Planar Waveguide Illuminator with Variable Directionality and - - PowerPoint PPT Presentation

SLIDE 1

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)

SLIDE 2

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

SLIDE 3

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

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

SLIDE 4

UCSD Photonics

Planar Micro-Optic Solar Concentrator Research

Worm drive motors

Output Uniformity

0.87 mm 0.36 mm 1.0 mm 1.0 mm BK7 Waveguide PMMA Polycarbon ate

• 30

° °

• 15

° 3 ° 1 5 ° 3 5 °

• 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

10 20 30 40 50 60 10 20 30 40 50 60 70 80 90 100

Normalized Optical Efficiency vs. Time

Time (minutes) Normalized Optical Efficiency

Trackin g “on” Trackin g “off” Cloud cover Concentrated & Uniform Output Coupling facets Lenlet Array Waveguide

Basic Concept: Low-cost planar concentrator optics

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

SLIDE 5

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
• utput 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.

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

SLIDE 6

Coupler Design

Approach

11/05/2013

Collimation h1, θ1 h2, θ2 Source

2 4 6 8 10 12 14 16 18 1 2 3 4 Conventional CPC Modified Bezier Curve

( ) ( ) ( ) [ ]

1 , , 1 2 1

2 2 1 2

∈ + − + − = t P t tP t P t t B

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

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

“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.

SLIDE 7

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

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

• ii. Curved Structure

Approaches square input aperture as aspect ratio increases. input

θ

• utput

t Router

        − =

−

• uter

R t 2 1 cos 1 θ

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

TIR limit planar guide

SLIDE 8

Analytic Model & Optimization

11/05/2013

( )

1 2

sin θ η =

beam

( ) ( ) ( )

β ϕ θ θ θ

π β 2 2 2 2 0 0 2

sin sin cos h n dS d d n G

S

= =

∫ ∫∫

( ) ( )

                        − =

− − 2 1 1 max

tan /# 2 1 tan sin sin θ ψ F n                         =

− −

f w n

facet

2 tan sin sin

1 1

ϕ

( ) ( )

2 2 1 1

sin sin θ θ h h = 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

( )

γ tan

wg facet

t w = θ

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

         + − − = =

−

θ θ θ θ ϕ θ sin cos 1 cos tan tan /# 2 cos

2 1

N N N F N

(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

2 facet facet

w A =

wg facet

t w 2 <

Geometry:

wg

t M h ⋅ =

2

(# of segments)

2 options: facets

• f

# = 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.

SLIDE 9

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

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

F/0.5

Desired: 1.5x104 lx Modeled: 1.3x104 lx

SLIDE 10

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 x x

dA x x Vis r x B dA x dA x E dA x B ' ' , cos cos '

2 '

π θ θ ρ X Y

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

SLIDE 11

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

• ut = 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

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

SLIDE 12

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.

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

SLIDE 13

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

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

9 feet Ceiling Prototype

SLIDE 14

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.

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Thank you

wmellett@ucsd.edu psilab.ucsd.edu