Bisdioxaborine Polymethines with Large Third-Order Nonlinearities for All-Optical Signal Processing

Organic materials that exhibit large real third-order optical nonlinearities, |Re(χ(3))|, and that also have low linear and nonlinear losses at telecommunication wavelengths may be useful for a range of all-optical signal-processing (AOSP) applications. Based on their solution linear and nonlinear optical characteristics, polymethine dyes in general, and chalcogenopyrylium-terminated heptamethines in particular, are a promising class of materials for AOSP, but the translation of their microscopic nonlinearity to device-relevant materials is hindered by significant aggregation of the molecules in high-chromophore density films.[1] An approach to minimize aggregation these dyes, in which bulky and rigidly out-of-plane groups are introduced both in the center of the polymethine bridge and on the heterocyclic end groups, has been developed and can lead to thin-film materials exhibiting combinations of large |Re(χ(3))|, large two-photon figure-of-merit, and low linear loss that are suitable for AOSP.[2] [1] Hales J. M., Matichak J., Barlow S., Ohira S., Yesudas K., Bredas J.-L., Perry J. W. and S. R. Marder, Science, 2010, 327, 1485. [2] Barlow S., Bredas J.-L., Getmanenko Y. A., Gieseking R. L., Hales J.M., Kim H., Marder S.R., Perry J. W., Risko C., Zhang Y., Materials Horizons, 2014, 1, 17.

Photonic technologies operate by the optical processing and transmission of information and require a variety of materials with appropriate properties to facilitate the modulation of light. Polymers containing organic nonlinear optical (NLO) chromophores allow the modulation of the phase, the state of polarization, and/or the frequency of light beams, as required for the optical encoding, transmission, and routing of information. Both secondand third-order NLO effects are potentially useful [1]. Materials with large secondand third-order nonlinearities can be useful for the doubling and tripling, respectively, of the frequency of optical signals. They can also be used for routing and switching applications in which NLO effects involving the ability to vary the refractive indices of the materials using an applied electric field are important. The refractive index of second-order NLO materials is dependent on electric field; this effect is known as the linear electro-optic (EO) or Pockels effect. Materials with large EO coefficients can be used for the fabrication of ultrafast low-power EO modulators that can be integrated with electronics. In third-order NLO materials, the refractive index is dependent on the intensity of light and so can bemodulated with an optical control pulse, negating the need to integrate electronics directly with the NLO material and facilitating all-optical modulation, which holds promise for ultrafast signal processing, potentially enabling much higher bandwidth communications. In organic materials with large secondor third-order nonlinearities, these nonlinearities are largely due to the interaction of light with conjugated p-systems. Here a simple model is described that has helped to provide design strategies for the optimization of second-order and third-order nonlinear optical effects in quasi-linear organic molecules.

By preventing aggregation of polymethine molecules at high number density, we have developed organic materials with large third-order nonlinearities and low nonlinear absorption in the near-infrared thereby enabling demonstration of an all-optical signal processing application.

Large third-order optical nonlinearity of ZnO–Bi2O3–B2O3 glass–ceramic containing Bi2ZnB2O7 nanocrystals

Germania/ormosil hybrid matrix with large third-order nonlinearity is prepared by a low-temperature sol–gel process. Z-scan measurements indicate that the film fabricated from the pure Germania/ormosil hybrid solution shows an excellent third-order nonlinearity at all measured wavelengths. In order to explore its potential to be a functional matrix, a well-investigated organic dopant disperse red 1 (DR1) azoaromatic chromophore is introduced into the Germania/ormosil system. As a comparison, the poly(methyl methacrylate) (PMMA) polymer is employed and doped with the same content of DR1 molecule. Results indicate that by employing Germania/ormosil matrix system, the figure of merit of DR1-doped material at 532 nm can be greatly improved as compared to that of the PMMA/DR1 polymer film and also other published reports. This improvement helps broaden the limited applications of DR1-doped material and make it acceptable for devices fabrication at 532 nm. Results demonstrate that the as-prepared hybrid matrix might be a promising candidate for all-optical applications.

Materials with large and fast third-order nonlinearities and low losses have proven difficult to find and use in all-optical switching device configurations. Large nonlinear phase shifts, however, can be obtained in non-centrosymmetric materials relying on a cascaded second-order effect, i.e. up-conversion of a fundamental beam into its second-harmonic and the subsequent down-conversion for a phase-mismatched interaction.[1-2] Because of the recent development of efficient second harmonic generation in waveguides, it appears that phase shifts of order π can be reached over centimeter distances with peak powers of 10's of Watts or less in KTP or poled polymers, an improvement of orders of magnitude over the current capabilities of third order materials.

Orbital angular momentum (OAM) beams may create a new paradigm for the future classical and quantum communication systems. A majority of existing OAM beam converters are bulky, slow, and cannot withstand high powers. Here, we design and experimentally demonstrate an ultra-fast, compact chalcogenide-based all-dielectric metasurface beam converter which has the ability to transform a Hermite–Gaussian (HG) beam into a beam carrying an OAM at near infrared wavelength. Depending on the input beam intensity, the topological charge carried by the output OAM beam can be switched between positive and negative. The device provides high transmission efficiency and is fabricated by a standard electron beam lithography. Arsenic trisulfide (As 2 S 3 ) chalcogenide glass (ChG) offers ultra-fast and large third-order nonlinearity as well as a low two-photon absorption coefficient in the near infrared spectral range.

The existence of large nonlinear optical coefficients is one of the preconditions for using nonlinear optical materials in nonlinear optical devices. For a crystal, such large coefficients can be achieved by matching photon energies with resonant energies between different bands, and so the details of the crystal band structure play an important role. Here we demonstrate that large third-order nonlinearities can also be generally obtained by a different strategy. As any of the incident frequencies or the sum of any two or three frequencies approaches zero, the doped or excited populations of electronic states lead to divergent contributions in the induced current density. We refer to these as intraband divergences, by analogy with the behavior of Drude conductivity in linear response. Physically, such resonant processes can be associated with a combination of intraband and interband optical transitions. Current-induced second order nonlinearity, coherent current injection, and jerk currents are all related to such divergences, and we find similar divergences in degenerate four wave mixing and cross-phase modulation under certain conditions. These divergences are limited by intraband relaxation parameters and lead to a large optical response from a high quality sample; we find that they are very robust with respect to variations in the details of the band structure. To clearly track all of these effects, we analyze gapped graphene, describing the electrons as massive Dirac fermions; under the relaxation time approximation, we derive analytic expressions for the third order conductivities and identify the divergences that arise in describing the associated nonlinear phenomena.

We report the spatial self-phase modulation (SSPM) effect for solution dispersions of black phosphorus (BP). The experimental results suggest that this concentration-dependent coherent light diffraction is due to the ultrafast and large third-order optical nonlinearity of BP. The third-order nonlinear susceptibility of BP has been simply obtained about 10−19 m2/V2 by analyzing the experimental results. The fast relaxation time during dynamic relaxation is obtained as 0.13 ps. Our experimental results imply novel potential application of BP in ultrafast nonlinear phase modulation devices based on their nonlinear optical response.

We present a study on the ultrafast third-order nonlinearities of a novel series of iso-polydiacetylene oligomers (iso-PDAs). Unlike polydiacetylenes that contain a linearly-conjugated backbone, iso-PDAs have a backbone that is cross-conjugated. A new Kerr-gate technique, differential optical Kerr effect (DOKE) detection, is used to measure third-order nonlinear susceptibilities, χ(3), and second hyperpolarizabilities, γ, of monomer, dimer, trimer, pentamer, and heptamer samples in tetrahydrofuran (THF) solutions. A linear increase in γ as a function of the number of repeat units is observed for all samples except the monomer, suggesting that the fixed-length linearly conjugated segments dominate the electronic polarizability. An added increase to the oligomer nonlinearities due to communication along the cross-conjugated path is not observed. The largest nonlinearity was observed in the heptamer sample, displaying a second hyperpolarizability relative to the THF solvent of γheptamer/γTHF=181±9. In addition, an interesting feature arising out of the signal decay tail is present in the samples but absent in our THF solvent reference.

Experiments with nonlinear self-refraction of Gaussian laser beams in silica sono-gels doped with copper tetrasulfonated phthalocyanine are reported. The propagation of laser beams inside nonlinear sol-gel samples with different Cu-phthalocyanine concentrations has been monitored by measuring the spatial beam profile in the near field and in the far field behind the sample. The experimental results are analyzed by a new simple theoretical approach, in which we assume that the incident Gaussian beam induces a phase shift that varies as a Gaussian function of the beam radius. The beam propagation behind the sample is determined by the Huygens–Fresnel integral formalism. By solving the Huygens–Fresnel integral, analytical expressions for the spatial beam profile in both the near field and the far field after the nonlinear sample are obtained. Experiments are carried out with a diode pumped frequency doubled Nd–YAG laser at 532 nm. We obtain very large third-order nonlinearities in these doped sol-gel samples at temperatures just above room temperature. When we compare the predictions of the theory with the experimental data, we find experimental values of the nonlinear third-order susceptibility up to −2.3×10−4 esu.

Bacteriorhodopsin, a natural occuring photochromic protein present in the purple membrane of certain halophilic bacteria has been shown to posses unique optical properties. The ground state has a broad absorption band (bR) centred at 570 nm (light adapted bacteriorhodopsin) and a metastable state (M) centred at 412 nm with a thermal relaxtion time of 10 ms. The metastable can be stimulated to decay to the ground state through light in 200 ns. The thermal relaxation time can, however, be extended by five orders of magnitude through suitable chemical treatment of the purple membrane, without compromising the stimulated decay of 200 ns. At the same time, there is a concomitant change in the dipole moment accompanying trans to cis isomerization and. charge translocation across the purple membrane. Bacteriorhodopsin is also a highly nonlinear optical material with a large third-order nonlinearity. A nonlinear Kerr coefficient of 10-4 cm2 /W has been reported for this material, and new mutants are reported to possess even higher nonlinearities. This high nonlinerity enables the use of even fairly low- powered lasers to investigate nonlinear optical propagation. The time constant of the nonlinearity is on the order of a few milliseconds. We report in this talk applications of bacteriorhodopsin thin films for holographic storage, coherent-to- incoherent conversion, incoherent-to-coherent conversion, and contrast reversal of images.

Organic compounds with π electron derealization are receiving much attention1 in recent years in an effort to identify materials with large third-order nonlinearity and fast response for various applications in switching, optical information processing, etc. Polymers have well known fabrication advantages including molding and fiber forming by injection extrusion, and thin film fabrication by spin coating or plasma deposition.

Poly(p-phenylenevinylene) (PPV) is a typical representative of conjugated polymers, which have a highly delocalized, one-dimensional conjugated π-electron system. These polymers have found much interest, because most of them can be processed rather easily to thin film waveguides and because of their large third-order nonlinearities [1-3]. Thin films of PPV are prepared by spin-coating of a soluble precursor polymer on fused silica substrates and thermal annealing under vacuum as described recently [4]. We have used thin films of PPV to develop and demonstrate a sensitive characterization method of the intensity dependent refractive index n = n0 + n2I and absorption coefficient α = α0 + α2I. The utility of any material for applications in photonics depends primarily on these quantities.

In this paper, a magnetophotonic crystal for enhanced absorption peak of one-way absorber is studied, in which two defect layers are introduced. The effects of magneto-optics and Tamm plasma polaritons are investigated. The optical properties of the novel photonic crystal with different periodic layer thicknesses and structures are shown in the wavelength range of 0.6–1.0 μm. Considering the large third-order nonlinearity and field localization, graphene is combined with the defect layer. Results showed that graphene can improve the absorption capacity of the absorber by 50%. Moreover, the influence of the relative position between graphene layer and magneto-optical layers on the absorption is further studied, which had found that this relative position can tune the absorption peak of the one-way absorber. Furthermore, the effect of incidence angle and the contour of electrical fields are also studied. Compared with the existing unidirectional devices, the structure has the advantages of small size, high efficiency, wide bandwidth and easy photoelectric integration. This work provides a new method for controllable perfect one-way absorber design in infrared wavelength range.