Microoptical artificial compound eyes [Elektronische Ressource] / von Jacques Duparre

Sujets

• Physik

Informations

• Publié par: friedrich-schiller-universitat_jena
• Publié le: 01 janvier 2005
• Nombre de lectures: 6
• Langue: English
• Poids de l'ouvrage: 11 Mo

Extrait

Microoptical Artiflcial Compound Eyes
Dissertation
zur Erlangung des akademischen Grades
doctor rerum naturalium (Dr. rer. nat.)
vorgelegt dem Rat der
Physikalisch-Astronomischen Fakult˜at
der Friedrich-Schiller-Universit˜at Jena
von
Diplomphysiker Jacques Duparr¶e
geboren am 23. M˜arz 1977 in ZwickauGutachter
1. Prof. Dr. rer. nat. habil. Andreas Tunnermann,˜ Friedrich-Schiller-Universit˜at Jena
2. Prof. Dr. rer. nat. habil. Stefan Sinzinger, Technische Universit˜at Ilmenau
3. Prof. Sadik Esener, Ph.D., University of California San Diego
Tag der letzten Rigorosumsprufung:˜ 07.06.05
Tag der ofien˜ tlichen Verteidigung: 23.06.05Contents
1 Introduction 1
2 Fundamentals 4
2.1 Natural Vision. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 Single Aperture Eye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Apposition Compound Eye . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.3 Superposition Compound Eye . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.4 Vision System of the Jumping Spider . . . . . . . . . . . . . . . . . . . . 11
2.2 State of the Art of Man-Made Vision Systems . . . . . . . . . . . . . . . . . . . 12
2.3 Scaling Laws of Imaging Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.1 Resolution and Space Bandwidth Product . . . . . . . . . . . . . . . . . 19
2.3.2 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4 3x3 Matrices for Paraxial Representation of MLAs . . . . . . . . . . . . . . . . . 25
3 Anamorphic Microlenses for Aberration Correction under Oblique Incidence 28
3.1 Gullstrand’s Equations of the Oblique Focal Length . . . . . . . . . . . . . . . . 29
3.2 Ellipsoidal Microlenses by Melting of Photo Resist . . . . . . . . . . . . . . . . . 31
3.3 Spot Size Determination Under Oblique Incidence . . . . . . . . . . . . . . . . . 32
4 Artiflcial Apposition Compound Eye Objective (APCO) 35
4.1 Principle { MLA with Assigned Array of Photo Receptors . . . . . . . . . . . . 35
4.2 Design and Simulation of APCO . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2.1 Angular Sensitivity Function . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2.2 Characteristic Parameters of the APCO . . . . . . . . . . . . . . . . . . 40
4.2.3 Interrelationship of Optical Properties under Scaling . . . . . . . . . . . 42
4.3 Fabrication of APCO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.3.1 Imaging System without Opaque Walls Between Adjacent Channels . . . 44
4.3.2 with Opaque Walls Between Channels . . . . . . . . . . 49
4.4 Experimental Characterization of APCO . . . . . . . . . . . . . . . . . . . . . . 50
4.4.1 Resolution and Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.4.2 Ghost and Flare Analysis { Test of the Opaque Walls . . . . . . . . . . . 55
IContents
4.4.3 Extension of the FOV by an Additional Diverging (Fresnel-) Lens . . . . 59
4.5 Summary and Outlook on APCO . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5 Cluster Eye (CLEY) 65
5.1 Principle { Array of Telescopes with Tilted Optical Axes . . . . . . . . . . . . . 65
5.2 Design and Simulation of CLEY . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.2.1 Paraxial Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.2.2 Sets of Equations Determining the Performance of the CLEY. . . . . . . 68
5.2.3 Determination of the Paraxial Geometrical Parameters . . . . . . . . . . 70
5.2.4 Paraxial System, Examples . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2.5 Considerations to Sensitivity and Equivalent F/# of the CLEY . . . . . 71
5.2.6 Transfer of Paraxial Lens Array Parameters to Chirped Real MLAs . . . 75
5.2.7 Simulation of Imaging Systems with Real Microlenses . . . . . . . . . . . 75
5.3 Fabrication of CLEY with 21x3 Channels . . . . . . . . . . . . . . . . . . . . . . 78
5.4 Experimental Characterization of CLEY . . . . . . . . . . . . . . . . . . . . . . 82
5.5 Summary and Conclusions on CLEY . . . . . . . . . . . . . . . . . . . . . . . . 85
6 Conclusions and Outlook 88
Bibliography 91
Appendix 101
A Anamorphic Microlenses by Re o w on an Ellipsoidal Base . . . . . . . . . . . . 101
B Further Simulation Methods of APCO . . . . . . . . . . . . . . . . . . . . . . . 107
C Elements of the CLEY Paraxial Transfer Matrix . . . . . . . . . . . . . . . . . . 111
D Further Conditions Determining the CLEY Performance . . . . . . . . . . . . . 111
E Paraxial Conditional Equations of CLEY . . . . . . . . . . . . . . . . . . . . . . 113
F Paraxial Optical Input and Geometrical Output Parameters of Analyzed CLEYs 115
G Concentrator- or Integrator Array . . . . . . . . . . . . . . . . . . . . . . . . . . 115
H Non-Sequential Raytracing Analysis of CLEY . . . . . . . . . . . . . . . . . . . 117
I Future Working Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Symbols and Abbreviations 125
Acknowledgements 131
Kurzfassung 133
Ehrenw˜ortliche Erkl˜arung 138
Lebenslauf 139
II1 Introduction
Naturalvision, inparticularnaturalcompoundeyes, havealwaysfascinatedmankind[1]. Com-
pound eyes combine small eye volumes with a large fleld of view, at the cost of comparatively
low spatial resolution. For small invertebrates as for instance ies or moths the compound eyes
are the perfectly adapted solution to obtain su–cient visual information about their environ-
ment without overloading their brain with the necessary image processing [2]. The compound
eye design is highly specialized for the natural living habitat, ambient illumination, required
sensing tasks and available processing time, eye size and energy for processing.
However, up to date little efiort has been made to technically adopt this principle in optics.
Classical imaging always had its archetype in natural single aperture eyes as, for example,
human vision is based on. But not always a high resolution image is required. Often the main
aim is on a very compact, robust and cheap vision system.
Miniaturized digital cameras and optical sensors are important features for next generation
customer products. Key speciflcations are resolution, sensitivity, power consumption, manu-
facturing and packaging costs and, maybe most important of all, overall thickness. Digital
microcameras which are based on miniaturized classical lens designs used today are rarely
3smaller than 5x5x5mm . The magniflcation is related to the system length. Recent improve-
ments of CMOS image sensors would allow further miniaturization. Nevertheless, as a result of
difiraction efiects, a simple miniaturization of known classical imaging optics would drastically
reduce the resolution [3] and potentially also the sensitivity. A simple scaling of the imaging
system to the desired size does not seem to be the clever way. How then to overcome these
limitations of optics? A fascinating approach is to look how nature has successfully solved
similar problems in the case of very small creatures [4].
During the last century, the optical performance of natural compound eyes was analyzed
exhaustively with respect to resolution and sensitivity [2]. Several technical realizations or
concepts of imaging optical sensors based on the principle of image transfer through separated
channels were presented in the last decade. A detailed list is provided in Chapter 2, Section
2.2. However, since the major challenge for a technical adoption of natural compound eyes
consists in the required fabrication and assembly accuracy, all those attempts have not lead
to a breakthrough because classical, macroscopic technologies were exploited to manufacture
microscopic structures. Sometimes only schematic macroscopic devices were fabricated. A
statement of one of the scientists working on artiflcial compound eyes in the nineties was: "...
Nature has to operate under certain material constraints for its optical designs, and artiflcial
compound eyes will be able to take advantage of a wider assortment of optical materials and
elements. ... On the other hand, it is unlikely that artiflcial compound eyes will be able to have
the huge numbers of ommatidia present in their biological counterparts, due to manufacturing
and connectivity limitations." [5]. For the early, rather macroscopic artiflcial compound eyes
[6{8], this may be true.
11 Introduction
It is the aim of this thesis to show that these limitations can be overcome by using state
of the art microoptics technology. This enables the generation of highly precise and uniform
microlens arrays and their accurate alignment to the subsequent optics-, spacing- and optoelec-
tronics structures. The result are thin, simple and monolithic imaging devices with the high
accuracy of microoptics photo lithography. Many imaging applications could beneflt from this
bioinspired microoptics, where classical objectives will never flnd their way in. Compound eye
cameras should for instance flt into tight spaces in automotive engineering, credit cards, stick-
ers, sheetsordisplays, securityandsurveillance, medicaltechnologyandshallnotberecognized
as cameras.
In contrast to other attempts, here the imaging optics itself is considered as the key com-
ponent to achieve this goal. (Opto-) Electronics and information processing will only take a
minor part of this work. The ma