coherent lidar for 3d- imaging through obscurants marti… · coherent lidar for 3d-imaging through...

www.thalesgroup.com OPEN

Coherent Lidar for 3D-

imaging through obscurants

AUDE MARTIN , JÉRÔME BOURDERIONNET, LUC

LEVIANDER, JOHN F. PARSONS, MARK SILVER, PATRICK FENEYROU THALES RESEARCH AND TECHNOLOGY, PALAISEAU, FRANCE

THALES LTD, 1 LINTHOUSE ROAD, GLASGOW, G51 4BZ, UK

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Thales Research & Technology France

FMCW coherent LiDAR for 3D-imaging

Main advantages of the system ?

• Directly measure range and velocity

• Versatile waveform defined through

software

• Reduced peak power and large

dynamic

• Insensitive to sunlight glare

• Resistant to jamming and hacking

• Signal processing easily discriminates

hard target from obscurants

P. Feneyrou, et al., Appl. Opt. 56, 9663-9675 (2017) P. Feneyrou, et al., Appl. Opt. 56, 9676-9685 (2017)

Smoke signal

Target

signal

Target

signal

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3 OPEN JPAL 2018 – 30/05/18


The FMCW coherent lidar setup

Electronics + fibered optics

+ power management

Optical head

InGaAs camera

Optical scanner

Free-space optics

Gimbal head

▌ Long pulse (few ms) to preserve eye safety

while increasing optical power of the laser amplifier

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Pre-Trial - System check - scene at 70m – 100m – no obscurant

Buildings

and trees

Grass

behind sign Road sign

Measurement on a

windy day… see later

Scanner

field of view Buildings

and trees

Road sign

Grass

LIDAR Range Image

Visible Image

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Pre-Trial - Detail on tilted Road sign

Trial system resolution ~30 cm

Mod. BW ~ 400 MHz

Range Velocity

Speed measurement should

help target recognition

Moving grass and trees (~5 cm/sec)

Stationary sign

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A Selection of Targets from 75m to 1400m at DSTL facilities

~700 m

~75 m

~1400 m

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Clear air images (NO SMOKE)

▌64 x 64 image in approx 90 sec

(acquisition + processing + plots)

Limited by current scan head speed and

processor hardware

Mast at 700m: Image 3.5x3.5m Average power : ~100 mW, 5 ms laser on per pixel

Mast and

attachments

Dirt tracks

Tent walls flapping in the wind (~ 20 cm/sec)

Tent at ~ 1400m: Image: 7 x 7m Average power : ~160 mW & 7 ms int. time

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8 OPEN JPAL 2018 – 30/05/18


Range Resolution and discrimination (NO SMOKE)

- 30 cm resolution @ 700m measured during trial

- Limited by current trial system.

1 m

range scale

Resolution

~30 cm

Mast at panel at 700m

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Mannequin (WITH SMOKE)

▌Simultaneous LIDAR acquisition and Visible picture…

▌Image obtained with a smoke transmission down to 0.04 % (double pass)

~4 attenuation lengths (single pass), confirmed with transmission data

Consistent with performance modeling

LIDAR Camera

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Main advantages of photonic integrated LiDAR

Monolithic integration

- Integrated function with both electronic and optical devices on the same chip

- Thermal / mechanical stability

- Active & passive devices integration Today: from optical devices to detectors, tomorrow : from laser to detectors

After : from laser to signal processing ?

Parallel manufacturing

- Cost reduction for mass production

Beam scanning though beam switching / forming

- Fast and reliable scanning with reduced power for driving electronics

Compatibility with fiber technology

- Fiber devices available to cope with (rare) un-mature PIC optical function

- Remote optical head still possible

But… technology not compatible with high peak power and for 𝜆 < 1100 𝑛𝑚

Frequency-modulated continuous-wave coherent LiDAR @ 1.55 𝝁𝒎

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Integrated multichannel FMCW LiDAR

▌8 emission channels

Addressed using cascaded MZ switch

network (SN2)

Each of the emission port covering desired

angle after passing through collimators

Avoid beam scanning

▌8 collection channels corresponding to the emission channels

Addressed using paired MZ switch network

(SN1)

▌8 PBD pairs for signal collection

Connected in // : photocurrents addition

▌Single waveform calibration channel

▌External DFB and circulators

Frequency

shifter

Scanning

system

Balanced

detectors

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Device fabrication and packaging

▌Device fabricated in the Imec ISiPP25G pilot line and packaging by Tyndall Institute

~20 DC connections for switch control

TIA amplifier for RF output -> limited by shot noise

20 optical I/O

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▌ Range up to 50 m with emitted power < 5 mW

▌ Checked switching

Simultaneous range and speed measurement

A. Martin et al., "Photonic integrated circuit based FMCW coherent LiDAR,” in Journal of Lightwave Technology (2018)

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Conclusion

▌Photonic ICs provides key building blocks

for LiDAR applications

Balanced detectors

Frequency shifter

Optical beam steering or switching

▌Demonstration of multichannel on-chip FMCW LiDAR

Speed and range measurement up to 50 m for

5mW emitted power

- Limited by laser linewidth (>100 kHz)

▌Perspectives towards complete monolithic integration

Increased power (longer range): hybrid SiN

platform or optical phased array

Narrow linewidth laser (10 kHz)

▌Field trial of scanning FMCW Lidar

Advantages of FMCW over other 3D

imaging tech.

- Large range dynamic

- Speed measurement

90 s for a 64x64 pixels image for this first

implementation

- Strongly limited by the scanning speed &

data transfer

- Already X3 image rate increase (30 s)

▌ Imaging through obscurants

4 attenuation lengths of smoke

▌Perspectives

Increase scanning and processing speed

- Use a laser with broader modulation

bandwidth and narrow linewidth

- Non Mechanical Beam Steering

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15 OPEN JPAL 2018 – 30/05/18


Conclusion

▌Photonic ICs provides key building blocks

for LiDAR applications

Balanced detectors

Frequency shifter

Optical beam steering or switching

▌Demonstration of multichannel on-chip FMCW LiDAR

Speed and range measurement up to 50 m for

5mW emitted power

- Limited by laser linewidth (>100 kHz)

▌Perspectives towards complete monolithic integration

Increased power (longer range): hybrid SiN

platform or optical phased array

Narrow linewidth laser (10 kHz)

▌Field trial of scanning FMCW Lidar

Advantages of FMCW over other 3D

imaging tech.

- Large range dynamic

- Speed measurement

90 s for a 64x64 pixels image for this first

implementation

- Strongly limited by the scanning speed &

data transfer

- Already X3 image rate increase (30 s)

▌ Imaging through obscurants

4 attenuation lengths of smoke

▌Perspectives

Increase scanning and processing speed

- Use a laser with broader modulation

bandwidth and narrow linewidth

- Non Mechanical Beam Steering

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Thank you

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2. Frequency

shifter

3. Scanning

system

Previous demonstrations of 3D imaging on chip

B. Behroozpour, et al., IEEE Journal of Solid-State Circuits, 1, 161-172,(2017)

C. Poulton, et al., Optics Letters, 42 (20), 4091(2017)

R =1.4 m

R = 0.5 m

F. Aflatouni, et al., Optics Express, 4(23), 5117-5125 (2015)

R =0.5 m

1. Balanced

detectors

Optical

Phased Arrays

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Photonic IC functional characterization

▌Switch networks :

Channel isolation > 25dB

<1 dB channel transmission uniformity

9 dB fiber-to-fiber insertion loss (~6 dB coupling, 1 dB for delay line interf., 2 dB switches)

▌PIC power handling

Maximum emitted power without nonlinear absorption in waveguides : 30 mW for 200 mW input

Transmission vs input power for the shunt waveguide:

1 dB compression input power at 22 dBm

▌Detectors

1dB compression point : 8 mA (10 mW optical power)

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▌ Emitted power < 5 mW Pupil diameter : 1 inch

▌ Frequency Bandwidth : 500 MHz/FFT -> resolution = 30 cm

▌ Range finding / Velocimetry > 50 m

Simultaneous measurement of speed and range

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▌Features

Advantages of coherent detection

RADAR Pulsed LiDAR FMCW Lidar

3D-imaging / axial resolution

Simultaneous high resolution Speed and Range

Versatile resolution and range ambiguity

Jamming/Hacking immunity

Sun insensitivity

Degraded vision environment proof (clouds, dust, fog)

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21 OPEN JPAL 2018 – 30/05/18


Device power handling

▌Specific input grating coupler/splitter (U. Ghent)

Fiber to chip coupling losses = 3.2 dB

▌Linear transmission up to almost 1 Watt of input power

T. Spuesens, et al., " Integrated Grating Coupler/Power Splitter for On-chip Optical Power Distribution," Group IV

Photonics Conference, Paris, 2014

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22 OPEN JPAL 2018 – 30/05/18


Balanced photodetection

▌Requirements for shot-noise limited measurement :

Photodiodes :

- Handle enough optical power to ensure

shot noise > thermal noise

Balanced scheme :

Reject RIN below shot noise at high input power

CMRR>50dB achieved

1 dB compression point at 11dBm

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23 OPEN JPAL 2018 – 30/05/18


Calibration of the waveform

▌Shorter delay line -> larger error on the waveform optimisation

-> demodulation error

Delay line : 𝜏 = 1 𝑛𝑠 Delay line : 𝜏 = 24 𝑛𝑠

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24 OPEN JPAL 2018 – 30/05/18


Temps de traitement

≈ 10 Hz

Data

presentation

Data Transfer

25

ms

25

ms

50

ms

Signal processing

Peak

Detection : 75 %

≈ 250 Hz

Data Transfer

5 m

s

< 1

ms

Signal processing

Before Now*

* Figure dilatée…

coherent lidar for 3d- imaging through obscurants marti… · coherent lidar for 3d-imaging through...

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