Current programmable photonic integrated circuits (PICs) are volatile and suffer from high optical signal losses – both of which prevent them from maintaining their programmed state. A team of researchers has now fabricated meter-scale single-mode photonic waveguides that boast only 0.03 dB/cm optical losses.
The researchers also used their waveguides to construct optical true delay lines (OTDLs), which are important components of many photonic devices – including future quantum information processors and sensors.
Lithium niobate on insulator (LNOI) has recently emerged as an attractive PIC substrate. It promises to make circuits with lower losses, higher density, and greater tunability than previous devices. The researchers have used a new technique called photolithography-associated chemo-mechanical etching (PLACE). The technique can produce smooth, meter-long photonic waveguides on the LNOI that can be integrated with micro-electrodes, allowing the devices to be tuned electro-optically later.
PLACE requires five major steps. The first step is to apply a thin chromium coating on the top surface of lithium niobate thin film using magnetron sputtering. Next, the researchers pattern the chromium film into a waveguide mask using space-selective femtosecond laser ablation. They then use a chemo-mechanical polishing (CMP) process to remove the lithium niobate selectively. The CMP process produces extremely smooth walls, leading to ultralow light propagation losses in the finished waveguides.
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