Planar Waveguide Illuminator with Variable Directionality ...psilab.ucsd.edu/publications/(presentation_2013)_Mellette_UCSD... · Planar Waveguide Illuminator with Variable Directionality

Planar Waveguide Illuminator with Variable Directionality and Divergence

Photonics Systems Integration Lab

William Maxwell Mellette, Glenn M. Schuster,

Ilya P. Agurok, Joseph E. Ford

Electrical & Computer Engineering Department

University of California, San Diego

11/05/13

Presented at 2013 OSA Optics & Photonics Conference: Renewable Energy and the Environment, Solid State & Organic Lighting (SOLED)

Motivation for New Illumination System

11/05/2013

Context: Conventional LED Illumination Systems • Directional, collimated “spot” illumination. • Diffuse “flood” illumination. • Cannot switch due to fixed optical path.

Walezak et al. US pat. 7,744,259

Maxik et al. US pat. D528,673 S

Bergmann et al. US pat. D587,832 S

Directional Illumination

Bolta et al. US pat. 7,234,844

Yuen US pat. D553,267 S

Diffuse Illumination

• Based on old technologies:

M. C. Meigs. US pat. 209,178 (1878)

Directional illumination = Localized source + reflector (lens)

C. H. Muckenhirn US pat. 1,288,124 (1918)

Diffuse illumination = Localized source + diffuser

Goal: System with variable directionality and divergence for efficient use of light energy

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Waveguide Based Illumination System

11/05/2013

1) LED Sources • High luminance, high efficacy.

2) Coupling

• Tradeoff between spatial power density and divergence.

3) Guiding and Extraction • Confinement by total internal

reflection. • Periodic extraction features

scatter light toward lens array.

LEDs

Couplers

Lens Array

Waveguide Extraction Features 4) Beam Steering & Divergence

• Lenses image extraction features to an infinite conjugate.

• Translations between lenslet and extraction arrays steer total beam by steering individual beams in the same direction.

• Rotations between arrays steer individual beams in different directions, altering divergence of the total beam.

Translated Rotated Aligned

Continuous control over directionality and divergence through small mechanical actuation


UCSD Photonics Planar Micro-Optic Solar Concentrator Research

Worm drive motors

Output Uniformity

0.87

mm

0.

36

mm

1.

0 m

m

1.0 mm

BK7 Waveguide

PMMA

Polycarbonate

-30°

0°

-15°

30°

15°

35°

-35° 70° field of view (2.5mm

path)

Wide Angle Doublet Microlens Design

Self-contained micro-tracking mechancial system prototype

Micro-Tracking Waveguide Concentrator

Higher-Efficiency Orthogonal Concentrators

“Lateral translation micro-tracking of planar micro-optic solar concentrator,” SPIE Conference on Solar Energy & Technology, Paper 7769-03 August 2010.

J. H. Karp et al, “Orthogonal and secondary concentration in planar micro-optic solar collectors,” Optics Express, May 2011.

Fresnel End Mirror & Angled Injection Facets

0 10 20 30 40 50 600

10

20

30

40

50

60

70

80

90

100Normalized Optical Efficiency vs. Time

Time (minutes)

Nor

mal

ized

Opt

ical

Eff

icie

ncy

Tracking

“on”

Tracking “off”

Cloud cover

Concentrated & Uniform

Output

Coupling facets

Lenlet Array

Waveguide

Basic Concept: Low-cost planar concentrator optics


Light Guiding & Extraction • Faceted extraction features: divergence

maintaining, broadband, axially symmetric. • Waveguide confines light by TIR. • Two configurations:

Want thin waveguide.

Design Considerations

LEDs • From conservation of radiance: brightness of

output determined by brightness of source.

Want large package high luminance LEDs.

11/05/2013

Cree Xlamp XM-L2 Active area: 2.5x2.5mm Emittance: 116.5 lm/mm2

Power: 6.2 W Efficacy: 159.13 lm/W

Input

Input

Output

2.5 mm

1) Constant Mode Volume 2) Stepped Mode Volume

Large Source Thin Waveguide

Coupler

Couplers • Efficient coupler must conserve radiance. • Impose above constraints, design becomes

etendue matching problem.

Needed: efficient coupling structure.

Lenses • Determine max. steering angle, crosstalk, and

min. divergence angle.

Want low F/#, low divergence source, small source.


Coupler Design

Approach

11/05/2013

Collimation

h1, θ1 h2, θ2

Source

0 2 4 6 8 10 12 14 16 180

1

2

3

4

Conventional CPCModified Bezier Curve

( ) ( ) ( ) [ ]1,0 , 121 22

102 ∈+−+−= tPttPtPttB

Parameterized by variable t. Points P0, P1, P2 ϵ R2.

CAD models Angular Output Spatial Output

CPC:

Bezier:

1) Collimation • Compound parabolic concentrators (CPCs)

provide nearly etendue limited concentration, and likewise, collimation.

• When used as a collimator, the conventional CPC has poor spatial uniformity at the output.

• Quadratic Bezier curve allows tradeoff between spatial uniformity and divergence.

Aperture Transformation

h2 x h2, θ2 Mh2 x twg, θ2


“Method to improve spatial uniformity with lightpipes”, Fournier, Cassarly, Rolland, Optics Letters, Vol. 33, No. 11, June 1, 2008.

• Optimized in Nonsequential Zemax. – Merit function:

• Minimize standard deviation (RMS from mean) of all nonzero intensity values.

• Minimize radial RMS from 0º (on axis) in polar space.

– Variables: • Control point (P1) and axial length.

Coupler Design

11/05/2013

2) Space Variant Aperture Transformation • Define structures which segment and rearrange a square aperture into a rectangular aperture. • Designed for perfectly collimated input, modeled in Zemax for varying degrees of divergence.

i. Faceted Structure


ii. Curved Structure

Approaches square input aperture as aspect ratio increases.

input

θ

output t

Router

−= −

outerRt

21cos 1θ

“Analysis of Curved Optical Waveguides by Conformal Transformation”, Heiblum, Harris, IEEE, Vol. QE-11, No. 2, Feb 1975

TIR limit planar guide

Analytic Model & Optimization

11/05/2013

( )12sin θη =beam

( ) ( ) ( )βϕθθθπ β

2222

0 0

2 sinsincos hndSddnGS

== ∫ ∫ ∫( ) ( )

−= −−

211

max tan/#2

1tansinsin θψF

n

= −−

fw

n facet

2tansinsin 11ϕ

( ) ( )2211 sinsin θθ hh = h1

h2

twg

f

φ

ψmax

θ1

θ2

D

1) Constant Mode Volume Waveguide

2) Stepped Mode Volume Waveguide

γ = 45º γ = 45º

D

D

wfacet wfacet

( )γtanwg

facet

tw =

θ

( ) ( )( )( ) ( )

( ) ( ) ( )

+−−

=

= −

θθθθ

ϕθ

sincos1costan

tan/#2cos2

1

NNN

FN

(Waveguide index) (Lens focal length)

(Facet width)

(Waveguide index) (Half divergence angle within waveguide)

(Lens F/# = f/D)

wfacet wfacet

Etendue:

Radiometry:

(Spatial extent) (Half div. angle)

Geometrical Optics:

2

2facet

facet

wA = wgfacet tw 2<

Geometry:

wgtMh ⋅=2

(# of segments) 2 options: facets of # =N

Motivation • Optimization difficult in standard raytracing software. • Create analytic optimization procedure. • Show that optimal designs have useful performance.

Analytic Approach • Use equations from imaging and nonimaging optics. • Find optimal designs in a constrained space. • Verify predicted performance using Zemax.

Optimized Design Performance

11/05/2013

N = 20 Aspect Ratio = 14:1

Input

Input Physical realization of optimal stepped mode volume design:

Optical Efficiency Zemax Model

Luminous Intensity (log scale)

Optical Efficiency Analytic Model Zemax Model Luminous intensity (linear scale)

No rotation Rotation

No translation Translation

Good agreement between models

• Cree Xlamp XML2 • Curved coupling structure • F/0.5 reflective spherical lenses • 40 x 40 lenses in full system.

2 feet 2 feet


F/0.5 Desired: 1.5x104 lx Modeled: 1.3x104 lx

Simulated System Application

11/05/2013

Conventional 2x2’ system (53W, 4000lm) UCSD SMV2a optimized design, 2x2’ aperture (54.82W, 5700lm)

*Nonlinear Scale

Rotation = 1º Translation: (Δx, Δy) = (-3, 3) mm

Far field intensity modeled in Zemax, exported as .ies file. Room illumination modeled in Dialux software using radiosity method.

• FEM approach to global illumination. Applies to Lambertian surfaces. Iterates through subsequent scattering steps until convergence.

Iterative solution to radiosity method.

Translation: (Δx, Δy) = (5, 0) mm

( ) ( ) ( ) ( ) ( )∫+=S

xx dAxxVisr

xBdAxdAxEdAxB '',coscos' 2'

πθθρ

X Y


Optimized System Components

11/05/2013

SMV2a Optimized Design Stepped mode volume waveguide

Flat faceted extraction features

Custom spherical reflective lenses

Curved coupling structure Cree Xlamp XML2

Prototype Components

Acrylic Sheet 0.1 x 24 x 24 inches. Machined with 1mm diameter hemispherical holes. Upper bound on absorption measured: α = 1 m-1

Refractive Fresnel lens array Two F/1.04 lenses oriented grooves out = F/0.7 lens in PMMA. Array is 4 x 4 lenses = 3 x 3 inches.

SunLED right angle SMD LED

Designed CPC, Sputtered Silver

Edge Coupler

PCB designed to provide adequate heat sinking using thin FR4 substrate and silver adhesive. LEDs registered with high precision using custom fixture during reflow soldering.

1mm dia. ball bearings

Detail


Zemax Model Analytic Model Measurement (a.u.) Far Field Pattern Cross Section, Luminous Intensity

Prototype Model and Measurement

11/05/2013

“Unit Cell System”: Lab measurement to determine performance. Far field intensity pattern:

Superposition of 3 patterns from 3 LEDs.

Measurement Model

Paraxial lens model for Zemax and analytic models

Fresnel Lens

• Good agreement between analytic model, Zemax model, and measurement.

• Non-ideal off-axis Fresnel lens performance eliminates crosstalk lobes.


Experimental System

11/05/2013

CAD Design • Magnetic eccentric cams as

actuation mechanism. • 28 x 28 lens array. • 304 LED sources coupled to 2

edges of waveguide.

2 x 2 foot aperture

System Fabrication and Test


9 fe

et

Ceiling

Prototype

Summary of Results

11/05/2013

• Design of new illumination system • Continuously variable directionality and divergence

allows efficient use of light energy. • Optimized designs can achieve performance

metrics matching those of conventional illumination systems, while simultaneously providing new functionality.

• Prototype demonstration • Measurements of unit cell prototype validate the

accuracy of Zemax and analytic models used in design process.

• Full 2’ x 2’ experimental system provides proof of principle in a large aperture system.


Thank you [email protected]

psilab.ucsd.edu

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Planar Waveguide Illuminator with Variable Directionality ...psilab.ucsd.edu/publications/(presentation_2013)_Mellette_UCSD... · Planar Waveguide Illuminator with Variable Directionality