Viewing angle measurements on curved displays ...

Viewing angle measurements on curved displays: measurements & simulations P. Boher*, T. Leroux*, T. Bignon*, V. Collomb-Patton and P. Blanc**, (*) ELDIM, 1185 rue d’Epron, 14200 Hérouville St Clair, France (**) Laboratoires d’Essai de la FNAC, 2 rue des Champarts, 91742 Massy, France

IMID EXCO, Daegu, Korea

Slide #1

Agenda

I.

Introduction

II. Experimental system III. Theoretical study 

Computation for all incidence and azimuth angles



Maximum of angular distortion

IV. Experimental results 

Curved BEF Film



OLED Phone cell display with curved edge

V. Conclusions


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Part I: Introduction


Slide #3

Part I: Introduction Flexible displays have shown important developments recently. Many types of technologies are currently investigated (LCD, OLED, AMOLED, electrophoretic,..) on different kinds of displays (metal, plastic, ultra-thin glass...) Few papers have recently been devoted to the emissive properties of such displays.  The impact of the stress induced by the curvature on curved LCD has been discussed by K. Vepakomma (SID San Jose , 42.2, 634 (2015))  The impact of the curvature on reflected parasitic light has been investigated by K. Blankenbach (SID San Jose , 42.1, 630 (2015)) The purpose of the present paper is to explain how to measurement the viewing angle of such curved displays. Simulation for variable curvature is in particular investigated


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Part II: Experimental system


Slide #5

Measurement parameters : spot size Standard goniometer

Fourier optics system

Schematic diagram of standard goniometric solution (left) and viewing angle system with Fourier optics (right) => Spot size is changing in 1/cosθ for both systems IMID EXCO, Daegu, Korea

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Part III: Theoretical study


Slide #7

Simulations for all angles in the space

in the (x,y) plane

R = radius of curvature, H defocus Intersection of a ray (θ,φ) on a curved surface bended along z => We compute the coordinates of point M IMID EXCO, Daegu, Korea

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Simulations for all angles For a concave surface:

For a concave surface: 2 (𝑥𝑀 − 2𝑅)2 +𝑦𝑀 = 𝑅2

2 2 𝑥𝑀 + 𝑦𝑀 = 𝑅2

We find that:

−𝐵 + 𝐵2 − AC 𝑥𝑀 = A

With:

−𝐵 − 𝐵2 − AC 𝑥𝑀 = A

𝐴 = 1 + 𝑡𝑎𝑛2 𝜃𝑐𝑜𝑠 2 𝜑 𝐵 = 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 𝑦𝑝 − 𝑥𝑝 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 𝐶 = (𝑦𝑝 − 𝑥𝑝 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑)2 −𝑅 2

𝐴 = 1 + 𝑡𝑎𝑛2 𝜃𝑐𝑜𝑠 2 𝜑 𝐵 = 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 𝑦𝑝 − 𝑥𝑝 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 − 2𝑅 𝐶 = (𝑦𝑝 − 𝑥𝑝 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑)2 +3𝑅2

yM and zM are deduced by: 𝑦𝑀 = 𝑥𝑀 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 + 𝑦𝑃 − 𝑥𝑃 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 𝑧𝑀 = 𝑥𝑀 𝑡𝑎𝑛𝜃𝑠𝑖𝑛𝜑 + 𝑧𝑃 − 𝑥𝑃 𝑡𝑎𝑛𝜃𝑠𝑖𝑛𝜑

𝑦𝑀 = 𝑥𝑀 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 + 𝑦𝑃 − 𝑥𝑃 𝑡𝑎𝑛𝜃𝑐𝑜𝑠𝜑 𝑧𝑀 = 𝑥𝑀 𝑡𝑎𝑛𝜃𝑠𝑖𝑛𝜑 + 𝑧𝑃 − 𝑥𝑃 𝑡𝑎𝑛𝜃𝑠𝑖𝑛𝜑


Slide #9

Simulations for all angles To simulate the emission of the curved display we express the coordinates of the ray (θ’,φ’) with regards to the normal of the curved surface. We define a new (M,x’,y’,z’) coordinate system by: 𝑥𝑀 𝑅 𝑥 ′ = 𝑦𝑀 𝑅 0

−𝑦𝑀 𝑅 𝑦 ′ = 𝑥𝑀 𝑅 0

The new orientation is given by:

0 𝑧′ = 0 1

For a concave surface:

𝜃′

𝑥𝑀 𝑐𝑜𝑠𝜃 + 𝑦𝑀 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜑 = 𝑎𝑟𝑐𝑜𝑠 𝑅

𝜃′

𝑥𝑀 𝑐𝑜𝑠𝜃 − 𝑦𝑀 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜑 = 𝑎𝑟𝑐𝑜𝑠 𝑅

𝜑′

𝑅𝑠𝑖𝑛𝜃𝑠𝑖𝑛𝜑 = 𝑎𝑟𝑡𝑎𝑛 𝑥𝑀 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜑 − 𝑦𝑀 𝑐𝑜𝑠𝜃

𝜑′

𝑅𝑠𝑖𝑛𝜃𝑠𝑖𝑛𝜑 = 𝑎𝑟𝑡𝑎𝑛 𝑥𝑀 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜑 + 𝑦𝑀 𝑐𝑜𝑠𝜃


Slide #10

Maximum of angular shifts ┴ to the curvature axis 𝜑 =0

In the plane perpendicular to z:

𝑥𝑀 = 𝑅 cos 𝜃 − 𝜃 ′ = 𝑅𝑐𝑜𝑠(∆𝜃)

𝑦𝑀 = 𝑅 sin(∆𝜃)

Angular variation is maximum at the border of the spot size D 𝐷 𝑥𝑝 = 𝑅 ± 𝐻 𝑦𝑝 = 2𝑐𝑜𝑠𝜃

𝑦𝑀 = 𝑥𝑀 𝑡𝑎𝑛𝜃 + 𝑦𝑃 − 𝑥𝑃 𝑡𝑎𝑛𝜃 𝑅 sin(∆𝜃) = 𝑅𝑐𝑜𝑠 ∆𝜃 If ∆𝜃 is small then ∆𝜃 =

𝑠𝑖𝑛𝜃 𝐷 𝑠𝑖𝑛𝜃 + − (𝑅 ± 𝐻) 𝑐𝑜𝑠𝜃 2𝑐𝑜𝑠𝜃 𝑐𝑜𝑠𝜃

sin(∆𝜃) ≈ ∆𝜃

cos ∆𝜃 ≈ 1

𝐷 𝐻 ± 𝑡𝑎𝑛𝜃 2𝑅𝑐𝑜𝑠𝜃 𝑅

=> Maximum of angular shift depends on R, D and H IMID EXCO, Daegu, Korea

Slide #11

Maximum of angular shifts ┴ to the curvature axis Variable Incidence , Focused position 100

0

50

60

70

80

10

Δθ

Measurements using goniometer or Fourier optics system with sufficiently small spot size give quasi exact results when the display is correctly adjusted and the radius of curvature large with regards to the spot size

1

Δθ < 1° if D/R Angular shift is maximum along horizontal IMID EXCO, Daegu, Korea

Slide #16

Simulations for BEF film

Flat

Simulated R =130mm, H =18mm

Simulated angular shifts for R = 130mm at focus (left) and R = 130mm and a defocus of H = 18mm (right) => Defocus increase the angular shifts drastically IMID EXCO, Daegu, Korea

Slide #17

Simulations for BEF film

Measurement

Simulation

Measured (left) and simulated transmittance (right) of BEF film for curved configuration (D=2mm, R=130mm, H=18mm) => Angular distortion can be computed for all the angles IMID EXCO, Daegu, Korea

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Viewing angle measurements on curved AMOLED

Samsung Galaxy S6 edge 5.1" HD Super AMOLED® 2560 x 1440, 577 PPI, Dual edge

We measure Red, Green and Blue states at center and on the edge IMID EXCO, Daegu, Korea

Slide #19


Luminance

Red state center

Red state edge

Luminance measured on red state at center (left) and on the edge (right) with a spot size of 1mm: scale in % of maximum  Angular distortion is easy to see  Luminance is two times higher on the edge IMID EXCO, Daegu, Korea

Slide #20


u’ color coordinate

Red state center

Red state edge

u’ color coordinate measured on red state at center (left) and on the edge (right) with a spot size of 1mm:  Angular distortion is also seen on color  Interference pattern is dumped by the curvature IMID EXCO, Daegu, Korea

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Simulations for curved AMOLED Center

Edge

Simulated

Luminance Blue

R = 5mm Green

H = 1.2mm

Red

Simulation using central measurement and fixed geometry IMID EXCO, Daegu, Korea

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Simulations for curved AMOLED Center

Edge

Simulated

u’ color coordinate

Blue

R = 5mm Green

H = 1.2mm

Red

Simulation using central measurement and fixed geometry IMID EXCO, Daegu, Korea

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Part V: Conclusions

IMID Exco, Daegu, Korea

Slide #24

Part IV: Conclusions

Viewing angle characterization of curved displays is possible using standard instruments 

Three main parameters: 

D = measurement spot size at normal incidence



R = radius of curvature



H = defocusing



At focus angular distortion is negligible if D/R < 0.5%



Out of focus angular distortion is negligible if H/R < 0.2%



Computation of any curvature for all incidence & azimuth angles is now possible with the new version of EZCom


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Thanks for your attention

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