Weak Signal Beam Research Articles

Strong light-matter interaction and non-linear effects in organic semiconducting CuPc nanotubes: realization of all-optical diode and switching applications.

Spatial self-phase modulation based on the optical Kerr effect has gained momentum in recent years to analyse the nonlinear optical properties of 2D inorganic nanomaterials. In the present work, we investigate the strong light-matter interaction of organic semiconducting materials based on SSPM, by developing Cu-phthalocyanine (CuPc) nanotubes via a solvothermal technique. The low bandgap of CuPc facilitates the study of its nonlinear optical properties for a broad spectrum range from 671 nm to 405 nm. Intense laser light passing through the CuPc dispersion produces concentric diffraction ring patterns at the far field from which high n2 and χ(3) values, 3.667 × 10-5 cm2 W-1 and 2 × 10-3 esu, respectively, are obtained for the 405 nm laser. This strong nonlinear optical response of CuPc has been utilized to realize non-reciprocal light propagation by constructing a CuPc/SnS2 hybrid structure, which makes an effective all-optical photonic diode. In addition, the all-optical switching is presented using CuPc nanotubes based on the spatial cross-phase modulation technique. In this technique a phase change is induced in the weak signal beam modulated by the strong controlling light beam, which helps to produce all-optical logic gates and all-optical switching devices. The experimental findings of this work unravel the potentially powerful applications of CuPc nanotubes in all-optical information transmission and all-optical photonic devices.

Tunneling induced swapping of orbital angular momentum in a quantum dot molecule

In this paper, we have examined the effectiveness exchange of optical vorticity via three-wave mixing (TWM) technique in a four-level quantum dot (QD) molecule by means of the electron tunneling effect. Our analytical analysis demonstrates that the TWM procedure can result in the production of a new weak signal beam that may be absorbed or amplified within the QD molecule. We have taken into account the electron tunneling as well as the relative phase of the applied lights to assess the absorption and dispersion characteristics of the newly generated light. We have discovered that the slow light propagation and signal amplification can be achieved. Our results show that the exchange of the orbital angular momentum of light can transfer from coupling optical vortex light to the new generated light in high efficiency.

Topological charge measurement in a four-level single layer graphene system

In this letter we have proposed a four-level graphene monolayer system for identifying the topological charge of Laguerre–Gaussian light. Here, we have shown that due to the four-wave mixing mechanism in the monolayer graphene system, a weak signal beam can be generated due to quantum coherence and interference effect. We have discussed the spatially dependent linear absorption spectrums of the weak probe and new generated signal beams via quantum mechanical density matrix formalism. We have found that by numbering the spot areas of the probe and signal beams, one can realize the topological charge of the Laguerre–Gaussian beam interacts by monolayer graphene system. Moreover, we have realized that for some topological charge the new generated signal beam can be amplified in the graphene system.

Realization of phase dependent optical bistability in a quantum dot molecule via three-wave mixing

In this paper, we have proposed a new model based on the electron tunneling effect for controlling the optical bistability (OB) and optical multistability (OM) in a defect slab structure with a quantum dot molecule (QDM). Due to the presence of the electron tunneling effect, an additional weak signal beam can be generated in the system which makes the medium becomes phase dependent. We have studied the refractive index properties of the QDM via optical susceptibility of the propagated probe light. We have discussed the relative phase effect on negative refractive index (NRI) of the QDM nanostructure due to presence of electron tunneling. Then, by using the transfer matrix method, we have studied the transmission coefficient for NRI of the QDM nanostructure. Then, we have investigated the properties of transmitted light versus incident light for realizing the OB and OM. We have considered the relative phase effect on OB and OM properties of the transmitted beam and find that the switching between them is possible when electron tunneling is present in the quantum dot. Moreover, the optical thickness of the defect layer is also investigated on OB and OM in resonance and non-resonance conditions.

Preparation of continuously tunable orthogonal squeezed light filed corresponding to cesium D<sub>1</sub> line

The non-classical light resonance on the cesium D<sub>1</sub> (894.6 nm) line has important applications in solid-state quantum information networks due to its unique advantages. The cesium D<sub>1</sub> line has a simplified hyperfine structure and can be used to realize a light-atom interface. In our previous work, we demonstrated 2.8-dB quadrature squeezed vacuum light at cesium D<sub>1</sub> line in an optical parametric oscillator(OPO) with a periodically poled KTP(PPKTP) crystal. However, the squeezing level is relatively low, and the tunability that has practical significance for squeezed light has not been further investigated. Theoretically, the increase of the transmittance of output mirror and the decrease of the intra-cavity loss of the OPO can improve the squeezing level. Here, we use super-polished and optimal coating cavity mirrors to improve the nonlinear process in OPO. We prepare 447.3 nm blue light from 894.6 nm fundamental light by a second harmonic generation cavity (SHG). The SHG is a two-mirror standing-wave cavity with a PPKTP crystal as the nonlinear medium. The power of generated blue laser is 32 mW when the incident infrared power is 120 mW. Using the blue light to pump an OPO, we achieve quadrature squeezed vacuum light at cesium D<sub>1</sub> line. The OPO is a two-mirror standing-wave cavity with a PPKTP crystal. The threshold of OPO is reduced to 28 mW. The squeezing level of generated quadrature squeezed vacuum light is increased to 3.3 dB when the pump power is 15 mW. Taking into account the overall detection efficiency, the actual squeezing reaches 5.5 dB. We inject a weak signal beam into the OPO cavity to act as an optical parametric amplifier (OPA), and test the tunability of squeezzed light. The blue light and the squeezed light are tuned by using a low-frequency triangular wave signal to scan the Ti: sapphire laser. Gradually increasing the amplitude of the scanning triangle wave signal, the generated bright squeezed light can be continuously tuned over a range around 80 MHz without losing the stability of the whole system. The generated squeezed light offers the possibility for the efficient coupling between the non-classical source and solid medium in the process of quantum interface.

Imaging with ghostly electrons

Electron Imaging Ghost imaging is a computational imaging approach that uses correlations between a signal beam that interacts with a sample and a reference beam that doesn't. The correlations are then used to reconstruct an image of the sample and can, in principle, be used to image samples with very weak signal beams that might otherwise be damaged with a typical probe beam. Already demonstrated for optics and atoms, Li et al. now extend the method of ghost imaging to electrons. To circumvent the difficulty of splitting an electron beam, they instead used a structured electron beam to probe the sample. They show that a reconstructed image of a sample with a lower electron dose than that used in direct imaging methods can be faithfully produced. This technique could reduce acquisition time and avoid damaging sensitive samples in electron imaging applications. Phys. Rev. Lett. 121 , 114801 (2018).

Flexoelectro-optic effect and two-beam energy exchange in a hybrid photorefractive cholesteric cell with a short-pitch horizontal helix.

We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive cholesteric cell with a short-pitch helix oriented parallel to the cell substrates (so-called uniformly lying helix configuration). Weak and strong light beams incident on the hybrid cell interfere and induce a periodic space-charge field in the photorefractive substrate of the cell, which penetrates into the cholesteric liquid crystal (LC). Due to the flexoelectro-optic effect an interaction of the photorefractive field with the LC flexopolarization causes the spatially periodic modulation of the helix axis in the plane parallel to the cell substrates. Coupling of a weak signal beam with a strong pump beam at the LC permittivity grating, induced by the periodically tilted helix axis, leads to the energy gain of the weak signal beam. Dependence of the signal beam gain coefficient on the parameters of the short-pitch cholesteric LC is studied.

Using degenerate parametric interaction of intense acoustic beams to amplify weak signals

The paper considers the degenerate parametric interaction of an intense acoustic pumping beam and a weak signal beam at the subharmonic. The use of a special emitter system with independent signal emission at the harmonic and subharmonic made it possible to study the features of nonlinear interaction both for different amplitude levels and arbitrary phase relations of the fields at these frequencies. Just as predicted in the theory, the experiment showed that signal amplification at the subharmonic hardly occurs at all. It is shown that the use of odd field harmonics, which are absent for a zero amplitude of the signal wave, makes it possible to substantially increase the efficiency of isolating a weak signal wave. The interaction of beams for large and small acoustic Reynolds numbers of the signal wave is studied.

Infrared sensitive liquid crystal light valve with semiconductor substrate.

A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n₂=-1 cm²/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

Simultaneous slow and fast light transmission-reflection with amplification in a defect slab via exciton spin relaxation

The absorption, transmission and reflection properties of two incident probe and signal pulses through a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15 nm Al0.3 Ga0.7 as barriers is theoretically discussed. It is shown that the biexciton coherence leads to the phase control of the absorption, transmission and reflection properties of two weak probe and signal beams. We will also show that the exciton spin relaxation between excitonic states can affect the slow and fast light propagation of transmitted and reflected pulses with amplification in a defect slab with dispersive material. Our results show that many particle interactions due to Coulomb correlations in semiconductors can lead to the controlling of light propagation through the defect dielectric medium.

Large phase shift of spatial soliton in lead glass by cross-phase modulation in pump-signal geometry

We investigate the co-propagation of a strong pump beam and a weak signal beam in lead glass, and find that the large phase shift of the strongly nonlocal spatial optical soliton (SNSOS) can be realized via cross-phase modulation. The theoretical study suggests a synchronous propagation of the pump SNSOS and the signal SNSOS under the required initial condition. A π-phase shift of the signal SNSOS is experimentally obtained by changing the power of the pump SNSOS by about 13 mW around the soliton critical power, which agrees qualitatively with our theoretical prediction. The ratio of the phase shift rate of the signal SNSOS to that of the pump SNSOS shows a close match to the reciprocal of the ratio between their wavelengths.

Frequency translation via four-wave mixing Bragg scattering in Rb filled photonic bandgap fibers

We demonstrate frequency translation at microwatt pump power levels in Rubidium vapor confined to a hollow-core photonic bandgap fiber using four-wave mixing Bragg scattering. The 5S(1/2)→5D(3/2) two-photon transition in 85Rb is employed for the four-wave mixing process. Using continuous-wave pump beams at 780 and 795 nm, a weak signal beam at 776 nm is translated to a wavelength of 762 nm with a 21% conversion efficiency at pump powers of 300 μW.

All-optical controlled switching in centrally coupled circular array of nonlinear optical fibers

We show that, in a nonlinear centrally coupled circular array of evanescently coupled fibers, the coupling dynamics of a weak signal beam can be efficiently influenced by a high-power control beam that induces nonlinear defects. When the intense control beam is launched into the central core and one core in the periphery, then localized solitons are formed and cause the fibers with induced defects (defected fibers) to decouple from the other array elements. In the presence of a high-intensity control beam, the propagation of weak signal is restricted to the defected optical fibers. The weak signal periodically couples between the induced defects. This oscillatory behavior depends on the sign of the (Kerr-type) nonlinearity and the initial phase difference between the control fields injected to the central and one of the peripheral fibers. This all-optical network has the advantage of routing and switching the weak signal field in a controlled way by adjusting the parameters of intense control field.

All-optical microdisk switch using EIT

We present theoretical results of a low-loss all-optical switch based on electromagnetically induced transparency and the quantum Zeno effect in a microdisk resonator. We show that a control beam can modify the atomic absorption of the evanescent field which suppresses the cavity field buildup and alters the path of a weak signal beam. We predict more than 35 dB of switching contrast with less than 0.1 dB loss using just 2 μW of control-beam power for signal beams with less than single photon intensities inside the cavity.

Repulsion and total reflection with mismatched three-wave interaction of noncollinear optical beams in quadratic media

The phenomenon of the total reflection of a weak signal beam from a high-power reference beam due to noncollinear mismatched parametric interaction in a quadratic medium is demonstrated. In a planar geometry the conditions of the signal beam reflection from the optical inhomogeneity induced by the reference beam are found. The analytical expression for the critical value of the signal beam tilt is obtained, and it is shown that total reflection occurs if the initial tilt is less than the critical value. The influence of the walk-off and the reference beam focusing on interaction dynamics are discussed. It is shown that in a bulk medium the beam reflection turns into scattering by an induced inhomogeneity. If reflection conditions are fulfilled, the cylindrical reference beam acts as a convex mirror and lunate distortions of the reflected beam profile occur.

Mutual-induced fractional Fourier transform in strongly nonlocal nonlinear medium

The effect of mutual-induced fractional Fourier transform (FRFT) between a weak signal beam and a strong pump beam in a strongly nonlocal nonlinear medium is described. The signal beam is an FRFT during propagation and the order of FRFT is dependent on the propagation distance and the power of the pump beam. When the propagation distance is fixed, the order of FRFT of the signal beam is proportional to the square root of the power of the pump beam. Mutual-induced FRFT is another method of light controlling light, and its properties contribute to the development of new type FRFT devices, optical information processing and optical imaging.

Nonlinear interaction and reflection of incoherent light beams

The interaction dynamics between two incoherent light beams in a medium with thermal nonlin-earity is studied both experimentally and theoretically. It is shown that in the mode of a nonlinear reflection the transformation of a spatial structure of a weak signal beam can be theoretically described in the framework of a spatially distributed model for a nonlinear change in the refractive index of the medium.

The nonlinear Faraday rotation-based dynamic holography in rubidium vapor

The nonlinear Faraday rotation in rubidium vapor can be used for efficient dynamic holography. The amplification of a weak signal beam is obtained in a three wave mixing process with an elliptically polarized pump beam.

All Optical Light Deflection and Displacement Using Nonlinear Slab Waveguide

The possibility of all optical control of light deflection and displacement through a planar nonlinear waveguide has been discussed in this article. In this scheme a strong command beam controls the propagation characteristics of a weak signal beam in a nonlinear waveguide. Employing variational approach, we have established a set of coupled nonlinear equations for the displacement of the center of gravity, beam size, deflection angle, and beam divergence of the signal beam. These equations have been solved numerically to confirm the possibility of all optical control of deflection and displacement of a signal beam by a command beam.

Weak-wave advancement in nearly collinear four-wave mixing

We identify a new four-wave mixing process in which two nearly collinear pump beams produce phase-dependent gain into a weak bisector signal beam in a self-defocusing Kerr medium. Phase matching is achieved by weak-wave advancement caused by cross-phase modulation between the pump and signal beams. We relate this process to the inverse of spatial modulational instability and suggest a time-domain analog.