We report on the fabrication and mode modulation of telecom-band depressed-cladding waveguides in SK1310 glass. To obtain high-quality depressed-cladding waveguides, the effects of two primary femtosecond-laser processing parameters (i.e., pulse energy and focusing depth) on track morphology have been investigated in detail. Based on analysis of track morphology and design of waveguide configurations, the telecom-band depressed-cladding waveguides have been successfully produced. It has also been found that, by increasing pulse energy for waveguide fabrication, telecom-band mode modulation from single-mode to multi-mode could be realized. The confocal micro-Raman (mu-Raman) spectroscopy indicates that original properties of SK1310 glass could be well preserved in waveguide cores. This work paves a way to fabricate telecom-band depressedcladding waveguides in SK1310 glass, having potential applications in integrated photonics and quantum optics.

In this work, we propose a practical solution to visible vortex laser emission at 532 nm based on second harmonic generation (SHG) in a well-designed waveguide-grating structure. Such an integrated structure is fabricated by femtosecond laser direct writing (FsLDW) in an LBO crystal. Confocal micro-Raman spectroscopy is employed for detailed analysis of FsLDW-induced localized crystalline damage. By optical excitation at 1064 nm, the guiding properties, SHG performance, as well as vortex laser generation of the waveguide-grating hybrid structure are systematically studied. Our results indicate that FsLDW waveguide-grating emitter is a reliable design holding great promise for nonlinear vortex beam generation in integrated optics.

The utilization of deformed microcavities, such as elliptical microdisks, has been widely acknowledged as an effective solution for achieving free-space emission in microcavity lasers. However, the deformations introduced in the microcavity structure tend to decrease the quality factor (Q factor), resulting in weakened output intensity. To address this issue, one potential approach is to employ highly efficient laser gain media that can compensate for the negative impact of the structure on the output intensity. In this study, we employed the exceptional laser crystal material Nd:YAG as the laser gain medium and successfully fabricated an elliptical microdisk laser with a major semiaxis of 15 µm and an eccentricity ratio of 0.15. By utilizing an 808 nm laser for pumping, we were able to achieve free-space laser emission with a slope efficiency of 1.7% and a remarkable maximum output power of 58 µW. This work contributes toward the advancement of the application of deformation microcavity lasers.

The integration of heterogeneous optical components onto an optical platform is crucial for the advancement of photonic chips. To achieve this, efficient coupling of optical signals between components and the platform is essential. Here, we have successfully integrated a Nd:YAG microdisk laser with a lithium-niobate-on-insulator (LNOI) photonic platform by modulating the propagation modes of LNOI. Ridge waveguides are fabricated on the LNOI by carefully adjusting the cross-sectional dimensions to enable the propagation of higher-order propagation modes. This ridge waveguide ensures that the effective refractive index of the higher-order mode closely matches that of the fundamental mode of the Nd:YAG microdisk, ensuring efficient waveguide–microdisk coupling. This on-chip laser, consisting of an Nd:YAG microdisk and LNOI integration, achieves a maximum output power of 23 µW, and a mode suppression ratio of 53.6 dB. This research presents an efficient approach for constructing highly functional heterogeneous integrated optical chips.

Two-dimensional (2D) carbides of transition metals, so called "MXenes", maintain excellent optical properties and unique layer stacking form via hydrogen bonds in contrast to other low-dimensional materials. These promising features have attracted increasingly research interest in the field of ultrafast photonics. In this work, titanium carbide (Ti(3)C(2)Tx) and tantalum carbide (Ta(4)C(3)Tx), as two promising MXene materials for photonic applications, are experimentally synthesized by the ultrasound-assisted liquid phase exfoliation technique. The morphology of prepared few-layer Ti(3)C(2)Tx and Ta(4)C(3)Tx has been systematically characterized by transmission electron microscopy and X-ray diffraction analysis. Density functional theory is performed to obtain their electronic band structures, demonstrating metallic properties and verifying their optical absorption at 1 mu m. Their tempting optical modulation properties for multi-gigahertz pulsed laser emission are demonstrated by using them as saturable absorbers in a waveguide laser cavity. Particularly, high-performance Q-switched mode-locked lasers with/without laser mirrors are realized based on the hybrid waveguide laser configuration, delivering 1 mu m laser pulses with durations as short as 30 ps. The results presented in this work show the great potential of metallic MXenes and waveguide structures for applications in functional photonic devices.

Nonlinear optical waveguides play a crucial role in the wavelength/frequency conversion of light. Femtosecond laser direct writing is an efficient and flexible technique to produce waveguides in dielectrics. We report on the nonlinear waveguides in LiB 3 O 5 crystals by femtosecond laser writing. The double-line and depressed-cladding structures inscribed by femtosecond laser pulses show excellent guiding properties at 405 nm or 810 nm for both TE and TM polarized light. The investigations of the confocal micro-Raman spectroscopy have indicated that lattice structures in waveguide cores remain almost unchanged compared with those of the bulk. Based on type-I phase matching condition, both second harmonic generation of 810 nm and spontaneous parametric down conversion of 405 nm have been obtained in the laser-written lithium triborate waveguides, suggesting potential applications in integrated nonlinear optics and quantum photonics.

Carbon ion irradiation and precise diamond blade dicing are applied to fabricate Nd:GdCOB ridge waveguides. The propagation properties of the fabricated Nd:GdCOB waveguides are investigated through experiments and theoretical analysis. Micro-Raman analysis reveals that the Nd:GdCOB crystal lattice expands during the irradiation process. Micro-second harmonic spectroscopic analysis suggests that the original nonlinear properties of the Nd:GdCOB crystal are greatly enhanced within the waveguide volume. Under pulsed 1064 nm laser pumping, second harmonic generation (SHG) at 532 nm has been achieved in the fabricated waveguides. The maximum SHG conversion efficiencies are determined to be ∼ 8.32 %⋅W −1 and ∼ 22.36 %⋅W −1 for planar and ridge waveguides, respectively.

By using femtosecond laser direct writing, we have fabricated depressed-cladding waveguides in periodically-poled lithium niobate (PPLN) crystals, with which the second harmonic generation (SHG) of 1064 nm has been realized. The third-order quasi-phase matching (QPM) has been adopted to achieve this SHG process. At optimal QPM temperature (similar to 94.9 degrees C), we have studied the guiding properties and SHG properties of waveguides in detail. The maximum conversion efficiency of similar to 0.075% has been obtained in our experiment. In addition, it has been found that the mode profiles at 532 nm can be tailored by changing cross-sections of waveguides. This work plays an essential part in creating novel and high-performance frequency converters by using femtosecond-laser-written PPLN depressed-cladding waveguides.

We report on an integrated 1 x 5 beam splitter based on optical waveguides with type I and type II modifications of femtosecond laser (fs-laser) writing in lithium tantalate (LiTaO3) crystal. The cladding waveguides consisting of type-II modified tracks are used for optical signal transmission, photon crosstalk reduction, and mode field regulation. The single-line waveguides with type I modification are utilized for light beam splitting. Type-I single-line waveguides are with relatively weak thermal stability, which are utilized to produce a recoverable and rewritable optical beam splitter, and the structure still possesses good transmission properties after the reconstruction. Especially, the type-I modified waveguides can be rewritten in very short time (1-2 min). The beam splitter shows good performance in outputting programmable optical signals, which provides a possible strategy for the development of erasable photonic data processors.

We report on microfabrication and optical characterization of buried channel waveguides defined in Nd:YCOB crystal by focused proton beam writing (PBW). In the fabrication process, the focused proton beam irradiation creates a local material modification region with geometrically symmetric positive index changes at the end of the proton trajectory, where efficient optical waveguiding can be locally supported within a fiber-like channel structure. The impact of the proton fluence (with different values ranging from 1015 to 1016 cm−2) on the optical waveguiding performance is well studied. The experimental results of the optical waveguide properties are in fairly good agreement with the simulation results.

We report on the frequency doubling properties of femtosecond (fs) laser direct-written lithium triborate (LBO) cladding waveguides. The guiding properties (mode profiles and propagation losses) of these waveguides are experimentally characterized. The maximum conversion efficiency values of 4.8% and 8.6% are achieved for frequency doubling processes of 1064 -> 532 nm and 1560 -> 780 nm, respectively, in the fabricated depressed-cladding waveguides at room temperature. Our results suggest the potential applications of fs-laser direct writing technique as well as LBO waveguides in constructing compact frequency converters.

The localized surface plasmon resonance (LSPR) from optical excitation of noble metallic nanoparticles enables intriguing applications for surface enhanced Raman spectroscopy. We propose a novel and subtle framework by encapsulating silver (Ag) nanoparticles into fused silica glass (hereby Ag NPs:glass) via ion implantation, and realize the significant Raman scattering enhancement without any frequency splitting and shifting. Benefitting from the LSPR effect excited by 633 nm laser, the Raman signal of probe molecules (CuPc) on Ag NPs:glass is enhanced by more than 40 times of magnitude in comparison with pure SiO2 substrate. More importantly, since the Ag nanoparticles are capsulated in the SiO2 wafer, i.e., Ag nanoparticles are non-contact with surface coated target materials, the Ag NPs:glass substrate exhibitexcellent environmental stability and reusability, maintaining higher enhancement ability after a number of repeated uses. Our work opens up a novel route to develop reusable, low-cost, reliable functional substrates for practical applications towards the weak-signal detection and label-free enhanced Raman scattering.

Two-dimensional (2D) ternary transition-metal dichalcogenides (TMDCs) are of great research interest because their superior layer-dependent optical modulation properties. In this work, three different kinds of TMDC nanosheets, including hafnium diselenide (HfSe2), titanium diselenide (TiSe2) and zirconium diselenide (ZrSe2), are prepared by liquid phase exfoliation (LPE) technique. The high-quality material properties of these TMDC nanosheets are confirmed by Raman spectroscopy and X-ray diffraction analysis. Furthermore, the bandgap information of five-layer MSe2 has been investigated via utilizing density functional theory. The calculation results exhibit ultra-narrow bandgap structure (lower than 1.1 eV) for all these three materials, indicating that MSe2 is suitable for broadband photonic applications. By applying the fabricated MSe2 as saturable absorbers, high-performance Q-switched mode-locked laser operation has been realized. The laser gain media are Nd:GdVO4 cladding waveguides fabricated by femtosecond laser direct writing. As a result, the pulsed waveguide lasers are able to deliver approximately 6-GHz laser pulses with a signal-to-noise ratio of over 45 dB. The minimum pulse width is determined to be as short as 26 ps. The results demonstrated in this work exhibit the great potential of TMDCs and waveguide structures in applications of pulsed lasers with compact footprints.

We report for the first time on optical waveguides in zinc oxide (ZnO) crystals fabricated by femtosecond laser direct writing. The confocal Raman microscopy under 488 nm laser excitation is used to investigate the micro-modifications of the laser irradiation, and guiding properties are studied via the end-face coupling at 632.8 nm. The mode modulation has been achieved by the adjustment of laser writing parameters. A minimum propagation loss of ∼6 dB/cm is obtained for the double-line waveguide structures. A Y-branch waveguide beam splitter is also fabricated, reaching a splitting ratio of nearly 1:1. The original optical properties in the guiding region have been well preserved, according to the confocal Raman investigation, which suggests potential applications of the ZnO waveguides for integrated photonics and nonlinear optics.

The direct femtosecond laser writing has been proved to be one of the most efficient techniques for micro-structuring of transparent materials, which can induce refractive index modifications to construct waveguide structures. In this work, laser-induced tracks with single-line configuration are formed inside the BK7 glass by using inscription of femtosecond laser pulses with 1 MHz repetition rate at wavelength of 1030 nm and 515 nm, respectively. The high-resolution confocal Raman spectra are obtained in the track regions to investigate the physical mechanisms of the modification. The results indicate that the specified regions inside the tracks induced by 1030-nm femtosecond laser expand and squeeze the adjacent area under certain writing conditions, leading to a refractive index increase in the core region. The 515-nm femtosecond laser brings out relatively more severe damage in comparison to the 1030-nm laser irradiation. A directional coupler structure has been fabricated by using the optimized writing parameters, showing a nearly balanced output with a ratio of 49.7:50.3 and an insertion loss of 1.36 dB for the single-line waveguide at 1064 nm.

Nonlinear interactions between light and matter give rise to a wide range of applications for both fundamental and applied research. Herein, near‐infrared switching of the optical response based on embedded Ag nanoparticles and laser‐written optical waveguides within yttrium vanadate (YVO4) crystal matrix is demonstrated. Using broadband transient absorption spectroscopy with a combination of femtosecond Z‐scan spectroscopy, the plasmon‐enhanced features of the third‐order optical nonlinearity in Ag:YVO4 nanocomposite at the near‐infrared band are elucidated. Meanwhile, an optical‐lattice‐like microscale waveguide is fabricated with well‐preserved photoluminescence properties by femtosecond laser writing. Taking advantage of the ultrafast on–off switching behavior of Ag:YVO4 saturable absorber, a Q‐switched pulsed laser operation in the waveguide platform, delivering 1 μm light pulses with high peak power of 298 mW, is demonstrated. This work indicates a possible path for the development of chip‐scale ultrafast photonic devices.

LiNbO3 is a widely used material for photonics. In this work, we have used femtosecond laser writing to inscribe both Type I and II structures in a same LiNbO3 crystal for direct comparison. The guiding properties of the laser-written waveguides are obtained, which indicates that only guidance along the extraordinary index polarization for both geometries. The micro-spectroscopy (i.e., photoluminescence and Raman) investigation reveals the difference on the crystal properties and lattice structural changes of two types of modifications. We have found that, the laser-induced modifications reveal the different structural changes of the LiNbO3 network for the Type I and II configurations, which reflects on the spectral properties of the spectra. The refractive index changes are correlated to the crystal defects and the stress field induced by the femtosecond laser pulses.

Trapezoidal ridge waveguides have been fabricated in YCOB nonlinear optical crystals by carbon ion irradiation and precise diamond-blade dicing. The diced ridges with smooth side-walls allow for near-infrared (1064 nm) light guiding with propagation losses around 1 dB/cm. Refractive index profile of a waveguide has been reconstructed in a reasonable manner. Green second harmonic light have been generated at room temperature via type I birefringent phase matching. Under the pump of continuous and pulsed lasers, conversion efficiencies for guided-wave frequency doubling can be up to similar to 1.10% W-1 and similar to 6.22%, respectively.

We report on the synthesis and features of copper (Cu) nanoparticles (NPs) embedded into LiNbO3 crystal. A linear optical absorption that peaked at 613 nm is observed, which correlates to the localized surface plasmon resonance (LSPR) effect. In addition, the Cu NPs embedded LiNbO3 (CuNP:LN) possesses ultrafast saturable absorption properties at a wavelength of 1 mu m. Based on these enhanced nonlinear optical properties, CuNP:LN is applied as a saturable absorber (SA) for pulsed laser generation in a waveguide laser system. Under an optical pump, the 8.6 GHz fundamentally Q-switched mode-locked laser operation has been efficiently implemented based on a Nd:YAG cladding waveguide fabricated by femtosecond laser writing. The measured pulse duration is as short as 55 ps and the slope efficiency is up to similar to 22.7%. This work suggests the promising application of LiNbO3 crystal embedded Cu NPs for ultrashort pulse generation. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Mid-infrared electro-optic Q-switched lasers with high repetition rates have many vital applications. However, the required voltage of electro-optic Q-switching is proportional to the wavelength leading to the severe piezoelectric ring effect, which limits its developments especially with high repetition rates. Based on the rate equation, this work designs a Langasite (LGS) electro-optic Q-switched laser with high repetition rates at 2 mu m by balancing the gain and loss in the cavity. The driven voltage determines the rotation of the polarization corresponding the loss in the cavity, and the gain depends on the incident pump power and repetition rate. By theoretical calculation, the driven voltage used in the high repetition rates is reduced to be 3.9 kV, which is 45% lower than the quarter-wave voltage. We demonstrated the LGS electro-optic Q-switched 2 mu m laser with a repetition rate of 200 kHz and pulse width of 5.52 ns. To the best of our knowledge, this work presents the highest repetition rate in the electric-optic Q-switched laser at 2 mu m and should be helpful for the design of Q-switched lasers with high repetition rates.