Mid-infrared chalcogenide microfiber knot resonators
Yu Xie, Dawei Cai, Hao Wu, Jing Pan, Ning Zhou, Chenguang Xin, Shaoliang Yu, Pan Wang, Xiaoshun Jiang, Jianrong Qiu, Xin Guo, Limin Tong
Abstract
A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>As</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> glass fibers and assembled into MKRs in liquid without surface damage. The measured <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> </mml:math> factor of a typical 824 μm diameter ChG MKR is about <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:mn>2.84</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> at the wavelength of 4469.14 nm. The free spectral range (FSR) of the MKR can be tuned from 2.0 nm (28.4 GHz) to 9.6 nm (135.9 GHz) by tightening the knot structure in liquid. Benefitting from the high thermal expansion coefficient of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>As</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> glass, the MKR exhibits a thermal tuning rate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"> <mml:mrow> <mml:mn>110</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>pm</mml:mi> <mml:mo>·</mml:mo> <mml:mo>°</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> at the resonance peak. When embedded in polymethyl methacrylate (PMMA) film, a 551 μm diameter MKR retains a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m6"> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> </mml:math> factor of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m7"> <mml:mrow> <mml:mn>1.1</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> </mml:mrow> </mml:math> . The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.