Optical Power Limiting Research Articles

Optical bistability via an external control field in all-fiber ring cavity

We demonstrate a new scheme for realizing the Optical Bistability (OB) inside an all-fiber ring cavity with an external control field. In the absence of the external control field, the pump power is fixed below the threshold value of laser, and there is no laser in the cavity. However, when the control signal of 1505 nm to 1520 nm is injected into the cavity, laser begins to oscillate and OB appears. We found that the wavelength and power of the control signal can affect the OB behavior dramatically, which can be used to manipulate efficiently the threshold intensity and the hysteresis loop. We also give an explanation of the bistability phenomenon based on numerical simulations, which are agreed very well with our experimental results. Our scheme may provide some new possibilities for technological applications in optical power limiters, switches or memories.

Optical and laser damage threshold studies on 1, 3, 5-triphenylbenzene scintillator crystal grown by Sankaranarayanan-Ramasamy (SR) technique

Unidirectional (<200> plane) 1, 3, 5-triphenylbenzene (3PB) single crystal 150mm long and 25mm diameter was grown by SR technique. The grown crystal was subjected to UV–vis-NIR spectral analysis determine linear optical properties over the range of 200–1100nm. The relevant optical parameters such as transmittance, absorption coefficient, extinction coefficient, band gap energy, reflectance, and refractive index were determined which reveal the suitability of crystal to couple with a photomultiplier tube or other light sensor. The wide band gap energy 3.65eV of the 3PB crystal shows significant transmittance in the Vis and NIR region. The refractive index of the crystal is determined to be constant above 350nm, and it confirms the required parameter to set high light yield. The temperature dependence refractive index was measured in the range of 30–70°C, it illustrates the faster propagation light in the crystal. Third order nonlinear optical parameters of the grown crystal were estimated by Z-scan technique. It showed that the low absorption coefficient and negative refractive index. The second order hyperpolarizability (γ) of 3PB molecule was found to be 8.6411×10−34 esu. The obtained all results in the present work which makes the 3PB crystal promising candidate for optical power limits, optical switching and other nonlinear optical applications. The Laser Damage Threshold (LDT) was determined to be 2.1612 GW/cm2 and it confirms the suitability of crystal for device fabrication.

Functionalized tetrafluorenylethylene-type chromophores: Synthesis, two-photon absorption and effective optical power-limiting properties in the visible-to-near IR region

A series of novel multipolar fluorophores based on tetra-substituted olefinic scaffold using functionalized fluorenyl and indenofluorenyl units as the aryl substituents has been synthesized and investigated for their two-photon-related properties in the femtosecond and nanosecond time domains. When probed by the femtosecond pulses, these chromophores are found to possess appreciable intrinsic two-photon absorptivities with their local maxima very close to the short-wavelength end of the dynamic tuning range of a Ti: sapphire laser. While under the irradiation of nanosecond pulses, these dye molecules exhibit promising nonlinear optical-power-attenuation properties across the visible-to-near infrared region. Combining with their medium-high fluorescence quantum efficiencies, such archetype represents a new class of structures that could be utilized as effective broadband optical power-limiters and frequency up-converters especially with great potentiality to work in the visible regime.

Multiple omnidirectional defect modes and nonlinear magnetic-field effects in metamaterial photonic superlattices with a polaritonic defect

We report the existence of multiple omnidirectional defect modes in the zero-n¯ gap of photonic stacks, made of alternate layers of conventional dielectric and double-negative metamaterial, with a polaritonic defect layer. In the case of nonlinear magnetic metamaterials, the optical bistability phenomenon leads to switching from negligible to perfect transmission around these defect modes. We hope these findings have potential applications in the design and development of multichannel optical filters, power limiters, optical-diodes and optical-transistors.

Synthesis and multi-photon absorption properties of symmetric bisarylacetylene chromophores using functionalized isomeric pyrazinoindenocarbazole units as the rigid aryl substituents

A pair of isomeric chromophores based on the skeleton of bisarylacetylene using functionalized pyrazinoindenocarbazole moieties as the aryl substituents has been synthesized and characterized for their two- and three-photon-related properties in the femtosecond and nanosecond regimes. Our experiments have found that both model fluorophores manifest strong two-photon absorption in the near infrared region with one of the isomers exhibiting superior maximum two-photon absorptivity. It is realized that both the isomeric forms of functionalized pyrazinoindenocarbazoles are useful π-units for the construction of highly two-photon active materials but the effectiveness of the units is unequal, which is probably attributed to the difference of their conjugated structures. Two-photon-based optical power-limiting and stabilization against nanosecond laser pulses of one isomer was demonstrated. Additionally, these two chromophores exhibit strong three-photon-induced fluorescence when excited by the nanosecond laser with longer wavelengths (≥1000 nm), implying their potential utility to serve as prototypes for the development of three-photon materials.

Link Design and Legacy Amplifier Limitation in Flex-Grid Optical Networks

Flex-grid technology is an effective means to improve the spectral efficiency of optical communication. For a given amplifier spectral bandwidth, it gives rise to the increase in the number of optical channels as it reduces channel spacing. Therefore, in order to reap full benefits from the flex-grid saved spectrum, further amplification power is required with respect to conventional fixed grid. This is a strong limitation if the legacy amplifiers cannot meet this new requirement due to their optical power limits. In this paper, we demonstrate that exploiting the link margins allows the support of this increase while maintaining in use legacy amplifiers.

Photophysical and optical power limiting behaviors of Au(I) acetylides with diethynyl aromatic ligands showing different electronic features

Three Au(I) acetylides have been prepared by coupling (PPh3)AuCl to the diethynyl aromatic ligands with different electronic features under mild condition. Their photophysical properties and optical power limiting (OPL) behaviors have been investigated in detail. The emission characters of the Au(I) acetylides can vary dramatically by exhibiting either singlet or triplet emission signal through changing the chemical structures of the diethynyl aromatic ligands. In addition, the OPL behaviors of the Au(I) acetylides are also affected by the diethynyl aromatic ligands to show different OPL mechanism. It has been shown that the diethynyl aromatic ligand with neither electron-rich nor electron-deficient features should benefit the OPL performance of the Au(I) acetylides in view of both OPL activity and transparency. Furthermore, the Au(I) acetylides can show comparable or even better OPL performances than the state-of-the-art C60, indicating their great potential in the field of laser protection. All the obtained results should provide valuable information for design high performance OPL materials based on Au(I) acetylides.

Synthesis, growth, structural and HOMO and LUMO, MEP analysis of a new stilbazolium derivative crystal: A enhanced third-order NLO properties with a high laser-induced damage threshold for NLO applications

A new organic third-order nonlinear optical crystal from stilbazolium family 2-[2-(4-methoxy-phenyl) vinyl]-1-methyl-pyridinium tetrafluoroborate (4MSTB) has been synthesized and grown by slow evaporation method for the first time. The grown crystal structure was confirmed by single crystal X-ray diffraction analysis, and it is revealed that the grown crystal crystallized in a triclinic crystal system with centrosymmetric space group P1¯. The HOMO and LUMO energies were calculated for the grown crystal explains charge transfer takes place within the molecule and confirms the suitability of the title crystal for NLO applications. The presence of various vibration modes of expected functional groups was identified by FT-IR analysis. The transmittance ability of the grown crystal was also analyzed by using UV–Vis–NIR spectral studies and shows that the crystal has no absorption of light in the entire Vis–NIR region. The thermal stability of the title crystal has been investigated by TGA/DTA studies and revealed that the material was thermally stable up to the melting point, 193°C. The hardness number, Meyer index, yield strength, and elastic stiffness constant has been estimated for the grown 4MSTB crystal using Vickers microhardness tester. Photoluminescence excitation studies showed green emission radiation occurred at 517nm. The dielectric properties of the grown crystal have been analyzed as a function of temperature over a wide range of frequency (50Hz–5MHz) by using LCR meter. The result of ac electrical conductivity of 4MSTB was found to be 5.25×10−5 (Ωm)−1. The laser damage threshold (LDT) energy for the grown crystal has been measured by using a Q-switched Nd:YAG laser as a source in single-shot mode (1064nm, 10Hz, 420mJ). The result of LDT indicates that grown title crystal has excellent resistance to laser radiation than those of known some inorganic NLO materials. The chemical etching studies were carried out to assess the perfection of the grown crystals. Its third-order nonlinear optical properties were investigated by Z-scan technique and proved that the 4MSTB crystal possesses two-photon absorptions (TPA) and the self-defocusing effect. The second-order molecular hyperpolarizability (γ) value at 632.8nm is calculated to be 3.555×10−34esu. The photoconductivity study of 4MSTB reveals that the negative photoconducting nature. The obtained all the results in the present work are making a 4MSTB promising candidate for the possible applications in optical switches, optical power limiter, and non-linear optical applications.

Synthesis and two-photon absorption properties of truxene-cored chromophores with functionalized pyrazine units fused as the end-groups

A new set of model chromophores derived from a truxene core fused with varied number and size of functionalized pyrazine units was designed and synthesized for the tentative exploration of possible connections between the molecular structure and their linear/nonlinear optical properties. The initial experimental results have indicated that these model compounds not only possess strong and widely dispersed two-photon absorption (2 PA) within the near-IR region but also show the ascending overall 2 PA when the molecular structure varies with increase in complexity and molecular weight, which implies that both the number of branches and the size of π-framework are important factors to the molecular 2 PA in this model chromophore system. On the other hand, the studied model chromophores also manifest very good photostability within their two-photon active spectral region even under a prolonged irradiation of IR laser pulses. In addition, a representative chromophore is selected to demonstrate optical power-limiting and power-stabilization performance against nanosecond laser pulses.

Chip-integrated optical power limiter based on an all-passive micro-ring resonator.

Recent progress in silicon nanophotonics has dramatically advanced the possible realization of large-scale on-chip optical interconnects integration. Adopting photons as information carriers can break the performance bottleneck of electronic integrated circuit such as serious thermal losses and poor process rates. However, in integrated photonics circuits, few reported work can impose an upper limit of optical power therefore prevent the optical device from harm caused by high power. In this study, we experimentally demonstrate a feasible integrated scheme based on a single all-passive micro-ring resonator to realize the optical power limitation which has a similar function of current limiting circuit in electronics. Besides, we analyze the performance of optical power limiter at various signal bit rates. The results show that the proposed device can limit the signal power effectively at a bit rate up to 20 Gbit/s without deteriorating the signal. Meanwhile, this ultra-compact silicon device can be completely compatible with the electronic technology (typically complementary metal-oxide semiconductor technology), which may pave the way of very large scale integrated photonic circuits for all-optical information processors and artificial intelligence systems.

Synthesis, spectral and third-order nonlinear optical properties of terpyridine Zn(II) complexes based on carbazole derivative with polyether group

Four novel Zn(II) terpyridine complexes (ZnLCl2, ZnLBr2, ZnLI2, ZnL(SCN)2) based on carbazole derivative group were designed, synthesized and fully characterized. Their photophysical properties including absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limiting (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations (TD-DFT). The influences of different solvents on the absorption and One-Photon Excited Fluorescence (OPEF) spectral behavior, quantum yields and the lifetime of the chromophores have been investigated in detail. The third-order nonlinear optical (NLO) properties were investigated by open/closed aperture Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080nm. These results revealed that ZnLCl2 and ZnLBr2 exhibited strong two-photon absorption and ZnLCl2 showed superior optical power limiting property.

Effect of laser-radiation polarization on the nonlinear scattering of light in nanodiamond suspensions

The effect of laser radiation polarization on the nonlinear scattering of light in aqueous suspensions of detonation nanodiamonds (DNDs) in a regime of optical power limiting (OPL) has been studied. It is established that the nonlinear transmission coefficient of DND suspension in the OPL regime in a field of nanosecond laser pulses with a wavelength of 532 nm is independent of the polarization of incident radiation. The nonlinear scattering of light observed at an angle of 90° in the plane perpendicular to the plane of polarization of the incident radiation depends on the polarization angle in accordance with a trigonometric law. It is shown that the ratio of the signals of scattered radiation for the vertical and horizontal polarizations exhibits nonmonotonic dependence on the laser-beam power density. The results are explained by the Rayleigh-Mie scattering and a change in the size of scattering centers as a result of the effect of a laser upon the DND suspension.

Third-order nonlinear optical studies of anthraquinone dyes using a CW He–Ne laser

We present investigations on the third-order optical nonlinearity and optical power limiting of anthraquinone dyes. Z-scan measurements were performed using a continuous wave He–Ne laser at 633 nm wavelength as an excitation source. The nonlinear refraction studies exhibited self-defocusing behavior of the dyes. The nonlinear absorption in the dyes was dominated by a reverse saturable absorption process. Self-diffraction ring patterns were observed due to the change in refractive index and thermal lensing. Increase of the electron donating ability of the substituents resulted in enhanced values of the nonlinear optical parameters, establishing the structure–property relationship. The optical limiting study revealed that the dyes possess a lower limiting threshold and clamping level which is very important for eye and sensor protection. Hence, the dyes investigated here emerge as promising candidates for future opto-electronic and photonic device applications such as optical power limiters.

Effect of conjugation length on nonlinear optical parameters of anthraquinone dyes investigated using He–Ne laser operating in CW mode

Abstract We report the studies on third-order optical nonlinearity and optical limiting of anthraquinone dyes. Z-scan technique was employed to evaluate the nonlinear parameters such as nonlinear absorption coefficient βeff and nonlinear index of refraction n2. Continuous wave He–Ne laser was used as the source of excitation. The estimated values of βeff, n2 and χ(3) are of the order of 10−3 cm/W, 10−5 esu and 10−7 esu respectively. The presence of donor and acceptor groups in the structure results in increase in conjugation length. This resulted in the enhancement of nonlinear optical parameters values of the dye. Multiple diffraction rings were observed when the samples were exposed to laser beam due to thermal lensing. Dyes exhibited good optical limiting behavior under the experimental conditions. The results indicate that the dyes investigated here are materialise as candidates for photonics device applications such as optical power limiters.

Structural, photoinduced optical effects and third-order nonlinear optical studies on Mn doped and Mn–Al codoped ZnO thin films under continuous wave laser irradiation

We report the photoinduced optical effects, third-order nonlinearity, and optical power limiting of Mn doped and Mn–Al codoped ZnO thin films. The thin films were prepared by the spray pyrolysis technique. The structural properties of the deposited films were examined by x-ray diffraction studies. Z-scan measurements were conducted to evaluate the nonlinear optical parameters using a He–Ne laser operating in continuous wave mode at 633 nm wavelength. The present study reveals that the introduction of Mn and Mn–Al into ZnO leads to significant changes in the third-order nonlinear susceptibility. Photoinduced second-harmonic generation studies also reveal the dependence of the nonlinear optical properties on the Mn content. Switching over from saturable absorption to reverse saturable absorption was observed. The optical limiting studies show that the films possess a lower limiting threshold and clamping level, which is essential for use in eye and sensor protection applications. Hence, the Mn doped and Mn–Al codoped ZnO thin films investigated here emerge as promising candidates for future optoelectronic and photonic device applications such as optical power limiters.

Synthesis, crystal structures and third-order nonlinear optical properties in the near-IR range of two novel Ni(II) complexes

Two novel Nickel(II) complexes (NiL21 and NiL22) with remarkable two-photon absorption (TPA) and optical power limiting (OPL) properties were synthesized and fully characterized. Single crystals were obtained and solved by X-ray diffraction analysis. Their photophysical properties had been further investigated both experimentally and theoretically. The third-order nonlinear optical (NLO) properties (TPA and OPL) were investigated by open/closed aperture Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080nm. The results revealed that the two Nickel(II) complexes exhibited strong two-photon absorption and superior optical power limiting properties, which are much better than that of the free ligands.

Third-Order Nonlinear Optical, Optical Power Limiting, and All-Optical Switching Studies on Palladium Complexes

The authors report the third-order nonlinear optical properties of two palladium complexes in solution and film form using nanosecond Z-scan technique at 532 nm. The nonlinear refractive index n2 of the investigated complexes is found to be negative. Both complexes exhibit strong reverse saturation absorption and show good optical power limiting of nanosecond pulses. Also the third-order nonlinear optical susceptibility of the complexes was determined using degenerate four-wave mixing technique. The variations of nonlinear response on donor and acceptor type of units present in the complexes are studied. The all-optical switching phenomenon was also demonstrated by using nanosecond pump-probe technique.

Azo doped polymer thin films for active and passive optical power limiting applications

Two novel optical power limiters, 2-[ethyl-(4-phenylazo-phenyl)-amino]-ethanol (E4PA) and 2-[ethyl-(4-trifluoromethyl-phenylazo-phenyl)-amino]-ethanol (E4TPA) were synthesized using a diazotization reaction. The purified azo material was made into thin films in a poly(methyl methacrylate) matrix using a gravity settling technique. The electronic nonlinearities of these films were investigated using an open aperture Z-scan technique in the fs excitation regime, resulting in nonlinear absorption due to a two-photon absorption (2PA) process. The 2PA coefficient for these films is of the order 10(-12) m W(-1) and the limiting threshold values are 1.1 J cm(-2) each. A non-degenerate pump probe set-up was employed with CW lasers to study the nonlinear behaviour arising from photo-induced anisotropy and excited-state absorption. The present study shows that these azo thin films are potential candidates for active and passive optical power limiting applications.

Nonlinear optical and all-optical switching studies of palladium(II) complex

Palladium complex with Schiff-base (PdL) was synthesized and composite films were fabricated on glass substrates by the spin coating technique. Z-scan and degenerate four wave mixing (DFWM) studies on the complex were performed using Q-switched Nd:YAG 7ns laser pulses at 532nm to reveal the third-order nonlinear optical (NLO) parameters. The third-order NLO susceptibility (χ(3)) and second-order hyperpolarizability (γh) in film form are estimated to be of the order of 10−11 and 10−30esu respectively. Large nonlinear absorption (NLA) due to reverse-saturable absorption (RSA) in the complex exhibits good optical power limiting (OPL) performance. All-optical switching (AOS) experiments were performed using the pump-probe method. The Z-scan investigations reveal that the switching is caused by excited-state absorption (ESA) of the He-Ne laser.

The effect of the size factor of nanodiamonds in suspensions on optical power limiting and nonlinear laser light scattering

The results of experimental studies of optical power limiting (OPL) and nonlinear light scattering (NLS) at a wavelength of 532 nm in suspensions of detonation-synthesis modified nanodiamonds (MNDs) with different grain-size compositions are described. It is found that, at the same nanoparticle concentration, OPL and NLS are more efficient in suspensions with large MNDs. It is shown that MND suspensions can exhibit a stable long-term operation as OPL in a field of laser pulses with a power density of 0.2 GW/cm2 at a repetition frequency of 1 Hz.