SOLID STATE LIDAR USING

THE LETI SILICON

PHOTONICS PLATFORM:

PROGRESS AND PERSPECTIVES

Daivid FowlerDepartment of Optics and Photonics, LETI

25/06/2019

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OVERVIEW

• LIDAR and Optical Phased Arrays

• Ongoing and future development

• Initial 2D beam-scanning demonstration using an

OPA based on LETI silicon photonics

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• RADAR λ = 10-2 to 102m

• LIDAR λ ~ 10-6m

• smaller wavelength leads to improved spatial resolution

• Applications: Automotive, aviation, archeology, etc.

INTEGRATED LIDAR

LiDAR = Light Detection And Ranging

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INTEGRATED LIDAR SYSTEM

scene

• Emitter

• Free space optics

• Photodetection

• Image processing

• Drive electronics

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INTEGRATED LIDAR EMITTER

• Mobile source RADAR • Phased array RADAR

Optical

Phased

Array

• Solid state LIDAR• Mobile source LIDAR

• Silicon photonics

• Lens free

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Near-field

Quasi-uniformillumination

𝐼(𝜃) = 𝐹𝑇 𝐴 𝑥

OPTICAL PHASED ARRAY BASIC PRINCIPLE

Far-field

I(θ)

θ

x

Point source

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ampl

phase

Near-field

Cosinusoidalillumination

𝐼(𝜃) = 𝐹𝑇 𝐴 𝑥

Two CoherentPoint sources

I(θ)

θ

x

Far-field

OPTICAL PHASED ARRAY BASIC PRINCIPLE

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Near-field

ShiftedCosinusoidalillumination

𝐼(𝜃) = 𝐹𝑇 𝐴 𝑥

OPTICAL PHASED ARRAY BASIC PRINCIPLE

Far-field

ampl

phase

I(θ)

θ

x

Two out-of-phase coherentPoint sources

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ampl

phase

Near-field 𝐼(𝜃) = 𝐹𝑇 𝐴 𝑥Far-field

Many coherentPoint sources (d>>λ)

I(θ)

θ

x

OPTICAL PHASED ARRAY BASIC PRINCIPLE

Multiple narrow peaks

d>>λ

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Near-field 𝐼(𝜃) = 𝐹𝑇 𝐴 𝑥Far-field

single narrowpeak

Many coherentPoint sources (d ~ λ)

I(θ)

θ

x

ampl

phase

d ~ λ

OPTICAL PHASED ARRAY BASIC PRINCIPLE

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Near-field 𝐼(𝜃) = 𝐹𝑇 𝐴 𝑥Far-field

single narrowpeak

Many coherentPoint sources (d ~ λ)

I(θ)

θ

x

ampl

phase

d ~ λ

OPTICAL PHASED ARRAY BASIC PRINCIPLE

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EXAMPLE OF OPTICAL PHASED ARRAY DIMENSIONS

• Operating wavelength, λ = 1µm

• 10cm object at 100m

• Unambiguous sweeping range +/-45°

, Φ (deg)

~1000 sources, each

separated by 1µm

d

n = 1 2 3 N

w

>90° between diffraction orders

ΔΦ ΔΦ = 90°

d = λ/sin(ΔΦ) = λ

Beam divergence ~ 1mRad ~ 0,05°

Φ3dB

Φ3dB = 1mRad,

N.d = 1,22λ/ Φ3dB = 1220 x λ

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INTEGRATED OPA USING SILICON PHOTONICS

phase

tuningPower splitter

Laser inputEmitter array

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INTEGRATED OPA USING SILICON PHOTONICS

Silicon photonics:

• Operating wavelength 0,5-

4µm

• Suited to high component

density

• CMOS compatible for high-

volume/low cost production

phase

tuningPower splitter

Laser inputEmitter array

Solid state beam scanning (in Ф)

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INTEGRATED OPA USING SILICON PHOTONICS

phase

tuningPower splitter

Laser inputEmitter array

What about the second dimension (θ)?

Silicon photonics:

• Operating wavelength 0,5-

4µm

• Suited to high component

density

• CMOS compatible for high-

volume/low cost production

Solid state beam scanning (in Ф)!

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OPA FOR TWO DIMENSIONAL BEAM STEERING

2D antenna array

• Need a point source

with an area < λ2

• NxN phase controls

Other solutions

• OPA + Ph crystals

• OPA + liquid crystals

• VCSEL arrays

• etc

Watts, MIT

Abiri, CIT

Yoo, Berkeley

Tuneable laser

• ~10nm per degree in θ

• need laser with a λ

range >100nm

Van Acoleyen, IMEC

Bowers, UCSB

Kwong, Uni of Texasθ

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• Multi-1D OPA

• One OPA per θ value

• Single source plus switch

• 2D beam steering at a

single wavelength with

a single laser

• Discrete sweeping in θ

• θ range/resolution limited

by OPA footprint

OPA FOR TWO DIMENSIONAL BEAM STEERING

θ =+15°

θ =+13°

θ =-15°

…

Velodyne VLP-16

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OPA FOR TWO DIMENSIONAL BEAM STEERING

• 905nm OPA based on SiN

waveguides/devices

N. A. Tyler et al. Optics Express, Feb. 2019.

Tyler, N. A., et al. CPMT Symposium BEST PAPER AWARD

• ‘2D’ beam steering at 905nm

demonstrated

• Wafer-scale automatic test facilities

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Sweeping range Φ/θ

resolution Φ/θ

1st LETI demo

(2018)

±17°/3°

4°/1°

2019 target

(In fabrication)

202? Target

± 30/8°

0,3°/1°

± 60/20°

0,1°/0,1°

• Change to ‘cooler’ phase modulator mechanism

• Reduce antenna pitch, increase channel number

• Reduce optical path length and/or Reduce WG phase errors

Circuit loss

Sweep frequency

Voltage per channel

-15dB

10KHz

1

mW per channel 80

-3dB

10KHz

<1

<-1dB

10MHz

<<1

20 <1

LETI OPA DEVELOPMENT AND PERSPECTIVES

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1550nm Si 900nm SiN 900nm SiN 900nm SiN

900nm

SiN

1550nm

Si

2016 2017 2018 2019

2019 onwards• IRT (National French funding)

• ECSEL VIZTA (European funding)

• Industrial clients

LETI OPA DEVELOPMENT AND PERSPECTIVES

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LETI LIDAR SYSTEM DEVELOPMENT

• CEA-LETI HAS THE CAPABILITY TO MAP THE LIDAR INTEGRATION STRATEGY

• THE OPA IS ONE OF THE (MANY) KEY TECHNOLOGIES

TECHNOLOGIES SYSTEM

VCSEL EEL

MEMs

mirrorOPA

APDs SiPM

Fiber

laser

Pulse

AVGAnalog

IC

Hetero-

dyne

Time to

Digital C

LensMEMs

mirror

Sigma

fusion

Sensor

fusion

Embedd

ed AI

Rotating

mirror

Feedbac

k loops

Optical source

Beam steering

Photodetection

System integration

Optics (Tx, Rx)

Data processing

PiNSPADs -

Gm

System driven device development

CO-DESIGN SOFTWARE-HARDWARE

WITH TEST BENCHES

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SUMMARY

• LIDAR systems for high resolution 3D imaging

• Demonstration of 2D beam-steering at 905nm using

a CMOS compatible Optical Phased Array circuit

• Significant future development to achieve target

system specifications

• Ongoing LETI development now guided by a system

based approach

• Optical Phased Arrays for solid-state beam scanning

Leti, technology research institute

Commissariat à l’énergie atomique et aux énergies alternatives

Minatec Campus | 17 rue des Martyrs | 38054 Grenoble Cedex | France

www.leti.fr

Thank you for your attention

Daivid.Fowler@cea.fr