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Second-harmonic generation (SHG) plays a significant role in modern photonic technology. Integrated photonic resonators fabricated with thin-film lithium niobate can achieve ultrahigh efficiencies by combining small mode volumes with high material nonlinearity. Cavity-enhanced SHG requires accurate phase and frequency matching conditions, where fundamental and second-harmonic wavelengths are both on resonance. However, this double-resonance condition can typically be realized only at a fixed random wavelength due to the high sensitivity of photonic resonances to the device geometry and fabrication variations. Here, we propose a novel method that can achieve the double-resonance condition over a large wavelength range. We combine thermal-optic and electro-optic (EO) effects to realize the separate tuning of fundamental and second-harmonic resonances. We demonstrated that the optimum SHG efficiency can be maintained over a wavelength range that exceeds the limit achievable with only thermal tuning. With this flexible tuning capability, we further show the precise alignment of SHG wavelengths of two separate thin-film lithium niobate resonators without sacrificing efficiencies.
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Selective passive tuning of cavity resonance by mode index engineering of the partial length of a cavity
Cavities in large-scale photonic integrated circuits (PICs) often suffer from a wider distribution of resonance frequencies due to fabrication errors. It is crucial to adjust the resonances of cavities using post-processing methods to minimize the frequency distribution. We have developed a concept of passive tuning by manipulating the mode index of a portion of a microring cavity, which we named mode index engineering (MIE). Through analytical studies and numerical experiments, we have found that depositing a thin film of dielectric material on top of the cavity or etching the material enables us to fine-tune the resonances and minimize the frequency distribution. This versatile method allows for the selective tuning of each cavity’s resonance in a large set of cavities in a post-fabrication step, providing robust passive tuning in large-scale PICs. We show that the proposed method achieves a tuning resolution below 1/Q and a range of up to 103/Q for visible to near-infrared wavelengths. Furthermore, this method can be applied and explored in various integrated photonic cavities and material configurations.
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- Award ID(s):
- 2013771
- PAR ID:
- 10569086
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 33
- Issue:
- 3
- ISSN:
- 1094-4087; OPEXFF
- Format(s):
- Medium: X Size: Article No. 4446
- Size(s):
- Article No. 4446
- Sponsoring Org:
- National Science Foundation
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