Ultralow-loss compact silicon photonic waveguide spirals and delay lines

Abstract

Low-loss and compact optical waveguides are key for realizing various photonic integrated circuits with long on-chip delay lines, such as tunable optical delay lines, optical coherence tomography, and optical gyroscopes. In this paper, a low-loss and compact silicon photonic waveguide spiral is proposed by introducing broadened Archimedean spiral waveguides with a tapered Euler S-bend. A 100-cm-long waveguide spiral is realized with a minimal bending radius as small as 10 μm by using a standard 220-nm-thick silicon-on-insulator foundry process, and the measured propagation loss is as low as 0.28 dB/cm. Furthermore, the present waveguide spirals are used to realize a 10-bit tunable optical delay line, which has a footprint as small as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mn>2.2</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>mm</mml:mi> <mml:mo>×</mml:mo> <mml:mn>5.9</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>mm</mml:mi> </mml:mrow> </mml:math> and a dynamic range of 5120 ps with a fine resolution of 10 ps.