Time & Frequency Transfer

The Regeneration Laser Station (RLS)

The RLS is a fully automated laser repeater station dedicated to long-distance optical frequency transfer using optical fibers. This unique industry-grade regeneration laser station has been developed in collaboration with LPL (Univ. Paris 13) and LNE-SYRTE (Observatoire de Paris) laboratories, in the frame of the REFIMEVE+ project.

The regeneration of the reference optical signal is achieved thanks to the heterodyne optical phase-locking of an integrated ultra low-noise laser diode on the reference signal. The regeneration station actively compensates for the phase noise accumulated due to the propagation along the fiber. As a result, it is an equipment of choice for state-of-the-art optical clock remote comparisons.

Key features

• Frequency stability at a level of 10^-20
• Compatible with DWDM telecom networks (dark channel and dark fiber).
• Robustness: the frequency lock remains locked for month without any action required from the user. It is robust with regard to temperature variations and vibrations.
• Fully Automated Phase-Lock Loops
• Remote access and real-time data retrieval

iXblue’s solution for optical frequency transfer can be deployed within a few days and has shown to provide uptimes as high as 99 % over a week. This is enabled by the remote and automated operation of the hardware supervised by a global supervision tool. The supervision tool is composed of:

• A supervision software: to monitor and control the REFIMEVE+ performances
• A database: store all the information useful to the network management
• A human-machine interface: for end users, academic teams and the telecom network manager

The supervision software is in charge of

• Monitoring the proper functioning and remotely control the equipment parameters in real-time.
• Detecting and managing bugs and alarms (cycle slips, polarization optimizations, …)
• Uploading the information collected on the field and store in the database (alarm, events, …)
• Administrating and troubleshooting system configurations
• Pre-processing data: outliers detection, Allan Deviation calculation, …

The supervision tool of the REFIMEVE+ network currently monitors more than 150 pieces of equipment (EDFA, RLS, frequency counters). It enables the secured full remote access to all the equipment (RLS, ES, UM, EDFA) via the hosting telecom network infrastructure.

Key features

• Fully secured communication for supervision protocol: SSH, SNMP
• Supervision tool deployable through usual internet connection
• User-friendly webapp interfaces
• Remote access and real-time data retrieval

Typical performances

The Repeater Laser Station (RLS) is a stand-alone system that actively compensates the phase noise introduced by the fiber links and provides an ultra-stable output laser in the ITU channel 44 (1542.14nm) (other wavelengths on demand). It enables also to cascade fiber links in order to set-up long-distance frequency dissemination. It has been designed to be installed in a Telecom network nodes in respect to NF/EN 60950-1 and NF/EN 60825-1 norms. It can work both on a dark channel and on a dark fiber.

Fig. 1: Fractional frequency instability calculated from data recorded with Λ-counter and 1 s gate time versus averaging time. Dark red squares, modified Allan deviation for a compensated 200 km laboratory link; light red circles, modified Allan deviation for the free-running 200 km laboratory link; dark green stars, modified Allan deviation for a short link to estimate the noise floor of the RLS; light green diamonds, modified Allan deviation for the free-running short link.

Fig 2: End-to-end phase fluctuations after propagation over a 680 km fiber link.

Data from F. Guillou-Camago et al., « First industrial-grade coherent fiber link for optical frequency standard dissemination», Applied Optics, Vol. 57, No. 25 (2018)

After several years of industrialization of RLS, iXblue is able to commit to excellent performances.