Multi-aperture camera module with 720presolution

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1 Multi-aperture camera module with 720presolution using microoptics A. Brückner, A. Oberdörster, J. Dunkel, A. Reimann, F. Wippermann, A. Bräuer Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Jena, Germany

2 Agenda Motivation Features of electronic cluster eyes Novel microlens technology Prototyping results Summary

3 Motivation Applications of miniaturized imaging systems information tech. life science consumer electronics automotive requirements: small z-height low mass low cost medical imaging sensor systems machine vision security ~2 billion devices shipped in 2013* *Yole (2013) 3

Motivation Scaling limits of state-of-the-art

decrease sensor & pixel size semiconductor

9µm [1] ) compact devices, slim package low

signal-to-noise ratio min. pixel size 1.

: number of photons d: pixel size [1] R.

(IISW), 2011. image source: www.clarkvision.

4 Motivation Scaling limits of state-of-the-art imaging systems digital imaging + advances in decrease sensor & pixel size semiconductor manufacturing (currently 0.9µm [1] ) compact devices, slim package low cost sufficient image quality reduction of signal-to-noise ratio min. pixel size 1.3µm (SNR=32, indoor daytime, 30 fps [2] ) N p : number of photons d: pixel size [1] R. Fontaine, International Image Sensor Workshop (IISW), image source: March 2011 [2] M. Schöberl et. al. J. Electron. Imaging, 21 (2),

$f-number loss of resolution image point ~ sum of Gaussian moments [1] : diffraction aberrations$ f-number: minimum pixel size according to optical resolution limit no way to further shrink size of

f-number: minimum pixel size according to optical resolution limit no way to further shrink size of

5 Motivation Scaling limits of state-of-the-art imaging systems reduction of pixel size + constant f-number loss of resolution image point ~ sum of Gaussian moments [1] : diffraction aberrations f-number: minimum pixel size according to optical resolution limit no way to further shrink size of camera module [1] A. Lohmann, Appl. Opt. 28, (1989). [2] A. Brückner et. al., Proc. SPIE 8616, pp ,

6 Motivation Natural & artificial imaging principles state-of-the-art cameras miniaturization limited (noise, diffraction, technology) K K further miniaturization 6

7 Agenda Motivation Features of electronic cluster eyes Novel microlens technology Prototyping results Summary

Features of electronic cluster eyes (ecley) array of miniature cameras each transmits partial image of a different part of FOV image processing to reconstruct final image from image segments

8 Features of electronic cluster eyes (ecley) array of miniature cameras each transmits partial image of a different part of FOV image processing to reconstruct final image from image segments electronic image stitching 50% optics z-height easier fabrication & assembly (wafer-level optics tech.) [1] A. Brückner et.al., Opt. Express 18 (24), (2010). granted patents many others pending: 2009: US , JP , KR : US , US Schematic working principle [1] FOV : Field of view 8

focusing = correction for parallax software

multiaperture parallax -> disparity Object

field (proportional to depth of focus) 1.

9 Features of electronic cluster eyes (ecley) Demonstrator ecley VGA d = 10 mm d = 25 mm Size comparison: VGA webcam lens vs. ecley VGA demonstrator d = 50 mm d = 250 mm focusing = correction for parallax software focusing / refocusing measured depth map multiaperture parallax -> disparity Object distance: 4m, 70 diagonal FOV DoF : Depth of field (proportional to depth of focus) 1.4mm optics z-height large DoF (4mm - ) depth imaging A. Oberdörster et. al., "Digital focusing and re-focusing with thin multi-aperture cameras", in Proc. SPIE 8299, p (2012). 9

10 Novel microlens technology opt. design recent prototypes were based on reflow of photo resist limited fill-factor, f/# and resolution standard micro lens array chirped array of ellipsoidal lenses enhance resolution need more degrees of freedom increase optical fill-factor new microlens technology: freeform microlens segment array 10

11 Novel microlens technology mastering Ultra precision diamond machining + Step&Repeat imprinting milling & planing generation of masters for single microlens arrays Step&Repeat process generation of array-masters for many MLAs on common substrate 11

12 Novel microlens technology Fabrication process chain Data compilation & transfer Single master Imprint tool Array master Optics modul surface description alignment marks yard structures UP-machining Aluminium / NiP UV transparent polymer / epoxybased Step & Repeat multiple imprint replication Mask Aligner replication & stacking Charakterisierung tactile und interferometrical characterization pre-compensation J. Dunkel, et. al.,proc. SPIE 8763, p (2013). F. Wippermann, et. al., 18th Microoptics Conference (MOC 13), (2013). 12

$master wafer with refractive freeform lenslet arrays 001-002-MS-005_chan00 001-002-MS-005_chan01 001-002-MS-005_chan02 001-002-MS-005_chan03 001-002-MS-005_chan04 001-002-MS-005_chan10$

13 Formabweichung [nm] (rms) Fraunhofer IOF Novel microlens technology Step & Repeat replication process measured master properties surface roughness ~ 8nm (RMS) master wafer with refractive freeform lenslet arrays MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan MS-005_chan73 av. shape deviation ~ 52nm (RMS) MS-005_chan74 J. Dunkel, et. al.,proc. SPIE 8763, p (2013). F. Wippermann, et. al., 18th Microoptics Conference (MOC 13), (2013). 13

$wafer with refractive freeform lenslet arrays double-sided replicated$ multi-aperture objective J. Dunkel, et. al.,proc. SPIE 8763, p.

14 Novel microlens technology Step & Repeat replication process 8 master wafer with refractive freeform lenslet arrays double-sided replicated multi-aperture objective J. Dunkel, et. al.,proc. SPIE 8763, p (2013). F. Wippermann, et. al., 18th Microoptics Conference (MOC 13), (2013). 14

15 Prototyping results Demonstrator ecley 720p customized image sensor* multi-aperture lens module camera module layout camera assembly 1.9mm optics z-height * developed by partner Fraunhofer IIS, Erlangen, fabricated by TowerJazz 15

Prototyping results Demonstrator ecley 720p on-axis MTF measurement preliminary camera demonstrator cutoff frequency: 300 cycles/mm Parameter diag. FOV Fno. image res. in pixels Value 70 2.

16 Prototyping results Demonstrator ecley 720p on-axis MTF measurement preliminary camera demonstrator cutoff frequency: 300 cycles/mm Parameter diag. FOV Fno. image res. in pixels Value x 768 TTL no. of cells no. of pixels per cell FOV per cell pixel pitch sensor die size 1.9mm 15 x 9 96 x µm 6.4mm x 4.15mm fill fact or* 31% A. Brückner, et. al., "Ultra-thin wafer-level camera with 720p resolution using microoptics," Proc. SPIE 9193, (2014). 16

17 Prototyping results Characterization through focus MTF measurement scanning 100µm defocus with 5µm steps > 30% over 40µm defocus off-axis MTF measurement intermediate field at 18 AOI MTF is in good agreement with simulation AOI : Angle of incidence 17

18 Prototyping results Image reconstruction Real time image reconstruction: Image acquisition (raw data) Flat-Field Correction Distortion correction Raw image (channel-wise) Pixel redistribution (Braiding pattern & parallax correction) braiding coded into optical module by design algorithms of low complexity frame rate: 30 fps possible in mobile devices Reconstructed image A. Oberdörster, et. al., "Interactive alignment and image reconstruction for waferlevel multi-aperture camera systems," Proc. SPIE 9217, (2014). 18

Prototyping results Image reconstruction Raw image Reconstructed image ongoing work: optimization of image reconstruction (correction of sensor pixel characteristics) small batch series

19 Prototyping results Image reconstruction Raw image Reconstructed image ongoing work: optimization of image reconstruction (correction of sensor pixel characteristics) small batch series applying precompensation integration with lens housing A. Oberdörster, et. al., "Interactive alignment and image reconstruction for waferlevel multi-aperture camera systems," Proc. SPIE 9217, (2014). 19

20 Agenda Motivation Features of electronic cluster eyes Novel microlens technology Prototyping results Summary

21 Summary multi-aperture enables new freedom for miniaturized imaging systems design by fusion of micro-optics micro-electronics image processing extreme miniaturization segmentation of field-of-view reduction of costs parallelized fabrication and partly assembly on wafer level unique features for slimmer consumer products 21

22 Thank you. The presented work has been funded by: in a project of the Fraunhofer Future Foundation

Lecture Notes 10 Image Sensor Optics. Imaging optics. Pixel optics. Microlens

Lecture Notes 10 Image Sensor Optics Imaging optics Space-invariant model Space-varying model Pixel optics Transmission Vignetting Microlens EE 392B: Image Sensor Optics 10-1 Image Sensor Optics Microlens