Dr. Veljko Milanović Profile

Dr. Veljko Milanović

CEO

SPIE Involvement:

Conference Program Committee | Author | Instructor

Proceedings Article | 2 March 2022 Presentation + Paper

Optical MEMS enable next generation solutions for robot vision and human-robot interaction

Daniel Lovell, Veljko Milanovic, Abhishek Kasturi, Frank Hu, Karan Soni, Derek Ho, Bryan Atwood, Lj Ristic, Xiaomeng Liu, Sanjeev Koppal

Proceedings Volume 12013, 1201304 (2022) https://doi.org/10.1117/12.2613458

KEYWORDS: Microelectromechanical systems, Visualization, LIDAR, Mirrors, Cameras, Projection systems, Robotics, Imaging systems, Sensing systems

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Proceedings Article | 28 February 2020 Presentation + Paper

Comparison of MEMS mirror LiDAR architectures

Abhishek Kasturi, Veljko Milanović, Daniel Lovell, Frank Hu, Derek Ho, Yu Su, Lj. Ristic

Proceedings Volume 11293, 112930B (2020) https://doi.org/10.1117/12.2556248

KEYWORDS: Mirrors, Microelectromechanical systems, LIDAR, Receivers, Transmitters, Sensors, Eye, Safety, Laser range finders

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Proceedings Article | 4 March 2019 Presentation + Paper

MEMS mirror module for programmable light system

Abhishek Kasturi, Veljko Milanovic, Frank Hu, Hong Joo Kim, Derek Ho, Daniel Lovell

Proceedings Volume 10931, 109310L (2019) https://doi.org/10.1117/12.2511074

KEYWORDS: Solid state lighting, Mirrors, Microelectromechanical systems, Visualization, Laser applications, Projection systems, Coating, Light sources and illumination, Aluminum, Electronics

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Proceedings Article | 22 February 2018 Presentation + Paper

Iterative learning control algorithm for greatly increased bandwidth and linearity of MEMS mirrors in LiDAR and related imaging applications

Veljko Milanović, Abhishek Kasturi, Hong Joo Kim, Frank Hu

Proceedings Volume 10545, 1054513 (2018) https://doi.org/10.1117/12.2291428

KEYWORDS: Mirrors, Microelectromechanical systems, Raster graphics, LIDAR, Control systems, Light sources and illumination, Prototyping, Laser applications, Sensors, Headlamps

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Gimbal-less dual axis point-to-point (quasistatic) MEMS mirrors have very wide bandwidths for laser beam steering, however users are often limited to only a third of the bandwidth due to the high Q-factor and use of low-pass filters in open-loop operation to avoid overshoot and oscillation. Closed-loop driving enables the use of the full bandwidth with additional complexity in optics and electronics, which can be undesirable in some low SWaP-C systems. But for many applications which require scanning repetitive patterns, such as LiDAR and biomedical imaging, bandwidth utilization and linearity can be greatly increased without any real-time feedback control by training the device and finding an optimal driving waveform using an iterative learning algorithm.

The algorithm drives the device with a trial waveform, measures the scan on a Position Sensing Device (PSD), calculates the error between the desired waveform and the measured position, and adjusts the drive waveform for the next iteration based on an approximate linear device model. This is repeated until the error is reduced to below an acceptable specification. The waveform is then saved in the MEMS Controller and can be reliably used for extended periods of operation. Multiple such drive signals can be trained and stored on the controller to perform different types of scans.

Several MEMS mirrors, including single- and dual-axis designs, were studied and three are reported here. Overall, in all cases a high accuracy of optical scans is achieved, typically to within ±0.025° of nominal. Repeatability after training, then running in open loop is better than ±0.01° - however, this measurement was limited by the lower resolution of the position detecting sensor. Scan rates achieved vary based on mirror design, but in each case are greatly improved from those achievable with basic driving approaches. Each mirror demonstrated higher quality vector graphics content at faster refresh rates and stable linear rasters at rates below resonance where lines are scanned with uniform velocity. Additionally, each mirror could achieve stable fast rasters with the line-scanning axis rates just below resonance, giving sinusoidal scans with line rates of ~1.6f_res. Finally, each mirror was also demonstrated achieving rasters with rates above resonance, giving line rates of ~2.5f_res. In all of those cases the other axis could scan linear and sharp sawtooth or triangle waveforms. Based on the symmetry of the MEMS design, we demonstrated the same performance at ddegerent angles, e.g. rastering at a 45° angle.

Proceedings Article | 5 May 2017 Presentation + Paper

Closed-loop control of gimbal-less MEMS mirrors for increased bandwidth in LiDAR applications

Veljko Milanović, Abhishek Kasturi, James Yang, Frank Hu

Proceedings Volume 10191, 101910N (2017) https://doi.org/10.1117/12.2264069

KEYWORDS: Mirrors, Microelectromechanical systems, LIDAR, Control systems, Micromirrors, Beam controllers, Laser range finders, Beam steering, Distance measurement, Linear filtering, Sensors, Silicon, Photodiodes, Signal to noise ratio

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In 2016, we presented a low SWaP wirelessly controlled MEMS mirror-based LiDAR prototype which utilized an OEM laser rangefinder for distance measurement [1]. The MEMS mirror was run in open loop based on its exceptionally fast design and high repeatability performance. However, to further extend the bandwidth and incorporate necessary eyesafety features, we recently focused on providing mirror position feedback and running the system in closed loop control. Multiple configurations of optical position sensors, mounted on both the front- and the back-side of the MEMS mirror, have been developed and will be presented. In all cases, they include a light source (LED or laser) and a 2D photosensor. The most compact version is mounted on the backside of the MEMS mirror ceramic package and can “view” the mirror‟s backside through openings in the mirror‟s PCB and its ceramic carrier. This version increases the overall size of the MEMS mirror submodule from ~12mm x 12mm x 4mm to ~15mm x 15mm x 7mm. The sensors also include optical and electronic filtering to reduce effects of any interference from the application laser illumination. With relatively simple FPGA-based PID control running at the sample rate of 100 kHz, we could configure the overall response of the system to fully utilize the MEMS mirror‟s native bandwidth which extends well beyond its first resonance. When compared to the simple open loop method of suppressing overshoot and ringing which significantly limits bandwidth utilization, running the mirrors in closed loop control increased the bandwidth to nearly 3.7 times. A 2.0mm diameter integrated MEMS mirror with a resonant frequency of 1300 Hz was limited to 500Hz bandwidth in open loop driving but was increased to ~3kHz bandwidth with the closed loop controller. With that bandwidth it is capable of very sharply defined uniform-velocity scans (sawtooth or triangle waveforms) which are highly desired in scanned mirror LiDAR systems. A 2.4mm diameter mirror with +/-12° of scan angle achieves over 1.3kHz of flat response, allowing sharp triangle waveforms even at 300Hz (600 uniform velocity lines per second). The same methodology is demonstrated with larger, bonded mirrors. Here closed loop control is more challenging due to the additional resonance and a more complex system dynamic. Nevertheless, results are similar - a 5mm diameter mirror bandwidth was increased from ~150Hz to ~500Hz.

Proceedings Article | 20 February 2017 Presentation + Paper

A fast single-pixel laser imager for VR/AR headset tracking

Veljko Milanović, Abhishek Kasturi, James Yang, Frank Hu

Proceedings Volume 10116, 101160E (2017) https://doi.org/10.1117/12.2253425

KEYWORDS: Microelectromechanical systems, Laser applications, Imaging systems, Mirrors, Cameras, Sensors, Optical tracking, Photodiodes, Laser systems engineering, Image resolution

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In this work we demonstrate a highly flexible laser imaging system for 3D sensing applications such as in tracking of VR/AR headsets, hands and gestures. The system uses a MEMS mirror scan module to transmit low power laser pulses over programmable areas within a field of view and uses a single photodiode to measure the reflected light. User can arbitrarily select the number of pixels to scan over an area and can thus obtain images of target objects at arbitrarily fast rates. The work builds on the previously presented “MEMSEye” laser tracking technology which uses a fast steering MEMS scan module with a modulated laser, and a tuned photosensor to acquire and track a retroreflector-marked object. To track VR/AR headsets, hands and similar objects with multiple markers or no markers at all, a single-point tracking methodology is not sufficient. Cameras could be more appropriate in such multi-point imaging cases but suffer from low frame rates, dependence on ambient lighting, and relatively low resolution when without zooming and panning capability. A hybrid method can address the problem by providing a system with its own light source (laser beam), and with full programmability of the pixel locations and scans such that frame rates of >100 Hz are possible over specific areas of interest. With a modest 1 Mpixel rate of measurement, scanning a sub-region of the field of view with 64 x 64 pixels results in ~200Hz update. Multiple such modules can be used to scan and image or track objects with multiple markers and fully obtain their position and attitude in a room with sub-5ms updates. Furthermore the room itself could be imaged and measured with wall markers or in conjunction with a camera for a total 3D scanning solution. Proof of concept demonstrator is presented here with pixel rates of only 30k-50k per second due to limitations of the present prototype electronics, resulting in refresh rates that are significantly lower than possible with the MEMS mirror scan modules.

Proceedings Article | 20 February 2017 Presentation + Paper

Novel packaging approaches for increased robustness and overall performance of gimbal-less MEMS mirrors

Veljko Milanović, Abhishek Kasturi, James Yang, Yu Roger Su, Frank Hu

Proceedings Volume 10116, 1011607 (2017) https://doi.org/10.1117/12.2253338

KEYWORDS: Microelectromechanical systems, Mirrors, Packaging, Gases, Actuators, Argon, Tolerancing, Silicon, Aluminum, Continuous wave operation

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2D quasistatic (point-to-point) gimbal-less MEMS mirrors enable programmable, arbitrary control of laser beam position and velocity - up to their maximum limits. Hence, they provide the ability to track targets, point lasercom beams, and to scan uniform velocity lines over objects in laser imaging. They are becoming increasingly established in applications including 3D scanning, laser marking and 3D printing, biomedical imaging, communications, and LiDAR. With the increased utility in applications that demand larger mirror sizes and larger overall angle*diameter (θ*D) figures of merit, the technology is continuously pushed against its limit. As a result we have implemented mirrors with larger diameters including 5.0mm, 6.4mm, and 7.5mm, and have designed actuators with larger torque and angles to match the Θ*D demand. While the results have been very positive in certain application cases, a limitation for their more wide-spread use has been the relatively high susceptibility of large- θ*D mirrors to shock and vibrations. On the other hand, one of the challenges of MEMS mirrors of small diameters is their lower optical power tolerance simply due to their smaller area and heat removal ability. Although they can be operated at up to 2-3W of CW laser power, new developments in dynamic solid state lighting in e.g. headlights demand operation at up to 10W or beyond.

In this work we study and present several package-level approaches to increase mechanical damping, shock robustness, and laser power tolerance. Specifically, we study back-filling of MEMS packages with different gases as well as with different (increased) pressures to control damping and in turn increase robustness and useable bandwidth. Additionally, we study the effects of specialized mechanical structures which were designed and fabricated to modify packages to significantly reduce volumes of space around moving structures.

In their standard form and packaging the MEMS mirrors tested in this study typically measure quality factors of 75-100. Increases of pressure up to 50psi have shown relatively modest reductions of the overall quality factor to the 40-50 range. Backfilling of packages with heavier inert gasses such as Ar and SF₆ results in lowering of the quality factor down to 20-30 range. Mechanical modifications of the package with special structures and reduced air-gap to the window yielded the best results, reducing the quality factor to ~9-14. Combination of specialized packaging structures and gas backfill and pressure control could provide a very efficient heat transfer from the mirror and the desired near-critical damping, but has not been demonstrated yet. The increased performance does not change the compactness and low power consumption - the improved MEMS mirrors still consume <1mW. So far, designs with mirror sizes through 3.0mm diameter with increased damping have passed 500G shock tests.

In terms of improved heat removal we have found that the packaging improvement greatly increased optical power tolerance of MEMS mirrors from few Watts of CW laser power to <10 Watts. The exact numbers for the upper limit are not yet available - in samples where the heat removing structure was added and air was replaced with Helium, our setup with 3 combined lasers was not able to damage any samples.

Proceedings Article | 25 May 2016 Paper

Novel fluidic packaging of gimbal-less MEMS mirrors for increased optical resolution and overall performance

Veljko Milanovic, Abhishek Kasturi, James Yang

Proceedings Volume 9836, 98362Z (2016) https://doi.org/10.1117/12.2224377

KEYWORDS: Mirrors, Microelectromechanical systems, Actuators, Packaging, Dielectrics, Liquids, Silicon, Refraction, 3D metrology, Epoxies

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Proceedings Article | 13 May 2016 Paper

UAV-borne lidar with MEMS mirror-based scanning capability

Abhishek Kasturi, Veljko Milanovic, Bryan Atwood, James Yang

Proceedings Volume 9832, 98320M (2016) https://doi.org/10.1117/12.2224285

KEYWORDS: Microelectromechanical systems, Mirrors, LIDAR, Cameras, Unmanned aerial vehicles, Laser range finders, Ranging, Imaging systems, Receivers, Head

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Proceedings Article | 27 February 2015 Paper

High brightness MEMS mirror based head-up display (HUD) modules with wireless data streaming capability

Veljko Milanovic, Abhishek Kasturi, Volker Hachtel

Proceedings Volume 9375, 93750A (2015) https://doi.org/10.1117/12.2082848

KEYWORDS: Heads up displays, Mirrors, Microelectromechanical systems, Neodymium, Laser applications, Semiconductor lasers, Visualization, RGB color model, Raster graphics, Diffusers

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Proceedings Article | 27 February 2015 Paper

Compact MEMS mirror based Q-switch module for pulse-on-demand laser range finders

Veljko Milanović, Abhishek Kasturi, Bryan Atwood, Yu Su, Kevin Limkrailassiri, John Nettleton, Lew Goldberg, Brian Cole, Nathaniel Hough

Proceedings Volume 9375, 93750H (2015) https://doi.org/10.1117/12.2082212

KEYWORDS: Mirrors, Microelectromechanical systems, Q switching, Q switched lasers, Silicon, Coating, Actuators, Semiconductor lasers, Pulsed laser operation, Neodymium

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Proceedings Article | 1 April 2013 Paper

Commissioning an EUV mask microscope for lithography generations reaching 8 nm

Kenneth Goldberg, Iacopo Mochi, Markus Benk, Arnaud Allezy, Michael Dickinson, Carl Cork, Daniel Zehm, James Macdougall, Erik Anderson, Farhad Salmassi, Weilun Chao, Vamsi Vytla, Eric Gullikson, Jason DePonte, M. S. Gideon Jones, Douglas Van Camp, Jeffrey Gamsby, William Ghiorso, Hanjing Huang, William Cork, Elizabeth Martin, Eric Van Every, Eric Acome, Veljko Milanovic, Rene Delano, Patrick Naulleau, Senajith Rekawa

Proceedings Volume 8679, 867919 (2013) https://doi.org/10.1117/12.2011688

KEYWORDS: Photomasks, Mirrors, Microscopes, Extreme ultraviolet, Fiber optic illuminators, Lenses, Reflectivity, Charge-coupled devices, Coating, Extreme ultraviolet lithography

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Proceedings Article | 14 February 2011 Paper

MEMSEye for optical 3D position and orientation measurement

V. Milanović, N. Siu, A. Kasturi, M. Radojičić, Y. Su

Proceedings Volume 7930, 79300U (2011) https://doi.org/10.1117/12.879150

KEYWORDS: Mirrors, Microelectromechanical systems, 3D metrology, Sensors, Light emitting diodes, Light sources, Retroreflectors, Micromirrors, 3D acquisition, Beam splitters

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Proceedings Article | 30 August 1999 Paper

Standard postprocessing technique for fabrication of large microsuspended structures in CMOS

Bahram Ghodsian, Veljko Milanovic, Orlando Villavicencio

Proceedings Volume 3874, (1999) https://doi.org/10.1117/12.361212

KEYWORDS: Etching, Anisotropic etching, Oxides, Fabrication, Semiconducting wafers, Silicon, Photomasks, CMOS technology, Low pressure chemical vapor deposition, Micromachining

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Showing 5 of 14 publications

Conference Committee Involvement (13)

MOEMS and Miniaturized Systems XXIV

27 January 2025 | San Francisco, California, United States

MOEMS and Miniaturized Systems XXIII

29 January 2024 | San Francisco, California, United States

MOEMS and Miniaturized Systems XXII

30 January 2023 | San Francisco, California, United States

MOEMS and Miniaturized Systems XXI

24 January 2022 | San Francisco, California, United States

MOEMS and Miniaturized Systems XX

6 March 2021 | Online Only, California, United States

Showing 5 of 13 Conference Committees

Course Instructor

SC236: Polysilicon Surface Micromachine Technology and Devices

This course is designed to introduce newcomers to micromachining technology and concepts as well as those with a basic familiarity with integrated circuit manufacturing technology about the emerging field of Micro Electro Mechanical Systems (MEMS). Both manufacturing technologies for these devices and examples of sensor and actuator devices will be presented. The course focuses on polysilicon surface micromachining, but will also include a brief overview of other MEMS manufacturing technologies and devices.

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