Influence of reflected waves at the bonded boundary in double-layered thickness-shear resonator using α-quartz

The influence of the reflected waves at the bonding boundary on the resonance waveform and temperature characteristics was investigated using α-quartz (QZ). The double-layered resonator specimen was fabricated using 129.55°Y- and 0°Y-cut QZ substrates with the thickness ratio x=0.520. The temperature characteristic at the range from 100°C to 300°C was deviated from the calculated values estimated by the equations considering thickness and electric flux density ratio proposed in the previous work, and the resonant waveform of the specimen was deteriorated as compared with that of single-layer resonators. In order to clarify these phenomena, the phase matching conditions and total amplitude in the specimen were examined. As a result, it was clarified that increase of the amplitude in the layer with lower acoustic impedance was affected to the temperature characteristic, and acoustic losses due to reflection / transmission at the bonding boundary was affected to the total amplitude of resonance.

Generation of 116-mW output power at 461 nm in a periodically poled lithium niobate waveguide

We demonstrate a second harmonic generation (SHG) of 116 mW at 461 nm in a periodically poled lithium niobate waveguide when the power of the 922-nm fundamental light is coupled into the waveguide was 350 mW. The waveguide is 12.5 μm wide, 12.0 μm thick, 22 mm long, and has a 1-mm-long slab window at the output facet of the waveguide. The temperature acceptance bandwidth of the phase-matching curve of the SHG is approximately 0.5 °C. The SHG system demonstrates good beam quality and is reliable for cold atom experiments, including research on optical lattice clocks.

Optically reconfigurable quasi-phase-matching in silicon nitride microresonators

Quasi-phase-matching has long been a widely used approach in nonlinear photonics, enabling efficient parametric frequency conversions such as second-harmonic generation. However, in silicon photonics the task remains challenging, as materials best suited for photonic integration lack second-order susceptibility (χ(2)), and means for achieving momentum conservation are limited. Here we present optically reconfigurable quasi-phase-matching in large-radius silicon nitride microresonators, resulting in up to 12.5-mW on-chip second-harmonic generated power and a conversion efficiency of 47.6% W−1. Most importantly, we show that such all-optical poling can occur unconstrained from intermodal phase-matching, leading to broadly tunable second-harmonic generation. We confirm the phenomenon by two-photon imaging of the inscribed χ(2) grating structures within the microresonators as well as by in situ tracking of both the pump and second-harmonic mode resonances during all-optical poling. These results unambiguously establish that the photogalvanic effect, responsible for all-optical poling, can overcome phase mismatch constraints, even in resonant systems.

High power supercontinuum generation by dual-color femtosecond laser pulses in fused silica

High power supercontinuum (SC) is generated by focusing 800 nm and 400 nm femtosecond laser pulses in fused silica with a microlens array. It is found that the spectrum of the SC is getting broader compared with the case of single laser pulse, and the spectral energy density between the two fundamental laser wavelengths is getting significantly higher by optimizing the phase matching angle of the BBO. It exceeds μJ/nm over 490 nm range which is from 380 nm to 870 nm, overcoming the disadvantage of relative lower power in the ranges far from fundamental wavelength.