EP-4735931-A1 - OPTICAL FILM AND OPTICAL SYSTEM INCLUDING SAME

Abstract

An optical film includes a plurality of alternating first and second layers. Differences of indices of refraction between the first and second layers along a first direction has a magnitude Dny. A dispersion of Dny as a function of wavelength has a valley within a blue-green wavelength range extending from about 420 nm to about 560 nm. The valley includes a minimum at a minimum wavelength. For a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has an optical reflectance Rp when the incident light is polarized along the second direction, where Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.

Inventors

• HAAG, ADAM D.
• ZHAO, LIN
• LE, JOHN D.
• HUSEBY, Kevin T.
• JOHNSON, STEPHEN A.
• AASTUEN, DAVID J.W.

Assignees

• 3M Innovative Properties Company

Dates

Publication Date

20260506

Application Date

20240620

Claims (15)

1. 1. An optical film comprising a plurality of alternating polymeric first and second interference layers numbering greater than 10 in total, each of the first and second interference layers having an average thickness of less than about 500 nm, differences of indices of refraction between the first and second interference layers along an in-plane same first direction and an orthogonal in-plane same second direction having respective magnitudes Dnx and Dny, a dispersion of Dny as a function of wavelength having a valley between a smaller first and a larger second wavelengths within a blue-green wavelength range extending from about 420 nm to about 560 nm, the valley comprising a minimum at a minimum wavelength and a corresponding minimum value of less than about 0.002, Dny being greater than about 0.001 at each of the first and second wavelengths, such that, for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second interference layers has an optical reflectance Rp when the incident light is polarized along the second direction, wherein Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.
2. 2. The optical film of claim 1, wherein for the substantially normally incident light having the minimum wavelength and polarized along the first direction, the plurality of alternating polymeric first and second interference layers has an optical transmittance Ts of less than about 2%.
3. 3. The optical film of claim 1, wherein for the substantially normally incident light polarized along the second direction, the optical reflectance Rp has a global maximum of greater than about 0.5% in a blue wavelength range extending from about 400 nm to about 450 nm.
4. 4. The optical film of claim 1, wherein for V-numbers defined as (nyb-l)/(nya-nyc), nya, nyb and nyc being refractive indices along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm, the first and second interference layers have respective first and second V-numbers VI and V2, a magnitude of a difference between VI and V2 being less than 5.
5. 5. The optical film of claim 1, wherein for at least one wavelength in a wavelength range of about 400 nm to about 750 nm, the first interference layers have an in-plane birefringence of greater than about 0.05 and the second interference layers have an in-plane birefringence of less than about 0.04.
6. 6. The optical film of claim 5, wherein the second interference layers have a V-number less than 20, the V-number being (nyb-l)/(nya-nyc), nya, nyb and nyc being refractive indices of the second interference layers along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm.
7. 7. The optical film of claim 5, wherein the second interference layers comprise a copolymerized blend of at least first and second copolyesters, the first copolyester comprising a copolymer of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), the second copolyester comprising a first glycol-modified PET comprising isosorbide-derived groups.
8. 8. An optical film comprising a plurality of alternating polymeric different first and second layers, a difference of indices of refraction between the first and second layers along an in-plane same pass direction having a magnitude Dny, a dispersion of Dny as a function of wavelength comprising a global minimum at a minimum wavelength, such that, for a substantially normally incident light, a first wavelength range extending from about 400 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has: an optical reflectance Rp when the incident light is polarized along the pass direction, Rp having a global maximum of greater than about 0.5% in the first wavelength range, and an average value of less than about 2% in the second wavelength range; and an optical transmittance Ts when the incident light is polarized along an in-plane block direction orthogonal to the pass direction, Ts having an average value of less than about 1% in an extended wavelength range extending from about 400 nm to about 750 nm.
9. 9. The optical film of claim 8, wherein the minimum wavelength is in a blue-green wavelength range extending from about 420 nm to about 560 nm.
10. 10. The optical film of claim 9, wherein for the substantially normally incident light polarized along the pass direction and for each of a wavelength range extending from about 420 nm to the minimum wavelength, a wavelength range extending from the minimum wavelength to about 560 nm, and a wavelength range extending from about 560 nm to about 750 nm, Rp has an average value of less than about 1%.
11. 11. An optical film comprising a plurality of alternating polymeric first and second layers numbering greater than 10 in total, each of the first and second layers having an average thickness of less than about 500 nm, such that for substantially normally incident light, the plurality of alternating polymeric first and second layers has: an average optical transmittance Ts for a first polarization state of less than about 2% in a bluegreen wavelength range extending from about 420 nm to about 560 nm; and an optical reflectance Rp for a second polarization state orthogonal to the first polarization state, Rp having a minimum in the blue-green wavelength range at a minimum wavelength, wherein for a first wavelength range extending from about 420 nm to the minimum wavelength, a second wavelength range extending from the minimum wavelength to about 560 nm, and a third wavelength range extending from about 560 nm to about 750 nm, Rp has an average value of less than about 0.9% in each of the first, second and third wavelength ranges.
12. 12. The optical film of claim 11, wherein for substantially normally incident light and the second polarization state, the optical reflectance Rp has a global maximum of greater than about 0.5% in a blue wavelength range extending from about 400 nm to about 450 nm.
13. 13. An optical system comprising at least one lens, a partial reflector and a reflective polarizer defining an optical cavity therebetween, and a retarder layer disposed in the optical cavity, the reflective polarizer being an optical film according to any one of claims 1 to 12.
14. 14. An optical system comprising a display, at least one lens, a partial reflector and a reflective polarizer defining an optical cavity therebetween, and a retarder layer disposed in the optical cavity, the optical system configured to form a virtual image of an image emitted by the display for viewing by a viewer, the reflective polarizer comprising a plurality of alternating polymeric different first and second layers, a difference of indices of refraction between the first and second layers along an in-plane same pass direction having a magnitude Dny, a dispersion of Dny as a function of wavelength comprising a global minimum at a minimum wavelength disposed between about 420 nm and about 560 nm, such that for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has an optical reflectance Rp when the incident light is polarized along the pass direction, wherein Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.
15. 15. The optical system of claim 14, wherein for V-numbers defined as (nyb-l)Z(nya-nyc), nya, nyb and nyc being refractive indices along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm, the first and second layers have respective first and second V-numbers VI and V2, a magnitude of a difference between VI and V2 being less than 5.

Description

OPTICAL FILM AND OPTICAL SYSTEM INCLUDING SAME TECHNICAL FIELD The present description relates generally to optical films, such as reflective polarizer films, and optical systems including an optical film. BACKGROUND An optical film can include polymeric interference layers for providing reflection for at least one polarization state in a desired wavelength range. An optical system can include the optical film. SUMMARY In some aspects, the present description provides an optical film including a plurality of alternating polymeric first and second interference layers numbering greater than 10 in total, where each of the first and second interference layers can have an average thickness of less than about 500 nm. Differences of indices of refraction between the first and second interference layers along an in-plane same first direction and an orthogonal in-plane same second direction have respective magnitudes Dnx and Dny. A dispersion of Dny as a function of wavelength has a valley between a smaller first and a larger second wavelengths within a blue-green wavelength range extending from about 420 nm to about 560 nm. The valley includes a minimum at a minimum wavelength and a corresponding minimum value of less than about 0.002. Dny is greater than about 0.001 at each of the first and second wavelengths, such that, for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second interference layers has an optical reflectance Rp when the incident light is polarized along the second direction, where Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range. In some aspects, the present description provides an optical film including a plurality of alternating polymeric different first and second layers. A difference of indices of refraction between the first and second layers along an in-plane same pass direction has a magnitude Dny, where a dispersion of Dny as a function of wavelength includes a global minimum at a minimum wavelength, such that, for a substantially normally incident light, a first wavelength range extending from about 400 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has: an optical reflectance Rp when the incident light is polarized along the pass direction, where Rp can have a global maximum of greater than about 0.5% in the first wavelength range, and an average value of less than about 2% in the second wavelength range; and an optical transmittance Ts when the incident light is polarized along an in-plane block direction orthogonal to the pass direction, where Ts has an average value of less than about 1% in an extended wavelength range extending from about 400 nm to about 750 nm. In some aspects, the present description provides an optical film including a plurality of alternating polymeric first and second layers numbering greater than 10 in total, where each of the first and second layers can have an average thickness of less than about 500 nm, such that for substantially normally incident light, the plurality of alternating polymeric first and second layers has: an average optical transmittance Ts for a first polarization state of less than about 2% in a blue-green wavelength range extending from about 420 nm to about 560 nm; and an optical reflectance Rp for a second polarization state orthogonal to the first polarization state, where Rp has a minimum in the blue-green wavelength range at a minimum wavelength. For a first wavelength range extending from about 420 nm to the minimum wavelength, a second wavelength range extending from the minimum wavelength to about 560 nm, and a third wavelength range extending from about 560 nm to about 750 nm, Rp can have an average value of less than about 0.9% in each of the first, second and third wavelength ranges. In some aspects, the present description provides an optical system including a display, at least one lens, a partial reflector and a reflective polarizer defining an optical cavity therebetween, and a retarder layer disposed in the optical cavity. The optical system can be configured to form a virtual image of an image emitted by the display for viewing by a viewer. The reflective polarizer includes a plurality of alternating polymeric different first and second layers. A difference of indices of refraction between the first and second layers along an in-plane same pass direction has a magnitude Dny. A dispersion of Dny as a function of wavelength has a global minimum at a minimum wavelength disposed between about 420 nm and about 560 nm, such that for a substantially normally incident light, a first wavelength range extending from