X. P. Hu

Efficient second-harmonic generation in nonlinear plasmonic waveguide

We theoretically studied a nonlinear optical process in a hybrid plasmonic waveguide composed of a nonlinear dielectric waveguide and a metal film with a separation of a thin air gap. Owing to the hybridization effect of guided mode and surface plasmon polariton mode, this particular waveguide is able to confine the optical-field in a deep subwavelength scale together with low propagation loss. Based on this, efficient second-harmonic generations (SHG) were revealed at the fundamental wavelength of λ=1.55 μm with good field confinement. The SHG efficiency, as well as the coupling coefficient and mode area, were analyzed and discussed in detail with respect to the structural parameters.

High-power red-green-blue laser light source based on intermittent oscillating dual-wavelength Nd:YAG laser with a cascaded LiTaO3 superlattice.

We demonstrate a high-power red-green-blue laser source based on the quasi-phase-matching and intermittent oscillating dual-wavelength laser technique. A cascaded LiTaO3 superlattice was used to achieve the generation of red light at 660 nm, green light at 532 nm, and blue light at 440 nm to obtain the output of red-green-blue laser light from a diode-side-pumped Q-switched intermittent oscillating dual-wavelength Nd:YAG laser. The average output power of red-green-blue of 1.01 W was achieved under the total fundamental power of 5.1 W, which corresponds to the conversion efficiency of 20%.

Fast response dual-frequency liquid crystal switch with photo-patterned alignments

A dual-frequency liquid crystal based optical switch with orthogonally photo-patterned alignments is designed and fabricated. The cell gap is theoretically optimized for high switching performance. The measured extinction ratio of first diffraction order is over 20 dB with a low electric field of 3  V/μm. The switch On-Off time are measured to be 350 μs and 600 μs, respectively, both of which have reached submillisecond scale. Moreover, the switch is polarization independent, which has been predicted theoretically and further proved experimentally. This design is suitable in wide applications requiring fast response and polarizer free properties.

Diode-pumped passively mode-locked Nd:YVO 4 laser at 1342 nm with periodically poled LiNbO 3

In this Letter, we demonstrate a nonlinear-mirror (NLM) mode-locked diode-pumped solid-state Nd:YVO4 laser operating at 1342 nm, in which the NLM comprises a periodically poled LiNbO3 crystal and a dichroic mirror. The self-starting threshold for cw mode locking is 1.5 W, which is significantly lower than that of saturable absorber mode locking. An average power of 1.52 W at 1342 nm is obtained under diode pump power of 10 W at 808 nm, with the slope efficiency being up to 16.8%. The pulse width and the repetition rate of the mode-locked laser output are about 9.5 ps and 101 MHz, respectively.

A bidirectional tunable optical diode based on periodically poled LiNbO 3

We propose a bidirectional tunable optical diode based on a periodically poled lithium niobate (PPLN) with defect. An acoustic wave propagates together with the light beam so that a collinear photon-phonon interaction happens, which affects the nonlinear optical processes in PPLN. The fundamental wave exhibits an optical diode effect, i.e., the light only may travel toward a single direction while the opposite way is isolated. However, the acoustic wave could be used to adjust the contrast of optical isolation from -1 to 1. A direction-optional operation is thus realized. Moreover, the advantages of our tunable PPLN optical diode are also discussed.

Nanoparticle decoration of ferroelectric domain patterns in LiNbO3 crystal

A scatheless visualization has demonstrated that the engineered and spontaneous domains of lithium niobate (LiNbO3) crystal can be delineated by means of the nanoparticle decoration. These nanoparticles were monodispersed in nonpolar solvent and negatively charged under the existence of aerosol-OT (AOT or sodium di-2-ethylhexylsulfosuccinate). This method was based on the process of electrostatic interaction, in which the LiNbO3 crystal wafers were heated in the presence of decorating colloid solvent. The charged nanoparticles deposited preferentially on the surfaces of those domains with the opposite charges. The delineated patterns corresponded with the polarization property of domain structures and consequently provided a domain contrast image with resolution down to micron scale. This decoration technique is effective, easily operated, nondestructive for sample, noninvasive for human body, and especially, is more suitable for the domain mapping of oxide ferroelectric crystals. In addition, the initial...

Engineered quasi-phase-matching for laser techniques [Invited]

The quasi-phase-matching (QPM) technique has drawn increasing attention due to its promising applications in areas such as nonlinear frequency conversion for generating new laser light sources. In this paper, we will briefly review the main achievements in this field. We give a brief introduction of the invention of QPM theory, followed by the QPM-material fabrication techniques. When combing QPM with the solid-state laser techniques, various laser light sources, such as single-wavelength visible lasers and ultraviolet lasers, red–green–blue three-fundamental-color lasers, optical parametric oscillators in different temporal scales, and passive mode-locking lasers based on cascaded second-order nonlinearity, have been presented. The QPM technique has been extended to quantum optics recently, and prospects for the studies are bright.

Efficient generation of red light by frequency doubling in a periodically-poled nearly-stoichiometric LiTaO3 crystal

An efficient generation of red light in a periodically-poled nearly-stoichiometric LiTaO3 (PPSLT) by extracavity single-pass frequency doubling of a diode-pumped, Q-switched Nd:YVO4 laser at 1342nm was realized. An average power of 1.4W of the 671nm red light is obtained at the fundamental power of ∼2.8W with the conversion efficiency of 50%. The high conversion efficiency and steady output of red light indicate that the thick PPSLT is a competitive candidate for frequency conversion in order to construct a compact all-solid-state red laser.

Efficiency-enhanced optical parametric down conversion for mid-infrared generation on a tandem periodically poled MgO-doped stoichiometric lithium tantalate chip

We report an efficiency-enhanced mid-infrared generation via optical parametric down conversion. A tandem periodically-poled MgO-doped stoichiometric lithium tantalate crystal is used to realize on-chip generation and amplification of mid-infrared radiation inside an optical parametric oscillator cavity. We achieved 21.2% conversion efficiency (24% slope efficiency), which is among the highest efficiencies for the pump-to-mid-infrared conversion, with 1064 nm Nd class laser pump. The maximum average output power at 3.87 μm reached 635 mW with a 3.0 W pump.

Multicolor Čerenkov conical beams generation by cascaded-χ(2) processes in radially poled nonlinear photonic crystals

We observe multiple simultaneous cascaded-χ(2) Cerenkov conical radiations in radially poled nonlinear photonic crystals. By using two incident fundamental waves ω1 and ω2, a variety of cascaded nonlinear up-conversion processes occur which result in high-frequency Cerenkov radiations at 2ωi+ωj(i,j=1,2) exhibiting as multicolor conical beams. Two types of phase-matching geometries with different emission angles are demonstrated for each kind of cascaded-χ(2) Cerenkov radiation. The external angle of the Cerenkov radiation exhibits strong dependence on the fundamental wavelengths. The experimental results agree well with the theoretical calculations.