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Figure
5.( a – d) Fabrication process:( a) adhesive bonding of the AlGaAs epitaxy on a silicon substrate;( b) GaAs substrate removal;( c) HSQ resist spun and patterned by electron beam lithography;( d) ICP RIE etching;( e) Ring resonators and bus waveguides;( f) SEM pictures of fabricated devices:( top left) bus waveguide and ring resonator in the evanescent coupling region;( top right) fabrication test of longitudinal corrugated PhC waveguides for dispersion engineering;( bottom left) waveguide end facet;( bottom right) SW grating coupler.( g) Optical transmission of a ring resonator and( h) its associated group index n g, calculated for each resonances( blue scatters) and fitted in function of k( red dashed line).
photonics at the telecom wavelengths. We found that Kerr-like cavity solitons can be formed and coupled to dispersive waves at SH, which tends to disperse most of the SH power. For broadband SHG applications, this represents a detrimental effect that is due to steep and hardly manageable dispersion profiles at 2x 0. Dispersion engineering [ 41, 42, 44, 58, 59 ] and inverse design [ 40, 43 ] approaches represent a valid perspective solution and it is currently under investigation.
A possible alternative is decoupling the v( 2) + v( 3) nonlinear problem and to design a Kerr nonlinear resonator with a purely quadratic SHG optical feedback. We have presented a U-shaped v( 2) design which is capable of about 16 % x 0? 2x 0 conversion with a minimal propagation length( 300 lm).
Interestingly, we have predicted a spectral symmetry breaking due to the spanning over different phase matching conditions, in a U-shaped or snaking waveguide geometries. Notably, symmetry breaking is a key concept in physics: besides being the basic mechanism for energy-to-mass conversion in Gauge theory [ 66 ], in the field of optics it is of crucial importance for spin glasses [ 67 ] or random lasers [ 68 ]. For Kerr mediums, a symmetry-breaking transition can be responsible of periodic pattern generation [ 69 ], and in the context of nonlinear passive resonators it can generate a trapping potential for CSs [ 70 ]. Eventually, symmetry can be recovered by a chirped pulse pump [ 8 ]. As a perspective, one can investigate the possibility of designing spectral potential traps, as well as broadband SHG integrated photonics.
Acknowledgments
The authors acknowledge Hamza Dely and Victor Turpaud( C2N, CNRS) for the fruitful discussions.
Funding
ANR-22-CE92-0065, DFG-505515860( Quadcomb); EU – NRRP, NextGenerationEU( PE00000001 – program“ RESTART”). LL acknowledges the support of French Agence-innovationdefense N ° DGA01D22020572. The work is partly supported by the French RENATECH network.
Conflicts of interest The authors declare no conflicts of interest.
Data availability statement
Data underlying the results presented in this paper are not publicly available but may be obtained from the authors upon reasonable request.