High Kerr Nonlinearity Research Articles

Enhanced optical Kerr nonlinearity of graphene/Si hybrid waveguide

In this work, we experimentally study the optical Kerr nonlinearities of graphene/Si hybrid waveguides with enhanced self-phase modulation. In the case of CMOS compatible materials for nonlinear optical signal processing, Si and silicon nitride waveguides have been extensively investigated over the past decade. However, Si waveguides exhibit strong two-photon absorption (TPA) at telecommunication wavelengths, which leads to a significant reduction of the nonlinear figure-of-merit (FOM). In contrast, a silicon nitride based material system usually suppresses the TPA but simultaneously leads to the reduction of Kerr nonlinearity by one order of magnitude. Here, we introduce a graphene/Si hybrid waveguide, which maintains the optical properties and CMOS compatibility of Si waveguides, while enhancing the Kerr nonlinearity, by transferring over to the top of the waveguides. The graphene/Si waveguides are measured to have an enhanced nonlinear parameter of 510 W−1 m−1, compared with that of the Si waveguide of 150 W−1 m−1. An enhanced nonlinear FOM of 2.48 ± 0.25 has been achieved, which is four times larger than that of the Si waveguide of 0.6 ± 0.1. This work reveals the potential application of graphene/Si hybrid waveguides with high Kerr nonlinearity and FOM for nonlinear all-optical signal processing.

Controllable nonlinear effects in a hybrid optomechanical semiconductor microcavity containing a quantum dot and Kerr medium

ABSTRACTWe theoretically investigate the nonlinear effects in a hybrid quantum optomechanical system consisting of two optically coupled semiconductor microcavities containing a quantum dot and a Kerr nonlinear substrate.The steady-state behaviour of the mean intracavity optical field demonstrates that the system can be used as an all optical switch. We further investigate the spectrum of small fluctuations in the mechanical displacement of the movable distributed Bragg reflectors and observe that normal mode splitting takes place for high Kerr nonlinearity and pump power. In addition, we have shown that steady state of the system exhibits two possible bipartite entanglements by proper tuning of the system parameters. The entanglement results suggest that the proposed system has the potential to be used in quantum communication platform. Our work demonstrates that the Kerr-nonlinearity can effectively control the optical properties of the hybrid system, which can be used to design efficient optical devices.

Possibilities of laser amplification and measurement of the field structure of ultrashort pulses in the range of 2.7 – 3μm in tellurite glass fibres doped with erbium ions

The amplification of ultrashort signals in the range 2.7 – 3 μm in active tellurite glass fibres with high Kerr nonlinearity and high concentration of erbium ions in the core is theoretically investigated under diode pumping at a wavelength of 0.975 μm. The possibility of producing pulses with the energy ∼10 nJ and the duration smaller than 100 fs with ∼20 dB gain is shown. Moreover, using a specially developed iterative computer algorithm, the possibility of determining the intensity and phase of the generated pulses by measuring their fundamental spectra and two additional spectra obtained by means of nonlinear-optical conversion in short pieces of these optical fibres is demonstrated. Optical fibre samples are made of high-purity TeO2 – ZnO – La2O3 – Na2O glasses with 1021 cm−3 concentration of erbium ions in the core and a low content of hydroxyl groups that causes small losses in the spectral range under consideration. The group velocity dispersions, effective mode fields, nonlinear coefficients and field overlap integrals of the LP01 fundamental modes with a doped core for optical fibres with different core diameters are calculated, and the emission and absorption cross sections are calculated basing on the experimental luminescence spectrum. The optimal parameters of the amplifier are determined by numerically modelling the dynamics of ultrashort pulses using the measured and calculated characteristics.

Invited Article: Enhanced four-wave mixing in waveguides integrated with graphene oxide

We demonstrate enhanced four-wave mixing (FWM) in doped silica waveguides integrated with graphene oxide (GO) layers. Owing to strong mode overlap between the integrated waveguides and GO films that have a high Kerr nonlinearity and low loss, the FWM efficiency of the hybrid integrated waveguides is significantly improved. We perform FWM measurements for different pump powers, wavelength detuning, GO coating lengths, and number of GO layers. Our experimental results show good agreement with theory, achieving up to ∼9.5-dB enhancement in the FWM conversion efficiency for a 1.5-cm-long waveguide integrated with 2 layers of GO. We show theoretically that for different waveguide geometries an enhancement in FWM efficiency of ∼20 dB can be obtained in the doped silica waveguides and more than 30 dB in silicon nanowires and slot waveguides. This demonstrates the effectiveness of introducing GO films into integrated photonic devices in order to enhance the performance of nonlinear optical processes.

High-gain, low-threshold and small-footprint optical parametric amplifier for photonic integrated circuits

A new model of an optical parametric amplifier is proposed based on a silicon-slab slotted photonic crystal waveguide (SPCW). The slot is considered to be filled with silicon nanocrystal material (SiNC/SiO2) having a high Kerr nonlinearity. The extreme optical confinement (spatial and temporal) of the SPCW has enhanced the optical nonlinearity, and thus, a high parametric gain is attained in a small length of the waveguide. Further, for analyses of pulse propagation, the coupled nonlinear Schrodinger’s equations have been modified to incorporate the enhancements in the linear and the nonlinear coefficients due to the slow-light effect. Simulations have been performed on both the high group index region and the low-dispersion regions of the guided band. The simulations on the high group index region, centered at ≈1584 nm, depict a 22.6 dB parametric gain and a 20.9 dB conversion efficiency at a waveguide length of 152 μm, with an effective pump power and peak input signal power of 700 mW and 0.25 Mw, respectively. The pulsating signal, with a pulse width of 5 ps, also experienced a negligible deterioration in its pulse shapes in this length of the SPCW. On the other hand, the simulations on the region of negligible dispersion, centered at 1530 nm, have produced an over 10 dB parametric gain and conversion efficiency through a long range of wavelengths, i.e., 1490–1568 nm, which covers half of the S-band and the complete C-band of the optical communication windows. The significant gain at a micrometer scale length of the waveguide is expected to advance the possibility of on-chip integration of a high-speed all-optical amplifier in photonic integrated circuits.

Mid-IR supercontinuum generated in low-dispersion Ge-on-Si waveguides pumped by sub-ps pulses.

Ge-on-Si is an attractive material platform for mid-IR broadband sources on a chip because of its wide transparency window, high Kerr nonlinearity and CMOS compatibility. We present a low-loss Ge-on-Si waveguide with flat and low dispersion from 3 to 11 µm, which enables a coherent supercontinuum from 2 to 12 µm, generated using a sub-ps pulsed pump. We show that 700-fs pump pulses with a low peak power of 400 W are needed to generate such a wide supercontinuum, and the waveguide length is around 5.35 mm.

Pushing the limits of CMOS optical parametric amplifiers with USRN:Si7N3 above the two-photon absorption edge

CMOS platforms operating at the telecommunications wavelength either reside within the highly dissipative two-photon regime in silicon-based optical devices, or possess small nonlinearities. Bandgap engineering of non-stoichiometric silicon nitride using state-of-the-art fabrication techniques has led to our development of USRN (ultra-silicon-rich nitride) in the form of Si7N3, that possesses a high Kerr nonlinearity (2.8 × 10−13 cm2 W−1), an order of magnitude larger than that in stoichiometric silicon nitride. Here we experimentally demonstrate high-gain optical parametric amplification using USRN, which is compositionally tailored such that the 1,550 nm wavelength resides above the two-photon absorption edge, while still possessing large nonlinearities. Optical parametric gain of 42.5 dB, as well as cascaded four-wave mixing with gain down to the third idler is observed and attributed to the high photon efficiency achieved through operating above the two-photon absorption edge, representing one of the largest optical parametric gains to date on a CMOS platform.

Normal modes of a superconducting transmission-line resonator with embedded lumped element circuit components

We present a method to identify the coupled, normal modes of a superconducting transmission-line with an embedded lumped element circuit. We evaluate the effective transmission-line non-linearities in the case of Kerr-like Josephson interactions in the circuit and in the case where the embedded circuit constitutes a qubit degree of freedom, which is Rabi coupled to the field in the transmission-line. Our theory quantitatively accounts for the very high and positive Kerr non-linearities observed in a recent experiment [M. Reh\'ak et.al., Appl. Phys. Lett. 104, 162604], and we can evaluate the accomplishments of modified versions of the experimental circuit.

Wideband nonlinear spectral broadening in ultra-short ultra - silicon rich nitride waveguides.

CMOS-compatible nonlinear optics platforms with high Kerr nonlinearity facilitate the generation of broadband spectra based on self-phase modulation. Our ultra – silicon rich nitride (USRN) platform is designed to have a large nonlinear refractive index and low nonlinear losses at 1.55 μm for the facilitation of wideband spectral broadening. We investigate the ultrafast spectral characteristics of USRN waveguides with 1-mm-length, which have high nonlinear parameters (γ ∼ 550 W−1/m) and anomalous dispersion at 1.55 μm wavelength of input light. USRN add-drop ring resonators broaden output spectra by a factor of 2 compared with the bandwidth of input fs laser with the highest quality factors of 11000 and 15000. Two – fold self phase modulation induced spectral broadening is observed using waveguides only 430 μm in length, whereas a quadrupling of the output bandwidth is observed with USRN waveguides with a 1-mm-length. A broadening factor of around 3 per 1 mm length is achieved in the USRN waveguides, a value which is comparatively larger than many other CMOS-compatible platforms.

Programmable Single-Bandpass Photonic RF Filter Based on Kerr Comb from a Microring

Microresonators with a high Kerr nonlinearity show great potential to generate optical frequency combs with ultrabroad spectra, high repetition rate, and high coherence between comb lines. The compact size and possibility of chip-level integration make the Kerr combs attractive for many applications, especially including photonic radiofrequency (RF) filters. In this paper we report the first demonstration of a programmable photonic RF filter based on the Kerr comb from a silicon nitride microring. A novel scheme enabled by the large frequency spacing of the Kerr comb is introduced in order to suppress unwanted RF passbands including the image and periodic passbands. As a result, a single passband is achieved. To the best of our knowledge, this is the first demonstration of a single-bandpass photonic RF filter employing a discrete-wavelength comb source.

Microwave generator based on tunnel-coupled semiconductor-metamaterial structure

We propose a model of a tunable laser based on a tunnel-coupled waveguide semiconductormetamaterial structure. The waveguide semiconductor channel has a positive refractive index and a high Kerr nonlinearity coefficient. In the frequency range under investigation, the channel formed by the magnetoactive metamaterial is characterized by a negative refractive index. Computer simulation is used for investigating the peculiarities of generation of microwave radiation under pumping due to modulated instability in the semiconductor channel and a distributed feedback. The generation frequency is controlled using the dependence of the refractive index of the metamaterial on the external magnetic field.

Modulation instability and short-pulse generation in media with relaxing Kerr nonlinearity and high self-steepening

The modulation instability in waveguides with high Kerr nonlinearity, characterised by a delayed nonlinear response, has been investigated with allowance for the self-steepening parameter and third-order dispersion. General expressions for the modulation gain are obtained. The influence of the waveguide parameters on the gain is analysed. It is shown that the joint effect of the delayed nonlinear response and negative nonlinearity dispersion leads to an increase in the modulation gain. The relations obtained are confirmed by numerical simulation. The results of this study can be used to design compact generators of high-frequency pulse trains.

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.

Optical properties of all-solid microstructured optical fibers

In this Letter, we study optical properties of all-solid microstructured optical fiber made of soft glass. Such fibers have various interesting features including good geometrical stability, low fundamental transmission losses, high Kerr nonlinearity, and large solubility of rare-earth ions. By investigating transmission mechanism, mode structure, and numerical aperture of the fibers and confronting the results with theoretical calculations we demonstrate that the fibers have optical properties similar to those observed in air-silica microstructured optical fibers. This makes the all-solid soft-glass microstructured fibers very attractive for many potential applications. Full Text: PDF References J. R. Hayes, J. C. Flanagan, T. M. Monro, D. J. Richardson, P. Grunewald, and R. Allott, "Square core jecketed air-clad fiber", Optics Express, 14(22):10345-10350, 2006 CrossRef N. A. Issa, "High numerical aperture in multimode microstructured optical fibers", Applied Optics, 43(33):6191-6197, 2004 CrossRef M. Antkowiak, R. Kotynski, T. Nasilowski, P. Lesiak, J. Wojcik, W. Urbanczyk, F. Berghmans, and H. Thienpont, "Phase and group modal birefringence of triple-defect photonic crystal fibres", Journal of Optics A: Pure and Applied Optics, 7(12):763, 2005 CrossRef W. Reeves, J. Knight, P. St. Russell, and P. Roberts, "Demonstration of ultra-flattened dispersion in photonic crystal fibers", Optics Express, 10(14):609-613, 2002 CrossRef C. Martelli, J. Canning, B. Gibson, and S. Huntington, "Bend loss in structured optical fibres", Optics Express, 15(26):17639-17644, 2007 CrossRef T. A. Birks, J. C. Knight, and P. St. Russell, "Endlessly single-mode photonic crystal fiber", Optics Letters, 22(13):961-963, 1997 CrossRef L. Rindorf, J. B. Jensen, M. Dufva, L. H. Pedersen, P. E. Hoiby, and O. Bang, "Photonic crystal fiber long-period gratings for biochemical sensing", Optics Express, 14(18):8224-8231, 2006 CrossRef R. Buczynski, D. Pysz, I. Kujawa, J. Korzeniowski, T. Martynkien. F. Berghmans, H. Thienpont, and R. Stepien, "Supercontinuum generation with microstructured fibers made of soft glass", Photonics Letters of Poland, 1(3):109-111, 2009 CrossRef M. Nielsen, C. Jacobsen, N. Mortensen, J. Folkenberg, and H. Simonsen, "Low-loss photonic crystal fibers for transmission systems and their dispersion properties", Optics Express, 12(7):1372-1376, 2004 CrossRef W. Wadsworth, R. Percival, G. Bouwmans, J. Knight, and P. Russell, "High power air-clad photonic crystal fibre laser", Optics Express, 11(1):48-53, 2003 CrossRef X. Feng, T. M. Monro, P. Petropoulos, V. Finazzi. and D. Hewak, "Solid microstructured optical fiber", Optics Express, 11(18):2225-2230, 2003 CrossRef R. Buczynski, I. Kujawa, R. Kasztelanic, D. Pysz, K. Borzycki, F. Berghmans, H. Thienpond, and R. Stepien, "Supercontinuum generation in all-solid photonic crystal fiber with low index core", Laser Physics, 22(4):784-790, 2012 CrossRef M. Grabka, S. Pustelny, P. Mergo, and W. Gawlik, "Application of continuous wavelet transform for determination of fiber birefringence", Optics Express, 20(13):13878-13885, 2012 CrossRef M. Grabka, B. Wajnchold, S. Pustelny, W. Gawlik, K. Skorupski, and P. Mergo, "Experimental and theoretical study of light propagation in suspended-core optical fibre", Acta Physica Polonica A, 118(6):1127-1132, 2010 DirectLink M. J. F. Digonnet, Hyang Kyun Kim, G. S. Kino, and Shanhui Fan, "Understanding Air-Core Photonic-Bandgap Fibers: Analogy to Conventional Fibers", Journal of Lightwave Technology, 23(12):4169-4177, 2005 CrossRef H. Ebendorff-Heidepriem, R. G. Moore, T. M. Monro, "Progress in the fabrication of the next-generation soft glass microstructured optical fibers", AIP Conference Proceedings, 1055(1):95-98, 2008 CrossRef

Ultrafast wavelength conversion via cross-phase modulation in hydrogenated amorphous silicon optical fibers

We present a characterization of the spectral modulation and wavelength shifting induced via cross-phase modulation (XPM) in a hydrogenated amorphous silicon (a-Si:H) core optical fiber. Pump-probe experiments using picosecond and femtosecond signal pulses are shown to be in good agreement with numerical simulations of the coupled nonlinear propagation equations. The large 10nm red-shifts obtained with the femtosecond probe pulses are attributed to the high Kerr nonlinearity of the a-Si:H material. Extinction ratios as high as 12 dB are measured for the conversion process at telecommunications wavelengths, indicating the potential for high-speed nonlinear optical control in a-Si:H fibers and waveguides.

Polarisation response of a gas medium in the field of a high-intensity ultrashort laser pulse: high order Kerr nonlinearities or plasma electron component?

The polarisation response of quantum systems modelling silver and xenon atoms in the field of a high-intensity femtosecond Ti : sapphire laser (photon energy ħω ≈ 1.5 eV), has been investigated by direct numerical integration of the Schrödinger equation. The applicability ranges of the perturbation theory and polarisation expansion in powers of field are determined. The contributions of excited atoms and electrons in the continuous-spectrum states to the polarisation response at the fundamental frequency, which arise as a result of excitation and photoionisation, are analysed. It is shown that specifically ionisation changes the sign of dielectric susceptibility with an increase in radiation intensity for the systems under consideration.

On the origin of the high Kerr coefficient measured in thallium–zinc–tellurite glasses

Measurements of Kerr electrooptical sensitivity of several zinc–thallium–tellurite glasses are presented, and composition dependence of Kerr sensitivity is compared with the dependence of the second harmonic generation efficiency collected for optically poled TeO2–TlO0.5–ZnO glasses. These data being analyzed jointly with Raman measurements data allowed us to conclude that the high electrooptical Kerr coefficient and nonlinearity of Tl2O–ZnO–TeO2 glasses, and their sharp increase with augmenting concentration of thallium oxide TlO0.5 above 15% should be attributed to the presence of Tl+ cations having very high non-linear polarizability most likely related to their electronic lone pairs.

Imaging the Kramers-Henneberger atom.

Today laser pulses with electric fields comparable to or higher than the electrostatic forces binding valence electrons in atoms and molecules have become a routine tool with applications in laser acceleration of electrons and ions, generation of short wavelength emission from plasmas and clusters, laser fusion, etc. Intense fields are also naturally created during laser filamentation in the air or due to local field enhancements in the vicinity of metal nanoparticles. One would expect that very intense fields would always lead to fast ionization of atoms or molecules. However, recently observed acceleration of neutral atoms [Eichmann et al. (2009) Nature 461:1261-1264] at the rate of 10(15) m/s(2) when exposed to very intense IR laser pulses demonstrated that substantial fraction of atoms remained stable during the pulse. Here we show that the electronic structure of these stable "laser-dressed" atoms can be directly imaged by photoelectron spectroscopy. Our findings open the way to visualizing and controlling bound electron dynamics in strong laser fields and reexamining its role in various strong-field processes, including microscopic description of high order Kerr nonlinearities and their role in laser filamentation [Béjot et al. (2010) Phys Rev Lett 104:103903].

Power and tuning characteristics of a broadly tunable femtosecond optical parametric oscillator based on periodically poled stoichiometric lithium tantalate

We report on power, tuning, and temporal characteristics of an optical parametric oscillator (OPO) based on a periodically poled stoichiometric lithium tantalate (PPSLT) crystal and pumped by a high-power mode-locked Ti:sapphire laser. Focus is given to the OPO operating range spanning from 900 to 1350 nm, which is important in nonlinear optical microscopy and spectroscopy. Generation of peak powers beyond the 10 kW level is strongly affected by the onset of intracavity power-dependent loss, which is due to the high ultrafast Kerr nonlinearity of the gain material. The crystal withstands combined power densities higher than 60 GW/cm2 for ∼100 fs optical pulses before breakdown occurs. A resonator design that mitigates self- and cross-beam focusing effects delivers ∼40 kW peak power for 85–160 fs pulses. The high parametric gain of the PPSLT allows OPO operation at the twelfth harmonic of the pump laser repetition rate (∼0.91 GHz). Stable operation with the possibility of broad wavelength tuning is demonstrated without active cavity length stabilization at a repetition rate of ∼530 MHz and average powers above 150 mW. In addition, up to 50 mW of power at ∼530 nm is output as a result of SHG of the 1060 nm signal beam resulting from third-order quasi phase matching.

Effect of self-phase modulation on the instabilities of quantum-cascade lasers

Theoretical analysis of lasing instability in quantum-cascade lasers was carried out. A mid-infrared quantum-cascade laser structure with triple resonance levels was chosen as the prototype of the lasing medium with high Kerr nonlinearity from optical transitions. The self-phase modulation effect induced by Kerr nonlinearity was found to possibly change the unstable frequency domain significantly, i.e., not only broaden the unstable domain but also drive it from single-mode to multi-mode. The instability mechanisms of quantum-cascade lasers include one like the coherent multi-mode Rishen-Nummedal-Graham-Haken instability and the spatial-hole-burning-induced single-mode instability.