Periodic Reporting for period 2 - PATTERN (Next generation ultra-high-speed microwave Photonic integrATed circuiTs using advancE hybRid iNtegration)
Reporting period: 2024-03-01 to 2025-08-31
PATTERN combines four different material platforms including InP, LNOI and YIG for photonics and Si for electronics with hybrid integration to cover the complete PIC value chain from components to complete systems. Particularly in PATTERN we propose:
• Development of new PIC building blocks:
Acousto-optics modulators (AOMs) in LNOI platform
Integrated magneto-optics (MO) isolators using the hybrid integration of LNOI and YIG
• Developing world first process design kit (PDK) and assembly design kit (ADK) for microwave photonics at frequencies >100 GHz
• Co-integration of electronics and photonics especially for ultra-speed operations
• Development of 6 demonstrator prototypes by 3 end-users covering wide range of applications from quantum applications to RF-over fiber for 5G and 6G antennas, sub-terahertz wireless antenna and optical phase locked loops (OPLLs) and low noise microwave generation and space communication systems.
• Development of new PIC building blocks:
Acousto-optics modulators (AOMs) in LNOI platform
Integrated magneto-optics (MO) isolators using the hybrid integration of LNOI and YIG
• Developing world first process design kit (PDK) and assembly design kit (ADK) for microwave photonics at frequencies >100 GHz
• Co-integration of electronics and photonics especially for ultra-speed operations
• Development of 6 demonstrator prototypes by 3 end-users covering wide range of applications from quantum applications to RF-over fiber for 5G and 6G antennas, sub-terahertz wireless antenna and optical phase locked loops (OPLLs) and low noise microwave generation and space communication systems.
The consortium had to spend more effort on basic studies before the realization of functional devices with acousto-optics waves and YIG material. CNRS (INSP) demonstrated that is possible to generate Rayleigh acoustic waves at frequencies up to 5GHz (limited by the lithography method) that propagate mainly in the Lithium Niobate film. This was achieved by optimization of the metal layer, the electrode geometry. CNRS (LabSTICC and Alber Fert laboratories) demonstrated deposition of several types of doped YIG films on LNOI. Magneto-optic effect was observed with the most optimized structure. Initial tests of reciprocal phase shift were not conclusive because the YIG layer was also deposited on the output grating couplers. New chips with MZI are being processed. Thanks to a CSEM newly developed polarization rotator, the magneto-optic effect might be observed for both TE and TM polarization. As a complementary approach, PHIX developed a heterogeneously integrated miniature free-space optical isolator on chip depicted below.
PATTERN puts together a comprehensive toolbox for RF from design to application. It covers:
· design and routing of 50 ohm impedance matched RF lines on LUCDEA IPKSS software. Options include rounded angle or mitered 90° angle corner (to prevent impedance drops).
• a newly innovative approach for connecting the PIC based on the connectors being soldered on the PIC. This avoids all the RF losses and impedance mismatches induces by the usual bounding. When better mastered, it could be extended to multiple RF contact connectors.
· dedicated CMOS amplifiers and transimpedance amplifiers for LNOI chip. IMEC tailored the amplifiers to drive GSG LNOI modulator with frequency >100GHz. The CMOS chip is flip-chipped on the LNOI chip with a process developed by CSEM and PHIX. Having an amplifier close to the modulator will allow compensating for the RF losses, relaxes the requirement on the RF power of the signal generator thus making the chip more user friendly
· united methodology to characterize modulators. IMEC, Thales, TAS and UCL realized that a common methodology to measure modulators (EE and EO S-parameters, cable/connectors/probes deembedding, Vp, later intermodulation distortion) was requested to be able to cross check and compare results at the different facilities. A methodology document is thus under preparation to be offered to the community.
Microwave Photonics performed some Kerr comb generation in an optical ring resonator. The figures below show a high resolution Optical Spectrum with the pump laser approaching a resonance (a) in order to initiate the comb formation visible in (b). (d) illustrate the SHG and THG, which are revealed due to scattering inside the ring.
UCL set a THz wireless bridge system that relies on LNOI modulators supporting first high bandwidths and to make it easier to drive low Vπ. The system was for a demonstration of wireless transmission of full HDTV at 200 GHz carrier frequency at UCL’s “Festival of Engineering” in the summer of 2024 with commercially available optical modulators to be replaced by the PATTERN modulator with W-SMP connectors soldered directly onto the LNOI chip.
Thales performed preliminary demonstrations of the effective compensation of the turbulences for the Free Space Comm application with a coherent recombining tree implemented in a LNOI chip. Stable power on the data detection photodiode was demonstrated despite turbulences (from Billault, V., Feugnet, G., Bourerionnet, J., Obara, K., Zarebidaki, H., Sattari, H., & Brignon, A. in 2024 IEEE Photonics Conference (IPC) (pp. 1-2). IEEE.). In this demonstration, the photodiodes were external and a new version is going to be tested with photodiodes integrated by PHIX on the chips.
The other demonstrators are also under development but will be reported at the end of the project.
PATTERN puts together a comprehensive toolbox for RF from design to application. It covers:
· design and routing of 50 ohm impedance matched RF lines on LUCDEA IPKSS software. Options include rounded angle or mitered 90° angle corner (to prevent impedance drops).
• a newly innovative approach for connecting the PIC based on the connectors being soldered on the PIC. This avoids all the RF losses and impedance mismatches induces by the usual bounding. When better mastered, it could be extended to multiple RF contact connectors.
· dedicated CMOS amplifiers and transimpedance amplifiers for LNOI chip. IMEC tailored the amplifiers to drive GSG LNOI modulator with frequency >100GHz. The CMOS chip is flip-chipped on the LNOI chip with a process developed by CSEM and PHIX. Having an amplifier close to the modulator will allow compensating for the RF losses, relaxes the requirement on the RF power of the signal generator thus making the chip more user friendly
· united methodology to characterize modulators. IMEC, Thales, TAS and UCL realized that a common methodology to measure modulators (EE and EO S-parameters, cable/connectors/probes deembedding, Vp, later intermodulation distortion) was requested to be able to cross check and compare results at the different facilities. A methodology document is thus under preparation to be offered to the community.
Microwave Photonics performed some Kerr comb generation in an optical ring resonator. The figures below show a high resolution Optical Spectrum with the pump laser approaching a resonance (a) in order to initiate the comb formation visible in (b). (d) illustrate the SHG and THG, which are revealed due to scattering inside the ring.
UCL set a THz wireless bridge system that relies on LNOI modulators supporting first high bandwidths and to make it easier to drive low Vπ. The system was for a demonstration of wireless transmission of full HDTV at 200 GHz carrier frequency at UCL’s “Festival of Engineering” in the summer of 2024 with commercially available optical modulators to be replaced by the PATTERN modulator with W-SMP connectors soldered directly onto the LNOI chip.
Thales performed preliminary demonstrations of the effective compensation of the turbulences for the Free Space Comm application with a coherent recombining tree implemented in a LNOI chip. Stable power on the data detection photodiode was demonstrated despite turbulences (from Billault, V., Feugnet, G., Bourerionnet, J., Obara, K., Zarebidaki, H., Sattari, H., & Brignon, A. in 2024 IEEE Photonics Conference (IPC) (pp. 1-2). IEEE.). In this demonstration, the photodiodes were external and a new version is going to be tested with photodiodes integrated by PHIX on the chips.
The other demonstrators are also under development but will be reported at the end of the project.
We believe the work on acoustic wave and YIG is quite innovative. There are reports of acoustic wave generation on LNOI but the wafer was in sapphire as this helps maintaining the acoustic wave in the Lithium Niobate layer, However, this is not a commercially available substrate. On the contrary, the work performed in PATTERN was demonstrated on standard LNOI substrates thus compatible with CSEM platform. PATTERN also demonstrated that YIG deposition on LNOI is possible, an open question before PATTERN. However, we believe that further research activities will be necessary to demonstrate functional devices. For optical isolator, the heterogeneously integration of a miniature free-space optical isolator on chip depicted is also rather innovative approach. It illustrates how PIC and non-PIC system can be combined to exploit the best of each world. This approach could be pursued to integrate for instance a miniature gas cell for laser referencing. The PIC would include the modulators, splitters, detectors while the gas cell will be free-space. On the longer term, such an approach could be even envisioned for cold atom sensors.
Soldered connectors was quite risky as the mechanical robustness was totally unclear. However, PHIX mastered the mounting and securing quite well to make it a reality. It could be one of the most efficient connecting solution as it removes the bounding which are usually one of the main bottlenecks to scale up the frequency. Worth noting, this approach is suitable for all type of connectors so it can be adapted to the newly 0.4-0.8 mm connectors under developments listed in the table below. Indeed, these connectors have outer dimensions similar to 1-mm connectors to ease adoption for now. However, the RF part is getting smaller and smaller as the RF frequency increases so nothing prevents the overall dimensions to decrease as well. This makes our solution even more attractive as it decreases the required space on the TFLN chip.
Soldered connectors was quite risky as the mechanical robustness was totally unclear. However, PHIX mastered the mounting and securing quite well to make it a reality. It could be one of the most efficient connecting solution as it removes the bounding which are usually one of the main bottlenecks to scale up the frequency. Worth noting, this approach is suitable for all type of connectors so it can be adapted to the newly 0.4-0.8 mm connectors under developments listed in the table below. Indeed, these connectors have outer dimensions similar to 1-mm connectors to ease adoption for now. However, the RF part is getting smaller and smaller as the RF frequency increases so nothing prevents the overall dimensions to decrease as well. This makes our solution even more attractive as it decreases the required space on the TFLN chip.