Silicon photonic MEMS breakthrough to help large-scale photonic integrated circuits
In the recent paper "Silicon photonic microelectromechanical systems in casting processes with additive and subtractive ring resonators" published in the Journal of Optical Microsystems [1], Hamed Sattari of the Ecole Polytechnique Fédérale de Lausanne (EPFL) and co-authors demonstrate a high power assembly for demultiplexing operations by physically moving a suspended silicon ring resonator in a photonic integrated circuit. The results will advance the realization of large-scale photonic integrated circuits.
01Efficient fiber optic communication systems: New, compact silicon photonic MEMS
In recent years, there has been an unprecedented acceleration in global digitization. Video streaming and video conferencing in home office and distance learning environments have led to a surge in residential broadband usage. Emerging applications such as artificial intelligence and self-driving cars will further accelerate the demand for data communications in the future. Today's Internet infrastructure is built on fiber optic communications, but how can fiber optic communication systems be made more efficient to meet the digital communication needs of the future?
To cope with increasing data rates, fiber optic communication systems use many separate communication channels on dedicated wavelengths, a technique known as wavelength division multiplexing. These channels are combined in a multiplexer before being transmitted through the fiber. In order to retrieve the data, the spectra are demultiplexed at the receiving end. Typically, this operation is performed through a photonic integrated circuit (PIC). the PIC confines and directs light into microscopic components that manipulate information in multiple wavelength channels, such as an array of waveguide gratings or an integrated ring resonator.
Schematic diagram of a MEMS add-drop filter (add-drop filter). The device is tuned by driving a vertically moving suspended ring resonator. The extremely compact size allows for fast operation and the electrostatic drive mechanism ensures extremely low power consumption, which makes this new filter highly energy efficient.
In this paper, Hamed Sattari and co-authors demonstrate a high power assembly for demultiplexing operation by physically moving a suspended silicon ring resonator in a photonic integrated circuit. The mechanical displacement of the ring resonator allows the extraction of a wavelength channel into the bus waveguide, effectively acting as a micromechanically operated interpolation filter. The electrostatic drive mechanism is built on microelectromechanical systems (MEMS), a technology widely used in consumer electronics such as micro-mirrors for video projectors. Compared to these well-established optical MEMS, the new silicon photonic MEMS demonstrated in this paper is three orders of magnitude smaller. The waveguide cross section of the ring resonator is less than 650 nm x 220 nm, and a displacement of less than 500 nm is sufficient to operate the filter. This compact size allows for fast operation compared to existing MEMS products, and the electrostatic drive mechanism ensures extremely low power consumption, making this new filter highly energy efficient.
Post-processing steps for releasing silicon photonic MEMS assemblies. (1) start stacking after preparing the remaining oxide on and between the waveguides for removal, (2) alumina passivation by ALD, (3) alumina patterning by dry/wet etching, and (4) VHF release etching to remove BOX.
Optical microscope image of the chip area of the MEMS.
SEM image of the add/drop filter (false color) showing the well-defined suspended actuator and waveguide.
03Technology milestone: Integratable, high-volume production
The silicon photonic MEMS additive and subtractive filters were realized by post-processing on a standard silicon photonics platform at IMEC, an international R&D organization based in Belgium. "The integration of MEMS in silicon photonics, manufactured in a standardized foundry process, represents a technological milestone. We have demonstrated that photonic MEMS can be integrated on-chip with existing high-performance photonic components and can be scaled to high volumes." Niels Quack, who led photonic MEMS development activities at EPFL in Switzerland (now at the University of Sydney), said [2].
