Illumination of DLP with Laser Light Sources. Völkel, “Illumination of DLP® with Laser Light...

Our MicroOptics set the Standards

Illumination of DLP® with Laser

Light Sources

Dr. Reinhard VoelkelSUSS MicroOptics SA, Neuchâtel, Switzerland

www.suss.ch, [email protected]

R. Völkel, “Illumination of DLP® with Laser Light Sources”, 4th International Symposium on Emerging and Industrial DLP® Applications”, Frankfurt, Germany, Nov 12, 2009

SUSS MicroOptics – We Set The Standards

World leading supplier of Micro-Optics

8‟‟ Wafer Technology, Wafer-Level Packaging, SUSS Imprint Lithography

More than 200 active customers, e.g. to SEMI equipment manufacturers, Laser

& Optics industry, Sensors & Metrology and Medical

Part of the SUSS MicroTec Group (www.suss.com)

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Neuchâtel, Swiss Watch Valley

SMO is “Preferred Supplier” for Carl Zeiss SMT AG:

DUV Laser Beam Shaping Solutions (ASML Steppers)


SUSS MicroOptics

Unwrapped phase / lambda

Zeiss Diffusor 6101 HH, 10-02-05 RV

SUSS MicroOptics

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0.00 1260.77252.15 504.31 756.46 1008.62

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10.02.2005

14:49:32

Mean -0.10

RMS 0.34

P-V 2.94

Refractive Microlens Arrays (ROE) Binary Optics Diffractive Optical Elements (DOE)

Random Diffusers Microlens Imprint

Lithography

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MO Exposure Optics (Mask Aligner)Wafer-Level

Camera (WLC)


Micro-Optics Solutions

Semiconductor Technology

Industrial Optics & Vision

Healthcare & Life Science

Metrology

Laser & Material Processing

Information Technology

Research

Unwrapped phase / lambda

Zeiss Diffusor 6101 HH, 10-02-05 RV

SUSS MicroOptics

x / norm. radius

0.00 1260.77252.15 504.31 756.46 1008.62

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no

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12

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Mean -0.10

RMS 0.34

P-V 2.94


DLP®? What are we talking about?

The Holy Grail of MEMS Technology!

Larry J. Hornbeck:

„The Weirdest Technoloy Ever Invented“

A very sucessful device that

our customers want to illuminate!

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DLP® Standard Mirror Postitions

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Illumination: Optics Is Light Work!

7

Light Sources Devices, Systems

„Collect all photons and illuminate the DLP®!“

Performance (brightness, contrast, color,

uniformity, efficiency)

Size (large, smaller device)

Costs (manufacturing, energy saving, lifetime)


Illumination Today: More Power – Less Energy!

Uniformity

Efficiency

Costs

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Optics: Our Gurus

Thousands of books and patents on optical lens design

How many books are describing illumination systems?

Illumination is always the “little brother” of the glorious lens design –

nobody wants to play with – except if we really have to!

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The Köhler Illumination Concept

A success-story since 1893


1893: August Köhler invented Köhler Illumination

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Image: htt

p:/

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w.m

ikro

skopie

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oehle

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In 1893 August Köhler (1866–1948) from Carl Zeiss in

Jena, introduced a new and revolutionary method for

uniform illumination of specimen in an optical

microscope in his doctoral thesis.

The Köhler method allows to adjust the size

and the numerical aperture of the object

illumination in a microscope independent

from each other.

August Köhler, Zeitschrift für wissenschaftliche

Mikroskopie, Band X, Seite 433-440 (1893)


The Basic Principle of Köhler Illumination

A. The collector lens images the light source to the plane of the aperture diaphragm

B. The aperture diaphragm is located in the front focal plane of the condenser lens

C. The field diaphragm is imaged to the object plane by properly adjusting the distance

of the condenser lens to the object plane.

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Field

Diaphragm

Aperture

Diaphragm

Collector

LensCondensor

Lens

Light

Source

Object

Plane

A

BC


Light Sources

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Egyptian God Ra with Madame Taperet , 1000 BC (Louvre, Paris)

Thomsas A. Edison (Patent 1880)


Lighting Roadmap

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Types of LASERs

Semiconductor lasers (laser diodes), quantum cascade lasers, surface-

emitting semiconductor lasers (VCSELs, VECSELs)

Solid-state lasers based on ion-doped crystals or glasses, pumped

with discharge lamps or laser diodes (Nd:YAG, Nd:YVO4, Nd:YLF,

Nd:glass, Yb:YAG, Yb:glass, Ti:sapphire, Cr:YAG and Cr:LiSAF).

Fiber lasers, based on optical glass fibers which are doped with some

laser-active ions in the fiber core.

Gas lasers (e.g. helium–neon lasers, CO2 lasers, and argon ion lasers)

and excimer lasers (ArF, KrF, XeF, and F2).

Chemical and nuclear pumped lasers, free electron lasers, and X-ray

lasers.

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http://www.rp-photonics.com/lasers.html


Richard Ulbricht Invented The Ulbricht Sphere

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Dr. Richard Ulbricht (1849 – 1923, Dresden)

Invented the Ulbricht Sphere when he was trying to find the optimium

optics for electrical illumination of Dresden„s train stations (≈ 1891)


LED

Reflector

LED

Substrate

Beam Collimation Beam Shaping

Intensity

Homogenization

Plastic, Glass

Tasks for Micro-Optics


Conservation of Etendue – Lagrange Invariant

Etendue is a property of an optical system, which characterizes how

"spread out" the light is in area and angle.

Lagrange invariant is a measure of the light propagating through an

optical system. For a given optical system, the Lagrange invariant is a

constant throughout all space, that is, it is invariant upon refraction and

transfer.

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Speckles

When traveling through an optical system,

the different laser modes acquire different phase shifts

and a speckle pattern is observed in the flat-top.

The contrast of this speckle pattern depends on the

coherence length of the transmitted beam. It will vanish if

the optical path length difference between the fastest and slowest

modes exceeds the longitudinal coherence length of the laser beam.

Temporary integration: A dynamic change in the speckle pattern from

shot to shot results in an averaging out of the residual granularity

contrast according to

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N

1


The Köhler Integrator* – Multiple Köhler

Illumination Systems in Parallel

*Also known as Fly‟s Eye Condenser, Optical Integrator,

Microlens Beam Homogenizer, Wabenkondensor, …


Köhler Integrator – Fly’s Eye Condenser

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Example: Gaussian intensity distribution at lens array LA1

Light

Source

Principle Ray

Field Lens

Projection Lens(Multiple images of source)

Object

Plane

Lens Array MLA1

(Conjugated to object)

Lens Array MLA2

(Images of light source)

Condenser Lens

Ima

ge

Pla

ne

Sourc

e: N

aum

ann, S

chrö

der,

Bauele

mente

der

Optik, H

anser

Verlag

Multiple Köhler illumination in parallel to further improve illumination.

Splitting of the field diaphragm.


Köhler Integrator – Fly‘s Eye Illumination

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Köhler Integrator for Laser Beam Homogenizing

Redistributing the irradiance of arbitrarily input beams to a flat-top

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I(x)

x

I(x)

x

Raw Beam Flat Top (Square) Flat Top (Line)

Microlens Array

Beam Homogenizier


Recent Patents by Zeiss, ASML, Nikon & Canon

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Most Popular Illumination Systems for DLP®

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Standard Mirror Postitions

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Illumination Systems for DLP®

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Light Mixing in Rod or Tunnel

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Refractive Homogenizer for Gaussian Laser Beams

http://www.mt-berlin.com/frames_home/homefr_set_shapers.htm

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POWELL LENS


Köhler Integrator for Laser Beam

Homogenizing


Köhler Integrator – Beam Homogenizer

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2112

21121

1221

21

1

: LAandLAofseparationa

ffafwhere

affff

fPD

LALALA

LALA

LALA

LAFTFL

FLLA

LALA

FL

FTLAIN

ff

pf

f

Dpd

1

22

2

1tan

Flat-Top Size Flat-Top Divergence

imaging

Literature: Fred M. Dickey and Scott C. Holswade

Laser Beam Shaping: Theory and Techniques

Publisher: Marcel Dekker, (2000).


Köhler Integrator illuminated with a Gaussian Beam

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Example:

Gaussian intensity distribution at lens array LA1

Simulation of superposition in object plane for two identical microlens arrays consisting of NxN identical lenses.


Where is the Problem?

The concepts of Köhler illumination and Köhler integrators are well

understood and successfully implemented in many optical systems.

High-quality microlens arrays in Fused Silica are well suited for high-

power laser applications and available on large scale.

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Köhler Integrator as Array Generator

For illumination with a coherent and collimated

laser beam, the flat-top in the object plane is

modulated – or even subdivided into sharp peaks.

Each focal spot corresponds to the Fourier

transformation of the light source [Streibl*].

The microlens pitch pLA and the focal length of the

condenser lens ƒFL define the period ΛFP in the

object plane.

The period ΛFP is given by:

The number of spots N is equivalent to the Fresnel

number FN of the microlens array.

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LA

FLFP

p

f

LA

LA

FNf

pN LA 4

2

*Norbert Streibl, Review Paper “Beam shaping with optical array generators”

Journal of Modern Optics, Vol.36, No.12, 1559-1573 (1989)


Microlens Array Generator for Medical Applications

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Dermatology

Hair Removal

Tattoo Removal

Pigment Treatment

Skin Rejuvenation

Source: www.palomarmedical.com


Interference and Talbot Effect


Illumination of DLP® using Laser and Köhler Integrator

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Talbot Effect for Periodic Microlens Arrays

Diffraction simulation (Gaussian Beamlets)

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Fractional Talbot plane


Modulation in the Flat-Top

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?


Random Diffusers


Rotating Ground-Glass Diffuser

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Rotating diffuser

- Time averaging

- Extended light source


Rotating Diffuser for Köhler Integrator

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No diffuser Rotating diffuser

Experiment: Laser Diode, 670 nm, condenser lens ƒFL = 40 mm

Uniformity: > 10 % Uniformity: << 5 %


m

m

70

160

2

1

m

m

160

500

2

1

m

m

100

300

2

1

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Shaping of Random Diffusers

Ground Glass Diffuser

Shaped Random Diffuser (2D)


Conclusion

Is there a chance for perfect illumination of DLP® using lasers?

YES, but not for all lasers and all applications.

Speckles, interference effects, Talbot, ... will always be a problem

The best solution seems to be a combination of different optical and micro-

optical elements.

A Köhler Integrator, the flat-top is placed into the entrance pupil of

A light mixing rod or – better tunnel, plus

A random diffusing element to introduce angular spreading of the

coherent source beam greater than the angular separation of the

interference effects due to the imaging homogenizer array

Temporary integration, time averaging of speckles by rotating diffuser,

membranes or other devices.

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SUSS.

Our Solutions

Set Standards

SUSS MicroTec: www.suss.com

SUSS MicroOptics www.suss.ch

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Online Shop: www.suss.ch/shop

Illumination of DLP with Laser Light Sources. Völkel, “Illumination of DLP® with Laser Light...

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