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Deploying advanced imaging solutions to robotic and autonomous systems by mimicking human vision requires simultaneous acquisition of multiple fields of views, named the peripheral and fovea regions. Among 3D computer vision techniques, LiDAR is currently considered at the industrial level for robotic vision. Notwithstanding the efforts on LiDAR integration and optimization, commercially available devices have slow frame rate and low resolution, notably limited by the performance of mechanical or solid-state deflection systems. Metasurfaces are versatile optical components that can distribute the optical power in desired regions of space. Here, we report on an advanced LiDAR technology that leverages from ultrafast low FoV deflectors cascaded with large area metasurfaces to achieve large FoV (150°) and high framerate (kHz) which can provide simultaneous peripheral and central imaging zones. The use of our disruptive LiDAR technology with advanced learning algorithms offers perspectives to improve perception and decision-making process of ADAS and robotic systems.
Concept of a metasurface-augmented FoV LidAR a Schematic representation of the LIDAR system. A triggered laser source, emitting single pulses for ToF detection, is directed to a synchronized acousto-optic deflector (AOD) offering ultrafast light scanning with low FoV (~2°). The deflected beam is directed to a scanning lens to scan the laser spot on the metasurface at different radial and azimuthal positions. The transmitted light across the metasurface is deviated according to the position of the impinging beam on the component to cover a scanning range between −75∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-75^\circ$$\end{document} and 75∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$75^\circ$$\end{document}. The scattered light from the scene is collected using a fast detector. Data are processed to extract the single echo ToF for 2D and 3D imaging of the scene. b Detail of the cascaded AOD-metasurface assembled deflection system. c Top view photography of the optical setup. d Bottom: Graphical representation of the metasurface phase distribution along the radial axis. Top: Representations of beam deflection according to the incident beam positioning on the metasurface. Inset equation represents the phase function designed. e Illustration of axial symmetry for the laser impact point. f Photography of the 1 cm MS fabricated using nanoimprinting lithography. g SEM image of the sample showing the nanopillar building blocks of varying sizes employed to achieve beam deflection by considering lateral effective refractive index variations.
3D imaging and wide-angle scanning capabilities a LIDAR line scanning of our laboratory room that show the large FoV on both Elevation (top) and Azimuth (bottom) angles. Note the top picture showing a scanning line profile covering the whole range from the ground to the ceiling of the testing room over 150°. b 3D ranging demonstration (top): the scene (bottom) was set up with actors wearing reflective suits positioned in the scene at distance Z varying from 1.2 to 4.9 m. Colors encodes distance. c Lissajous scanning using deflecting functions as θ=Asinαt+Ψ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\theta=A{\sin }\left(\alpha t+\varPsi \right)$$\end{document} and =Bsinβt\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$=B{\sin }\left(\beta t\right)$$\end{document} for different parameters α\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} and β\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta$$\end{document} to illustrate the laser projection capabilities on a fast beam scanning, in a large FoV configuration. Ψ was set to be 0° and A = B = 30, although any configuration can be actively changed.
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Metasurface-enhanced light detection and
ranging technology
Renato Juliano Martins
, Emil Marinov
, Christina Kyrou
Mathilde Joubert
, Constance Colmagro
, Colette Turbil
Pierre-Marie Coulon
, Massimo Giudici
Charalambos Klitis
Deploying advanced imaging solutions to robotic and autonomous systems by
mimicking human vision requires simultaneous acquisition of multiple elds
of views, named the peripheral and fovea regions. Among 3D computer vision
techniques, LiDAR is currently considered at the industrial level for robotic
vision. Notwithstanding the efforts on LiDAR integration and optimization,
commercially available devices have slow frame rate and low resolution,
notably limited by the performance of mechanical or solid-state deection
systems. Metasurfaces are versatile optical components that can distribute the
optical power in desired regions of space. Here, we report on an advanced
LiDAR technology that leverages from ultrafast low FoV deectors cascaded
with large area metasurfaces to achieve large FoV (150°) and high framerate
(kHz) which can provide simultaneous peripheral and central imaging zones.
The use of our disruptive LiDAR technology with advanced learning algorithms
offers perspectives to improve perception and decision-making process of
ADAS and robotic systems.
Autonomous mobile systems such asautonomous carsand warehouse
robots include multiple sensors to acquire information of their sur-
rounding environments, dening their position, velocity, and accel-
eration in real time. Among them, range sensors, and in particular
optical ranging sensors, provide vision to robotic systems13and are
thus at the core of the automation of industrial processes, theso-called
4.0 industrial revolution. Several optical imaging techniques are cur-
rently integrated into industrial robots for 3D image acquisition,
including stereoscopic camera, RADAR, structured light illumination,
and laser range nders or LiDARs. LiDAR is a technological concept
introduced in the early 60s, when Massachusetts Institute of Tech-
nology (MIT) scientists reported on the detection of echo signals upon
sending optical radiation to the moon surface4. Since the pioneering
MIT work,LiDARs have been using laser sources to illuminate targeted
objects and to collect the returning echo signals offering the
possibility of reconstructing highly resolved three-dimensional (3D)
images. Conventional LiDARs rely on time-of-ight (ToF) measure-
ment, which employs a pulsed laser directed toward a distant reective
object tomeasure the round-trip time of light pulses propagating from
the laser to the scanned scene and back to a detection module. All
LiDAR components must act synchronously to tag single returning
pulses for ranging imaging reconstruction. The formula, 2d=cToF ,
holds for the recovered distance, where cis the speed of light and ToF
is the ToF. To sense the space, the LiDAR source must be able to sweep
a large Field of View (FoV). The objects in the scene are then detected,
point-by-point by measuring the ToF from every single direction to
build an optical echo map. The other measurement processes known
as Amplitude Modulation Continuous Wave (AMCW)5,6,Frequency
Modulation Continuous Wave (FMCW)7,8or Stepped Frequency Con-
tinuous Wave (SFCW)9employ continuous waves with constant or
Received: 7 April 2022
Accepted: 20 September 2022
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Université Cote dAzur, CNRS, CRHEA, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne, France.
NAPA-Technologies, 74160 Archamps, France.
Université Côte dAzur, Centre National de La Recherche Scientique, Institut de Physique de Nice, F-06560 Valbonne, France.
School of Engineering,
University of Glasgow, Glasgow G12 8LT, UK.
Institute of Technologies for Communication, Information and Perception (TeCIP), SantAnna School of
Advanced Studies, Via Moruzzi 1, 56127 Pisa, Italy. e-mail:
Nature Communications | (2022) 13:5724 1
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time-modulated frequency to measure the round-trip time of the
modulated light information. LiDAR systems enable the real-time 3D
mapping of objects located at long, medium or short-range distances
from the source, nding a vast variety of applications beyond robotic
vision, spanning from landscape mapping Chase1012,atmospheric
particle detection1316, wind speed measurements17,18, static and/or
moving object tracking1922,AR/VR
23, among others. Generally, LiDARs
are classied into scanning or non-scanning (Flash LiDAR) systems
depending on whether the laser sources simply illuminate24 or scan the
targeted scene. A scanning LiDAR system can be essentially described
in terms ofthree key components, (i) the light source for illumination,
(ii) the scanning module for fast beam direction at different points in
the scene, and (iii) the detection system for high-speed recovering of
the optical information received from the scene. Over the past dec-
ades, nanophotonics-based LiDAR systems have blossomed, and more
advanced scanning and detection techniques have been proposed25,26.
The expected massive use of LiDARs in the automotive industry for
advanced driver-assistance systems (ADAS) or even full-autonomous
driving brought out new challenges for the scanning systems, includ-
ing low fabrication complexity, potential for scalable manufacturing,
cost, lightweight, tolerance to vibrations and so on. Today, industrially
relevant LiDARs mainly use macro-mechanical systems to scan the
entire 360° FoV. Besides their large FoV, these bulk systems present
limited imaging rates of the order of few tens of Hz. A promising
evolution in mechanical scanners are the micro-electromechanical
systems27 (MEMS) which shift the scanning frequency to the kHz range.
However, a major drawback of MEMS is the low FoV, typically not
exceeding 25° for horizontal and 15° for vertical scanning. At the
research level, beam steering with optical phased arrays (OPA)28,29
provides remarkable speeds while reaching FoV around 60°. However,
OPA technology is less likely to be massively deployed in industrial
systems due to its manufacturing challenges. The industrially mature
liquid crystal modulators are also not adequate as LiDAR scanners due
to their poor FoVs usually remaining below 20° depending on the
wavelength, as well as their kHz modulation frequency30,31.Moreover,
acousto-optic deectors (AODs) enabling ultrafast MHz scanning32,33,
have never been considered in LiDARs because of their narrow FoV
reaching at maximum 2°, imposing a compromise between high-speed
imaging and large FoV.
During the last decade, metasurfaces (MS)34 have spurred the
interest of the entire international photonic community by unveiling
the possibility of engineering the properties (i.e., the amplitude, the
phase, the frequency and/or the polarization) oflight at will35.Theyare
at optical components made of arrangements of scattering objects
(meta-atoms) of subwavelength size and periodicity. Currently, four
light modulation mechanisms are used to create metasurfaces: light
scattering from resonant nanoparticles36,37,geometric phase occurring
during polarization conversion (PancharatnamBerry phase)38,accu-
mulated propagation phase in pillars with controllable effective
Refractive Index (ERI)39 and the topological phase in vicinity of
singularities40. Usually, MSs comprise inherently passive components,
designed to perform a xed optical functionality after fabrication.
For instance, by properly selecting the size and the spacing of the
meta-atoms, MSs allow to redirect a laser beam at any arbitrary but
xed angle dictated by the generalized Snells law. Clearly, passive
MS alone cannot be used in LiDARs requiring real-time beam scan-
ning. On the contrary, dynamic MSs designed byor combined with
materials possessing tunable optical properties caused by external
stimuli4145 stand as promising alternatives for real-time deection.
Recently, the US startup company LUMOTIVE introduced electrically
addressable reective resonant MSs inltrated with liquid crystals
and demonstrated scanning frequency that exceeds the switching
speed of common liquid crystal displays, as well as a FoV of around
120°46. The latter approach has been proven auspicious for minia-
turized, scalable LiDARs but it involves complex electronic
architectures, and likely signicant optical losses in case of metallic
MS building blocks.
Here, we propose an alternative high-frequency beam scanning
approach that exploits the light deecting capabilities of passive MSs
to expand the LiDAR FoV to 150× 150°, and to achieve simultaneous
low- and high-resolution multizone imaging. We make use of an ERI
multibeam deecting MS cascaded with a commercial AOD. The sys-
tem offers large exibilities in terms of beam scanning performance,
operation wavelength and materials. The angular resolution, referring
to the ability of the system to distinguish adjacent targets and retrieve
shapes, becomes very important in applications requiring simulta-
neous long and short-range detections. Our multizone LiDAR imaging
demonstration can mimic human vision by achieving simultaneous
high frame rate acquisition of high- and low-eld zones with different
spatial resolution. The large design exibility of MSs provides imaging
capabilities of interest to LiDAR systems, meanwhile offering new
industrial applications.
Ultrafast and high-FoV metasurface scanning module
MHz beam scanning can be achieved over a large FoV, by coupling
AODs with ERI MSs exhibiting spatially varying deection angles.
Figure 1a illustrates the experimental concept where a modulated
laser source at λ= 633 nm (TOPTICA i-beam smart) generates single
pulses at any arbitrary rate up to 250 MHz. For single-pulse LIDAR,
the repetition rate frep is related to the maximum ranging distance
dmax by the expression:
dmax =1
The focused beam with a small deection is angularly increased
to scan in both azimuthal θand elevation φangles. A detailed scheme
of the FoV amplifying system is shown in Fig. 1b. A photograph of the
built proof-of-concept system is shown in Fig. 1c where we high-
lighted (shaded red region) the expansion of the small two degrees
(2°) AOD FoV into an enhanced 150° FoV. The deected angle by the
MS is controlled by the impact position of the impinging focused
beam on the MS plane, associated with the radial and angular coor-
dinates rand θMS, respectively (see Fig. 1e). By applying voltage into
the AOD, one can actively re-point the beam at any arbitrary angle
within the × FoV, thus sweeping the focused beam across the
metasurface to vary θMS and r, in the range of [0 2π]and[0rmax ],
respectively, where rmax is the radius of the metasurface. Note that
θMS and rdenote, in polar coordinate, the position of the impact
beam on the metasurface according to Fig. 1e. For simplicity in
connecting incident and deected angles, we designed a circular
metasurface with radially symmetric phase-delaying response, but
given the versatility in controlling the optical wavefront, various MS
with any other beam defecting properties can be adjusted according
to specic application. We must also highlight that, in principle,
there is no limitation on the observed FoV as it is fully dependent on
the metasurface phase function, within the limit ½0, πfor transmis-
sion scheme. In this initial demonstration, we implemented (Fig. 1f, g)
the simple concept of ERI MS designed to spatially impart linearly
increasing momentum with respect to the radial dimension rgiven
by the expression:
where, k0is the free space momentum, and Φthe local-phase
retardation. Such design results in parabolic-phase retardation as
represented in Fig. 1d. In this design, the deected beam will be
delayed by a maximum phase retardation of Φ=πrmax
λand Φ=0 for
Nature Communications | (2022) 13:5724 2
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the peripherical points ± rmax and central points, respectively. More-
over, Eq. (2) transformed in Cartesian coordinates determines the
value of the deected angles in both axes, denoted as ðθ,φÞ,according
to the generalized Snell laws41:
where the phase gradient is dened at the metasurface plane at z=0.
Considering small incident angles originating from the AOD, the
expressions simplify as:
rmax cosθMS
rmax sinθMS
Such expression validates the linearity observed for small angles
[40°, 40°] according to the experimental measurements of the vol-
tage dependence of the deection angles (Supplemental Fig. S2c).
2D and 3D LiDAR image acquisition
To show the angular and depth 2D imaging capabilities of our LIDAR
system, we start performing 1D scanning of three distinct objects
placed on a table, (1) a square reector mounted on a post, (2) a round
deector and (3) a box reector, angularly distributed at different
locations as shown in Fig. 2a. The associated 2D LIDAR ranging image is
displayed in Fig. 2b, indicating that high reectivity objects are
observed at LIDAR positions matching to those observed with a con-
ventional camera (Fig. 2a). Particularly, we found that the three objects
shown in Fig. 2c were located at the following width [x], and depth [z]
positions: [0.4m,1.5m],[0.1m, 2.4 m] and [0.6 m, 3.5 m] for the
square, the round, and the box reector, respectively. In the graph, we
also observe the difference in reectivity of the three objects at various
distances leading to distinct intensities: the objects on the left and
right (square and box deectors) correspond to lower signals due to
their angular locations, size and distance, while the round deector in
the middle has higher reectivity and appears with higher reectance.
This rst example validates the short-range (~5 m) imaging capabilities
of our LiDAR system.
To further investigate the capabilities of the system, we exten-
ded the performance to achieve 3D imaging. To this end, an addi-
tional FoV dimension is added by cascading a second AOD,
orthogonally oriented, in the elevation axis. The extended FoV is now
improved over both dimensions considering a MS with radial sym-
metry, as schematized in Fig. 1b. To demonstrate the two-axis scan-
ning capability, we present in Fig. 3a the elevation (top) and the
azimuthal (bottom) line scanning, respectively, to highlight that 150°
FoV (Supplementary Materials S1) is accessible for both scanning axis
(see video V1 in supplement materials). These examples of line
scanning are realized by xing the voltage value on the one deector
and scanning the voltage of the second deector over the entire
range at a scanning rate that exceeds the acquisition speed of either
our eye or the CCD refreshing frame rate, resulting in an apparent
continuous line scan. We prepared a scene (Fig. 3b)bottom) with
three different actors located at different angular and depth posi-
tions of 1.2, 2.7, and 4.9 m to demonstrate 3D imaging. Due to low
laser pulse peak power (about 10 mW), we performed our demon-
strations in an indoor environment using high reective suits, con-
siderations of power and losses are addressed in Section S2 of
Supplemental Materials. For the demonstration, we choose a visible
laser operating at λ= 633 nm, which is very convenient to observe
and monitor the deected beam. After calibrating the system (see
Fig. 1 | Concept of a metasurface-augmented FoV LidAR. a Schematic repre-
sentation of the LIDAR system. A triggered laser source, emitting single pulses for
ToF detection, is directed to a synchronized acousto-opticdeector (AOD)offering
ultrafast light scanning with low FoV (~2°). The deectedbeamisdirectedtoa
scanning lens to scan the laser spot on the metasurface at different radial and
azimuthal positions. The transmitted light across the metasurface is deviated
according to the position of the impinging beam on the component to cover a
scanning range between 75and 75. The scattered light from the scene is col-
lected using a fast detector. Data are processed to extract the single echo ToF for
2D and 3D imaging of the scene. bDetail of the cascaded AOD-metasurface
assembled deection system. cTop view photography of the optical setup.
dBottom: Graphical representation of the metasurface phase distribution along
the radial axis. Top: Representations of beam deection according to the incident
beam positioningon the metasurface. Inset equation represents thephase function
designed. eIllustration of axial symmetry for the laser impact point. fPhotography
of the 1 cm MS fabricated using nanoimprinting lithography. gSEM image of the
sample showing the nanopillar building blocks of varying sizes employed to
achievebeam deection by considering lateral effective refractiveindex variations.
Nature Communications | (2022) 13:5724 3
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Supplementary Material), arbitraryor random accessbeam scan-
ning along high FoV can be realized and arbitrary intensity patterns
can be projected by rapidly steering the beam at different locations
at very short time intervals (see Supplementary Video V2). Figure 3c
shows examples of several scanning proles implemented to the
metasurface beam scanner to project Lissajous curves demonstrat-
ing random-point access mode.
Mimicking human peripheral and fovea vision with multizone
LiDAR imaging
Previous experiments were performed by focusing the light deected
by the AOD onrelatively small metasurfaces (1, 2, and 3 mm diameters)
using a scanning lens. This conguration favors a small spot (of the
order of 50 μm) to contain the MS angular divergence to a small
parametric region, i.e., scanning the MS with smallspot prevents large
Fig. 2 | 1D time-of-ight imaging. a Photography of the scene. bRanging image of
three objects displaced on a table using high reective tapes to improve the
intensity of the returned signal. In (1) a post with a small reector was used in (2) a
round object with a reector and in (3)there is a box reector witha tape around it.
The graph shows the image in the correct ranging distance X(scanning dimension)
and Z(ranging dimension) showing the capabilitiesto sense all of the three objects.
cPositionof single objects according to ranging image in (b). dRawsignal collected
for the respective image, showing that objects oriented in the normal direction
have bigger scattering intensity, the inset display single pulses used to determine
the ToF ranging distance.
Fig. 3 | 3D imaging and wide-angle scanning capabilities. a LIDAR line scanning
of our laboratory room that show the large FoV on both Elevation (top) and Azi-
muth (bottom) angles. Note the top picture showing a scanning line prole cov-
ering thewhole range from theground to the ceiling of the testing room over 150°.
b3D ranging demonstration (top): the scene (bottom) was set up with actors
wearing reective suits positioned in the scene at distance Zvarying from 1.2 to
4.9 m. Colors encodes distance. cLissajous scanning using deecting functions as
θ=Asin αt+ΨðÞand = Bsin βtðÞfor different parameters αand βto illustrate the
laser projectioncapabilitieson a fast beam scanning, in a large FoV conguration. Ψ
was set to be and A=B= 30, although any conguration can be activelychanged.
Nature Communications | (2022) 13:5724 4
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overlap with thespatially varying deecting area. The beam divergence
as a function of the metasurface size is provided in Supplementary
Material S5, indicating that a 3 mm device results in a divergence lower
than 1.5°. Robotic systems interested in reproducing human vision
requires peripheral and central vision as illustrated in Fig. 4a, where
several zones featuring different spatial resolutions are acquired
simultaneously. A low-resolution peripheral eld provides coarse
scene exploration, usually needed for human to direct the eye to focus
to a highly resolved fovea region for sharp imaging. The scene thus
needs to be scanned differently according to the zones of interest. To
reduce further beam divergence and improve as needed the resolu-
tion, it is necessary to increase the diameter and complexity of the
metasurface and work with fully collimated beams. For this purpose,
we realized a cm-size metasurface deector using nanoimprint litho-
graphy(NIL), as shown in Fig. 1f, g (further details on the fabrication are
provided in S9). In the latter conguration, the deector is directly
placed after the AOD without utilizing a scanning lens. We specically
designed a large area deector that achieve moderate 1st order
deection efciency of ~40% and took advantage of the non-deected
zero-order narrow scanning FoV to simultaneously scan two zones
with different FoVs and resolutions. This demonstration specically
exploits the multibeam addressing capability of metasurfaces, result-
ing in a dual mode imaging: (i) a high-resolution scanning provided by
the near collimated zero-order beam deected by the AOD only, and
(ii) a large FoV, lower resolution image provided by the 1st order beam
deected by the metasurface. As illustrated in Fig. 4b, inset, we spa-
tially selected the returned/scattered signal from the different parts of
the scene. For this purpose, we used a double-detector monitoring
scheme. The rst detector collects light from the full numerical aper-
ture (~2πsolid angle) but it blocks the central small numerical aperture
(a beam blocker is placed in front of the detector). The second
detector covers only a small NA for the narrow FoV resulting from
zero-order light scanning (a spatial lter is used to select the obser-
vation area). A dual-beam metasurface scanning scheme is used to
imageascene(Fig.4b, top) with two elds of interest: (i) three actors
placed at different regions of the space periphery, as measured in
Fig. 4c (top) and a highly resolved chessboard-like object placed in the
forward direction at a small FoV, measured in Fig. 4c (bottom). The
images presented in Fig. 4c correspond to low- and highly resolved
imaging, acquired by both detectors simultaneously. Multizones
scanning with a high resolution forward, and low lateral resolution
over a high-FoV peripherical vision could be a disruptive solution for
addressing the needs of advanced driver-assistance systems (ADAS).
High-speed velocimetry and time-series imaging
To characterize the MHz deection speed and the possibility of
achieving real-time frame rate imaging, we measured the beam
deection speed, i.e., the minimum frequency at which the beam can
be re-pointed to a new direction. To do so, we placed highly reecting
tapes on the wall, and measured the amplitude of the backscattered
signal for distinct scanning frequencies. We dene as system cutoff
frequencythe condition when the amplitude of the reected signal
decays to 3dB point (see Supplementary Information S4). The mea-
surements were made by considering: (i) a single scanner in the
Fig. 4 | Multizone imaging. a Schematic representation of a human multizone
viewing with the concept to be adapted in ADAS systems. Such mimicking char-
acteristics enables double vision for dual-purpose imaging features for high-reso-
lution, long range, in the center and lower resolution, bigger FoV, for the
peripherical view. bExperimental realization to test the dual-zone imaging func-
tionality of the LIDAR system, including dual detection scheme (inset) for simul-
taneousimage multiplexed collection. The central0th diffractionorder beam scans
a small area with high resolution directed at the center of the image while the 1st
diffracted order scans the whole eld. cTop: We show the result of the scanned
scenes described in (b). Top represents the LIDAR large FoV ranging image. The
image is obtained by blocking the central part of the numerical aperture using an
obstacle as sketched in (b). The bottom LIDAR ranging high-resolution image
presentsthe central part scene captured using the0th diffractionbeam, covering a
FoV of about 2°.
Nature Communications | (2022) 13:5724 5
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azimuth angle (see Supplementary Fig. S5b red curve) and (ii) a cas-
caded system comprised by two orthogonally oriented deectors, for
scanning at both azimuthal and elevation angles, (see Supplementary
Fig. S5b) blue curve). The results indicate less than 3dB loss up to
around 6 MHz and 10 MHz for single and double-axis scanning,
respectively. We also demonstrate the modulation of a laser beam over
an large FoV (>140°) at MHz speed and correct imaging with scanning
frequency up to 6.25 MHz (see Supplemental Fig. S5c)). This corre-
sponds to about two orders of magnitude faster than any other beam-
pointing technology reported so far. Operating beyond the 3dBloss
at higher frequency was also realized, leading to reduced resolution
but increased imaging frame rate, up to 1 MHz for 1D scanning at
40 MHz (see discussion in Supplementary Materials in Section S7).
Measurements of time events were performed to investigate
dynamic imaging. The most convenient dynamic system observable in
our laboratory was a spinning chopper composed of a rotating wheel
at nominally 100 Hz rotation speed. We prepared the scene composed
of a chopper, located at 70 cm away from the source, decorated with a
high reective tape in one of the mechanical shutters, as illustrated in
Fig. 5a (top). As described in Supplemental Table 1, we performed
three time-series experiments using acquisition frame rates of 741,
1020, and 3401 fps (see Supplementary Information S8 and Supple-
mentary Videos SGIF 13).Wetrackedthecenterpositionofthe
reective tape in both the space and time domains by integrating the
radial axis of the ranging image from the center of the chopper and
tting a Gaussian curve plotted over the entire ½0,2πangular axis (see
Fig. 5a, bottom). The curves are manually offset by 6πto differentiate
the experiments. All experiments revealed an averaged rotation speed
measured and nominal speed of 100 Hz to the phase-jitter control
mechanism on the chopper. In principle, rotating mechanical shutters
are designed with a closed loop circuitry providing an electronic signal
that maintains linear rotation speed. Interestingly, displaying time
events on the angular dimension reveals small wobbling wheel
imperfection caused by the presence of the reective tape, resulting in
a slowdown at the angles around 3π=2asevidencedinFig.5b
(Experiment 21020 fps). One can indeed observe a rotation slope-
change during periodic times corresponding to the position of the
reective tape at the bottom (for instance at t= 1.0 ms/10.8 ms in
Fig. 5b) (bottom panel)). Using the recovered ranging information, we
estimate the size of the tape to 4 cm, as illustrated in Fig. 5c (bottom).
The 1 cm difference to the real object (Fig. 5c, top) is due to the high
reectivity of the screws located close to the center and causing
additional scattering at the same ranging distance.
We realize an ultrafast beam scanning system composed of a fast
deector and a passive metasurface to achieve beam steering at MHz
speed over 150 × 150°FoV, improving the wide-angle scanning rate of
mechanical devices by ve orders of magnitude. We performed fast
steering in one and two angular dimensions and retrieved the asso-
ciated time of ight for ranging measurements leading to high-speed
LiDAR imaging of very fast-moving objects on a large FoV. Employing
parameters described on the second row of Supplementary Table 1, we
achieved a time step of 980 µs, see Fig. 5b. An object traveling at the
speed of the sound (1234 Km/h) at 15m away from the source will take
~74 ms to cover a 120°FoV. Such supersonic object can be detected
within 76 time-series events. Considering the Nyquist limit i.e., four
time series to recover the speed, the maximum event detection can
increase up to a speed of 47 mega-meter/h.
High-speed scanning modules for LiDAR applications have to
trade-off between the maximum distance and spatial resolution (see
Supplementary Information S5, S10). The frame rate of a single ToF
system can be expressed as:
fRate =c
where cis the speed of the light. Equation (5) thus indicates that both
the number of pixels in the image (n) and the maximum ambiguity
distance, ðdmaxÞ,denes theimaging frame rate. Suchechoing time can
be reduced by encoding the signal sent in each scanning direction with
aspecicidentication code namely Code-division multiple access
(CDMA)47. Multiplexed observation is realized by decorrelating the
ToF signal using matched lter technique. LiDAR companies often
multiplex the source with an array of diode lasers to increase frame
rate, increasing the lidar complexity, and multiplying the system cost
by the number of sources. Such CDMA technique realistically could be
exploited in combination with our fast beam deection system to
reach imaging frame rate of 125 frames/s with high spatial resolution of
200 × 200 pixels. Beyond application for ADAS industry, beam
steering systems with similar performances have potential in real-
time imaging for applications requiring short ambiguity distance, for
example in microscopy and wide-angle optical coherence
tomography48. Our main limitation to achieve high frame-rate is
related to the extremely large volume of real-time data treatment to be
realized synchronously during the acquisition. Here we only per-
formed calculation using conventional CPULabView basedas such,
we cannot output and save data as the same speed as their acquisition.
Fig. 5 | Measurement of fast in real-time-series events. a Top: Illustration of the
scene: a mechanical chopper of was set up with a nominal speed of 100 Hz and
some slabs were covered using a reective tape. Bottom: Measurement of the
rotation speed for three different frame rates. bTop: Normalized intensity map for
the radial axis, illustrating the dynamics of the wheel. Note the different slope for
the rotation angles around 3π=2 representing a lessening of the speed. Bottom:
Single-frame intensity data illustrating various angular positions. cTop: photo-
graphy of the chopper and the size of the reective tape. Bottom: Ranging image
for t= 1.0ms and the measurement of the tape from the recovered data.
Nature Communications | (2022) 13:5724 6
Content courtesy of Springer Nature, terms of use apply. Rights reserved
The Supplementary Video V3 showing a moving person in 3D space is
taken by achieving the best compromise, that is by acquiring single
frames raw data (with 200 ×200 pixels for instance) and outputting
data directly to SSD driverframe-by-frame. Our data treatment process
creates latencies related to asynchronous data storage, which result in
stuttered or choppy movements with occasional video speeding-up
movements. This problem is generally mitigated in LiDAR by
implementing FPGA/ASICS processing.
Our approach also offers random-access beam steering cap-
abilities. Multizone ranging images mimicking human vision at high
frame rate have been realized. The versatility of MS for wavefront
engineering could improve the capabilities of simultaneous localiza-
tion and mapping algorithms. Furthermore, incorporating this system
in ADAS could provide a disruptive solution for medium/long-range
perception, in which the central view scans the front scene, while the
peripheral view provides additional sensing for pedestrian safety for
example. We nally demonstrated time-event series for imaging at a
real-time regime (>1k fps and up to MHz frame rate for 1D scanning).
Outperforming existing LiDAR technologies, our tool offers a per-
spective for future applications, in particular by participating to
reducing the low decision-making latency of robotic and advanced
driver-assistance systems.
Experimental methodology
A collimated beam is sent to an AOD device (AA Opto-electronic
DTSXY-400-633) to deect light at small arbitrary angles, within 49
mrad. The AOD is driven by a voltage-controlled RF generator (AA
Opto-electronics DRFA10Y2X-D-34-90.210). The deected signal is
directed to a scanning lens (THORLABS LSM03-VIS) that focuses the
light at different transverse positions on the MS. The MS acts as a
designer-dened passive device to convert the small × FoV into an
enhanced 150° × 150° FoV. ToF is obtained by monitoring the scattered
light at each scanned angle using a detector (Hamamatsu C14193-
1325SA); and the reconstructed ranging image is built by associating
each period ð1
frepÞto individual pixels and extracting the ToF. In our
detection scheme, the detection path is separated to the excitation
path, which may result in not overlapped illumination/observation
regions. We believe that a mono-static approach could as well be
implemented in our conguration by utilizing a beam splitter before
sending the laser beam into the acousto-optics deector. A PXI
(National Instruments) system is used for data generation, recovery,
and treatment (more details can be found in Section S6 of Supple-
mental Materials). The angular scanning of the whole 1D was per-
formed in a single shot, during which we orchestrated pulse
repetition, scanning position angles and collection for precise mea-
surement of ToF in the system. With an acquisition scope card of
3Gsamples/s sample rate and considering a rise time on the detector
smaller than ~330 ps, the maximum z (depth) resolution of single
echo per laser shot measurement is about Δz=5cm.InFig.2d, we
show the collected raw signal corresponding to the three objects. For
ToF recovery, we used the derivative of the signal and collected the
peak of the differentiated signal. Single pulses were collected (inset
Fig. 2d) and separated to evaluate the ToF for each scanned direction
and then folded at the scanning frequency to form an image. The
fabrication of the different MS has been realized using GaN on sap-
phire nanofabrication processes. Details are available in the supple-
mentary materials.
Data availability
The Source data are available from the corresponding author upon
request. All data needed to evaluate the conclusion are present in the
manuscript and/or the Supplementary Information. Videos are avail-
able as Supplementary Materials, and the associated raw data would be
available upon request.
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This work was nancially supported by the European Research Council
proof of concept (ERC POC) under the European Unions Horizon 2020
research and innovation program (Project i-LiDAR, grant number
874986), the CNRS prématuration, and the UCA Innovation Program
(2020 startup deepTech) and the French defense procurement agency
under the ANR ASTRID Maturation program, grant agreement number
ANR-18-ASMA-0006. CK and MS acknowledge inputs of the technical
staff at the James Watt Nanofabrication Centre at Glasgow University. C.
Kyrou has been supported with a postdoctoral fellowship grant by the
Bodossaki Foundation (Athens, Greece).
Author contributions
Sample fabrication: C.C., V.G., C.T., P.M.C., D.T., C. Klitis, and M.S.;
conceptualization and supervision: P.G.; Instrumentation support: M.G.;
experimental realization: R.J.M. and P.G.; data collection: R.J.M., E.M.,
A.B.Y., and M.J.; data analysis: R.J.M., E.M., A.B.Y. and P.G.; manuscript
writing: R.J.M., P.G., C. Kyrou, E.M., A.B.Y., and S.K.
Competing interests
A patent has been led on this technology/Renato J Martins, Samira
Khadir, Massimo Giudici, and Patrice Genevet, SYSTEM AND METHOD
Additional information
Supplementary information The online version contains
supplementary material available at
Correspondence and requests for materials should be addressed to
Patrice Genevet.
Peer review information Nature Communications thanks the other
anonymous reviewer(s) for their contribution to the peer review of this
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... Laser-ranging technology, distinguished by its high resolution, robust coherence and exceptional interference resistance, finds extensive application in aerospace, large-scale equipment production, energy-related equipment and manufacturing processes [1][2][3]. Common laser-ranging techniques encompass the timed pulse method [4], phase comparison method [5], frequency-modulated continuous wave (FMCW) method [6][7][8][9][10][11][12] and femtosecond frequency comb method [13][14][15][16]. The timed pulse method, while widely used, offers a limited resolution; therefore, it is not suitable for industrial applications. ...
... Expanding Equation (2) in series with the Bessel functions of the first kind, we obtain Equation (3): ...
Full-text available
In this study, we propose a frequency measurement and estimation approach based on a lock-in analysis for precise frequency determination in polarization-modulated ranging signals. In this method, the modulation signal of an electro-optic modulator (EOM) is manipulated to introduce an intermediate frequency (IF) component into the detected signal. Subsequently, the detected signal is analyzed using lock-in analysis techniques to extract the necessary frequency component, and a new swept frequency waveform is generated, facilitating the frequency acquisition and distance calculation. We conducted theoretical derivations, simulations and experiments to validate the effectiveness of this method. The research findings suggest that our method can enhance the accuracy of frequency measurements by a factor of approximately ten when compared to a direct detection approach, leading to a corresponding improvement in ranging precision. Furthermore, even with larger sweep step sizes and smaller modulation frequencies, the proposed approach can achieve superior ranging results.
... These metasurfaces have the unexpected ability to manipulate the amplitude, phase, and polarization of electromagnetic waves. Through the appropriate engineering of the sizes and arrangements of artificial meta-atoms, different types of metasurfaces, spanning from microwaves to visible lights, have been demonstrated to implement versatile functionalities, including anomalous refraction [11,12], focusing [13,14], holography imaging [15,16], and Bessel beams [17,18], to name a few. Benefiting from their ultrafine nature and unparalleled control over electromagnetic waves, this allows metasurfaces to serve as a novel platform for the generation of terahertz vortex beams and the realization of versatile applications involving these beams [19,20]. ...
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Currently, vortex beams are extensively utilized in the information transmission and storage of communication systems due to their additional degree of freedom. However, traditional terahertz metasurfaces only focus on the generation of narrowband vortex beams in reflection or transmission mode, which is unbeneficial for practical applications. Here, we propose and design terahertz metasurface unit cells composed of anisotropic Z-shaped metal structures, two dielectric layers, and a VO2 film layer. By utilizing the Pancharatnam–Berry phase theory, independent control of a full 2π phase over a wide frequency range can be achieved by rotating the unit cell. Moreover, the full-space mode (transmission and reflection) can also be implemented by utilizing the phase transition of VO2 film. Based on the convolution operation, three different terahertz metasurfaces are created to generate vortex beams with different wavefronts in full-space, such as deflected vortex beams, focused vortex beams, and non-diffraction vortex beams. Additionally, the divergences of these vortex beams are also analyzed. Therefore, our designed metasurfaces are capable of efficiently shaping the wavefronts of broadband vortex beams in full-space, making them promising applications for long-distance transmission, high integration, and large capacity in 6G terahertz communications.
... The control of light wave amplitude and phase is crucial for designing light detection and ranging devices (LIDAR). Significant advances in subwavelength technologies, such as photo-or electronic lithography, have made it possible to create solid-state LIDARs [1][2][3], in which the optical properties of light are controlled by metasurfaces-structures consisting of subwavelength elements. Metasurfaces open up new opportunities for implementation of holograms [4], lenses [5], media with anomalous reflection [6,7], lasers [8,9], perfect absorbers with critical coupling [10,11], sensors [12,13] etc. ...
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The dynamic steering of a beam reflected from a photonic structure supporting Tamm plasmon polariton is demonstrated. The phase and amplitude of the reflected wave are adjusted by modulating the refractive index of a transparent conductive oxide layer by applying a bias voltage. It is shown that the proposed design allows for two-dimensional beam steering by deflecting the light beam along the polar and azimuthal angles.
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Light detection and ranging (LiDAR) sensor is widely recognized as a critical component for accurate perception. However, there are a host of challenges that impede their performance, including low spatial resolution, high costs, large size, low reliability, and susceptibility to interference. It is challenging to overcome these issues using a single LiDAR module, necessitating the need for a review of current LiDAR technologies. The paper commences by introducing the fundamental principles of various laser rangefinders and discussing the optical modulation technologies used to prevent interference and ghost images. Next, the paper delves into the latest developments in laser technology, with a focus on enhancing the switching rate, compliance with eye safety regulations, miniaturization, and improving stability. One highly promising innovation is the photonic crystal surface emitting laser (PCSEL), a novel light source that boasts high‐speed, small divergence angles, and high‐power output. Finally, the paper discusses the advancements made in non‐solid‐state scanning and solid‐state scanning, such as improving stability, increasing scanning angles, and optimizing the manufacturing of mechanical and micro‐electromechanical systems (MEMS). Additionally, the paper highlights the recent advancements in nanotechnology, specifically metasurface technology, which offers superior capabilities such as beam deflection, enhanced field‐of‐view (FOV), and dynamic modulation.
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Spatial light modulators have desirable applications in sensing and free space communication because they create an interface between the optical and electronic realms. Electro-optic modulators allow for high-speed intensity manipulation of an electromagnetic wavefront. However, most surfaces of this sort pose limitations due to their ability to modulate intensity rather than phase. Here we investigate an electro-optic modulator formed from a silicon-organic Huygens’ metasurface. In a simulation-based study, we discover a metasurface design immersed in high-performance electro-optic molecules that can achieve near-full resonant transmission with phase coverage over the full 2 π range. Through the electro-optic effect, we show 140 ∘ (0.79 π ) modulation over a range of -100 to 100 V at 1330 nm while maintaining near-constant transmitted field intensity (between 0.66 and 0.8). These results potentiate the fabrication of a high-speed spatial light modulator with the resolved parameters.
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Microscopic imaging in three dimensions enables numerous biological and clinical applications. However, high-resolution optical imaging preserved in a relatively large depth range is hampered by the rapid spread of tightly confined light due to diffraction. Here, we show that a particular disposition of light illumination and collection paths liberates optical imaging from the restrictions imposed by diffraction. This arrangement, realized by metasurfaces, decouples lateral resolution from the depth of focus by establishing a one-to-one correspondence (bijection) along a focal line between the incident and collected light. Implementing this approach in optical coherence tomography, we demonstrate tissue imaging at a wavelength of 1.3 µm with ~3.2 µm lateral resolution, maintained nearly intact over a 1.25 mm depth of focus, with no additional acquisition or computational burden. This method, termed bijective illumination collection imaging, is general and might be adapted across various existing imaging modalities. A custom-designed metasurface for sample illumination and light collection in optical coherence tomography overcomes the usual trade off in lateral resolution and depth of field.
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Upon reflection, modulate phase Metasurfaces provide a platform to fabricate optical devices in a compact form much thinner than their corresponding bulk optical components. Recognizing that metasurfaces are also open systems interacting with their environment, Song et al . designed a metasurface that exploits those non-Hermitian properties such that they can encircle an exceptional point. Subsequent scattering from such an exceptional point was shown to be polarization dependent, thus providing an additional control knob in designing metasurfaces for wave front engineering. —ISO
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Light detection and ranging (LiDAR) technology, a laser-based imaging technique for accurate distance measurement, is considered one of the most crucial sensor technologies for autonomous vehicles, artificially intelligent robots and unmanned aerial vehicle reconnaissance. Until recently, LiDAR has relied on light sources and detectors mounted on multiple mechanically rotating optical transmitters and receivers to cover an entire scene. Such an architecture gives rise to limitations in terms of the imaging frame rate and resolution. In this Review, we examine how novel nanophotonic platforms could overcome the hardware restrictions of existing LiDAR technologies. After briefly introducing the basic principles of LiDAR, we present the device specifications required by the industrial sector. We then review a variety of LiDAR-relevant nanophotonic approaches such as integrated photonic circuits, optical phased antenna arrays and flat optical devices based on metasurfaces. The latter have already demonstrated exceptional functional beam manipulation properties, such as active beam deflection, point-cloud generation and device integration using scalable manufacturing methods, and are expected to disrupt modern optical technologies. In the outlook, we address the upcoming physics and engineering challenges that must be overcome from the viewpoint of incorporating nanophotonic technologies into commercially viable, fast, ultrathin and lightweight LiDAR systems. This Review highlights the technological challenges linked to the application of nanophotonics for light detection and ranging (LiDAR).
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Active metasurfaces promise reconfigurable optics with drastically improved compactness, ruggedness, manufacturability and functionality compared to their traditional bulk counterparts. Optical phase-change materials (PCMs) offer an appealing material solution for active metasurface devices with their large index contrast and non-volatile switching characteristics. Here we report a large-scale, electrically reconfigurable non-volatile metasurface platform based on optical PCMs. The optical PCM alloy used in the devices, Ge2Sb2Se4Te (GSST), uniquely combines giant non-volatile index modulation capability, broadband low optical loss and a large reversible switching volume, enabling notably enhanced light–matter interactions within the active optical PCM medium. Capitalizing on these favourable attributes, we demonstrated quasi-continuously tuneable active metasurfaces with record half-octave spectral tuning range and large optical contrast of over 400%. We further prototyped a polarization-insensitive phase-gradient metasurface to realize dynamic optical beam steering. An electrically reconfigurable optical metasurface using a Ge2Sb2Se4Te phase change material shows half an octave spectral tuning and promising performances for optical beam steering applications.
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Accurate three-dimensional (3D) imaging is essential for machines to map and interact with the physical world1,2. Although numerous 3D imaging technologies exist, each addressing niche applications with varying degrees of success, none has achieved the breadth of applicability and impact that digital image sensors have in the two-dimensional imaging world3–10. A large-scale two-dimensional array of coherent detector pixels operating as a light detection and ranging system could serve as a universal 3D imaging platform. Such a system would offer high depth accuracy and immunity to interference from sunlight, as well as the ability to measure the velocity of moving objects directly¹¹. Owing to difficulties in providing electrical and photonic connections to every pixel, previous systems have been restricted to fewer than 20 pixels12–15. Here we demonstrate the operation of a large-scale coherent detector array, consisting of 512 pixels, in a 3D imaging system. Leveraging recent advances in the monolithic integration of photonic and electronic circuits, a dense array of optical heterodyne detectors is combined with an integrated electronic readout architecture, enabling straightforward scaling to arbitrarily large arrays. Two-axis solid-state beam steering eliminates any trade-off between field of view and range. Operating at the quantum noise limit16,17, our system achieves an accuracy of 3.1 millimetres at a distance of 75 metres when using only 4 milliwatts of light, an order of magnitude more accurate than existing solid-state systems at such ranges. Future reductions of pixel size using state-of-the-art components could yield resolutions in excess of 20 megapixels for arrays the size of a consumer camera sensor. This result paves the way for the development and proliferation of low-cost, compact and high-performance 3D imaging cameras that could be used in applications from robotics and autonomous navigation to augmented reality and healthcare.
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Relying on the local orientation of nanostructures, Pancharatnam–Berry metasurfaces are currently enabling a new generation of polarization-sensitive optical devices. A systematical mesoscopic description of topological metasurfaces is developed, providing a deeper understanding of the physical mechanisms leading to the polarization-dependent breaking of translational symmetry in contrast with propagation phase effects. These theoretical results, along with interferometric experiments contribute to the development of a solid analytical framework for arbitrary polarization-dependent metasurfaces.
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Spatial light modulators are essential optical elements in applications that require the ability to regulate the amplitude, phase and polarization of light, such as digital holography, optical communications and biomedical imaging. With the push towards miniaturization of optical components, static metasurfaces are used as competent alternatives. These evolved to active metasurfaces in which light-wavefront manipulation can be done in a time-dependent fashion. The active metasurfaces reported so far, however, still show incomplete phase modulation (below 360°). Here we present an all-solid-state, electrically tunable and reflective metasurface array that can generate a specific phase or a continuous sweep between 0 and 360° at an estimated rate of 5.4 MHz while independently adjusting the amplitude. The metasurface features 550 individually addressable nanoresonators in a 250 × 250 μm² area with no micromechanical elements or liquid crystals. A key feature of our design is the presence of two independent control parameters (top and bottom gate voltages) in each nanoresonator, which are used to adjust the real and imaginary parts of the reflection coefficient independently. To demonstrate this array’s use in light detection and ranging, we performed a three-dimensional depth scan of an emulated street scene that consisted of a model car and a human figure up to a distance of 4.7 m.
This paper aims to review the state of the art of Light Detection and Ranging (LiDAR) sensors for automotive applications, and particularly for automated vehicles, focusing on recent advances in the field of integrated LiDAR, and one of its key components: the Optical Phased Array (OPA). LiDAR is still a sensor that divides the automotive community, with several automotive companies investing in it, and some companies stating that LiDAR is a 'useless appendix'. However, currently there is not a single sensor technology able to robustly and completely support automated navigation. Therefore, LiDAR, with its capability to map in 3 dimensions (3D) the vehicle surroundings, is a strong candidate to support Automated Vehicles (AVs). This manuscript highlights current AV sensor challenges, and it analyses the strengths and weaknesses of the perception sensor currently deployed. Then, the manuscript discusses the main LiDAR technologies emerging in automotive, and focuses on integrated LiDAR, challenges associated with light beam steering on a chip, the use of Optical Phased Arrays, finally discussing current factors hindering the affirmation of silicon photonics OPAs and their future research directions.
A slim beam deflector that satisfies both a large steering angle and a large area can be very useful in various applications. However, a smaller electrode pitch for a large steering angle and enlargement of its area are trade-off relations due to the limited number of control channels in an electrically tunable beam deflector system. For a large steering angle in the active area where actual diffraction occurs, an indium tin oxide electrode of 2 µm pitch was implemented through a stepper lithography. The via-hole process was developed to expand the reduced active area due to the small electrode pitch. We developed a beam deflector with 7200 controllable channels in an active area of 14.4mm×14.4mm. The maximum steering angle is 7.643° at a wavelength of 532 nm.