Silicon-Based Electro-Optical Device Delivers Narrowband Multi-GHz Filtering


This article is part of the TechXchange: Silicon Photonics.

What you’ll learn:

How an electro-optic PIC can implement RF filtering functions.
Which E-O components are needed for passband and notch filtering.
How the overall device was fabricated and the test results.

 

It’s a very safe bet that a wireless or wired system uses at least one filter—and likely many more—in their various forms: low-pass, high-pass, notch, or bandpass. As operating frequencies increase into the gigahertz and tens of gigahertz range, it’s increasingly difficult to create filters with narrow bandpass or notch performance, especially using discrete-device versions which are almost always impractical in that range.

While there are ways to create such filters using surface-acoustic-wave (SAW) and bulk-acoustic-wave (BAW) technologies, even these technologies struggle to keep up with the demands for narrow bandwidth filtering at these ever-higher frequencies.

Chalcogenide Glass + Silicon

Recognizing the need and opportunity, the photonic and electro-optical (E-O) community is doing a great deal of research to overcome these barriers. For example, researchers at the University of Sydney (Australia) Nano Institute devised a compact semiconductor chip that provides for the heterogeneous integration of chalcogenide glass with silicon to create specialty filters.

Their effort has resulted in a notch filter with narrow 37-MHz 3-dB bandwidth and deep 51-dB RF rejection, tunable from 2.5 and 15 GHz (Fig. 1). Chalcogenide glass contains one or more chalcogens (sulfur, selenium, tellurium) but excludes oxygen—they have high optical transparency in the infrared (IR) region of telecommunication windows of 3 to 5 μm and 8 to 12 μm.



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