FINAL PRESS RELEASE

The cFLOW project reaches successful conclusion!

cFLOW is a H2020 European project consisting of a consortium of 7 partners:

  • III-V Lab (France), coordinator
  • KTH (Sweden)
  • ENS (France)
  • mirSense (France)
  • CSEM (Switzerland)
  • TUW (Austria)
  • FOI (Sweden)

cFLOW set itself the ambitious goal to develop an integrated photonic platform based on Quantum Cascade technology for coherent free-space optical communications (FSOC) in the Long-wave infrared (LWIR) transmission window. In particular, the technology developed in the project operates at a wavelength λ = 9.124 μm (approx. 30 THz), which has been identified as optimal wavelength for LWIR based optical links by numerical studies on atmospheric channel transmission. Numerical modeling confirmed that atmospheric interference and attenuation is minimal in the LWIR, thus providing an ideal channel for free-space communication between earth and space, but also for direct communication established on ground.

The 9-μm-based technology developed in the framework of cFLOW combines two main advantages with respect to other competing FSOC technologies established in the mm/THz or in the 1.55 μm telecom domains: an optical carrier at 30 THz for high capacity and long reach communication links, and a channel that is considerably less sensitive and fluctuating in adverse atmospheric conditions. One of the main challenges in developing such a technology was the low maturity of the devices operating at such a wavelength range, the lack of packaging standardization, and the complexity of advanced high-speed modulation techniques. Furthermore, high performance was typically confined to cryogenic temperature operation at these wavelengths, due to thermodynamic limitations or standard direct detection schemes.

The cFLOW project tackled the problem by bringing photonic integrated circuits (PIC) concepts from the telecom industry to Quantum Cascade technology to create an emitter and receiver PIC.

This required the development of several novel components and concepts:

  • A high power, single mode Quantum Cascade Laser (QCL) and a Semiconductor Optical Amplifier (SOA) on a Master Oscillator Power Amplifier (MOPA) architecture, to produce a sufficiently strong optical signal;
  • A compact integrated waveguide Stark modulator to encode information on the QCL signal;
  • Broadband low-loss plasmonic waveguides and multimode interferometers for beam routing, splitting and combining across the photonic platforms;
  • Quantum Cascade Detectors (QCD) in ridge configuration with state-of-the-art performance at LWIR wavelengths;
  • A bi-functional QCLD material for monolithic integration of both laser source and QCD detectors on the same photonic chip;
  • Metamaterial-based versions of the Stark modulator and the QCD, which enabled even higher data transmission speeds;
  • Heterogeneous and monolithic devices integration approaches to realize the source and receiver photonic integrated chips.
  • Development of test bench systems for high transmission rate FSO with Quantum Cascade components and improved DSP algorithms for coding/decoding of multilevel modulated signals

These components were then used to perform free-space data transmission experiments at LWIR wavelengths, employing different modulation formats (OOK, PAM4, …) and architectures. Groundbreaking record data rates of 55 Gbit/s (below 6.25% HD FEC limit) were achieved, and other modulation standards and different limits were tested, and in several cases data rate records were broken by cFLOW.

The partners are now eager to continue the collaboration beyond the project by taking the next step and assembling a first prototype that integrates all the devices, provides a 9-µm coherent link with a target data rate of 20 Gbit/s which can operate at room temperature in real atmospheric conditions.