Optical Kerr Coefficient Research Articles

Designing ultra-fast all-optical full-subtractor using the photonic crystal structure

In this paper, a photonic crystal-based structure for an all-optical full-subtractor has been proposed. The structure includes six nonlinear resonant rings to transmit the incoming optical waves toward the output ports. Using the different radii for nonlinear rods made the possibility of the dropping operation for different amounts of optical intensities. The nonlinear rods are made of a doped-glass with an optical Kerr coefficient of 10–15 m2/W. To calculate the components of the optical waves throughout the structure, the finite-difference time-domain method has been used. The simulation results prove the correct functionality of the proposed structure. Besides, the maximum rise time of the device is equal to 2 ps. The contrast ratio and the area of the structure are around 8.08 dB and 2790 µm2, respectively.

Optical Kerr nonlinearity and multiphoton absorption of DSTMS measured by the Z-scan method

We investigate the optical Kerr nonlinearity and multiphoton absorption (MPA) properties of 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium 2, 4, 6-trimethylbenzene-sulfonate (DSTMS) excited by femtosecond pulses at a wavelength of 1.43 µm, which is optimal for terahertz generation via difference frequency mixing. The MPA and the optical Kerr coefficients of DSTMS at 1.43 µm are strongly anisotropic, indicating a dominating contribution from cascaded second-order nonlinearity.

Giant Enhancement and Sign Inversion of Optical Kerr Nonlinearity in Random High Index Nanocomposites near Mie Resonances

AbstractHigh‐index dielectric nanoantennas excited at Mie‐type resonances have exhibited enormous enhancement of optical nonlinearity. Such nanostructures have been actively studied by researchers in recent years. Here, a numerical analysis study of the optical Kerr effect of nanocomposites consisting of high refractive index (GaP) spheres at the wavelength of 532 nm is presented. This is done by means of 3D finite‐difference time‐domain simulations. The effective nonlinear refractive index of 0.8 µm thick nanocomposites and metasurfaces is evaluated. It is shown that the optical Kerr nonlinearity of the nanocomposites rises by orders in proximity to Mie resonances and may exceed the second‐order refractive index of the bulk material. It is revealed that the sign of the effective optical Kerr coefficient is inverted near the Mie resonances. This effect may be of interest in developing nonlinear optical metadevices.

Influence of optical Kerr coefficient on photonic band structures of hexagonal-lattice function photonic crystals

در این مقاله، بلورهای فوتونی تابعی را که در آنها ثابت دی‌الکتریک مراکز پراکندگی (میله‌ها) تابعی از مکان است، مورد مطالعه قرار داده‌ایم. شبکه مورد بررسی هگزاگونال بوده و سطح مقطع میله‌ها نیز دارای تقارن دایروی است که در زمینه هوا قرار گرفته‌اند. ساختار نوار فوتونی در هر دو قطبش الکتریکی و مغناطیسی برای امواج الکترومغناطیس محاسبه شده و نتایج به دست آمده وجود نواحی ممنوعه بسامدی (گاف نوار فوتونی) را نشان می‌دهند. فرض می‌شود که میله‌های دی‌الکتریک از مواد کر تشکیل یافته‌اند. بنابراین با در نظر گرفتن توزیع‌های متفاوت شدت نور، صورت‌های مختلفی برای تابعیت مکانی ثابت دی‌الکتریک میله‌ها حاصل خواهد شد. اثر ضریب تابع (متناسب با ضریب کر) بر روی ساختارهای نوار فوتونی به طور نظری بررسی شده است. نتایج به دست آمده نشان می‌دهند که پهنا و تعداد گاف‌های نوار فوتونی در بلورهای فوتونی تابعی نسبت به بلورهای فوتونی مرسوم قابلیت کنترل پذیری بیشتری دارند و می‌توانند در طراحی ابزارهای نوری بسیار مفید باشند.

Bi-directional top-hat D-Scan: single beam accurate characterization of nonlinear waveguides

The characterization of a third-order nonlinear integrated waveguide is reported for the first time by means of a top-hat dispersive-scan (D-Scan) technique, a temporal analog of the top-hat Z-Scan. With a single laser beam, and by carrying two counterdirectional nonlinear transmissions to assess the input and output coupling efficiencies, a novel procedure is described leading to accurate measurement of the TPA figure of merit, the effective two-photon absorption (TPA), and optical Kerr (including the sign) coefficients. The technique is validated in a silicon strip waveguide for which the effective nonlinear coefficients are measured with an accuracy of ±10%.

Study of Structure–Third-Order Susceptibility Relation of Indandione Derivatives

By using the Z-scan method we studied the third-order nonlinear optical parameters of several aminobenziliden-1,3-indandione (ABI) derivatives that have previously been shown to own second-order nonlinear optical properties. Measurements were carried out using two 1064 nm Nd:YAG lasers with picosecond (ps) and nanosecond (ns) pulse widths, respectively. When ns laser was employed in the Z-scan setup, a strong thermal lensing took place resulting in severe overestimation of optical Kerr coefficients. Due to this reason the ps laser was employed to evaluate correct magnitude of Kerr effect. For investigated organic molecules, experimental results show that two-photon absorption at 1064 nm is in correlation with molar extinction coefficient at 532 nm. Here we demonstrate good linear correlation between values of second-order molecular hyperpolarizability determined experimentally and those obtained by quantum chemical modeling.

Concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in a periodically modulated laser field

Based on a one-dimensional Smoluchowski equation we have developed the theory of concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in an interference laser field. The numerical solution of a system of recurrence equations resulting from the Smoluchowski equation after expansion of the microsphere concentration in the harmonic series has allowed us to determine the dependence of the concentration nonlinearity settling time on the intensity of the incident radiation. In the diffusion limit, we have derived the expression for the optical Kerr coefficient, which is found to be for an aqueous suspension of latex microspheres with a radius of and a concentration of . Diffraction of a probe wave on a light-induced concentration grating is considered as a method for studying a nonlinear concentration response of an artificial highly efficient nonlinear medium for laser radiation of long pulse duration.

Comprehensive analysis of the optical Kerr coefficient of graphene

We present a comprehensive analysis of the the nonlinear optical Kerr effect in graphene. We directly solve the S-matrix element to calculate the absorption rate, utilizing the Volkov-Keldysh- type crystal wave functions. We then convert to the nonlinear refractive index coefficients through the Kramers-Kronig relation. In this formalism, the source of Kerr nonlinearity is the interplay of optical fields that cooperatively drive the transition from valence to conduction band. This formalism makes it possible to identify and compute the rates of distinct nonlinear processes that contribute to the Kerr nonlinear refractive index coefficient. The four identified mechanisms are two photon absorption, Raman transition, self coupling, and quadratic AC Stark effect. We also present a comparison of our theory with recent experimental and theoretical results.

Enhanced optical Kerr nonlinearity of MoS_2 on silicon waveguides

A quasi-two-dimensional layer of MoS2 was placed on top of a silicon optical waveguide to form a MoS2–silicon hybrid structure. Chirped pulse self-phase modulation measurements were carried out to determine the optical Kerr nonlinearity of the structure. The observed increase in the spectral broadening of the optical pulses in the MoS2–silicon waveguide compared with the silicon waveguides indicated that the third-order nonlinear effect in MoS2 is about 2 orders of magnitude larger than that in silicon. The measurements show that MoS2 has an effective optical Kerr coefficient of about 1.1×10−16 m2/W. This work reveals the potential application of MoS2 to enhance the nonlinearity of hybrid silicon optical devices.

Enhanced parametric frequency conversion in a compact silicon-graphene microring resonator.

We demonstrate four-wave mixing (FWM) in a 10-μm-radius silicon microring resonator with the assistance of giant nonlinearity of the monolayer graphene. A maximum enhancement of 6.8 dB of conversion efficiency in the silicon-graphene microring (SGM) resonator is observed. A nonlinear propagation model is established and the optical Kerr coefficient of the silicon-graphene hybrid waveguide is three times larger than that of the silicon waveguide.

Electro-Optical Properties in Polymer-Stabilized Blue Phase of n-OCB Homologue Chiral Nematic Liquid Crystal Mixtures

In this study, the chemical structures and physical property dependencies of the electro-optical properties were investigated in polymer-stabilized blue phase (BP) using the four kinds of 4-n-alkyloxy-4′-cyanobiphenyl (n-OCB) homologue chiral nematic LCs. It was confirmed that the optical response time and Kerr coefficient in polymer-stabilized BP was varied with the molecular parity as determined by the alkyl chain length of the n-OCB homologue chiral nematic LC mixtures.

Tunable optical Kerr effects of DNAs coupled to quantum dots

The coupling between DNA molecules and quantum dots can result in impressive nonlinear optical properties. In this paper, we theoretically demonstrate the significant enhancement of Kerr coefficient of signal light using optical pump-probe technique when the pump-exciton detuning is zero, and the probe-exciton detuning is adjusted properly to the frequency of DNA vibration mode. The magnitude of optical Kerr coefficient can be tuned by modifying the intensity of the pump beam. It is shown clearly that this phenomenon cannot occur without the DNA-quantum dot coupling. The present research will lead us to know more about the anomalous nonlinear optical behaviors in the hybrid DNA-quantum dot systems, which may have potential applications in the fields such as DNA detection.

Application of the Z-scan technique to determine the optical Kerr coefficient and two-photon absorption coefficient of magnetite nanoparticles colloidal suspension

We investigate the occurrence of the optical Kerr effect and two-photon absorption when an oil-based magnetic Fe3O4 nanoparticles colloidal suspension is illuminated with high intensity femtosecond laser pulses. The frequency of the pulses is controlled and the Z-scan technique is employed in our measurements of the nonlinear optical Kerr coefficient (n2) and two-photon absorption coefficient (β). From these values it was possible to calculate the real and imaginary parts of the third-order susceptibility. We observed that increasing the pulse frequency, additional physical processes take place, increasing artificially the absolute values of n2 and β. The experimental conditions are discussed to assure the obtention of reliable values of these nonlinear optical parameters, which may be useful in all-optical switching and optical power limiting applications.

Nano‐droplet formation in polymer dispersed liquid crystals

AbstractIn this work we analyse the fabrication of Polymer Dispersed Liquid Crystals (PDLCs) using SU8‐2002‐2007 photoresist and 5CB and E7 Liquid Crystals. Also we report the nonlinear optical behaviour for these materials and for Polymer Dispersed Liquid Crystals with a Twisted Cell (T‐PDLC). We found that depending of several parameters, the droplets size varies from nano to micro dimensions. We report for first time, to our best knowledge, the synthesis of a SU8 Polymer Dispersed Liquid Crystal (PDLC) by using the polymer SU8 photoresist and liquid crystals (LC) and also the nonlinear behaviour of T‐PDLC. We have characterized the droplets formation from nano to micron size depending of the different variables in the synthesis. We have used this PDLC in microfabrication as planar waveguides of different thickness over Si wafers. Our results also show that PDLCs present low NL optical Kerr coefficient (n2 about 10‐9cm2/W) and that it is three orders of magnitude larger in T‐PDLC. Nevertheless, the fabrication processes of T‐PDLCs make impossible their use in microfabrication. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrafast nonlinear effects in hydrogenated amorphous silicon wire waveguide

We, for the first time, present the ultrafast optical nonlinear response of a hydrogenated amorphous silicon (a-Si:H) wire waveguide using femtosecond pulses. We show cross-phase and cross-absorption modulations measured using the heterodyne pump-probe method and estimate the optical Kerr coefficient and two-photon absorption coefficient for the amorphous silicon waveguide. The pumping energy of 0.8 eV is slightly lower than that required to achieve two-photon excitation at the band gap of a-Si:H (approximately 1.7 eV). An ultrafast response of less than 100 fs is observed, which indicates that the free-carrier effect is suppressed by the localized states in the band gap.

A mechanical Kerr effect in deformable photonic media

We theoretically introduce a mechanism for achieving the mechanical analog of optical Kerr nonlinearity. By exploiting optomechanical interactions in deformable waveguide structures, a nonlinear phase shift proportional to the optical field intensity is induced. Resulting Kerr coefficients several orders of magnitude larger than the intrinsic silicon optical Kerr coefficient are predicted.

THE OPTICAL KERR EFFECT IN WURTZITEGaN-BASED DOUBLE QUANTUM WELLS: INFLUENCES OF PIEZOELECTRICITY AND SPONTANEOUS POLARIZATION

Taking the influences of piezoelectricity and spontaneous polarization into consideration, the nonlinear optical Kerr effect in a nitride semiconductor coupling double quantum well (DQW) has been theoretically investigated by using the compact density matrix approach and iterative treatment. The electronic eigenstates in a nitride DQW are exactly solved based on the built-in electric field model already constituted in recent reference. The band non-parabolicity effect of nitride heterostructures has been taken into account. A typical wurtzite GaN / AlGaN DQW is chosen to perform numerical calculations. The calculated results reveal that the optical Kerr coefficients sensitively depend on the structural parameters of the coupling DQW system. Moreover, a strong optical Kerr effect can be realized in the nitride DQW by choosing a group of optimum structural parameters and doped fraction.

Electromagnetically induced transparency in quantum dot systems

Electromagnetically induced transparency (EIT) in quantum dot exciton systems in which the exciton behaves as a two-level system is investigated theoretically. It is shown that due to strong exciton–phonon coupling EIT can occur in such a quantum dot system and ultraslow light can propagate. The nonlinear optical absorption and Kerr coefficient based on EIT are also calculated. The numerical results show that giant nonlinear optical effects can be obtained while the frequency of the signal field differs only by an amount of LO phonon frequency from the exciton frequency in quantum dot systems.

Ultrafast and Large Third-Order Nonlinear Optical Properties of CdS Nanocrystals in Polymeric Film

We report the ultrafast and large third-order nonlinear optical properties of CdS nanocrystals (NCs) embedded in a polymeric film. The CdS NCs of 2 nm radius are synthesized by an ion-exchange method and highly concentrated in the two layers near the surfaces of the polymeric film. The two-photon absorption coefficient and the optical Kerr coefficient are measured with laser pulses of 250 fs duration at 800 nm wavelength. The one-photon and two-photon figures of merit are determined to be 3.1 and 1.3, respectively, at irradiance of 2 GW/cm(2). The observed nonlinearities have a recovery time of approximately 1 ps. The two-photon-generated free carrier effects have also been observed and discussed. These results demonstrate that CdS NCs embedded in polymeric film are a promising candidate for optical switching applications.

Four-wave mixing in a liquid suspension of dielectric microspheres

In this work a theory of the degenerate four-photon parametric scattering (FPS) is developed in a liquid suspension of transparent microspheres (heterogeneous medium), the nonlinearity of which is caused by the change in the microsphere concentration under the action of gradient forces in the electromagnetic field of interacting waves. It is shown that the water suspension of latex spheres with diameter d = 0.234 μm and concentrationN0 = 6.5·10 cm, in effect of the FPS process, corresponds to a cubic nonlinear medium with the optical Kerr coefficient n2 that is larger by a factor of 10 than in the case of CS2.