Continuous-wave mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

This paper reports a continuous-wave （CW） mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate （PPLN） pumped by a diode-end-pumped CW Nd：YVO4 laser. Considering the thermal lens effects, it adopted an optical ballast lens and the near-concentric cavity for better operation. At the PPLN＇s grating period of 28.5 μm and the temperature of 140℃, the maximum idler output power of 155 mW at 3.86 μm has been achieved when the 808 nm pump power is 8.5 W, leading to an optical-to-optical conversion efficiency of 1.82%.

High efficiency continuous-wave tunable signal output of an intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

In this paper we report on a continuous-wave （CW） intracavity singly resonant optical parametric oscillator （ICSRO） based on periodically poled LiNbO3 （PPLN） pumped by a diode-end-pumped CW Nd：YVO4 laser. Considering the thermal lens effects and diffraction loss, an optical ballast lens and a near-concentric cavity are adopted for better operation. Through varying the grating period and the temperature, the tunable signal output from 1406 nm to 1513 nm is obtained. At a PPLN grating period of 29 pm and a temperature of 413 K, a maximum signal output power of 820 mW at 1500 nm is achieved when the 808 nm pump power is 10.9 W, leading to an optical-to-optical conversion efficiency of 7.51%.

Three-wavelength generation from cascaded wavelength conversion in monolithic periodically poled lithium niobate

Tunable coherent emission is generated in a single-pass, cascaded wavelength conversion process from mode-locked laser-pumped monolithic periodically poled lithium niobate（PPLN）. Three ranges of wavelength, including visible output from 628 nm to 639 nm, near-infrared output from 797 nm to 816 nm, and mid-infrared output from 3167 nm to 3459 nm,were obtained from the monolithic PPLN, which consists of a 10-mm section for 532-nm-pumped optical parametric generation（OPG） and a 7-mm section for 1064-nm-pumped sum frequency generation（SFG）. A pump-to-signal conversion efficiency of 23.4% for OPG at 50°C and a quantum efficiency of 26.2% for SFG at 200°C were obtained.

1-W,high-repetition-rate room temperature operation of mid-infrared optical parametric oscillator based on periodically poled MgO-doped LiNbO

In this paper a high-repetition-rate mid-infrared （mid-IR） optical parametric oscillator based on periodically poled MgO-doped LiNbO3 （PPMgLN） at room temperature was demonstrated. The maximum average mid-IR output power at 3.63μm was 1.02 W with the repetition rate of 60kHz and corresponding efficiency from the pump to the idler was 26.7%. The temperature tuning and the period tuning characteristics were also discussed.

Compact efficient optical parametric generator internal to a Q-switched Nd:YVO_4 laser with periodically poled MgO:LiNbO_3

This paper demonstrates a compact efficient optical parametric generator internal to a Q-switched dlode-endpumped Nd：YVO4 laser with periodically poled MgO：LiNbO3（PPMgLN）. With the Q-switch set at a repetition rate of 25kHz and the PPMgLN crystal operated at room temperature （25℃）, the intracavity optical parametric generator threshold was reached as a diode pump power of 0.9 W. A maximum signal output power of 0.34 W with a pulse width of 25 ns and a beam quality factor of 1.4 was obtained at an incident diode power of 3.4 W, leading to a conversion efficiency of 10% with a slope efficiency of 14.4%. By varying the crystal temperature from 25 to 200℃, the output signal wavelengths were tuned in range of 1506-1565 nm. Over a 30-minutes interval, the instability of the signal power was measured to be less than 1%. In addition, the threshold pump intensity for the intracavity optical parametric generator is theoretically investigated, and the obtained result is in good agreement with the experimental results.

Temperature-dependent second harmonic generation process based on an MgO-doped periodically poled lithium niobate waveguide

The temperature dependency of a 5-mo1% MgO-doped periodically poled lithium niobate waveguide was investi- gated in this paper. We started with the temperature-dependent refractive index equation for the waveguide. Secondly, the temperature dependency of the second harmonic generation effect was experimentally researched under different temperatures and pump powers. The quasi-phase matched wavelengths, efficiency bandwidths and peak efficiencies of the waveguide were measured. The experimental results agreed with theoretical simulations, which are indispensable in the following all-optical sampling studies based on the cascaded second harmonic generation/difference-frequency generation process in the current device.

Performance of Optical Sampling Based on SHG in CPPLN Waveguide

Sampling efficiency and bandwidth of the optical sampling system based on second harmonic generation （SHG） in chirped periodically poled LiNbO3 （CPPLN） are numerically researched. A broad sampling bandwidth can be obtained by adjusting chirp coefficient and waveguide length of CPPLN, and sampling efficiency can be improved by using higher pump power, increasing waveguide length and choosing appropriate chirp coefficient. Results show that both sampling bandwidth and efficiency in CPPLN waveguides are controllable and that CPPLN waveguides are more suitable for multiwavelength optical sampling systems.

Experimental investigation of nonlinear process based on cSHG/DFG in PPLN waveguide

Effects of second harmonic generation （SHG） and cascaded second harmonic generation/difference frequency generation（cSHG/DFG） based on the quasi-phase-matching （QPM） condition in periodically poled lithium niobate （PPLN） waveguide were investigated experimentally. SHG conversion efficiency of -13.6dB and QPM bandwidth of 0.45nm were achieved using a 16.1dBm power of fundamental wave at 1550.4nm. Using pulsed all-fiber passive mode locked laser and tunable continuous wave laser, cSHG/DFG effect utilized for optical sampling was observed. Conversion efficiencies were calculated, and 11.88nm-wide QPM bandwidth was achieved through changing the wavelength of input signal. Conversion efficiency of cSHG/DFG effect increased linearly with the total injected power.

Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator

We report an efficient continuous-wave （CW） tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode （LD） end-pumped CW 1064 nm Nd：YVO4 laser as the pump source. A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability. The signal tuning range is 1401 1500 nm obtained by varying the domain period. The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.

THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves

We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).

Second-harmonic generation in periodic fork-shaped χ^((2)) gratings at oblique incidence

Three-dimensional(3D) nonlinear photonic crystals have received intensive interest as an ideal platform to study nonlinear wave interactions and explore their applications. Periodic fork-shaped gratings are extremely important in this context because they are capable of generating second-harmonic vortex beams from a fundamental Gaussian wave, which has versatile applications in optical trapping and materials engineering. However, previous studies mainly focused on the normal incidence of the fundamental Gaussian beam, resulting in symmetric emissions of the second-harmonic vortices. Here we present an experimental study on second-harmonic vortex generation in periodic fork-shaped gratings at oblique incidence, in comparison with the case of normal incidence. More quasi-phase-matching resonant wavelengths have been observed at oblique incidence, and the second-harmonic emissions become asymmetric against the incident beam.These results agree well with theoretic explanations. The oblique incidence of the fundamental wave is also used for the generation of second-harmonic Bessel beams with uniform azimuthal intensity distributions. Our study is important for a deeper understanding of nonlinear interactions in a 3D periodic medium. It also paves the way toward achieving highquality structured beams at new frequencies, which is important for manipulation of the orbital angular momentum of light.

Nonlinear Talbot self-healing in periodically poled LiNbO_3 crystal [Invited]

The nonlinear Talbot effect is a near-field nonlinear diffraction phenomenon in which the self-imaging of periodic objects is formed by the second harmonics of the incident laser beam. We demonstrate the first, to the best of our knowledge, example of nonlinear Talbot self-healing, i.e., the capability of creating defect-free images from faulty nonlinear optical structures. In particular, we employ the tightly focused femtosecond infrared optical pulses to fabricate LiNbO_(3) nonlinear photonic crystals and show that the defects in the form of the missing points of two-dimensional square and hexagonal periodic structures are restored in the second harmonic images at the first nonlinear Talbot plane. The observed nonlinear Talbot self-healing opens up new possibilities for defect-tolerant optical lithography and printing.

The Fabrication and SHG Test of QPM Periodically Poled KTiOPO_4

The Quasi-phase-matching periodically poled flux-grown KTP by high electrical field method is researched. A 8×5×1mm3,∧=9.0μm PPKTP wafer is successfully fabricated for the first order QPM SHG. The interactive length of the sample is about 3mm. The SHG scheme of Nd: YAG at 1064nm tested that the output power of cw 532nm green light is 0.2mw at room temperature with fundamental power of 1.2w. The normalized conversion efficiency is about 0.09% (W·cm)-1.

Discrete spatial solitons formed in periodically poled lithium niobate by electro-optical effect

We report the numerical observation of discrete spatial solitons in a periodically poled lithium niobate waveguide array by applying an electrical field through electro-optical effect. We show that discrete spatial soliton can be controlled by applied voltage in the periodically poled lithium niobate.

A periodically poled LiNbO_3 optical parametric generator in wavelength conversion from 2 to 3.88——4.34 μm

A periodically poled lithium niobate （PPLN） optical parametric generator （OPG） pumped by a laser diode （LD）-pumped Q-switched Tm,Ho：GdVO4 laser operated at 2.048 μm with pump pulse of 25 ns and repetition rate of 10 kHz is reported. A continuous tunable middle-infrared （mid-IR） spectrum of 3.88 - 4.34 μm is obtained by changing the crystal temperature from 50 to 124℃. When the incident pump power is 3 W, the total OPG output power is 95 mW, corresponding to optical conversion efficiency of 3.2%.

Theoretical analysis of periodically poled LiNbO_(3) nonlinear mirror and its application in a passively mode-locked Nd:YSAG laser

In this paper, we report a passively mode-locked Nd∶Y3Sc2Al3O12(Nd:YSAG) laser using a periodically poled Li Nb O3(PPLN)superlattice. Nonlinear mirror mode locking based on PPLN intracavity frequency doubling was theoretically analyzed. The modulation depth of nonlinear reflectivity of the nonlinear mirror is approximately 8.8%. Optical performances of the modelocked laser including output power, radio frequency spectrum, and optical spectrum were experimentally investigated. An average output power of 710 m W with a slope efficiency of 14.6% was obtained at the pump power of 6.5 W. The repetition rate is 101.7 MHz, and the signal-to-noise ratio of the mode-locked pulse is 45 d B. The mode-locked pulse width was approximately 9 ps.

Cross-correlation frequency-resolved optical gating scheme based on a periodically poled lithium niobate waveguide for an optical arbitrary waveform measurement

This study proposes a novel scheme of a cross- correlation frequency-resolved optical gating （X-FROG） measurement for an optical based on the sum frequency arbitrary waveform （OAW） generation （SFG） effect of a periodically poled lithium niobate （PPLN） waveguide. Based on the SFG effect and combined with the principal component generalized projects algorithm on a matrix, the theory model of the scheme is established. Using Matlab, the proposed OAW measurement X-FROG scheme using the PPLN waveguide is simulated and studied. Simulation results show that a rectangular pulse is a suitable gate pulse because of its low errors. Moreover, the increased complexity of OAW and phase mismatch decrease measurement accuracy.

Tunable rectangular array illuminator in periodically poled LiNbO_3 crystal

An electro-optic tunable rectangular array illuminator in one-dimensional periodically poled LiNbO3 （PPLN） crystal is presented experimentally which result is in good agreement with results from simu- lation. The illuminator is formed based on the Talbot self-imaging effect by applying an electric field on PPLN. The intensi~.y distribution of rectangular array could be precisely modulated. Compared with other array illuminators, this tunable illuminator uses a lower voltage and could get a more concentrated intensity distribution. The influence of the incident angle to the self-imaging patterns is studied for the first time.

Creation of periodical domain structure by local polarization reversal in planar waveguide produced by soft proton exchange in LiNbO_(3)

The paper presents the results of an experimental study of the local polarization reversal and creation of domains by a biased tip of scanning probe microscope(SPM)in lithium niobate single crystals of congruent composition with a surface layer modified by soft proton exchange(SPE).The depth dependence of Ht ions concentration in the SPE-modified layer measured by confocal Raman microscopy demonstrates a sufficient composition gradient.The creation of isolated domains and stripe domain structures has been done by two switching modes:(1)point switching by field application in separated points and(2)line scanning switching by motion of the biased tip being in contact with the sample surface.For point switching for pulse durations less than 10 s,the logarithmic dependence of the domain diameter on the pulse duration was observed.The change of the dependence to a linear one for pulse duration above 10 s has been attributed to the transition from the stochastic step generation at the domain wall to the deterministic one at the domain vertexes.The periodical structure of stripe domains was created in SPE CLN planar waveguides by scanning at elevated temperature.The revealed switching regime suppresses electrostatic interaction of neighboring domains and leads to a significant improvement of the domain structure regularity.The creation of the stable periodical domain structure with submicron periods in SPE CLN planar waveguides was demonstrated.

Simultaneous broadband generation of second and third harmonics from chirped nonlinear photonic crystals

Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics,chemistry and materials science to information communications and processing.Here we present the design and fabrication of a chirped periodically poled lithium niobate(CPPLN)nonlinear photonic crystal that supports multiple orders of quasiphase matching with finite bandwidth and allows for the simultaneous broadband generation of second and third harmonics with high conversion efficiency.Moreover,the chirp rate has a significant influence on the conversion efficiency and bandwidth.The CPPLN scheme offers a promising approach for the construction of short-wavelength laser sources and enables the generation of the three primary colors—red,green and blue—from a single crystal,which may have potential applications in large-screen laser displays.