Ultracompact, polarization-independent, and highly scalable optical power splitting model employing fan-out bending metamaterials

Abstract

Optical power splitters (OPSs) are essential components in the photonic integrated circuits. Considerable power splitting schemes have been reported on the silicon-on-insulator platform. However, the corresponding device lengths are enlarged, and polarization-sensitive operations are usually encountered when the splitting channels are increased from two to five. In this paper, a novel power splitting model is proposed to overcome these limitations. Here, fan-out bending subwavelength grating (FBSWG) metamaterials instead of classical straight SWGs are leveraged to expand the input TE/TM mode in an ultracompact region and further bend its wavefronts. By using <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> </mml:math> -angled tapers to match bending wavefronts, the light expanded by FBSWGs can be collected and evenly distributed into <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> </mml:math> output channels. Based on such a model, three OPSs are designed and experimentally demonstrated, which are the shortest polarization-independent <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:math> OPSs reported until now to our knowledge. The characterizations show low insertion losses ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m6"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>1.2</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m7"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>1.35</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m8"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>1.65</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> ) and uniformities ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m9"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>0.9</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m10"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>1</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m11"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>1</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> ) over bandwidths of 54 nm, 49 nm, and 38 nm for the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m12"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m13"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m14"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:math> OPSs, respectively. For the first time, an ultracompact device length of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m15"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>4.3</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μm</mml:mi> </mml:mrow> </mml:math> and a polarization-independent operation can be maintained simultaneously as the output splitting channels are increased.