International audienceWe are designing and realizing an instrument for the spectroscopy of the volatile metabolome of the soil microorganisms. The use of optical telecommunication elements makes it possible to realize a compact source with a wide range of accessible frequencies (100 GHz-1 THz range; 3-33 cm⁻ ¹) with an accuracy of 10⁵ Hz (3.10⁻⁶  cm⁻¹), as well as a low bandwidth detection system. The instrument will discriminate among complex polar molecules. We report on the preliminary performances of parts of the source system

Binet, Francoise

Bondu, Francois

Carré, Anthony

Daburon, Virginie

Ducournau, Guillaume

Frein, Ludovic

Hamel, Cyril

Lampin, Jean-Francois

Loas, Goulc'Hen

HAL-INSU

An optical instrument for the submillimeter spectroscopy of the volatile metabolome

HAL Descartes

Lampin, Jean-François

DABURON, Virginie

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An optical instrument for the submillimeter
spectroscopy of the volatile metabolome
Francois Bondu, Goulc’Hen Loas, Ludovic Frein, Cyril Hamel, Anthony Carré,
Guillaume Ducournau, Jean-François Lampin, Virginie Daburon, Francoise
Binet
To cite this version:
Francois Bondu, Goulc’Hen Loas, Ludovic Frein, Cyril Hamel, Anthony Carré, et al.. An optical
instrument for the submillimeter spectroscopy of the volatile metabolome. 44th International Con-
ference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), Sep 2019, Paris, France.
pp.19149312. ￿hal-02292414￿
Abstract—We are designing and realizing an instrument for 
the spectroscopy of the volatile metabolome of the soil 
microorganisms. The use of optical telecommunication elements 
makes it possible to realize a compact source with a wide range of 
accessible frequencies (100 GHz - 1 THz range; 3-33 cm⁻ ¹) with 
an accuracy of 10⁵ ⁻ ⁶ ⁻ Hz (3.10  cm ¹), as well as a low 
bandwidth detection system. The instrument will discriminate 
among complex polar molecules. We report on the preliminary 
performances of parts of the source system. 
I. INTRODUCTION 
ACKLING the complex  ecological situations of living 
bodies adequate tools. This complexity has multiple 
aspects. No vegetal or animal living organism is on its 
own: it always needs the contribution of diverse communities 
of microorganisms. Most species of microorganisms can not 
be grown alone in Petri dishes, making it hard to pinpoint 
them. Scale laws in ecology suggest that the ratio of known 
species of microorganisms to unknown ones might be a ratio 
of the order of 10⁻ ⁵  [1]. There is a difficulty to match the 
results on microorganism population presence given with the 
genomics techniques compared to the techniques that observe 
living material. The soil itself is a large reservoir of 
microorganisms, with a number of 10  to 10  per gram. ⁶ ⁶ How 
the bacterial diversity and function in soil are linked to biotic 
control is an open issue [2]. The use of new instruments 
targeting the volatile metabolomes of microorganisms may 
contribute to the global comprehension of the possible 
equilibrium or dynamical evolution of complex communities, 
a goal that looks way ahead today. 
The submillimeter spectroscopy has been historically 
developed for astronomy purposes [3], leading to the 
identification of molecules as complex as alanine in the inter 
stellar medium. This technique has not been used, up to now, 
for the analysis of the metabolism of microorganisms. One 
possible reason might be the complexity of operation and 
space requirements of the existing apparatus. Even in the lab, 
the change from one frequency band to another one, with 
various multipliers, amplifiers, connectors, waveguides, is 
tedious. However, the submillimeter spectroscopy would 
present advantageous characters. Contrary to the 
chromatography - mass spectrometry instruments and similar 
apparatus, it does not require heat or high pressures, thus 
promises a better integrity of the complex biological 
molecules. Even more, at low pressure and at room 
temperature, the absorption linewidths reduce to the range of 
some hundreds of kHz, thus simultaneously making a clear 
discrimination between molecules types and conformations 
and improving the signal to noise ratio. 
The analysis of the metabolism of a variety of 
microorganisms requires sensitivity to a wide range of organic 
molecules. The access to a wide range of attainable 
frequencies seems thus to be a desirable target: for one given 
organic molecule, public tables (HITRAN, JPL, CDMS) 
indicate that the absorption peak that gives the maximum 
sensitivity can not be constrained to a restricted frequency 
band. For that prospect, the techniques based on optical 
photomixing [4] seem to be more promising than the 
techniques based on up-conversion of microwave signals [5]. 
We aim to build a compact instrument based on optical 
elements designed for the optical telecommunications. A 
challenge with optical techniques is that the accessible range 
for the frequency of a laser is often a compromise between the 
linewidth and a robust and repeatable operation. We 
demonstrate here that these key elements are simultaneously 
under control, still with simple and compact elements. 
II. RESULTS 
The submillimeter wave synthesizer source is based on 
three commercial fibered distributed feedback laser diodes 
(DFB) at a wavelength of 1.5 μm, cf. figure 1. The frequency 
difference of lasers 1 and 2 is adjustable between DC and 
753 GHz with constant laser output powers, with the change 
of the temperature of the free-running DFB chips. The laser 
lines  are locked to two resonances using the Pound-Drever-
Hall technique [6], with 10’s of MHz bandwidth home-made 
electronics. The frequency difference is then a multiple of 1 
GHz, the free spectral range of the commercial optical 
resonator. The frequency difference of lasers 2 and 3 can be 
swept continuously in a 5-10 GHz range, when this difference 
is controlled with a phase locked loop. Ultimately, the 
submillimeter synthesizer frequency will be the difference 
between lasers 1 and 3, continuously tunable by contiguous 
segments between DC and 763 GHz. A “UTC photodiode” 
and associated antenna, designed and realized for the project, 
have a bandwidth of several hundreds of GHz. 
 
François Bondu1, Goulc’hen Loas1, Ludovic Frein1, Cyril Hamel1, Anthony Carré1, Guillaume 
Ducournau2, Jean-François Lampin2, Virginie Daburon3, Françoise Binet3 
1Institut FOTON - UMR CNRS 6082, Univ Rennes, CNRS, , Rennes, France  
2IEMN - UMR CNRS 8520, Université de Lille 1, Villeneuve d’Ascq, France 
3Ecobio - UMR 6553, Univ Rennes, CNRS, France 
An optical instrument for the submillimeter spectroscopy  
of the volatile metabolome 
T
 
Fig. 1. Principle of the submillimeter spectroscopy instrument. On the left
side, the submillimeter wave synthesizer, based on commercial
telecommunication optical elements, at a wavelength of 1.5 µm. A dedicated
UTC photodiode and antenna convert the optical radiation into a
submillimeter wave in free space. 
Up to now, we have demonstrated experimentally the 
locking loops between laser 1 and 2 and between laser 2 and 3 
separately. Figure 2 shows the performance of the phase noise 
of the beat notes that are measured by photomixers. The phase 
noise will be therefore negligible in the final system, as the 
linewidth of the synthesizer line is of the order of a few 10’s 
of Hz.  
The required accuracy, for spectroscopy, is of the order of 
10 kHz for the radiated submillimeter wave. It seems to be at 
reach. The commercial optical resonator has a 1.6 GHz/K 
sensitivity for one optical carrier. Temperature stabilization at 
1/10th of a degree will be enough to disambiguate the 
interrogated resonance. The beat note accuracy at the 10 kHz 
range should be attained with a temperature control of the 
cavity at a few mK level.  
III. NEXT STEPS 
We are now aiming at showing the performances of the full 
optical submillimeter synthesizer, and then at the detection 
system. 
REFERENCES 
 
[1] K. J. Locey et J. T. Lennon, « Scaling laws predict global microbial 
diversity », Proc. Natl. Acad. Sci., vol. 113, no 21, p. 59705975, mai 
2016. 
[2] C. Monard, P. Vandenkoornhuyse, B. Le Bot, et F. Binet, « Relationship 
between bacterial diversity and function under biotic control: the soil 
pesticide degraders as a case study », ISME J., vol. 5, no 6, p. 
10481056, juin 2011. 
[3] F. C. De Lucia, « The submillimeter: A spectroscopist’s view », J. Mol. 
Spectrosc., vol. 261, no 1, p. 117, mai 2010. 
[4] F. Hindle et al., « Widely tunable THz synthesizer », Appl. Phys. B, vol. 
104, no 4, p. 763, août 2011. 
[5] C. F. Neese, I. R. Medvedev, G. M. Plummer, A. J. Frank, C. D. Ball, et 
F. C. D. Lucia, « Compact Submillimeter/Terahertz Gas Sensor With 
Efficient Gas Collection, Preconcentration, and ppt Sensitivity », IEEE 
Sens. J., vol. 12, no 8, p. 25652574, août 2012. 
[6] A. Hallal, S. Bouhier, et F. Bondu, « Synthesis of a 30-Hz Linewidth 
Wave Tunable Over 500 GHz », IEEE Trans. Microw. Theory Tech., 
vol. 65, no 4, p. 13671371, avr. 2017. 
 
 
Fig. 2. Performance of the phase noise of two subsets of the frequency
synthesizer source.  


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An optical instrument for the submillimeter spectroscopy of the volatile metabolome

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