Recent progress in thin-film lithium niobate photonic crystal[Invited]

Lithium niobate is a material that exhibits outstanding electro-optic,nonlinear optical,acousto-optic,piezoelectric,photorefractive,and pyroelectric properties.A thin-film lithium niobate photonic crystal can confine light in the sub-wavelength scale,which is beneficial to the integration of the lithium niobate on-chip device.The commercialization of the lithium niobate on insulator gives birth to the emergence of high-quality lithium niobate photonic crystals.In order to provide guidance to the research of lithium niobate photonic crystal devices,recent progress about fabrication,characterization,and applications of the thin-film lithium niobate photonic crystal is reviewed.The performance parameters of the different devices are compared.

Chip-scale spontaneous quasi-phase matched second harmonic generation in a micro-racetrack resonator

In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but exploits the anisotropy of the crystals to allow the phase-matching condition to be fulfilled spontaneously as the TE-polarized light circulates in a specifically designed racetrack resonator.In experiment,normalized on-chip conversion efficiencies of 1.01×10-4/W and 0.43×10-4/W are achieved by 37th-order and 111th-order SQPM,respectively.The configurable SQPM will benefit the application of nonlinear frequency conversion and quantum source generation in chip-scale integrated photonics compatible with standard CMOS fabrication processes.

On-chip ultraviolet second-harmonic generation in lithium-tantalate thin film microdisk

The compact and reliable ultraviolet[UV]source has attracted remarkable attention for its potential use in optical measurement systems,high-density optical storage,and biomedical applications.We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator[LTOI]microdisk via modal phase matching.The 50-μm-diameter microdisk was milled by a focused ion beam[FIB]and followed by chemo-mechanical polishing[CMP]to smooth the disk surface and edge,and the Q-factor reaches 2.74×10~5in the visible band.On-chip UV coherent light with a wavelength of384.3 nm was achieved,which shows great promise for using LTOIs in integrated ultraviolet source platforms.

On-chip erbium-doped lithium niobate microcavity laser

The commercialization of lithium niobate on insulator(LNOI) wafer has resulted in significant on-chip photonic integration application owing to its remarkable photonic,acousto-optic,electro-optic,and piezoelectric nature.In recent years,a variety of high-performance on-chip LNOI-based photonic devices have been realized.In this study,we developed a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate and fabricated an erbium-doped LNOI microdisk with high quality factor(~1.05×105).C-band laser emission at ~1530 and ~1560 nm(linewidth 0.12 nm) from the high-Q erbium-doped LNOI microdisk was demonstrated with 974-and 1460-nm pumping,with the latter having better thermal stability.This microlaser would play an important role in the photonic integrated circuits of the lithium niobate platform.

Solubility of CO_(2) in solid-state PET measured by pressure-decay method

The solubility of CO_(2) in solid-state PET was measured using a pressure-decay method.In order to calculate the solubility of CO_(2) in the amorphous region of PET,the crystallinity of solid state PET dissolved in CO_(2) at different pressures and temperatures was measured by differential scanning calorimetry(DSC).The solubility increases with increasing pressure and it follows a linear relationship and obeys Henry’s law when the pressure is below 8 MPa.The effect of temperature on solubility is weak and the solubilities at different temperatures are almost the same under low pressures.At higher pressure,the solubility decreases with an increase in temperature.The solubility of CO_(2) in the amorphous region of PET at 373.15 K,398.15 K and 423.15 K was correlated with the Sanchez-Lacombe equation of state with a maximal correlation error of 6.69%.