Design and Control Recipes for Complex Photonic Integrated Circuits

In the last decades optical communications contributed to the huge diffusion of the telecommunication market, pushing the development of new technologies to enable higher performances and lower costs.

AlGaInAs Multi-Quantum Well Lasers on Silicon-on-Insulator Photonic Integrated Circuits Based on InP-Seed-Bonding and Epitaxial Regrowth

The tremendous demand for low-cost, low-consumption and high-capacity optical transmitters in data centers challenges the current InP-photonics platform. The use of silicon (Si) photonics platform to fabricate photonic integrated circuits (PICs) is a promising approach for low-cost large-scale fabrication considering the CMOS-technology maturity and scalability. However, Si itself cannot provide an efficient emitting light source due to its indirect bandgap. Therefore, the integration of III-V semiconductors on Si wafers allows us to benefit from the III-V emitting properties combined with benefits offered by the Si photonics platform. Direct epitaxy of InP-based materials on 300 mm Si wafers is the most promising approach to reduce the costs. However, the differences between InP and Si in terms of lattice mismatch, thermal coefficients and polarity inducing defects are challenging issues to overcome. III-V/Si hetero-integration platform by wafer-bonding is the most mature integration scheme. However, no additional epitaxial regrowth steps are implemented after the bonding step. Considering the much larger epitaxial toolkit available in the conventional monolithic InP platform, where several epitaxial steps are often implemented, this represents a significant limitation. In this paper, we review an advanced integration scheme of AlGaInAs-based laser sources on Si wafers by bonding a thin InP seed on which further regrowth steps are implemented. A 3 µm-thick AlGaInAs-based MutiQuantum Wells (MQW) laser structure was grown onto on InP-SiO2/Si (InPoSi) wafer and compared to the same structure grown on InP wafer as a reference. The 400 ppm thermal strain on the structure grown on InPoSi, induced by the difference of coefficient of thermal expansion between InP and Si, was assessed at growth temperature. We also showed that this structure demonstrates laser performance similar to the ones obtained for the same structure grown on InP. Therefore, no material degradation was observed in spite of the thermal strain. Then, we developed the Selective Area Growth (SAG) technique to grow multi-wavelength laser sources from a single growth step on InPoSi. A 155 nm-wide spectral range from 1515 nm to 1670 nm was achieved. Furthermore, an AlGaInAs MQW-based laser source was successfully grown on InP-SOI wafers and efficiently coupled to Si-photonic DBR cavities. Altogether, the regrowth on InP-SOI wafers holds great promises to combine the best from the III-V monolithic platform combined with the possibilities offered by the Si photonics circuitry via efficient light-coupling.

High-speed programmable photonic circuits in a cryogenically compatible, visible–near-infrared 200 mm CMOS architecture

Recent advances in photonic integrated circuits have enabled a new generation of programmable Mach–Zehnder meshes (MZMs) realized by using cascaded Mach–Zehnder interferometers capable of universal linear-optical transformations on N input/output optical modes. MZMs serve critical functions in photonic quantum information processing, quantum-enhanced sensor networks, machine learning and other applications. However, MZM implementations reported to date rely on thermo-optic phase shifters, which limit applications due to slow response times and high power consumption. Here we introduce a large-scale MZM platform made in a 200 mm complementary metal–oxide–semiconductor foundry, which uses aluminium nitride piezo-optomechanical actuators coupled to silicon nitride waveguides, enabling low-loss propagation with phase modulation at greater than 100 MHz in the visible–near-infrared wavelengths. Moreover, the vanishingly low hold-power consumption of the piezo-actuators enables these photonic integrated circuits to operate at cryogenic temperatures, paving the way for a fully integrated device architecture for a range of quantum applications.

Finite element modeling of coupling characteristics of directional coupler for multiplexer and de-multiplexer application

Numerical simulation of directional coupler that is based on the finite element method was conducted using the COMSOL Multiphysics software. The distributions of electric field and power flow of light propagates in two cores of directional coupler were analyzed. The results showed the dependencies of coupling length and maximum transfer power between cores on the cores separation and the wavelength, the characteristic of a subwavelength directional coupler can be used for photonic integrated circuits. Asymmetric directional coupler was also designed by changing in the device dimension, as the core width. The variation of coupling length with the core width were analysed. It was found that the power switching between cores is reduced when introducing a small difference in the one core width of directional coupler, followed by increased coupling length. At the same time, the coupling length can be decreased efficiently by increasing the difference in one core width; therefore, a directional coupler with large core width is more convenient to reduce the power switching between cores than the smaller core width. This study is useful for determining the coupling characteristics between the cores that may be used as a platform for future photonic integrated circuits in optical communication systems.

Features of the construction of photonic integrated circuits for communication systems

The article discusses the main methods of signal processing in a coherent optical transport network based on a photonic integrated circuit to increase the speed and the onset of the terabit era in optical transport networks, cloud and high-performance computing systems. The properties and operational characteristics of the main material platforms of photonic integrated circuits and their future technological units are considered.

Optical meta-waveguides for integrated photonics and beyond

The growing maturity of nanofabrication has ushered massive sophisticated optical structures available on a photonic chip. The integration of subwavelength-structured metasurfaces and metamaterials on the canonical building block of optical waveguides is gradually reshaping the landscape of photonic integrated circuits, giving rise to numerous meta-waveguides with unprecedented strength in controlling guided electromagnetic waves. Here, we review recent advances in meta-structured waveguides that synergize various functional subwavelength photonic architectures with diverse waveguide platforms, such as dielectric or plasmonic waveguides and optical fibers. Foundational results and representative applications are comprehensively summarized. Brief physical models with explicit design tutorials, either physical intuition-based design methods or computer algorithms-based inverse designs, are cataloged as well. We highlight how meta-optics can infuse new degrees of freedom to waveguide-based devices and systems, by enhancing light-matter interaction strength to drastically boost device performance, or offering a versatile designer media for manipulating light in nanoscale to enable novel functionalities. We further discuss current challenges and outline emerging opportunities of this vibrant field for various applications in photonic integrated circuits, biomedical sensing, artificial intelligence and beyond.

Ultra-fast germanium photodiode with 3-dB bandwidth of 265 GHz

On a scalable silicon technology platform, we demonstrate photodetectors matching or even surpassing state-of-the-art III–V devices. As key components in high-speed optoelectronics, photodetectors with bandwidths greater than 100 GHz have been a topic of intense research for several decades. Solely InP-based detectors could satisfy the highest performance specifications. Devices based on other materials, such as germanium-on-silicon devices, used to lag behind in speed, but enabled complex photonic integrated circuits and co-integration with silicon electronics. Here we demonstrate waveguide-coupled germanium photodiodes with optoelectrical 3-dB bandwidths of 265 GHz and 240 GHz at a photocurrent of 1 mA. This outstanding performance is achieved by a novel device concept in which a germanium fin is sandwiched between complementary in situ-doped silicon layers. Our photodetectors show internal responsivities of 0.3 A W−1 (265 GHz) and 0.45 A W−1 (240 GHz) at a wavelength of 1,550 nm. The internal bandwidth–efficiency product of the latter device is 86 GHz. Low dark currents of 100–200 nA are obtained from these ultra-fast photodetectors.