Optical Power Limiting Research Articles

Optical power limiter in the femtosecond filamentation regime

We present the use of a power limiting apparatus to evaluate ultrafast optical nonlinearities of transparent liquids (water and ethanol) in the femtosecond filamentation regime. The setup has been previously employed for the same purpose, however, in a longer pulsewidth (> 20 ps) regime, which leads to an ambiguous evaluation of the critical power for self-focusing. The uncertainty originates from the existence of a threshold power for optical breakdown well below the critical power for self-focusing within this timeframe. Contrarily, using the proposed apparatus in the femtosecond regime, we observe for the first time a unique optical response, which features the underlying physics of laser filamentation. Importantly, we demonstrate a dependence of the optical transmission of the power limiter on its geometrical, imaging characteristics and the conditions under which a distinct demarcation for the critical power for self-focusing can be determined. The result is supported by numerical simulations, which indicate that the features of the observed power-dependent optical response of the power limiting setup are physically related to the spontaneous transformation of the laser pulses into nonlinear conical waves.

Securing Practical Quantum Communication Systems with Optical Power Limiters

Controlling the energy of unauthorized light signals in a quantum cryptosystem is an essential criterion for implementation security. Here, we propose a passive optical power limiter device based on thermo-optical defocusing effects providing a reliable power limiting threshold which can be readily adjusted to suit various quantum applications. In addition, the device is robust against a wide variety of signal variations (e.g. wavelength, pulse width), which is important for implementation security. Moreover, we experimentally show that the proposed device does not compromise quantum communication signals, in that it has only a very minimal impact (if not, negligible impact) on the intensity, phase, or polarization degrees of freedom of the photon, thus making it suitable for general communication purposes. To show its practical utility for quantum cryptography, we demonstrate and discuss three potential applications: (1) measurement-device-independent quantum key distribution with enhanced security against a general class of Trojan-horse attacks, (2) using the power limiter as a countermeasure against bright illumination attacks, and (3) the application of power limiters to potentially enhance the implementation security of plug-and-play quantum key distribution.

Ultrafast optical switching and power limiting in intersubband polaritonic metasurfaces

Highly nonlinear optical materials with fast third-order nonlinear optical response are crucial for the operation of all-optical photonic devices, such as switches for signal processing and computation, power limiters, and saturable absorbers. The nonlinear response of traditional optical materials is weak, thus requiring large light intensities to induce significant changes in their properties. Here we show that optical control of the coupling rate in subwavelength patch antennas coupled to intersubband transitions in multi-quantum-well semiconductor heterostructures can provide a giant third-order nonlinear response, on the order of 3.4 × 10 − 13 m 2 / V 2 , with a response time < 2 p s . We utilize this effect to realize intersubband polaritonic metasurfaces and demonstrate their operation as highly nonlinear saturable and reverse saturable absorbers, enabling optical power limiters and other elements for all-optical modulation and control. Our approach enables a plethora of compact, low-power, highly nonlinear devices with spectral, temporal, and structured wavefront responses tailored by design.

Enhanced Two–Photon Absorption and Promising Broad Energy Range Optical Power Limiting Properties ofTransoidandCisoidBenzodipyrrolenine-Fused Squaraine Dimers

Molecular symmetry is a decisive factor for the two-photon absorption (2PA) properties of an organic chromophore. In order to explore its impact on the 2PA cross section of squaraine dyes, we synthesized two isomers in which two indolenine squaraines are fused by two different benzodipyrrolenine bridges leading to either a chromophore with C2h symmetry or with C2v symmetry. The excited states of these two chromophores were characterized by steady-state one-photon absorption spectroscopy, one-photon fluorescence excitation anisotropy, and 2PA-induced fluorescence spectroscopy in comparison with the time-dependent and quadratic response density functional theory. Both chromophores show strong absorption and emission in the near infrared spectral region. While the C2v symmetric chromophore displays significant 2PA cross sections over the entire manifold of excited states, the C2h symmetric chromophore shows the expected symmetry selection for totally symmetric and asymmetric excited states. In this chromophore, the 2PA cross section reaches extremely high values of ca. 14,000 GM at 16,000 cm–1 and 90,000 GM at 22,000 cm–1, which are among the highest reported for organic chromophores to date. The C2h symmetric chromophore could accordingly be used as an efficient optical power limiter both in solution and as a film in the polystyrene matrix throughout the excited-state manifold.

High-Performance Optical Power Limiting Filters at Telecommunication Wavelengths: When Aza-BODIPY Dyes Bond to Sol–Gel Materials

An optical power limiter (OPL) device can change its optical properties depending on the input light intensity: it is ideally transparent at low incident power and presents a decrease in transmissi...

Cyclometalated Pt(II) complexes with tetradentate Schiff base ligands: Synthesis, photophysics, electrochemical studies and optical power limiting performance

Pt(II) complexes with tetradentate Schiff base ligands (Pt-1–Pt-5) were prepared, and their detailed photophysics were studied using steady-state, transient spectroscopies and density functional theory systematically. Pt-1–Pt-5 all exhibit 1π,π* transitions and metal-to-ligand/intraligand charge transfer transitions in the UV–vis region. Meanwhile, these complexes are emissive in solution at room temperature (λem = 400–800 nm, Φem = 0.008–0.196). Triplet transient absorption (TA) demonstrated that except Pt-3, all complexes exhibit broad and strong triplet excited-state absorption from 400 to 750 nm. What's more, nonlinear transmission experiment demonstrated that Pt-1–Pt-5 show robust reverse saturable absorption (RSA) at 532 nm ns laser pulses. Among them, Pt-5 shows the strongest nonlinear absorption performance, which could potentially be used as optical power limiting (OPL) materials.

Enhanced and tunable nonlinear optical responses of nitrogen-doped nickel oxide induced by femtosecond laser excitation

In this work, we report the impact of nitrogen (N) doping in nickel oxide films on nonlinear optical responses (NORs) utilizing 532 nm, 330 fs laser pulses with both linear and radial polarization states. The pristine and N-doped NiO films are grown through radio frequency magnetron sputtering technique and further characterized by AFM, UV–Vis transmittance spectra and XPS. The experimental results demonstrate that NORs, including reverse saturable absorption and optical Kerr refraction, of the as-prepared NiO films along with their optical power limiting (OPL) are intimately related to the N doping and the laser polarization patterns. More specifically, both the NORs and OPL increase scalingly with the doping concentration under the linearly polarized laser excitation. The strongest optical nonlinear absorption coefficient, optical nonlinear refraction index and OPL efficiency are in turn determined to be 4.55 × 10−7 m/W, 6.5 × 10−16 m2/W and 50% for the heaviest N-implanted NiO film. In a sharp contrast, for the raidally polarized beam impinging onto the pristine and doped NiO films, the NORs and OPL initially drop off and then strengthen together as the increases of N-implanted content. Such enhanced and tunable NORs are due to the fact that the involvement of doping state gives rise to promoted optical transitions originating from the narrowing of band gap, as well as the use of ultrafast vectorial laser induces anisotropic nonlinearity and intricate light-matter interplay. Our results will open a new perspective to develop optical power limiter and ultrafast photonic devices.

Enhanced nonlinear instabilities in photonic circuits with exceptional point degeneracies

We propose a conceptual design of optical power limiters with abrupt limiting action and enhanced power-handling capabilities that is based on exceptional point degeneracies (EPDs). The photonic circuit consists of two coupled cavities with differential Q factors. One of the cavities includes a Kerr-like nonlinear material. The underlying mechanism that triggers an abrupt transmittance suppression relies on the interplay between a nonlinear instability and an abrupt destruction of EPDs due to a resonance detuning occurring when the incident power exceeds a critical value. Our proposal opens up possibilities for the use of EPDs in optical power switching, Q switching, routing, and so on.

OE-CAM: A Hybrid Opto-Electronic Content Addressable Memory

A content addressable memory (CAM) is a type of memory that implements a parallel search engine at its core. A CAM takes as an input a value and outputs the address where this value is stored in case of a match. CAMs are used in a wide range of applications including networking, cashing, neuromorphic associative memories, multimedia, and data analytics. Here, we introduce a novel opto-electronic CAM (OE-CAM) utilizing the integrated silicon photonic platform. In our approach, we explore the performance of an experimental OE-CAM and verify the efficiency of the device at 25 Gbit/s while maintaining the bit integrity under noise conditions. We show that OE-CAM enables a) two orders of magnitude faster search functionality resulting in b) a five orders of magnitude lower power-delay-product compared to CAMs implementations based on other emerging technologies. This remarkable performance potential is achieved by utilizing i) a high parallelism of wavelength-division-multiplexing in the optical domain, combined with ii) 10's of GHz-fast opto-electronic components, packaged in iii) integrated photonics for 10–100's ps-short communication delays. We further verify the upper optical input power limit of this OE-CAM to be given by parasitic nonlinearities inside the silicon waveguides, and the minimal detectable optical power at the back-end photoreceiver's responsivity given channel noise. Such energy-efficient and short-delay OE-CAMs could become a key component of functional photonic-augmented ASICS, co-processors, or smart sensors.

Observation of Stimulated Brillouin Scattering in Silicon Nitride Integrated Waveguides.

Silicon nitride (Si_{3}N_{4}) has emerged as a promising material for integrated nonlinear photonics and has been used for broadband soliton microcombs and low-pulse-energy supercontinuum generation. Therefore, understanding all nonlinear optical properties of Si_{3}N_{4} is important. So far, only stimulated Brillouin scattering (SBS) has not yet been reported. Here we observe, for the first time, backward SBS in fully cladded Si_{3}N_{4} waveguides. The Brillouin gain spectrum exhibits an unusual multipeak structure resulting from hybridization with high-overtone bulk acoustic resonances of the silica cladding. The reported intrinsic Si_{3}N_{4} Brillouin gain at 25GHz is estimated as 4×10^{-13} m/W. Moreover, the magnitude of the Si_{3}N_{4} photoelastic constant is estimated as |p_{12}|=0.047±0.004, which is nearly 6 times smaller than for silica. Since SBS imposes an optical power limitation for waveguides, our results explain the capability of Si_{3}N_{4} to handle high optical power, central for integrated nonlinear photonics.

Optimization of growth parameters and investigations on the physico-chemical properties of an organometallic guanidinium chromate single crystal for nonlinear optical and optical limiting applications

Guanidinium chromate, a semi- organic nonlinear optical crystal has been successfully synthesized and grown adopting solvent evaporation method using deionized water as solvent at a constant temperature. Solubility of the synthesized guanidinium chromate crystal was experimentally tested using various solvents at different temperatures and solubility data was determined from deionized water, as the solute dissolved completely only in water solvent. In addition, metastable zone width and induction period values were determined in order to optimize the growth parameters. Single crystal X-ray diffraction study confirmed the crystal structure and lattice parameters of the grown crystal. The presence of expected functional groups of the titular material was identified by FT-IR spectroscopic study. The optical transmittance spectrum of guanidinium chromate has been recorded using UV–vis–NIR spectral analysis and its linear optical constants such as the absorption coefficient, band gap, extinction coefficient, refractive index and electrical susceptibility have been calculated. The thermal analysis assessed by TG-DTA reveals that the title compound is thermally stable up to 184 °C. Nd: YAG laser (1064 nm) was utilized to find out the laser damage threshold of the grown crystal. The third order nonlinear optical property of the title crystal was investigated in detail by Z-scan technique using Nd:YAG laser at 532 nm. The encouraging result of the Z-scan studies confirms that the title crystal might serve as a possible candidate for applications such as photonic devices, optical switches and optical power limiters. Optical limiting study reveals that the transmitted output energy step-up linearly with respect to the increasing input energy at lower power realms and deviation of linearity is observed beyond the saturation point.

Third-order optical nonlinearity of the CuCo0.5Ti0.5O2 nanostructure under 120 fs laser irradiation.

Recently, titanium-based nanostructures with high nonlinear optical properties have found use in ultrafast photonic system applications. Here, we report a study of the third-order nonlinear optical property of the ${{\rm CuCo}_{0.5}}{{\rm Ti}_{0.5}}{{\rm O}_2}$CuCo0.5Ti0.5O2 (CCoTO) nanostructure synthesized via a simple chemical route. The 40-70 nm CCoTO nanoparticles with centrosymmetric crystalline structure show strong absorption in the 325-850 nm wavelength range due to the presence of different crystalline phases and surface vacancies. A Z-scan technique is used to study the electronic third-order nonlinearity of the synthesized nanoparticles, where a low-repetition-rate 120 fs laser source is employed to minimize thermal agitation-related nonlinearity. The CCoTO nanoparticles possess high surface defects due to oxygen- and copper-related vacancies, which are able to enhance the exciton oscillator strength resulting from the high value of third-order optical nonlinearity. The estimated values of nonlinear refractive index (${n_2}$n2) and nonlinear absorption coefficient ($\beta $β) of the CCoTO are $ - {1.24}\; \times \;{{10}^{ - 15}}$-1.24×10-15 and ${3.79} \times {{10}^{ - 11}}$3.79×10-11, respectively, under ${188}\,\,{{\rm GW/cm}^2}$188GW/cm2 incident intensity. The intensity-dependent nonlinear optical property of the synthesized nanoparticles is also studied under different incident laser irradiation (62.7, 93, and ${188}\,\,{{\rm GW/cm}^2}$188GW/cm2). In the two-photon absorption (TPA)-dominated third-order nonlinear optical process, the values of ${n_2}$n2 and $\beta $β of CCoTO are increased with intensifying the incident laser irradiation. The obtained high value of third-order optical nonlinearity of the synthesized nanostructure can be exploited in optical power limiters, pulse power reshaping, and optical switching applications.

An Optical Power Limiting and Ultrafast Photophysics Investigation of a Series of Multi-Branched Heavy Atom Substituted Fluorene Molecules

A common molecular design paradigm for optical power limiting (OPL) applications is to introduce heavy atoms that promote intersystem crossing and triplet excited states. In order to investigate this effect, three multi-branched fluorene molecules were prepared where the central moiety was either an organic benzene unit, para-dibromobenzene, or a platinum(II)–alkynyl unit. All three molecules showed good nanosecond OPL performance in solution. However, only the dibromobenzene and Pt–alkynyl compounds showed strong microsecond triplet excited state absorption (ESA). To investigate the photophysical cause of the OPL, especially for the fully organic molecule, photokinetic measurements including ultrafast pump–probe spectroscopy were performed. At nanosecond timescales, the ESA of the organic molecule was larger than the two with intersystem crossing (ISC) promoters, explaining its good OPL performance. This points to a design strategy where the singlet-state ESA is balanced with the ISC rate to increase OPL performance at the beginning of a nanosecond pulse.

Unraveling the Two-Photon and Excited-State Absorptions of Aza-BODIPY Dyes for Optical Power Limiting in the SWIR Band

We describe the linear and nonlinear optical properties of substituted aza-boron-dipyrromethene (aza-BODIPY) dyes with a focus on the impact of the spatial position and electronic nature of the sub...

Photophysical properties and optical power limiting ability of Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at different positions

Two series of Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at different positions have been synthesized. In the absorption spectra, the Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at 3,6-position have blue-shift with respect to the corresponding analogs bearing fluorene-type ligands with ethynyl units at 2,7-position, showing better transparency in the visible light region. Moreover, the Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at 3,6-position show stronger triplet emission than corresponding analogs bearing fluorene-type ligands with ethynyl units at 2,7-position in the photoluminescent (PL) spectra. Furthermore, these Pt(II) polyynes were applied to optical power limiting (OPL) field. The Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at 2,7-position show better OPL performance than the corresponding analogs with fluorene-type ligands of ethynyl units at 3,6-position. Therefore, changing the position of the ethynyl units in fluorene-type ligands can not only effectively control the photophysical properties of the Pt(II) polyynes, but also has an important effect on their OPL ability.

Role of Ba in engineering band gap, photoluminescence and nonlinear optical properties of SnO2 nanostructures for photovoltaic and photocatalytic applications

In this article, we present the role of Ba doping in tuning energy gap, photoluminescence (PL) and third-order optical nonlinearity χ(3) of SnO2 nanostructures. Surface morphology analysis indicates the fragmentation of larger grains upon Ba incorporation possibly caused by the lattice mismatch effects. X-ray diffraction reveals polycrystalline nature of the nanostructures with rutile tetragonal structure. A shift in preferential growth orientation plane (200, 211, 110) has been observed with increase in Ba concentration. PL spectroscopy studies confirms the crystallinity of the films ruling out the presence of Sn interstitials. The green luminescent center at 550 nm and trap emission at 578 nm are attributed to singly ionized charge state of the oxygen and defect levels in band gap. Relatively large change in the band gap (3.64 eV −3.13 eV) arises due to Ba doping points the credibility of SnO2 thin films for use in photovoltaic and photocatalytic applications. Third-optical nonlinearity of the films investigated by Z-scan technique shows χ(3) as high as 3.37 × 10−3 esu indicating the suitability of SnO2 nanostructures in nonlinear optical (NLO) devices such as optical power limiters and switches.

Facile hydrothermal synthesis of CdFe2O4-reduced graphene oxide nanocomposites and their third-order nonlinear optical properties under CW excitation

Third-order nonlinear optical response of cadmium ferrite loaded upon various content of reduced graphene oxide was studied by single beam Z-scan technique using Nd: YAG laser (532nm, 50mW). In XRD disappearance of characteristic peak of graphene oxide (10.7°, (100)) and appearance of peaks of reduced graphene oxide (23.3°, (002)) along with cadmium ferrite (34.2°, (311)) confirms the trimming of CdFe2O4 upon rGO. Further the successful trimming of rGO with CdFe2O4 was further evidenced by FTIR and high-resolution C 1s XPS. FESEM and TEM image of GO show folded sheets of graphene layers due to strong oxidation and reduction process. And pure CdFe2O4 grow themselves as nanorods which upon trimming on the surface of graphene sheets suffered a morphological change with respect to the content of graphene oxide (rods to platelets). Absorption spectra of decorated composites possess, absorption peaks at 230nm (π-π* transition in aromatic CC), 292nm (n-π* transition in CO bonds) and 425nm (cadmium ferrite). Z-scan results showed that both pure and decorated samples showed saturable absorption and self-defocusing behavior along with optical limiting action. Also the nonlinear refraction was found to be more dominant than nonlinear absorption due to strong contribution arising from thermal components. Upon trimming, the nonlinear refractive index (10−8cm2/W), nonlinear absorption coefficient (10−3cm/W) and third-order nonlinear optical susceptibility (10−6esu) were found to be increasing with increase in graphene content. Variation in the distribution and morphology of CdFe2O4 has resulted in the tunability of third-order NLO coefficients and limiting threshold (9.3–30.4mW). Nanoplatelet CdFe2O4–40wt% rGO displays good optical power handling capability of laser beam at the experimental wavelength, indicating the possible photonics device application such as optical power limiters.

Investigation on the behavioral difference in third order nonlinearity and optical limiting of Mn0.55Cu0.45Fe2O4 nanoparticles annealed at different temperatures

Mn0.55Cu0.45Fe2O4 nanoparticles were synthesized by wet chemical co-precipitation method. The obtained samples were annealed at different temperatures (500 °C to 1250 °C). All annealed samples were characterized for their structural, magnetic, linear and non-linear optical properties. XRD results confirm single phase cubic spinel structure only for samples annealed at 800 °C and 1250 °C. The average crystallite sizes of the samples are in the range of 11–37 nm. HR-SEM image of the sample annealed at 800 °C exposed spherical morphology. The quantitative analysis of EDX results is close to the expected values. Bandgaps were evaluated from UV-DRS. The FTIR spectrum showing the essential peaks around 452.1 and 567.2 cm−1 prove the formation of spinel nanoparticles. In PL spectrum, a broad emission peak is attained in visible region at 485 nm. The saturation magnetization (Ms), coercivity (Hc) and remanence magnetization (Mr) are obtained from the hysteresis curve. Nonlinear absorption coefficients (10−4 cm W−1), nonlinear indices of refraction (10−8 cm2 W−1) and the third order nonlinear susceptibilities (10−6 esu) are determined using Z-scan experiment. CW laser beam is utilized to study the optical limiting characteristics and the results prove these materials to be a potential candidate for device applications like optical switches and power limiters.

Synergistically Enhanced Optical Limiting Property of Graphene Oxide Hybrid Materials Functionalized with Pt Complexes.

Recently, graphene-based materials have become well-known nonlinear optical materials for the potential application of laser protection. Two new graphene oxide-platinum complex (GO-Pt) hybrid materials (GO-Pt-1, GO-Pt-2) have been fabricated through covalent modification and electrostatic adsorption of different Pt complexes with GO. The structural and photophysical properties of the resultant hybrid materials were studied. The nonlinear optical properties and optical power limiting (OPL) performance of Pt complexes, GO, and GO-Pt hybrid materials were investigated by using Z-scan measurements at 532 nm. At the same transmittance, the results illustrate that functionalization of GO makes GO-Pt hybrid materials possess better nonlinear optical properties and OPL performance than individual Pt complexes and GO due to a combination of nonlinear scattering, nonlinear absorption, and photoinduced electron and energy transfer between GO and Pt complex moieties. Furthermore, the nonlinear optics and OPL performance of GO-Pt-2 are better than those of GO-Pt-1, due to not only the excellent optical limiting of Pt-2 and more molecules per area of GO but also the way of combination of Pt-2 and GO.

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.