Lille, FRANCE

Fiber frequency combs for environmental sensing

Debanuj Chatterjee

Marie Curie Postdoctoral Researcher @ University of Lille, France

11^th September 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

Fiber frequency combs for environmental sensing

Technology

Application

Debanuj Chatterjee

Marie Curie Postdoctoral Researcher @ University of Lille, France

11^th September 2026

4

Lille, FRANCE

Fiber

Technology

What is an optical fiber?

• Thin cylindrical waveguide (Silica)
• Carry light over long distance

½ Nobel Prize

2009

Charles Kao

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

5

Lille, FRANCE

Fiber

Technology

What is an optical frequency comb?

Frequency comb

• Equally spaced coherent frequency modes
• Ruler of light frequencies

Ultrafast optics

6

Motivation

• Generation of multiple frequency combs in fiber platform

• High mutual coherence
• Frequency agility

Fiber Drawing Facility

What to do with multiple fiber frequency combs?

7

Besançon, 20/09/2017

Workshop SUPUVIR

Lille 10/04/2017

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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

8

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.

9

Dual-comb applications

Autonomous cars

Precise distance metrology

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

Atmospheric monitoring

Label-free imaging

Fast spectroscopy of gasses

Dual-comb CARS

• Roger Ding, et al, Optica sensing congress 2025
• Eber, Alexander, et al. Optics Express 32, no. 4 (2024): 6575-6586.

• Takuro Ideguchi, et al. Nature, 2013.
• B. Liu et al. Photonics (Vol. 13, No. 2, p. 173). MDPI AG 2026.

Deep tissue imaging

Optomechanical sensing

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

Distributed remote sensing

Dual-comb fiber DAS

THz imaging

THz generation and detection

• Li, Jian-Ting, et al. Science Advances 10, no. 3, 2024
• Wang et al,, Journal of Lightwave Technology, vol 44, Issue 5, 2021

Jerez, Borja, et al. Optics Letters 44, no. 2 (2019)

How to generate the dual-comb?

10

Besançon, 20/09/2017

Workshop SUPUVIR

Lille 10/04/2017

EOM dual-combs vs mode-locked dual-combs

• High power/short pulses
• High mutual coherence
• Complex f_CEO locking electronics
• Cumbersome to operate
• Not agile in frequency
• Low pulse repetition rate (~100 MHz)

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B. Lomsadze, et al, "Tri-comb spectroscopy," Nature Photonics 12, 676 (2018).

J. Kim, et al. J. Phys. Chem. Lett. 11, 2864–2869 (2020).

• Mode-locked laser (MLL) dual-combs

f_CEO

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Fiber-based ultrashort dual comb source

FS

80%

20%

f_shift

10 GHz-Δf

CW Laser

10 GHz

EOMC 1

EOMC 2

lock

lock

RFS

RFS

RFS

1545 nm

50%

50%

FBC

Dual-comb

light

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Fiber-based ultrashort dual comb source

FS

80%

20%

f_shift

10 GHz-Δf

CW Laser

10 GHz

EOMC 1

EOMC 2

lock

lock

RFS

RFS

RFS

1545 nm

50%

50%

FBC

Dual-comb

light

EOFC : Electro-optic frequency comb, RFS : Radio frequency synthesizer, IM: intensity modulator, PM : Phase modulator, EDFA: Erbium doped fiber amplifier, CFBG : chirped fiber Bragg grating, FBC : fiber beam combiner, FS : frequency shifter, C: circulator, HNLF : highly nonlinear fiber, SMF : single mode fiber, PS : Phase shifter

3 ps pulse

Norm. disp.

Anomalous disp.

Fabio Motetta,

PhD student

Dual comb

First Raman signal day

D Chatterjee et al, (under review in ACS Photonics), arXive:2609.08416

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Bi₁₂GeO₄

f=10 GHz, Δf=500 kHz

Lens

SMF

f

FBC

Collection

PD

Oscilloscope

Lens

SPF

Sample

LPF

f-Δf

Post processing

Shifted by f_IQ

Cut combs

Anti-Stokes combs

Anti-Stokes combs

Down-conversion

f_cut

Dual-comb coherent anti-Stokes Raman scattering (CARS) : PoC

• BGO has low frequency Raman modes : 60 cm^-1, 90 cm^-1
• Optically transparent at 1550 nm

Electronic+Raman combs

Retrieve Raman modes

Interferogram

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56 cm^-1

86 cm^-1

f= 10 GHz

∆f= 0.5 MHz

500 averages

Dual-comb CARS of BGO : Results

Two Raman modes

Short Time Fourier Transform

Supergaussian window

Fourier Transform

Fourier Transform

slide

90 cm^-1

60 cm^-1

High freq pass filtering

Ultrafast interferogram acquisition rate so far (required for fast imaging)

• Beating between Raman modes
• Decayed oscillation

D Chatterjee et al, (under review in ACS Photonics), arXive:2609.08416

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Dual-comb CARS : State-of-the-art (no pulse programming)

Achievements :

• Highest interferogram acquisition rate in dual comb CARS (without time-programming)
• All fiber configuration (compact)

Future :

• Burst mode EO operation to reduce average power with same pulse duration (required for biological samples)
• Shorter pulse duration (using dispersion engineering in compression fibers)

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Dual-comb CARS : Long term perspectives

• Fast, compact label-free imaging systems (low-frequency Raman)

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• Virus

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• 2D materials like MoS₂

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• Semiconductor materials

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​

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• Si : 521 cm^-1
• GaAs : 290 cm^-1
• D.R.Carlson,D.D.Hickstein,andS.B.Papp,“Broadband,electro-optic,dual-comb spectrometer for linear and nonlinear measurements,” Opt.Express 28 (2020).

​

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• Trilayer MoS₂: 22 cm^-1, 42 cm^-1
• Y. Zhao, X. Luo, H. Li, et al., “Interlayer breathing and shear modes in few-trilayer mos2 and wse2,” Nano letters 13,1007–1015 (2013).

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• Low frequency acoustic vibration modes in virus : ~ 0.5 cm^-1
• Y. Zhang, et al., “Nanoscopic acoustic vibrational dynamics of a single virus captured by ultrafast spectroscopy,” Proc. National Acad. Sci. 122 (2025).

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Fiber-based ultrashort dual comb source : 3 ps tap

FS

80%

20%

f_shift

10 GHz-Δf

CW Laser

10 GHz

EOMC 1

EOMC 2

lock

lock

RFS

RFS

RFS

1545 nm

50%

50%

FBC

Dual-comb

light

D Chatterjee et al, (under review in ACS Photonics), arXive:2609.08416

18

Motivation : Deep tissue imaging

Depth

Spatial resolution

Temporal resolution

Tissue

Miller, et al, "Deep tissue imaging with multiphoton fluorescence microscopy." Current opinion in biomedical engineering 4 (2017): 32-39.

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Optical vs Acoustic

Contrast

Acoustics

vs

Depth

❌

Contrast

Depth

❌

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Photoacoustic 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

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Photoacoustic sensing : Challenge

3 µm

Pressure sensitive Fabry Perot Cavity (FPC)

T. Chaigne

J. Saucourt, et al. "Fast interrogation wavelength tuning for all-optical photoacoustic imaging." Op. Exp.  (2023)

Thickness

inhomogeneities

Fabry-Perot Resonance frequency varies >200 GHz across surface

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Photoacoustic sensing : Parallel interrogation with dual combs

• Interrogate with a comb rather than CW
• Near each point’s FP resonance, there is at least a few comb lines for interrogation
• Spectro spatial mapping
• Dual combs enable fast interrogation of any point on the surface
• No tuning the interrogation wavelength

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How to solve?

Interrogation comb line

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Fiber based broadband ultrasound sensor

⇨Monitoring of 10 MHz acoustic waves (3 comb lines)

• 10 MHz signal retrieved

Sliding window

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

PoC demonstration

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Partial Conclusion

• Enabling Technology
• Fiber optics
• Frequency combs
• Platform
• Fiber-based dual-comb spectrometer
• Applications
• Dual-comb CARS for fast, compact and label-free imaging systems
• Ultrasound sensing for photoacoustic deep-tissue imaging

Future research

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What else can we do with a fiber dual-comb source?

High impact for society

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Research proposition : Microsonograph for ultrasound sensing

⇨Professor Shonku by Satyajit Ray

MICROSONOGRAPH

Ultrasound

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Opto-mechanical microsonograph for plants

⇨ Ultrasounic communication and sensing in plants

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Advanced microsonograph

Sound card

Isolated sensing

VS

Agriculture

Dense network of microphones!

• Costly
• EM interference
• High signal loss

29

Fiber-based distributed microsonograph

Sound card

Distributed sensing

Isolated sensing

VS

MUX

Fiber switch

Fiber dual-comb

~km

1XN

Ultrasound

sensor

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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

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Distributed sensing : 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)

A large part of public fiber infrastructure (BharatNet 70%) is unoperational

CAG's Audit Report No. 19 of 2026, Union Government

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Agri-photonic sensor (national strategic importance)

Agriculture

What else affects agriculture (and society by large)?

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Drought

Forest fire

Extinction

Ice sheet melting

Flood

Extreme events

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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?

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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

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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 in the future!

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Open path dual comb spectroscopy : Challenges & Solution

• No alignment error
• Fiber minimize vibration in the collimators
• 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)

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⇨Short path length proposal

Fiber

Movement

Movement

Solution?

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Potential collaboration at IIT BBS

Dr. Rajan Jha

Dr. Raktim Haldar

Spectrally multiplexed acoustic sensing with dual comb fiber hydrophones

Quantum state characterization with dual frequency combs

Dual combs

Hydrophone

FBG2

Hydrophone

FBG3

Hydrophone

FBG1

Fiber link

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Conclusion

Fiber optics

Frequency comb

Dual comb CARS for fast, compact, label-free imaging

Platform

Dual comb ultrasound sensor for high-resolution deep-tissue imaging

Dual comb ultrasound sensor for distributed acoustic sensing for agriphotonic sensing

Open path UAV mounted dual comb spectroscopy for realtime gas monitoring

Advanced imaging

Distributed environmental sensing

Fiber technology

(lab to field)

40

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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