Mid-IR frequency measurement using an optical frequency comb and a long-distance remote frequency reference

We have built a frequency chain which enables to measure the absolute frequency of a laser emitting in the 28-31 THz frequency range and stabilized onto a molecular absorption line. The set-up uses an optical frequency comb and an ultrastable 1.55 $\mu$m frequency reference signal, transferred from LNE-SYRTE to LPL through an optical link. We are now progressing towards the stabilization of the mid-IR laser via the frequency comb and the extension of this technique to quantum cascade lasers. Such a development is very challenging for ultrahigh resolution molecular spectroscopy and fundamental tests of physics with molecules

Ultra-stable long distance optical frequency distribution using the Internet fiber network

We report an optical link of 540 km for ultrastable frequency distribution over the Internet fiber network. The stable frequency optical signal is processed enabling uninterrupted propagation on both directions. The robustness and the performance of the link are enhanced by a cost effective fully automated optoelectronic station. This device is able to coherently regenerate the return optical signal with a heterodyne optical phase locking of a low noise laser diode. Moreover the incoming signal polarization variation are tracked and processed in order to maintain beat note amplitudes within the operation range. Stable fibered optical interferometer enables optical detection of the link round trip phase signal. The phase-noise compensated link shows a fractional frequency instability in 10 Hz bandwidth of 5x10-15 at one second measurement time and 2x10-19 at 30 000 s. This work is a significant step towards a sustainable wide area ultrastable optical frequency distribution and comparison network

Cascaded multiplexed optical link on a telecommunication network for frequency dissemination

We demonstrate a cascaded optical link for ultrastable frequency dissemination comprised of two compensated links of 150 km and a repeater station. Each link includes 114 km of Internet fiber simultaneously carrying data traffic through a dense wavelength division multiplexing technology, and passes through two routing centers of the telecommunication network. The optical reference signal is inserted in and extracted from the communication network using bidirectional optical add-drop multiplexers. The repeater station operates autonomously ensuring noise compensation on the two links and the ultra-stable signal optical regeneration. The compensated link shows a fractional frequency instability of 3 \times 10-15 at one second measurement time and 5 \times 10-20 at 20 hours. This work paves the way to a wide dissemination of ultra-stable optical clock signals between distant laboratories via the Internet network

Phylogeography and Molecular Epidemiology of Yersinia pestis in Madagascar

Plague, caused by the bacterium Yersinia pestis, has been a problem in Madagascar since it was introduced in 1898. It mainly affects the central highlands, but also has caused several large outbreaks in the port city of Mahajanga, after it was reintroduced there in the 1990s. Despite its prevalence, the genetic diversity and related geographic distribution of different genetic groups of Y. pestis in Madagascar has been difficult to study due to the great genetic similarity among isolates. We subtyped a set of Malagasy isolates and identified two major genetic groups that were subsequently divided into 11 and 4 subgroups, respectively. Y. pestis appears to be maintained in several geographically separate subpopulations. There is also evidence for multiple long distance transfers of Y. pestis, likely human mediated. Such transfers have resulted in the reintroduction and establishment of plague in the port city of Mahajanga where there is evidence for multiple transfers both from and to the central highlands. The maintenance and spread of Y. pestis in Madagascar is a dynamic and highly active process that relies on the natural cycle between the primary host, the black rat, and its flea vectors as well as human activity

Quantum cascade laser frequency stabilisation at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared "molecular fingerprint" region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species

Ultra-stable frequency transfer with optical link and application to the phase-stabilization of a mid-infrared laser

Ce manuscrit présente le transfert d’une référence de fréquence optique ultra-stable à un lien optique et son application à la stabilisation en fréquence d’un laser moyen-infrarouge. Un lien optique permet de transférer une fréquence ultra-stable par fibre optique sans dégrader sa stabilité grâce à une compensation du bruit apportée lors de la propagation. Nous avons étendu cette technique à des liens de grande longueur en transférant la référence de fréquence simultanément avec les données du réseau Internet. Ainsi des liens de 300 km puis 540 km ont été démontrés avec une stabilité de l’ordre de 10⁻ ¹⁹ à 10⁴ s. Ce dispositif à été utilisé au LPL pour asservir un laser CO² émettant à 10 µm sur une référence de fréquence développée au LNE-SYRTE, à l’Observatoire de Paris. Celle-ci est constituée d’un laser ultra-stable émettant à 1,54 µm, dont la fréquence est mesurée par rapport aux étalons primaires du LNE-SYRTE grâce à un laser femtoseconde. Cette référence est transférée par un lien optique jusqu’au LPL où elle permet de stabiliser la fréquence de répétition d’un second laser femtoseconde et de mesurer ou contrôler la fréquence d’un laser CO² . Lorsque celui-ci est asservi sur une référence moléculaire (OsO₄), la stabilité est de 4.10⁻¹⁴ à 1 s. Les performances sont encore meilleures lorsque le laser CO² est asservi directement sur la référence optique. Le laser stabilisé pourra ensuite être utilisé pour l’expérience d’observation de la violation de parité dans les molécules chirales développées au LPL. Ceci démontre la faisabilité d’expériences de spectroscopie moléculaire à ultra haute résolution dans les laboratoires ne disposant pas d’étalons de fréquence.This manuscript details the transfer of an ultra-stable optical frequency reference by means of an optical link and its application to the phase-lock of a mid-infared laser. An optical fiber link allows the ultra-stable transfer of a frequency by using a scheme wich compensates the propagation noise. We extended this system to longer links, and transferred the optical frequency reference simultaneously witn internet data. A cascaded link of 300 km and a simple link of 540 km had been demonstrated with a stability of 10⁻ ¹⁹ at 10⁴ s. Such a link as been used to lock a CO² laser at LPL, emitting at 10 µm, to a frequency reference developed at LNE-SRTE, Observatoire de Paris. This reference is an ultra-stable laser, emitting at 1.54 µm, the frequency of wich is measured against the primary standards of LNE-SYRTE by using a femtosecond laser. This reference is tranferred by an optical link to LPL, in order to stabilize the repetition rate of a second femtosecondlaser and to measure or control the frenquency of a CO² laser. When the CO² laser is locked to a molecular reference (OsO₄), the stability is 4.10⁻¹⁴ at 1s. The performances are even better when the CO² laser is locked directly to the optical reference. Then the laser coulb be used for the experiment of observation of the parity violation in chiral molecules, in progress at LPL. This shows the feasability of high resolution molecular spectroscopy experiments in laboratoratories in wich there is no primary standards

Transfert à très haute résolution d'une référence de réquence ultra-stable par lien optique et application à la stabilisation d'un laser moyen-infrarouge

This manuscript details the transfer of an ultra-stable optical frequency reference by means of an optical link and its application to the phase-lock of a mid-infrared laser. An optical fiber link allows the ultrastable transfer of a frequency by using a scheme which compensates the propagation noise. We extended this system to longer links, and transferred the optical frequency reference simultaneously with Internet data. A cascaded link of 300 km and a simple link of 540 km had been demonstrated with a stability of 10-19 at 104 s. Such a link has been used to lock a CO2 laser at LPL, emitting at 10 µm, to a frequency reference developed at LNE-SYRTE, Observatoire de Paris. This reference is an ultra-stable laser, emitting at 1.54 µm, the frequency of which is measured against the primary standards of LNE-SYRTE by using a femtosecond laser. This reference is transferred by an optical link to LPL, in order to stabilize the repetition rate of a second femtosecond laser and to measure or control the frequency of a CO2 laser. When the CO2 laser is locked to a molecular reference (OsO4), the stability is 4.10-14 at 1 s. The performances are even better when the CO2 laser is locked directly to the optical reference. Then the laser could be used for the experiment of observation of the parity violation in chiral molecules, in progress at LPL. This shows the feasibility of high resolution molecular spectroscopy experiments in laboratories in which there is no primary standards.Ce manuscrit présente le transfert d'une référence de fréquence optique ultra-stable grâce à un lien optique et son application à la stabilisation en fréquence d'un laser moyen-infrarouge. Un lien optique permet de transférer un signal ultrastable de fréquence par fibre optique sans dégrader sa stabilité grâce à une compensation du bruit apportée lors de la propagation. Nous avons étendu cette technique à des liens de grande longueur en transférant la référence de fréquence simultanément avec les données du réseau internet. Ainsi des liens de 300 km puis 540 km ont été démontrés avec une stabilité de l'ordre de 10-19 à 104 s. Ce dispositif a été utilisé au LPL pour asservir un laser CO2 émettant à 10 µm sur une référence de fréquence développée au LNE-SYRTE, à l'Observatoire de Paris. Celle-ci est constituée d'un laser ultra-stable émettant à 1,54 µm, dont la fréquence est mesurée par rapport aux étalons primaires du LNE-SYRTE grâce à un laser femtoseconde. Cette référence est transférée par lien optique jusqu'au LPL où elle permet de stabiliser la fréquence de répétition d'un second laser femtoseconde et de mesurer ou contrôler la fréquence d'un laser CO2. Lorsque celui-ci est asservi sur une référence moléculaire (OsO4), la stabilité est de 4.10-14 à 1 s. Les performances sont encore meilleures lorsque le laser CO2 est asservi directement sur la référence optique. Le laser stabilisé pourra ensuite être utilisé pour l'expérience d'observation de la violation de parité dans les molécules chirales développée au LPL. Ceci démontre la faisabilité d'expériences de spectroscopie moléculaire à ultra haute résolution dans les laboratoires ne disposant pas d'étalons de fréquences

Mid-IR frequency measurement using an optical frequency comb and a long-distance remote frequency reference

International audienc

Mid-IR frequency measurement using an optical frequency comb and a long-distance remote frequency reference

International audienc

Mid-IR frequency measurement using an optical frequency comb and a long-distance remote frequency reference

We have built a frequency chain which enables to measure the absolute frequency of a laser emitting in the 28-31 THz frequency range and stabilized onto a molecular absorption line. The set-up uses an optical frequency comb and an ultrastable 1.55 µm frequency reference signal, transferred from LNE-SYRTE to LPL through an optical link. We are now progressing towards the stabilization of the mid-IR laser via the frequency comb and the extension of this technique to quantum cascade lasers. Such a development is very challenging for ultrahigh resolution molecular spectroscopy and fundamental tests of physics with molecules