The isolation of graphene in 2004 from graphite was a defining moment for the “birth” of a field: two-dimensional (2D) materials In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement Here, we review significant recent advances and important new developments in 2D materials “beyond graphene” We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (ie, silicene, phosphorene, etc) and transition metal carbide- and carbon nitride-based MXenes We then discuss the doping and functionalization of 2

Recent Advances in Two-Dimensional Materials beyond Graphene

The nonlinearities in silicon are diverse. This Review covers the wealth of nonlinear effects in silicon and highlights the important applications and technological solutions in nonlinear silicon photonics. The increasing capability for manufacturing a wide variety of optoelectronic devices from polymer and polymer–silicon hybrids, including transmission fibre, modulators, detectors and light sources, suggests that organic photonics has a promising future in communications and other applications.

Nonlinear silicon photonics

Emerging applications based on optical beams carrying orbital angular momentum (OAM) will probably require photonic integrated devices and circuits for miniaturization, improved performance, and enhanced functionality. We demonstrate silicon-integrated optical vortex emitters, using angular gratings to extract light confined in whispering gallery modes with high OAM into free-space beams with well-controlled amounts of OAM. The smallest device has a radius of 3.9 micrometers. Experimental characterization confirms the theoretical prediction that the emitted beams carry exactly defined and adjustable OAM. Fabrication of integrated arrays and demonstration of simultaneous emission of multiple identical optical vortices provide the potential for large-scale integration of optical vortex emitters on complementary metal-oxide–semiconductor compatible silicon chips for wide-ranging applications.

/pdf/integrated-compact-optical-vortex-beam-emitters-1443e933nn.pdf

Integrated Compact Optical Vortex Beam Emitters

A passive optical diode effect would be useful for on-chip optical information processing but has been difficult to achieve Using a method based on optical nonlinearity, we demonstrate a forward-backward transmission ratio of up to 28 decibels within telecommunication wavelengths Our device, which uses two silicon rings 5 micrometers in radius, is passive yet maintains optical nonreciprocity for a broad range of input power levels, and it performs equally well even if the backward input power is higher than the forward input The silicon optical diode is ultracompact and is compatible with current complementary metal-oxide semiconductor processing

https://science.sciencemag.org/content/sci/335/6067/447.full.pdf

An All-Silicon Passive Optical Diode

Significant effort in optical-fibre research has been put in recent years into realizing mode-division multiplexing (MDM) in conjunction with wavelength-division multiplexing (WDM) to enable further scaling of the communication bandwidth per fibre. In contrast, almost all integrated photonics operate exclusively in the single-mode regime. MDM is rarely considered for integrated photonics because of the difficulty in coupling selectively to high-order modes, which usually results in high inter-modal crosstalk. Here we show the first microring-based demonstration of on-chip WDM-compatible mode-division multiplexing with low modal crosstalk and loss. Our approach can potentially increase the aggregate data rate by many times for on-chip ultrahigh bandwidth communications.

/pdf/wdm-compatible-mode-division-multiplexing-on-a-silicon-chip-31lge0lodq.pdf

WDM-compatible mode-division multiplexing on a silicon chip

Silicon waveguide asymmetric Y junction mode multiplexers and demultiplexers are demonstrated for applications in on-chip mode-division multiplexing (MDM). We measure demultiplexed crosstalk as low as -30 dB, <-9 dB over the C band, and insertion loss <1.5 dB for multimode links up to 1.2 mm in length. The frequency response of these devices is shown to depend upon Y junction angle and multimode interconnect length. Interference effects are shown to be advantageous for low-crosstalk MDM, even while using compact Y junctions designed to be outside the mode-sorting regime.

Asymmetric Y junctions in silicon waveguides for on-chip mode-division multiplexing

We report the first demonstration of a silicon photonic microring modulator with modulation data rate up to 128 Gb/s (64 Gbaud PAM4). The microring modulator exhibits an electro-optic phase efficiency of V $_\pi \cdot$ L = 0.52 V $\cdot$ cm, an electro-optic bandwidth of 50 GHz, and a measured transmitter dispersion eye closure quaternary of 3.0 dB at this data rate. In addition, the resonant wavelength of the microring modulator can be tuned across a full free spectral range using an integrated heater with a thermo-optic phase efficiency of 19.5 mW $/\pi$ -phase shift.

/pdf/a-128-gb-s-pam4-silicon-microring-modulator-with-integrated-2s0l8j4ydz.pdf

A 128 Gb/s PAM4 Silicon Microring Modulator With Integrated Thermo-Optic Resonance Tuning

Silicon (Si) photonics research and development started more than 30 years ago and has intensified in the last 15 years as levels of device functionality, photonic integration, and commercialization have all increased [1]. The key drivers for using Si in photonics arise from the quality of wafers and the superior processing capabilities developed and funded by the microelectronics industry. It has the promise to revolutionize the photonics industry in the same way that CMOS design and processing revolutionized the microelectronics industry, by driving down photonic chip cost while enabling higher levels of photonic integration and functionality. Commercialization, so far, has focused on optical communication (Telecom [2] and data center [3]) and biosensing [4], with a wealth of future application areas, including high-performance computing [5], automotive (lidar) [6], optical switches [7], and artificial intelligence [8].

Heterogeneously Integrated InP\/Silicon Photonics: Fabricating Fully Functional Transceivers

We demonstrate the presence of strong longitudinal electric fields (E(z)) in silicon nanowire waveguides through numerical computation. These waveguide fields can be engineered through choice of waveguide geometry to exhibit amplitudes as high as 97% that of the dominant transverse field component. We show even larger longitudinal fields created in free space by a terminated waveguide can become the dominant electric field component, and demonstrate E(z) has a large effect on waveguide nonlinearity. We discuss the possibility of controlling the strength and symmetry of E(z) using a dual waveguide design, and show that the resulting longitudinal field is sharply peaked beyond the diffraction limit.

Large longitudinal electric fields (Ez) in silicon nanowire waveguides

Mode-division-multiplexing (MDM) and wavelength-division-multiplexing (WDM) are employed simultaneously in a multimode silicon waveguide to realize on-chip MDM and MDM-WDM transmission. Asymmetric Y-junction MDM multiplexers and demultiplexers are utilized for low coherently suppressed demultiplexed crosstalk at the receiver. We demonstrate aggregate bandwidths of 20 Gb/s and 60 Gb/s for MDM and MDM-WDM on-chip links, respectively, with measured 10−9 BER power penalties between 0.1 dB and 0.7 dB per channel.

Jeffrey B. Driscoll

Papers

Asymmetric Y junctions in silicon waveguides for on-chip mode-division multiplexing

A 128 Gb/s PAM4 Silicon Microring Modulator With Integrated Thermo-Optic Resonance Tuning

Heterogeneously Integrated InP\/Silicon Photonics: Fabricating Fully Functional Transceivers

Large longitudinal electric fields (Ez) in silicon nanowire waveguides

A 60 Gb/s MDM-WDM Si photonic link with < 0.7 dB power penalty per channel