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Developing efficient catalysts to degrade pollutants in water is a very important way to alleviate water pollution. However, it is crucial but challenging to broaden the functions of conventional photocatalysts and improve their environmental adaptability. In this paper, Bi(Er3+/Yb3+)OBr/polyacrylonitrile (BOB-EY/PAN) composite fibers with a swallowed-embedded structure assembled with nanopetal-rich microflowers were designed and fabricated, integrating photocatalytic and temperature-monitoring functions simultaneously. Their unique structure brings a large specific surface area, and the doping of rare earth ions improves the separation efficiency of electron–hole pairs, which enhances the photocatalytic efficiency and endows the fibers with a temperature-monitoring function at the same time. Under simulated sunlight irradiation, the nanofibers show a maximum degradation efficiency of 99.2% for tetracycline hydrochloride (TC) with a degradation constant of Kas high as 0.078 min–1. Based on the fluorescence intensity ratio (FIR), the two thermally coupled levels of Er3+in the nanofibers, 2H11/2and 4S3/2, provide real-time temperature feedback, displaying a maximum relative sensitivity as high as 0.0215 K–1at 303 K. Dual-functional BOB-EY/PAN composite nanofibers show great potential for industrial wastewater disposition, providing solutions for wastewater purification in special scenarios.

Bi2WO6:Ho3+, Yb3+/g-C3N4(BHY/CN) photocatalysts are successfully loaded on polyacrylonitrile (PAN) nanofibers by electrospinning technology, which combines an upconversion effect and heterojunctions to achieve dual-functional characteristics. Polymer-modified photocatalytic materials offer a large specific surface area of 24.1 m2/g and a pore volume of 0.1 cm3/g, promoting the utility of solar energy. The introduction of rare earth ions and g-C3N4optimizes the structural band gap, which broadens the light absorption range and promotes electron transfer. Moreover, the heterojunction between Bi2WO6and g-C3N4has suppressed the complexation of photoinduced carriers, further improving catalytic performance. The optimized photocatalysts have higher photocatalytic activity with degrading 92.6% tetracycline-hydrochloride (120 min) under simulated sunlight irradiation. The optical thermometry has also been achieved based on the fluorescence intensity ratio technique, where the maximum absolute and relative sensitivity values of BHY/CN-1:6@PAN are 3.322% K–1and 0.842% K–1, respectively. This dual-functional nanofibers with excellent mechanical properties provide noncontact temperature feedback and efficient catalytic performance for better wastewater treatment and ecological restoration in extreme harsh environments.

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. Using a compact 5 mm long waveguide, we demonstrate an on-chip net gain of >5dB for 1530 nm signal light with a relatively low pump power of 21 mW at 980 nm. The efficient LNOI waveguide amplifiers could become an important fundamental element in future lithium niobate photonic integrated circuits.

Laser-active interference with high confidentiality and convenience opens up a cutting-edge path for releasing and hiding key targets; however, its development still faces enormous challenges owing to the difficulty of concealing objects. Herein, a novel conceptual design for laser-controlled information release and hiding (LIRH) is proposed and successfully realized. Cs2NaInCl6:Er3+, Yb3+(CNIC:Er, Yb) perovskite microcrystal is adopted as a carrier for LIRH implementation, exhibiting excellent up-conversion (UC) emission under NIR (980 and 1530 nm) irradiation due to its ultralow phonon energy. The fluorescence intensity crossover and outstanding photon output capacity are revealed in comparison with Er3+/Yb3+codoped and Er3+single-doped CNIC phosphors under different laser sources, and the obvious difference in quantum yields (QY) under 980 and 1530 nm excitation provides theoretical possibility for LIRH. More importantly, the obtained LIRH features high stability at temperatures up to 413 K, showing good adaptability in various potential scenarios. Moreover, CNIC:Er, Yb is further combined with polyacrylonitrile (PAN) polymer to form fluorescent fibers with exceptional crystal stability and composite flexibility, thus making the LIRH code a reality based on perovskite composite phosphors. The laser-active invisibility offers an innovative idea for LIRH, further extending the application of LIRH in the field of information encryption, which has promising prospects in information safety, advanced anticounterfeiting, and smart responsive materials.

Using CMOS-compatible Pd catalysts, we demonstrated the formation of high-mobility ⟨111⟩-oriented GaSb nanowires (NWs) viavapor–solid–solid (VSS) growth by surfactant-assisted chemical vapor deposition through a complementary experimental and theoretical approach. In contrast to NWs formed by the conventional vapor–liquid–solid (VLS) mechanism, cylindrical-shaped Pd5Ga4catalytic seeds were present in our Pd-catalyzed VSS-NWs. As solid catalysts, stoichiometric Pd5Ga4was found to have the lowest crystal surface energy and thus giving rise to a minimal surface diffusion as well as an optimal in-plane interface orientation at the seed/NW interface for efficient epitaxial NW nucleation. These VSS characteristics led to the growth of slender NWs with diameters down to 26.9 ± 3.5 nm. Over 95% high crystalline quality NWs were grown in ⟨111⟩ orientation for a wide diameter range of between 10 and 70 nm. Back-gated field-effect transistors (FETs) fabricated using the Pd-catalyzed GaSb NWs exhibit a superior peak hole mobility of ∼330 cm2V–1s–1, close to the mobility limit for a NW channel diameter of ∼30 nm with a free carrier concentration of ∼1018cm–3. This suggests that the NWs have excellent homogeneity in phase purity, growth orientation, surface morphology and electrical characteristics. Contact printing process was also used to fabricate large-scale assembly of Pd-catalyzed GaSb NW parallel arrays, confirming the potential constructions and applications of these high-performance electronic devices.

We have designed and fabricated a plastic power adaptor operating in the millimeter range by commercially available injection-molding methods. Both numerical simulations and experimental results demonstrate that broadband and low-loss energy transfer between metallic and dielectric waveguides have been realized by using the fabricated plastic adaptors. The results show that the fabricated adaptor can be applied in practical millimeter wave functional devices.

We report on a Ti-diffused near-stoichiometric (NS) LiTaO_3 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. Optical studies show that the waveguide is in an NS composition environment, supports TE and TM single-mode propagation at 1.5 μm wavelength, is polarization insensitive, and has a shallow mode field profile and a loss of 0.2/0.3 dB/cm for the TE/TM mode. Secondary ion mass spectrometry analysis shows that the Ti profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of the waveguide. With the optimized fabrication condition, the waveguide is promising for developing an optical-damage-resistant device that requires a shallow mode field profile.

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^4+-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 1.5 μm wavelength, and has a loss of ≤0.6/0.8  dB/cm for the TE/TM modes. A secondary ion mass spectrometry analysis shows that the Zr^4+-profile part with a concentration above the threshold of photorefractive damage entirely covers the waveguide, implying that the waveguide would be optical-damage resistant.

We report an electro-optically tunable optical filter based on a parallel structure of two long period gratings in the two same Ti:LiNbO_3 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 1.1–1.3 (1.4–1.6) μm spectral region for the grating pitch 675 (880) μm. Its contrast increases linearly to ∼30  dB as the voltage is increased to 300 V, and the linearity is similar for the two cases of 675 and 880 μm pitches. Higher than 300 V, the contrast decreases due to photorefractive (PR) effect and/or over-coupling. Accompanying the contrast modulation, the resonant wavelength is simultaneously linearly tuned by making use of the PR effect. For the 675 (880) μm pitch, the tuning range is 160 (200) nm for the 400 (300) V voltage change range. With the two gratings, one can realize >360  nm super-broadband filtering.

We demonstrate the repeated utilization of self-assembled colloidal spheres for rapid nanopattern generations. Highly ordered micro-/nanosphere arrays were interlinked and confined by a soft transparent polymer (polydimethylsiloxane, PDMS), which can be used as light-focusing elements/photomasks for area-selective exposures of photoresist in contact. Because of the stiffness of the colloidal spheres, the photomasks do not encounter feature-deformation problems, enabling reliable production of highly uniform patterns over large areas. The geometrical feature of the patterns, including the size, pitch, and even the shape, can be finely tuned by adjusting the mask design and exposure time. The obtained patterns could be used as deposition or etching mask, allowing easy pattern transfer for various applications.

In this work, we experimentally studied sharp plasmonic resonance on gold gratings in both amplitude and phase domains using a spectroscopic ellipsometry technique. We used numerical and analytical models to analyze the phase delay of TM and TE waves under a surface plasmon excitation condition, and the calculated result fits well with the experimental observations. In addition, the ellipsometry method used here provides an important tool to characterize the phase information in plasmonic and metamaterial devices.

Semiconductor–noble metal hybrid nanostructures are of current interest in the development of bioimaging agents. To enhance photoluminescence of cadmium sulfide nanoparticles via surface plasmon mode coupling, cadmium sulfide conjugated silver nanoplates (denoted as CdS-Ag NP) have been prepared by a forward–reverse cation exchange method. The morphology, crystallinity, and atomic composition of the CdS-Ag NP have been investigated by energy dispersive X-ray spectroscopy and high-resolution transmission electron spectroscopy, and the CdS-Ag NP can be described as Cd2+-rich CdS nanoparticles covalently bonded to the surfactant of Ag nanoplates. Photoluminescence enhancement of CdS measured is attributed to the matching between the emission bands of cadmium sulfide and the tailor-made localized surface plasmons resonance bands provided by the Ag NP. Application of the CdS-Ag NP in cell imaging has also been demonstrated.

Rare-earth doped heavy metal germanium tellurite (NZPGT) glass fibers with lower maximum phonon energy of 793?cm^−1 and UV-sensitivity property have been designed and fabricated. Bright and compact upconversion traces have been observed in Er^3+/Yb^3+ and Tm^3+/Yb^3+ codoped NZPGT glass fibers, which exhibit favorable flexibility and excellent thermal stability, indicating that the NZPGT glasses are a desirable candidate for fiber amplifiers. The Er^3+/Yb^3+ codoped NZPGT glasses present a broad emission at ~1.5?μm with the FWHM of 72.7?nm, and the maximum internal gain of 12.59?dB with a remarkable gain coefficient of 2.38?dB/cm in the C-band were achieved in a Er^3+/Yb^3+ codoped NZPGT glass fiber. The efficient three-photon blue and two-photon near-IR upconversion emissions of a Tm^3+/Yb^3+ codoped NZPGT glass fiber demonstrate that low phonon energy NZPGT glasses have promising potential applications in Tm^3+ single-doped glass fibers for S-band signal amplification, and the further development of O- and U-band fiber amplifiers and lasers in Pr^3+ and Ho^3+ doped NZPGT glass fibers.

Different silver (Ag) island films were formed by annealing Ag films that were deposited on SiO_2/Si substrates for different durations. Enhanced fluorescence of Eu(TTFA)_3-doped SU8 films was demonstrated by these island Ag films. The enhancement was much greater than that by the unannealed Ag films and varied with these island films. The relative changes of the radiative and nonradiative transition rates of europium ions were also deduced in presence of 23nm annealed Ag films; the former one could increase to 1.625, the latter one could decrease to 0.505, and the quantum efficiency was enhanced to 1.376.

We report the design and fabrication of a Bragg grating device on a silicone-based elastomer rib waveguide, constructed using solvent-assisted microcontact molding and polymer casting techniques. The waveguide design utilizes polydimethylsiloxane (PDMS) and hard polydimethylsiloxane (hPDMS) polymers as core and cladding materials, with a period of ~0.55 μm, a depth of ~350 nm, and a grating length of 6 mm. Fabrication is relatively simple, with the hPDMS/PDMS waveguide and gratings cast from a two-layer mold made of a phenolic resin-based positive photoresist and an epoxy Novolak resin-based negative photoresist. The mold we have designed has a demonstrated operational lifespan in excess of ten successful waveguide fabrications. The transmission spectra of the resulting gratings were measured, with test results showing a band-rejection gain of −17 dB and a 3 dB bandwidth of ~3 nm at transmission.

Refractive indices of congruent LiNbO_3 crystals codoped with 0.5 mol% Er_2O_3 and 0-5.0 mol% MgO were measured at room temperature in a wavelength range from 473 to 1536 nm using critical angle measurement and minimum deviation methods. For reference, measurements by the critical angle method were also performed on a congruent LiNbO_3 and a congruent MgO (5 mol%):LiNbO_3. The measured data are compared with previously reported theoretical and/or experimental results of pure and MgO-doped LiNbO_3, especially with the results predicted by the MgO content-related Sellmeier equation (SE) reported by Schlarb and Betzler. It is shown that the Schlarb and Betzler SE consistently predicts a lower index, by as much as 4×10^−3, than what is actually measured by the authors for both congruent LiNbO_3 and for MgO:LiNbO_3, whether it is codoped with Er or not. To check the Er doping effect, measurements by the critical angle method were also performed on some congruent LiNbO_3 crystals singly doped with 0-1.0 mol% Er_2O_3. The results show that Er doping has no measurable effect. It is concluded that there may be a systematic error as one uses the Schlarb and Betzler SE to predict the index of the undoped, only MgO-doped, and Er/Mg-codoped crystals. The Schlarb and Betzler SE parameters are refined to fit our experimental data. The corrected version of the SE suitable for MgO:LiNbO_3 with or without Er doping is given.

A theoretical study on the sensitivity of the resonant wavelength of long-period waveguide gratings (LPWGs) to temperature and pressure is reported. Starting with the phase-matching condition of the LPWG, general expressions for the temperature and pressure sensitivities are derived. The temperature sensitivity considers the thermo-optic and thermal expansion effects, and the pressure sensitivity takes into account the elasto-optic and elastic deformation effects of the materials involved, as well as the modal dispersion effect. Focusing on the extensively studied glass and polymer waveguides, the contributions of these effects to the temperature or pressure sensitivity were roughly evaluated and illustrated in the form of histograms in order to show the roles of these effects straightforwardly. The results show that a LPWG based on a polymer waveguide is preferred to that based on a glass waveguide for obtaining high temperature or pressure sensitivity. The temperature sensitivity is dominated by the modal dispersion effect and the difference between the thermo-optic coefficients of the waveguide and the cover layer materials, while the thermal expansion effects make only a minor contribution to the sensitivity for the cases of both glass and polymer waveguides. The pressure sensitivity is dominated by the modal dispersion effect and the difference between the elasto-optic coefficients of the channel waveguide and the cover layer materials. In particular, in the case of the polymer LPWG the elastic deformation effects of the waveguide and grating materials make a moderate contribution to the pressure sensitivity and cannot be ignored. The minor contributions from the thermal expansion effects or the elastic effects may play a role in designing a temperature- or a pressure-insensitive LPWG device. Finally, the possibility that the waveguide loss affects the LPWG temperature/pressure sensitivity is discussed.

We have demonstrated the possibility that near-stoichiometric Ti:LiNbO_3 strip waveguides are fabricated by carrying out vapor transport equilibration at 1060°C for 12 h on a congruent LiNbO_3 substrate with photolithographically patterned 4-8 μm wide, 115 nm thick Ti strips. Optical characterizations show that these waveguides are single mode at 1.5 μm and show a waveguide loss of 1.3 dB/cm for TM mode and 1.1 dB/cm for TE mode. In the width/depth direction of the waveguide, the mode field follows the Gauss/Hermite-Gauss function. Secondary-ion-mass spectrometry (SIMS) was used to study Ti-concentration profiles in the depth direction and on the surface of the 6 μm wide waveguide. The result shows that the Ti profile follows a sum of two error functions along the width direction and a complementary error function in the depth direction. The surface Ti concentration, 1/e width and depth, and mean diffusivities along the width and depth directions of the guide are similar to 3.0×10^21 cm^−3, 3.8 μm, 2.6 μm, 0.30 and 0.14 μm^2/h, respectively. Micro-Raman analysis was carried out on the waveguide endface to characterize the depth profile of Li composition in the guiding layer. The results show that the depth profile of Li composition also follows a complementary error function with a 1/e depth of 3.64 μm. The mean ([Li_Li]+[Ti_Li])/([Nb_Nb]+[Ti_Nb]) ratio in the waveguide layer is about 0.98. The inhomogeneous Li-composition profile results in a varied substrate index in the guiding layer. A two-dimensional refractive index profile model in the waveguide is proposed by taking into consideration the varied substrate index and assuming linearity between Ti-induced index change and Ti concentration. The net waveguide surface index increments at 1545 nm are 0.0114 and 0.0212 for ordinary and extraordinary rays, respectively. Based upon the constructed index model, the fundamental mode field profile was calculated using the beam propagation method, and the mode sizes and effective index versus the Ti-strip width were calculated for three lower TM and TE modes using the variational method. An agreement between theory and experiment is obtained.

We propose and demonstrate potassium bismuth gallate (KBG) glasses as suitable hosts for the rare-earth ion Tm^3+ (thulium) operating at the 1.47-μm wavelength. The optical properties of Tm^3+-doped KBG glasses were investigated. The bandwidth of the ^3H_4?^3F_4 transition is ∼120 nm and is higher than that of Tm^3+-doped, tellurite-based glasses. The measured fluorescence lifetime is 0.15 ms at room temperature, and the quantum efficiency is 88%. Multiphonon relaxation rates for various transitions were evaluated and compared with other glass hosts. The energy transfer in Tm^3+–Ho^3+-codoped KBG glasses was also investigated, and these results indicate that Tm^3+-doped KBG glasses are promising candidates for efficient broadband optical amplifiers operating in the 1.47-μm wavelength range.

We propose and demonstrate potassium bismuth gallate (KBG) glasses as suitable hosts for the rare-earth ion Tm3+ (thulium) operating at the 1.47-µm wavelength. The optical properties of Tm3+ -doped KBG glasses were investigated. The bandwidth of the 3H4-->3F4 transition is ~120 nm and is higher than that of Tm3+ -doped, tellurite-based glasses. The measured fluorescence lifetime is 0.15 ms at room temperature, and the quantum efficiency is 88%. Multiphonon relaxation rates for various transitions were evaluated and compared with other glass hosts. The energy transfer in Tm3+ - Ho3+ -codoped KBG glasses was also investigated, and these results indicate that Tm3+ -doped KBG glasses are promising candidates for efficient broadband optical amplifiers operating in the 1.47-µm wavelength range.

The point-matching method has been extended to analyse a travelling-wave electrode structure for shielded velocity-matched Ti:LiNbO3 Mach-Zehnder optical modulators. This method provides a simple and fast approach to analysing the coplanar waveguide with buffer layer, cover shield, and electrodes of finite thickness. The calculated characteristic impedances and microwave effective indices agree well with those obtained using the spectral domain technique and the finite-element method. It is found that in the coplanar waveguide without cover shield it is difficult to achieve velocity matching. The coplanar waveguide with cover shield can be used to achieve velocity matching, but the corresponding characteristic impedance is lower than 50O. Both velocity matching and impedance matching can be obtained using a narrow centre electrode. The calculated electric field has been used to estimate the modulation efficiency of the device. Velocity matching can be achieved by adjusting the height of the cover shield, but a compromise must be made between high interaction efficiency and low microwave reflection when choosing the buffer layer thickness and the electrode thickness.

Ba(Y1–x–yErxYby)F5/polyacrylonitrile (BYF-EY/PAN) composite fibers have been prepared by adopting the electrospinning technology, and fusiform-polycrystalline-implanted fibers can be fused with a thermal response function and excellent flexibility. Upconversion emission displays quadratic and cubical dependence of the photoluminescence intensity on the pumping power, confirming two-photon- and three-photon-induced processes, respectively. Among them, the intense green emission ascribed to 2H11/2/4S3/2→ 4I15/2transitions is appointed as the main indicator of noncontact temperature sensing, and the faintish blue-violet emission originated from 4G11/2/2H9/2→ 4I15/2transitions can be served as an auxiliary monitoring channel to calibrate deviation, thereby improving operational accuracy. At a relatively moderate working temperature (363 K), the absolute sensitivity and relative sensitivity of composite fibers reach as high as 0.455 and 0.832% K–1for main sensing and 0.391 and 2.176% K–1for auxiliary sensing, respectively. The developed BYF-EY/PAN fiber with outstanding dual-feedbacked temperature sensing is promising to act as flexible sensing elements in fabrics and biomedical devices.

Er3+/Yb3+-doped NaGdF4crystal-implanted fiber (CIF) is synthesized by the electrospinning technique, which possesses excellent crystal dispersibility, glorious flexibility, and high crystal utilization, realizing temperature sensing in complex and harsh environments. The combination of main and auxiliary sensing endows CIF with self-calibration functionality to realize accurate temperature measurement. Serving as the main thermal response signal for a noninvasive nanothermometer, the absolute and relative sensitivities for effective green emissions are up to 0.446% K–1at 423 K and 1.018% K–1at 303 K, respectively. Further, the introduction of a blue emission peak is to participate in the thermal response as an auxiliary indicator to inspect the accuracy of the main thermal sensing data where the absolute and relative sensitivities reach 28.473 and 1.522% K–1at 313 and 303 K, respectively. The flexible CIF with cooperative response thermometry possesses a broad prospect in nanodomain optical thermometers, which present extraordinary potential in nondestructive temperature monitoring and flexible temperature sensing elements.

A tunable multichannel nonreciprocal perfect absorber with the asymmetric metal-photonic crystal hetero-structure is theoretically proposed. By using the transfer matrix method, the linear and nonlinear properties of the absorber are investigated. An ultra-narrow perfect absorption channel is realized in the linear case due to the impedance matching, and the channel number can be adjusted by changing the period of the photonic crystal. Bistable absorption and reflection are achieved in the nonlinear case due to the positive feedback between the metal nonlinear permittivity and the inner electric field, while the bistable thresholds can be altered by varying the incident light wavelength. Moreover, the absorber exhibits the intrinsic nonreciprocity in both absorption and reflection, and shows the polarization-independent directional characteristics when the incident angle is less than 40°.

Superbroadband near-infrared (NIR) emission covering 1250 to 1680?nm wavelength has been obtained in praseodymium (Pr^3+) singly doped bismuth gallate glasses. The emission originates from the G_41?H_53 and D_21?G_41 transitions at 1330 and 1490?nm wavelengths, respectively, and is due to the extremely low phonon energy (∼690?cm^−1) and the unique ligand field of the glasses. It is shown that the emission line shape can be modified by adjusting the Pr^3+ concentration and the energy transfers involved. The results confirm that other than bismuth (Bi), chromium (Cr), nickel (Ni), and other chemical elements, Pr^3+ singly doped system is a promising alternative in achieving superbroadband NIR emission.

Europium (Eu^3+)-doped epoxy-based resin Norland optical adhesive (NOA) polymers have been prepared and characterized optically. Quartz capillary tube encapsulated Eu^3+-doped NOA polymeric waveguides have been fabricated via a simple withdrawal molding technique. Optical amplification at 612 nm wavelength has been demonstrated in these waveguide devices, and the signal enhancements for different lengths of the devices have been measured. A maximum signal enhancement of ~30 dB has been obtained for a 16 mm long device.

Efficient emission at 1.38 μm wavelength from holmium (Ho^3+)-doped low-phonon-energy gallate bismuth lead (GBL) oxide glasses, owing to the Ho^3+: (^5S_2,^5F_4)?^5I_5 transition, was observed, and the stimulated emission cross section was calculated to be 2.4×10^−21 cm^2. Population inversions between the (^5S_2,^5F_4) and ^5I_5 levels have been achieved, and a broad gain bandwidth from 1350 to 1450 nm was obtained. The large product of emission cross section and measured lifetime also support this characteristic. The results indicate that a Ho^3+-doped GBL glass system is a promising candidate for the development of E-band (1360-1460 nm) fiber-optic amplifiers.

We report a systematic study on the dependence of nanowire evanescent wave coupling efficiency on wavelength, cross angle, and core diameter. An 800 nm diameter silica taper was used for light launching. Three poly(trimethylene terephthalate) nanowires with 640 nm, 790 nm, and 950 nm diameters were used for light transmission. Five wavelengths (visible, 473, 532, 650 nm; near-IR, 1310 and 1550 nm) were used as transmission signals. The dependence of coupling efficiency was investigated at cross angles from 90° to 0° with a 5° changing step. It is observed that the coupling efficiency is higher for longer wavelength of light, smaller cross angle, and smaller nanowire diameter.

One-dimensional (1D) Y2Ti2O7(YTO): Ho3+/Yb3+nanofibers with diameters ranging from 300 to 400 nm were synthesized by an electrospinning technology and the structure of YTO nanofibers was identified as face-centered cubic pyrochlores. The detected green and red signals in the upconversion emission spectra under 980 nm laser excitation are due to the radiative transitions (5F4, 5S2) → 5I8and 5F5→ 5I8of Ho3+ions, respectively. YTO: Ho3+/Yb3+nanofibers have the characteristics of porosity, three-dimensional braidability, high specific surface area and controllable structure, which improves the performance of optical temperature sensing. Furthermore, the nanofiber membranes consisting of YTO: Ho3+/Yb3+with temperature sensing performance can work steadily at medium temperature range in view of its fast responses and high stability, moreover, a maximum sensitivity about 0.18% K−1at 423 K, which indicates that the nanofibers have good thermal sensitivity. 1D nanostructure rare earth ion-doped cubic pyrochlore material was proven to obtain excellent upconversion luminescence properties, which provides a new route for the development of sensitive optical temperature-sensing materials.

Multi‐peak red fluorescence emissions in Sm3+‐doped multicomponent‐alkali‐alkaline‐borate (MCAAB) glasses for laser‐induced illumination are quantitatively characterized, revealing that the quantum yield (QY) is closely related with the wavelength of pumping sources. Under the excitation of 370 nm UVA‐LED, the net emission photon numbers of 1.00 wt% Sm2O3‐doped MCAAB glasses are derived to be 58.0 × 1012cps, and the QY reaches to 25.3% which is about twice as much as 12.2% under 469 nm blue‐LED pumping, which is attributed to the better excitability in UVA spectral region. In order to extend the effective excitation range to UVB, Ce3+is co‐doped in Sm3+‐doped MCAAB glasses as a sensitizer, which results in an enhancement of Sm3+excitation intensity by a maximum sensitization factor of 9.16 in the UVB region. Absolute spectral parameters under 453 nm blue laser excitation exhibit that net emission photon numbers are up to 199.4 × 1012cps in 1.00 wt% Sm2O3doping case, and QY is solved to be 6.2%. Higher QY of the Sm3+‐doped MCAAB glasses is expected to be achieved by further adopting wavelength‐matched pumping laser, implying that Sm3+‐doped MCAAB glasses is a promising candidate as high power‐density light source in special laser‐induced illumination. Sm3+‐doped MCAAB glasses are investigated as laser‐driven illumination materials. Their effective excitation range is extended to UVB by co‐doping of Ce3+. Laser‐induced radiation behaviors are exhibited by absolute spectral characterization. Quantum‐yield dependence on excitability of pumping wavelength is identified. Efficient red fluorescence for special lighting is expected under matched laser pumping.

The surface composition of 5 mol% (in growth melt) MgO-doped z-cut LiNbO3crystal was modified using Li-poor vapor transport equilibration (VTE) process. The VTE-induced surface Li2O-content reduction ΔC was evaluated from the measured birefringence, and the ΔC dependence on VTE temperature T and time twere studied. The results show that the effect of T on ΔC follows the Arrhenius law, with a surface Li2O-content reduction constant of (1.3 ± 0.1) × 1011mol% and an activation energy of 3.0 ± 0.1 eV, and the effect of tonΔC is a square-root dependence, with ΔC = 0.17t0.51. Thus, a generalized empirical expression can be obtained to show the dependence of ΔC on T and t. A comparative study on undoped pure LN shows that the MgO doping has slight effect on ΔC. Based on the obtained dependence of ΔC on t, the solution to the Li+out-diffusion equation is shown and verified experimentally to be an integral of complimentary error function. The results indicate that Li-deficient MgO-doped LiNbO3material with desired surface Li2O-content can be produced by controlling the VTE temperature and duration.

Surface etching of a MgO-doped LiNbO3crystal is demonstrated by annealing a sandwich structure formed by Mg:LiNbO3/Tifilm/Mg:LiNbO3at 1050–1100°Cin a wet O2atmosphere. The etching depth, raised Ti layer height and surface roughness were studied as a function of initial Ti film thickness, annealing temperature, and duration. The results show that the maximum etching depth can reach 260 nm while the surface roughness is <5nm. The features of the raised Ti layer height and surface roughness of the etched surface and raised Ti layer are discussed on the basis of the Ti diffusion mechanism. Combined studies of X-ray single-crystal diffraction, Raman scattering, energy-dispersive X-ray, waveguiding characteristics, surface refractive index, and secondary-ion mass spectrometry show that the etched surface not only retains the LiNbO3crystalline phase and the original crystal composition but is also Ti-free. An etching mechanism based upon an electrochemical reaction process is proposed. The MgO doping effect on the etching rate and surface roughness is discussed and explained in terms of the MgO doping effect on Ti solubility. A comparison of the +Zand −Zsurface etching is made. Finally, the present method is compared with other etching techniques and its possible application is suggested.

Annealing properties of proton-exchanged optical planar waveguides in z-cut LiNbO3fabricated using octanoic acid have been studied systematically. Waveguide propagation losses decrease with annealing time, and variations in the surface refractive index and waveguide depth with annealing time follow a power law relationship. The annealing process is shown to be an effective means of improving and modifying waveguide properties.

A rare-earth ion, namely erbium, was doped into silicon (Si) using thermal indiffusion. Codoping using ytterbium oxide (Yb2O3) and germanium (Ge) to increase photoluminescence (PL) intensity was also demonstrated, and the effect of different Yb/Er ratios on Si was studied. Room temperature PL intensity relative to Er-diffused sample was found to increase by ?30 times using Yb/Er (27/1) codopant. When a SiGe/Yb/Er layer was used, room temperature PL intensity was further increased to more than 60 times.