Abstract
Quasi-phase-matching (QPM) has become one of the most common approaches for increasing the efficiency of nonlinear three-wave mixing processes in integrated photonic circuits. Here, we provide a study of dispersion engineering of QPM second-harmonic (SH) generation in stoichiometric silicon nitride ( Si 3 N 4 ) waveguides. We apply waveguide design and lithographic control in combination with the all-optical poling technique to study the QPM properties and shape the waveguide dispersion for broadband spectral conversion efficiency inside Si 3 N 4 waveguides. By meeting the requirements for maximal bandwidth of the conversion efficiency spectrum, we demonstrate that group-velocity matching of the pump and SH is simultaneously satisfied, resulting in efficient SH generation from ultrashort optical pulses. The latter is employed for retrieving a carrier-envelope-offset frequency of a frequency comb by using an f − 2 f interferometric technique, where supercontinuum and SH of a femtosecond pulse are generated in Si 3 N 4 waveguides. Finally, we show that the waveguide dispersion determines the QPM wavelength variation magnitude and sign due to the thermo-optic effect.
Highlights
In recent years, photonic integrated circuits have experienced significant advancements, driven by the promise of compactness, efficiency, low cost, and mass production
By meeting the requirements for maximal conversion efficiencies (CEs) bandwidth for continuous wave (CW) operation, we demonstrate that GV matching for a short-pulsed pump and SH is simultaneously satisfied
The CE bandwidth can be increased by minimizing gradients of propagation constant mismatch Δβ with respect to the wavelength
Summary
Photonic integrated circuits have experienced significant advancements, driven by the promise of compactness, efficiency, low cost, and mass production. A wide range of passive and active functionalities, from electro-optical modulation to frequency conversion, has been demonstrated on various platforms such as silicon [1,2], stoichiometric silicon nitride (Si3N4) [3,4], lithium niobate (LN) [5,6], and aluminum nitride [7,8,9]. The method is simple to implement and allows inscription of self-organized nonlinear gratings for QPM at a selected pump wavelength in a manner of minutes [20] This method is useful for studying the influence of dispersion on QPM properties, without the need for fabricating many samples. By meeting the requirements for maximal CE bandwidth for CW operation, we demonstrate that GV matching for a short-pulsed pump and SH is simultaneously satisfied The latter provides means for SH generation from a CW signal, i.e., long and ultrashort optical pulses, without sacrificing efficiency of either regime.
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