Efficient erbium-doped thin-film lithium niobate waveguide amplifiers.

Lithium niobate on insulator (LNOI) is an emerging photonic platform with great promise for use in future optical communications, nonlinear optics, and microwave photonics. An important integrated photonic building block, active waveguide amplifiers, however, are still missing in the LNOI platform. Here, we report an efficient and compact waveguide amplifier based on erbium-doped LNOI waveguides, achieved using a sequence of erbium-doped crystal growth, ion slicing, and lithography-based waveguide fabrication.

Judd-Ofelt spectroscopic properties of Er-doped NaLa(WO) polycrystalline powder.

Er-doped NaLa(WO) is a promising phosphor material for applications in many fields including the ratiometric thermometry based on thermal effect of fluorescence intensity ratio (FIR) of green fluorescence of Er, which is directly correlated with Judd-Ofelt parameters Ω (i = 2, 4, 6). Present paper reports synthesis and Judd-Ofelt spectroscopic properties of Er-doped NaLa(WO) µm-sized phosphor. The phosphor was synthesized by solid-state chemical reaction and characterized by X-ray diffraction and Raman scattering techniques.

Error evaluation of Judd-Ofelt spectroscopic analysis.

Judd-Ofelt (J-O) spectroscopic knowledge of a rare-earth-doped luminescent material is crucial to its application. Although a large number of papers with regard to the J-O study of various rare-earth-doped luminescent materials have been reported each year, few papers presented the errors of the J-O intensity parameters Ω (i = 2, 4, 6) and radiative probabilities evaluated from them. Present study focuses on the error evaluation of the J-O parameters and radiative probabilities.

Sextuple ratiometric thermometry based on 980-nm-upconverted green fluorescence of Er ions in submicron crystals.

980-nm-upconverted 530 and 550 nm Er green fluorescence spectra of Er/Yb-codoped NaGd(WO) submicron crystals were measured in the temperature range of 298-383 K. A sextuple ratiometric thermometry is proposed. It is established on the basis of six schemes of fluorescence intensity ratio (FIR) that considers three component peaks of the 530 nm emission band and two component peaks of the 550 nm emission band, which involve electronic transitions between two Stark sublevels of Er.

Measurement of refractive index of powder by prism coupler.

Refractive index of optical material of powder is measured not as easily as a bulk material. Here, the prism coupling technique in combination with the immersion method is proposed to measure the refractive index of an optical material of powder. First, the powder material to be measured was dispersed in α-bromonaphthalene (CHBr) liquid to form a suspension mixture.

A simple, compact, low-cost, highly efficient thermometer based on green fluorescence of Er/Yb-codoped NaYF microcrystals.

We developed a highly efficient optical thermometer based on intensity ratio of upconversion green fluorescence of Er/Yb-codoped NaYF microcrystals. The sensor consists simply of a 980nm laser diode, one narrow-band interference filter, two lenses, one Si-photocell and one multimeter, while being without use of spectrometer and additional electronics. The device not only has a simple, compact structure (hence a low cost), but also displays highly efficient sensing performance, characterized by large signal-to-noise ratio due to strong fluorescence intensity, high thermal resolution and sensitivity, which have the values 1.

Optical damage resistant Ti-diffused Zr/Er-codoped lithium niobate strip waveguide for high-power 980 nm pumping.

Ti-diffused Zr/Er-codoped LiNbO strip waveguide was fabricated on an X-cut LiNbO substrate by thermal diffusion in sequence of Er, Zr and Ti. Secondary ion mass spectrometry study shows that the Ti ions follow a sum of two error functions in the width direction and a Gauss function in the depth direction of the waveguide. Both Er and Zr profiles follow the desired Gauss function, and entirely cover the Ti profile.

Note: Electro-optic coefficients of Li-deficient MgO-doped LiNbO crystal.

A number of Li-deficient MgO-doped LiNbO (LN) crystals with different LiO contents ranging from 43.4 mol. % to 44.

Polarization-insensitive, shallow Ti-diffused near-stoichiometric LiTaO strip waveguide for integrated optics.

We report on a Ti-diffused near-stoichiometric (NS) LiTaO strip waveguide fabricated by diffusion of an 8 μm wide, 160 nm thick Ti-strip followed by Li-rich vapor transport equilibration. It is found that the waveguide surface caves in ∼60  nm below the crystal surface. X-ray single-crystal diffraction shows that the indentation is due to Ti-induced lattice contraction.

Near-stoichiometric Ti-diffused LiNbO(3) strip waveguide doped with Zr(4+).

We report a near-stoichiometric Ti:Zr:LiNbO(3) strip waveguide fabricated from a congruent substrate with a technological process in the following sequence: Zr-diffusion-doping, diffusion of 8-μm-wide, 100-nm-thick Ti strips, and post-Li-rich vapor transport equilibration. We show that Zr(4+)-doping has little effect on the LiNbO(3) refractive index, and the waveguide is in a near-stoichiometric environment. The waveguide well supports both the TE and TM modes, shows weak polarization dependence, is in single mode at the 1.

Electro-optically tunable super-broadband filter based on long period grating in Ti:LiNbO₃ waveguide.

We report an electro-optically tunable optical filter based on a parallel structure of two long period gratings in the two same Ti:LiNbO3 strip waveguides: one 675-μm-pitch grating in one waveguide and another 880-μm-pitch grating in the other waveguide. The stop-band is observed in the 1.1-1.

Diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals.

Diffusion-doping is an effective, practical method to improve material properties and widen material application. Here, we demonstrate a new physical phenomenon: diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals. We exemplify Ti(4+)/X(n+) (X(n+) = Sc(3+), Zr(4+), Er(3+)) co-diffusion in the widely studied LiNbO3 and LiTaO3 crystals.

Symmetry-selective third-harmonic generation from plasmonic metacrystals.

Nonlinear processes are often governed by selection rules imposed by the symmetries of the molecular configurations. The most well-known examples include the role of centrosymmetry breaking for the generation of even harmonics, and the selection rule related to the rotational symmetry in harmonic generation for fundamental beams with circular polarizations. While the role of centrosymmetry breaking in second harmonic generation has been extensively studied in plasmonic systems, the investigation of selection rules pertaining to circular polarization states of harmonic generation is limited to crystals, i.