Xuanyi Yu

An increase of photorefractive sensitivity in In:LiNbO3 crystal

The high sensitivity of photorefractive effect in indium doped lithium niobate was observed based on the two-wave mixing experiment. The sensitivity S was measured up to 2 cm 3 /J, even larger than the iron doped samples under the same configuration. The slightly indium doping seems to be an effective method to improve the photorefractive sensitivity of lithium niobate. 2002 Elsevier Science B.V. All rights reserved.

5.2-W high-repetition-rate eye-safe laser at 1525 nm generated by Nd:YVO 4 –YVO 4 stimulated Raman conversion

We report herein an efficient eye-safe Raman laser, which is based upon Nd:YVO₄₋YVO₄ and in-band pumped by a wavelength-locked laser diode array at 878.6 nm. By virtue of mitigated thermal load and improved pump absorption, a maximum average output power of 5.2 W at 1525 nm is obtained under the incident pump power of 30.6 W with the pulse repetition frequency of 140 kHz, corresponding to an optical efficiency of 17.0%.

Continuous-wave mid-infrared intra-cavity singly resonant PPLN-OPO under 880 nm in-band pumping

We report herein a continuous-wave mid-infrared intra-cavity singly resonant optical parametric oscillator (ICSRO) which is the first example of ICSRO that utilize in-band pumped Nd-doped vanadate laser as pump source. A 1064 nm Nd:YVO₄ laser in-band pumped by 880 nm LD and a periodically poled lithium niobate (PPLN) crystal are employed as the parent pump laser and the nonlinear medium, respectively. The idler output wavelength tuning range is 3.66-4.22 µm. A maximum output power of 1.54 W at 3.66 µm is obtained at absorbed pump power of 21.9 W, with corresponding optical efficiency being 7.0%. The control experiment of ICSRO under 808 nm traditional pumping is also carried out. The results show that in-band pumped ICSRO has better performance in terms of threshold, power scaling, efficiency and power stability than ICSRO traditionally pumped at 808 nm.

Optical refocusing three-dimensional wide-field fluorescence lifetime imaging microscopy

Three-dimensional fluorescence lifetime microscopy is achieved by combining wide-field fluorescence lifetime imaging with a remote optical refocusing method. As required for some applications in dynamic research for physics, chemistry, or biology, it is thereby not necessary to move the sample, i.e., the specimen is not disturbed during measurement. Using a fluorescent microsphere the performance of the system has been tested successfully with respect to three-dimensional fluorescence lifetime microscopy as well as time-resolved fluorescence spectroscopy.

Ultra-strong enhancement of electromagnetic fields in an L-shaped plasmonic nanocavity.

Enhancements up to four orders of magnitude for electric intensity and three orders of magnitude for magnetic intensity are realized in a novel 2D L-shaped nanocavity. This structure makes full use of the dimension confinement, cavity resonance and tip enhancement to increase the electromagnetic intensity. An impedance matching model is developed to design this cavity by regarding the cavity as a load impedance where electromagnetic fields are maximally enhanced when maximum electromagnetic energy is delivered to the load impedance. Our L-shaped nanocavity promises a variety of useful functionalities in sensing, nonlinear spectroscopy and signal processing.

Continuous-wave intra-cavity singly resonant optical parametric oscillator with resonant wave output coupling

We report herein the enhancement in both power and efficiency performance of a continuous-wave intra-cavity singly resonant optical parametric oscillator (ICSRO) by introducing finite resonant wave output coupling. While coupling out the resonant wave to useful output, the output coupling increases the SRO threshold properly thus suppresses the back-conversion under high pump power. Therefore, the down-conversion efficiency is maintained under high pump without having to raise the threshold by defocusing. With a T = 9.6% signal wave output coupler used, the SRO threshold is 2.46 W and the down-conversion efficiency is 72.9% under the maximum pump power of 21.4 W. 1.43 W idler power at 3.66 μm and 5.03 W signal power at 1.5 μm are obtained, corresponding to a total extraction efficiency of 30.2%. The resonant wave out coupling significantly levels up the upper limit for the power range where the ICSRO exhibits high efficiency, without impeding its advantage of low threshold.

Nanoscale beam splitters based on gradient metasurfaces

Beam splitters are essential components in various optical and photonic applications, for example, interferometers, multiplexers, and so on. Present beam splitters based on cubes or plates are normally bulky. Realizing beam splitters in nanoscales is useful to reduce the total size of photonic devices. We demonstrate here a beam splitter with nanoscale thickness based on a gradient metasurface comprising lithium niobate cylinder arrays. Since one unit cell of metasurface comprising two cylinder rows shows two opposite phase gradients, the incident light is split into different directions according to the generalized Snells law. The split ratio is proven to be effectively tunable.

Tunable dual-wavelength fiber laser with unique gain system based on in-fiber acousto-optic Mach–Zehnder interferometer

A fast tunable dual-wavelength laser based on in-fiber acousto-optic Mach-Zehnder interferometer (AO-MZI) with new fabrication process is proposed. Not only could the center wavelength of the output laser be optimized with enhanced tuning range about 30 nm by tuning the polarization and the driving frequency of the radio frequency (RF) signal accordingly, but also the spectral spacing between the two output wavelengths could be tuned from ~0 nm to 2.65 nm by controlling the power of the RF signal. The tuning mechanism was also discussed.

Mode conversion in a tapered fiber via a whispering gallery mode resonator and its application as add/drop filter.

Based on the conversion between the fundamental mode (LP01) and the higher-order mode (LP11) in a tapered fiber via a whispering gallery mode resonator, an add/drop filter was proposed and demonstrated experimentally, in which the resonator only interacted with one tapered fiber, rather than two tapered fibers as in conventional configurations. The filter gains advantages of easy alignment and low scattering loss over the other filters based on tapered fiber and resonator, and will be useful in application.

Efficient Eye-Safe Nd:YVO 4 Self-Raman Laser In-Band Pumped at 914 nm

An efficient Q-switched eye-safe Nd:YVO4 self-Raman laser, which we believe to be the first one in-band pumped at 914 nm, is presented, and 2.58 W of 1525-nm Stokes output was generated under the absorbed pump power of 10.2 W with a high repetition rate of 100 kHz, corresponding to a conversion efficiency of 25.3%. The optical efficiency with respect to incident pump also reached 16.4%. Influences of crystal temperature and dopant concentration on the performance of the eye-safe self-Raman laser were experimentally investigated.