Design of a coated thinly clad chalcogenide long-period fiber grating refractive index sensor based on dual-peak resonance near the phase matching turning point

A novel method for designing chalcogenide long-period fiber grating(LPFG) sensors based on the dual-peak resonance effect of the LPFG near the phase matching turning point(PMTP) is presented. Refractive index sensing in a high-refractive-index chalcogenide fiber is achieved with a coated thinly clad film. The dual-peak resonant characteristics near the PMTP and the refractive index sensing properties of the LPFG are analyzed first by the phase-matching condition of the LPFG. The effects of film parameters and cladding radius on the sensitivity of refractive index sensing are further discussed. The sensor is optimized by selecting the appropriate film parameters and cladding radius. Simulation results show that the ambient refractive index sensitivity of a dual-peak coated thinly clad chalcogenide LPFG at the PMTP can be 2400 nm/RIU, which is significantly higher than that of non-optimized gratings. It has great application potential in the field of chemical sensing and biosensors.

Angular spectrum characters of high gain non-critical phase match optical parametric oscillators

The angular spectrum gain characters and the power magnification characters of high gain non-walk-off colinear optical parametric oscillators have been studied using the non-colinear phase match method for the first time. The experimental results of the KTiOAs04 and the KTiOP04 crystals are discussed in detail. At the high energy single resonant condition, low reflective ratio of the output mirror for the signal and long non-linear crystal are beneficial for small divergence angles. This method can also be used for other high gain non-walk-off phase match optical parametric orocesses.

Phase matched scanning optical parametric chirped pulse amplification based on pump beam deflection

Combined with the optical beam deflection,a novel approach of phase matched broadband scanning optical parametric chirped pulse amplification(OPCPA)was proposed.For this scheme,there was no superfluous operations to the chirped signal pulse which propagated in a changeless direction straightforward,but the pump beam were deflected in space with time by passing through a KTN crystal,which was applied with varied driving voltage.The theories of phase matching of each chirped signal frequency based on pump beam deflection was analyzed detailedly.And the type-I amplification of chirped signal with 800 nm central wavelength and 20 nm bandwidth pumped by 532 nm in BBO crystal was simulated as a case in point.The simulation results showed that the spectral distribution of chirped signal pulse was almost the same as the initial form,i.e.,there was nearly no narrowing on the amplified spectrum by using of the scanning OPCPA based on pump beam deflection.In addition,the simulations demonstrated that it was worth minimizing the voltage deviation applied to KTN crystal as much as possible for the sake of better waveform,larger bandwidth and higher conversion efficiency of amplified signal pulse in the proposed scanning OPCPA.

Adaptive Phase Matching in Grover’s Algorithm

When the Grover’s algorithm is applied to search an unordered database, the successful probability usually decreases with the increase of marked items. In order to solve this problem, an adaptive phase matching is proposed. With application of the new phase matching, when the fraction of marked items is greater , the successful probability is equal to 1 with at most two Grover iterations. The validity of the new phase matching is verified by a search example.

Enhancement of Phase Matching Ability in One-Dimensional Photonic Crystal through Plasma Materials

We have theoretically studied the modal dispersion equation and effective refractive index of one-dimensional plasma photonic crystals (1-D PPCs) having different materials in one unit cell. The dispersion relations related for such structure is derived by solving Maxwell’s equation using the transfer matrix method. It is found that the presence of plasma in a unit cell enhanced the phase matching ability and provides additional degree of freedom to control phase matching condition compared to the conventional one-dimensional photonic crystals (1-D PCs).

Improved statistical fluctuation analysis for two decoy-states phase-matching quantum key distribution

Phase-matching quantum key distribution is a promising scheme for remote quantum key distribution,breaking through the traditional linear key-rate bound.In practical applications,finite data size can cause significant system performance to deteriorate when data size is below 1010.In this work,an improved statistical fluctuation analysis method is applied for the first time to two decoy-states phase-matching quantum key distribution,offering a new insight and potential solutions for improving the key generation rate and the maximum transmission distance while maintaining security.Moreover,we also compare the influence of the proposed improved statistical fluctuation analysis method on system performance with those of the Gaussian approximation and Chernoff-Hoeffding boundary methods on system performance.The simulation results show that the proposed scheme significantly improves the key generation rate and maximum transmission distance in comparison with the Chernoff-Hoeffding approach,and approach the results obtained when the Gaussian approximation is employed.At the same time,the proposed scheme retains the same security level as the Chernoff-Hoeffding method,and is even more secure than the Gaussian approximation.

Phase-matching analysis of four-wave mixing induced by modulation instability in a single-mode fiber

Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will provide guidance for fiber communication and sensing systems using wavelength division multiplexing technology.

Phase Matching Achieved by Bandgap Widening in Infrared Nonlinear Optical Materials[ABa_(3)Cl_(2)][Ga_(5)S_(10)](A=K,Rb,and Cs)

Large nonlinear optical(NLO)coefficient(d_(ij)),high laser damage threshold(LDT),and phase matching(PM)are crucial for the practical applications of IR NLO crystals.A great number of IR NLO materials with high dij have been explored,but many of them suffer from non-PM,which dramatically decreases their ultimate NLO output efficiencies.To settle this problem,we have developed a new strategy involving modulating normal dispersion via bandgap(E_(g))widening to achieve PM in this work.We synthesized successfully three new wide E_(g)(∼4.0 eV)IR NLO salt-inclusion sulfides[ABa_(3)Cl_(2)][Ga_(5)S_(10)](A=K,1;Rb,2;and Cs,3)with PM behaviors,mainly ascribed to the PM cut-off wavelength blue shift that originated from the wide Eg values,with less contribution from birefringence enhancement.All the compounds possessed large second-harmonic-generation(SHG)efficiency(∼1×AgGaS_(2))and hitherto the highest LDTs(188–200 MW/cm^(2),at 1.06μm,10 ns pulse width)for known chalcogenides with SHG efficiencies comparable to that of commercial silver gallium sulfide(AgGaS_(2))crystal.

Plasma effect on the phase matching of high harmonic generation

By optimizing the phase matching condition of high harmonic generation （HHG） from a supersonic neon gas jet, the enhanced HHG in the region of 60-70 eV has been selected. Three-dimensional numerical calculation shows that plasma plays a significant role in the phase matching process of HHG in a supersonic gas jet with short medium length. Due to plasma formation, the harmonic emission decays as the laser intensity reaches over 3.5 ~ 1014 W/cm^2. The plasma induces the broadening and blue shift of the HHG spectra, which provides a method for fine-tuning the harmonic wavelength.

Phase matching characteristics of deuterated ammonium dihydrogen phosphate crystals

Refractive indices for crystals ammonium dihydrogen phosphate （ADP）, 30% deuterated ADP （DADP）, 50% DADP, and 70% DADP are measured from 253 to 1529 nm with 5 × 10^-6 accuracy. Numerical fits to modified double-pole Sellmeier equation are made. Second-harmonic generation, third-harmonic generation phase match- ing （PM） angles, and noncritical PM （NCPM） wavelengths are calculated using the Sellmeier parameters. The deuterated crystals show smaller PM angles than pure crystal. Fourth-harmonic generation process can be real- ized by DADP in smaller deuterium content than deuterated potassium dihydrogen phosphate （DKDP）. The measured NCPM wavelengths are consistent with the calculated value. PM characteristics are compared between DADP and DKDP.

Phase-matched second-harmonic generation in hybrid polymer-LN waveguides

Here we propose a hybrid polymer-LN waveguide for achieving phase-matched second-harmonic generation(SHG).From the aspect of super-mode theory,the geometric parameters of the hybrid semi-nonlinear waveguide were optimized to utilize both symmetric(even)and antisymmetric(odd)modes of the pump and SHG waves so as to facilitate phase matching with large modal overlap.Phase matching between a fundamental even(TE_(00)-like)mode at 1320 nm and a fundamental odd(TE_(01)-like)mode at 660 nm was found with a calculated modal overlap integral of 0.299,while utilizing the largest nonlinear coefficient d_(33),and achieving an efficient calculated normalized conversion efficiency of 148%W^(-1)·cm^(-2).Considering the fabrication feasibility of such hybrid waveguide with features including etchless,large dimension,and low structural sensitivity,we believe our findings would provide a useful reference for future on-chip efficient nonlinear conversion devices.

A two-mode squeezed light based on a double-pump phase-matching geometry

We theoretically investigate the frequency-nondegenerate and frequency degenerate squeezed lights with a four-wave mixing process(4WM)driven by two pump fields crossing at a small angle.Different from a 4WM process driven by a single pump field,the refractive index of the corresponding probe field,np,can be converted to a value that is greater than 1 or less than 1 by an angle adjustment.In the new region with np<1,the bandwidth of the gain is relatively large due to the slow change in the refractive index with the two-photon detuning.In this region with an exchange of the roles of the pump and probe beams,the frequency degenerate and spatial nondegenerate twin beams can be generated,which has potential application in quantum information and quantum metrology.

Robust modal phase matching in subwavelength x-cut and z-cut lithium niobate thin-film waveguides

We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation(SHG) in subwavelength x-cut and z-cut lithium niobate(LN) thin-film waveguides and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguides explicitly.Under the scheme of optimal modal phase matching(MPM), two types of LN thin films can achieve highly efficient frequency doubling of a 1064 nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second-harmonic wave with efficient overlap between them.Such a robust MPM for high-efficiency SHG in both the subwavelength x-cut and z-cut LN thin-film waveguides is further confirmed in a broad wavelength range, which might facilitate design and application of micro–nano nonlinear optical devices based on the subwavelength LN thin film.

Rejection of Direct Blast Interference Based on Signal Phase-Matching Array Processing

In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.

Multiple-mode phase matching in a single-crystal lithium niobate waveguide for three-wave mixing

Developing natural “free space” frequency upconversion is essential for photonic integrated circuits. In a singlecrystal lithium niobate thin film planar waveguide of less than 1 μm thickness, we achieve type I and type II mode phase-matching conditions simultaneously for this thin film planar waveguide. Finally, by employing the mode phase matching of e t e → e with d_（33） at 1018 nm, we successfully achieve a green second-harmonic wave output with the conversion efficiency of 0.12%∕（W·cm^2）, which verifies one of our simulation results. The rich mode phase matching for three-wave mixing in a thin film planar waveguide may provide a potential application in on-chip frequency upconversions for integrated photonic and quantum devices.

Enhancement of Sensitivity by Initial Phase Matching in SU(1,1) Interferometers

We derive a general phase-matching condition(PMC) for enhancement of sensitivity in SU(1,1) interferometers. Under this condition, the quantum Fisher information(QFI) of two-mode SU(1,1) interferometry becomes maximal with respect to the relative phase of two modes, for the case of an arbitrary state in one input port and an even(odd) state in the other port, and the phase sensitivity is enhanced. We also find that optimal parameters can let the QFI in some areas achieve the Heisenberg limit for both pure and mixed initial states. As examples, we consider several input states: coherent and even coherent states, squeezed vacuum and even coherent states, squeezed thermal and even coherent states. Furthermore, in the realistic scenario of the photon loss channel, we investigate the effect of photon losses on QFI with numerical studies. We find the PMC remains unchanged and is not affected by the transmission coefficients for the above input states. Our results suggest that the PMC can exist in various kinds of interferometers and the phase-matching is robust to even strong photon losses.

MULTI-PEAK MATCH INTENSITY RATIO METHOD OF QUANTI-TATIVE X-RAY DIFFRACTION PHASE ANALYSIS

A new method for quantitative phase analysis is proposed by using X-ray diffraction multi-peak match intensity ratio. This method can obtain the multi-peak match intensity ratio among each phase in the mixture sample by using all diffraction peak data in the mixture sample X-ray diffraction spectrum and combining the relative intensity distribution data of each phase standard peak in JCPDS card to carry on the least square method regression analysis. It is benefit to improve the precision of quantitative phase analysis that the given single line ratio which is usually adopted is taken the place of the multi-peak match intensity ratio and is used in X-ray diffraction quantitative phase analysis of the mixture sample. By analyzing four-group mixture sample, adopting multi-peak match intensity ratio and X-ray diffraction quantitative phase analysis principle of combining the adiabatic and matrix flushing method, it is tested that the experimental results are identical with theory.

Algorithm of far-field centre estimation based on phase-only matched filter

Estimation of the far-field centre is carried out in beam auto-alignment. In this paper, the features of the far-field of a square beam are presented. Based on these features, a phase-only matched filter is designed, and the algorithm of centre estimation is developed. Using the simulated images with different kinds of noise and the 40 test images that are taken in sequence, the accuracy of this algorithm is estimated. Results show that the error is no more than one pixel for simulated noise images with a 99% probability, and the stability is restricted within one pixel for test images. Using the improved algorithm, the consumed time is reduced to 0.049 s.

Phase-Matching and Parametric Conversion for the Mid-Infrared in As₂S₃Waveguides

We illustrate two As2S3 waveguide designs for four-wave mixing, which can generate 3.03 μm mid-infrared light from a 1.55 μm near-infrared signal source and a 2.05 μm pump source. Through simulations, we verify that four-wave mixing phase-matching efficiencies up to 100% can be achieved using dispersion engineering to maintain the dispersion at 2.05 μm near to zero. The best conversion efficiency is –10 dB. When the waveguide length is 1 cm, the parametric conversion bandwidth is 1525 nm. We also evaluated the shift of 100% phase-matching efficiency wavelengths based upon fabrication tolerances.