Title: Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures
Abstract Nanophotonics research has focused recently on the ability of nonlinear optical processes to mediate and transform optical signals in a myriad of novel devices, including optical modulators, transducers, color filters, photodetectors, photon sources, and ultrafast optical switches. The inherent weakness of optical nonlinearities at smaller scales has, however, hindered the realization of efficient miniaturized devices, and strategies for enhancing both device efficiencies and synthesis throughput via nanoengineering remain limited. Here, we demonstrate a novel mechanism by which second harmonic generation, a prototypical nonlinear optical phenomenon, from individual lithium niobate particles can be significantly enhanced through nonradiative coupling to the localized surface plasmon resonances of embedded gold nanoparticles. A joint experimental and theoretical investigation of single mesoporous lithium niobate particles coated with a dispersed layer of ~10 nm diameter gold nanoparticles shows that a ~32-fold enhancement of second harmonic generation can be achieved without introducing finely tailored radiative nanoantennas to mediate photon transfer to or from the nonlinear material. This work highlights the limitations of current strategies for enhancing nonlinear optical phenomena and proposes a route through which a new class of subwavelength nonlinear optical platforms can be designed to maximize nonlinear efficiencies through near-field energy exchange. more »« less
Rusing, M.; Roeper, M.; Amber, Z.; Kirbus, B.; Eng, L.M.; Zhao, J.; Mookherjea, S.
(, 2020 Joint Conference of the IEEE International Frequency Control Symposium and International Symposium on Applications of Ferroelectrics (IFCS-ISAF))
null
(Ed.)
Ultra-short poling periods of 1 μm and below in lithium niobate will allow nonlinear optical devices with operation to the UV regime or narrow-band counter-propagating single-photon generation. However, fabrication of such periods in bulk Lithium Niobate penetrating the complete modal areas of waveguides has been challenging. In this work, we demonstrate the fabrication of periodic domain grids with submicrometer periodicity in 300 nm x-cut thin-film lithium niobate. The poling was achieved through application of a single, shaped electrical pulse and electrodes fabricated with a combination of electron-and direct laser-writing lithography. The poling results were investigated with piezo-response force microscopy and second-harmonic microcopy and indicate the poled domains to penetrate fully across the complete film thickness. This will enable the fabrication of novel nonlinear optical devices combining the high efficiency of thin films with ultra-short domain periods.
Thin-film lithium niobate is an attractive integrated photonics platform due to its low optical loss and favorable optical nonlinear and electro-optic properties. However, in applications such as second harmonic generation, frequency comb generation, and microwave-to-optics conversion, the device performance is strongly impeded by the photorefractive effect inherent in thin-film lithium niobate. In this paper, we show that the dielectric cladding on a lithium niobate microring resonator has a significant influence on the photorefractive effect. By removing the dielectric cladding layer, the photorefractive effect in lithium niobate ring resonators can be effectively mitigated. Our work presents a reliable approach to control the photorefractive effect on thin-film lithium niobate and will further advance the performance of integrated classical and quantum photonic devices based on thin-film lithium niobate.
Nagy, Jonathan_Tyler; Reano, Ronald_M
(, Optical Materials Express)
Periodically poled second-order nonlinear materials with submicrometer periods are important for the development of quasi-phase matched backward-wave nonlinear optical processes. Interactions involving counter-propagating waves exhibit many unique properties and enable devices such as backward second harmonic generators, mirrorless optical parametric oscillators, and narrow-band quantum entangled photon sources. Fabrication of dense ferroelectric domain gratings in lithium niobate remains challenging, however, due to lateral domain spreading and merging. Here, we report submicrometer periodic poling of ion-sliced x-cut magnesium oxide doped lithium niobate thin films. Electric-field poling is performed using multiple bipolar preconditioning pulses that improve the poling yield and domain uniformity. The internal field is found to decrease with each preconditioning poling cycle. The poled domains are characterized by piezoresponse force microscopy. A fundamental period of 747 nm is achieved.
Second-order optical nonlinearity is widely used for both classical and quantum photonic applications. Due to material dispersion and phase matching requirements, the polarization of optical fields is pre-defined during the fabrication. Only one type of phase matching condition is normally satisfied, and this limits the device flexibility. Here, we demonstrate that phase matching for both type-I and type-II second-order optical nonlinearity can be realized simultaneously in the same waveguide fabricated from thin-film lithium niobate. This is achieved by engineering the geometry dispersion to compensate for the material dispersion and birefringence. The simultaneous realization of both phase matching conditions is verified by the polarization dependence of second-harmonic generation. Correlated photons are also generated through parametric down conversion from the same device. This work provides a novel approach to realize versatile photonic functions with flexible devices.
BACKGROUND Electromagnetic (EM) waves underpin modern society in profound ways. They are used to carry information, enabling broadcast radio and television, mobile telecommunications, and ubiquitous access to data networks through Wi-Fi and form the backbone of our modern broadband internet through optical fibers. In fundamental physics, EM waves serve as an invaluable tool to probe objects from cosmic to atomic scales. For example, the Laser Interferometer Gravitational-Wave Observatory and atomic clocks, which are some of the most precise human-made instruments in the world, rely on EM waves to reach unprecedented accuracies. This has motivated decades of research to develop coherent EM sources over broad spectral ranges with impressive results: Frequencies in the range of tens of gigahertz (radio and microwave regimes) can readily be generated by electronic oscillators. Resonant tunneling diodes enable the generation of millimeter (mm) and terahertz (THz) waves, which span from tens of gigahertz to a few terahertz. At even higher frequencies, up to the petahertz level, which are usually defined as optical frequencies, coherent waves can be generated by solid-state and gas lasers. However, these approaches often suffer from narrow spectral bandwidths, because they usually rely on well-defined energy states of specific materials, which results in a rather limited spectral coverage. To overcome this limitation, nonlinear frequency-mixing strategies have been developed. These approaches shift the complexity from the EM source to nonresonant-based material effects. Particularly in the optical regime, a wealth of materials exist that support effects that are suitable for frequency mixing. Over the past two decades, the idea of manipulating these materials to form guiding structures (waveguides) has provided improvements in efficiency, miniaturization, and production scale and cost and has been widely implemented for diverse applications. ADVANCES Lithium niobate, a crystal that was first grown in 1949, is a particularly attractive photonic material for frequency mixing because of its favorable material properties. Bulk lithium niobate crystals and weakly confining waveguides have been used for decades for accessing different parts of the EM spectrum, from gigahertz to petahertz frequencies. Now, this material is experiencing renewed interest owing to the commercial availability of thin-film lithium niobate (TFLN). This integrated photonic material platform enables tight mode confinement, which results in frequency-mixing efficiency improvements by orders of magnitude while at the same time offering additional degrees of freedom for engineering the optical properties by using approaches such as dispersion engineering. Importantly, the large refractive index contrast of TFLN enables, for the first time, the realization of lithium niobate–based photonic integrated circuits on a wafer scale. OUTLOOK The broad spectral coverage, ultralow power requirements, and flexibilities of lithium niobate photonics in EM wave generation provides a large toolset to explore new device functionalities. Furthermore, the adoption of lithium niobate–integrated photonics in foundries is a promising approach to miniaturize essential bench-top optical systems using wafer scale production. Heterogeneous integration of active materials with lithium niobate has the potential to create integrated photonic circuits with rich functionalities. Applications such as high-speed communications, scalable quantum computing, artificial intelligence and neuromorphic computing, and compact optical clocks for satellites and precision sensing are expected to particularly benefit from these advances and provide a wealth of opportunities for commercial exploration. Also, bulk crystals and weakly confining waveguides in lithium niobate are expected to keep playing a crucial role in the near future because of their advantages in high-power and loss-sensitive quantum optics applications. As such, lithium niobate photonics holds great promise for unlocking the EM spectrum and reshaping information technologies for our society in the future. Lithium niobate spectral coverage. The EM spectral range and processes for generating EM frequencies when using lithium niobate (LN) for frequency mixing. AO, acousto-optic; AOM, acousto-optic modulation; χ (2) , second-order nonlinearity; χ (3) , third-order nonlinearity; EO, electro-optic; EOM, electro-optic modulation; HHG, high-harmonic generation; IR, infrared; OFC, optical frequency comb; OPO, optical paramedic oscillator; OR, optical rectification; SCG, supercontinuum generation; SHG, second-harmonic generation; UV, ultraviolet.
Ali, Rana Faryad, Busche, Jacob A., Kamal, Saeid, Masiello, David J., and Gates, Byron D. Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures. Light: Science & Applications 12.1 Web. doi:10.1038/s41377-023-01092-8.
Ali, Rana Faryad, Busche, Jacob A., Kamal, Saeid, Masiello, David J., & Gates, Byron D. Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures. Light: Science & Applications, 12 (1). https://doi.org/10.1038/s41377-023-01092-8
Ali, Rana Faryad, Busche, Jacob A., Kamal, Saeid, Masiello, David J., and Gates, Byron D.
"Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures". Light: Science & Applications 12 (1). Country unknown/Code not available: Nature Publishing Group. https://doi.org/10.1038/s41377-023-01092-8.https://par.nsf.gov/biblio/10408934.
@article{osti_10408934,
place = {Country unknown/Code not available},
title = {Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures},
url = {https://par.nsf.gov/biblio/10408934},
DOI = {10.1038/s41377-023-01092-8},
abstractNote = {Abstract Nanophotonics research has focused recently on the ability of nonlinear optical processes to mediate and transform optical signals in a myriad of novel devices, including optical modulators, transducers, color filters, photodetectors, photon sources, and ultrafast optical switches. The inherent weakness of optical nonlinearities at smaller scales has, however, hindered the realization of efficient miniaturized devices, and strategies for enhancing both device efficiencies and synthesis throughput via nanoengineering remain limited. Here, we demonstrate a novel mechanism by which second harmonic generation, a prototypical nonlinear optical phenomenon, from individual lithium niobate particles can be significantly enhanced through nonradiative coupling to the localized surface plasmon resonances of embedded gold nanoparticles. A joint experimental and theoretical investigation of single mesoporous lithium niobate particles coated with a dispersed layer of ~10 nm diameter gold nanoparticles shows that a ~32-fold enhancement of second harmonic generation can be achieved without introducing finely tailored radiative nanoantennas to mediate photon transfer to or from the nonlinear material. This work highlights the limitations of current strategies for enhancing nonlinear optical phenomena and proposes a route through which a new class of subwavelength nonlinear optical platforms can be designed to maximize nonlinear efficiencies through near-field energy exchange.},
journal = {Light: Science & Applications},
volume = {12},
number = {1},
publisher = {Nature Publishing Group},
author = {Ali, Rana Faryad and Busche, Jacob A. and Kamal, Saeid and Masiello, David J. and Gates, Byron D.},
}
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