Periodically Poled LiNbO3 Research Articles

Power instability of singly resonant optical parametric oscillators: Theory and experiment

We present a theoretical model on the effects of mechanical perturbations on the output power instability of singly-resonant optical parametric oscillators (SR-OPOs). Numerical simulations are performed based on real experimental parameters associated with a SR-OPO designed in our laboratory, which uses periodically-poled LiNbO3 (PPLN) as the nonlinear crystal, where the results of the theoretical model are compared with the measurements. The out-coupled power instability is simulated for a wide range of input pump powers the SR-OPO oscillation threshold. From the results, maximum instability is found to occur at an input pump power of ~1.5 times above the OPO threshold. It is also shown theoretically that the idler instability is susceptible to variations in the cavity length caused by vibrations, with longer cavities capable of generating more stable output power. The validity of the theoretical model is verified experimentally by using a mechanical vibrator in order to vary the SR-OPO resonator length over one cavity mode spacing. It is found that at 1.62 times threshold, the out-coupled idler suffers maximum instability. The results of experimental measurements confirm good agreement with the theoretical model. An intracavity etalon is finally used to improve the idler output power by a factor of ~2.2 at an input pump power of 1.79 times oscillation threshold.

Optical parametric oscillator pumped by relaxation oscillation pulses of a mechanically Q-switched Nd:YAG laser

We report the generation of mid-infrared pulsed radiation between 2.2 and 3 μm range using a singly-resonant optical parametric oscillator (SR-OPO) based on a 40-mm-long crystal of periodically-poled LiNbO3 (PPLN) pumped by mechanically Q-switched pulses from a Nd:YAG laser, obtained by chopping the beam inside the laser resonator over a 1–10 kHz duty cycle. An appreciable reduction in pulse width as well as the number of relaxation oscillation pulses of the Nd:YAG pump laser is observed when the frequency of the Q-switch chopper is increased up to 10 kHz. Sub-nanosecond relaxation oscillation pulses of about 170–210 ns duration are generated under the width of the idler envelope varying from 4.6 to 8.55 μs. The same behavior is observed for the signal wave. A maximum extraction efficiency of 22 % is obtained for the idler, corresponding to 785 mW of output power at 10 kHz. The tuning of the signal and idler beams were performed by temperature variation of the PPLN crystal within 100–200 °C range.

Acousto-optic tunable second-harmonic Talbot effect based on periodically poled LiNbO_3 crystals

Based on nonlinear Talbot effect, we propose an acousto-optic tunable second-harmonic (SH) array in a one-dimensional periodically poled LiNbO3 (PPLN) crystal. The SH array is the self-imaging of χ(2) in the PPLN crystal. By applying an acoustic wave, we can tune the period, the distribution, and even the dimension of the array. Such a phenomenon has potential applications in tunable high-resolution Talbot illuminators, beam shapers, and image processing.

Generating a 2.4-W cw Green Laser by Intra-Cavity Frequency Doubling of a Diode-Pumped Nd:GdVO4 Laser with a MgO:PPLN Crystal

High-power cw green laser radiation is generated by intra-cavity frequency doubling of a diode-pumped Nd:GdVO4 laser with a MgO-doped periodically-poled LiNbO3 (MgO:PPLN) crystal at room temperature. An average power of 2.4 W at 0.53 μm is obtained under the pump 15 W at 808 nm, corresponding to an overall optical-to-optical conversion efficiency of 16%. The M2 factor of the green beam is 3.90 and 1.34 for the horizontal and vertical direction, respectively. In addition, the power fluctuation is measured to be about ±5%.

Dual-channel, single-photon upconversion detector at 13 μm

We demonstrate a two-channel, upconversion detector for counting 1300-nm-wavelength photons. By using two pumps near 1550 nm, photons near 1300 nm are converted to two spectrally distinct channels near 710 nm using sum-frequency generation (SFG) in a periodically poled LiNbO3 (PPLN) waveguide. We used spectral-conversion engineering to design the phase-modulated PPLN waveguide for simultaneous quasi-phasematching of two SFG processes. The two channels exhibit 31% and 25% full-system photon detection efficiency, and very low dark count rates (650 and 550 counts per second at a peak external conversion efficiency of 70%) through filtering using a volume Bragg grating. We investigate applications of the dual-channel upconversion detector as a frequency-shifting beamsplitter, and as a time-to-frequency converter to enable higher-data-rate quantum communications.

Phase sensitive amplification with noise figure below the 3 dB quantum limit using CW pumped PPLN waveguide

The noise figure (NF) of a phase sensitive amplifier (PSA) based on a periodically poled LiNbO3 (PPLN) waveguide was evaluated in the optical and electrical domains. Phase sensitive amplification was realized using degenerate parametric amplification in the PPLN waveguide, which was pumped by the second harmonic frequency of the signal. Second harmonic pumping enables direct observation of the intrinsic amplified spontaneous emission (ASE), which determined the NF of the PSA. An NF below the 3 dB quantum limit was obtained by observing the intrinsic ASE. The low NF was also confirmed via the noise floor measurement of a cascaded PSA and erbium doped fiber amplifier in the electrical domain. The PSA was used as a preamplifier for detecting a 40 Gbit/s phase shift keying signal. The low noise characteristics were confirmed by the improved sensitivity.

Experimental studies in generation of high-purity photon-pairs using cascaded χ^(2) processes in a periodically poled LiNbO_3 ridge-waveguide device

We report detailed experimental studies in a single wavelength-band system of correlated photon-pair generation in a 1.5 μm telecommunication wavelength-band using cascaded χ(2):χ(2) processes, second-harmonic generation, and the following spontaneous parametric down conversion (c-SHG/SPDC), in a periodically poled LiNbO3 (PPLN) ridge-waveguide device. By using a PPLN module with 600%/W of the SHG efficiency, we achieved a coincidence-to-accidental ratio (CAR) of 2380 at 1.8×10−4 of the mean number of the signal photon per pulse. Detailed investigation on the origin of uncorrelated noise photons was also discussed in this paper. We revealed that the noise photons mainly originated from spontaneous Raman scattering induced in pigtail optical fibers and also that the PPLN device itself had poor contribution to the noise photons. This feature of the c-SHG/SPDC process is promising for the realization of a noise-photon-free, high-purity quantum entangled photon-pair source.

A Study of Observing Optical Waveform Applying All Optical Signal Sampling Technique Using a Chirped Periodically Poled Lithium Niobate Wavelength Converter

In order to observing a waveform of a high symbol-rate optical signal, all optical signal sampling technique using a periodically poled LiNbO3 (PPLN) wavelength converter is experimentally investigated. An optical gate is realized by a chirped PPLN having 2.2-nm QPM wavelength range where caused difference frequency generation between a high symbol rate optical signal and short pulses for sampling. An experiment of optical signal sampling is carried out by injecting an optical pulse train with 2.8-ps time width and an 160 Gb/s signal to the PPLN thus basic operation of the proposed scheme is confirmed.

Split domain antiresonance in micromachined lithium niobate

The micromachined periodically poled LiNbO3 (PPLN) demonstrates acoustic superlattice properties. Different acoustic modes in PPLN wafer have their stop-bands with low FL and upper FU cutoff frequencies. The micromachined transducers based on such structures operate at frequencies near FL and FU; they have a strong domain resonance-antiresonance when acoustic half-wavelength is close to domain length. In this work, we investigate structures with 300- and 450-micron long domains micromachined in a 0.5-mm-thick Z-cut lithium niobate wafer. The metal electrodes are deposited onto multi-domain structures having up to 90 total inversely poled domains. Experimentally, two modes of operation are investigated: (1) acousto-electric current excitation of domain vibrations when rf current passes through the whole multidomain structure and (2) plate-waves excitation and detection at two opposite ends of domain pattern when acoustic vibration travels through the multidomain pattern. In both cases, the split antiresonances are observed, and they are characterized by two main minima coinciding with the FL and FU frequencies. The difference (FL − FU) constitutes the stop-band for propagating zero antisymmetric mode, at which PPLN transducer operates. The experimental data are in agreement with theoretical calculations. Possible application of the split antiresonance effect for micromachined ultrasonic transducers is discussed. [This work is made possible in part due to the research grant “Nonlinear vibrations of piezoelectric resonators,” UM, 2011.]

A continuous-wave tunable orange-red source based on sum-frequency generation in an intra-cavity periodicallypoled LiNbO3 singly resonant optical parametric oscillator cavity

This work demonstrates a tunable continuous-wave (CW) all-solid-stateorange-red source based on sum-frequency generation (SFG), using a tunable 1.4–1.5 µm signal and a 1064 nm pump of an intra-cavity periodically poledLiNbO3 optical parametricoscillator in a BBO (β-BaB2O4) crystal. Elaborate intra-cavity design ensured efficient CW singly resonant opticalparametric oscillator (SRO) operation. Intra-cavity SFG made full use of the highcirculating pump and signal power of the SRO under an external laser diode (LD) pumppower that was ten times higher than the SRO threshold. The output wavelength tuningrange was 605–623 nm. The maximum output power was 370 mW at 622.8 nmwith 17.1 W LD pump power, corresponding to an overall conversion efficiency of2.2%.

131 W, high-beam-quality, narrow-linewidth continuous-wave fiber-based source at 970 nm

We report an efficient fiber-laser-based source of high-power, continuous-wave (cw), linearly-polarized radiation at 970 nm in a simple, compact, and practical design. Using direct single-pass second-harmonic-generation (SP-SHG) of a cw thulium fiber laser at 1940 nm in a 40-mm-long periodically-poled LiNbO3 (PPLN) crystal, we have generated 13.1 W of output power at 970 nm for a fundamental power of 40 W at a conversion efficiency as high as 32.7%. The generated second-harmonic output exhibits a passive power stability better than 1.4% (1σ value) over 1 hour, has a linewidth better than 0.3 nm, and a TEM(00) spatial beam profile with M(2)<1.6. Relevant theoretical calculations for the characterization of SP-SHG in the crystal have also been performed.

Surface second-harmonic generation based on periodically poled LiNbO3 nonlinear optical crystal

We have generated a second-harmonic generation (SHG) of a Q-switched microchip Nd:YAG laser on the surface of a periodically poled LiNbO3 (PPLN) nonlinear crystal near the grazing incidence angle. Three individual SHG waves as transmitted homogeneous, inhomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd:YAG laser as pump source on the PPLN surface. The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory. Comparison between calculated and measured data shows that they are in good agreement with each other.

Power Characteristics of cw Second-harmonic Generation in Periodically Poled LiNbO3

We verified through a noncritical phase-matched second-harmonic generation experiment that the periodically-poled LiNbO₃ (PPLN) had a large effective nonlinear optical coefficient, demonstrating that the QPM grating was uniform throughout the entire length of PPLN. The quasi-phase matching temperature was 193.4℃. The maximum SHG output power at the fundamental power of 2.0 W was found to be 18.0 mW; generated second-harmonic beam was found to have no photorefractive effect.

Review of recent efforts on efficient generation of monochromatic THz pulses based on difference-frequency generation

We review our recent efforts on power scaling of THz pulses generated from several nonlinear-optical crystals. By using a high-resistivity GaP crystal, we have significally increased the output peak power to as high as 722 W. By stacking three GaP wafers, we have further increased the highest output peak power to 2.36 kW. On the other hand, by using CO2 laser pulses, we have obtained the average output power of 260 μW. We have also used these laser pulses to scale up the output power for the THz pulses to 29.8 μW by stacking GaAs wafers. Indeed, by stacking up to ten wafers, we have increased the output power by a factor of 160. Finally, by using ultrafast laser pulses, we have achieved record-high output powers for the THz pulses generated from multi-period periodically-poled LiNbO3 crystals based on a backward configuration. The highest output power obtained by us so far is 10.7 μW.

Efficient Up-Conversion Detection of 1550 nm Photons Using Bulk Periodically-Poled LiNbO3

We demonstrate efficient up-conversion detection of photons at 1550 nm utilizing bulk periodically-poled LiNbO3 (PPLN) and nanosecond-pulsed pumping. An internal conversion efficiency of 96% and an overall photon detection efficiency of 19% including the efficiency of a visible photon detector were achieved with a low dark count rate.

A pump-resonant signal-resonant optical parametric oscillator for spectroscopic breath analysis

We report on a widely tunable continuous-wave single-frequency pump-resonant signal-resonant optical parametric oscillator (PRSRO) delivering 20 mW to 50 mW of idler power spanning an octave bandwidth in the mid-infrared (1.7 µm and 3.5 µm). The PRSRO is pumped by a Ti:Al2O3 ring laser delivering 760 mW around λ p =795 nm, and thanks to the pump enhancement a threshold as low as 110 mW is achieved with a multi-grating temperature-tuned MgO-doped periodically-poled LiNbO3. This PRSRO will be used for multi-species trace gas sensing based on cavity ring-down spectroscopy.

RECENT PROGRESS ON PARAMETRIC GENERATION OF MONOCHROMATIC THz PULSES

We review our recent progress on power scaling of THz pulses generated from several nonlinear-optical crystals. By using a high-resistivity GaP crystal, we have significally increased the output peak power to as high as 722 W. By stacking three GaP wafers, we have further increased the highest output peak power to 2.36 kW. On the other hand, by using CO2 laser pulses, we have obtained the average output power of 260 μW. We have also used these laser pulses to scale up the output power for the THz pulses to 29.8 μW by stacking GaAs wafers. Indeed, by stacking up to ten wafers, we have increased the output power by a factor of 160. Finally, by using ultrafast laser pulses, we have achieved record-high output powers for the THz pulses generated from multi-period periodically-poled LiNbO3 crystals based on a backward configuration. The highest output power measured by us so far is 10.7 μW.

Spatial Wave Dynamics in 2-D Periodically Poled LiNbO$_{3}$ Waveguides

Recent results on parametric spatial solitary waves arising from multiple resonances in purely nonlinear 2-D lattices are presented. Theory and experiments highlight new possibilities for light self-confinement and steering via engineered planar nonlinear structures in periodically poled materials.

Mid-infrared ethene detection using difference frequency generation in a quasi-phase-matched LiNbO_3 waveguide

A periodically poled LiNbO3 (PPLN) crystal waveguide has been used to produce up to 200 microW of mid-infrared light around 3081 cm(-1) with a wide tunability range of approximately 35 cm(-1). Two commercial near-infrared diode lasers at 1.064 microm (pump) and 1.583 microm (signal) are mixed in a nonlinear optical crystal to achieve difference frequency generation. The 48 mm long directly-bonded quasi-phase-matched (QPM) PPLN waveguide shows a conversion efficiency of 12.3% W(-1). Applications in trace gas detection have been demonstrated for ethene, using multipass absorption coupled with wavelength modulation spectroscopy, and cavity enhanced absorption spectroscopy with a lock-in detection scheme: bandwidth reduced sensitivities of alpha(min)=8 x 10(-9) and 1.6 x 10(-8) cm(-1) Hz(-1/2)(2sigma), respectively, have been achieved.

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 μm 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%.