082 - Low noise frequency tunable microwave generation using photonic integrated microcombs

Ground based optical free space communication experiments have enabled >1 Tb/second communication links based on the multitude of carriers that are individually modulated to carry information. Optical frequency combs with line spacings that match the ITU grid have potential to implement free space communications in space. 

These advances utilize the unique features of microcombs: in contrast to conventional mode locked lasers, microcombs (also called Kerr frequency combs) can operate with line spacings directly in the microwave range, relevant to optical communications, can accommodate clock signals, and can output spectra that cover a full optical octave, which are necessary for coherent microwave-to-optical frequency links. Despite major advances in microcombs, a challenge has been to develop microcombs that have sufficient power for direct use of the individual comb lines for free space-based communications, which necessitates the integration of amplifiers. Recent advances in both the development of heterogeneous integration of Lithium Niobate on Silicon Nitride for high-speed modulators, as well as the development of erbium on chip amplifiers, make high power transceivers that combine on a single die, or use multiple dies, to realize a wafer scale, foundry compatible, and low Size Weight & Power (SWaP) and power efficient transmitters and receivers.

Today’s lowest noise optoelectronic oscillators achieve exceptionally low phase noise and are based on optical frequency division using femtosecond laser combs. However, these high performing solutions sacrifice spectral purity for size, weight, and power as well as environmental sensitivity, which makes them unsuitable for space applications.  Over the past decade a new technology for frequency comb generation, soliton micro-combs, has emerged. The miniaturization and integration of frequency combs through lithographic microelectronic fabrication have established a new paradigm in optical microsystem capability, cost, performance, and manufacturability.
 

Objective: One objective shall be to demonstrate the advantages of photonic integrated micro-combs and develop integrated laser sources with ultra-low phase noise performance to explore the implementation possibilities within PNT applications. 

As a preliminary step the phase noise performance shall meet or exceed that of the best discrete oscillator modules yet occupy a compact volume typical of a far noisier chip-scale voltage-controlled oscillators (VCO).

The proposed development also requires a demonstration of wafer scale (manufacturable) photonic microwave generation systems. These shall provide low noise microwaves, based on the conversion of a soliton pulse stream into a microwave signal using direct detection with fast commercial diodes. The approach shall be based on recent advances that have demonstrated that soliton microcombs can generate low noise X- and K-band microwaves and the demonstration of hybrid and heterogeneous integration of this technology. 

The platform, based on the ultra-low loss integrated photonics circuits based on Silicon Nitride shall also include MEMS based Aluminium Nitride (AlN) technology for ultrafast tuning of the generated microwaves over >25% of the carrier frequency for fast frequency reconfiguration. Together a demonstration of a new class of low noise microwave oscillators based on photonic integrated circuits based micro-combs shall be developed.

Finally, the capability of this type of platform to perform both transmission and receiver functions shall be included to position this technical approach for applications in free-space optical communication and ranging.

Description of innovation: The proposed project approach is to lay the foundation for space based optical communications in a navigation context, by developing a frequency comb-based transmitter for coherent optical telecommunication, which is space compatible, compact and in which all key components are based on photonic integrated circuits.  
 

Tasks: Demonstrate: 

1. Greater than 1Tb/second data rate in a laboratory communication experiment
2. Optical Analogue to Digital Conversion (ADC) and Photonic assisted ADC
3. The transmission and detection capabilities for typical free space applications in LEO/MEO
4. Optical Oscillators delivering low jitter clock signals (Photonic Integrated Low Noise Microwave generation)
5. Photonic sampling (photonic RADAR and subnoise detection)
6. Laser oscillators using hybrid integrated III-V lasers (including laser integration and photonic packaging)

Expected output of Activity

The main output shall be the demonstration of the capability of photonically integrated optical frequency combs in the receiver and transmitter path for implementation in PNT systems for Optical ADC, low jitter clock signals and photonic assisted detection systems.