Optical Kerr Nonlinearity Research Articles

Third-order nonlinear optical properties of organic azo dyes by using strength of nonlinearity parameter and Z-scan technique

In this paper, two chemically synthesized organic azo dyes, 2-(2,5-Dichloro-phenyazo)-5,5-dimethyl-cyclohexane-1,3-dione (azo dye (i)) and 5,5-Dimethyl-2-tolylazo-cyclohexane-1,3-dione (azo dye (ii)), have been studied from optical Kerr nonlinearity point of view. These materials were characterized by Ultraviolet-visible spectroscopy. Experiments were performed using a continous wave diode-pumped laser at 532nm wavelength in three intensities of the laser beam. Nonlinear absorption (β), refractive index (n2) and third-order susceptibility (χ(3)) of dyes, were calculated. Nonlinear absorption coefficient of dyes have been calculated from two methods; 1) using theoretical fits and experimental data in the Z-scan technique, 2) using the strength of nonlinearity curves. The values of β obtained from both of the methods were approximately the same. The results demonstrated that azo dye (ii) displays better nonlinearity and has a lower two-photon absorption threshold than azo dye (i). Calculated parameter related to strength of nonlinearity for azo dye (ii) was higher than azo dye (i), It may be due to presence of methyl in azo dye (ii) instead of chlorine in azo dye (i). Furthermore, The measured values of third order susceptibility of azo dyes were from the order of 10−9esu. These azo dyes can be suitable candidate for optical switching devices.

Length Dependence of Ultrafast Optical Nonlinearities in Vertically Aligned Multiwalled Carbon Nanotube Films

Tube-length-dependent optical nonlinearities of vertically aligned multiwalled carbon nanotube (MWNT) films have been investigated by Z-scan and transient absorption measurements with femtosecond laser pulses in the near-IR spectral range from 780 to 1550 nm. Both saturable absorption and optical Kerr nonlinearity are found to be dependent on excitation wavelength and tube length, indicating that band-filling in semiconducting tubes and longitudinal surface plasmon resonance in metallic tubes play an important role, respectively. The 1 ps relaxation time for the nonlinear response of the MWNT films, however, is independent of tube length, as evidenced from dissipation of excited energy in the radial direction. Such ultrafast vertically length-dependent in CNT can significantly contribute to fabricate vertically nanochips in various types of integrated nanodevices just like a creation of a living three-dimensional fish bone (a kind of cowfish).

Enhanced third-order and fifth-order Kerr nonlinearities in a cold atomic system via Rydberg-Rydberg interaction

We investigate the optical Kerr nonlinearities of an ensemble of cold Rydberg atoms under the condition of electromagnetically induced transparency (EIT). By using an approach beyond mean-field theory, we show that the system possesses not only enhanced third-order nonlinear optical susceptibility, but also giant fifth-order nonlinear optical susceptibility, which has a cubic dependence on atomic density. Our results demonstrate that both the third-order and the fifth-order nonlinear optical susceptibilities consist of two parts, contributed respectively by photon-atom interaction and Rydberg-Rydberg interaction. The Kerr nonlinearity induced by the Rydberg-Rydberg interaction plays a leading role at high atomic density. We find that the fifth-order nonlinear optical susceptibility in the Rydberg-EIT system may be five orders of magnitude larger than that obtained in traditional EIT systems. The results obtained may have promising applications in light and quantum information processing and transmission at weak-light level.

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.

Optical Kerr effect exhibited by carbon nanotubes and carbon/metal nanohybrid materials

Structural modification of carbon nanotubes in combination with metallic nanoparticles is reported. An enhancement in the nonlinear optical refraction of multi-wall carbon nanotubes by the incorporation of platinum nanoparticles was observed. Comparative results were analyzed taking into account the participation of single-wall carbon nanotubes that originate a decrease in the nonlinear optical response of the multi-wall carbon nanotubes integrating a thin film. A Nd:YAG laser system featuring 532nm wavelength with 4ns pulse duration in a two-wave mixing experiment was employed for exploring the studied optical nonlinearities of the samples. The contribution of optical processes to mechanical characteristics dependent on high optical irradiance in carbon nanotubes was described. A variation in the mass density associated to the optically irradiated tubes allowed us to calculate the change in Young's modulus in a thin film configuration. The estimation of an opto-mechanical phenomenon was based on the evaluation of the nonlinearity of index responsible for the optical Kerr effect. According to Raman and optical evaluations, the inclusion of metallic nanoparticles in carbon structures results in a modification of surface that also gives origin to noticeable optical Kerr nonlinearities. Potential applications for developing laser-induced controlled opto-mechanical nanohybrid systems can be contemplated.

Nonlinear dynamic reciprocity

Kerr optical nonlinearities are known to be well suited for achieving optical isolation, but the fact that the degree of non-reciprocity is signal-level dependent brings new opportunities as well as limitations.

Third-order nonlinearity and passive Q-switching of Cr⁴⁺:YGG garnet crystal.

We demonstrate the third-order nonlinear optical properties of Cr(4+):Y(3)Ga(5)O(12) (Cr(4+):YGG) and Q-switched lasers with Cr(4+):YGG as the saturable absorber for the first time to our knowledge. The third-order nonlinear properties, including the optical Kerr nonlinearity and saturable absorption, were systematically measured and analyzed in detail by using a Z-scan technique. The measured data show that Cr(4+):YGG has a large nonlinear refractive index, ground-state absorption cross section, and excited-state absorption cross section in contrast to Cr(4+):Y(3)Al(5)O(12) (Cr(4+):YAG). With a Nd:YGG crystal as the gain medium and a Cr(4+):YGG crystal as the saturable absorber, the passively Q-switched laser was performed. The shortest pulse width and largest pulse energy were achieved at the absorbed pump power of 8 W with the values of 9.1 ns and 26.1 μJ, respectively, corresponding to the average output power of 0.87 W and peak power of 2.9 kW. The results indicate that Cr(4+):YGG is an available and promising optical switcher for pulsed lasers.

Low Threshold, Wide Dynamic Range, Tunable, All-Optical Self-Modulator Based on Fano Resonance and Out-of-Plane Coupling in a Slab Photonic Crystal with a Graphene Layer

We demonstrate an all-optical modulator based on self-modulation in a one-dimensional slab photonic crystal (PhC) by using optical Kerr nonlinearity of graphene and Fano resonance effect. It has been shown that the effect of Fano resonance in a one-dimensional slab PhC for intensity enhancement can provide low threshold (~1 MW/cm2), high frequency (>1 THz), and wide dynamic range (>3 THz) tunability for the all-optical self-modulator. Such a self-modulator can find applications in optical pulse generations, optical clocks, frequency shifting, and so forth.

Green, red, and IR frequency comb line generation from single IR pump in AlN microring resonator

On-chip frequency comb generations enable compact broadband sources for spectroscopic sensing and precision spectroscopy. Recent microcomb studies focus on the infrared spectral regime and have difficulty accessing the visible regime. We demonstrate comb-like visible frequency line generation through second-harmonic, third-harmonic, and sum-frequency conversion of a Kerr comb within a high-Q aluminum nitride (AlN) microring resonator pumped by a single telecom laser. The strong power enhancement, in conjunction with the unique combination of Pockels (χ2) and Kerr (χ3) optical nonlinearity of AlN, leads to cascaded frequency conversions in the visible spectrum. High-resolution spectroscopic study of the visible frequency lines indicates matched free spectrum range over all the bands. This frequency doubling and tripling effect in a single microcomb structure offers great potential for comb spectroscopy and self-referencing comb.

Optical Kerr nonlinearity in a high-Q silicon carbide microresonator.

We demonstrate a high-Q amorphous silicon carbide (a-SiC) microresonator with optical Q as high as 1.3 × 10(5). The high optical quality allows us to characterize the third-order nonlinear susceptibility of a-SiC. The Kerr nonlinearity is measured to be n2 = (5.9 ± 0.7) × 10(−15) cm(2)/W in the telecom band around 1550 nm. The strong Kerr nonlinearity and high optical quality render a-SiC microresonators a promising platform for integrated nonlinear photonics.

Hotspot-mediated ultrafast nonlinear control of multifrequency plasmonic nanoantennas.

Plasmonic devices have a unique ability to concentrate and convert optical energy into a small volume. There is a tremendous interest in achieving active control of plasmon resonances, which would enable switchable hotspots for applications such as surface-enhanced spectroscopy and single molecule emission. The small footprint and strong-field confinement of plasmonic nanoantennas also holds great potential for achieving transistor-type devices for nanoscale-integrated circuits. To achieve such a functionality, new methods for nonlinear modulation are required, which are able to precisely tune the nonlinear interactions between resonant antenna elements. Here we demonstrate that resonant pumping of a nonlinear medium in a plasmonic hotspot produces an efficient transfer of optical Kerr nonlinearity between different elements of a multifrequency antenna. By spatially and spectrally separating excitation and readout, isolation of the hotspot-mediated ultrafast Kerr nonlinearity from slower, thermal effects is achieved.

Interaction of femtosecond pulses of a two-harmonic Ti:Sapphire laser with liquid media

The interaction of ultrashort laser pulses having wavelengths of 400 and 800 nm with liquid media, including organic solutions, has been experimentally studied. It is shown that transparent drops evaporate and boil (with partial mass ejection in the form of vapor and liquid fragments) in the field of ultrashort light pulse. A large-scale change in the spectrum of laser pulse during its interaction with a water particle is revealed. This change is caused by self-modulation of the light phase due to the Kerr optical nonlinearity of liquid and the formation of plasma. Filamentation in continuous liquid media is analyzed; specifically, the dependences of the number of filaments, the lasing spectrum width, the nonlinear-focusing distance, and the filamentation region diameter on the laser pulse power are measured. It is noted that there is a range of relative powers where the number of filaments very rapidly increases. It is shown that the spectral broadening at filamentation, observed for fixed pulse energy with a change in pulse width, overlaps the entire visible spectral range. This circumstance makes it possible to obtain width-tunable pulses and use them, e.g., in optoacoustic diagnostics of media.

Nonlinear magneto-optic ellipsometry

The ellipsometric parameters for light reflection from a dielectric film with Kerr optical nonlinearity on a bigyrotropic magneto-electric film are theoretically investigated. The combined contributions of cubic optical nonlinearity and magneto-electric coupling allow us to control the ellipsometric parameters and thus, for example, the Kerr rotation with the incoming light intensity, in particular at incidence angles close to the pseudo-Brewster angle.

Terahertz-induced Kerr effect in amorphous chalcogenide glasses

We have investigated the terahertz-induced third-order (Kerr) nonlinear optical properties of the amorphous chalcogenide glasses As2S3 and As2Se3. Chalcogenide glasses are known for their high optical Kerr nonlinearities which can be several hundred times greater than those of fused silica. We use high-intensity, single-cycle terahertz pulses with a maximum electrical field strength exceeding 400 kV/cm and frequency content from 0.2 to 3.0 THz. By optical Kerr-gate sampling, we measured the terahertz-induced nonlinear refractive indices at 800 nm to be n2=1.746×10−14cm2/W for As2S3 and n2=3.440×10−14 cm2/W for As2Se3.

Numerical simulation of nonlinear properties of fullerene-containing one-dimensional photonic crystal

A model of interaction between a one-dimensional photonic crystal (PC) containing a defect (nonlinear optical layer of C60 fullerene) and radiation with a wavelength λ0= 1064 nm under steady-state conditions has been considered. This structure is a Fabry-Perot microcavity: a fullerene layer (with a thickness multiple of λ0/2) is placed between the interference mirrors formed by alternating layers λ0/4 thick. The PC under consideration (1) has a narrow transmission band in the vicinity of λ0 against the background of a relatively wide 100%-reflection band (photonic band gap) in the linear mode and (2) provides multiple amplification of the radiation intensity in the intermediate layer with respect to the external radiation intensity. Since C60 fullerene exhibits a significant optical Kerr nonlinearity, the optical thickness of the intermediate layer under irradiation deviates from the value multiple of λ0/2; as a result, 100% transmission for λ0 changes to almost 100% reflection at a certain radiation intensity. Thus, this structure behaves as a peculiar optical limiter.

Pattern-effect-free all-optical wavelength conversion using a hydrogenated amorphous silicon waveguide with ultra-fast carrier decay

Ultra-fast carrier decay, recently discovered in a hydrogenated amorphous silicon waveguide, can be exploited for pattern-effect-free all-optical signal processing based on optical Kerr nonlinearity. In this study, we utilized a 10 Gbit/s RZ-OOK data stream as a pump for degenerate four-wave mixing in a low-loss hydrogenated amorphous silicon waveguide. The propagation loss of the waveguide used was 1.0±0.2 dB/cm at 1550 nm. Unlike crystalline silicon waveguides, no noticeable difference was observed in the BER characteristics between the cases of PRBS 2(7)-1 and 2(31)-1.

Participation of the Third Order Optical Nonlinearities in Nanostructured Silver Doped Zinc Oxide Thin Solid Films

We report the transmittance modulation of optical signals in a nanocomposite integrated by two different silver doped zinc oxide thin solid films. An ultrasonic spray pyrolysis approach was employed for the preparation of the samples. Measurements of the third‐order nonlinear optical response at a nonresonant 532 nm wavelength of excitation were performed using a vectorial two‐wave mixing. It seems that the separated contribution of the optical nonlinearity associated with each film noticeable differs in the resulting nonlinear effects with respect to the additive response exhibited by the bilayer system. An enhancement of the optical Kerr nonlinearity is predicted for prime number arrays of the studied nanoclusters in a two‐wave interaction. We consider that the nanostructured morphology of the thin solid films originates a strong modification of the third‐order optical phenomena exhibited by multilayer films based on zinc oxide.

Counter-polarized single-photon generation from the auxiliary cavity of a weakly nonlinear photonic molecule

We propose a scheme for the resonant generation of counter-polarized single photons in double asymmetric cavities with a small Kerr optical nonlinearity (as that created by a semiconductor quantum well) compared to the mode broadening. Due to the interplay between spatial intercavity tunneling and polarization coupling, by weakly exciting with circularly polarized light one of the cavities, we predict strong antibunching of counter-polarized light emission from the non-pumped auxiliary cavity. This scheme due to quantum interference is robust against surface scattering of pumping light, which can be suppressed both by spatial and polarization filters.

Propagation of light in stratified media with optical Kerr nonlinearity under externalelectric fields

We analyze the controlled behavior of light propagation in a stratified Kerr-nonlinear mediumwith its photonic band structure tuned by applying an external electric field. The transmittanceT of light is significantly influenced by nonlinear effects induced by boththe external field and the incident light. Transmission resonance (T = 1) is induced by two mechanisms, band-edge resonance and gap soliton resonance. TheT–Eex graph has two turning points and consists of three solution branches. One unstable branch is locatedbetween the turning points, and connected with a stable solution branch at each turning point. AsEex increases and then decreases through the region of the turning points, the transition betweenthe stable states on different branches produces optical bistability and hysteresis. As inputlight intensity grows, the upper stable solution branch separates itself from the unstablebranch at the turning point, and both branches extend down to the ordinate axis atEex = 0. We have greatly enhanced single-envelope solitons on the upper stable branch from theseparation point to the line of zero external field.

Realization of a Knill-Laflamme-Milburn controlled-NOT photonic quantum circuit combining effective optical nonlinearities

Quantum information science addresses how uniquely quantum mechanical phenomena such as superposition and entanglement can enhance communication, information processing, and precision measurement. Photons are appealing for their low-noise, light-speed transmission and ease of manipulation using conventional optical components. However, the lack of highly efficient optical Kerr nonlinearities at the single photon level was a major obstacle. In a breakthrough, Knill, Laflamme, and Milburn (KLM) showed that such an efficient nonlinearity can be achieved using only linear optical elements, auxiliary photons, and measurement [Knill E, Laflamme R, Milburn GJ (2001) Nature 409:46–52]. KLM proposed a heralded controlled-NOT (CNOT) gate for scalable quantum computation using a photonic quantum circuit to combine two such nonlinear elements. Here we experimentally demonstrate a KLM CNOT gate. We developed a stable architecture to realize the required four-photon network of nested multiple interferometers based on a displaced-Sagnac interferometer and several partially polarizing beamsplitters. This result confirms the first step in the original KLM “recipe” for all-optical quantum computation, and should be useful for on-demand entanglement generation and purification. Optical quantum circuits combining giant optical nonlinearities may find wide applications in quantum information processing, communication, and sensing.