Lille, FRANCE

Fiber optic environmental sensing across scales

Debanuj Chatterjee

Marie Curie Postdoctoral Researcher @ University of Lille, France

27^th May 2026

1

BS-MS

2017

2013-4

NIUS Physics

2022-3

Charpak Rsearch

Internship

IIT Madras

2015

2023-6

2018

-21

PhD

2

Lille, FRANCE

PhLAM laboratory

3

Besançon, 20/09/2017

Workshop SUPUVIR

Lille 10/04/2017

​

Winter School on nonlinear photonics

Trento 2018

4

Optical fiber technology

• Thin cylindrical waveguide that can carry light over long distances

2009

Charles Kao

Core

Cladding

Cross section

Marra, Giuseppe et al, Science 376, no. 6595 (2022): 874-879.

5

Frequency comb technology

• Ruler of light : equally spaced frequency lines

Theodor Hänsch

Jan Hall

2005

Diddams, Scott A., et al, Science 369, no. 6501 (2020)

6

Besançon, 20/09/2017

Workshop SUPUVIR

Lille 10/04/2017

​

Winter School on nonlinear photonics

Trento 2018

Motivation

• Generation of multiple frequency combs in fiber device

Rich nonlinear dynamics

Applications

• High mutual coherence
• Frequency agility

7

Dual comb spectroscopy

Time domain

Frequency domain

Vernier effect

f₁

f₂=f₁+Δf

Δf

f_AOM

1/f₁

1/f₂

Optical

RF

Optical

RF

Scott Diddams, Science, 2020

Ideguchi, Takuro. "Dual-comb spectroscopy." Optics and Photonics News 28, no. 1 (2017): 32-39.

8

Dual comb applications

(Scott Diddams, Science, 2020)

Autonomous cars

Precise distance metrology

Zebin Zhu, et al, Engineering 4, no. 6 (2018): 772-778.

Atmospheric monitoring

Photoacoustic imaging

Fast spectroscopy of gasses

Optomechanical sensor

Roger Ding, et al, Optica sensing congress 2025

Debanuj Chatterjee, et al., IOP Journal of Physics B, 58 (15) 153501 (2025)

Jacob Nürnberg, et al. Optics Express 29, no. 16 (2021): 24910-24918.

Ahmed Bahgat et al. Journal of Optical Microsystems 4, no. 3 (2024): 034502-034502.

Alexander Eber, et al. Optics Express 32, no. 4 (2024): 6575-6586.

9

Dual comb ultrasound sensing

Pulsed laser light

Ultrasound (10 MHz)

Tissue

Blood vessels

Probe

Photoacoustics

Debanuj Chatterjee, et al., “Real time electro optic dual comb detection of ultrasound” IOP Journal of Physics B, 2025

Pulsed laser

Optical absorption

Thermo-elastic expansion

Broadband acoustic wave emission

Ultrasound detection

Gateau et al., Optics Letters, 38(22), 2013

10

Fiber based broadband ultrasound sensor

⇨Real time monitoring of acoustic waves

• 10 MHz signal retrieved

Sliding window

What else can we do with it?

Debanuj Chatterjee, et al., “Real time electro optic dual comb detection of ultrasound” IOP Journal of Physics B, 2025

11

Microsonograph for ultrasound sensing

⇨Professor Shonku by Satyajit Ray

MICROSONOGRAPH

Ultrasound

12

Opto-mechanical microsonograph for plants

⇨ Ultrasounic communication and sensing in plants

13

Advanced microsonograph

Sound card

Isolated sensing

VS

Agriculture

Many many microphones!

• Costly
• EM interference
• High signal loss

14

Fiber-based distributed microsonograph

Sound card

Distributed sensing

Isolated sensing

VS

MUX

Fiber switch

Fiber dual-comb

~km

1XN

Ultrasound

sensor

15

Fiber-based distributed microsonograph

Distributed sensing

MUX

Fiber switch

Fiber dual-comb

~km

1XN

Ultrasound

sensor

• Realtime health monitoring
• Remote location access
• Intra and inter-species communication
• Existing telecom infrastructure

Communication

16

Partial Conclusion

• Expertise
• Fiber optics
• Frequency combs
• Technology
• Fiber dual-comb-based ultrasound sensor
• Applications
• Photoacoustic deep-tissue imaging
• Agri-photonic sensor (national strategic importance)

Agriculture

What else affects agriculture?

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Drought

Forest fire

Extinction

Ice sheet melting

Flood

Extreme events

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Atmospheric CO₂ (greenhouse gas) level and temperature

⇨Temperature and CO₂ levels are strongly correlated

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Atmospheric CO₂ levels in the past

⇨CO₂ levels are at all time high (recorded past)

Source : climate.nasa.gov

Motivation : Precision metrology of greenhouse gases like CO₂, CH₄, etc

How to use fibers and combs?

20

Open path dual comb spectroscopy over 1 km: CO₂, CH₄

⇨CO₂ and CH₄ have absorption features around 1.6 𝛍m

Coburn, Sean, et al. "Regional trace-gas source attribution using a field-deployed dual frequency comb spectrometer." Optica 5, no. 4 (2018): 320-327.

Comb 1

Comb 2

PD

Plumes

Source

1 km

⇨Compatible with fiber frequency combs

21

Open path dual comb spectroscopy : Other approaches

⇨UAV mounted retro-reflector

Cossel, Kevin C., et al. "Ground-to-UAV, laser-based emissions quantification of methane and acetylene at long standoff distances." Atmospheric Measurement Techniques 16, no. 22 (2023): 5697-5707.

⇨100 km DCS (Nanshan to Gaoyazi)

Han, J.J., Zhong, et al., 2024. Dual-comb spectroscopy over a 100 km open-air path. Nature Photonics, 18(11), pp.1195-1202.

113 km

⇨Ground to satellite DCS link?

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Open path dual comb spectroscopy : Challenges & Solution

• No alignment error
• Fiber acts as vibration insulator
• Mobile system with 3D scan
• Compensating for lower path length:
• Time programming
• Compressive sensing

⇨Long path length (~km) challenges

• High alignment error
• Stationary system
• Higher cost

Debanuj Chatterjee et al., Sensitivity improvement of dual comb spectroscopy with time programmed electro-optic frequency combs, JLT (2024)

​

⇨Short path length proposal

Fiber

Movement

Movement

Solution?

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Molecules to particles

Molecular regime

Particle regime

Aggregation

~nm scale

~𝛍m scale

Spectroscopy

Microscopy, scattering, …

24

Detection of particulate matters : Challenges

• Particles scatter light
• Scattered light intensity correlates with size
• Particle size distribution extracted

• No information on particle shape

Light scattering method

How to know particle shapes?

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Detection of particulate matters : Challenges

• Electrons are incident on object surface
• Back scattered electrons are recorded
• Particle shape is recovered

• Expensive method

Scanning Electron Microscopy

Shi, Yuanyuan, et al. "Nanoscale characterization of PM2. 5 airborne pollutants reveals high adhesiveness and aggregation capability of soot particles." Scientific reports 5, no. 1 (2015): 11232.

How do we use fiber combs?

26

3D printing of optical micro-components : LFBG

• Use of two photon polymerization for printing
• Grating directly printed on fiber facet
• Used for temperature and pressure sensing

• Cost effective method
• Reconfigurable
• High printing resolution (~20 nm)

3D printed lamellar fiber Bragg grating

Fiber core

Grating

SEM

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Design of grating parameters for LFBG

SEM

Slab thick

• Reflectance vs slab thickness vs reflected wavelength (Python simulation)
• Grating pitch=4 𝛍m
• Maximize reflectance for 1.5 𝛍m wavelength

Mohammed, Zahraa Hummam. "The fresnel coefficient of thin film multilayer using transfer matrix method tmm." In IOP Conference Series: Materials Science and Engineering, vol. 518, no. 3, p. 032026. IOP Publishing, 2019.

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Dual comb interrogation of LFBG

SEM

LFBG

Prism

Core

Cladding

Dual

comb

PD

2.5 μm

Wavelength

Refl.

SEM

Particle

Prism

Core

Cladding

Dual

comb

PD

Wavelength

Refl.

• Grating with and without particle
• Dual comb interrogation
• Reflectance spectra change with time due to particle
• Time resolved dynamics
• Grating pitch limit particle size

Exaggerated scale

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Dual comb interrogation of LFBG : Possibilities

• Time resolved dynamics depends on particle shape
• Classification of particles with ML
• Biosensing in water (river system monitoring)

SEM

Particle

Prism

Core

Cladding

Dual

comb

PD

Wavelength

Refl.

Time dependent

3D printed

optical fiber probe

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Partial Conclusion

• Micro scale
• Micro particle sensor with 3D printing on fiber tip

​

• Macro scale
• Agri-photonic sensor
• Fast atmospheric gas monitoring

Grand scale!

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Distributed Acoustic Sensing (DAS) with fiber

Phase change

Any optical fiber can act as a spatial microphone!

32

Distributed Acoustic Sensing (DAS) : Different sensing

Source : Earthscope consortium

• Traffic
• Earthquakes
• Volcanoes
• Ships
• Whales

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Distributed Acoustic Sensing (DAS) : Whale tracking

20 Hz whale calls

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Distributed Acoustic Sensing (DAS) : Dual comb

• SNR improvement with dual comb
• 2x sensing distance

Li, Jian-Ting, et al. "Coherently parallel fiber-optic distributed acoustic sensing using dual Kerr soliton microcombs." Science Advances 10, no. 3 (2024).

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DAS: Indian public fiber optic networks

Source : Telco and infrastructure

• BharatNet : 690K km (rural fiber backbone)
• National Knowledge Network (NKN) : ~20K km (Educational institution connectivity)
• Railtel : ~60K km (Railway connectivity)
• BSNL : ~1000K km (std internet backbone)
• POWERTEL : ~70K km (along powergrids)

We are sitting on a data goldmine!

36

DAS for cryosphere monitoring

Fibers

Visible and IR image

From Sentinel-2

Rhone glacier (Swiss Alps)

Fiber-optic DAS

• Satellite imaging :
• Large spatial coverage
• Low spatial resolution

​

• Fiber DAS :
• High spatial resolution
• Subsurface monitoring

No fiber-optic DAS in Himalayan glaciers!

Andreas Fichtneret al. "Fibre-optic exploration of the cryosphere." Geophysical Journal International 244, no. 2 (2026)

37

Conclusion

Fiber optics

Frequency comb

Across scales

Across disciplines

Micro

Macro

Grand

Phy

Chem

Bio

Earth Sci

Data Sci

Fiber-tip μ-particle sensor

Agri-photonic sensor

Cryospehere sensor

Inter-species

communication

μ-particle

dynamics

Atmospheric

chemistry

Data classification

Glacial dynamics

Exciting time to do science!

38

Besançon, 20/09/2017

Workshop SUPUVIR

Lille 10/04/2017

​

Winter School on nonlinear photonics

Trento 2018

Thank you for your attention!

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