Proceedings Volume 4106

Linear, Nonlinear, and Power-Limiting Organics

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Proceedings Volume 4106

Linear, Nonlinear, and Power-Limiting Organics

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Volume Details

Date Published: 29 November 2000
Contents: 9 Sessions, 46 Papers, 0 Presentations
Conference: International Symposium on Optical Science and Technology 2000
Volume Number: 4106

Table of Contents

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Table of Contents

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  • Planar Waveguides: Passive
  • Optical Fibers
  • Planar Waveguides: Active
  • Poster Session
  • Polymers
  • Molecules
  • Optical Power Limiters
  • Nonlinear Optical Materials and Characterization
  • Poster Session
  • Section
  • Poster Session
  • Molecules
Planar Waveguides: Passive
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High volume manufacturing of polymer planar waveguides via UV embossing
A process is described here which is capable of creating very low cost single or multimode waveguides. To reuce the cost of manufacture to the lowest levels, one must move away from intensive individual processing steps such as wafer- based spin coating, lithography, and development. Here, a process is described which is inspired by the printing industry; especially the printing of raised features to form simple, low cost holograms typically used for product security. All efforts must be approached with a level of precision and engineering not typically required in the embossing industry. Precision resist masters of 12' dimension were created using commercially available photoresists and photomasks. High fidelity molds (and embossing tools) were made by replicating the master in both metal and elastomer. PET film was coated with an underclass layer which uniformly reproduced waveguide channel features. The filling process of waveguide cores proceeded through the coating of the channels followed by lamination of an overcoating. Finally, end face preparation was examined through die cutting, slitting, and laser cutting techniques.
Polymer optical waveguide devices for low-cost WDM module
In order to simultaneously realize high-speed data transmission, low-cost and lightweight network in automotive applications, a 3(lambda) WDM has been considered to be a suitable solution. We have developed two types of low-cost WDM modules using a polymer optical circuit. As the first method, we developed a planar optical circuit for interconnection between an optical fiber and an LD/PD chip using a PMMA waveguide having out-of-plane branching mirrors, fabricated simultaneously with a waveguide from a polymer film, using a newly-developed temperature-controlled RIE (Reactive Ion Etching) technique. The waveguide has a large diameter (100 x 100micrometers ) and a high-(Delta) (NA=0.5) structure. Transmission losses were 0.1 dB/cm (660nm), and 0.3 dB/cm (1320nm). As the second method, we employed a light-induced waveguide technology for the WDM module fabrication. When a GI optical fiber is soaked in two kinds of light-hardening resin blends in which the hardening wavelength differs ((lambda) 1>(lambda) 2) , the resin is irradiated with (lambda) 1 light through the fiber, a hardened polymer waveguide having uniform diameter geometry would grow from the fiber tip. This method does not need any fiber alignment and packaging process; therefore, cost-effective module fabrication can be expected. This technique utilizes the self-focusing phenomenon of the optical fiber's outgoing beam by a refractive index increase in the material hardening process. We could also confirm two key component formations necessary for the WDM module: regrowth of the waveguide form the backside of a WDM filter after passing through it, and a 90 degree(s) reflected waveguide using a 45 degree(s) mirror.
Fabrication and characterization of planar and channel waveguides in hybrid sol-gel systems
Anne-Claire Le Duff, Michael Canva, Tomas Pliska, et al.
We report on linear optical properties of Disperse Red 1 (DR1) doped sol-gel planar and channel waveguides. The refractive index and optical propagation losses of the guiding layer were measured between 0.756 micrometers and 1.64 micrometers . In the telecommunications window, the attenuation is dominated by the overtones of the O-H bonds vibration bands. We also report on photobleached channel waveguides. Propagation losses were measured at 1.064 micrometers as a function of the waveguide width. Attenuation coefficients as low as 1 cm-1 in 4 to 8 micrometers wide channel waveguides were demonstrated. A good confinement of the light is observed in a 3 hours bleached sample. The suitability of plasma etching as an alternative technique for fabricating channel waveguides is demonstrated.
Polymer-based optical single-arm waveguide interferometer as a chemical sensor
We report on a single-arm double-mode waveguide interferometer being used as a chemical sensor for detection of presence of ammonia and other pollutants in ambient air. The sensor is based on thin films of polymers such as poly(methyl methacrylate) and polymide doped with various indicator dyes such as bromocresol purple. These dye-doped polymer materials significantly increase their optical absorbance in the presence of the pollutants. The absorbance change is accompanied by the change of the refractive index of the materials in the region of optical transmittance. The change of the refractive index can be converted into a change of the light intensity in the single arm interferometer. The sensor employs interference between two propagating modes of the same polarization. Single-arm configuration makes it rigid but yet sensitive enough to detect concentrations of ammonia of the order of 10 ppm and less. The device also exhibits high sensitivity to ambient temperature change (of the order of 1 degree(s)C per 2(pi) -phase shift). We analyze effects of various factors such as polymer composition, light wavelength, ambient humidity and atmospheric pressure on the performance of the sensor. Various design and fabrication issues are also discussed. The problem of particular interest is coupling the sensor to the optical fiber transmission line, reduction of losses and sensitivity improvement.
High-performance polymeric materials for waveguide applications
Konstantin Glukh, John-Henry Lipian, Richard Mimna, et al.
The ever-increasing need for economical, reliable, and high- performance optical interconnects for telecommunication and data communication markets demands new innovative solutions. Polymer technology being developed at BFGoodrich is focused on satisfying this demand. It is based on proprietary polynorbornene polymers that exhibit excellent optical, thermal and mechanical properties essential for fabrication of reliable components for integrated optics. Typical polymer waveguide systems exhibit a tradeoff between thermal and optical performance. The uniqueness of the polynorbornene system is that these tradeoffs are minimized. The intrinsic properties of the polynorbornene system include low transmission loss (<0.1 dB/cm at 820 nm), wide spectral range (<0.4 dB/cm at 450 nm and <0.1 dB/cm at 515-870nm), low birefringence ((Delta) n(in plane)<10-5, (Delta) n(out of plane) <10-3 at 820 nm, consistent difference in index over a wide temperature range, long-term thermal stability (>2000 hours at 125 degree(s)C), high glass transition temperature (>280 degree(s)C), and low moisture absorption (<0.1%). The combination of these characteristics offers advantages over existing plastic materials for visible and near IR applications such as those used in the datacom market. Candidate materials have been identified as core and cladding components for optical waveguides. The refractive index of a typical core material is 1.53, and of a typical clad material, 1.50 at 820 nm. The difference in index between core and cladding is approximately 0.03 over a broad range of wavelength (515-870nm). Preliminary results indicate that the difference in index between core and cladding tracks with temperature, which is in line with out expectation since these polymers have similar structures at the molecular level. Fabrication of functional waveguides has been demonstrated using a conventional cast and cure process at the lab scale. Optical performance of the constituent materials and the waveguide devices will be discussed in the paper.
Optical Fibers
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Routes to practical plastic optical fiber systems
Whitney R. White, Lee L. Blyler Jr., Giorgio Giaretta, et al.
Plastic optical fiber (POF) has long been seen as a potential medium for implementing simple, very low cost optical links, but has not yet found significant application in data communication. In the near future, this situation is likely to change, as a new generation of POF with dramatically improved optical properties becomes commercially available. Unlike conventional POF, the new POF is based on amorphous perfluorinated polymers that are transparent in the near infrared. In order to develop useful fibers based on these new polymer materials, it has been necessary to better understand their fundamental optical properties, and to develop methods for manufacturing low-loss fiber. Since the available manufacturing methods typically result in graded-index POF's with very non-ideal index profiles, the possibility of severe bandwidth limitations has long been a concern. In addition, significant improvements in connection loss will be required to support high-speed systems. In this paper, we describe techniques that we and others have developed to eliminate or overcome these obstacles.
Luminescence characterization of rhodamine-B-doped plastic optical fibers using the side induced fluorescence method
Carl W. Dirk, Albert Peralez, Sarah Kopecky, et al.
Acrylic plastic optical fibers containing the laser dye Rhodamine B chloride have been drawn from unclad doped acrylic preforms. The fibers strongly emit waveguided fluorescence light produced form ambient side illumination along the length of the fiber. We have characterized the loss in the wavelength region of strong absorption by measuring the attenuation of the side induced fluorescence (SIF) produced by He-Ne (green) and He-Cd (blue) laser lines. We can accurately quantify the loss in the high loss spectral region using SIF. Attenuation data and the associated SIF analysis will be discussed.
Plastic optical fibers with in-line electrode structures
Osvaldo Rodriguez, Carl W. Dirk, Albert Peralez, et al.
We report on a procedure to prepare plastic optical fibers with in-line indium electrodes alongside a wave-guiding core. The goal is the realization of an electro-optic modulator device structure entirely contained with the cladding of the fiber. This work is analogous to that of Kuzyk and others at Washington State University, though we report on a different procedure to manufacture the preform from which the fiber is drawn.
Planar Waveguides: Active
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Fabrication and optical properties of an organic crystal waveguide
A ridge waveguide of an organic salt, 4-N,N-methyl- stilbazorium tosylate, DAST, which has the largest second- order optical nonlinearities among organic materials, was fabricated for the first time to our knowledge. DAST crystal was covered by poly (methyl methacrylate) as a protect layer for a photo-resist solution, then standard photolithography and oxygen reactive ion etching (RIE) processes were applied. DAST ridge waveguide, 34x20 micrometers and 6x6 micrometers channel s with 2mm in length were successfully fabricated by this process. To reduce the refractive index of the crystal, photo bleaching was effectively applied for DAST crystal. So, photobleaching can be applied to fabricate a cladding layer for the ridge waveguide.
Temperature-controlled beam steering in polymer waveguide arrays
Thomas Pertsch, Ulrich Streppel, Thomas Zentgraf, et al.
Inspired by the observation of Bloch oscillations of electrons in semiconductor supperlattices we recently predicted the existence of Wannier-Stark states as well as Wannier-Stark ladders and consequently the emergence of optical Bloch oscillations in evanescently coupled optical waveguide arrays. Here we show that the required linear variation of the propagation constant across the array can be realized by using the thermo-optic effect in polymers. Beyond the fundamental interest in waveguide arrays for the study of dynamical effects in discrete systems, they have a fair potential in all-optical signal processing. We demonstrate that waveguide arrays allow for temperature- controlled beam steering, while simultaneously minimizing the diffractive beam spreading. Homogeneous arrays of 75 waveguides are fabricated in an inorganic-organic polymer, with each waveguide guiding a single mode (<0.5 dB/cm) at a wavelength of 633 nm. By heating and cooling the opposite sides of the samples, a transverse linear temperature gradient is established. Exciting a few waveguides using a wide Gaussian beam we measure the oscillating transverse motion of the undiffracted output beam for an increasing temperature gradient.
Accelerated aging of tunable thermo-optic polymer planar waveguide devices made of fluorinated acrylates
Constantina Poga, MacRae Maxfield, Lawrence W. Shacklette, et al.
Planar wave guide device components, made from photocurable fluoroacrylates, demonstrated stability under conditions that exceed those needed to operate planar polymer thermo- optic switches. Fluoroacrylate polymers exhibited negligible decomposition at 200 degree(s)C. Insertion loss and polarization-dependent loss showed no increase at temperatures up to 257 degree(s)C. The reflected spectrum of a Bragg grating showed no monotonic change in (lambda) B, width, or strength in 105 days at 125 degree(s)C. Humidity changes from 0 to 90%RH caused a reversible blue shift in (lambda) B of only 0.00004. Light flux of 130mW exhibited no impact on n, (delta) n, or IL. Heaters showed no degradation at 85 degree(s)C/85%RH. Bonding to substrate, heaters, and pigtails remained intact throughout the testing.
Photostability and residual red-tail absorption of different chromophore-doped polymers
Michael Canva, A. Galvan-Gonzalez, George I. Stegeman, et al.
Doped polymers exhibit many attractive features for nonlinear optics. The performance demonstrated with some of these materials appears promising for application in real devices. However, the Achilles' heel of this class of chromophore-doped materials lies most certainly in their relatively modest chemical stability, especially their photostability. Our aim has been to quantify such side- effect phenomenon, systematically linked to the optical use of these materials. Photodegradation is a 2-step process: first, absorption, that may be characterized by (sigma) ((lambda) ), the absorption cross section, and, second, chemical reactivity from the induced excited-states, which may be quantified by B-1((lambda) ), the overall quantum efficiency of degradation. The photodegradation rate under a photon flux n is thus given by (tau) =B/((sigma) .n). We use the quantity C=B/(sigma) as a material figure of merit for photostability. Given long enough illumination times, C can always be measured. How precisely B is quantified is directly related to how precisely (sigma) is measured, which decreases dramatically as the wavelength of interest is shifted from the main absorption band towards the IR telecommunication spectral windows. Increasing future device lifetimes requires a simultaneous increase in the B parameter and a decrease in the loss due to the residual red-tail absorption. We report the systematic behavior that was found concerning the dependence of C on wavelength.
Poster Session
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Control of polarization evolution in helically wound active fibers
In a helically wound single-mode fiber the mode degeneracy is lifted by the geometric form and the photo-elastic effect. Fiber bending induces linear birefringence' and the presence of torsion is responsible for circular birefringence.2 Considering the geometrical properties of a helix and using Jones calculus, it has been shown3 that a helically wound fiber can be described as the combination of two distributed homogeneous retarders: a linear retarder and a circular retarder. Since linear and circular retardation can be easily followed on the Poincaré sphere, we use Mueller calculus to describe the polarization optics of helical fiber structures.4 Because of the strong absorption and the subsequent emission that active fibers present within the amplification band, the signal becomes depolarized and it is not possible to characterize the birefringence properties of active fibers at these wavelengths. In this work, the birefringence performance of active fibers is evaluated in the neighborhood of the amplification band, using signals with a high signal to noise ratio at the active fiber output. We present the birefringence characterization of a helically wound erbium fiber. This helical fiber structure was built with a commercial fiber. Since the birefringence parameters we measured agree with the values predicted by the theoretical model, we propose that we can make use of this model to design the helix structure and, to select the input polarization states of the pump and the signal that can be used to control the polarization evolution of the amplified signal as it propagates along the fiber.
Material glass transition temperature, device thickness, and operational temperature effects on absorption of electro-optic polymer films
Anne-Claire Le Duff, Michael Canva, Yves Levy, et al.
In chromophore doped materials, the trade-off between nonlinear coefficients and absorption is a critical issue. In particular, X(2):X(2) cascading based applications at 1.55 micrometers impose stringent conditions on the absorption at the second-harmonic wavelength. Transmission spectroscopy through a thin film does not provide sufficient resolution to measure the absorption coefficient on the red side of the main absorption band. However, assuming Voigt profiles, it is possible to extrapolate the absorption coefficient in the near infrared (NIR) from the main electronic resonance. We report on the dramatic impact of the host polymer matrix on the near infrared absorption of azobenzene chromophores. The effect is directly correlated to the host polymer glass transition temperature. The case of hybrid sol-gel material is also discussed. In particular, we present here an interesting correlation between the poling temperature and some spectroscopic properties. This correlation and thermo- spectroscopic measurements lead us to define an effective Tg in the sol-gel system. We also report on film thickness dependent absorption properties.
Polymers
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Photo-orientation movement of photoisomerizable chromophores: quantifying analytical theory and application to spectrally overlapping and distinguishable isomers
Zouheir Sekkat, Hidekazu Ishitobi, Daisuke Yasumatsu, et al.
We introduce the analytical theory of couples photoisomerization and photo-orientation both for individualizable and spectrally overlapping isomers, and we use it to quantify the photo-orientation movement of chromophores in polymers including photoisomerization quantum yields. We study photo-orientation processes in A - B photoisomerizable systems where B is unknown. We contrast systems where the isomers are individualizable and without thermal A implied by B isomerization, namely diarylethene and spiropyran-type chromophores in films of poly-methyl- methacrylate, respectively, and systems of nondistinguishable isomers, namely push-pull azobenzenes attached to polyurethane polymers. When diarylethene and spiropyrans are oriented by polarized excitation, the apparent optical orientation changes sign for the ultra- violet versus the visible photochemical transitions: a feature which is due to perpendicular transition dipoles of the B isomer of these chromophores. Photo-orientation reveals the symmetry nature of photoisomerization transitions. We also report on the observation of near-pure photo-orientation by photoisomerization of azo dye in polymers; an observation which is attributed to both the particular molecular structure of the polymer studied and to appropriate photoisomerization quantum yields as well as as fast trans implied by cis thermal isomerization, and is rationalized by the study of photo-orientation of a series of azo-polyurethanes each with distinct differences in the molecular structure of the unit building blocks.
Depth profiling of the Chi(2) distribution in poled nonlinear optical polymer films
Robert Blum, Kersten Pfeifer, Manfred Eich
We present experimental and theoretical details on how to analyze the polarization distribution in poled second order nonlinear optical polymers in three dimensions. The polar order can be analyzed in both the lateral and the vertical directions by scanning second harmonic microscopy (SSHM) at various wavelengths along the absorption tail of the polymer. Local thermal reorientation was accomplished using an Argon laser at a wavelength of 488nm, and the resulting change in polarization was analyzed by multi-(lambda) SSHM. We could demonstrate that the relative change in polarization is strongest at the surface that was irradiated with the Argon laser and decreases towards the opposite surface.
Alignment and aggregation studies of highly dipolar TCNQ adducts in guest-host systems
Nancy-Ann Hackman, David Bloor, Graham Hugh Cross, et al.
Highly dipolar non-linear optical chromophores with absorption typically in the range of 350-500 nm have been synthesized by the reactions of amines with tetracyanoquinodimethane (TCNQ). These materials show interesting fluorescence properties with the emission strongly dependent on the host environment. One of the advantages of these materials is the large figure of merit ((mu) (beta) ), which is calculated to be -765 x 10-48esu, allowing large non-linear optical coefficients to be obtained. Guest-host polymer films of these materials have been corona poled using a constant current corona triode. These materials are highly dipolar which leads to the formation of aggregates within the doped polymer films. Studies of the second order non-linearities using second harmonic generation (SHG have revealed the presence of such aggregation. The magnitude of the SHG that can be obtained form such systems is therefore severely limited by this aggregation. This phenomenon was then confirmed with optical spectroscopy and electric field induced second harmonic generation (EFISH) studies.
Linear and nonlinear optical properties of polyvinyl carbazole and polyvinyl-carbazole-substituted thin films
Veronica Bermudez, Francois Kajzar, S. Niziol, et al.
Linear and nonlinear optical properties of thin films of polyvinyl carbazol (PVK) and its derivatives were studied by UV-VIS spectroscopy and by harmonic generation techniques. Refractive index and its dispersion was measured for PVK and functionalized PVK by m-lines technique. PVK is an interesting polymer because of its high glass transition temperature and photoconducting properties. Functionalized with coumarine may be used for LED's applications and shows also interesting second order NLO properties when poled. The poled polymers may be reversibly depoled with UV light. However, such a process, whose kinetics depends on temperature, leads to a decrease of second-order NLO process. The third-order NLO susceptibility X(3)(- 3(omega) ;(omega) ,(omega) ,(omega) ) is about three times larger for modified PVK and comparable to that found in polysilanes with a larger transparency range.
Synthesis and characterization of maleic anhydride derived crosslinkable polymers for nonlinear optical applications
Sam-Shajing Sun, Shahin Maaref, Enver Alam, et al.
The synthesis and characterization of maleate type crosslinkable nonlinear optical (NLO) polymers derived form maleic anhydride and fumaryl chloride is described. Preliminary results demonstrated this is a convenient, inexpensive, and versatile method of fabricating crosslinked NLO polymer thin films. These maleate type polyesters containing NLO chromophores such as Disperse Red 19 are capable of crosslinking to form a hardened lattice under thermal or high-energy radiation conditions. Crosslinking is a critical nano-scale technique for second order nonlinear optical as well as other potential photonic applications where molecular orientations need to be aligned and be stabilized against molecular thermal motions. Photolithographic techniques may be readily employed in this system to fabricate patterned polymer waveguide.
Molecules
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Material optimization for electro-optic modulation and cascading
Jorge Reyes, Bruno Darracq, Michael Canva, et al.
A large effort has been devoted to the preparation of organic polymeric materials for electro-optic modulation and more recently for cascading based processes. These materials contain push-pull chromophores either incorporated as guest in a high Tg polymeric matrix (doped polymers) or grafted onto the polymeric matrix. These systems present several advantages but require significant improvement at the molecular level- by designing optimized chromophores with very large molecular figure of merit specific to each application targeted. The sol-gel route was used to prepare hybrid organic-inorganic materials, for the fabrication of amorphous solids of various shapes (bulk, think films...). The results obtained on optimized chromophore-doped poled thin films emphasize that intermolecular interactions have to be taken into account, as already pointed out by Dalton and coworkers. By combining a molecular engineering strategy for getting large molecular figure of merit and by controlling the intermolecular dipole-dipole interactions via both tuning the push-pull chromophore concentration and the incorporation screening carbazole moieties in high concentration. This strategy allows us to obtain a r33 of about 50 pm/V at 831 nm for a new optimized chromophore structure. In parallel, these thin films are being processed to be used as passive components for integrated optics.
Evidence for ring spinning in rotaxanes induced with an alternate electric field
Veronica Bermudez, Nathalie Capron, Torsten Gase, et al.
An alternating electric field is used to address the structure of two hydrogen bond-assembled rotaxanes and their interlocked molecular fragments by recording the electro- optic Kerr effect. Both rotaxanes consist of two nitrogen hydrogen bond acceptors 1 and a fumaramide unit 2 in the thread. The macrocycle is common. The experimentally determined Kerr constant as a function of the frequency of the applied AC field shows a resonance at 50Hz for both rotaxanes. This resonance is absent for the corresponding uninterlocked components or the solvent itself. A second resonance, around 80Hz was found for the fumaramide rotaxane but not for the nitrone one. The resonances have been shown to be field strength and temperature dependent, shifting to lower values with increasing the applied voltage and or temperature. Nuclear Magnetic Resonance (NMR) spectrometry shows that the only possible process is a 180 degree(s) circumrotation of the macrocycle around the thread. The rate of the macrocycle circumrotation measured by NMR is in the regime of that seen for the Kerr effect resonance. Theoretical simulations of the submolecular motion show that in 1 the macrocycle ring rotates smoothly with little further perturbations. In comparison 2 presents a more complicated picture where several processes are coupled.
Dispersion of the first hyperpolarizability of an azulenic donor-acceptor chromophore
Chia Chen Hsu, Sean Liu, Chen Chi Wang, et al.
The first hyperpolarizabilities ((beta) ) of an azulenic donor-acceptor chromophore at different wavelengths were measured by a tunable wavelength hyper-Rayleigh scattering (HRS) experiments. The (beta) values measured at different wavelengths are used to investigate the dispersion relation of one-dimensional charge transfer organic chromophores. The validity of the well known un-damped two-level model and some modified models which include the damping and the vibronic effects are discussed.
Linear correlation between first hyperpolarizabilities and modified reaction field function
Chuan-Lang Zhan, Duo-Yuan Wang
We have studied the solvent effects on the molecular first hyperpolarizabilities of the R-4-(N-methyl-pyridinio)- stilbazolium iodide dyes determined by solvatochromism and those of p-nitroaniline and 1-anilinonaphthalene-8-sulfonic acid determined by using HRS techniques, and observed that they are in a linear correlation with the modified reaction field function, a[L((epsilon) )r-bL(n2)] + gETN, with high correlation coefficient ((gamma) >=0.950) in nonselected solvents, in which all of the points are divided into two groups and can be fitted to form two lines which intersect at one point for each compound. From the ordinate of the intersection, the intrinsic molecular first hyperpolarizabilities for each compound in pure solid state can be estimated, according to the hypothesis of the equal energy levels of the polarized surrounding molecules (solute or solvent) to influence on the solute molecule both in solid state and in some solution systems. Therefore we developed a simple experimental method for determining the intrinsic first hyperpolarizabilities of the stilbazolium- like dyes, which excludes the solvent effects.
Optical Power Limiters
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Developing photorefractive fibers for optical limiting
Gary Cook, Jason P. Duignan, Lesley L. Taylor, et al.
Fe:LiNbO3 in a simple focal plane geometry has already demonstrated its potential as an efficient optical limiter of low power continuous wave visible lasers. However, widespread use of this material is hampered by a severe reduction in performance in fast optical systems. Coherent bundles of photorefractive optical fibers, used in place of bulk crystalline material, will allow efficient optical limiting in fast optical systems. Owing to the crystalline nature of the photorefractive media, the fabrication of large numbers of high quality photorefractive fibers is extremely challenging. This paper describes some of the options available, including novel composite photorefractive materials.
Modeling nonlinear photonics of nonlinear fiber core for optical limiting application
Iam-Choon Khoo, Michael V. Wood, Pao H. Chen, et al.
A quantitative model for nonlinear photonic absorption processes in a liquid and their effects in the nonlinear transmission and limiting of a laser pulse are studied. The theoretical simulation results accounting for two-photon- and excited-state absorption processes, and the dynamic evolution of the molecular level populations and propagation of picosecond and nanosecond laser pulses through a fiber core formed by such liquid are in good agreement with experimental observations. In pump-prove studies using picosecond and nanosecond laser pump pulses and cw probe, we have also observed oscillatory transmission associated with laser induced thermal/density effects. We also discuss applications of the supra optical nonlinearity of nematic liquid crystal film for anti-laser jamming and optical limiting operation against long-pulse or cw lasers.
Comparison of experimental results and numerical analysis of multicell stepped limiters
Landa Hoke, Brian R. Kimball, Richard A. Whalen, et al.
The application of a numerical algorithm to the design procedure of a multi-cell limiter (MCL) is discussed and calculated numerical results are compared to experimental results. This application illustrates the ability to predict optical limiting under circumstances that are comparable to the design process of a MCL. Both the optical limiting and the temperature profile through the MCL are determined for three design cases. Also, the numerical analysis is used to investigate thermal damage using the calculated temperature profile. The results illustrate the potential application of a numerical simulation in designing a MCL and that the accuracy of the numerical model is on the same order as the experimental uncertainties.
Solvent effect on optical limiting of zinc tetrabenzoporphyrin compounds
Brian R. Kimball, Masato Nakashima, Barry S. DeCristofano, et al.
We carried out systematic experiments to study the effect of solvents on power limiting in zinc meso-tetra (p- methoxyphenyl) tetrabenzoporphyrin (ZnTBP). We used Toluene, pyridine, acetone, dichloromethane (DCM) and a toluene pyridine mixture to evaluate polarity and complex formation of the solvent and solute molecules. Z-scan data were generated using picosecond and nanosecond laser pulses at 532 nm. These data were then curvefit to a 5-level model to obtain excited state and two photon absorption coefficients, and the intersystem crossing rates. An f/5 optical limiting setup was used to determine limiting thresholds. Results indicate that toluene and DCM give the lowest limiting thresholds and that pyridine ligation can be used as a means of molecular modification for future molecular studies.
Optical limiting properties of derivatized carbothiacyanine dyes
Carl E. Bonner Jr., LaQuieta Huey, James H. Haliburton, et al.
The nonlinear optical absorption of a range of dialkyl- carbothiacyanine dyes has been measured using intensity dependent transmission measurements of the absorption cross- section at 532 nm. The ground and effective excited state absorption cross-section for each of the dyes has been determined. It was observed that with increasing bridge conjugation length between the carbothiacyanine end groups, the absorption cross section of ground state decreases slightly while the absorption cross-section of the excited state increases leading to an overall increase in the absorption cross-section ratio by an order of magnitude from 0.3 to 5.29. The absorption cross-section ratio tracks linearly with the difference between the energy of the pump laser and the energy of the ground state absorption. The counter ions of the dyes also affect the nonlinear absorption significantly. These organic materials exhibit good potential for optical limiting applications.
Nonlinear Optical Materials and Characterization
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Solvent effect on the third-order nonlinearity and optical limiting ability of a stilbazolium-like dye
Wenfang Sun, Michael M. McKerns, Christopher M. Lawson, et al.
Stilbazolium-like dyes, which contain different heterocyclic groups as electron donors and an N-methylpyridinium iodide group as an electron acceptor, are very interesting optical limiting materials. These materials exhibit low linear absorption, but potentially very strong nonlinear absorption at high intensities. In this paper, the results from investigations of the third-order susceptibilities and nonlinear refractive indices of a stilbazolium-like dye, trans-4-[2-(pyrryl)vinyl]-1-methylpyridinium iodide (PVPI), in different solvents using degenerate four wave mixing (DFWM) and Z-scan techniques with 6.8 ns laser pulses at 532 nm are reported. The molecular second-order hyperpolarizability of PVPI increases from 1.6x10-31 esu in methanol to 3.4x10-29 esu in chloroform, a factor of 212. The third-order nonlinearity of this compound is dominated by nonlinear absorption, which leads to strong optical limiting of nanosecond laser pulses. The strength of the optical limiting is dramatically influenced by the solvent used, with limiting decreasing in the order chloroform>dichloromethane, 1,2- dichloroethane>methanol, acetonitrile. While both nonlinear absorption and nonlinear scattering contribute to the optical limiting, nonlinear absorption is the dominant mechanism.
Up-converted emission observed from hybrid inorganic:organic composite thin film generated via laser-assisted molecular beam deposition
Robert L. DeLeon, Mukesh P. Joshi, Eric F. Rexer, et al.
Laser Assisted Molecular Beam Deposition (LAMBD) is a pulsed laser ablation technique which utilizes a train of gas pulses to precisely control the chemistry and transport of species to be deposited on a substrate. The LAMBD technique has been used to grow films on a variety of substrates and to ablate a variety of target materials including: metals, metal oxides, metal halides, Si, C and SiC. In addition, a variety of more complex composite films such as Cu embedded polymers, Yba2Cu3O7-x and organic doped TiO2 and Al2O3 have also been produced. These films have been analyzed by Raman scattering, SEM, EDX, FTIR, ESCA, NMR, mass spectrometry surface profile measurements to determine film structure and composition. Recently a successful program has been undertaken to show the potential of LAMBD to generate photonic films. Work done on up-conversion of IR light into the visible using LAMBD generated composite TiO2:APSS films will be described. These results demonstrate the potential of using LAMBD sources as a means of depositing a variety of high quality photonic films.
Nonlinear optical properties and optical limiting performances of penta-azadentate metal complexes in solution
Fengqi Guo, Wenfang Sun, Yun-Jing Li, et al.
The passive optical limiters are of significant for protecting sensors and human eyes from high intensity laser. The selection of materials is still one of the key for optical power limiters. The nonlinear optical properties of pentaazadentate metal complexes (PMC) were measured, the third-order optical nonlinear polarizabilities of 1.19~3.38x10-13esu were obtained, from which the molecular second order hyperpolarizabilities of 8.0x10-32~2.83x10-31esu were calculated. The optical limiting performances for PMC have been studied at 532nm for 8ns and 35ps pulses by using nonlinear absorption technique, in which the reverse saturable absorptions in the T1 and S1 states were responsible for the optical limitings. Experimental results demonstrated that the peripheral substituents and center metal ions influenced the third-order optical nonlinearities and the optical limiting performances of PMC.
Poster Session
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Influence of the photovoltaic effect on optical limiting with lithium niobate
Gary Cook, David C. Jones, Jason P. Duignan
Fe:LiNbO3 in a simple focal plane geometry has demonstrated efficient optical limiting through two-beam coupling. The magnitude of the observed optical limiting implies an optical gain coefficient which greatly exceeds that predicted by standard photorefractive diffusion theory. Experimental measurements have confirmed that the optical gain coefficient is approximately five times greater than can be accounted for through normal change diffusion. The photovoltaic effect has been identified as the most likely mechanism for generating the observed high optical gain. We have made a direct observation of the role of the photovoltaic effect in counter-propagating two-beam coupling in photorefractive iron doped lithium niobate. We have found experimentally that the photovoltaic effect is indeed the dominant mechanism for two beam coupling in an optical limiting geometry. The contribution to optical limiting from the photovoltaic effect is approximately five times greater than that arising form diffusion mechanisms alone, in agreement with earlier optical gain measurements.
Section
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Linear and nonlinear optical properties of rotaxanes: novel versatile photonic materials
Veronica Bermudez, Pierre-Alain Chollet, Francesco G. Gatti, et al.
Linear and nonlinear optical properties of newly synthesized amide based rotaxane films are investigated. The dispersion curves of refractive indices have been characterized. A relatively large anisotropy of refractive indices is observed. The vacuum deposited thin film can be poled by a static electric field. This fact shows some degree of freedom for the mobility of macrocycle with respect to the thread. The induced d33 susceptibility after static electric field polarization at (lambda) =1.064micrometers is 0.57 pm/V and 3.43 pm/V for rotaxane 1 and 2 respectively. Kinetics of poling and relaxation at different temperatures was studied by in situ SHG technique. From the poling kinetics the characteristic response times of the system were evaluated. Third harmonic generation was measured at 1.064micrometers and 1.907micrometers fundamental wavelengths. The electronic part of the third order NLO susceptibility (chi) (3) (-3(omega) ;(omega) ,(omega) ,(omega) ) was found to be (6.4+/- 0.2)*10-13esu and (4.1+/- 0.8)*10-13esu at 1.604micrometers and (6.9+/- 0.4)*10-13esu and (4.2+/- 0.3)*10-13esu at 1.907micrometers for 1 and 2 respectively. Upon UV irradiation a clipping movement induced by a trans-cis isomerization process has been identified.
Molecular engineering for two-photon absorption in the visible
Remi Anemian, Chantal Andraud, Jean-Michel Nunzi, et al.
A molecular engineering strategy, based on the role of the charge transfer conjugated system, and of donor substituents on theoretical linear and two-photon absorption (TPA), is developed. The best trade-off TPA-linear absorption is fulfilled by two tetraphenyl-diamine derivatives (biphenyl and fluorene), which could allow, if mixed, to cover efficiently the visible range. Furthermore, the theoretical study of two-photon absorption (TPA) properties of polyphenyls (with the number of benzene monomer units n=1 to 6) is related to cooperative effects between monomers. These effects lead to an increase of the TPA cross-section with n without saturation according to a power law.
Nonlinear optical properties of the salts of "diffuse" anions
A. Todd Yeates, Douglas S. Dudis, John S. Wilkes
A new class of materials, which demonstrates a potentially high third-order nonlinear optical (NLO) response based on highly polarizable anions, is discussed. Two examples of such ions included in this article are trithiocarbonate (CS32-) and aci-nitro-dithioacetate (NO2CHCS22-. The NLO response of any real materials containing these ions will be highly dependent on the nature of the cation present. It is expected that smaller and more localizing cations will have a smaller NLO response. We have performed ab initio finite-field computations of several anions along with some salts of the aci-nitro-dithioacetate anion to illustrate this effect.
Dynamic hologram recording and relaxation in C60 solutions
Anna L. Pyajt, Victor G. Bespalov
We performed numerical experiments on dynamic hologram (grating) recording and relaxation in fullerene C60 solutions and carried out the comparison with experiment on self-diffraction (intensity up to 50 MW/cm2, pulse duration 10nm, wavelength 532 nm, angle between pump beams 0.16 rad). The grating recording was numerically simulated by the differential equations: (1) balanced equations system describing population in six-level system, (2) time-space equation for absorption from different levels, (3) equation for the hologram thermal relaxation. Using this method the time-space dependence of medium refraction index due to thermal absorption was determined. Based on phase grating recording the estimation of diffraction efficiency in different diffraction orders was determined. It was shown that during the recording the shape of phase thermal grating becomes nearly rectangular due to absorption on exited singlet and triplet sublevels. The long time of life of triplet sublevels of C60 influences phase grating relaxation. The calculated values of diffraction efficiency in 1-5 levels are almost equal to the values form the experiment. According to our results of numerical analysis we can make a conclusion that the model successfully describes recording and relaxation of thermal phase hologram in fullerene solution. Results of phase grating relaxation can be used for investigation of fullerene properties and life-times of triplet sublevels. Our model can be used for numerical simulation of phase and amplitude grating recording and relaxation in fullerene solution and fullerite with pumping by nano-pico and femtosecond pulses and CW radiation.
Is there a fundamental limit on nonlinear molecular susceptibilities?
Nonlinear optical materials have been the focus of studies to maximize their nonlinear optical susceptibility because of their possible applications. Complex quantum expressions are often simplified with two and three state models that consider the competition between excited states, symmetry, and bond length alternation. We ask the question: Is there a fundamental upper limit of the nonlinear susceptibility, and, can this limit be achieved? We use the Thomas-Kuhn quantum sum rules, which are general and apply to any system and find that the off-resonant diagonal components of the second and third-order susceptibilities are bounded by a function that depends on the number of electrons and the transition energy to the first excited state. A large set of measurements form the literature are all found to be bounded by this horizon function as predicted. Further improvements in susceptibilities will therefore require more creative approaches that are presently used.
Precise and absolute measurements of complex third-order optical susceptibility
Stephane Santran, Lionel Canioni, Thierry Cardinal, et al.
We present precise and absolute measurements of full complex third order optical susceptibility on different fused silica and original glasses composed of tellurium, titanium, niobium erbium. These materials are designed to be the key point for applications ranging form high power laser systems to optoelectronics, their nonlinear index of refraction is a major property and thus must be accurately known. Due to the accuracy and sensitivity of our technique, we have been able to find a large dispersion (more than 30%) of the non linear index of fused silica glasses as a function of their processing mode. On the other hand, measurements on tellurium glasses have shown very strong nonlinearities (40 times higher than fused silica), to be linked to the configurations of their cations and anions. Although the titanium and niobium glasses are less nonlinear, they can be promising matrices for addition of luminescent entities like erbium leading to very interesting laser amplification materials. The experimental set-up is a collinear pump-probe (orthogonally polarized) experiment using transient absorption technique. It is built with around a 100 femtosecond laser oscillator. A fast oscillating delay between the pump and the probe allows us to measure the electronic nonlinearity in quasi real-time. This experiment has the following specifications: an absolute measurement accuracy below 10% mainly due to the laser parameters characterization, a relative measurement accuracy of 1% and a resolution less than 5.10-24m2/V2(50 times less than fused silica).
Thin film Z-scan measurements of the nonlinear response of novel conjugated silicon-ethynylene polymers and metal-containing complexes incorporated into polymeric matrices
The third-order optical nonlinearities of new conjugated poly[(arylene)(ethynylene)silylene]s, and a variety of chromium, neodymium or cobalt complexes incorporated into polymeric matrices as thin sol-gel or polyacrylonitrile films have been determined by using a single beam Z-scan technique. The samples were pumped by a single ultrashort pulse of a mode-locked Nd-phosphate glass laser (wavelength 1054 nm) with a 5ps pulse duration (full width at half- maximum), the repetition rate of the Gaussian beam being low (0.3Hz) ro avoid thermal effects. The spot radius of the focused pulse was ca. 60micrometers , its beam waist being in the sample (intensity up to 4x1013 Wm-2). Calibration was done with chloroform and benzene, the value of N2 for the latter (2x10-12esu) being similar to that previously reported. A small-aperture Z-scan (S=0.03) was used to measure the magnitude and the sign of the nonlinear refractive index, n2. Very high nonlinear refractive indices were found for a film containing (a) a poly[(arylene)(ethynylene)silylene]s with pentacoordinated silicon (c 5 gl-1) in a sol-gel matrix (N2 = 6 x 10-13 cm2W-1), (b) a film containing a poly[(arylene)(ethynylene)silylene] with tetracoordinated silicon (c 0.5 gl-1) and a very small proportion of fullerene-C70 incorporated into an NH2-containing sol-gel matrix (n2 = 5x10-13 cm2W-1, and (c) a thin polyacrylonitrile film of polycyanoethylate bis-arenechromium(I) hydroxide (n2 = -5 x 10-12 cm(superscript 2W-1.
Light amplification in dye-doped DNA-surfactant complex films
Yutaka Kawabe, Lili Wang, T. Koyama, et al.
We observed amplified spontaneous emission (laser action without cavities) from several kinds of dyes doped in films of salmon DNA (deoxyribonucleic acid) derivatives. We employed laser dye Rhodamine-6G, Pyrromethene 556, and nonlinear optical dye DMASDPB for dopants. Most of sample films with several micrometers thickness were prepared as follows: 1) DNA aqueous solution was mixed with hexadecyltrimethylammonium chloride aqueous solution. 2) precipitated DNA-lipid complex and dyes were dissolved in ethanol or chloroform. 3) Films were formed on substrates by casting from the solution. The amplified spontaneous emission was observed when the films were pumped with a nanosecond laser of 532 nm at the intensity above a threshold value. Spectral narrowing occurred at the threshold energy, and it was accompanied with superlinear dependence of the emission intensity on the pumping intensity. Dye molecules in DNA films can be intercalated in the double helix structure. Because molecules are separated form one another, it is possible to increase chromophore concentration without fluorescence quenching due to aggregation. Furthermore, it is known that DNA shows a good conducting property. We will discuss the possibility of optical and electronic devices utilizing these characteristics.
Low-power nonlinear optical interaction in dye-doped sol-gel glasses
Sio Kuan Lam, Man-shih Athena Chan, Dennis Y. Lo
Organic dye-doped solids show strong third-order optical non-linearity due to the enhancement of the lifetime of the lowest triplet state of the dye in solid environment. The long triplet state lifetime leads to low absorption saturation intensity. As a result, the third order nonlinear optical behavior is observable at very low light power (i.e. tens of mW). Dye-doped solid of large third order nonlinearity finds application in many photonic devices. Boric acid glass, polymer (such as PMMA, PVA, PAA), sol-gel silica, and organically modified sol-get silicate (ORMOSIL) have been used as host materials for dyes. We will concentrate our interest on the dye-doped sol-gel silica and dye-doped ORMOSIL. We have performed degenerate four wave mixing (DFWM) experiment to demonstrate optical phase conjugation by eosin Y-doped sol-gel silica in vacuum ambient. We have also performed Z-scan measurement to study the nonlinear refractive index of fluorescein 548- doped ORMOSIL. Absorption saturation experiments are conducted to determine the absorption intensity and (chi) (3).
Poster Session
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CW SRS generation and amplification in high-finesse Fabry-Perot cavity
The processes of transient SRS generation and amplification of continuous Stokes radiation were investigated by mathematical modeling. The detailed calculations of Stokes generation evolution in gaseous hydrogen, methane, crystal hydrogen and in barium nitride were carried out using high finesse resonators. It was shown, that the distinctive feature of resonator continuous SRS is the presence of relaxation oscillations at the initial moments of development of Stokes generation. The 100 times amplification fo the input pulsed Stokes signals with duration determined by the time characteristics of the resonator and SRS medium was shown. The results of numerical calculations correspond to the results of experiments.
Substituent dependence of the third-order nonlinear optical properties of 2,5-dialkoxy-PPV derivatives
Tiziana Cassano, Raffaele Tommasi, Michele Ferrara, et al.
The influence of the chemical structure on the (chi) (3) of organic molecules has been selectively investigated in three poly(2,5-dialkoxy-1,4-phenylenevinylene) polymers. They have similar degrees of polymerization and polydispersity indexes and differ only for the structure of the side groups in the 2.5 positions of the phenylene rings, that are respectively C8 linear and C5 branched alkoxy chains and C12 bridged closed dialoxy chain. Z-scan measurements show that all the investigated substituted-PPVs exhibit a small Im (chi) (3) and a large, negative Re (chi) (3) at (lambda) =1064nm. The obtained results yield evidence of a considerable dependence of the third-order nonlinear optical properties on the steric effect of the substituents.
Classical theory of dispersion of high-intensity light
Alexander A. Korolev, Sergei A. Kozlov, Sviatoslav A. Stumpf
In present paper we introduce a new model of interaction of laser radiation and dielectric medium. The model correctly describes the dispersion of third order nonlinear medium polarization response in a wide spectral range and is suitable for analysis of propagation of intensive extremely short laser pulses with a very wide spectrum. Also we include into this model a description of plasma-related effects, which are noticed when intensity of pulses increases high enough to initiate free electron generation process. A new wave equation, describing wide-spectrum femtosecond pulse propagation in nonlinear medium with induced plasma nonlinearity, is obtained.
Difference frequency generation in organic vapors
Rashid A. Ganeev, Shavkat R. Kamalov, M. K. Kodirov, et al.
Investigations of nonlinear-optical frequency conversion of Nd:YAG laser radiation in naphthalene vapors are presented. Third harmonic generation caused by difference frequency generation in six-photon process was offered. Optimum temperature for naphthalene vapor was found to be 170 degree(s)C, at which the synchronous conversion of pump radiation to the third harmonic radiation was carried out. Third harmonic generation conversion efficiency varied within the 10-10 depending on pump intensity and cell temperature. Third-and fifth-order nonlinear-optical susceptibilities of naphthalene vapors were calculated.
Molecules
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First-order hyperpolarizabilities of multipolar molecules: experimental and theoretical analysis
Xue-Lin Yang, Remi Anemian, Thomas Zabulon, et al.
By Hyper-Rayleigh Light Scattering (HLS) experiments, we obtained the first-order hyperpolarizabilities (beta) for a series of 1D polyeno-dipolar and C3h polyenoctupolar molecules. Theoretically, we applied the additive model to analyze (beta) for multipolar nonlinear optical (NLO) molecules. The hyperpolarizability is dissected into an additive term and an interaction term, and the equations for evaluating the additive (beta) A and interaction (beta) I terms were derived for multipolar molecules. The structure and substituent effects were analyzed for various planar C3h and C2v multipolar molecules, based on the calculation results of the (beta) ijk from a CNDO/S program. The relations of experimental (parallel)(beta) (parallel) with conjugation lengths were given, which agree well with out theoretical results.