Single Nonlinear Crystal Research Articles

Error correction based artificial neural network in multi-modes CV-QKD with simultaneous type-I and type-II parametric-down conversion entangled photon source

We model simultaneous type-I and type-II phase matching in a single non-linear crystal (NLC), based on a double periodically poled lithium niobate crystal. We also discuss entanglement based continuous variable quantum key distribution (CV-QKD), and the security of such scheme is analyzed considering an eavesdropper being capable of individual attacks. We further demonstrate efficiency of the artificial neural network (ANN) algorithm during post-processing or errors correction in such CV-QKD protocols. Results show that employing simultaneous type-I and type-II SPDC process in single NLC is a potential source to generate high dimensional (or hyper-entangled) states, strongly required for quantum information processing tasks, an example of CV-QKD. Security analysis of such a CV-QKD protocol shows a strong advantage of employing the above entangled photon state source, given that it provides a higher secure key rate and thus a secure communication within a larger distance. In addition, the suggested error correction algorithm is less time consuming and highly efficient, since full synchronization is achieved just after a few number of updates of trusted parties’ tree-parity-machines. Our results sufficiently demonstrate that the suggested CV-QKD is able to distribute secure keys in nearby inter-city areas, and therefore allows lower-cost secure communication networks.

Ultra-phase-stable infrared light source at the watt level.

Ultrashort pulses at infrared wavelengths are advantageous when studying light-matter interaction. For the spectral region around 2 µm, multi-stage parametric amplification is the most common method to reach higher pulse energies. Yet it has been a key challenge for such systems to deliver waveform-stable pulses without active stabilization and synchronization systems. Here, we present a different approach for the generation of infrared pulses centered at 1.8 µm with watt-level average power utilizing only a single nonlinear crystal. Our laser system relies on a well-established Yb:YAG thin-disk technology at 1.03 µm wavelength combined with a hybrid two-stage broadening scheme. We show the high-power downconversion process via intra-pulse difference frequency generation, which leads to excellent passive stability of the carrier envelope phase below 20 mrad-comparable to modern oscillators. It also provides simple control over the central wavelength within a broad spectral range. The developed infrared source is employed to generate a multi-octave continuum from 500 nm to 2.5 µm opening the path toward sub-cycle pulse synthesis with extreme waveform stability.

Controllable transitions among phase-matching conditions in a single nonlinear crystal

Controllable transitions among phase-matching conditions in a single nonlinear crystal

Nonlinear manipulation of orbital angular momentum spectra with second- and third-harmonic generation in a quasi-periodically poled crystal

Optical orbital angular momentum (OAM), as an important degree of freedom of light, has been attracting extensive attention due to its intrinsic feature of the natural discrete infinite dimension. Manipulation of OAM spectra is crucial for many impressive applications from classical to quantum realms, in particular, nonlinear manipulation of OAM spectra. Here, we realized the nonlinear manipulation of OAM spectra by using the simultaneous second- and third-harmonic generation in a single nonlinear crystal of quasi-periodically poled potassium titanyl phosphate, for fundamental waves with a variety of OAM spectra, especially for customized OAM spectra of the second and third harmonics. The experimental results confirmed the theoretical predictions. Our approach not only provides a way to manipulate OAM spectra at shorter wavelengths that are hard to be directly generated but also may find applications toward multiplexing in classical optics and high-dimensional information processing in quantum optics.

Enhanced cascaded up-conversion from periodically poled lithium niobate in a double-pass configuration

Quasi-phase matching (QPM) offers the potential to satisfy the phase-matching conditions for cascaded up-conversion from a single nonlinear crystal. We experimentally demonstrate a high repetition rate visible laser pulse from periodically poled lithium niobate (PPLN) in a double-passed pump configuration. The highest output power of 0.28 W of up-converted wavelengths in the visible range is obtained at the incident pump power of 3.55 W. The temporal and spectral properties of the cascaded up-converted wavelengths for the double-passed scheme are characterized as well. The tunability of up-converted wavelengths broadens feasible applications of pulsed laser in the visible region.

Generation of a localized hollow laser beam using crossed nonlinear optical crystals

A nonlinear optical approach to generate a localized hollow laser beam and its array using crossed nonlinear ZnSe crystals is proposed. We calculate the intensity distributions of the hollow beam and its propagating properties in free space, and study the dependences of the dark spot size of the hollow beam on the incident beam waist radius and the crystal length. Our studies show that the longitudinal size of the hollow beam can be reduced by ∼660 times than that generated by a single nonlinear crystal. Such laser beam with a dark hollow region and a large intensity gradient can be used to trap cold neutral atoms, molecules and microscopic particles.

Trapping and guiding of large-size particles in hollow beams produced by nonlinear crystals

Since 1970, the trapping of the small objects in space by optical radiation pressure, such as nano particles and other atomic living cells, has been successfully developed and used in the applied physics, life sciences and other fields. As the optical radiation pressure is very weak, the use of radiation pressure on the particle will be strictly limited by the particle size. Also, the manipulated particles can move particle with only hundreds of microns. Therefore, it is not suitable for trapping and long-distance transporting particles with large size (micron). In recent years, with the development of the manipulation technology for large particles, a new control force-photophotetic force has gradually entered into people's vision field. Compared with the optical radiation pressure, the photophoretic force is much large under the same light intensity. Therefore, the photophoretic force makes it possible to manipulate and trap the large particles. With the development of laser beam-shaping technology, the species of laser beams become more and more abundant, which makes it more attractive to study particle manipulation based on the photophoretic force. For example, a hollow beam is used to capture and guide carbon nanoclusters in the air. A tapered optical fiber is used to trap, migrate and separate SiO2 particles. A Bessel Gaussian beam is used to trap and manipulate magnetic particles. An airy beam is used to trap glass carbon particles of absorption type. In this paper, a trapping and guiding scheme for large-size particles by using the photophoretic force of the hollow beams generated by nonlinear ZnSe crystals is proposed and analyzed theoretically. Our calculated results can be concluded as follows. 1) For the cases of two-dimensional particle trapping and one-dimentional particle guiding using a hollow beam generated by a single nonlinear ZnSe crystal, the magnitude of the longitudianl optical force is proportional to the ratio between particle size and hollow beam size to the fourth power and is proportional to the power of the hollow beam, and the direction is the same as that of the beam propagation. The closer to the hollow beam size the particle size, the greater the transverse optical force is. The results show that the photophoretic force can achieve the two-dimensional trapping of large-size particles, and a long distance (in a meter region) guiding. 2) For the case of three-dimensional particle trapping using a localized hollow beam generated by two nonlinear ZnSe crystals, the dependence of transverse photophoretic forceand that of longitudinal photophoretic force on the system parameters are similar to the scenario for the particles trapping in the hollow beam produced by a single nonlinear crystal. The difference is that under this condition, the direction of the longitudinal photophoretic force points to the center of the beam. So this scheme can achieve the effective three-dimensional trapping of large-size particles. Above all, the hollow beams generated by nonlinear ZnSe crystals can be used as an effective noncontact controlling tool for large-size particels, and might have potential applications in modern optics and biomedicine.

Intensity Noise Transfer Through a Diode-Pumped Titanium Sapphire Laser System

In this paper, we investigate the noise performance and transfer in a titanium sapphire (Ti:S) laser system. This system consists of a distributed Bragg-reflector tapered diode laser, which is frequency doubled in two cascaded nonlinear crystals and used to pump the Ti:S laser oscillator. This investigation includes electrical noise characterizations of the utilized power supplies, the optical noise of the fundamental light, the second harmonic light, and finally the optical noise of the femtosecond pulses emitted by the Ti:S laser. Noise features originating from the electric power supply are evident throughout the whole transfer chain. It is demonstrated that improving the electrical noise provides an easy method for reducing the relative intensity noise (RIN) in all stages. The frequency doubled light is shown to have a higher RIN than the fundamental light. In particular, the cascaded system is seen to exhibit higher RIN than a setup with only a single nonlinear crystal. The Ti:S is shown to have a cutoff frequency around 500 kHz, which means that noise structures of the pump laser above this frequency are strongly suppressed. Finally, the majority of the Ti:S noise seems to originate from the laser itself, which partly can be explained by the effect of relaxation oscillation frequency.

Synthesis, crystal structure, optical, thermal and dielectric studies of a potential novel organic material: l-histidinium fumarate fumaric acid monohydrate single crystal

l-histidinium fumarate fumaric acid monohydrate (LHFFA), a new amino acid based organic single nonlinear optical crystal has been successfully grown from aqueous solution by slow solvent evaporation method. The crystal structure was determined by single crystal X-ray diffraction analysis and it belongs to monoclinic system with the space group C2. The thermal stability of the crystal has been investigated by means of thermogravimetric analysis and different thermal analysis. The result of UV–Vis study showed that the crystal was about 50% transparent in the visible region. The optical band gap of the grown crystal was also calculated. The dielectric response of the crystal with varying frequencies in the temperature region from 40°C to 80°Chas studied. The crystal is subjected to Kurtz-Perry powder SHG test to prove its optical nonlinearity.

Multifunctional optical correlator for picosecond ultraviolet laser pulse measurement.

A compact multifunctional optical correlator system for pulse width measurement of ultrashort ultraviolet (UV) pulses has been designed and experimentally demonstrated. Both autocorrelation and cross-correlation functions are measured using a single nonlinear crystal, and the switching between two measurements requires no adjustment of phase matching and detector. The system can measure UV pulse widths from sub-picoseconds to 100ps, and it involves no auxiliary pulse in the measurement. The measurement results on a burst-mode picosecond UV laser show a high-quality performance on speed, accuracy, resolution, and dynamic range. The proposed correlator can be applied to measure any ultrashort UV pulses produced through sum-frequency generation or second-harmonic generation.

High efficiency, high energy, CEP-stabilized infrared optical parametric amplifier

A high efficiency, tunable, carrier-envelope-phase (CEP) stabilized near-infrared optical parametric amplifier (OPA) is demonstrated with just a single BBO crystal. A white-light continuum produced by a CEP-stabilized laser is seeded into the two stages of the type II OPA system. We achieved a pump-to-signal conversion efficiency of 34% with a single nonlinear crystal. To our knowledge this is the highest conversion efficiency reported in broadband optical parametric amplification, using the two stages. This work demonstrates a compact way to for tunable femtosecond pulses with CEP stabilization.

Compensation of anisotropy effects in the generation of two-photon light.

We analyse a method to compensate for anisotropy effects in the spatial distribution of parametric down-conversion (PDC) radiation in bulk crystals. In this method, a single nonlinear crystal is replaced by two consecutive crystals with opposite transverse walk-off directions. We implement a simple numerical model to calculate the spatial distribution of intensity and correlations, as well as the Schmidt mode structure, with an account for the anisotropy. Experimental results are presented which prove the validity of both the model and the method.

Review Article: Quasi-phase-matching engineering of entangled photons

Quasi-phase-matching (QPM) technique has been successfully applied in nonlinear optics, such as optical frequency conversion. Recently, remarkable advances have been made in the QPM generation and manipulation of photon entanglement. In this paper, we review the current progresses in the QPM engineering of entangled photons, which are finished mainly by our group. By the design of concurrent QPM processes insides a single nonlinear optical crystal, the spectrum of entangled photons can be extended or shaped on demand, also the spatial entanglement can be transformed by transverse inhomogeneity of domain modulation, resulting in new applications in path-entanglement, quantum Talbot effects, quantum imaging etc. Combined with waveguide structures and the electro-optic effect, the entangled photons can be generated, then guided and phase-controlled within a single QPM crystal chip. QPM devices can act as a key ingredient in integrated quantum information processing.

Quantum holographic teleportation of entangled two-color optical images

We introduce and theoretically investigate a scheme for teleportation of two-frequency entangled optical images in which the quantum channel is formed by four-frequency multimode states, generated in a single nonlinear photonic crystal by coupled parametric interactions. We study in detail the performance of the scheme. Namely, we evaluate its fidelity and the spatial-frequency spectra of the quadrature components characterizing the deterioration of the entanglement in the initial images due to the teleportation process. We analyze the influence of the spatial bandwidth of entanglement on the fidelity of teleportation. We investigate the performance of the scheme both in the near and the far diffraction field. Our analysis suggests that bandwidth matching of the quantum channel field with that of the images is generally necessary for high-quality teleportation. We show that entangled images are more fragile and more difficult to teleport than their coherent counterparts.

Concurrent nonlinearities in a single nonlinear crystal with multiple phase matching

We develop a rigorous theory to describe coupled multiple nonlinear processes in a single nonlinear multilayer structure using iteration technique and transfer-matrix method. Pump depletion is taken into account. The validity of the theory is confirmed by analyzing coupled third-harmonic generation (CTHG). The CTHG process consists of two processes: second-harmonic generation and sum-frequency generation. These two processes are coupled together when their phase-matching conditions are satisfied simultaneously. The conversion efficiencies of second-harmonic and third-harmonic under various phase-matching conditions are studied numerically. The results demonstrate that our theory can efficiently and accurately deal with the coupled nonlinearity problem. The model can deal with periodic or aperiodic nonlinear structures. Our approach may be helpful in designing nonlinear photonic crystals and quasi-phase-matching structures.

Cascaded carbon monoxide laser frequency conversion into the 43–49 μm range in a single ZnGeP_2 crystal

Collinear cascaded mid-IR frequency conversion in a single nonlinear optical crystal was accomplished. Concurrent collinear generation of the sum frequency of multiline fundamental band carbon monoxide laser radiation as a first frequency conversion cascade resulted in collinear difference frequency generation within the 4.3 to 4.9 μm spectral range when mixing this sum frequency radiation with the fundamental one as the second cascade in the same ZnGeP(2) nonlinear optical crystal.

Novel mode-locked carbon monoxide laser system achieves high accuracy

Extending the emission range of gas lasers is an attractive proposition, for example, in laser spectroscopy, atmosphere sensing, laser media diagnostics, initiating chemical reactions, and separating elemental isotopes. In this context, carbon monoxide (CO) lasers offer several advantages over other sources of IR radiation, including control of output energy and pulse duration over a wide dynamic range. Moreover, they ensure high average power in repetitively pulsed modes. An electric discharge CO laser can operate on every spectral line from among a few hundred in both fundamental ( 4.7–8.2 m)1 and firstovertone ( 2.5–4.2 m) spectral bands.2–4 In addition, parametric frequency conversion (i.e., frequency doubling, or sum or difference frequency generation) of CO laser radiation using a single nonlinear crystal can cover both midand far-IR spectral ranges. However, to achieve high-frequency conversion efficiency, CO laser radiation must have high peak power. The first mode-locked (i.e., pulsing) laser was reported decades ago. But it had a peak power of only a few kilowatts because it operated at room temperature. No efforts have been made since then to obtain substantially higher power. We have developed a cryogenically cooled, electron-beamsustained-discharge (EBSD) mode-locked CO laser that produces a train of 5–15ns full width at half-maximum spikes with a pulse repetition rate of 10MHz in the mid-IR range of 5 m.5 We obtained maximum output power of up to 120kW for a multiline mode and 70kW for a single-line mode of operation. As suggested elsewhere,6 such radiation could be used to pump an optical parametric amplifier for stochastic cooling in a relativistic heavy-ion collider (see Figure 1). Figure 1. Imaginary layout of the optical stochastic cooling system for the relativistic heavy-ion collider (Brookhaven National Laboratory, US). The storage ring measures 4km. CO: Carbon monoxide. : Wavelength. OPA: Oscillator-power amplifier. : Wavelength.

High-efficiency single-crystal third-harmonic generation in BiB_3O_6

Third-harmonic generation of high-intensity, sub-100-fs idler pulses from a Ti:sapphire-laser-pumped optical parametric amplifier is demonstrated by using a single nonlinear crystal of BiB₃O₆ (BIBO). Maximum internal energy conversion as high as 11% from the fundamental to the third harmonic is achieved by phase- and group-velocity matching for the direct cubic nonlinear process together with the velocity-mismatched cascading quadratic processes.

Wavelength tunability of tandem optical parametric oscillator based on single PPMgOLN crystal

The theoretical analysis and experimental results of the wavelength tunability of a tandem optical parametric oscillator (TOPO) based on a single nonlinear crystal are presented. TOPO is a configuration wherein the signal laser is used as a pump laser to generate secondary optical parametric oscillator (OPO). The cascaded parametric interactions are achieved synchronously in a single-grating-period MgO doped periodically poled lithium niobate (PPMgOLN). Tunable multiple-wavelength mid-infrared (mid-IR) lasers are obtained by changing the temperature of the crystal. When the PPMgOLN crystal with a grating period of 31.2 µm is operated at 148 oC, the dual OPOs generate an identical mid-IR laser of 2.83 µm. The secondary OPO transforms into an optical parametric amplifier, in which different frequency mixing from the signal laser results in the amplification of the idler laser in the first OPO. TOPO is a useful configuration for multiple laser output, broad tuning range, and high-efficiency mid-IR lasers.

Correlations in photon-numbers and integrated intensities in parametric processes involving three optical fields

Two strongly-pumped parametric interactions are simultaneously realized in a single nonlinear crystal in order to generate three strongly correlated optical fields. By combining together the outputs of two of the three detectors measuring intensities of the generated fields, we obtain the joint photocount statistics between the single field and the sum of the other two. Moreover, we develop a microscopic quantum theory to determine the joint photon-number distribution and the joint quasi-distributions of integrated intensities and prove nonclassical nature of the three-mode state. Finally, by performing a conditional measurement on the single field, we obtain a state endowed with a sub-Poissonian statistics, as testified by the analysis of the conditional Fano factor. The role of quantum detection efficiencies in this conditional state-preparation method is discussed in detail.