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• Photonics Research
• Vol. 9, Issue 4, 04000596 (2021)
Yanmei Cao1, Ezgi Sahin1、2, Ju Won Choi1, Peng Xing1, George F. R. Chen1, D. K. T. Ng3, Benjamin J. Eggleton4、5, and Dawn T. H. Tan1、*
Author Affiliations
• 1Photonics Devices and Systems Group, Singapore University of Technology and Design, 8 Somapah Road, Singapore 487372, Singapore
• 2Current address: Photonic Systems Laboratory (PHOSL), Ecole Polytechnique Fédérale de Lausanne, STI-IEL, Station 11, CH-1015 Lausanne, Switzerland
• 3Institute of Microelectronics, A*STAR, 2 Fusionopolis Way, #08-02, Innovis Tower, Singapore 138634, Singapore
• 4Institute of Photonics and Optical Science, School of Physics, The University of Sydney, Sydney, New South Wales 2006, Australia
• 5The University of Sydney Nano Institute (Sydney Nano), The University of Sydney, Sydney, New South Wales 2006, Australia
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Abstract

Spectral tunability methods used in optical communications and signal processing leveraging optical, electrical, and acousto-optic effects typically involve spectral truncation that results in energy loss. Here we demonstrate temperature tunable spectral broadening using a nonlinear ultra-silicon-rich nitride device consisting of a 3-mm-long cladding-modulated Bragg grating and a 7-mm-long nonlinear channel waveguide. By operating at frequencies close to the grating band edge, in an apodized Bragg grating, we access strong grating-induced dispersion while maintaining low losses and high transmissivity. We further exploit the redshift in the Bragg grating stopband due to the thermo-optic effect to achieve tunable dispersion, leading to varying degrees of soliton-effect compression and self-phase-modulation-induced spectral broadening. We observe an increase in the bandwidth of the output pulse spectrum from 69 to 106 nm as temperature decreases from 70°C to 25°C, in good agreement with simulated results using the generalized nonlinear Schrödinger equation. The demonstrated approach provides a new avenue to achieve on-chip laser spectral tuning without loss in pulse energy.
 $G(z)=(Gapod−G1)×cos2(πx)+G1,wherex={z2Lapod,if z≤Lapod,0.5,if LapodLCMBG−Lapod,,$(1)

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 $∂A∂z=∑k=24ik+1k!βk∂kA∂tk−α2A+iγeff(|A|2A).$(2)

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Yanmei Cao, Ezgi Sahin, Ju Won Choi, Peng Xing, George F. R. Chen, D. K. T. Ng, Benjamin J. Eggleton, Dawn T. H. Tan. Thermo-optically tunable spectral broadening in a nonlinear ultra-silicon-rich nitride Bragg grating[J]. Photonics Research, 2021, 9(4): 04000596