Periodic Reporting for period 4 - PISSARRO (Photonic integrated devices for second order nonlinear optical processes)
Periodo di rendicontazione: 2023-01-01 al 2023-12-31
Full on-chip photonic integration holds the promise of bringing advanced optical technologies close to end users and enabling mass producible, low cost, and compact devices. Among the various necessary functionalities needed on-chip, efficient optical nonlinearity is key for enabling a wide variety of applications, such as linked to frequency conversion and light generation. Yet, despite remarkable developments of the field in the last years there still seems to be an undeniable trade-off between available device functionality, fabrication and integration costs.
Silicon nitride, with tunable material composition, ultra-low losses from the visible to the mid infrared, and CMOS-fabrication compatible, is now considered one of the most mature photonic material. In its stoichiometric form, Si3N4 is remarkable owing to its excellent linear optical properties which allows for the fabrication of advanced photonic circuitry, meter long waveguides, and high-quality factor microresonators. Si3N4 has also been very successfully exploited for its 3rd order nonlinear properties since Si3N4,due to its amorphous nature, does not exhibit bulk 2nd-order susceptibility. This is a crippling weakness for such promising platform given the range of applications enabled by 2nd order nonlinearity, including three-wave mixing processes and the linear electro-optic effect. While new materials with intrinsic 2nd order nonlinearitiy are actively studied, due to fabrication challenges state of the art equipment still carries 2nd order nonlinear mixing processes off the chip.
PISSARRO aimed at unlocking 2nd order frequency mixing processes in a mature CMOS platform, with the efficiency and flexibility required by many applications. To that end we have studied the all-optical poling process in SiN and demonstrated for the first time optically induced self-organized nonlinear gratings in such platform. We showed that this simple method, applied to standard SiN structures, provides all-optical control and reconfigurability of the nonlinearity essential for simple yet universal designs. We demonstrated some of the missing functionalities in SiN such as efficient and tunable second-harmonic generation, difference-frequency generation, or spontaneous parametric down conversion in waveguides, as well as dynamic and cascaded nonlinear processes in microresonators for extended wavelength conversion and frequency combs generation. The action led to the demonstration of a proof-of-principle hybrid integrated narrow linewidth second harmonic source and opened the path towards electro-optical modulation in SiN. The successful work carried during PISSARRO shows that such advanced nonlinear functionalities can be available in foundry-grade devices and represents a necessary step to move beyond laboratory equipment towards real products.
Silicon nitride, with tunable material composition, ultra-low losses from the visible to the mid infrared, and CMOS-fabrication compatible, is now considered one of the most mature photonic material. In its stoichiometric form, Si3N4 is remarkable owing to its excellent linear optical properties which allows for the fabrication of advanced photonic circuitry, meter long waveguides, and high-quality factor microresonators. Si3N4 has also been very successfully exploited for its 3rd order nonlinear properties since Si3N4,due to its amorphous nature, does not exhibit bulk 2nd-order susceptibility. This is a crippling weakness for such promising platform given the range of applications enabled by 2nd order nonlinearity, including three-wave mixing processes and the linear electro-optic effect. While new materials with intrinsic 2nd order nonlinearitiy are actively studied, due to fabrication challenges state of the art equipment still carries 2nd order nonlinear mixing processes off the chip.
PISSARRO aimed at unlocking 2nd order frequency mixing processes in a mature CMOS platform, with the efficiency and flexibility required by many applications. To that end we have studied the all-optical poling process in SiN and demonstrated for the first time optically induced self-organized nonlinear gratings in such platform. We showed that this simple method, applied to standard SiN structures, provides all-optical control and reconfigurability of the nonlinearity essential for simple yet universal designs. We demonstrated some of the missing functionalities in SiN such as efficient and tunable second-harmonic generation, difference-frequency generation, or spontaneous parametric down conversion in waveguides, as well as dynamic and cascaded nonlinear processes in microresonators for extended wavelength conversion and frequency combs generation. The action led to the demonstration of a proof-of-principle hybrid integrated narrow linewidth second harmonic source and opened the path towards electro-optical modulation in SiN. The successful work carried during PISSARRO shows that such advanced nonlinear functionalities can be available in foundry-grade devices and represents a necessary step to move beyond laboratory equipment towards real products.
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)
(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)
-We established the formation rules of optically written gratings in SiN waveguide, revealing for the first-time important information on the microscopic nature of the induced 2nd order nonlinearity and establishing fundamentally new understanding of the phenomena.
-We showed extreme tunability and reconfigurability of 2nd-order frequency converters in SiN and showed for the first time highly efficient generation in microresonator. We have reached record combined tunability and efficiency, relying on a standard SiN platform that does not require any additional processing.
-We established a generalized model of the effect, predicting the possibility to have multiple simultaneous conversion processes which ee experimentally confirmed. This is a new path towards the generation visible light in SiN by solely requiring a standard telecom light source. We foresee impact for quantum application as well as widely tunable light generation on chip.
-We demonstrated a simple hybrid integrated SHG source on SiN not only with ultra-high conversion efficiency and mW level powers, but also tunable and ultra-narrow linewidth, much beyond what can be reached by standard standalone semiconductor lasers.
-We demonstrated a novel way to bring the electro-optic effect in SiN.
-We showed extreme tunability and reconfigurability of 2nd-order frequency converters in SiN and showed for the first time highly efficient generation in microresonator. We have reached record combined tunability and efficiency, relying on a standard SiN platform that does not require any additional processing.
-We established a generalized model of the effect, predicting the possibility to have multiple simultaneous conversion processes which ee experimentally confirmed. This is a new path towards the generation visible light in SiN by solely requiring a standard telecom light source. We foresee impact for quantum application as well as widely tunable light generation on chip.
-We demonstrated a simple hybrid integrated SHG source on SiN not only with ultra-high conversion efficiency and mW level powers, but also tunable and ultra-narrow linewidth, much beyond what can be reached by standard standalone semiconductor lasers.
-We demonstrated a novel way to bring the electro-optic effect in SiN.