PISSARRO focused on 4 pillars:
(I) Investigation of the photogalvanic effect in SiN: we performed studies on how the self-organized inscription of gratings is influenced by temperature, waveguide length and optical power. We quantified grating decay with temperature and showed good stability at room temperature. We observed the existence of a power threshold to the process. As an important step in understanding the coherent photogalvanic effect (CPGE), we imaged inscribed gratings in various devices using two photon microscopy. The CPGE can lead to gratings with very short periods we allowed us to demonstrated backward SHG with some of the highest efficiencies ever achieved on-chip. Finally, we established and confirmed experimentally a generalized model for the CPGE beyond SHG, showing that multiple gratings can be simultaneously inscribed and allowing cascaded frequency conversion processes in a single device.
E. Nitiss et al. ACS Photonics 7 (1), (2020); O. Yakar, et al. Laser & Photonics Reviews 16 (12), 2200294 (2022), J. Hu, et al. Science Advances 8 (50), eadd8252 (2022)
(II) Waveguide engineering: we proved that QPM is automatically satisfied between the pump and its SH, completely uncoupled from waveguide dispersion, a unique feature of the process self-organization. We showed that dispersion can still be a use to engineer the conversion process bandwidth. We validated our findings experimentally showing that narrow band and wideband operation without sacrificing efficiency. We combined waveguide engineering and the flexibility of the all optical poling to demonstrate other three wave mixing effects such as DFG. This allows to inscribe gratings for linking three wavelengths between 800 nm and 2000nm using only a single writing beam in the telecom.
E. Nitiss, et al. Photonics Research 8(9), (2020); E. Sahin, et al., Nanophotonics 10 (7), (2021)
(III) Improving efficiencies: We have been investigating ways to increase efficiencies by self-seeding or externally seeding the process which also improves speed and decrease the power requirements of the pump and allow to pole short devices. In an other significant step to increase efficiencies, we demonstrated that all optical poling can occur in microresonator and showed for the first time QPM for SHG in SiN microrings. Beyond the first observations we went on to further engineering of the ring for deterministic and high output power operation.
E. Nitiss et al. Nature Photonics, 16, (2022); E. Nitiss, et al. Opt. Express 31, (2023)
(IV) Applications: we have shown how SiN waveguides can process femtosecond pulses by combining octave spanning supercontinuum and SHG. This full SiN scheme allowed for detecting frequency comb carrier envelope offset frequency. We also demonstrated a hybrid SHG source based on the combination of a self injection locked DFB and an optically poled ring, for a standalone compact high coherence light source. Finally we extended the concept of poling SiN to thermally assisted electric field poling to write uniform electric fieldsThis has led to the first demonstration of an electro-optic microring modulator in SiN.
R. Dalidet, et al. Optics Express 30 (7), (2022); M. Clementi, et al. Light Sci Appl 12, 296 (2023), B. Zabelich, et al. APL Photonics 9 (1): 016101 (2024)
