Photonics Research
Co-Editors-in-Chief
Eric Cassan, Christian Grillet, David Moss, and Dragomir Neshev
Vol. 6, Issue 5, 2018
Editor(s): Eric Cassan, Christian Grillet, David Moss, and Dragomir Neshev
Year: 2018
Status: Published

Advances in integrated optoelectronics and nanophotonics have been very rich in recent years. These include the spectacular developments of nonlinear group four photonic platforms as well as the integration of components and functions based on III-V semiconductor materials. One of the strongest trends for the future is the development of all-optical signal processing functions within integrated, compact, low-loss devices, paving the way for new applications. This approach, relying on materials, components and the integration of optical functions, is based on a wide range of exciting physical phenomena, exploiting the nonlinear optical response of materials for the generation of frequency combs, the conversion of light wavelength, the generation of supercontinuum radiation, and many other phenomena exploiting the unprecedented power of light control by waves. This special issue has drawn a critical overview of the recent and significant burgeoning advances in the field, as well as to identify the next technological and scientific milestones to come for the development of integrated nonlinear photonics. Meanwhile, it aims to shed light on the interdisciplinary dimension of the work carried out in the field, based, for example, on the control of optical waves by acoustic waves, opening the way to the fields of nonlinear optomechanics and optoacoustics.

Contents 12 article(s)
Nonlinear integrated photonics
Eric Cassan, Christian Grillet, Dragomir N. Neshev, and David J. Moss

The field of nonlinear photonics is in full development. This special issue of Photonics Research takes you through the current issues of this fast-growing field of research, drawing on the current state of the art and seeking, through a selection of articles, to outline some trends for the future.

Photonics Research
May. 01, 2018, Vol. 6 Issue 5 0500NIP1 (2018)
All-optical switching in silicon photonic waveguides with an epsilon-near-zero resonant cavity [Invited]
Andres D. Neira, Gregory A. Wurtz, and Anatoly V. Zayats

Strong nonlinearity of plasmonic metamaterials can be designed near their effective plasma frequency in the epsilon-near-zero (ENZ) regime. We explore the realization of an all-optical modulator based on the Au nonlinearity using an ENZ cavity formed by a few Au nanorods inside a Si photonic waveguide. The resulting modulator has robust performance with a modulation depth of about 30 dB/μm and loss less than 0.8 dB for switching energies below 600 fJ. The modulator provides a double advantage of high mode transmission and strong nonlinearity enhancement in the few-nanorod-based design.

Photonics Research
Mar. 27, 2018, Vol. 6 Issue 5 050000B1 (2018)
Tuning the second-harmonic generation in AlGaAs nanodimers via non-radiative state optimization [Invited]
Davide Rocco, Valerio F. Gili, Lavinia Ghirardini, Luca Carletti, Ivan Favero, Andrea Locatelli, Giuseppe Marino, Dragomir N. Neshev, Michele Celebrano, Marco Finazzi, Giuseppe Leo, and Costantino De Angelis

Dielectric nanocavities are emerging as a versatile and powerful tool for the linear and nonlinear manipulation of light at the nanoscale. In this work, we exploit the effective coupling of electric and toroidal modes in AlGaAs nanodimers to locally enhance both electric and magnetic fields while minimizing the optical scattering, thereby optimizing their second-harmonic generation efficiency with respect to the case of a single isolated nanodisk. We also demonstrate that proper near-field coupling can provide further degrees of freedom to control the polarization state and the radiation diagram of the second-harmonic field.

Photonics Research
Apr. 11, 2018, Vol. 6 Issue 5 050000B6 (2018)
Hybrid silicon nonlinear photonics [Invited]
Ming Li, Lin Zhang, Li-Min Tong, and Dao-Xin Dai

Nonlinear silicon photonics has shown an ability to generate, manipulate, and detect optical signals on an ultracompact chip at a potential low cost. There are still barriers hindering its development due to essential material limitations. In this review, hybrid structures with some specific materials developed for nonlinear silicon photonics are discussed. The combination of silicon and the nonlinear materials takes advantage of both materials, which shows great potential to improve the performance and expand the applications for nonlinear silicon photonics.

Photonics Research
Apr. 11, 2018, Vol. 6 Issue 5 05000B13 (2018)
Dual-polarization wavelength conversion of 16-QAM signals in a single silicon waveguide with lateral p-i-n diode [Invited]
Francesco Da Ros, Andrzej Gajda, Erik Liebig, Edson P. da Silva, Anna Pęczek, Peter D. Girouard, Andreas Mai, Klaus Petermann, Lars Zimmermann, Michael Galili, and Leif K. Oxenløwe

A polarization-diversity loop with a silicon waveguide with a lateral p-i-n diode as a nonlinear medium is used to realize polarization insensitive four-wave mixing. Wavelength conversion of seven dual-polarization 16-quadrature amplitude modulation (QAM) signals at 16 GBd is demonstrated with an optical signal-to-noise ratio penalty below 0.7 dB. High-quality converted signals are generated thanks to the low polarization dependence (≤0.5 dB) and the high conversion efficiency (CE) achievable. The strong Kerr nonlinearity in silicon and the decrease of detrimental free-carrier absorption due to the reverse-biased p-i-n diode are key in ensuring the high CE levels.

Photonics Research
Apr. 11, 2018, Vol. 6 Issue 5 05000B23 (2018)
Photonic microwave true time delays for phased array antennas using a 49  GHz FSR integrated optical micro-comb source [Invited]
Xingyuan Xu, Jiayang Wu, Thach G. Nguyen, Tania Moein, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss

We demonstrate significantly improved performance of a microwave true time delay line based on an integrated optical frequency comb source. The broadband micro-comb (over 100 nm wide) features a record low free spectral range (FSR) of 49 GHz, resulting in an unprecedented record high channel number (81 over the C band)—the highest number of channels for an integrated comb source used for microwave signal processing. We theoretically analyze the performance of a phased array antenna and show that this large channel count results in a high angular resolution and wide beam-steering tunable range. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.

Photonics Research
Apr. 12, 2018, Vol. 6 Issue 5 05000B30 (2018)
Nonlinear optical properties of integrated GeSbS chalcogenide waveguides
Samuel Serna, Hongtao Lin, Carlos Alonso-Ramos, Anupama Yadav, Xavier Le Roux, Kathleen Richardson, Eric Cassan, Nicolas Dubreuil, Juejun Hu, and Laurent Vivien

In this paper, we report the experimental characterization of highly nonlinear GeSbS chalcogenide glass waveguides. We used a single-beam characterization protocol that accounts for the magnitude and sign of the real and imaginary parts of the third-order nonlinear susceptibility of integrated Ge23Sb7S70 (GeSbS) chalcogenide glass waveguides in the near-infrared wavelength range at λ=1580 nm. We measured a waveguide nonlinear parameter of 7.0±0.7 W 1·m 1, which corresponds to a nonlinear refractive index of n2=(0.93±0.08)×10 18 m2/W, comparable to that of silicon, but with an 80 times lower two-photon absorption coefficient βTPA=(0.010±0.003) cm/GW, accompanied with linear propagation losses as low as 0.5 dB/cm. The outstanding linear and nonlinear properties of GeSbS, with a measured nonlinear figure of merit FOMTPA=6.0±1.4 at λ=1580 nm, ultimately make it one of the most promising integrated platforms for the realization of nonlinear functionalities.

Photonics Research
Apr. 13, 2018, Vol. 6 Issue 5 05000B37 (2018)
Nonlinear gallium phosphide nanoscale photonics [Invited]
Aude Martin, Sylvain Combrié, Alfredo de Rossi, Grégoire Beaudoin, Isabelle Sagnes, and Fabrice Raineri

We introduce a nanoscale photonic platform based on gallium phosphide. Owing to the favorable material properties, peak power intensity levels of 50 GW/cm2 are safely reached in a suspended membrane. Consequently, the field enhancement is exploited to a far greater extent to achieve efficient and strong light–matter interaction. As an example, parametric interactions are shown to reach a deeply nonlinear regime, revealing cascaded four-wave mixing leading to comb generation and high-order soliton dynamics.

Photonics Research
Apr. 13, 2018, Vol. 6 Issue 5 05000B43 (2018)
Nonlinear optics on silicon-rich nitride—a high nonlinear figure of merit CMOS platform [Invited]
D. T. H. Tan, K. J. A. Ooi, and D. K. T. Ng

CMOS platforms with a high nonlinear figure of merit are highly sought after for high photonic quantum efficiencies, enabling functionalities not possible from purely linear effects and ease of integration with CMOS electronics. Silicon-based platforms have been prolific amongst the suite of advanced nonlinear optical signal processes demonstrated to date. These include crystalline silicon, amorphous silicon, Hydex glass, and stoichiometric silicon nitride. Residing between stoichiometric silicon nitride and amorphous silicon in composition, silicon-rich nitride films of various formulations have emerged recently as promising nonlinear platforms for high nonlinear figure of merit nonlinear optics. Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters (5x–500x) than those in stoichiometric silicon nitride. This paper reviews recent developments in the field of nonlinear optics using silicon-rich nitride platforms, as well as the outlook and future opportunities in this burgeoning field.

Photonics Research
Apr. 16, 2018, Vol. 6 Issue 5 05000B50 (2018)
Type-II micro-comb generation in a filter-driven four wave mixing laser [Invited]
Hualong Bao, Andrew Cooper, Sai T. Chu, Dave J. Moss, Roberto Morandotti, Brent E. Little, Marco Peccianti, and Alessia Pasquazi

We experimentally demonstrate the generation of highly coherent Type-II micro-combs based on a micro-resonator nested in a fiber cavity loop, known as the filter-driven four wave mixing (FD-FWM) laser scheme. In this system, the frequency spacing of the comb can be adjusted to integer multiples of the free-spectral range (FSR) of the nested micro-resonator by properly tuning the fiber cavity length. Sub-comb lines with single FSR spacing around the primary comb lines can be generated. Such a spectral emission is known as a “Type-II comb”. Our system achieves a fully coherent output. This behavior is verified by numerical simulations. This study represents an important step forward in controlling and manipulating the dynamics of an FD-FWM laser.

Photonics Research
Apr. 16, 2018, Vol. 6 Issue 5 05000B67 (2018)
Toward mid-infrared nonlinear optics applications of silicon carbide microdisks engineered by lateral under-etching [Invited]
David Allioux, Ali Belarouci, Darren Hudson, Eric Magi, Milan Sinobad, Guillaume Beaudin, Adrien Michon, Neetesh Singh, Regis Orobtchouk, and Christian Grillet

We report the fabrication and characterization of silicon carbide microdisks on top of silicon pillars suited for applications from near- to mid-infrared. We probe 10 μm diameter disks with different under-etching depths, from 4 μm down to 1.4 μm, fabricated by isotropic plasma etching and extract quality factors up to 8400 at telecom wavelength. Our geometry is suited to present high Q single-mode operation. We experimentally demonstrate high-order whispering-gallery mode suppression while preserving the fundamental gallery mode and investigate some requirements for nonlinear optics applications on this platform, specifically in terms of quality factor and dispersion for Kerr frequency comb generation.

Photonics Research
Apr. 19, 2018, Vol. 6 Issue 5 05000B74 (2018)
Inverse-designed photonic fibers and metasurfaces for nonlinear frequency conversion [Invited]
Chawin Sitawarin, Weiliang Jin, Zin Lin, and Alejandro W. Rodriguez

Typically, photonic waveguides designed for nonlinear frequency conversion rely on intuitive and established principles, including index guiding and bandgap engineering, and are based on simple shapes with high degrees of symmetry. We show that recently developed inverse-design techniques can be applied to discover new kinds of microstructured fibers and metasurfaces designed to achieve large nonlinear frequency-conversion efficiencies. As a proof of principle, we demonstrate complex, wavelength-scale chalcogenide glass fibers and gallium phosphide three-dimensional metasurfaces exhibiting some of the largest nonlinear conversion efficiencies predicted thus far, e.g., lowering the power requirement for third-harmonic generation by 104 and enhancing second-harmonic generation conversion efficiency by 107. Such enhancements arise because, in addition to enabling a great degree of tunability in the choice of design wavelengths, these optimization tools ensure both frequency- and phase-matching in addition to large nonlinear overlap factors.

Photonics Research
Apr. 20, 2018, Vol. 6 Issue 5 05000B82 (2018)
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