Permanent mitigation of loss in ultrathin silicon-on-insulator high-Q resonators using ultraviolet light

Abstract

Mitigation of optical losses is of prime importance for the performance of integrated microphotonic devices. In this paper, we demonstrate strip-loaded guiding optical components realized on a 27 nm ultra-thin SOI platform. The absence of physically etched boundaries within the guiding core suppresses majorly the scattering loss, as shown by us previously for a silicon nitride (Si3N4) platform [Stefan et. al., OL 40, 3316 (2015)]. Unexpectedly, the freshly fabricated Si devices showed large losses of 5 dB/cm, originating from absorption by free carriers, accumulated under the positively charged Si3N4 loading layer. We use 254 nm ultraviolet (UV) light exposures to neutralize progressively and permanently silicon nitride's bulk charge associated with diamagnetic K+ defects. This in turn leads to a net decrease of electron concentration in the SOI layer, reducing thus the propagation loss down to 0.9 dB/cm. Detailed MOS-capacitance measurements on test samples were performed to monitor the UV-induced modification of the electronic properties of the system. The evolution of loss mitigation was directly monitored both by Beer-Lambert approach in waveguide transmission experiments, as well as through more accurate cavity linewidth measurements. In the last case, we demonstrate how intrinsic cavity Q's boost from 60,0000 to up to 500,000 after UV treatment. Our results may open routes towards engineering of new functionalities in photonic devices employing UV-modification of space charges and associated local electric fields, unveil the origin of induced optical nonlinearities in Si3N4/Si micro-photonic systems, as well as envisage possible integration of these with ultra-thin SOI electronics.

Second‐Harmonic Generation in Strained Silicon Metasurfaces

“…[42] Furthermore, it is well known that charged defects at the Si/SiN x interface could be suppressed by UV irradiation. [43][44][45] To evaluate its contribution to the enhanced SHG, we measured SHG signals of a SiN x -coated Si film before and after 23 h of UV exposure and observed no significant change in the SHG intensity, as shown in Figure 4b. Therefore, we infer that the applied stress, instead of the charged defects, may play the most significant role in the enhanced SHG in the strained silicon metasurface.…”

Laser trimming of the operating wavelength of silicon nitride racetrack resonators

“…The refractive index of silicon oxide, silicon nitride and silicon oxynitride can also be modified by either e-beam or UV irradiation [41][42][43]. Furthermore, UV exposure of silicon nitride devices fabricated on ultra-thin silicon-on-insulator platform can permanently reduce propagation losses which may occur due the presence of electrical charge in the silicon nitride layer, originating from paramagnetic defects (dangling bonds) [44]. Haeiwa et al presented a method for permanently tuning the resonant wavelength of vertically coupled silicon nitride microring resonators by UV irradiation.…”

Tunable hybrid silicon nitride and thin-film lithium niobate electro-optic microresonator

“…[7]. Historically, microring resonators have been widely investigated in different material systems including Si [7][8][9], Si 3 N 4 [9,10], graphene-Si [11], LiNbO 3 [12][13][14][15][16], Si-LiNbO 3 [17][18][19][20], Si-GaN [21], InP [22], AlN [23], GaAs [24], polymers [25], chalcogenide [26], etc. The tuning methods explored in these materials include the plasma dispersion effect, the thermo-optic effect, the electro-absorption effect, electro-optomechanics, and the electro-optic (EO) effect [12,17,26,27].…”