Corrado Sciancalepore

CMOS-Compatible Ultra-Compact 1.55- μ m Emitting VCSELs Using Double Photonic Crystal Mirrors

In this letter, the authors report the first demonstration of laser operation in long-wavelength optically-pumped vertical-cavity surface-emitting lasers for photonics-on-complementary metal-oxide-semiconductor back-end integration using 1-D double photonic crystal mirrors. The full exploitation of surface-addressable slow Bloch modes in such photonic architectures promotes an optimized tailoring of light confinement resulting in compact single-mode emitters capable to operate continuous-wave with thresholds in the sub-mW range.

Quasi-3D Light Confinement in Double Photonic Crystal Reflectors VCSELs for CMOS-Compatible Integration

A novel architecture of one-dimensional photonic crystal membrane (PCM) reflectors embodying a heterostructure is proposed as a robust design aimed at a 3-D efficient confinement of light in single-mode polarization-controlled 1.55-μm vertical-cavity surface-emitting laser (VCSEL) microsources for heterogeneous integration on complementary metal-oxide-semiconductor (CMOS). On the basis of a theoretical approach, the paper focuses on the deep interweaving between the kinetics of light transport in the mirrors and the physical nature of the exploited Fano resonances. An example of VCSEL design for optical pumping employing heterostructure-confined photonic crystal mirrors is presented. The predicted photons kinetics along with the considerable improvement in cavity modal features owing to the enhanced mirror architecture have been confirmed by performing rigorous three-dimensional finite-difference time-domain (3-D FDTD) calculations. Finally, experimental observations of photoluminescence (PL) emission performed on first-ever fabricated devices for optical pumping show striking agreement with theoretical considerations and ab initio modelling.

Thermal, Modal, and Polarization Features of Double Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

Long-wavelength vertical-cavity surface-emitting lasers (VCSELs) for photonics-on-complementary metal-oxide-semiconductor (CMOS) integration based on a double set of Si/SiO2 photonic crystal mirrors (PCMs) have been recently fabricated. In the present communication, an extensive overview about modal, polarization, and thermal features of optically pumped demonstrators is presented. Capable of operating continuous-wave up to 43°C at low thresholds, such VCSELs show single-mode polarization-stable operation at 1.55-μm with uncooled output powers in excess of 0.4 mW. This paper aims at singling out notably the device optical features arising from the excellent flexibility of the photonic architecture used. Noticeably, the light molding obtained through the engineering of Si/SiO2 photonic crystals allows for a tailored modal selection and full polarization control. Furthermore, the high-throughput cost-effective Si-based process technology developed is ideally well-suited for perspective industrial development.

1310 nm hybrid InP/InGaAsP on silicon distributed feedback laser with high side-mode suppression ratio

We report on the design, fabrication and performance of a hetero-integrated III-V on silicon distributed feedback lasers (DFB) at 1310 nm based on direct bonding and adiabatic coupling. The continuous wave (CW) regime is achieved up to 55 °C as well as mode-hop-free operation with side-mode suppression ratio (SMSR) above 55 dB. At room temperature, the current threshold is 36 mA and the maximum coupled power in the silicon waveguide is 22 mW.

III-V-on-Si Photonic Crystal Vertical-Cavity Surface-Emitting Laser Arrays for Wavelength Division Multiplexing

Double photonic crystal mirror vertical-cavity surface-emitting laser (PCM-VCSEL) arrays for the heterogeneous integration on a complementary metal-oxide semiconductor are presented. The trimming of one-dimensional photonic crystal mirrors spectral and modal features allows a fine tailoring of the lightwave which results in compact VCSEL arrays exhibiting a fully controllable dense wavelength distribution. Optically pumped double PCM-VCSELs emit 1.55-μm single-mode beams within the C-band with sub-milliwatt thresholds and spectral purity, making these devices highly suitable for telecommunication-oriented applications. The intrinsic capability exhibited by PCM-VCSEL arrays for a selective addressing of dense wavelength division multiplexing (DWDM) channels suggests a strong perspective potential for several applications such as high-capacity ultra-wideband optical interconnects, passive optical networks, free-space data transmission and sensing.

Toward athermal silicon-on-insulator (de)multiplexers in the O-band.

We report on the design, fabrication, and characterization of a 1×4 silicon-on-insulator (SOI) demultiplexer exhibiting a significant reduction of its thermo-optical sensitivity in the O-band. The optical filtering is achieved by cascading several Mach-Zehnder interferometers (MZIs) fabricated on a 300-nm-thick SOI platform. Owing to an asymmetric design of the confinement for each MZIs, we found an athermal criterium that satisfies the spectral requirements. The thermal sensitivity of the structure is analyzed by a semi-analytical model in order to create an athermal multiplexer. Fiber-to-fiber thermo-optical testing reveals a thermal sensitivity of around 17  pm/°C reduced by 75% compared to the standard devices with promising performances for both the crosstalk (15 dB), the insertion losses (4 dB), and absolute lambda registration (<0.25  nm).

Double photonic crystal vertical-cavity surface-emitting lasers

The periodic patterning of the optical medium achieved through photonic crystal membranes (PCMs) can be employed for controlling the resonant coupling of external radiation continuum to above-the-light-line flat edges of the folded band structure in strongly corrugated waveguides, resulting in high reflectivity for an efficient quasi-3D light harnessing. Recently, vertical-cavity surface-emitting lasers (VCSELs) emitting in C-band using a double set of one-dimensional Si/SiO2 photonic crystals as compact, flexible, and power efficient mirrors have been realized within a mass-scale fabrication paradigm by employing standard 200-mm microelectronics pilot lines. Conceived as the basic building block for photonics-on-silicon back-end integration of group III-V laser microsources, the extreme flexibility of the novel photonic architecture enables to perform a tailored modal selection of the optical cavity, including polarization and far-field control. It also offers a wide range of functionality, such as on-chip optical routing and a variety of efficient wavelength tuning-trimming schemes. Device compactness ensures a considerable reduction in the device footprint, power consumption, and parasitics. Furthermore, high fabrication yields obtained thanks to the state-of-the-art molecular wafer bonding of III-V alloys on silicon conjugate excellent device performances with cost-effective high-throughput production, indicating strong perspective industrial potential.

Surface addressable photonic crystal membrane resonators: generic enablers for 3D harnessing of light

Conceptual approaches used to analyse optical properties of surface-addressable photonic crystal membrane (PCM) resonators will be briefly presented. It will be pointed out that these photonic structures can also be referred to as high-contrast gratings (HCGs) and that bridges can be made with other approaches proposed in the recent literature to analyse the latter. It will be demonstrated that high reflection mirrors, with arbitrarily adjustable bandwidth, can be designed along the PCM approach, where leaky wave-guided slow Bloch modes play the primary role. Implementation examples of such reflectors are presented, with a special emphasis on the use of large bandwidth PCM reflector: vertical-cavity surface-emitting lasers (VCSELs) using hybrid III-V / Si microcavities, based on double PCM reflectors, have been recently fabricated. These devices are meant to be compatible with their heterogeneous integration on complementary metal-oxide-silicon (CMOS). It will be shown that the operation of this new class of VCSEL is based on hybrid optical modes, whose properties can be fully monitored by appropriate design of the PCM reflectors. For example, specific architectures can be targeted for laser emission either in free space, or into silicon waveguides. The latest achievements in technological processing, optical mode engineering and laser performances will be presented as well.

Power-efficient carrier-depletion SOI Mach-Zehnder modulators for 4x25Gbit/s operation in the O-band

In this paper, we communicate on the design, fabrication, and testing of optical modulators for Silicon-based photonic integrated circuits (Si-PICs) in the O-band (1.31 μm), targeting the 100GBASE-LR4 norm (4 wavelengths at 25 Gbit/s). The modulators have been conceived to be later coupled with hybrid-III-V/Si lasers as well as echelle grating multiplexer, to create a hetero-integrated optical transmitter on a silicon-on-insulator (SOI) platform. The devices are based on a Mach-Zehnder Interferometer (MZI) architecture, where a p-n junction is implanted to provide optical modulation through carrier depletion. A detailed study focusing on the best doping scheme for the junction, aimed at optimizing the overall transmitter performance and power-efficiency is presented. In detail, the trade-off between low optical losses and high modulation efficiency is tackled, with a targeted CMOS-compatible voltage drive of 2.5 V. Process simulations of the junction are realized for the doping profile optimization. Modulators of different lengths are also investigated to study the compromise between extinction ratio, insertion losses and bandwidth. Furthermore, coplanar-strip (SGS) travelling-wave electrodes are designed to maximize the bandwidth, to reach the targeted bit rate of 25 Gbit/s. Measurements show modulation efficiencies up to 19 °/mm (or 2.4 V.cm) for a 2.5 V input voltage, with doping-related losses below 1 dB/mm, in line with theoretical estimates, and well-suited to enhance the Si-PIC transmission and power-efficiency. Finally, an electro-optical (EO) bandwidth at 1.25 V bias is measured above 28 GHz.

Low-crosstalk fabrication-insensitive echelle grating multiplexers and passives for the silicon photonics toolbox

In this communication, we report about the design, fabrication, and testing of echelle grating (de-)multiplexers for the 100GBASE-LR4 norm and other passive architectures such as vertical fiber-couplers and slow-wave waveguides in the O-band (1.31-μm) for Silicon-based photonic integrated circuits (Si-PICs). In detail, two-point stigmatic 20th-order echelle gratings (TPSGs) on the 300-nm-thick SOI platform designed for 4x800-GHz-spaced wavelength division multiplexing featuring extremely low crosstalk (< -30 dB), precise channel spacing and optimized average insertion losses (~ 3 dB) are presented. Distributed Bragg reflectors (DBRs) are used to improve the grating facets reflectivity, while multi-mode interferometers (MMIs) are used in optimized perfectly-chirped echelle gratings (PCGs) for pass-band flattening. Moreover, 200-mm CMOS pilot lines processing tools including VISTEC variable-shape e-beam lithography are employed for the fabrication. In addition, wafer-level statistics of the multiplexers clearly shows the echelle grating to be inherently fabrication-insensitive to processing drifts, resulting in a minimized dispersion of the multiplexer performances over the wafer. In particular, the echelle grating spectral response remains stable over the wafer in terms of crosstalk, channel spacing and bandwidth, with the wavelength dispersion of the filter comb being limited to just 0.8 nm, thus highlighting the intrinsic robustness of design, fab pathways as well as the reliability of modeling tools. As well as that, apodized one-dimensional vertical fiber couplers, optimized multi-mode interferometers (MMIs) and extremely low-losses slow-light waveguides are demonstrated and discussed. The adiabatic apodization of such 1-D gratings is capable to provide band-edge group indices ng as high as 30 with propagation losses equivalent to the indexlike propagation regime.