Wideband Spectral Enhancement through On‐Chip Bragg‐Soliton Dynamics

• Published in: Advanced photonics research Vol. 2; no. 8
• Main Authors: Sahin, Ezgi, Blanco-Redondo, Andrea, Sohn, Byoung-Uk, Cao, Yanmei, Chen, George F. R., Ng, Doris K. T., Eggleton, Benjamin J., Tan, Dawn T. H.
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01.08.2021; Wiley-VCH
• Subjects: Bragg gratings; coherences; Electrons; integrated nonlinear optics; solitons; Spectrum analysis; supercontinuum generations
• ISSN: 2699-9293; 2699-9293
• DOI: 10.1002/adpr.202100107

Supercontinuum generation (SCG) through soliton fission provides high‐brightness, spectrally‐rich light needed for hyperspectral imaging, broadband spectroscopy, and fluorescence microscopy. The prospect of miniaturization has led to many demonstrations of this phenomenon in integrated platforms. However, due to the moderate dispersion and nonlinearity generally available in channel waveguides, femtosecond pulses have typically been required to date, as the use of picosecond pulses would require unpractically long devices to achieve soliton fission. Here, spectral bandwidth enhancement of the supercontinuum process through Bragg grating induced soliton‐effect compression and soliton fission is demonstrated. This approach uses picosecond pulses on a complementary metal oxide semiconductor (CMOS)‐compatible, millimeter‐scale platform, consisting of a monolithically integrated cladding‐modulated Bragg grating with a channel waveguide. The strong dispersion near the stopband of the grating enables compression and fission of picosecond higher‐order solitons, which enhances the spectral broadening in the channel waveguide. A 4.3 spectral bandwidth enhancement is reported, with respect to a reference waveguide of the same length. The output spectra are further studied both through simulations and experiments and determined to possess high spectral coherence. These results highlight a simple route to significantly augment the bandwidth of nonlinear processes such as SCG while maintaining low power and compact footprint. Harnessing grating‐induced soliton‐effect compression and soliton fission, spectral bandwidth of generated supercontinuum is enhanced using a monolithic device that consists of an integrated cladding‐modulated Bragg grating with a channel waveguide on a CMOS‐compatible platform. By injecting picosecond pulses, a 4.3× spectral bandwidth enhancement and high spectral coherence in the generated supercontinuum spectrum are reported.