In femto-iCOMB, we develop the first integrated femtosecond laser-based frequency comb that can serve as the basis for a wide variety of optical and Radio-Frequency (RF) technologies ranging from high resolution environmental and health sensing to LIDAR and RADAR. femto-iCOMB is based on the successful EIC-pathfinder project FEMTOCHIP, where we demonstrate an integrated high power femtosecond laser enabling extremely low jitter on chip scale. Here, we tam the free running comb from the integrated femtosecond laser with on-chip continuum generation, carrier-envelope and repetition rate locking to an optical reference to become a fully stabilized femtosecond laser frequency comb (FSLFC) with extremely high frequency stability. We use the femto-iCOMB to pursue photonic microwave oscillators for a variety of applications ranging from autonomous driving to ultra-low phase noise oscillators for advanced signal generators and RF-test and measurement equipment and demonstrate these devices in relevant industrial environments for each application. These prototype field tests will validate the TRL levels achieved for each application and together with surveys of potential customers will inform the business case to be made for each potential product line.
Achieving the breakthrough femto-iCOMB technology starting from an integrated femtosecond laser producing already an extremely low jitter optical pulse train, implies a series of further interlinked technical developments in concert with business development. After amplification of its output in four channels, one will be used for conversion into a microwave signal by photodetection with an MUTC photodiode. The second output is used as the optical signal output. The third output will be used to beat the comb with a highly stable MRR-stabilized reference laser and the error signal will be feed back to the heater for repetition rate tuning. The fourth output will be spectrally broadened in a Lithium Niobate waveguide and simultaneously frequency doubled. Where the fundamental and resulting second harmonic spectrally overlap, a beat signal with the carrier-envelope frequency is produced upon photodetection and used to control the dispersion via the heater near the apodized chirped Bragg grating in the MLL. There will be cross talk between these locks and one needs to properly orthogonalize the feedback between the two heaters to achieve stable frequency comb stabilization.
The FSL-FC is intrinsically based on the strongly nonlinear dynamics of the underlying fs laser. It is a major accomplishment to tame the laser dynamics to the desired stable single-pulse per roundtrip operation. There is a myriad of other possible states which are avoided by skilful design of the integrated MLL. We use this already matured integrated ultrashort pulse laser to build on it a FC and apply it to fabricate a greatly miniaturized photonic microwave oscillator based on optical frequency division. Our technology is also of very high power, i.e. at the Watt level, therefore there are many other potential applications that can also be addressed like super continuum generation or frequency conversion to the mid and far-Infrared and actually also UV, since the Al2O3 waveguide we have already in our overall platform is also UV compatible and with Lithium Niobate on the platform we can implement both broadband super continuum generation and UV generation as was demonstrated recently with table-top lasers in Lithium-Niobate waveguides. We are demonstrating the usefulness of integrated FSL-FCs in photonic microwave generation, but it is also straight forward to use these oscillators for chip-scale optical atomic clocks or using two integrated FSL-FCs with slightly tuned repetition rate for dual comb spectroscopy. Skills and talents of many university researchers and company developers are fostered during project implementation. Afterwards, there are plenty possibilities for them to accelerate their careers at CYCLE, LIGENTEC, ALUVIA, their suppliers or users of the technology.
