Integrated photonic systems require reliable, low power consumption phase shifters in order to scale circuit complexity. Micro-electromechanical systems (MEMS) are a viable candidate to provide low-power phase shifting, without the significant drawbacks of thermo-optic effects (high power usage and cross-talk). Previous works have demonstrated MEMS phase tuning through vertically displaced microbridges. However, these require > 40 V for a π phase shift [1] using gradient electric fields, though lower voltage requirements have been demonstrated for direct electrostatic actuation [2]. Ultra-low voltage (∼ 1 V) designs using horizontal slot waveguides have recently been demonstrated [3–5] although these methods require complex mechanical structures that must be released using vapor-HF or critical point drying post-processing. Here we present low-voltage phase tuning of vertically actuated beams that are released at wafer level with a vapor XeF2 etch completely in-house. Our process is carried out on an i-line photolithography stepper to define the waveguiding, metal, and MEMS structures. We use a sacrificial polysilicon layer between the SiN waveguide and the SiN beam. The XeF2 undercuts the beam, enabling a simple MEMS release process that does not undercut the waveguide. The movable SiN beam on top of the waveguide utilizes a single-sided anchor so that it resembles a wide and short single-clamped cantilever. This enables a phase shifter that is capable of a π phase shift with < 10 V and length < 100 μm. We measure the optical transmission versus applied voltage for multiple voltage sweeps and extract the phase shift per voltage at various wavelengths. We demonstrate reliable tuning over multiple sweeps with an average voltage of 7 V ± 0.5 V for a π phase shift. This phase shifter is central to the scalability of programmable photonic circuits, including quantum photonics.
We review our recent work on compact and low power silicon photonic components based on microelectromechanical systems (MEMS) and implemented in imec’s iSiPP50G foundry platform. Large scale reconfigurability is attractive for emerging applications such as photonic accelerators for AI workloads. However, the large power consumption and footprint of current components prohibits scaling to large circuits. Silicon MEMS offer 10000x lower power consumption, a small footprint, and excellent mechanics. We show phase shifters, couplers, and wavelength filters . The devices have small footprints of a few tens of micrometers per side, low insertion losses of the order of 0.1 dB and time constants of the order of 1 µs.
Optical spectroscopy is among the most important chemical analysis techniques, due to its high specificity and long-term stability. For spectroscopic analysis of gas compositions, the mid infrared (mid-IR) region is particularly important, owing to the rovibrational resonances in that spectral range. Hence, there is great interest in miniaturizing and reducing the power consumption of optical spectroscopic sensors, but until recently the mid-IR range has been out of reach. We demonstrate spectroscopic sensing of carbon dioxide using an integrated silicon waveguide at the strong absorption peak at 4.23 µm wavelength. We show different measurement principles that leverage the power of integrated optics in innovative ways.
In recent years, two-dimensional semiconductor quantum emitters have gotten substantial attention from the solid-state quantum photonics community. Their potential for on-chip integration in silicon-based photonics makes them an ideal candidate to realize large-scale hybrid quantum photonic circuits.
Given the strain-induced quantum emitter formation in two-dimensional WSe2, coupling of such quantum emitters into a SiN photonic waveguides is very promising. However, demonstration of single-photon emission into a waveguide has been elusive so far. Here, we show single-photon emission of strain-induced quantum emitters in a 2D flake integrated into a SiN waveguide. We take advantage of the waveguide edges as nucleation sites for quantum emitters. We observe single-photon emission coupled into the waveguide with a g(2)(0) = 0.15±0.09. This result opens up the way towards large-scale 2D emitter integration in on-chip quantum photonic circuits.
In the European project MORPHIC we develop a platform for programmable silicon photonic circuits enabled by waveguide-integrated micro-electro-mechanical systems (MEMS). MEMS can add compact, and low-power phase shifters and couplers to an established silicon photonics platform with high-speed modulators and detectors. This MEMS technology is used for a new class of programmable photonic circuits, that can be reconfigured using electronics and software, consisting of large interconnected meshes of phase shifters and couplers. MORPHIC is also developing the packaging and driver electronics interfacing schemes for such large circuits, creating a supply chain for rapid prototyping new photonic chip concepts. These will be demonstrated in different applications, such as switching, beamforming and microwave photonics.
Silicon photonics is the study and application of integrated optical systems which use silicon as an optical medium, usually by confining light in optical waveguides etched into the surface of silicon-on-insulator (SOI) wafers. The term microelectromechanical systems (MEMS) refers to the technology of mechanics on the microscale actuated by electrostatic actuators. Due to the low power requirements of electrostatic actuation, MEMS components are very power efficient, making them well suited for dense integration and mobile operation. MEMS components are conventionally also implemented in silicon, and MEMS sensors such as accelerometers, gyros, and microphones are now standard in every smartphone. By combining these two successful technologies, new active photonic components with extremely low power consumption can be made. We discuss our recent experimental work on tunable filters, tunable fiber-to-chip couplers, and dynamic waveguide dispersion tuning, enabled by the marriage of silicon MEMS and silicon photonics.
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