LCD Backlight & Polarization Control

* Note: Part of the present presentation was cited from lecture notes in the following website http://www.physics.gatech.edu/gcuo/lectures/index.html

Jae-Hyeon KoDept. of Physics, Hallym University

전자물리학과

Contents

I. Introduction

II. Optics for Backlight

III. Polarization Control in Backlight

IV. Summary

전자물리학과

Contents

I. Introduction

II. Optics for Backlight

III. Polarization Control in Backlight

IV. Summary

전자물리학과

◆ Emissive Display vs. Non-emissive Display

NonNon--emissive Displayemissive Display

White Light

Filters(Pixel)

Emissive DisplayEmissive Display

LIGHTSOURCE(=PIXEL)

CRT, PDP, FED, EL…. LCD, DMD…

전자물리학과

◆ Liquid Crystal Display

+ polarizer: controls transmission

controls the color separation

supplies white light

•• LCD belongs to nonLCD belongs to non--emissive displays.emissive displays.•• LCD thus needs an independent lightLCD thus needs an independent light--generating part whichgenerating part which

supplies LCD with bright, uniform white light. supplies LCD with bright, uniform white light. Backlight Unit (BLU) !Backlight Unit (BLU) !

전자물리학과

◆ Normal white mode of TN (twisted nematic) liquid crystal cell

전자물리학과

◆ Basic Structure of LCD Module

LGPlight source

diffuser

prism film

bright, uniform white light

supply white lightsupply white light

polarizercolor filter

polarizer

liquid crystals

alignment layer

ITO electrode

TFT

protection tilm

reflection film

LCD Panel

Backlight

Light Source: Generation of Visible Light

Optical Components:• Spreading/Guiding• Homogenizing• Collimating• Polarization Control

* LGP = Light Guide Plate (도광판)

전자물리학과

◆ The Energy Flow in LCD

* Edge-lit case

~

•• Main losses occur at the polarizer (55~60%) and the colorMain losses occur at the polarizer (55~60%) and the colorfilter (~70%). filter (~70%).

•• The panel transmission of LCD TV is only 4~5 %. The panel transmission of LCD TV is only 4~5 %. •• Polarization controlPolarization control is important for higher light utilization. is important for higher light utilization.

Total transmission

전자물리학과

◆ Basic Roles of BLU

Function Edge-lit BLU Direct-lit BLU

Light generation

Spreading/Guiding

Diffusing

Collimating

LED, CCFL

Reflection sheetLight Guide Plate

Diffusion sheet

Prism sheet

Polarization Control Reflective polarizer

CCFL, EEFL, FFL, LED ...

Reflection sheet

Diffusion plateDiffusion sheet

Prism sheet

Reflective polarizer

Homogeneous, collimated, bright 2D light source!Homogeneous, collimated, bright 2D light source!

전자물리학과

◆ Edge-lit BLU vs. Direct-lit BLU for LCD

Type Edge-lit BLU Direct-lit BLU

Structure

Application Mobile, Note PC, Monitor LCD TV

Luminance 100 ~ 300 cd/m2 400 ~ 500 cd/m2

Typical film configuration

CCFL(side) Reflector LGP diffuser sheet 1 or 2 prism films

protection film

Reflector CCFL(below) diffuser plate diffuser sheet prism film reflective polarization film

Number of CCFL-type

BLU

Note PC 1Monitor 10 ~ 15” 2 ~ 4Monitor 17” ~ 4 ~ 6 (Mobile 1~3 white LED)

20 ~ 22” 6 ~ 1226 ~ 32” ~ 1633 ~ 37” ~ 2040” ~ 22 ~

* CCFL=Cold-cathode fluorescent lamp (냉음극형광램프)

전자물리학과

◆ Light Sources for LCD Backlight

CCFL (cold cathode fluorescent lamp)냉음극형광램프

EEFL (external electrode fluorescent lamp) 외부전극형광램프

FFL (Flat fluorescent lamp)면광원, 평판형 형광램프

LED (Light Emitting Diode)고체발광다이오드

FEL (Field Emission lamp) 전계방출램프

OLED (Organic Light Emitting Diode) or EL Lamps

전자물리학과

◆ Light Sources for LCD Backlight

Type Characteristics CompanyCCFL Cold-cathode type (Many)EEFL DBD LG-Philips...

FFL DBD or cold-cathode

Field-emission Lamps- Cathodoluminescence

- CNT-based cathode- diode or triode

Nano-pacific, Nikkiso...

CCFL+LEDHybrid-type Enhanced deep-R component Sharp

HCFL Hot-cathode (Arc discharge) Philips

Samsung Corning, Mirae

LEDWhite-LED mobile, note PCRGB LED LCD TV, monitor

Sony, Samsung, LG-Philips, NEC ...

CCFL/EEFL

Cold-cathode or external electrode UshioXe-

typeFFL DBD Osram, CPT...

Solid-state Lighting- e-h recombination- Electroluminescence OLED/EL White OLED ITES, KDT...

Hg-type

Discharge Lamps- Non-equilibrium, low-pressure discharge(Te>>Ti~Tn)- Diffusion-controlled loss mechanism- Photoluminescence

No Polarization

Control !

* DBD: Dielectric Barrier Discharge* HCFL=Hot-cathode fluorescent lamp (열음극형광램프)

전자물리학과

Contents

I. Introduction

II. Optics for Backlight

III. Polarization Control in Backlight

IV. Summary

전자물리학과

◆ Control of the Light in the Edge-lit BLU

Reflection Scattering

Guiding

Diffusing

Collimating

PolarizationControl

전자물리학과

◆ Functions of optical films

Diffusion

Substrate

Back layerPET

확산반사

산란/굴절

굴절

편광제어

확산투과

◆ Optics for Backlight

전자물리학과

GeometricalOptics

λ << dimensions of equipments Photon energy: negligible

WaveOptics

λ ~ dimensions of equipments Photon energy: still negligible

Photon energy: very largeparticle nature

QuantumOptics

전자물리학과

Maxwell’s equations: displacement current under ac field

0

t

t

ρ

∂∇× = −

∂∂

∇× = +∂

∇ • =∇ • =

BΕ

DH J

BD

Coulomb법칙

no magnetic monopoles

Ampere 법칙

Faraday 법칙 displacement current(변위전류)

James Clerk Maxwell(1831-1879)

전자물리학과

A time-varying magnetic field will have an electric field associated with it.

A time-varying electric field will be accompanied by a magnetic field.

No isolated magnetic monopolesMagnetic Gauss’s law

The total of the electric flux out of a closed surface is determined by the charge enclosed.

전자물리학과

In empty space without any sources,

22

2 2

22

2 2

1

1c t

c t

∂∇ =

∂∂

∇ =∂

EE

HH0

0

00

t

t

µ

ε

∂∇× = −

∂∂

∇× =∂

∇ • =∇ • =

HΕ

EH

HE

1/ 20 0( )c µ ε −=

Changes in the fields Eand H propagate through empty space with a speed equal to c.

70

120

4 10 H/m

8.854 10 F/m

µ π

ε

−

−

= ×

= × ( )

( )

i t

i t

e

e

ϖ

ϖ

• −

• −

=

=

k r0

k r0

E E

H H

plane wave solution:

전자물리학과

( )

( )

i t

i t

e

e

ϖ

ϖ

• −

• −

=

=

k r0

k r0

E E

H Hcos( )cos( )

tt

ϖϖ

= • −= • −

0

0

E E k rH H k r

복소수화

k

The three vectors k, E, and H constitute a mutually orthogonal triad!

◆ Spectrum of electromagnetic waves

전자물리학과

전자물리학과

선형편광(Linear Polarization)

( )

( )

i t

i t

e

e

ϖ

ϖ

• −

• −

=

=

k r0

k r0

E E

H H만약 진폭 E0와 H0가

실수인 상수라면,

0 0If , ( ) cos( )x yE E kz tϖ= ± −k z E i jz축으로 진행하면서 x-y평면 내에서 선형편광 상태를 보이는 전기장의 가장 일반적인 형태는,

전기장의 방향은 E0에 의해고정되고 이를 선형편광이라부른다.

• 선형편광의 방향은 전기장의 진동방향으로 정의한다. • 선형편광자(linear polarizer)는 입사광을 특정방향으로 선형편광시키는 장치이다. 이때 선형편광자가 편광시키는 방향을 투과축( “transmission axis”)이라 한다.

E0x

E

θ선형편광자의 투과축

0

20

cos

cosx

x

E E

I I

θ

θ

=

=

x

E0y

y 선형편광자를 통과하고 나온 후의 전기장 세기의 각도 의존성

입사광의 편광

전자물리학과

45° Polarization

0 0

0 0

If , ( ) cos( )x y

x y

E E kz t

E E

ϖ= ± −

=

k z E i j

전자물리학과

편광의 측정

이상적인 편광자는 원하는 편광방향의 빛을 100% 투과시키고 이방향에 직교하는 빛을 100% 차단해야 하나, 현실에서는 이런편광자는 존재하지 않는다.

투과된 빛 중 편광자 방향과 나란한 빛과 수직인 빛의 세기의상대비를 “Extinction ratio” 또는 “Extinction coefficient”라고 부른다. 이 양이 무한대가 되는 경우가 이상적인 편광자에 해당될 것이다.

2EE

η⊥

=

Type of polarizer Ext. Ratio CostCalcite: 106 $1000 - 2000

Dielectric: 103 $100 - 200

Polaroid sheet: 103 $1 - 2

전자물리학과

원형(Circular) 및 타원편광(Elliptic Polarization)

원형편광(circular polarization): 동일한 전기장 진폭을 가지고 위상차이가 π/2 인두 선형편광을 중첩시키면 원형편광을 얻을 수 있다.

0[ cos( ) sin( )]R E kz t kz tϖ ϖ= − + −E i j 우편광 상태(right circular)

0[ cos( ) sin( )]L E kz t kz tϖ ϖ= − − −E i j 좌편광 상태(left circular)

x

yE-field variation over time (at, for example, z=0)

kz-ωt = 0°kz-ωt = -90°

회전에 대한 정의: 공간상 주어진 한 점에서 전자기파가 진행하는 것을 마주보면서 진행방향에 대해 역으로 바라보았을 때 전기장 벡터가 돌아가는 방향으로정의함.

우편광 빛에 대한 snapshot

전자물리학과

Complexnotation

0

exp ( ) exp ( / 2)

( )exp ( )

i kz t i kz t

E i i kz t

ϖ ϖ π

ϖ

= − + − ±

→ = ± −

E i j

E i j

x

y

+

이 복소수 표현의 실수부를 취하면 전페이지의 식이 도출되어야 함.

[QUIZ] y

= ?x

* 같은 진폭을 가진 우편광의 원형편광과 좌편광의 원형편광 빛을 중첩시키면 어떤 편광의 빛이 될 것인가? ?

전자물리학과

* 위상차이가 π/2이라도 진폭이 같지 않거나, 더 일반적으로 위상차이가 π/2가 아닌 경우에는타원편광의 상태를 보인다.

0 0

0 0

cos( ) sin( )]

or more generally,

cos( ) cos( )]

x y

x y

E kz t E kz t

E kz t E kz t

ϖ ϖ

ϖ ϖ ϑ

= − + −

= − + − +

E i j

E i j

x

yE-field variation over time (and space)

0 0x yE E≠

위상차이가 π/2이지만 진폭이 틀린 경우위상 차이가 임의인 경우0 0

0 0

cos( ) sin( )]x y

x y

E kz t E kz t

E E

ϖ ϖ= − ± −

≠

E i j0 0cos( ) cos( )]x yE kz t E kz tϖ ϖ ϑ= − + − +E i j

Elliptically Polarized(타원편광)

전자물리학과

If we employ a complex vector amplitude ,0 0 0x yE E= +E i j

exp ( )i kz tϖ= −0E E : 어떤 형태의 편광상태도표현가능함.

0 0

0 0

x

y

ix x

iy y

E E e

E E e

φ

φ

=

=

위상 차이 φx-φy 진폭 관계 편광의 형태

-E0x=E0y

π/2 or -π/2 E0x≠E0y Elliptically polarized

general

0 or π Linearly polarizedπ/2 or -π/2 Circularly polarized

general Elliptically polarized

• 선형편광과 원형편광은 타원편광의 특수한 경우들이다.

전자물리학과

The Mathematics of Polarization

1

x

y

yx

x

EE

E

E EE

E

⎡ ⎤= ⎢ ⎥

⎣ ⎦⎡ ⎤⎢ ⎥= ⎢ ⎥⎢ ⎥⎣ ⎦

Define the polarization state of a field as a 2D vector—“Jones vector” —containing the two complex amplitudes:

For many purposes, we only care about the relative values:

(alternatively normalize this vector to unity magnitude)

Specifically: 0° linear (x) polarization: Ey /Ex = 090° linear (y) polarization: Ey /Ex = ∞45° linear polarization: Ey /Ex = 1Arbitrary linear polarization: sin( ) tan( )

cos( )y

x

EE

α αα

= =

전자물리학과

편광의 행렬표현: 존스 방법(Jones methods)

0 0 0x yE E= +E i j가장 일반적으로, (이 경우 E0x와 E0y는 모두 복소수이다.)

0 0

0 0

x

y

ix x

iy y

E E e

E E e

φ

φ

=

=

00

0 0

x

y

ixx

iy y

E eEE E e

φ

φ

⎡ ⎤⎡ ⎤⎢ ⎥=⎢ ⎥⎢ ⎥⎣ ⎦ ⎣ ⎦

“Jonesvector”

(1) Linear polarization

Jonesvector

편광방향

10

⎡ ⎤⎢ ⎥⎣ ⎦

01

⎡ ⎤⎢ ⎥⎣ ⎦

1112

⎡ ⎤⎢ ⎥⎣ ⎦

( ) / 2+i jji

전자물리학과

(2) Circular polarization

( )( )

exp ( )

[cos( ) sin( )]

cos( ) sin( )

i i kz t

i kz t i kz t

kz t kz t

ϖ

ϖ ϖ

ϖ ϖ

+ −

= + − + −

= − − −

i j

i j

i j

1A

i⎡ ⎤⎢ ⎥⎣ ⎦ Take

real!

“left-circularly polarized”

( )exp ( )

.........

cos( ) sin( )

i i kz t

kz t kz t

ϖ

ϖ ϖ

− −

= − + −

i j

i j

1A

i⎡ ⎤⎢ ⎥−⎣ ⎦

“right-circularly polarized”

전자물리학과

(3) Elliptic polarization

( ) ( )

00

0 0

0 0 0 0

or11

/ /

x

y

y x

ixx

iy y

iy x y x

E eEE E e

E E E E e

φ

φ

φ φ−

⎡ ⎤⎡ ⎤⎢ ⎥=⎢ ⎥⎢ ⎥⎣ ⎦ ⎣ ⎦

⎡ ⎤⎡ ⎤⎢ ⎥=⎢ ⎥⎢ ⎥⎣ ⎦ ⎣ ⎦

전자물리학과

1. How can we know or calculate the result of adding two or more waves of given polarizations? Jones notation simplifies it.

1 1 1 1 2 12

0 0i i i i+⎡ ⎤ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤

+ = = =⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎢ ⎥− − +⎣ ⎦ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦

• Linearly polarized in x, • Twice that of either of the circular components

Left-circular

Right-circular

2. How can we compute the effect of inserting linear optical elements into a beam of light of a given polarization? Jones matrix simplifies it.

Optical elementsAB

⎡ ⎤⎢ ⎥⎣ ⎦입사광

'

'

AB

⎡ ⎤⎢ ⎥⎣ ⎦출사광

전자물리학과

'

'

a b A Ac d B B

⎡ ⎤⎡ ⎤ ⎡ ⎤= ⎢ ⎥⎢ ⎥ ⎢ ⎥

⎣ ⎦ ⎣ ⎦ ⎣ ⎦

2x2 Jones matrix of the optical element

'2 2 1 1

'2 2 1 1

n n

n n

a b a b a b A Ac d c d c d B B

⎡ ⎤⎡ ⎤ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤= ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎢ ⎥

⎣ ⎦⎣ ⎦ ⎣ ⎦⎣ ⎦ ⎣ ⎦

represents a train of optical elements

No light output!1 0 0 00 0 1 0

⎡ ⎤ ⎡ ⎤ ⎡ ⎤=⎢ ⎥ ⎢ ⎥ ⎢ ⎥

⎣ ⎦ ⎣ ⎦ ⎣ ⎦

[예]

x방향 편광자 y축 선형편광 빛

전자물리학과

Optical Element Jones Matrix

linear horizontal polarizer

linear vertical polarizer

linear polarizer at +45°

linear polarizer at -45°

quarter-wave plate, fast axis vertical

quarter-wave plate, fast axis horizontal

circular polarizer, right-handed

circular polarizer, left-handed

전자물리학과

10

⎡ ⎤∝ ⎢ ⎥

⎣ ⎦

01

⎡ ⎤∝ ⎢ ⎥

⎣ ⎦Uniaxial

Liquid crystals

◆ The Fresnel’s Equations

전자물리학과

y

k=ki

incident

exp ( )i tϖ• −k r

θ k’=kr

reflected 'exp ( )i tϖ• −k r

θ’

k”=kttransmitted(refracted)

"exp ( )i tϖ• −k r

φ

n1=ni

입사광 반사광

굴절광 혹은 투과광xn2=nt

전자물리학과

• 세 파동은 모두 같은 주파수를 갖는다. ω는 전자기파가 만들어지는 source에 의해 결정된다.

i i r r t t

t ii r t t

i t

u k u k u ku nk k k ku n

ϖ = = =

= = =

• 경계면의 모든 점에 대해, 그리고 주어진 모든 시간에 대해 어떤일정한 상수관계가 성립할려면, 세 파동을 기술하는 지수함수의지수가 경계면에서 동일해야 한다.

( )( ) ( )( ) ( ) ( ) , at 0.i ti t i te e e yϖϖ ϖ • −• − • −+ = =ti r k rk r k r

Must be equal.

전자물리학과

' "• = • = •k r k r k r

sin 'sin ' "sink k kθ θ φ= =

'k k=

'θ θ= 2

1

" / " / "/ /

sinsin

k u c u n nk u c u n

n

ϖϖθφ

= = = =

→ =

' ' " "x z x z x zk x k z k x k z k x k z+ = + = +

' "

' "x x x

z z z

k k k

k k k

= =

= =(만약 kz 성분이0이라 하면)

경계면에서 위상이 같다는 조건에서,

(at the boundary, y=0)

(1) The law of reflection

(2) The Snell’s law of refraction

(3) The three k’s are coplanar. “plane of incidence”

전자물리학과

θi

θt

( ) ( ) ( ) ( )1 1 2 2 3 3sin sin sin ... sinm mn n n nθ θ θ θ= = = =

◆ The Fresnel’s Equations for TE polarization (s-polarization)

전자물리학과

TE(transverse electric) polarization or s-polarization(전기장이 매질의 경계면과 나란한 경우)

ni

nt

ik rk

tk

θi θr

θt

EiHi

Er

Hr

Et

Ht

InterfaceBeam geometryfor light with itselectric field per-pendicular to theplane of incidence(i.e., out of the page)

x

y

z

전자물리학과

Maxwell 방정식의 적분형

0

t

t

ρ∇ • =∇ • =

∂∇× = −

∂∂

∇× = +∂

DB

BΕ

DH J

0

fs

s

L S

fL S

d Q

d

dd ddt

dd I ddt

• =

• =

• = − •

• = + •

∫

∫

∫ ∫

∫ ∫

D a

B a

E l B a

H l D a

Gauss’ theoremStokes’ theorem

S는 닫힌임의의 곡면

S는 닫힌 고리 L로둘러싸인 임의의 면

전자물리학과

0

fs

s

L S

fL S

d Q

d

dd ddt

dd I ddt

• =

• =

• = − •

• = + •

∫

∫

∫ ∫

∫ ∫

D a

B a

E l B a

H l D a

1 2 fD D σ⊥ ⊥− =

1 2 0B B⊥ ⊥− =

1 2 0− =E E

1 2 0− =H H(No free surface current)

경계면에서 자유표면전하나 자유표면전류가 없다면 하기의 경계조건을 적용할 수 있다.

1 1 2 2 0E Eε ε⊥ ⊥− = 1 2 0B B⊥ ⊥− =

1 2 0− =E E 1 21 2

1 1 0µ µ

− =B B

전자물리학과

00

µϖεϖ

× =× = −• =• =

k Ε Hk H Ek Hk E

1 (incident)

1 (reflected)

1 (transmitted)

i i i

r r r

t t t

µϖ

µϖ

µϖ

= ×

= ×

= ×

H k E

H k E

H k E

경계조건(Boundary conditions): [ 전자기학 교과서 참조]

경계면에서 전기장과 자기장의 경계면과 나란한 성분(Tangential Components)이 연속이어야 한다.

Ei(x, y = 0, z, t) + Er(x, y = 0, z, t) = Et(x, y = 0, z, t)–Hi(x, y = 0, z, t) cosθi + Hr(x, y = 0, z, t) cosθr = –Ht(x, y = 0, z, t) cosθt–kiEi(x, y = 0, z, t) cosθi + krEr(x, y = 0, z, t) cosθr = –ktEt(x, y = 0, z, t) cosθt

전자물리학과

TE polarization에 대한 반사계수(coefficient of reflection):

[ ] [ ] [ ]2 2

2 2

/ cos cos / cos cos

cos sincos cos sin( ) cos cos sin( ) cos sin

s r i i i t t i i t tTE

i ii t i t t

i t i t ii i

r E E n n n n

nn nnn nn

θ θ θ θ

θ θθ θ θ θθ θ θ θ θ θ

= = − +

− − ⎛ ⎞− −= = − = =⎜ ⎟− + + − ⎝ ⎠

TE polarization에 대한 투과계수(coefficient of transmission):

[ ] [ ]/ 2 cos / cos cos

2cos 2cos sin cos cos sin( )

s t i i i i i t tTE

i i t

i t i t

t E E n n n

n

θ θ θ

θ θ θθ θ θ θ

= = +

= =+ +

Fresnel’s equations for TE polarization

◆ The Fresnel’s Equations for TM polarization (p-polarization)

전자물리학과

x

y

zni

nt

ik rk

tk

θi θr

θt

EiHi Er

Hr

EtHt

InterfaceBeam geometryfor light with itselectric fieldparallel to the plane of incidence(i.e., in the page)

×

TM(transverse magnetic) polarization or p-polarization(자기장이 매질의 경계면과 나란한 경우)

전기장과 자기장의 tangential성분이 같아야 한다는 경계조건으로부터, Hi - Hr = Ht

kiEi - krEr = ktEt

Eicosθi + Ercosθr = Etcosθt

전자물리학과

TM polarization에 대한 반사계수(coefficient of reflection):

[ ] [ ] [ ]2 2 2

2 2 2

/ cos cos / cos( ) cos( )

cos sincos cos tan( ) cos cos tan( ) cos sin

p r i i t t i i t t iTM

i ii t i t

i t i t i i

r E E n n n n

n nnn n n

θ θ θ θ

θ θθ θ θ θθ θ θ θ θ θ

= = − +

− + −− + −= = − =

+ + + −

[ ] [ ]/ 2 cos( ) / cos cos

2cos sin sin( )cos( )

p t i i i i t t iTM

i t

i t i t

t E E n n nθ θ θ

θ θθ θ θ θ

= = +

=+ −

TM polarization에 대한 투과계수(coefficient of transmission):

Fresnel’s equations for TM polarization

전자물리학과

Reflectance and Transmittance2 2

2 2

2 22 2

1

1

trs s s s s s

i iTE TE

trp p p p p p

i iTM TM

EER r T t R TE E

EER r T t R TE E

= = = = + =

= = = = + =

211s p

nR Rn

−⎡ ⎤= = ⎢ ⎥+⎣ ⎦

For normal incidence (θι=0), (수직입사의 경우)

에너지 보존법칙(흡수는 없다고 가정함)

즉, 입사광의 약 4% 정도가경계면에서 반사됨If n~1.5, R ~ 4%.

전자물리학과

Air-to-glass surface(External reflection, n>1)

Glass-to-air surface(Internal reflection, n<1)

Incidence angle, θi

Ref

lect

ion

coef

ficie

nt, r

1.0

.5

0

-.5

-1.0

rp

rs

0° 30° 60° 90°

Brewster’s anglerp=0!

Incidence angle, θi

Ref

lect

ion

coef

ficie

nt, r

1.0

.5

0

-.5

-1.0

rp

rs

0° 30° 60° 90°

Total internal reflection

Brewster’s angle

Criticalangle

Criticalangle

전자물리학과

Reflectance and Transmittance for anAir-to-Glass Interface

TE polarization

Incidence angle, θi

1.0

.5

00° 30° 60° 90°

R

T

TM polarization

Incidence angle, θi

1.0

.5

00° 30° 60° 90°

R

T

전자물리학과

Reflectance and Transmittance for aGlass-to-Air Interface

TE polarization

Incidence angle, θi

1.0

.5

00° 30° 60° 90°

R

T

TM polarization

Incidence angle, θi

1.0

.5

00° 30° 60° 90°

R

T

◆ TIR (Total Internal Reflection)

전자물리학과

• 전반사(Total internal reflection) : 굴절률이 큰 매질에서 작은매질로 진행하는 경우(n<1인 경우), “critical angle”이라 불리는 각도에서 sinθ=n이 성립한다. 이 각도보다 큰 경우는R=1 및 T=0로써 입사광은 100% 반사된다. 유리에서 공기에 입사되는 경우의 임계각(critical angle)은,

1 1 osin (1/ ) sin (1/1.5) 41nθ − −= = ≈

Total Internal Reflection

Brewster’s angle

전자물리학과

Prism: Beam steerers(프리즘; 빔의 방향변환자)

Optical fibers (광섬유)

ncore > ncladding

◆ Brewster’s angle

전자물리학과

• 브루스터 각(Brewster’s angle): TM편광을 가진 빛이 입사할 경우에는 반사계수가 0이 되는 특정 각도가 존재하는데이를 브루스터 각이라 부른다 .

• air-to-glass 조건에서는 브루스터 각이 대략 57 도이고, glass-to-air 조건에서는 약 33 도이다.

• 만약 자연편광인 상태의 빛이 브루스터 각도로 경계면에입사한다면 반사광은 TE편광만 반사하게 되어 TE편광된상태를 유지하고 투과광은 TM편광의 경우는 TM성분이 약간 많은 부분편광(partially polarized)된 상태를 보인다. .

1tan nθ −=

◆ Uniaxial crystals(일축성 결정)

전자물리학과

Uniaxial crystals은 빛이 광축에대해 편광되어 있을 경우에 대한굴절률(ne)과 광축에 대해 수직인두 방향에 대해 편광되어 있을경우의 굴절률(no)을 생각할 수있다.

광축에 나란히 편광되어 있는빛을 이상광선(extraordinaryray)이라 하고 광축에 수직한방향으로 편광되어 있는 빛을정상광선(ordinary ray)이라 한다. 이 두 편광방향들은 결정의주축들(“principal axes”)이다.

주축 이외 다른 방향의 편광을 가지고 진행하는 빛은 그것의정상광선 성분과 이상광선 성분으로 나누어 개별적으로 고려한후에 재결합해서 파악해야 한다.

◆ 복굴절(Birefringence)

전자물리학과

스넬의 법칙에 따라 서로 다른 편광을 가진빛은 경계면에서 서로 다른 정도로 굴절된다. (double refraction)

no

ne

o-ray

e-ray

( ) ( ) ( )θθθ sinsin 1 ⋅=⋅ nnair

• ordinary wave:( ) ( )0011 sinsin θθ ⋅=⋅ nn

• extraordinary wave:

( ) ( ) ( )eenn θθθ sinsin 11 ⋅=⋅

◆ Calcite (방해석)

전자물리학과

Halite (cubic sodium chloride crystal, optically isotropic)

Calcite (optically anisotropic)

Calcite는 calcium carbonate (CaCO3)로 이루어진 결정으로서, 가장잘 알려진 복굴절 결정 중 하나이다. no = 1.6584ne = 1.4864

◆ Uniaxial Birefringent Crystals

전자물리학과

a measure of the birefringencee on n n∆ = − →

◆ Wollaston Polarizing Beam Splitter

전자물리학과

The Wollaston polarizing beam splitter는 두 개의 회전된 복굴절프리즘을 이용하지만 오직 굴절에만 의존한다.

정상광선과 이상광선은 서로 다른 굴절률을 가지고 있고 따라서 서로 다른

방향으로 발산한다.

yne

E

◆ Wave plates or retarders

xno• 한 빔이 복굴절 매질 내를 통과한다면, 한 편광

성분은 다른 편광성분 보다 더 긴 위상 지연(phase delay)를 느낀다.

• 만약 두 편광성분이 같이 존재한다면 복굴절효과는 x와 y 성분의 상대적인 위상을 바꾸게되고 따라서 편광을 회전시키는 효과를 가져온다.

• retardation plates (wave plates)는 편광상태변환기(polarization-state converters)이다. 빛의 편광상태는 적당한 retardation plate를이용해서 다른 어떤 상태의 편광으로도 바뀔수 있다.

• retardation plates (wave plates)는 편광상태 변환기(polarization-state converters)이다. 빛의 편광상태는 적당한 retardation plate를 이용해서 다른 어떤 상태의 편광으로도 바뀔 수 있다. • 일축성 결정을 이용해서 retardation plate를 만들 경우에는 보통 광축 c가 plate 평면 내에 포함되도록 일축성 결정을 자른다. Ordinary wave 및 extraordinary wave를만들어 내는 편광의 방향은 서로 수직이고, 만약 no > ne라면 이들은 각각 “slow” axis 및 “fast” axis라고 불린다. 만약 no < ne 이면 반대로 명명된다.

no > ne

“Negative”no < ne

“Positive”y fast axisne

y slow axisne

x slow axisno

x fast axisno

E

yne

일축성 결정을 이용해서 retardation plate를 만들 경우에는 보통 광축 c가 plate 평면 내에 포함되도록 일축성 결정을 자른다.

두께 d인 retardation plate에 대해서 입사광이x, y 방향의 성분을 모두 가지고 입사한다고 하자. 두께 d를 지나간 두 편광성분의 위상 차이는,

xno

(비교)

0

2o e o e ok n n d n n dπϕ

λ∆ = − = −

0 0y xE E=

( ) ( )0 0

1

/ y xiy xE E e φ φ−

⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦

0

1

2exp e oi n n dπλ

⎡ ⎤⎢ ⎥

⎛ ⎞⎢ ⎥−⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

45도의 선형편광이 입사될때 두께 d인 retardation

plate를 빠져 나오는 빛의편광상태를 나타내는

Jones vector

Wave plates

0

1

2exp e oi n n dπλ

⎡ ⎤⎢ ⎥

⎛ ⎞⎢ ⎥−⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Wave plate 출력 편광 상태:

(45도 입력 편광에 대해)

0 0

45 Linear0 1Left Circular/2

45 Linear13 /2 Right Circular2 1 45 Linear

Output2 2 exp Polarization Statee o e o

i

i

n n d i n n d

ππππ

π πλ λ

−−−

⎛ ⎞− −⎜ ⎟

⎝ ⎠“Quarter-wave

plate”

“Half-wave plate” “Full-wave plate”

• 복굴절 효과에 의해 형성된 위상 차이에 의해 입력 편광이 다양한편광상태로 바뀌는 것을 알 수 있다. quarter-wave plate는 직선편광을원형 편광으로 바꾸어주고, half-wave plate는 직선편광을 그것에 수직인다른 직선편광으로 바꾸어 준다.

• 추가로 2mπ을 더해주어도 출력 편광 상태는 바뀌지 않는다. (m은 정수)

Half-Wave Plate

어떤 빔이 half-wave plate를 진행하면, 한 편광 성분은 다른 성분에 비해반파장의 위상 지연을 경험하게 된다.

• 만약 입사광의 편광이 주축에 대해 45° 기울어져 있다면 출사 편광은 입사 편광이 90°만큼 회전한 선형편광으로 이루어진다.

• 만약 입사 편광이 wave plate의 주축과 나란하다면 편광의 회전은일어나지 않는다.

• 원형/타원 편광이 입사하면 half-wave plate는 편광 회전 방향을바꾸어 놓는다.

Circular polarizers

Circularly polarized light

원형 편광자는 입사되는 자연편광을우선 선형 편광으로 만든 후 그것을회전시켜 원형 편광으로 만든다. 이것은 선형 편광자 뒤에 quarter wave plate를 달아서 이루어진다.

Unpolarized input light

* 전압을 인가하지 않은 상태에서의 TN mode (90도)는 투과도가 0이다. Normal black(NB) state

2 2' ' 22

2 2 2

2 2

2

sin

sin 1

1

x y

x y

E E XTXE E

u

u

φ

φ

+= =

+

⎡ ⎤+⎣ ⎦=

+

10

⎛ ⎞⎜ ⎟⎝ ⎠

sin sincos2

sin sincos2

X XX iX X

X XX iX X

φ

φ

Γ⎡ ⎤−⎢ ⎥⎢ ⎥

Γ⎢ ⎥− +⎢ ⎥⎣ ⎦

sincos2

sin

XX iX

XX

φ

Γ⎛ ⎞−⎜ ⎟⎜ ⎟⎜ ⎟−⎜ ⎟⎝ ⎠

0 00 1

⎛ ⎞⎜ ⎟⎝ ⎠

0sin X

Xφ

⎛ ⎞⎜ ⎟⎜ ⎟−⎜ ⎟⎝ ⎠

전자물리학과

Contents

I. Introduction

II. Optics for Backlight

III. Polarization Control in Backlight

IV. Summary

전자물리학과

◆ Control of the Light in the Edge-lit BLU

Reflection Scattering

Guiding

Diffusing

Collimating

PolarizationControl

전자물리학과

◆ Polarization Control: Reflective polarizer

Multi-layer type CLC type Wire-grid type

Structure

- PEN-coPEN multi-layer stack total 4 groups - each group consisting of 120~150 layers

- three CLC layers serving as reflection layers in the R, G, B ranges- additional λ/4 plate

- sub-wavelength metal (usually Al) grating structure

Process Co-extrusion stretching CLC coating lamination attach λ/4 plate Nano-imprinting lithography

Status Commercialized Commercialized Under development for BLU

Properties

- generalization of Fresnelequation free adjustment of Brewster angle- each layer-group controls reflectivity of p-polarization over ~ 100nm 4 layer-groups cover visible range

- adjust pitch/alignment of CLC for achieving circular dichroism in visible range- additional λ/4 plate necessary for change of circularly polarized light to linearly polarized light

- wire-grid acts as a metal mirror to the s-polarization- performances are dependent on the period, linewidth, and depth of the grid elements- lower transmission in the blue range of visible light

Company 3MNitto-Denko, Samsung Fine Chemicals

LG Electronics, NanoOpto Co., Eastman Kodak, MoxTek, ....

* PEN: polyethylene naphthalate* CLC: Cholesteric Liquid Crystal

전자물리학과

◆ Polarization Control: Reflective polarizer (I) -DBEF

•• Transmit the polarization component parallel to the polarizationTransmit the polarization component parallel to the polarization direction of the bottomdirection of the bottompolarizer of LCD panel while reflect the orthogonal component polarizer of LCD panel while reflect the orthogonal component down to the BLUdown to the BLUresulting in polarization recycling via change of the polarizaresulting in polarization recycling via change of the polarization state. tion state.

30~65% increase in luminance30~65% increase in luminance

• The light has to be depolarized and re-emitted.• The luminance gain depends on the condition of

the lower part of BLU onto which downward rayswill be reflected, depolarized and recycled.

alternatively-stacked multilayer of isotropic and birefringentmaterials

stretching

* M. F. Weber et al., Science Vol.287, 2451 (2000)* http://cms.3m.com/cms/US/en/2-136/cRciRFF/view.jhtml

전자물리학과

◆ Polarization Control: Reflective polarizer (I) –DBEF (Continued)

one reflection band for p-polarized light in the green range centered at 550 nm

extinction ratio of 300:1

( )( )

22

2

1 4, arcsin1

NH L H L

DBEF NDBEF H LH L

n n n nRn nn n

λλ π

⎡ ⎤− − ⎛ ⎞∆ −⎡ ⎤= =⎢ ⎥ ⎜ ⎟⎢ ⎥ +⎣ ⎦− +⎢ ⎥ ⎝ ⎠⎣ ⎦

4 layer-groups

(N: number of film pairs)

nHnL

nL nL

Giant Giant birefringentbirefringent optics--. generalization of . generalization of FresnelFresnel equations for equations for birefringentbirefringent

materials materials --. improved control of the reflectivity of p. improved control of the reflectivity of p--polarized light:polarized light:

all of the characteristics of the normal incidence reflectionall of the characteristics of the normal incidence reflectionband are maintained for highband are maintained for high--incidence pincidence p--polarized light polarized light

--. free adjustment of the Brewster. free adjustment of the Brewster’’s angle between 0 ~ 90s angle between 0 ~ 90o

optics

o

* M. F. Weber et al., Science Vol.287, 2451 (2000)* W. J. Jeong, IDW’06 Digest, p.999 (2006)

전자물리학과

◆ Polarization Control: Reflective polarizer (II) - CLC

2 22

2 2

2 2

2tanh2

2

e oCLC

e o

e o

CLC e o

n nR Ln n

n nn n

πλ

λλ

⎡ ⎤−⎢ ⎥=⎢ ⎥+⎣ ⎦

⎛ ⎞−∆⎡ ⎤ ⎜ ⎟=⎢ ⎥ ⎜ ⎟⎣ ⎦ +⎝ ⎠

* T. Nakajima, Nitto Denko Tech. Rep. Vol.41, 30 (2003) * W. J. Jeong, IDW’06 Digest, p.999 (2006)* P. Yeh and C. Gu, “Optics of Liquid Crystal Displays” (Wiley-Interscience)

B

G

R

(L: film thickness)

* http://www.chelix.com/

overlap of three bands

Effect of CLC polarizer

Wire Grid Polarizer

전자물리학과

The light can excite electrons to move along the wires, which thenemit light that cancels the input light. This cannot happen perpen-dicular to the wires. Such polarizers work best in the IR.

Polaroid sheet polarizers use the same idea, but with long polymers.

Input light contains both polarizations

전자물리학과

Visible wire-grid polarizer performance

Transmission

A polarizer’s performance can vary with wavelength and incidence angle.

Extinction ratio

The overall transmission is also important, as is the amount of the wrong polarization in each beam.

전자물리학과

◆ Polarization Control: Reflective polarizer (III) – wire-grid polarizer

* www.moxtex.com, ProFlux

* J. J. Wang, Appl. Phys. Lett., Vol.89, 141105 (2006)

* E. Hecht, “Optics” (Addison Wesley)

* J. J. Wang, Appl. Phys. Lett., Vol.89, 141105 (2006)* X.-D. Mi, SID’05 Digest, 1004 (2005)* S. H. Kim, Nanotechnology, Vol.17, 4436 (2006)

•• It is important to achieve as high a It is important to achieve as high a PP as possible while maintainingas possible while maintainingenough CR. enough CR. LinewidthLinewidth of the grid is critical to obtaining high of the grid is critical to obtaining high PP..

•• The shorter the period, the shorter the operating wavelength. The shorter the period, the shorter the operating wavelength.

double-side Al WGP

Parameters Definition Remarks

Transmission contrast ratio (CR) Tp / Ts

tradeoff relationship with energy efficiency

Total energy efficiency (P) Tp + Rp (or 1-lossTM) always less than 1 due to

the internal loss.

TM transmission (Tp)Power transmission coefficient for p-polarized light

very sensitive to the linewidth of the grid

전자물리학과

Nano imprint lithography

* J. J. Wang, Appl. Phys. Lett., Vol.89, 141105 (2006)

전자물리학과

◆ Guiding: Light Guiding Plate (I) Structure and Functions

•• LGP is used for the transformation of point or line sources intoLGP is used for the transformation of point or line sources into 22--dimensional planar illumination in edgedimensional planar illumination in edge--lit lit BLUsBLUs. .

•• The main body of LGP consists of transparent plate in which visThe main body of LGP consists of transparent plate in which visible light isible light isguided via total internal reflection (TIR). guided via total internal reflection (TIR).

•• In order to extract light from LGP, the condition of TIR shouldIn order to extract light from LGP, the condition of TIR should be brokenbe brokenby scattering pattern on the backside of LGP. by scattering pattern on the backside of LGP.

* Source: CVCE 2005, Wooyoung

typical plate: PMMA (Polymethylmethacrylate)transmission: 92% (~ 96%2)refractive index: 1.49 (θc=42.2o)

light source: CCFL or LED

injection(사출)thickness: 0.6~2mm

extrusion(압출)thickness: 2~10mm

전자물리학과

◆ Guiding: Light Guiding Plate (II) Light in the LGP

( )1 omax2 2sin sin 90 /air LGPn nθ −= = 48.2o > θc(=42.1o) for PMMA (n=1.5)

50.9o > θc(=39.1o) for PC (n=1.585)iθ

= 41.8o for PMMA (n=1.5)39.1o for PC (n=1.585)

* source: 김차연 “BLU 기술시장 동향 및 분석” (2005, 산업교육연구소)

max2θ iθLGP

mirror

•• All rays entering the LGP are guided through the All rays entering the LGP are guided through the lightguidelightguide via TIR. via TIR.

satisfy the condition of TIRsatisfy the condition of TIRlight trapped in the LGPlight trapped in the LGPneed to break the condition of TIRneed to break the condition of TIRfor light extraction from LGPfor light extraction from LGP

전자물리학과

◆ Guiding: Light Guiding Plate (III) Extraction of light from LGP

typetype Diffuse scattering typeDiffuse scattering type Reflection/refraction typeReflection/refraction type

Principle• scatter the guided light from diffuse, white dots or etchedsurfaces on the bottom of LGP

• reflect the guided-light via TIR• control the direction of the reflectedlight and thus the direction of theillumination

Process

• printing dot pattern made of whiteink materials such as TiO2

pigment by silk-printing process• etching the bottom of mold forLGP

• molding 3D structures such asprism(V grooves), microlens, gratingson the bottom and/or top of LGP

Design parameters

• density• size• pattern density in dots• randomization

• density• pitch (grating, groove...)• 3D shape of microlens• randomization

Pro & Con• long history, cost-effective• needs 3~4 additional sheets

• cost-ineffective • appropriate for hybrid LGP

전자물리학과

◆ Guiding: Light Guiding Plate (IV) Design of Patterns

uniformity

extraction efficiency

available light power

(example 2) Kalantar, SID ’99 Digest (1999)

* Source: CVCE 2005, Wooyoung(example 1) 사종엽 외, 대한기계학회논문집, 28권, 362 (2004)

전자물리학과

◆ Guiding: Light Guiding Plate (V) Recent developments

1st generation 2nd generation 3rd generation 4th generationGeneral Reverse-prism LGP Hybrid LGP Polarizing LGP

Status

• long history, cost-effective• many components necessary

• High on-axis luminance, narrower viewing angle • smaller components

• only 1 (or 2) component• not enough uniformity and on-axis luminance

• polarize the light emitted from LGP• not enough extinction ratio

Structure

Protection film1~2 Prism sheetsDiffuser sheetLGP (bottom-patterned)Reflection sheet

(protection film)Reverse prism sheetPrism LGPReflection sheet

(diffuser sheet)Hybrid LGP(Reflection sheet)

Polarizing LGP(reflection sheet)

components 5~6 3~4 1~3 1~2

Schematicdrawings

전자물리학과

◆ Polarization Control: Polarized LGP

Brewster angle selective TIR Sub-wavelength grating

Anisotropic scattering

Operating principle

• utilize either reflected or transmitted light incident at the Brewster’s angle

• polarization selection via polarization-dependent TIR at an isotropic-anisotropic interface

• extraction of p-polarized light via grating • conversion from s- to p-polarized light via λ/4 plate

• anisotropic scattering centers transmit index-matched polarization while scatter the orthogonal component

Structure

• coupled prismatic polarizer light pipe•Wedge-shaped LGP whose angle is controlled based on the Brewster’s angle

• a bicomponent structure consisting of an isotropic LGP on which a micro-structured birefringentpolymer film is coated

• sub-wavelength grating formed on LGP• λ/4 plate is put below LGP

• composite materials such as oriented polymer and an isotropic dispersed phase

Properties

• not enough CR• low enhancement• poor angular characteristics

• CR up to 64~100• gain factor ~1.6• Smooth surface is important.

• gain factor ~ 1.7• additional λ/4 required.• performances are sensitive to the conditions of grating

• CR ~ 20• lower efficiency• lower uniformity

Research Group IBM Japan Philips, Eindhoven Univ.,

National Chiao Tung Univ.National Chiao TungUniv., Tsinghua Univ.

Philips, EindhovenUniv. ...

전자물리학과

◆ Polarization Control: Polarized LGP (I) based on Brewster’s angle

* E. Hecht, “Optics” (Addison Wesley)

highly colli-mated light

TIR

more p-polarized

s-polarized

stack of lots of plates

* M. Suzuki, SID Digest

21 0 1

2 21 0 1

cos / 2n nn n n

φ −⎛ ⎞

= ⎜ ⎟⎜ ⎟+⎝ ⎠λ/4 plate

•• Contrast ratio ~ 5 with 20 platesContrast ratio ~ 5 with 20 plates•• enhancement factor ~ 12%enhancement factor ~ 12%•• too complex structuretoo complex structure

* H. Tanase, SID’97 Digest, p.365

1500 µm

n=1.514

n=1.538

highly colli-mated light

Sample 1: laser input•• not enough contrast rationot enough contrast ratio•• poor angular characteristicspoor angular characteristics•• collimation of light source is collimation of light source is

necessarynecessary

전자물리학과

Nicol Polarizer는 두 개의 동일한 calcite 프리즘과 optical cement 및 전반사를 이용한다.

광축이 나란한 두 calcite 프리즘을 Canada balsam cement (n = 1.55)를 이용하여 붙인다.

정상광선no = 1.6584

이상광선ne = 1.4864

스넬의 법칙에 의해 입사광은 분리된다. 광축에 수직인 편광성분은고굴절률(1.66)에서 저굴절률(1.55)로 입사하면서 전반사하고, 다른편광 성분은 브루스터 각 근처의 각도에서 투과한다.

전자물리학과

◆ Polarization Control: Polarized LGP (II) Based on selective TIRPlease remind the picture of Nicol prism from “Optics” by E. Hecht. •• Polarization separation is based on the polarizationPolarization separation is based on the polarization--

dependent TIR at an isotropicdependent TIR at an isotropic--anisotropic interface. anisotropic interface. •• LGP based on microLGP based on micro--structured structured birefringentbirefringent foil showedfoil showed

better performances with a maximum CR of 64~100 andbetter performances with a maximum CR of 64~100 andenhancement factor of 1.6~1.78. enhancement factor of 1.6~1.78.

•• Higher birefringence is required for better performance. Higher birefringence is required for better performance.

Surface micro-relief structure for outcoupling

PMMA o en n n<

* K.-W. Chien, Appl. Opt. Vol.43, p.4672 (2004)* H. Jagt, SID’02 Digest, p.1236 (2002)* N. Stutzmann, Jpn. J. Appl. Phys. Vol.40, p.5966 (2001)

전자물리학과

Form Birefringence

q = a/Λ: fill factor

전자물리학과

◆ Polarization Control: Polarized LGP (III) Based on sub-wavelengthgrating

Polarization separation at the subPolarization separation at the sub--wavelength grating wavelength grating

Polarization conversion from sPolarization conversion from s-- to pto p--polarization polarization via double pass through via double pass through λλ/4 plate/4 plate λλ/4 plate can be replaced by LGP in which /4 plate can be replaced by LGP in which

stressstress--induced birefringence is induced by induced birefringence is induced by stress freezing technique. stress freezing technique.

y xn n n Cσ σ σ∆ = − = ∆

stress difference

* Yang, Appl. Phys. Lett., Vol.88, p.221109 (2006)

* K.-W. Chien, Appl. Opt. Vol.43, p.1830 (2004)

전자물리학과

◆ Polarization Control: Polarized LGP (IV) Based on anisotropic scattering

•• Polarization separation is based on the anisotropic scattering: Polarization separation is based on the anisotropic scattering: ss--polarized light is polarized light is strongly scattered and coupled out of the LGP linearly polarizstrongly scattered and coupled out of the LGP linearly polarized while the ped while the p--polarized light is much less coupled out and recycled in the Lpolarized light is much less coupled out and recycled in the LGP. GP.

•• There exist inherent difficulties in achieving enough uniformitThere exist inherent difficulties in achieving enough uniformity. It also suffers fromy. It also suffers fromlow CR and efficiency. low CR and efficiency.

* H. J. B. Jagt, IDW’00 Digest, p.387 (2000)* Figure from I. Amimori, J. Appl. Phys. Vol.93, 3248 (2003)

전자물리학과

◆ Polarization Control: Summary

Absorbing polarizerAbsorbing polarizer Reflective polarizerReflective polarizer Scattering polarizerScattering polarizer

• Iodine-doped PVA films• absorb more than 50 %

of incident light• contribute to the large

loss in LCD along with that from color filter

• (1) isotropic-anisotropic multi-layer stack type, (2) CLC stacktype, (3) wire-grid type

• reasonably good performances • costly in BLU, thus tends to try

to omit this technology

• anisotropic scattering centers dispersed in isotropic matrix, or viceversa

• lower performances andlower cost than reflectivetypes

* Figures from I. Amimori, J. Appl. Phys. Vol.93, 3248 (2003)

전자물리학과

◆ Hybrid Films Integrating Multi-functions

Prism sheet + reflective polarizer:- fewer components, thinner design • How to combine collimating

function and diffusing function?

- How to integrate collimating function into the diffuser plate? - Can holographic diffuser or other diffuser of new concept replace “prism film + diffuser sheet”?

전자물리학과

Contents

I. Introduction

II. Optics for Backlight

III. Polarization Control in Backlight

IV. Summary

전자물리학과

•• Polarization control is very important for achieving high Polarization control is very important for achieving high brightness on LCD panel. brightness on LCD panel. •• MultiMulti--layerlayer--type reflective polarizer is the most dominant type reflective polarizer is the most dominant optical component used in backlight for polarization control. optical component used in backlight for polarization control. •• Several attempts have been tried to develop polarizing LGP, Several attempts have been tried to develop polarizing LGP, but nothing has yet been commercialized. but nothing has yet been commercialized.

<references> <references> 1. [Optics] (Hecht, Addison Wesley) 1. [Optics] (Hecht, Addison Wesley) 2. [Optics of Liquid Crystal Displays] (2. [Optics of Liquid Crystal Displays] (YehYeh, Wiley Inter, Wiley Inter--science)science)3. CD3. CD--ROM ROM

전자물리학과

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