Cavity-enhanced harmonic generation in silicon rich nitride photonic crystal microresonators

Abstract

We report second and third harmonic generation in photonic crystal cavities fabricated in a suspended silicon-rich nitride membrane under resonant continuous-wave excitation at telecom wavelength. Two-dimensional photonic crystal cavities with a far-field optimized line-width modulated design were employed. A quality factor at fundamental wavelength as high as Q = 1.3 × 104 and a coupling efficiency ηc ≈ 30% enabled us to exploit the cavity field enhancement to achieve the generation efficiencies ρSH = (4.7 ± 0.2) × 10−7 W−1 and ρTH = (5.9 ± 0.3) × 10−5 W−2. The absence of saturation effects at high power and the transparency of the device at the second harmonic wavelength suggest the absence of two-photon absorption and related detrimental effects.

Silicon Nitride Photonics for the Near-Infrared

“…With the aim of exploiting the large nonlinear response of the Si-rich silicon nitride, we employed this material for the fabrication of PhC waveguides [48] and high-Q PhC microcavities [49], [50]. The PhC membrane was obtained in a 300 nm thick film of material with a refractive index n=2.48 patterned with a triangular lattice of air holes of period a=580 nm and radius r = 0.3a.…”

“…The discrepancy with the numerical estimate is mainly due to the residual linear absorption of the material, which limits the maximum ring-down time of the cavity mode. In order to probe the nonlinear optical properties of these structures, we produced samples optimized for efficient second-and third-harmonic generation (HG) [50]. By appropriately adjusting the radius of specific holes (marked bold in Dig.…”

Doubly resonant second-harmonic generation of a vortex beam from a bound state in the continuum

“…Doubly resonant conditions have been proposed and experimentally demonstrated in dual period Bragg mirrors [16][17][18], birefringently phase-matched waveguides [19], geometric dispersion-tuned microring resonators [20,21], and plasmonic nanoantennas [22]. Photonic crystal (PhC) defect cavities patterned in two-dimensional (2D) slabs, which allow for very tight field confinement in purely dielectric resonators, have been shown to produce significant SHG enhancement in a singly resonant regime at FH [23][24][25][26][27][28][29][30][31]. However, implementing a doubly resonant condition in PhC slab cavities is a longstanding challenge, because the SH frequency range generally lies entirely inside the light cone of the cladding materials, such that efficient confinement in the out-of-plane direction is prevented, not to mention the difficulty of engineering photonic bandgaps around both frequencies to favor the in-plane confinement.…”

Doubly resonant second-harmonic generation of a vortex beam from a bound state in the continuum

“…Doublyresonant cavities have been proposed and experimentally demonstrated in dual period Bragg mirrors [16][17][18], birefringently phase-matched waveguides [19], and geometric dispersion-tuned micro-ring resonators [20,21]. Photonic crystal (PhC) defect cavities patterned in twodimensional (2D) slabs, which allow for very tight field confinement in purely dielectric resonators, have been shown to produce significant SHG enhancement in a singly-resonant regime at FH [22][23][24][25][26][27][28][29][30]. However, imple- * jun.wang@epfl.ch menting a doubly-resonant condition in PhC slab cavities is a longstanding challenge, because the SH frequency range generally lies entirely inside the light cone of the cladding materials, such that efficient confinement in the out-of-plane direction is prevented, not to mention the difficulty of engineering photonic bandgaps around both frequencies to favor the in-plane confinement.…”