Simultaneous wavelength conversion and pulse compression exploiting cascaded second-order nonlinear processes in LiNbO3 waveguides

Simultaneous wavelength conversion and pulse compression are proposed and demonstrated exploiting cascaded second-order nonlinear processes in periodically domain-inverted LiNbO₃ waveguides. The influences of initial pulse widths and waveguide length on the conversion efficiency and converted pulse compression are theoretically analyzed. Tunable wavelength conversion is performed for the signal pulse with the temporal width of 7.5 ps and repetition rate of 40 GHz. Conversion efficiency of more than −24 dB is obtained for 35-nm conversion span under average signal power of 10 dBm when a CW control wave is adopted.     

FWM in silicon nanocrystal-based sandwiched slot waveguides

The observation of four-wave mixing in a 6 mm long sandwiched slot waveguide filled with Si-nc/SiO₂ is reported for optical powers usually employed in telecommunication systems. A −47 dB conversion efficiency is measured in fabricated waveguides for input signal powers around 12 dBm on chip and a waveguide length of 6 mm. Furthermore, the calculated non-linear coefficient is found to be n₂ = 2.67 × 10⁻¹⁷ m²/W. It is also expected that, by using longer waveguides, it would be possible to achieve wavelength conversion.     

Wavelength conversion in a Ti:PPSMgLN channel waveguide

A periodically poled titanium (Ti)-diffusion waveguide in near-stoichiometric MgO:LiNbO₃ (SMgLN) was fabricated that exhibits a second harmonic generation (SHG) efficiency of 63%. The device shows very high resistance to photorefractive damage at room temperature. All optical wavelength conversion by difference frequency generation (DFG) has been demonstrated in a periodically poled SMgLN (PPSMgLN) with Ti-diffusion channel waveguides. The wavelength conversion efficiency was measured to be −7.3 dB with the pump power of 150 mW and the signal power of 50 mW at room temperature.     

Diode-pumped passively Q-switched Nd:LuxY1−xVO4 laser at 1.34 μm with two V:YAG saturable absorbers

Laser performance with the mixed Nd:Lu_0.15Y_0.85VO₄ crystal at 1.34 μm wavelength has been demonstrated. The continuous wave (cw) operation was carried out in a simple plano-concave resonator with an optical conversion efficiency of 23% and a slop efficiency of 25%. At a pump power of 6.78 W, the Q-switched pulses with the largest average output power of 349 mW, the shortest pulse width of 30.6 ns, the largest repetition rate of 42.5 kHz, the highest peak power of 268 W and the largest pulse energy of 8.2 μJ were obtained, corresponding to the V:YAG with initial transmission of 89%.     

High-power 1.5 and 3.4 μm intracavity KTA OPO driven by a diode-pumped Q-switched Nd:YAG laser

With a non-critically phase-matched KTA crystal, a high-power intracavity optical parametric oscillator (IOPO) driven by a diode-side-pumped acousto-optically Q-switched Nd:YAG laser has been realized. The maximum average output power of 13.6 W at the signal wavelength of 1534 nm and 3 W at the idler wavelength of 3472.7 nm were obtained with the repetition rate of 18 kHz, giving the optical-optical conversion efficiency of about 5.7% from diode-power at 808 nm to OPO signal output, which was the highest conversion efficiency for intracavity KTA OPO with diode-side-pumping configurations to our best knowledge. At the highest output power of 13.6 W, the signal pulse duration of 5.46 ns was obtained, corresponding to the single pulse energy of 756 μJ and peak power of 138 kW, respectively.     

基于PPLN光波导和频与差频级联型全光波长转换的研究

介绍了基于准相位匹配周期极化反转铌酸锂光波导的和频与差频(SFG DFG)级联型全光波长转换技术的基本原理.计算了SFG DFG级联型波长转换的转换效率,分析了抽运光功率以及两个抽运光之间的间距对转换效率的影响,抽运光功率越大,转换效率越高;转换效率随着间距的增大先增大后减小.单抽运调节时的抽运带宽为0.5 nm,同时对信号光脉冲还有压缩作用,压缩比是0.68.     

Tunable wavelength conversion between picosecond pulses using cascaded second-order nonlinearity in LiNbO3 waveguides

Tunable wavelength conversion between picosecond pulses is demonstrated by exploiting cascaded secondorder nonlinearity in periodically poled LiNbO₃ waveguides when the pump pulse with 40-GHz repetition rate and 7.5-ps pulse width is adopted. No external continuous-wave input is required in the proposed wavelength converter. The converted signal wavelength can be tuned from 1519 to 1562.6 nm as the lasing wavelength is changed from 1534.5 to 1572.1 nm.This revised version was published online in August 2005 with a corrected cover date.     

Circular arc plasmonic waveguide couplers between two-dimensional dielectric slab waveguides and plasmonic waveguides

We investigate the properties of arc plasmonic waveguide coupler between two-dimensional dielectric slab waveguides and plasmonic waveguides with two-dimensional finite difference time domain methods. The simulation results show that transmission efficiency between high index dielectric slab waveguides with width 300 nm and silver-air-silver waveguides with width 40 nm connected by the coupler can reach to 90.4% at optical communication wavelength. And, by optimizing the shapes near the ends of the coupler, the transmission efficiency can be improved to 98.4%.     

LD end-pumped intracavity frequency doubled Yb:YAG laser

A laser diode end-pumped 10 at.% doped Yb:YAG microchip crystal intracavity frequency doubled all solid-stated green laser is reported in this paper. Using one plano-concave resonator, with the pump power of 1.2 W, 44.2 mW TEM₀₀ continuous wave (CW) laser at 525 nm was obtained, the optical conversion efficiency was about 3.7%. When a Cr:YAG crystal with initial transmission of 95.5% inserted in the resonator, the maximum output power of 6.4 mW, pulse duration width of 49.1 ns, pulse repetition rate of 2.45 kHz, and peak power of 53.1 W at 515 nm were achieved when the pump power was 1.2 W. The wavelength changed from 525 nm to 515 nm and the threshold was only 725 mW.     

Low cost fabrication of SiO2 optical waveguides by laser direct writing on Ti-doped Sol-Gel films

A commercial direct laser writing (DLW) system operating at 1070 nm was used to fabricate SiO₂ optical waveguides on silicon wafers. A Ti-doped SiO₂ Sol-Gel film was deposited on the SiO₂/Si substrate by the dip-coating technique, based on which SiO₂ optical waveguides were patterned by DLW using a Ytterbium fiber laser and followed by chemical etching. The effects of laser parameters and the preheated temperature of Sol-Gel films on the dimensions of optical waveguides were studied systematically. The differences of etching rate between laser irradiated and non-irradiated areas in Sol-Gel films preheated at various temperatures are characterized by measuring the thickness of the films. Results demonstrate that the available laser power density range for laser densification and the width of the patterned optical waveguides are influenced strongly by the preheated temperature of the Sol-Gel films. The width of the optimized optical waveguide in this work is 25 μm. The minimum propagation loss of the fabricated optical waveguides is 1.7 dB cm⁻¹ at the wavelength of 1550 nm.     

All-Optical Wavelength Conversion Based on Four-Wave Mixing in Dispersion-Engineered Silicon Nanowaveguides

We demonstrate experimentally all-optical wavelength conversion based on four-wave mixing in dispersion-engineered silicon nanowaveguides with a picosecond pulse pump. We find that the conversion efficiency is significantly limited by nonlinear losses induced by the two-photon absorption and freecarrier absorption. Using a picosecond pulse pump centered at 1,550 nm, we show that the input continuous-wave signals can efficiently be converted into a broadband idler pulse in silicon waveguides with various dimensions. Conversion efficiencies versus signal wavelengths are different for silicon waveguides with different dimensions due to the variation in the phase mismatch; we obtain a conversion efficiency of – 32 dB in silicon nanowaveguides with a length of 5.8 mm. Such on-chip optical wavelength converters can find important potential applications in highly-integrated optical circuits for all-optical ultrafast signal processing.     

Continuous wave and passively Q-switched laser performance of the mixed crystal Nd:Lux(x = 0.5)Y1 − x VO4

Diode end-pumped continuous-wave and passively Q-switched Nd:Lu_x(x = 0.5)Y_1 − xVO₄ mixed crystal lasers were demonstrated. At the pump power of 12.6 W, the maximum output power of 6.7 W around 1066.5 nm was obtained with the output transmission of 27%. The optical conversion efficiency is 53.2%, corresponding to a slope efficiency of 55.8%. For pulsed operation, the shortest pulse width attained was 8.6 ns, with the pulse repetition frequency of 99 kHz, and the single pulse energy and the peak power were estimated to be 25.5 μJ and 2.96 kW, respectively.     

Pulse LDA-pumped single-frequency Nd:YVO4-KTP green laser using Brewster plate

A pulse laser-diode-array (LDA)-pumped, single-axial-mode, intracavity frequency-doubled Nd:YVO₄ laser has been demonstrated by using an birefringent filter consisting of a KTP crystal and two Brewster plates (BP). Up to 72.4 mW average output power is obtained for 800 mW pumping power with an optical-to-optical conversion efficiency of 9.1%. The maximum peak power of the single-frequency green laser is 22.3 W with the pulse width 162 μs.     

Femtosecond pulse compression based on second harmonic generation from a frequency chirped pulse

A 49 fs pulse at the wavelength of 800 nm was converted to a 26 fs pulse at the wavelength of 400 nm by temporal stretching (frequency chirping) and second harmonic generation from a chirped pulse with subsequent compression. The energy conversion efficiency of 35% was achieved.     

Low-threshold diode-pumped CW passively mode-locked Nd:YVO4 laser

A low-threshold passively continuous-wave (CW) mode-locked Nd:YVO₄ solid-state laser was demonstrated by use of a semiconductor saturable absorber mirror (SESAM). The threshold for continuous-wave mode-locked is relatively low, about 2.15 W. The maximum average output power was 2.12 W and the optical to optical conversion efficiency was about 32%. The pulse width was about 15 ps with the repetition rate of 105 MHz.     

Highly efficient third-harmonic generation with electro-optically Q-switched diode-end-pumped Nd:YVO4 slab laser

We have achieved efficient third-harmonic generation (THG) with an electro-optically Q-switched diode-end-pumped slab laser by cascading second-harmonic and sum-frequency generation in a lithium triborate (LBO) crystal. The high conversion efficiency, short pulse length and high pulse energy is the characteristic of the output 355 nm light. An average power of 11.1 W at a repetition rate of 10 kHz was achieved. The pulse energy is 1.1 mJ and the pulse length is 5 ns. The peak power of pulse is 0.22 MW. The conversion efficiency from 1064 nm to 355 nm reached 44.4% which is to our knowledge the highest conversion efficiency. Furthermore, the 355 nm light is near TEM₀₀ mode. The beam quality is M² < 1.5. In this paper, the experimental setup, results and the factors which can affect the conversion efficiency are discussed.     

Formation of periodic structures by the space-selective precipitation of Ge nanoparticles in channel waveguides

Thermally stabilized channel waveguides with Bragg gratings were fabricated by the space-selective precipitation technique of crystalline Ge nanoparticles using KrF excimer laser irradiation. The periodic structures consisting of Ge nanoparticles were formed in Ge-B-SiO₂ thin glass films after exposure to an interference pattern of the laser followed by annealing at 600 °C. The channel waveguides with the periodic structures were fabricated by the cladding of the patterned Cr layers on the films. The diffraction peak for the TE-like mode of 11.8 dB depth was observed clearly at a wavelength of 1526.4 nm, indicating that the periodic structure also served as the optical band-pass filter in optical communication wavelength. The spectral shape, diffraction efficiency, and diffraction wavelength remained unchanged even after annealing at 400 °C. Furthermore, a low temperature dependence of the diffraction wavelength - as low as 8.1 pm/°C - was achieved. The diffraction efficiency was further enhanced after subsequent annealing at 600 °C. The space-selective precipitation technique is expected to be useful for the fabrication of highly reliable optical filters or durable sensing devices operating at high temperature.     

A Q-switched Nd:YAlO3 laser emitting 1080 and 1342 nm

In this paper, the study of a switchable electro-optic Q-switched Nd:YAlO₃ laser emitting 1080 and 1342 nm wavelength was demonstrated. The two-wavelength lasers were eradiated by a Nd:YAlO₃ crystal pumped by a xenon lamp. Two KD*P Pockels cells were adopted as Q-switches. The output energy of 277.2 mJ at 1080 nm wavelength with a pulse width of 20 ns and that of 190.67 mJ at 1342 nm wavelength with a pulse width of 40 ns was obtained, respectively, in our experiment. By switching on or off the voltages applied to the Pockels cells, the operation of the two-wavelength lasers can be selected in free running mode or Q-switching mode.     

Optimization of optical parametric chirped pulse amplification with different pump wavelengths

Optical parametric chirped pulse amplification with different pump wavelengths was investigated using LBO crystal, at signal central wavelength of 800 nm. According to our theoretical simulation, when pump wavelength is 492.5 nm, there is a maximal gain bandwidth of 190 nm centered at 805 nm in optimal noncollinear angle using LBO. Presently, pump wavelength of 492.5 nm can be obtained from second harmonic generation of a Yb:Sr₅(PO₄)₃F laser. The broad gain bandwidth can completely support ∼6 fs with a spectral centre of seed pulse at 800 nm. The deviation from optimal noncollinear angle can be compensated by accurately tuning crystal angle for phase matching. The gain spectrum with pump wavelength of 492.5 nm is much better than those with pump wavelengths of 400, 526.5 and 532 nm, at signal centre of 800 nm.     

Passively Q-switched laser operation in a composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal with a GaAs saturable absorber

By using a piece of GaAs wafer as the saturable absorber, the performance of the passively Q-switched composite Nd:YVO₄ laser with different output couplers has been demonstrated for the first time as far as we know. The largest continuous wave output power of 1.52 W is obtained at the incident pump power of 5.31 W, giving an optical conversion efficiency of 28.7% and a slope efficiency of 30.2%. The shortest pulse width of 11 ns, the largest single-pulse energy of 2.49 μJ and the highest peak power of 190 W are also obtained.