Sum-frequency Process Research Articles

Quadripartite quantum steering generated by single-pass cascaded nonlinear processes

Quantum steering has become an important resource for quantum information due to its unique asymmetry. In this paper, quadripartite quantum steering generated by single-pass nondegenerate optical parametric amplification cascaded with a sum-frequency process is investigated. Firstly, an idler beam is produced by a different-frequency process between pump and signal. Secondly, a sum-frequency beam is generated by a cascaded sum-frequency process between idler beam and pump in the same optical superlattice. Quadripartite quantum steering among pump, signal, idler and sum-frequency beams is demonstrated based on the criterion for multipartite quantum steering. The influences of nonlinear coupling coefficients κ, dimensionless propagation length ξ, and the initial values of pump and signal on the variation characteristic of the quadripartite steering are also investigated. The results indicate that slightly larger nonlinear coupling coefficients of cascaded nonlinear processes and weaker signals can achieve better quadripartite quantum steering. This simple quadripartite quantum steering preparation scheme does not require a resonant cavity and is easier to implement experimentally, with potential applications in quantum communication and computing.

Genuine five-partite quantum steering generated by an injection signal optical parametric oscillation cascaded with two sum-frequency processes

Multipartite quantum steering is an important quantum resource and the basis of quantum computing and quantum secure communication. In this paper, a scheme is proposed to produce genuine five-partite quantum steering by an injected signal optical parametric oscillation cascaded with two sum-frequency processes. First, an idler beam is generated by a difference-frequency generation process between the pump and the injected signal in an optical superlattice. By using the quasi-phase-matching technique, two sum-frequency beams are generated by the sum-frequency processes of pump and idler beams as well as pump and injected signals in the same optical superlattice. It is found that the genuine five-partite steering exists by applying a criterion for genuine multipartite quantum steering. Finally, the variation properties of the quantum steering with parameters are discussed. The genuine five-partite quantum steering generated by the present scheme has potential applications in quantum computing and quantum secure communication.

Efficient Cascaded Third‐Harmonic Generation in Sampled‐Grating Periodically‐Poled Lithium Niobate Waveguides

AbstractPeriodically poled thin‐film lithium niobate (PPTFLN) waveguides enable efficient quadratic nonlinear processes due to the strong light confinement and the utilization of the largest nonlinear coefficient d33 of lithium niobate. Here, an efficient third harmonic (TH) generation is reported with a normalized conversion efficiency of 6481% W−2 cm−4 in a sampled‐grating PPTFLN waveguide under the pump of a continuous laser, which is improved by 4 orders of magnitude compared with reported results. Such an efficient TH generation is realized by cascaded second‐harmonic (SH) generation and sum‐frequency (SF) generation supported by a sampled‐grating domain structure with two Fourier coefficients of 0.44 and 0.37, respectively. Phase matching conditions for the SH and cascaded SF processes are simultaneously achieved by finely tuning the geometric dispersion, domain structure, and operating temperature of the PPTFLN waveguides.

High-average-power single-longitudinal-mode pulse laser based on a pulse saturation seed-injection locking OPO.

A high-average-power and narrow-linewidth nanosecond (ns) pulse 824 nm laser is a crucial source for the generation of deep-ultraviolet (DUV) 248 nm laser by means of the sum-frequency process with the 354.5 nm laser. To this purpose, in this Letter, we present a seed-injection-locked high-average-power ns pulse single-longitudinal-mode (SLM) 824 nm laser. By developing a novel, to the best of our knowledge, pulse-saturated seed-injection locking method, disturbance of the pulse laser on the locking of the injected seed laser is successfully eliminated. As a result, the output power of 824 nm laser is up to 21.2 W at the incident pump power of 48.1 W, and the pulse width is 15 ns. Especially, the signal-to-noise ratio of the detected modulated sideband signal exceeds 28 dB, which ensures that the achieved linewidth of the 824 nm laser is as narrow as 38.8 MHz. These results demonstrate the potential of the proposed pulse saturation seed-injection locking OPO cavity for high-power and narrow-linewidth laser applications.

Theoretical exploration of sensitive terahertz detection by cascaded difference-frequency generation

Nonlinear optical frequency conversion technologies, including the optical parametric process and difference-frequency and sum-frequency processes, have demonstrated good performance for terahertz (THz) wave detection. The quantum efficiencies of the above technologies cannot break through the Manley–Rowe limit. In this work, we present a novel scheme for THz wave detection based on cascaded difference-frequency generation in combination with optical parametric oscillations. By superimposing a weak THz wave and an intense pump wave in an aperiodic periodically poled lithium niobate crystal, a series of Stokes waves and a series of anti-Stokes waves are generated. The Stokes waves oscillating in a resonant cavity are transferred to high-order Stokes waves continuously and repeatedly. The high-sensitivity THz wave detector is realized by measuring the intensities of the Stokes waves or the enlarged THz wave. This research enables a comprehensive understanding of the physics of the cascading second-order nonlinear detection and provides a worthy reference for subsequent experimental design.

Coupling effects of the sum-frequency process and difference-frequency process on upconversion terahertz-wave detection via a DAST crystal.

Frequency upconversion technology with good performance including high sensitivity, fast response, and room-temperature operation is a promising method for terahertz-wave detection. The sum-frequency conversion and difference-frequency conversion jointly affect the detection ability for upconversion detection using organic crystals as nonlinear media. The concurrence of both processes has been ignored in past studies, which results in discrepancies between theoretical simulations and experimental results. In this paper, four-wave interaction equations involving two nonlinear conversion processes are proposed, and the effect of the sum-frequency process is analyzed in upconversion terahertz-wave detection via a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. The ratio of the sum-frequency signal to the difference-frequency signal varies for different terahertz frequencies and crystal thicknesses. Experiments suggest that theoretical simulations are good at predicting physical processes. Under certain conditions, the detection efficiency can be improved by simultaneously utilizing the two signals. The total signal photon number is not sensitive to the crystal thickness. Furthermore, the theoretical exploration of terahertz single-photon detection provides a noteworthy reference for future experiments.

Sum-frequency generation of a laser and its background in an on-chip lithium-niobate microdisk

Lithium-niobate microcavities have not only the ability to resonantly enhance light–matter interaction but also excellent nonlinear optical properties, thereby providing an important platform for nonlinear optical investigations. In this paper, we report the observation of multi-peak spectra in the near infrared range in lithium-niobate microcavities on a chip under the pump of a 1550 nm continuous laser. Such a multi-peak spectrum was attributed to the sum-frequency of the pump laser and its background. The conversion efficiencies of the sum-frequency processes are of the order of 61.5%W-1. The influences of the phenomenon on nonlinear processes were further discussed.

Bright-soliton frequency combs and dressed states in χ(2) microresonators

We present a theory of the frequency comb generation in the high-Q ring microresonators with quadratic nonlinearity and normal dispersion and demonstrate that the naturally large difference of the repetition rates at the fundamental and 2nd harmonic frequencies supports a family of the bright soliton frequency combs providing the parametric gain is moderated by tuning the index-matching parameter to exceed the repetition rate difference by a significant factor. This factor equals the sideband number associated with the high-order phase-matched sum-frequency process. The theoretical framework, i.e., the dressed-resonator method, to study the frequency conversion and comb generation is formulated by including the sum-frequency nonlinearity into the definition of the resonator spectrum. The Rabi splitting of the dressed frequencies leads to the four distinct parametric down-conversion conditions (signal-idler-pump photon energy conservation laws). The parametric instability tongues associated with the generation of the sparse, i.e., Turing-pattern-like, frequency combs with varying repetition rates are analysed in details. The sum-frequency matched sideband exhibits the optical Pockels nonlinearity and strongly modified dispersion, which limit the soliton bandwidth and also play a distinct role in the Turing comb generation. Our methodology and data highlight the analogy between the driven multimode resonators and the photon-atom interaction.

Noncollinear matched broadband third-harmonic generation based on angular dispersion

Broadband laser can effectively reduce the nonlinear effect in the process of laser plasma interaction. This paper proposes a noncollinear matching broadband third-harmonic generation based on angular dispersion, which uses the noncollinear sum frequency of the broadband fundamental wave and the narrowband second harmonic to generate broadband third harmonic, and the sum frequency process is realized by a specially designed gradient grating. The fundamental laser beams of different frequencies are incident at a specific angle, which compensates for the phase mismatch caused by the wavelength difference, so that the whole waveband meets the match condition of phase. Theoretical simulation shows that using KDP crystal type II phase matching, high efficiency broadband third-harmonic generation can be achieved by combining the broad-band fundamental wave (center wavelength 1058 nm, bandwidth 10 nm) and the second harmonic (526.5 nm).

Thermometry in dynamic and high-temperature combustion filed based on hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering

Temperature, as an important parameter in combustion diagnostic process, will directly affect the combustion efficiency and the generation of combustion products. The accurate measuring of combustion temperature and then controlling of combustion state can not only contribute to avoiding the generation of harmful waste gas, such as carbon monoxide (CO) and oxynitride (NO<sub><i>x</i></sub>), but also improve the combustion efficiency, thereby saving the energy. However, in practical applications, dynamic and high-temperature combustion field has strict requirements for measurement accuracy and response speed of the thermometry technology. As an advanced spectral thermometry technology, coherent anti-Stokes Raman scattering (CARS) has a much higher spatial resolution, and can achieve accurate temperature measurement in high-temperature environment, so CARS has the potential applications in complex combustion field. For the temperature measurement requirements in the complex dynamic and high-temperature combustion field, we demonstrate a hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering thermometry method through using the second harmonic bandwidth compression method, and achieve accurate measurements and dynamic response to temperature in dynamic and high-temperature combustion field. By using the narrow-band picosecond pulse obtained from the sum frequency process of femtosecond pulse in the BBO crystal as a probe pulse, this thermometry method can achieve single-shot, 1-kHz temperature measurement in high-temperature flame. We utilize the standard burner to simulate dynamic combustion field in a range of 1700–2200 K by changing the equivalence ratio quickly, and carry out continuous temperature measurement in 70 s by our thermometry method in this simulated dynamic and high-temperature flame. The least square method is used to fit the theoretical spectrum library to the actual single spectrum, and the fitting temperature corresponding to the actual single spectrum is obtained from the curve of fitting error. The continuous temperature measurements in 70 s exhibit superior performance in dynamic and high-temperature flame with a temperature inaccuracy less than 1.2% and a precision less than 1.8% at four different temperatures, and can track the temperature variation process within 0.2 s dynamically. These results verify the accuracy, stability and response speed in dynamic and high-temperature environment, and provide a new system scheme for thermometry in practical harsh combustion field.

Genuine quadripartite quantum steering generated by an optical parametric oscillation cascaded with a sum-frequency process

Quantum steering is the essential resource for quantum information processing. In this letter, a scheme is proposed to generate genuine quadripartite Einstein-Podolsky-Rosen (EPR) steering by an optical parametric oscillation cascaded with a sum-frequency process. Idler beam is generated by a difference frequency generation process between pump and injected signal in an optical superlattice. Then, a sum-frequency beam is produced by the cascaded sum-frequency process between pump and idler beams in the same optical superlattice by the quasi-phase-matching technique. The genuine quadripartite EPR steering among pump, signal, idler, and sum-frequency beams is confirmed in this scheme by applying a criteria for genuine multipartite EPR steering. The variation properties of the EPR steering with pump and nonlinear coupling coefficients are also discussed.

High-efficiency second-harmonic generation of low-temporal-coherent light pulse.

The nonlinear frequency conversion of low-temporal-coherent light holds a variety of applications and has attracted considerable interest. However, its physical mechanism remains relatively unexplored, and the conversion efficiency and bandwidth are extremely insufficient. Here, considering the instantaneous broadband characteristics, we establish a model of second-harmonic generation (SHG) of a low-temporal-coherent pulse and reveal its differences from the coherent conditions. It is found that the second-harmonic spectrum distribution is proportional to the self-convolution of that of a fundamental wave. Because of this, we propose a method for realizing low-temporal-coherent SHG with high efficiency and broad bandwidth, and experimentally demonstrate a conversion efficiency up to 70% with a bandwidth of 3.1THz (2.9nm centered at 528nm). To the best of our knowledge, this is the highest efficiency and broadest bandwidth of low-temporal-coherent SHG to date. Our research opens the door for the study of low-coherent nonlinear optical processes.

Five-partite continuous-variable entanglement generated by cascaded nonlinear processes in only one optical superlattice

We theoretically investigate the generation of five-partite continuous-variable (CV) entanglement through injection-seeded non-degenerate optical parametric amplification cascaded two sum-frequency processes in only one optical superlattice without optical cavities. The idle can be generated by optical parametric amplification of pump and signal. Then, one beam will be generated by the cascaded sum-frequency process of pump and idle, and another beam will be produced by the cascaded sum-frequency process of pump and signal in the same optical superlattice. The phase-mismatching in the cascaded nonlinear processes can be compensated by three reciprocals of the optical superlattice by a quasi-phase-matching technique. The conversion dynamics among the cascaded nonlinear processes is analyzed by using a quantum stochastic method. The five-partite entanglement among pump, signal, idle, and two sum-frequency beams are discussed by applying a sufficient inseparability criteria for the five-partite CV entanglement proposed by Van Loock and Furusawa. This scheme of five-partite entanglement generation with different frequencies has potential applications in quantum communication and computation networks.

Geometrical representation of coherent tunneling process in two-waveguide and three-waveguide coupler**Project supported by the National Natural Science Foundation of China (Grant Nos. 11304247 and 61505161) and the Shaanxi Provincial Research Plan for Young Scientific and Technological New Stars, China (Grant No. 2015KJXX-40).

We propose an identical geometrical representation scheme for both Landau–Zener (LZ) tunneling process in two-waveguide coupler with a cubically bent structure and stimulated Raman adiabatic passage (STIRAP) in three-waveguide coupler, similar to the geometrical representation of sum frequency process. The results show that although the two-waveguide coupler with a cubically bent axis has not aperiodic structure, it acts as a chirped quasi-phase-matching (QPM) grating and corrects the relative phase between the two supermodes in the curved coupler system. We present a scheme about how to choose the parameters to design the curved beam splitter.

Three-color entanglement generated by single-pass cascaded sum-frequency processes

Three-color continuous-variable (CV) entangled beams can be produced by single-pass cascaded sum-frequency processes of third-harmonic generation by quasi-phase-matching technique in only one optical superlattice. Firstly, second-harmonic field is generated by the first double-frequency process of the fundamental field. Then, the third-harmonic field can be generated by the second cascaded sum-frequency process between the second-harmonic and the fundamental fields by quasi-phase-matching technique in the same optical superlattice. By using the quantum stochastic method, we investigated the conversion dynamics of the cascaded sum-frequency processes and the quantum correlation nature among the fundamental, second-harmonic, and third-harmonic fields. The results show that the higher conversion efficiency of third-harmonic generation can be achieved with the larger nonlinear coupling parameter of the second cascaded sum-frequency process. We also show that the fundamental, second-, and third-harmonic beams are CV entangled with each other according to the necessary and sufficient CV entanglement criterion. This scheme of three-color entanglement generation without involving optical cavity is easy to realize in experiment. Moreover, the three-color entangled beams are separated by an octave in frequency which has potential applications in quantum communication and computation networks.

Quadripartite continuous-variable entanglement generation by nondegenerate optical parametric amplification cascaded with a sum-frequency process

Quadripartite continuous-variable (CV) entanglement with different optical frequencies can be generated by nondegenerate optical parametric amplification cascaded with a sum-frequency process in only one optical superlattice. Firstly, the idler beam is generated by a different frequency process between pump and signal beams. Then, the sum-frequency beam will be generated by a cascaded sum-frequency process between pump and idler beams in the same optical superlattice. The conversion dynamics of the cascaded nonlinear processes is investigated by using a quantum stochastic method. The quantum correlations among pump, signal, idler and sum-frequency beams are calculated by applying a sufficient inseparability criteria for quadripartite CV entanglement. The results show that quadripartite CV entangled beams can be produced by this single-pass cascaded nonlinear process in one optical superlattice.

Towards a quantum interface between telecommunication and UV wavelengths: design and classical performance

We propose and characterize a quantum interface between telecommunication wavelengths (1311 nm) and an Yb-dipole transition (369.5 nm) based on a second order sum frequency process in a PPKTP waveguide. An external (internal) conversion efficiency above 5% (10%) is shown using classical bright light.

Conical second harmonic generation in one-dimension nonlinear photonic crystal

We observed conical second-harmonic generation in a one-dimension anomalous-dispersion-like medium, which manifests itself as scattering-assisted nonlinear interaction via quasi-phase-matching sum frequency process. The parameters for the ring-shaped second harmonic beam are analyzed experimentally and theoretically, which disclose the structure information of the nonlinear photonic crystal and imply potential applications as characterization methods. Furthermore, by varying the angles of incident beam, the conical beam can be significantly enhanced owing to collinear nonlinear coupling between the input beam and the scattering light.

Nonlinear Cascaded Femtosecond Third Harmonic Generation by Multi-grating Periodically Poled MgO-doped Lithium Niobate

Nonlinear cascaded femtosecond third harmonic generation was experimentally investigated pumped by 100 fs pulses at optical communication band 1550 nm using a multi-grating 5 mol. % MgO-doped periodically poled lithium niobate crystal. The optimized efficiency of 10.8% was achieved with the simultaneous phase-matching of the second harmonic and sum frequency process. And the third harmonic spectrum reached as broad as 8.7 nm because of the choosing of a small group velocity mismatching between the fundamental and second harmonic pulses. Nonlinear cascaded method will provide a reference for the efficient frequency conversion in the high intensity range.

Application of frequency conversion of starlight to high-resolution imaging interferometry. On-sky sensitivity test of a single arm of the interferometer

Abstract We investigate the sensitivity of frequency conversion of starlight using a non-linear optical sum frequency process. This study is being carried out in the context of future applications of optical interferometry dedicated to high-resolution imaging. We have implemented a complete experimental chain from telescope to detector. The starlight frequency is shifted from the infrared to the visible using an optically non-linear crystal. To fulfil the requirements of interferometry, our experimental setup uses spatially single-mode and polarization maintaining components. Due to the small size of the collecting aperture (8 inches Celestron C8) with a 3 nm spectral bandwidth, on-sky tests were performed on bright stars in the H band. The detection was achieved in a true photon counting operation, using synchronous detection. Betelgeuse (HMag =−3.9), Antares (HMag =−3.6) and Pollux (HMag =−1) were successfully converted and detected in visible light. Despite the low transmission of our experiment, our results prove that the efficiency of frequency conversion offers sufficient sensitivity for future interferometric applications.