Toward calibration-free Mach–Zehnder switches for next-generation silicon photonics

Abstract

Silicon photonic Mach–Zehnder switches (MZSs) have been extensively investigated as a promising candidate for optical systems. However, conventional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> MZSs are usually prone to the size variations of the arm waveguides due to imperfect fabrication, resulting in considerable random phase imbalance between the two arms, thereby imposing significant challenges for further developing next-generation <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mi mathvariant="italic">N</mml:mi> <mml:mo>×</mml:mo> <mml:mi mathvariant="italic">N</mml:mi> </mml:mrow> </mml:math> MZSs. Here we propose a novel design toward calibration-free <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"> <mml:mrow> <mml:mi mathvariant="italic">N</mml:mi> <mml:mo>×</mml:mo> <mml:mi mathvariant="italic">N</mml:mi> </mml:mrow> </mml:math> MZSs, employing optimally widened arm waveguides, enabled by novel compact tapered Euler S-bends with incorporated mode filters. With standard 180 nm CMOS foundry processes, more than thirty <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> MZSs and one <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m6"> <mml:mrow> <mml:mn>4</mml:mn> <mml:mo>×</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> Benes MZS with the new design are fabricated and characterized. Compared with their conventional counterparts with 0.45-μm-wide arm waveguides, the present <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m7"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> MZSs exhibit significant reduction in the random phase imbalance. The measured extinction ratios of the present <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m8"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m9"> <mml:mrow> <mml:mn>4</mml:mn> <mml:mo>×</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> MZSs operating in the all-cross state are 27-49 dB and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m10"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mn>20</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> across the wavelength range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m11"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mn>60</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>nm</mml:mi> </mml:mrow> </mml:math> , respectively, even without any calibrations. This work paves the way toward calibration-free large-scale <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m12"> <mml:mrow> <mml:mi mathvariant="italic">N</mml:mi> <mml:mo>×</mml:mo> <mml:mi mathvariant="italic">N</mml:mi> </mml:mrow> </mml:math> MZSs for next-generation silicon photonics.