Fabien Kéfélian

Long-distance frequency transfer over an urban fiber link using optical phase stabilization

We transferred the frequency of an ultra-stable laser over 86 km of urban fiber. The link is composed of two cascaded 43-km fibers connecting two laboratories, LNE-SYRTE and LPL in Paris area. In an effort to realistically demonstrate a link of 172 km without using spooled fiber extensions, we implemented a recirculation loop to double the length of the urban fiber link. The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz linewidth. The fiber-induced phase noise is measured and cancelled with an all fiber-based interferometer using commercial off the shelf pigtailed telecommunication components. The compensated link shows an Allan deviation of a few 10-16 at one second and a few 10-19 at 10,000 seconds.

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 x 10(-15) at one second measurement time and 5 x 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.

Ultralow-frequency-noise stabilization of a laser by locking to an optical fiber-delay line

We report the frequency stabilization of an erbium-doped fiber distributed-feedback laser using an all-fiber-based Michelson interferometer of large arm imbalance. The interferometer uses a 1 km SMF-28 optical fiber spool and an acousto-optic modulator allowing heterodyne detection. The frequency-noise power spectral density is reduced by more than 40 dB for Fourier frequencies ranging from 1 Hz to 10 kHz, corresponding to a level well below 1 Hz2/Hz over the entire range; it reaches 10(-2) Hz2/Hz at 1 kHz. Between 40 Hz and 30 kHz, the frequency noise is shown to be comparable to the one obtained by Pound-Drever-Hall locking to a high-finesse Fabry-Perot cavity. Locking to a fiber delay line could consequently represent a reliable, simple, and compact alternative to cavity stabilization for short-term linewidth reduction.

High-resolution optical frequency dissemination on a telecommunications network with data traffic.

We transferred the frequency of an ultrastable laser over a 108-km-long urban fiber link comprising 22 km of an optical communications network fiber simultaneously carrying Internet data traffic. The metrological signal and the digital data signal were transferred over two different frequency channels in a dense wavelength-division multiplexing scheme. The metrological signal was inserted in and extracted from the communication network using bidirectional off-the-shelf optical add-drop multiplexers. The link-induced phase noise was measured and canceled with a round-trip technique using an all-fiber-based interferometer. The compensated link showed an Allan deviation of a few 10(-16) at 1 s and below 10(-19) at 10,000 s. This work paves the way to a wide dissemination of ultrastable optical clock signals between distant laboratories via the Internet.

An agile laser with ultra-low frequency noise and high sweep linearity

We report on a fiber-stabilized agile laser with ultra-low frequency noise. The frequency noise power spectral density is comparable to that of an ultra-stable cavity stabilized laser at Fourier frequencies higher than 30 Hz. When it is chirped at a constant rate of approximately 40 MHz/s, the max non-linearity frequency error is about 50 Hz peak-to-peak over more than 600 MHz tuning range. The Rayleigh backscattering is found to be a significant frequency noise source dependent on fiber length, chirping rate and the power imbalance of the interferometer arms. We analyze this effect both theoretically and experimentally and put forward techniques to reduce this noise contribution.

Multiplexed optical link for ultra-stable frequency dissemination

We transfer the frequency of an ultra-stable laser over a cascaded optical link comprising two compensated links of 150 km and a repeater station. Each link passes through two important nodes of the telecommunication network and includes 114 km of Internet fiber simultaneously carrying data traffic, through a dense wavelength division multiplexing scheme. The metrological signal is inserted in and extracted from the communication network using bidirectional optical add-drop multiplexers. The repeater station is working independently without any remote control. The phase noise on the two links is compensated with the usual round-trip technique. The 300-km multiplexed cascaded link shows an Allan deviation of 3×10−15 at one second and 7×10−20 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.

High-resolution optical frequency dissemination on a telecommunication network

We transferred the frequency of an ultrastable laser over a 108-km-long urban fiber link comprising 22 km of an optical communication network fiber simultaneously carrying Internet data traffic. The metrological signal and the digital data signal were transferred over two different frequency channels in a dense wavelength-division multiplexing scheme. The metrological signal was inserted in and extracted from the communication network using bidirectional off-the-shelf optical add-drop multiplexers. The link-induced phase noise was measured and canceled with a round-trip technique using an all-fiber-based interferometer. The compensated link showed an Allan deviation of a few 10−16 at one second and below 10−19 at 10,000 s This work paves the way to a wide dissemination of ultrastable optical clock signals between distant laboratories via the Internet network.

Ultra Low Frequency Noise Laser Stabilized On Optical Fiber Spool

In this paper, the development of an ultra low frequency noise laser has been presented. This laser is obtained by frequency stabilizing a fiber laser to a 1-km fiber length-unbalanced Michelson interferometer with heterodyne detection configuration. The laser frequency noise power spectral density is reduced by more than 40 dB for Fourier frequencies ranging from 1 Hz to 10 kHz, corresponding to a level well below 1 Hz2/Hz over the whole range. Between 30 Hz and 10 kHz, the frequency noise of the laser is shown to be comparable to that obtained by Pound-Drever-Hall locking of the laser to an ultra-stable cavity. Moreover this laser has the great advantage of no optical alignment and no polarization adjustment due to the utilization of an all-fiber system. It is therefore intrinsically more compact, light, robust and flexible than cavity-based systems. This stabilization technique allows the frequency tunability of the low noise laser.

Ultra low frequency noise laser by locking to an all-fibered interferometer

Very low frequency noise lasers are important tools for many applications such as high-resolution spectroscopy, optical atomic clock local oscillator, interferometric sensor (including gravitational waves detection), and coherent optical communications systems.

Long-distance ultrastable frequency transfer over urban fiber link: toward a European network

Experiments of transmission of sub-Hz cavity-stabilized 1542 nm laser frequency using a pair of 43 km dark fibers in urban environment are reported on successively 86 km and 172 km, with fractional frequency instability in the 10-19 range. A new approach is then introduced consisting in using part of an optical telecommunications network carrying simultaneously data traffic using a DWDM scheme to multiplex the metrological signal. This method is experimentally implemented using 22 km of fiber linking Université Paris 13 to its internet access point without degradation of the link instability. We finally present a project of large scale link between Paris and the German border using RENATER network which could constitute the first step of the building of a European optical network for ultrastable frequency dissemination and comparison.