摘要 : We demonstrate an on-chip microring laser on ${{\rm Yb}^{3 +}}$-doped thin film lithium niobate (Yb:TFLN) fabricated by photolithography-assisted chemo-mechanical etching technology. Multiwavelength laser emissions around 1025 nm from the microring resonator pumped by a 980 nm laser diode are observed with the lasing threshold of 10 mW. Experimentally, up to 14 longitudinal modes are obtained from the fabricated Yb:TFLN microring laser, and this on-chip microring laser is a promising light source for multiple wavelength channels in optical communications and biosensors.

摘要 : We demonstrate fabrication of a 30-cm-long thin-film lithium niobate (TFLN) optical delay line (ODL) incorporated with segmented microelectrodes of 24-cm total length using the femtosecond laser lithography technique. The transmission spectra of the unbalanced Mach–Zehnder interferometers (MZIs) reveal an ultra-low propagation loss of 0.025 dB/cm. The device exhibits a low half-wave voltage of 0.45 V, corresponding to a voltage-length product of 10.8 V·cm, which is equivalent to 5.4 V·cm in the push-pull configuration. We also demonstrate a high electro-optic (EO) tuning efficiency of 3.146 fs/V and a continuous tuning range of 220 fs in the fabricated ODL.

摘要 : This work demonstrates a robust low-loss optical interface by tiling passive (i.e., without doping of active ions) thin film lithium niobate (TFLN) and active (i.e., doped with rare earth ions) TFLN substrates for monolithic integration of passive/active lithium niobate photonics. The tiled substrates composed of both active and passive areas allow for patterning the mask of the integrated active passive photonic device at once using a single continuous photolithography process. The interface loss of tiled substrate is measured as low as 0.26 dB. Thanks to the stability provided by this approach, a four-channel waveguide amplifier is realized in a straightforward manner, which shows a net gain of 5 dB at a 1550-nm wavelength and 8 dB at a 1530-nm wavelength for each channel. The robust low-loss optical interface for passive/active photonic integration will facilitate large-scale high performance photonic devices that require on-chip light sources and amplifiers.

摘要 : We experimentally investigated clean optical emissions from multiple combustion intermediates including free radicals C2, CH, and CN at multiple wavelengths induced by ultrashort 1, 030-nm laser pulses. We systematically study the evolution of the fluorescence emissions induced by the femtosecond laser filament in the combustion field with the parameters such as the laser pulse energy, pulse duration, and focal length. Compared with the previous work, we promote that the fluorescence emissions of the combustion product can be manipulated effectively by controlling the femtosecond laser characteristics including pulse energy, duration, and the focusing conditions. This process helps to optimize its signal-to-noise ratio, which provides a further application of the femtosecond laser pulses to sense the combustion intermediates.

摘要 : We overcome the difficulty in realizing a monolithic waveguide-coupled microring laser integrated on an erbium-doped thin film lithium niobate (Er: TFLN) using a photolithography assisted chemo-mechanical etching (PLACE) technique. We demonstrate an integrated single-frequency microring laser operating around 1531 nm wavelength. The PLACE technique, enabling integrated Er: TFLN photonics with low propagation loss, can thus be used to realize low cost mass production of monolithic on-chip microlasers with applications ranging from optical communication and photonic integrated circuit (PIC) to precision metrology and large-scale sensing.

摘要 : We report a comparative experimental investigation of femtosecond laser-induced third harmonic generation (THG) in an ethanol flame and in air. It was found that the third harmonic (TH) signal produced in the presence of a combustion field can be greatly enhanced, in comparison to that generated in air, and that the enhancement factor depends strongly on the experimental parameters, such as the focal length, relative position of the flame and filament, and laser repetition frequency. Moreover, by replacing the flame with a point temperature controller, a similar signal enhancement of THG was observed, and the TH signal exhibited a nonlinear growth with the heating temperature. Further analysis indicated that the observed enhancement of THG originates from the suppression of Gouy-phase-induced destructive interference due to the disturbed gas density under high-temperature heating. The high sensitivity of the TH signal to the combustion temperature helps formulate an effective and straightforward approach to achieve nonintrusive temperature measurements in the combustion field.

摘要 : Erbium doped integrated waveguide amplifier and laser prevail in power consumption, footprint, stability and scalability over the counterparts in bulk materials, underpinning the lightwave communication and large-scale sensing. Subject to the highly confined mode in the micro-to-nanoscale and moderate propagation loss, gain and power scaling in such integrated devices prove to be more challenging compared to their bulk counterparts. In this work, a thin cladding layer of tantalum pentoxide (Ta2O5) is employed in the erbium doped lithium niobate (LN) waveguide amplifier fabricated on the thin film lithium niobate on insulator (LNOI) wafer by the photolithography assisted chemo-mechanical etching (PLACE) technique. Above 20 dB small signal internal net gain is achieved at the signal wavelength around 1532 nm in the 10 cm long LNOI amplifier pumped by the diode laser at ∼980 nm. Experimental characterizations reveal the advantage of Ta2O5 cladding in higher optical gain compared with the air-clad amplifier, which is further explained by the theoretical modeling of the LNOI amplifier including the guided mode structures and the steady-state response of erbium ions.

摘要 : Lithium niobate (LiNbO3, LN) on insulator (LNOI) is a promising material platform for integrated photonics to realize high-capacity and high-speed information communication. Here, we developed the 515 nm femtosecond laser micro-machining technique with a 316 nm processing accuracy and demonstrated the fabrication of monolithically integrated waveguide-coupled micro-resonators with the quality factors (Q) of $1.8\times 10^{5}$ using 515 nm femtosecond laser ablation assisted ions beam etching (IBE) process. The chemical–mechanical polishing (CMP) is adopted to smoothing the etched edge of the hard mask patterned by femtosecond laser ablation. These fabrication techniques are compatible with high efficiency and high precision wafer-scale production, without counting on the UV/E-beam lithography technique, which is essential for LN photonic devices moving towards industrial applications.

摘要 : We propose a hybrid laser microfabrication approach for the manufacture of three-dimensional (3D) optofluidic spot-size converters in fused silica glass by a combination of femtosecond (fs) laser microfabrication and carbon dioxide laser irradiation. Spatially shaped fs laser-assisted chemical etching was first performed to form 3D hollow microchannels in glass, which were composed of embedded straight channels, tapered channels, and vertical channels connected to the glass surface. Then, carbon dioxide laser-induced thermal reflow was carried out for the internal polishing of the whole microchannels and sealing parts of the vertical channels. Finally, 3D optofluidic spot-size converters (SSC) were formed by filling a liquid-core waveguide solution into laser-polished microchannels. With a fabricated SSC structure, the mode spot size of the optofluidic waveguide was expanded from ~8 μm to ~23 μm with a conversion efficiency of ~84.1%. Further measurement of the waveguide-to-waveguide coupling devices in the glass showed that the total insertion loss of two symmetric SSC structures through two ~50 μm-diameter coupling ports was ~6.73 dB at 1310 nm, which was only about half that of non-SSC structures with diameters of ~9 μm at the same coupling distance. The proposed approach holds great potential for developing novel 3D fluid-based photonic devices for mode conversion, optical manipulation, and lab-on-a-chip sensing.