Energy-Efficient Adaptive 3D Sensing

Author(s):

Tilmon, Brevin; Sun, Zhanghao; Koppal, Sanjeev; Wu, Yicheng; Evangelidis, Georgios; Zahreddine, Ramzi; Krishnan, Guru; Ma, Sizhuo & Wang, Jian

Abstract:

“Active depth sensing achieves robust depth estimation but is usually limited by the sensing range. Naively increasing the optical power can improve sensing range but induces eye-safety concerns for many applications, including autonomous robots and augmented reality. In this paper, we propose an adaptive active depth sensor that jointly optimizes range, power consumption, and eye-safety. The main observation is that we need not project light patterns to the entire scene but only to small regions of interest where depth is necessary for the application and passive stereo depth estimation fails. We theoretically compare this adaptive sensing scheme with other sensing strategies, such as full-frame projection, line scanning, and point scanning. We show that, to achieve the same maximum sensing distance, the proposed method consumes the least power while having the shortest (best) eye-safety distance. We implement this adaptive sensing scheme with two hardware prototypes, one with a phase-only spatial light modulator (SLM) and the other with a micro-electro-mechanical (MEMS) mirror and diffractive optical elements (DOE). Experimental results validate the advantage of our method and demonstrate its capability of acquiring higher quality geometry adaptively.”

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Publication: Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)
Issue/Year: 2023
Link: https://btilmon.github.io/e3d.html

One-Dimensional High-Resolution Wavefront Sensor Enabled by Subwavelength Compound Gratings

Author(s):

Meng, Yunlong; Shen, Xinyu; Xie, Junyang; Peng, Yao; Shao, Xiaowen; Yan, Feng & Yang, Cheng

Abstract:

“Angle sensors are widely used for wavefront measurements, which is attributed to their
integration and robustness. Currently, commercial sensors are available with pixel sizes in the order
of wavelengths. However, the spatial resolution of angle sensors still lags far behind. Here, we report
a one-dimensional, high-resolution wavefront sensor. It was produced by introducing subwavelength
compound gratings above the pixels. The gratings involved could be replaced by the sensor’s intrinsic
readout circuitry without additional operation. The experimental results showed that it had a spatial
resolution of 1.4 μm, two orders of magnitude higher than that of the Shack–Hartmann wavefront
sensor. The significant increase in spatial resolution enables angle sensors to reconstruct complex
wavefronts accurately.”

Link to Publications Page

Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 4; Pages 420; 2023
DOI: 10.3390/photonics10040420

Multi-Bessel Beams Generated by an Axicon and a Spatial Light Modulator for Drilling Applications

Author(s):

Lutz, Christian; Schwarz, Simon; Marx, Jan; Esen, Cemal & Hellmann, Ralf

Abstract:

“We report on an optical setup to generate multi-Bessel beam profiles combining a refractive axicon and a spatial light modulator. Based on their particular beam profile, Bessel beams offer advantageous properties for micro drilling processes and internal volume processing, especially for transparent materials. In addition, the laser power of industrial, ultrashort pulsed lasers has increased significantly over the last few years, offering the possibility for highly efficient processes
using multi-spot profiles. Our optical concept combines the dynamic possibilities of beam splitting using a spatial light modulator with the benefits of Bessel beams, which facilitates multi-Bessel beam processing. Beside the simulation and experimental evaluation of the generated multi-Bessel beams, we exemplify the applicability of the developed module for the perforation of thin metal foils by micro drilling.”

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Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 4; Pages 413; 2023
DOI: 10.3390/photonics10040413

Multi-Focal Laser Direct Writing through Spatial Light Modulation Guided by Scalable Vector Graphics

Author(s):

Duan, Linhan; Zhu, Yueqiang; Bai, Haoxin; Zhang, Chen; Wang, Kaige; Bai, Jintao & Zhao, Wei

Abstract:

“Multi-focal laser direct writing (LDW) based on phase-only spatial light modulation (SLM) can realize flexible and parallel nanofabrication with high-throughput potential. In this investigation, a novel approach of combining two-photon absorption, SLM, and vector path-guided by scalable vector graphics (SVGs), termed SVG-guided SLM LDW, was developed and preliminarily tested for fast, flexible, and parallel nanofabrication. Three laser focuses were independently controlled with different paths, which were optimized according to the SVG to improve fabrication and promote time efficiency. The minimum structure width could be as low as 81 nm. Accompanied by a translation stage, a carp structure of 18.10 μm × 24.56 μm was fabricated. This method shows the possibility of developing LDW techniques toward fully electrical systems, and provides a potential way to efficiently engrave complex structures on nanoscales.”

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Publication: Micromachines
Issue/Year: Micromachines, Volume 14; Number 4; Pages 824; 2023
DOI: 10.3390/mi14040824

Azimuthal backflow in light carrying orbital angular momentum

Author(s):

Ghosh, Bohnishikha; Daniel, Anat; Gorzkowski, Bernard & Lapkiewicz, Radek

Abstract:

“M.V. Berry’s work [J. Phys. A: Math. Theor. 43, 415302 (2010)] highlighted the correspondence
between backflow in quantum mechanics and superoscillations in waves. Superoscillations refer to
situations where the local oscillation of a superposition is faster than its fastest Fourier component.
This concept has been used to demonstrate backflow in transverse linear momentum for optical
waves. In this work, we examine the interference of classical light carrying only negative orbital
angular momentum and observe in the dark fringes of such an interference, positive local orbital
angular momentum. This finding may have implications for the studies of light-matter interaction
and represents a step towards observing quantum backflow in two dimensions.”

Link to Publications Page

Publication: arXiv
Issue/Year: arXiv, 2023
arXiv: 10.48550/arXiv.2304.13124

Extending the Imaging Depth of Field through Scattering Media by Wavefront Shaping of Non-Diffraction Beams

Author(s):

Han, Tongyu; Peng, Tong; Li, Runze; Wang, Kaige; Sun, Dan & Yao, Baoli

Abstract:

“Increasing the depth of field (DOF) is a crucial issue for imaging through scattering media. In this paper, an improved genetic algorithm is used to modulate the wavefront of light through scattering media, by which high-quality refocusing and imaging through scattering media are achieved. Then, the DOF of the imaging system is effectively extended by further modulating the refocused beam into a non-diffraction beam. Two kinds of non-diffraction beams, i.e., a Bessel beam and Airy beam, were produced as a demonstration. The experimental results show that compared to the Gaussian beam, the DOF of the imaging system by combining the wavefront shaping and non-diffraction Bessel beam or Airy beam can be improved by a factor of 1.1 or 1.5, respectively. The proposed method is helpful for the technical development of high-quality imaging through scattering media with a large DOF.”

Link to Publications Page

Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 5; Pages 497; 2023
DOI: 10.3390/photonics10050497

Multi-Plane Light Conversion: A Practical Tutorial

Author(s):

Zhang, Yuanhang & Fontaine, Nicolas K.

Abstract:

“Multi-plane light conversion (MPLC) has recently been developed as a versatile tool for manipulating spatial distributions of the optical field through repeated phase modulations. An MPLC Device consists of a series of phase masks separated by free-space propagation. It can convert one orthogonal set of beams into another orthogonal set through unitary transformation, which is useful for a number of applications. In telecommunication, for example, mode-division multiplexing (MDM) is a promising technology that will enable continued scaling of capacity by employing spatial modes of a single fiber. MPLC has shown great potential in MDM devices with ultra-wide bandwidth, low insertion loss (IL), low mode-dependent loss (MDL), and low crosstalk. The fundamentals of design, simulation, fabrication, and characterization of practical MPLC mode (de)multiplexers will be discussed in this tutorial.”

Link to Publications Page

Publication: arXiv
Issue/Year: arXiv, 2023
DOI: 10.48550/arXiv.2304.11323

Controllable nonlinear propagation of partially incoherent Airy beams

Author(s):

Chen, Kaijian; Zhang, Peiyu; Liu, Nana; Tan, Liu; Hong, Peilong; Zou, Bingsuo; Xu, Jingjun & Liang, Yi

Abstract:

“The self-accelerating beams such as the Airy beam show great potentials in many applications including optical manipulation, imaging and communication. However, their superior features during linear propagation could be easily corrupted by optical nonlinearity or spatial incoherence individually. Here we investigate how the interaction of spatial incoherence and nonlinear propagation affect the beam quality of Airy beam, and find that the two destroying factors can in fact balance each other. Our results show that the influence of coherence and nonlinearity on the propagation of PIABs can be formulated as two exponential functions that have factors of opposite signs. With appropriate spatial coherence length, the PIABs not only resist the corruption of beam profile caused by self-focusing nonlinearity, but also exhibits less anomalous diffraction caused by the self-defocusing nonlinearity. Our work provides deep insight into how to maintain the beam quality of self-accelerating Airy beams by exploiting the interaction between partially incoherence and optical nonlinearity. Our results may bring about new possibilities for optimizing partially incoherent structured field and developing related applications such as optical communication, incoherent imaging and optical manipulations.”

Link to Publications Page

Publication: arXiv
Issue/Year: arXiv, 2023
DOI: 10.48550/ARXIV.2304.02326

A Low-Complexity Joint Compensation Scheme of Carrier Recovery for Coherent Free-Space Optical Communication

Author(s):

Tang, Xinyu; Wang, Liqian; Zhang, Wei; Cai, Shanyong; Li, Yuemei & Zhang, Zhiguo

Abstract:

“In this paper, a low-complexity joint compensation scheme of carrier recovery (JCSCR) for coherent free-space optical (CFSO) communication is proposed. We applied the carrier recovery joint compensation approach to a CFSO communication system in the quadrature phase shift keying (QPSK) modulation format. A signal-preprocessing stage, which effectively avoided the repetitive operations found in traditional carrier recovery schemes, was proposed. Unlike in existing carrier recovery algorithms, the modulated phase of the received signal could be accurately removed using only the sum and subtraction of real absolute values in the signal-preprocessing stage, greatly reducing the complexity of the operation. Since this algorithm avoids the traditional fourth operation, the system’s complexity is reduced while additional noise generated by fourth cross-terms would be prevented and system noise immunity would be greatly enhanced. In addition, this algorithm uses joint compensation of phase errors in the final compensation stage, further reducing the complexity of the computation of the whole algorithmic scheme. A 10 Gbps QPSK CFSO communication transmission experiment was conducted in an atmospheric turbulence channel to verify the proposed technique and improvement in receiver sensitivity.”

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Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 4; Pages 389; 2023
DOI: 10.3390/photonics10040389

Efficient High-Refractive-Index Azobenzene Dendrimers Based on a Hierarchical Supramolecular Approach

Author(s):

Fusco, Sandra; Oscurato, Stefano Luigi; Salvatore, Marcella; Reda, Francesco; Moujdi, Sara; Oliveira, Michael De; Ambrosio, Antonio; Centore, Roberto & Borbone, Fabio

Abstract:

“Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the light-induced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)–carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers.”

Link to Publications Page

Publication: Chemistry of Materials
Issue/Year: Chemistry of Materials, 2023
DOI: 10.1021/acs.chemmater.3c00550
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