Photonic chips are becoming increasingly complex, combining even more optical building blocks on the same chip. With this growing complexity we also see an expanding need for, and use of electrical tuning. This imposes opportunities, as photonic circuits can now become reconfigurable at run time, even to the point of creating arbitrary connectivity between functional building blocks, serving as a general-purpose optical processor. But at the same time, large-scale configurability comes with some tremendous challenges in terms of power consumption, electrical and optical packaging, driver electronics and control algorithms. We will discuss our recent progress in these domains in our path to building general-purpose programmable photonic chips. Expanding silicon photonics with high-efficiency electro-optic tuners, high-density packaging solutions, and electronics and software layers to govern the behavior of these photonic circuits that can be used for both photonic and microwave analog signal processing.
KEYWORDS: Waveguides, Microelectromechanical systems, Phase shifts, Liquid crystals, Silicon photonics, Silicon, Photonic integrated circuits, Electrodes, Oxides, Back end of line
The demand for efficient actuators in photonics has peaked with increasing popularity for large-scale general-purpose programmable photonics circuits. We present our work to enhance an established silicon photonics platform with low-power micro-electromechanical (MEMS) and liquid crystal (LC) actuators to enable largescale programmable photonic integrated circuits (PICs).
We give an overview the progress of our work in silicon photonic programmable circuits, covering the technology stack from the photonic chip over the driver electronics, packaging technologies all the way to the software layers. On the photonic side, we show our recent results in large-scale silicon photonic circuits with different tuning technologies, including heaters, MEMS and liquid crystals, and their respective electronic driving schemes. We look into the scaling potential of these different technologies as the number of tunable elements in a circuit increases. Finally, we elaborate on the software routines for routing and filter synthesis to enable the photonic programmer.
Photonic add-drop filters are crucial components for the implementation of wavelength division multiplexing (WDM) in fiber-optic communication systems. The recent progress in photonic integration has shown the potential to integrate photonic add-drop filters alongside high-performance photonic building blocks on a chip to construct compact and complex photonic-integrated circuits for WDM. Typically, implementations are based on micro-ring resonators with integrated heaters or free carrier dispersion-based modulators to adjust the filter wavelength. However, heaters suffer from high power consumption, and free carriers result in optical absorption losses, limiting the scalability toward very-large-scale circuits. We demonstrate the design, simulation, fabrication, and experimental characterization of a compact add-drop filter based on a vertically movable, MEMS-actuated ring resonator. The MEMS-actuated add-drop filter is implemented in IMEC’s iSiPP50G silicon photonics platform and realized using a short post-processing flow to safely release the suspended MEMS structures in a wafer-level compatible process. The filter exhibits a through port linewidth of ∼1 nm (124.37 GHz) at 1557.1 nm, and it retains a port extinction of 20 dB and a port isolation of >50 dB under 27 V of actuation voltage. The combination of low-power consumption and a compact footprint demonstrates the suitability for very-large-scale integration in photonic circuits.
We present our work in the European project MORPHIC to extend an established silicon photonics platform with low-power and non-volatile micro-electromechanical (MEMS) actuators to demonstrate large-scale programmable photonic integrated circuits (PICs).
We present our work to extend silicon photonics with MEMS actuators to enable low-power, large scale programmable photonic circuits. For this, we start from the existing iSiPP50G silicon photonics platform of IMEC, where we add free-standing movable waveguides using a few post-processing steps. This allows us to implement phase shifters and tunable couplers using electrostatically actuated MEMS, while at the same time maintaining all the original functionality of the silicon photonics platform. The MEMS devices are protected using a wafer-level sealing approach and interfaced with custom multi-channel driver and readout electronics.
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.
Silicon (Si) photonic micro-electro-mechanical systems (MEMS), with its low-power phase shifters and tunable couplers, is emerging as a promising technology for large-scale reconfigurable photonics with potential applications for example in photonic accelerators for artificial intelligence (AI) workloads. For silicon photonic MEMS devices, hermetic/vacuum packaging is crucial to the performance and longevity, and to protect the photonic devices from contamination. Here, we demonstrate a wafer-level vacuum packaging approach to hermetically seal Si photonic MEMS wafers produced in the iSiPP50G Si photonics foundry platform of IMEC. The packaging approach consists of transfer bonding and sealing the silicon photonic MEMS devices with 30 μm-thick Si caps, which were prefabricated on a 100 mm-diameter silicon-on-insulator (SOI) wafer. The packaging process achieved successful wafer-scale vacuum sealing of various photonic devices. The functionality of photonic MEMS after the hermetic/vacuum packaging was confirmed. Thus, the demonstrated thin Si cap packaging shows the possibility of a novel vacuum sealing method for MEMS integrated in standard Si photonics platforms.
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.
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