Optical Parametric Down-conversion Research Articles

Auto-pump-depleted stable single-longitudinal-mode 1.5 μm source with the assistance of SHG.

To realize a stable single-longitudinal-mode (SLM) 1550-nm light source for the generation of non-classical states, a ring auto-pump-depleted singly resonant optical parametric oscillator (SRO) with the assistance of second-harmonic-wave generation (SHG) is designed and built in this Letter. A magnesium oxide doped periodically polarized lithium niobate (MgO:PPLN) crystal and a lithium triborate (LBO) crystal are employed as the optical parametric downconversion (OPDC) and SHG crystals, respectively. Especially, the introduced SHG can firstly increase the loss difference between the lasing and non-lasing modes so that the dual-mode or multi-mode coupling in the achieved SRO can be effectively eliminated and the stable SLM operation is achieved. At the same time, the SHG will automatically adjust the output coupling efficiency of SRO, so as to achieve efficient conversion efficiency and auto-pump depletion of SRO. In addition, due to the SHG, it is easy to achieve the low-intensity noise multi-wavelength output for the stable SLM SRO. As a result, the output powers of the SLM 1550 nm and 775 nm are up to 4.05 W and 3.25 W, respectively, and the total optical conversion of the built SRO can achieve 45.58%. The presented method paves a way to develop a compact stable SLM multi-wavelength SRO, and the obtained SRO is further beneficial to develop compact continuous-variable non-classical light fields.

Continuous variable spin-orbit total angular momentum entanglement on the higher-order Poincaré sphere.

Optical spin-orbit coupling is an important phenomenon and has fruitful applications. Here, we investigate the spin-orbit total angular momentum entanglement in the optical parametric downconversion process. Four pairs of entangled vector vortex modes are experimentally generated directly using a dispersion- and astigmatism-compensated single optical parametric oscillator, and for the first time, to the best of our knowledge, the spin-orbit quantum states are characterized on the quantum higher-order Poincaré sphere, and the relationship of spin-orbit total angular momentum Stokes entanglement is demonstrated. These states have potential applications in high-dimensional quantum communication and multiparameter measurement.

Engineering multipartite coupling in doubly pumped parametric down-conversion processes

We investigate the quantum state generated by optical parametric down-conversion in a $\chi^{(2) } $ medium driven by two noncollinear light modes. The analysis shows the emergence of multipartite, namely 3- or 4-partite, entangled states in a subset of the spatio-temporal modes generated by the process. These appear as bright spots against the background fluorescence, providing an interesting analogy with the phenomenology recently observed in two-dimensional nonlinear photonic crystals. We study two realistic setups: i) Non-critical phase-matching in a periodically poled Lithium Tantalate slab, characterized by a 3-mode entangled state among hot spots. ii) A type I setup in a Beta-Barium Borate crystal, where the spatial walk-off between the two pumps can be exploited to make a transition to a quadripartite entangled state. In both cases we show that the properties of the state can be controlled by modulating the relative intensity of two pump waves, making the device a versatile tool for quantum state engineering.

Imaging Spatial Quantum Correlations through a thin Scattering Medium

We image with cameras entangled photon light transmitted through a thin scattering medium. Near-field and far-field spatial quantum correlations show that entangled photon pairs (bi-photons) generated by spontaneous optical parametric down-conversion exhibit speckle patterns. In contrast, no information from the thin scattering medium can be extracted using incoherent light issued from one photon of the pair.

High-average and high-peak output-power terahertz-wave generation by optical parametric down-conversion in MgO:LiNbO3

A widely tunable terahertz (THz)-wave generation that has a high repetition rate and a narrow line width is demonstrated in this paper by injection-seeded THz-wave parametric generation (is-TPG) in a MgO:LiNbO3 crystal. By pumping the crystal using a passively Q-switched neodymium-doped yttrium vanadate microchip laser with a time duration of 140 ps and an average power of up to 5 W, a THz-wave output with an average output power of 30 μW, a peak power of 4 W, a pulse duration of 73 ps, and a pulse-repetition frequency of 100 kHz is obtained. To prevent laser damage and photorefractive damage to the crystal, the constraints on the pumping condition of the MgO:LiNbO3 crystal are experimentally studied by changing the pumping parameters. As a result, we achieved the stable generation of the THz-wave signal in the 100 kHz regime. Moreover, we performed THz-wave imaging by using the developed is-TPG source. The obtained THz image indicated that the developed system has a good stability over long periods of time.

Giant Amplification of Terahertz Waves in a Nonlinear Graphene Layered Medium

In this letter, a novel technique for terahertz (THz) wave amplification based on subjecting a nonlinear graphene layered medium to two intensive optical waves is proposed. The principle of operation is based on generating a backward-propagating THz wave at the expense of the THz input wave, by properly designing the medium dispersion, graphene nonlinear response, and optical frequency spacing. The generated THz wave interacts, in turn, with the co-propagating (THz and optical) waves, enabling an energy exchange regime. It is shown that, via proper design of the propagation length, a giant THz gain can be achieved by means of optical parametric downconversion. The presented numerical evaluations show a possible 50-dB-THz gain for a few centimeters of propagation lengths with reasonable optical input intensities. The proposed scheme is tunable, simple, and operates at room temperature.

Efficiency-enhanced picosecond mid-infrared optical parametric downconversion based on a cascaded optical superlattice

We demonstrate an efficiency-enhanced picosecond (ps) mid-infrared radiation via optical parametric downconversion. Based on a cascaded periodically poled MgO-doped stoichiometric lithium tantalate crystal (MgO:sPPLT), a tandem optical parametric oscillation-optical parametric amplification (OPO-OPA) process is achieved. Compared with a single OPO process, the conversion efficiency obtains an enhancement of 71%.

Caracterización de la generación de segunda armónica y conversión espontánea paramétrica descendente óptica a partir de cristales periódicamente polarizados de LiNbO3 (PPLN)

Caracterización de la generación de segunda armónica y conversión espontánea paramétrica descendente óptica a partir de cristales periódicamente polarizados de LiNbO3 (PPLN)

Optomechanically induced transparency and self-induced oscillations with Bogoliubov mechanical modes

Bogoliubov mechanical modes have the mathematical form of two-mode squeezed states and can form in an optomechanical system in which two mechanical modes couple to an optical mode via respective red and blue sideband couplings. Analogous to optical parametric downconversion, these special mechanical excitations can enable the generation of phonon pairs as well as mechanical entanglement. Here we report experimental studies of Bogoliubov mechanical modes using a silica microsphere as a model three-mode optomechanical resonator. We have employed optomechanically induced transparency to characterize the effective optomechanical coupling of the Bogoliubov mode. Self-induced oscillations of the Bogoliubov mode further reveal that Stokes photons generated from blue sideband coupling are converted via red sideband coupling to phonons in another mechanical mode, demonstrating a key process for the optomechanical generation of phonon pairs.

Towards single-cycle squeezing in chirped quasi-phase-matched optical parametric down-conversion

We propose a method for generation of single-cycle squeezed light by parametric down-conversion in a chirped quasi-phase-matched nonlinear crystal. We find an exact quantum solution for this process valid for an arbitrary parametric gain (under an assumption of nondepleted pump), and discover an ultrabroadband squeezing in the down-converted light with a flat squeezing spectrum comprising the full optical octave. We describe a scheme for observation of this kind of squeezing using second-harmonic generation as an ultrafast correlator.

Direct observation of the degree of correlations using photon-number-resolving detectors

Optical parametric down-conversion is a common source for the generation of nonclassical correlated photonic states. Using a parametric down-conversion source and photon-number-resolving detectors, we measure the two-mode photon-number distribution of up to 10 photons for different degrees of correlation. The degree of correlation is controlled by collecting different spatial and spectral single modes for each polarization and varying the amount of spectral and spatial overlap between them. Clear evidence for photon-number correlations is presented despite detector imperfections such as low detection efficiency and other distorting effects. Two criteria, derived directly from the raw data, are shown to be good measures for the degree of correlation. Additionally, using a fitting technique, we find a connection between the measured photon-number distribution and the degree of correlation of the reconstructed original two-mode state. These observations are only possible as a result of the detection of high photon number events.

Experimental Study on the Imaging of the Squeezed State Light with -4.93dB Quantum-Noise Reduction at 1064 nm

A stable amplitude squeezed state light was generated by utilizing the optical parametric down-conversion (OPDC) technique based on periodically poled KTiOPO4(PPKTP) in an optical parametric oscillator (OPO) resonator. We observed a -4.93dB of squeezing in homodyne measurement. The imaging experiments of resolution target were conducted. It shown that the imaging resolution with squeezed state light as light source was 1.26 times that of the resolution with coherent light as light source. The squeezed state light was applied for imaging of real objects and we found that the imaging with squeezed light as light source is more distinct and has less distortion.

Measurements of the dependence of the photon-number distribution on the number of modes in parametric down-conversion

Optical parametric down-conversion (PDC) is a central tool in quantum optics experiments. The number of collected down-converted modes greatly affects the quality of the produced photon state. We use Silicon Photomultiplier (SiPM) number-resolving detectors in order to observe the photon-number distribution of a PDC source, and show its dependence on the number of collected modes. Additionally, we show how the stimulated emission of photons and the partition of photons into several modes determine the overall photon number. We present a novel analytical model for the optical crosstalk effect in SiPM detectors, and use it to analyze the results.

Quantum imaging and spatio-temporal correlations

We report on recent progress for two topics in the field of Quantum Imaging. The first is the detection of faint amplitude objects with a sensitivity which surpasses the standard quantum limit. The second is the theoretical/numerical analysis of spatio-temporal entanglement in optical parametric down-conversion.

Experimental study on the imaging of the squeezed state light at 1064 nm

Stable, low noise, infrared squeezed state tight at 1064 nm is generated by utilizing optical parametric down-conversion (OPDC) technique based on periodically poled KTiOPO4 in a optical parametric amplifier (OPA) resonator. A non-classical noise reduction of 2.58 dB below the shot noise is observed through balanced homodyne detection. The squeezed state light is used to set up an imaging system for high-resolution imaging, and it is found that the resolution of image based on the amplitude-squeezed light is 1.26 times larger than that of infrared coherent light under the same intensity. The experimental results indicate that squeezed light is an important non-classical light, which can overcome the coherent laser shot-noise, the classical diffraction limit and limit of quantum noise.

Lossless single-photon shaping via heralding

Using spontaneous optical parametric downconversion, we experimentally demonstrate heralded generation of shaped single photons, whose modes are tailored indirectly by applying amplitude modulation on the pump field that drives the downconversion process. Our experiment opens a door to creating high-quality, mode-shaped single photons at a substantially higher efficiency than is possible with the existing method of direct single-photon shaping.

Quantum Light from a Whispering-Gallery-Mode Disk Resonator

Optical parametric down-conversion has proven to be a valuable source of nonclassical light. The process is inherently able to produce twin-beam correlations along with individual intensity squeezing of either parametric beam, when pumped far above threshold. Here, we present for the first time the direct observation of intensity squeezing of -1.2 dB of each of the individual parametric beams in parametric down-conversion by use of a high quality whispering-gallery-mode disk resonator. In addition, we observed twin-beam quantum correlations of -2.7 dB with this cavity. Such resonators feature strong optical confinement and offer tunable coupling to an external optical field. This work exemplifies the potential of crystalline whispering-gallery-mode resonators for the generation of quantum light. The simplicity of this device makes the application of quantum light in various fields highly feasible.

Photon-added coherent states in parametric down-conversion

Photon-added coherent states have been realized in optical parametric down-conversion by Zavatta et al. [Science 306, 660 (2004)]. In this report, it is established that the states generated in the process are ideal photon-added coherent states. It is shown that the scheme can generate higher-order photon-added coherent states. A comparative study of the down-conversion process and atom-cavity interaction in generating the photon-added coherent states is presented.

Bright quadripartite entanglement from competingχ(2)nonlinearities

In this Brief Report, we investigate the generation of bright quadripartite entanglement of continuous variables in an experimentally realizable system involving second-order harmonic generation with competing nondegenerate optical parametric downconversion. By using the well-known van Loock--Furusawa criterion for continuous variable correlations, we find that the genuine quadripartite entanglement can be generated in the system over a wide range of controllable parameters. Besides this, it is shown that the bipartite entanglement between any two field modes can be achievable. In addition, the dependence of the quantum correlations on the pump parameter is also discussed.

Optical rogue waves on demand

Researchers achieve generation of stable and coherent optical rogue waves. A Viewpoint on: Seeded Supercontinuum Generation with Optical Parametric Down-Conversion D.R.Solli, B.Jalali and C.Ropers Phys. Rev. Lett. 105(23), 233902 (2010) – Published November 29, 2010