Selective tuning of optical modes in a silicon comb-like photonic crystal cavity

Abstract

Realizing multiply resonant photonic crystal cavities with large free spectral range is key to achieve integrated devices with highly efficient nonlinear response, such as frequency conversion, four-wave mixing, and parametric oscillation. This task is typically difficult owing to the cavity modes' sensitivity to fabrication disorder, which makes it hard to reliably achieve a comb-like spectrum of equally spaced modes even when a perfect matching is theoretically predicted. Here we show that a comb-like spectrum of up to 8 modes with very high quality factor and diffraction limited volumes can be engineered in the bichromatic-type potential of a two-dimensional photonic crystal cavity fabricated in a thin silicon membrane. To cope with the tight tolerance in terms of frequency spacings and resonance linewidths, we develop a permanent post-processing technique that allows the selective tuning of individual confined modes, thus achieving an almost perfect frequency matching of high Q resonances with record finesse in silicon microresonators. Our experimental results are extremely promising in view of ultra-low power nonlinear photonics in silicon.

Photonic crystal optical parametric oscillator

“…In particular, achieving squeezing on chip using a degenerate OPO has drawn a lot of interest recently[ 38 , 42 – 44 ], Moreover, it has been shown very recently that a network of coupled degenerate OPO could be implemented on chip to implement a coherent Ising machine [ 45 ], A different idea has also been proposed recently to use a degenerate OPO, as a "noise eater" 46 ], In ring resonator, there are strategies to control higher order interactions, for instance by inducing sidewall corrugation[ 47 ] or adding an auxiliary resonator [ 36 , 38 ] or implementing narrowband FWM by implementing a special dispersion profile[ 21 , 23 ]. Here, the devices operates naturally as a degenerate triply resonant OPO, although it could in principle be possible to achieve efficient cascaded interactions with some additional engineering[ 48 ] and tuning. In conclusion, we demonstrated, to the best of our knowledge, the parametric oscillation regime in a Photonic Crystal Cavity.…”

Thermo-Optically Induced Transparency on a photonic chip

“…In the case of OMIT, this would require the exact matching of both the mechanical and optical resonance frequency of multiple high Q-factor cavities. For TOIT on the other hand only the optical resonance wavelengths need to be matched (within the cavity linewidth) and the ability to use moderate Q-factor cavities -38,000 vs 500 million (12) or 26 million (9) -greatly simplifies this task, which can be easily and accurately performed after the device fabrication (24). Therefore, as sketched in Fig.…”

Thermo-optically induced transparency on a photonic chip

“…In the case of OMIT, as an example, this would require the exact matching of both the mechanical and optical resonance frequencies of multiple high Q-factor cavities. On the other hand, for TOIT only the optical resonance wavelengths need to be matched (within the cavity linewidth), and the possibility to use moderate Q-factor cavities—38,000 in this work vs 500 million in a table-top Fabry-Pérot cavity 25 greatly simplifies this task, which can be easily and accurately performed after the device fabrication 31 . Therefore, as sketched in Fig.…”