Singly resonant optical parametric oscillation in periodically poled lithium niobate waveguides

We report quasi-phase-matched singly resonant optical parametric oscillation in electric-field-poled lithium niobate waveguides. Parametric gains as high as 250%/W, an oscillation threshold of 1.6 W (peak), idler output powers of 220 mW, and a tuning range of 1180-2080 nm for pump wavelengths of 756-772 nm have been observed. Pump depletion is limited to 40% because of the multiple launched transverse modes at the pump wavelength. We predict that fully optimized waveguide singly resonant oscillators can have thresholds of ~100 mW, accessible to cw diode pumping.     

Cascaded optical parametric oscillation with a dual-grating periodically poled lithium niobate crystal

We demonstrate continuous-wave cascaded optical parametric oscillation in which the signal field of the primary parametric oscillator internally pumps the secondary parametric oscillator. Wavelength tuning is achieved with temperature tuning and a fan-out grating structure of a dual-grating periodically poled lithium niobate crystal. Above the secondary threshold the primary signal power is clamped, and all the other output powers increase linearly with the input pump power, in accordance with theory. Cascaded parametric oscillation offers a convenient and efficient way to generate multiple tunable outputs.     

Microlaser-pumped periodically poled lithium niobate optical parametric generator-optical parametric amplifier

For what is believed to be the first time, a single-longitudinal-mode passively Q-switched Nd:YAG microlaser is used to pump a narrow-bandwidth periodically poled lithium niobate (PPLN) optical parametric generator-optical parametric amplifier (OPG-OPA). Before amplification in the OPA, the output of the OPG stage was spectrally filtered with an air-spaced etalon, resulting in spectroscopically useful radiation (bandwidth, ~0.05 cm(-1) FWHM) that was tunable in 15-cm(-1) segments anywhere in the signal range 6820-6220 cm(-1) and the idler range 2580-3180 cm(-1). The ability to pump an OPG-OPA with compact, high-repetition-rate, intrinsically narrow-bandwidth microlasers is made possible by the high gain of PPLN. The result is a tunable light source that is well suited for use in portable spectroscopic gas sensors.     

Distributed-feedback optical parametric oscillation by use of a photorefractive grating in periodically poled lithium niobate

We report a demonstration of distributed-feedback (DFB) optical parametric oscillation (OPO) by writing photorefractive gratings in periodically poled lithium niobate (PPLN). The photorefractive DFB structures were fabricated by illumination of PPLN with UV light through a photomask and by writing of PPLN with UV-light gated interfering laser beams at 532 nm. Evidence of OPO was observed from the spectral narrowing at the 1438.8- and the 619.3-nm signal wavelengths from 1064- and 532-nm-pumped PPLN crystals with the DFB grating periods phase matched to the 4084.5- and 3774-nm idler wavelengths, respectively.     

Optical parametric oscillation in periodically poled lithium niobate driven by a diode-pumped Q-switched erbium fiber laser

We describe what is to our knowledge the first nanosecond periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) driven by a fiber laser. The source was frequency doubled by a PPLN sample before pumping a second, 20-mm-long, PPLN crystal. The OPO threshold was <10muJ, with pump depletions of as much as 45% and a tunable signal range of 945-1450 nm (1690-4450-nm idler range). We demonstrated 130-nm signal tuning by varying the pump wavelength and doubling crystal's temperature. Also, we achieved 15-nm tuning with all crystals at a constant temperature. The results demonstrate the potential of the fiber laser:PPLN combination for practical, versatile, and tunable sources.     

Tunable terahertz-wave generation from DAST crystal by dual signal-wave parametric oscillation of periodically poled lithium niobate

The first known demonstration of tunable terahertz-wave generation by difference-frequency generation of dual signal-wave quasi-phase-matched optical parametric oscillation was performed with periodically poled LiNbO(3) (PPLN) with a series of gratings. An organic ionic salt, 4-dimethylamino-N-methyl-4-stilbazolium-tosylate (DAST), was used as a nonlinear crystal. A compact terahertz-wave source resulted, and changing the temperature of the PPLN permitted the wavelength to be varied from 120 to 160 mum. The wavelength could be tuned from 100 to 700 mum by proper selection of combinations of periodically poled gratings.     

High-power picosecond optical parametric oscillator based on periodically poled lithium niobate

A high-power picosecond optical parametric oscillator (OPO) based on a 47-mm periodically poled lithium niobate crystal is described. More than 12 W of total average power-almost 8 W of signal power at 1.85 microm and more than 4 W of idler radiation at 2.5 microm -is simultaneously extracted from less than 18 W of average pump power. The OPO is synchronously pumped by 80-ps (FWHM) cw mode-locked pulses at 1.064 microm , and its output is tunable from 1.7 to 2.84microm . Nearly transform-limited signal pulses are obtained following the introduction of two intracavity etalons.     

Angle-tuned signal-resonated optical parametric oscillator based on periodically poled lithium niobate

We demonstrate an angle-tuned signal-resonated optical parametric oscillator (OPO) with periodically poled lithium niobate (PPLN) pumped by a diode-pumped Nd:YVO4 laser. 1499.8 - 1506.6 nm of signal wavelength is achieved at 140℃ by rotating a 29-μm period PPLN from 0° - 10.22° in the x-y plane while keeping the pump wave vertical to the resonator mirrors. Two pairs of the signal and idler waves of the same wavelengths can be achieved symmetrically for each pair of angles of rotation with same absolute value and opposite sign. Theoretical analyses on angle-tuned PPLN-OPO with pump wave vertical to the resonator mirrors are presented and in good agreement with our experimental results. It is also found that all interacting waves in the cavity (not inside the crystal) are always collineax for PPLN-OPO with the pump wave vertical to the resonator mirrors while phase-matching is noncollinear within the crystal.     

Fabrication of periodically poled lithium niobate chips for optical parametric oscillators

An electric-field poling process was established that yielded uniform periodically poled lithium niobate (PPLN) in 0.5 mm thick lithium niobate substrate. We have fabricated 50 mm long fanned as well as multigrating PPLNs having period variations from 25 μm to 32 μm. These PPLNs are required for quasi-phase-matched (QPM) optical parametric oscillator (OPO) applications. We have also configured a bench-top OPO set-up based on these PPLNs.     

Continuous wave monolithic quasi-phase-matched optical parametric oscillator in periodically poled lithium niobate

We demonstrate a monolithic and quasi-phasematched singly resonant cw optical parametric oscillator in periodically poled lithium niobate. The threshold is 1.0 W and the OPO delivers up to 0.98 W signal power tunable between 1750 and 1950 nm (2710 and 2340 nm idler, respectively). We identify cascaded parasitic oscillation effects and analyze their behavior theoretically, showing good agreement with our experiment. The analysis of parasitic effects points the way to improved device designs that should enable stable, compact, and frequency-tunable sources.     

周期性极化铌酸锂晶体光参量振荡调谐与容差特性分析

研究了周期性极化铌酸锂晶体光参量振荡的工作机理,并讨论了其波长调谐特性与极化反转光栅周期、抽运光波长与晶体温度的关系.在此基础上,通过对相位失配因子求微分的方案,分析了光参量振荡的增益与光栅周期、抽运光波长与晶体温度的关系,以及光栅周期、抽运光波长与晶体温度容差的关系 关键词： 准相位匹配 周期性极化铌酸锂 光参量振荡     

Frequency-agile kilohertz repetition-rate optical parametric oscillator based on periodically poled lithium niobate

We report kilohertz repetition-rate pulse-to-pulse wavelength tuning from 3.22 to 3.7 mum in a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO). Rapid tuning over 400 cm(-1) with random wavelength accessibility is achieved by rotation of the pump beam angle by no more than 24 mrad in the PPLN crystal by use of an acousto-optic beam deflector. Over the entire tuning range, a near-transform-limited OPO bandwidth can be obtained by means of injection seeding with a single-frequency 1.5-mum laser diode. The frequency agility, high repetition rate, and narrow bandwidth of this mid-IR PPLN OPO make it well suited as a lidar transmitter source.     

Diffusion-bonded stacks of periodically poled lithium niobate

We constructed diffusion-bonded stacks of periodically poled lithium niobate (PPLN). Such crystals combine the advantages of planar processing used to make PPLN wafers with the power-handling capability of large apertures. We demonstrated an optical parametric oscillator that uses a 3-mm-thick diffusion-bonded stack consisting of three 1-mm-thick PPLN crystals.     

High-temperature-recorded index gratings in periodically poled lithium niobate

Holographic index gratings based on a zero-electric-field photorefractive effect are recorded at high temperatures in copper-doped periodically poled lithium niobate crystals. The interplay between the domain structure and the index grating is studied: the fundamental grating with spatial frequency K is strongly suppressed. Pronounced sideband gratings with K(s)=K+sG appear, where G is the domain grating vector and s is an integer number. After development, an additional grating based on the electro-optic effect shows up. In contrast with the previously mentioned gratings, this grating allows anisotropic diffraction.     

Nonlinear directional coupler in periodically poled lithium niobate

Nonlinear wave propagation was investigated experimentally in coupled waveguides by means of the cascaded nonlinearity in quasi-phase-matched second-harmonic generation. With a specially designed wave-vector-mismatch distribution along the propagation axis, cascading was optimized for low fundamental depletion. High-contrast, ultrafast all-optical switching with switching powers of tens of watts was observed.     

Broadly tunable mid-infrared femtosecond optical parametric oscillator using all-solid-state-pumped periodically poled lithium niobate

We describe a high-repetition-rate femtosecond optical parametric oscillator (OPO) that was broadly tunable in the mid infrared. The all-solid-state-pumped OPO was based on quasi-phase matching in periodically poled lithium niobate. The idler was tunable from approximately 1.7 mum to beyond 5.4 mum, with maximum average power levels greater than 200 mW and more than 20 mW of average power at 5.4 mum. We used interferometric autocorrelation to characterize the mid-infrared idler pulses, which typically had durations of 125 fs. This OPO had a pumping threshold as low as 65 mW of average pump power, a maximum conversion efficiency of >35% into the near-infrared signal, a slope efficiency for the signal of approximately 60%, and a maximum pump depletion of more than 85%.     

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:YVO$_{4}$ 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\,$\mu$m and the temperature of 140\du, the maximum idler output power of 155\,mW at 3.86\,$\mu$m has been achieved when the 808\,nm pump power is 8.5\,W, leading to an optical-to-optical conversion efficiency of 1.82{\%}.     

Aperture scaling effects with monolithic periodically poled lithium niobate optical parametric oscillators and generators

We used elliptical beams to demonstrate aperture scaling effects in nanosecond single-grating and multigrating periodically poled lithium niobate (PPLN) monolithic optical parametric oscillators and generators. Increasing the cavity Fresnel number in single-grating crystals broadened both the beam divergence and the spectral bandwidth. Both effects are explained in terms of the phase-matching geometry. These effects are suppressed when a multigrating PPLN crystal is used because the individual gratings provide small effective subapertures. A flood-pumped multigrating optical parametric generator displayed a low output beam divergence and contained 19 pairs of signal and idler frequencies.     

Electro-optic Solc-type wavelength filter in periodically poled lithium niobate

We demonstrate an electro-optic Solc-type wavelength filter in periodically poled lithium niobate (PPLN). A Solc-type transmission spectrum is observed experimentally in PPLN with four periods from 20.2 to 20.8 microm. Modulation of the transmission power of the filter is realized by application of electric fields along the Y axis of the PPLN. It is observed that the wavelength can also be tuned by temperature.