about 90 GHz comprises at least one frequency in a 5G band as defined by the 3GPP Release 15 or at least one frequency in a range of about 64 GHz to about 71 GHz.
8 . The housing of claim 1 , wherein an optical stack comprises the optical film and further comprises an optical layer disposed on and substantially coextensive with the optical film, the optical layer being substantially optically absorptive for at least one visible wavelength.