Giant electro-optic effect in Ge/SiGe coupled quantum wells

International audienceSilicon-based photonics is now considered as the photonic platform for the next generation of on-chip communications. However, the development of compact and low power consumption optical modulators is still challenging. Here we report a giant electro-optic effect in Ge/SiGe coupled quantum wells. This promising effect is based on an anomalous quantum-confined Stark effect due to the separate confinement of electrons and holes in the Ge/SiGe coupled quantum wells. This phenomenon can be exploited to strongly enhance optical modulator performance with respect to the standard approaches developed so far in silicon photonics. We have measured a refractive index variation up to 2.3 × 10 −3 under a bias voltage of 1.5 V, with an associated modulation efficiency V π L π of 0.046 V cm. This demonstration paves the way for the development of efficient and high-speed phase modulators based on the Ge/SiGe material system. Silicon photonics has generated strong advances in recent years for on-chip optical communications. Silicon based-optoelectronic devices have been intensively studied and the recent advances proved the capability of silicon photonics to offer some viable solutions for many applications including optical telecommunications and optical interconnects. In this context Ge rich-Ge/SiGe quantum wells (QW) have received a growing interest since the first demonstration of the quantum-confined Stark effect (QCSE) in these structures in 200

Silicon nitride waveguide-integrated Ge/SiGe quantum wells optical modulator

Silicon-based photonics has generated a strong interest in recent years, mainly for optical interconnects and sensing on photonic integrated circuits. The main rationales of silicon photonics are the reduction of energy consumption and photonic system costs via integration on a standard Si chip. Waveguide-integrated silicon based-optoelectronic modulators have been particularly studied as a key building block. Ge-rich Ge/SiGe quantum well waveguides are promising for compact and low energy consumption modulators thanks to the demonstration of direct gap related optical transitions in these structures, while silicon nitride (SiN) waveguide could be a promising alternative to Si waveguide. This paper studies an integration approach between passive SiN waveguide and active Ge/SiGe multiple quantum wells (MQWs) optoelectronic modulators. Photocurrent measurements at different bias voltages demonstrated strong optical modulation within the O-band wavelength (1.26 - 1.36 μm) from Ge/SiGe MQWs, while 3D-FDTD calculations confirm a compact and efficient integration with SiN waveguide on Si wafer

O-band quantum-confined Stark effect optical modulator from Ge/Si0.15Ge0.85 quantum wells by well thickness tuning

open7openPapichaya Chaisakul; Jacopo Frigerio; Delphine Marris-Morini; Vladyslav Vakarin; Daniel Chrastina; Giovanni Isella; Laurent VivienPapichaya, Chaisakul; Frigerio, Jacopo; Delphine Marris, Morini; Vladyslav, Vakarin; Chrastina, Daniel; Isella, Giovanni; Laurent, Vivie

Non-linear optical properties of Ge-rich SiGe waveguides in the near and mid infrared

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Nonlinear Properties of Ge-rich Si1-xGexMaterials with Different Ge Concentrations

Silicon photonics is a large volume and large scale integration platform for applications from long-haul optical telecommunications to intra-chip interconnects. Extension to the mid-IR wavelength range is now largely investigated, mainly driven by absorption spectroscopy applications. Germanium (Ge) is particularly compelling as it has a broad transparency window up to 15 μm and a much higher third-order nonlinear coefficient than silicon which is very promising for the demonstration of efficient non-linear optics based active devices. Si1-xGexalloys have been recently studied due to their ability to fine-Tune the bandgap and refractive index. The material nonlinearities are very sensitive to any modification of the energy bands, so Si1-xGexalloys are particularly interesting for nonlinear device engineering. We report on the first third order nonlinear experimental characterization of Ge-rich Si1-xGexwaveguides, with Ge concentrations x ranging from 0.7 to 0.9. The characterization performed at 1580 nm is compared with theoretical models and a discussion about the prediction of the nonlinear properties in the mid-IR is introduced. These results will provide helpful insights to assist the design of nonlinear integrated optical based devices in both the near-and mid-IR wavelength ranges

Ge-rich SiGe waveguides for supercontinuum generation in the mid-IR

International audienceThe third-order nonlinear parameter of Ge-rich SiGe waveguides are experimentally retrieved using a bi-directional top hat D-scan at λ = 1.58 µm. The obtained values are then used to fit the theoretical equation, providing promising values in the mid-IR, where the nonlinear effects are no longer limited by two-photon absorption. New Ge-rich SiGe waveguide designs are provided to exploit the nonlinear properties in the mid-IR, showing a flat anomalous dispersion over one octave spanning from λ = 3 µm to λ = 8 µm and a γ parameter that decreases from γ = 10 W-1 m-1

Ge-rich graded-index Si1-xGex racetrack resonators for long-wave infrared photonics

International audienceMid-infrared racetrack resonators are demonstrated working at 8µm wavelength. The devices are based on a graded SiGe platform providing low propagation loss on a large wavelength range in the mid-IR. Different resonators designs have been fabricated, with varying gap distances in the directional coupler. Q factors of more than 3000 have been experimentally demonstrated. These results pave the way towards compact mid-IR sensors or efficient active devices

On-chip fourier-transform spectrometer based on spatial heterodyning tuned by thermo- optic effect

International audienceMiniaturized optical spectrometers providing broadband operation and fine resolution have an immense potential for applications in remote sensing, non-invasive medical diagnostics and astronomy. Indeed, optical spectrometers working in the mid-infrared spectral range have garnered a great interest for their singular capability to monitor the main absorption fingerprints of a wide range of chemical and biological substances. Fourier-transform spectrometers (FTS) are a particularly interesting solution for the on-chip integration due to their superior robustness against fabrication imperfections. However, the performance of current on-chip FTS implementations is limited by tradeoffs in bandwidth and resolution. Here, we propose a new FTS approach that gathers the advantages of spatial heterodyning and optical path tuning by thermo-optic effect to overcome this tradeoff. The high resolution is provided by spatial multiplexing among different interferometers with increasing imbalance length, while the broadband operation is enabled by fine tuning of the optical path delay in each interferometer harnessing the thermo-optic effect. Capitalizing on this concept, we experimentally demonstrate a mid-infrared SiGe FTS, with a resolution better than 15 cm−1 and a bandwidth of 603 cm−1 near 7.7 μm wavelength with a 10 MZI array. This is a resolution comparable to state-of-the-art on-chip mid-infrared spectrometers with a 4-fold bandwidth increase with a footprint divided by a factor two

On-chip integrated resonators for long-wave infrared photonics

International audienceOn-chip optical resonators are extensively applied to many fields such as light sources through lasing or enhancement of material nonlinear effects, chemical and biological sensing, and optical network monitoring. Silicon-based on-chip resonators have been reported previously in near infrared (NIR) and shortwave infrared (SWIR), however integrated resonant structures remain still challenging for long-wave infrared (LWIR). In this work, we experimentally demonstrate the first on-chip integrated resonators in LWIR up to 8.4 µm. Two types of resonators, Fabry-Perot cavities and racetrack ring resonators, have been both investigated. Maximum quality factors Q = 2200 and Q = 3200 have been respectively observed for Fabry-Perot cavity and racetrack ring resonator at a wavelength around 8 µm. These resonant structures lay the foundation for new generation of integrated photonics circuits that open the path towards miniaturized multi-functional LWIR systems

Mid-infrared integrated wideband duel-polarization Fourier-transform spectrometer

International audienceDue to the unique vibrational/rotational frequencies in the mid infrared (MIR) fingerprint region, which scans from 500 to 1500 cm-1, molecules can be assuredly identified and quantified. Thus integrated on-chip mid infrared spectroscopic systems, with low power consumption and high performance, would show great value for numerous applications, such as medical diagnosis, astronomy, chemical and biological sensing or security. Different solutions can be envisioned as on-chip integrated spectrometers, such as Fourier-Transform spectrometers, echelle gratings, or arrayed waveguide gratings. Integrated spatial heterodyne Fourier-Transform spectrometer (SHFTS) shows relaxed fabrication tolerances while applying a phase and amplitude correction algorithm. Meanwhile, it provides high optical throughput and high spectral resolution compared with AWG or echelle gratings. However, up to now in the literature, most of the development of Fourier-Transform based spectrometer is based on silicon-on-insulator operating in the near infrared typically at 1.55 µm wavelength. Thereby the development of integrated Fourier-Transform spectrometer operating in the MIR covering the wide fingerprint region is highly desirable. In this work, we experimentally demonstrate the first polarization insensitive Fourier-Transform spectrometer operating in the mid infrared beyond 5 µm wavelength. The fabricated FTS which is based on the graded-index Ge-rich SiGe platform, contains 19 Mach-Zehnder interferometers with a linearly increasing path difference. A spectral resolution better than 15 cm-1 has been demonstrated within an unprecedented spectral range of 800 cm-1 (5 to 8.5 µm wavelength)