Maker Fringe Analysis Research Articles

Low-loss c-axis oriented Zn0.72Mg0.28O nonlinear planar optical waveguides on silicon.

A material platform of highly c-axis oriented Zn1-xMgxO thin films is developed for nonlinear planar waveguides and electro-optic modulators on Si. Mg content in the film greatly influences the quality of film growth. The second harmonic generation measurement and Maker-fringe analysis reveal that the second-order nonlinear susceptibility tensor element χ33 of the annealed Zn0.72Mg0.28O is approximately 4.2 times larger than that of ZnO. The propagation loss of 633 nm wavelength light in the annealed air/Zn0.72Mg0.28O/SiO2 slab waveguide is 0.68 ± 0.09 dB/cm and 0.48 ± 0.03 dB/cm for the TE0 and TM0 modes, respectively. These results suggest the great potential of the c-axis oriented Zn0.72Mg0.28O nonlinear planar waveguides for applications in on-chip optical interconnects.

Effect of sodium addition and thermal annealing on second-order optical nonlinearity in thermally poled amorphous Ta2O5 thin films

We demonstrate second-order optical nonlinearity (SON) induced in amorphous tantalum pentoxide (Ta2O5) films by thermal poling. The effects of sodium addition and thermal annealing on the efficiency and stability of second harmonic generation (SHG) have been investigated. Maker fringe analysis has been used to quantify the poling-induced SON. χ(2) of 0.46 ± 0.02 pm/V and 0.34 ± 0.02 pm/V was achieved for sodium-containing and pure Ta2O5 films, respectively. Both the strength and the temporal stability of the induced nonlinearity are discussed with respect to the poling mechanisms and measured electrical conductivity. The lower density of uncombined charges of the Ta2O5 thin films is believed to play a role in the strength of SHG signal, and the rate of SHG decay decreases with thermal annealing.

Closed-form Maker fringe formulas for poled polymer thin films in multilayer structures

We report new closed-form expressions for Maker fringes of anisotropic and absorbing poled polymer thin films in multilayer structures that include back reflections of both fundamental and second-harmonic waves. The expressions, based on boundary conditions at each interface, can be applied to multilayer structures containing a buffer and a transparent conducting oxide layer, which might enhance multiple reflections of fundamental and second-harmonic waves inside a nonlinear thin film layer. This formulation facilitates Maker fringe analysis for a sample containing additional multilayer structures on either side of a poled polymer thin film. Experimental data and numerical simulations are given to indicate the importance of inclusion of such a reflective layer in analyses for reliable characterization of second-harmonic tensor elements.

Poling of visible chromophores in millimeter-thick PMMA host

We report the direct high-voltage poling of the chromophores 4-methoxy-4’-nitrostilbene (MNS) and 2-methyl-4-nitroaniline (MNA) in a 1.2 mm thick polymethylmethacrylate (PMMA) host. The DC fields used to pole the guest-host system varied in strength from 58 to 67 Vμm−1, and the presence of chromophore orientation in the poled samples was subsequently analyzed via Maker fringe analysis. We observed values of the SHG coefficient d33 of 0.7 to 1.75pm/V at 532nm.

Second-harmonic generation in thermally poled chalcohalide glass

Second-harmonic generation in 60GeS(2)-20Ga(2)S(3)-20KBr chalcohalide glass was investigated by the thermal poling method. A large second-order nonlinear susceptibility, as high as 7.0 pm/V, was obtained in a poled sample by Maker fringe analysis. We believe this to be the first time that a clear second-harmonic wave was observed in chalcohalide glasses containing large amount of alkali ions (6.25 at. %). Such observation is of great potential use in all optical waveguide devices.

Second-harmonic generation in transparent surface crystallized glasses in the BaO–B2O3–TeO2 system

A transparent glass–ceramic containing borate crystallites in tellurite glass is reported. Controlled heat treatment resulted in surface crystallization of BaB4O7 in the BaO–B2O3–TeO2 glass system. The second-order optical nonlinearities observed in these surface crystallized glasses were attributed to the distortion present in the BaB4O7 unit cell as evidenced by x-ray powder diffraction studies. A d33 value of 0.08pm∕V was obtained from the Maker fringe analysis for a surface crystallized glass.

Bridged Polysilsesquioxanes with Improved Second Order Nonlinear Optical Properties and Stability

ABSTRACTWe report the synthesis and sol-gel polymerization of 4-nitro-N,N-bis[(3- triethoxysilyl)propyl]aniline 1. An efficient synthesis of the monomer was developed by the hydrosilylation of N, N-diallyl-4-nitroaniline. Optical quality thin films were synthesized by spin coating an n-butanol solution of 1 using formic acid as catalyst and source of water. We improved the temporal stability of the NLO signal from films prepared from 4-nitro-N,N-bis[(3-triethoxysilyl)propyl]aniline by increasing the intensity of the poling field and extending the heating period during the poling/curing stage. By Maker fringe analysis, a X(2) value of 9 × 10−8 esu was measured for these polysilsesquioxanes. If one assumes that the major component of the NLO effect is along the z-axis, the X(2) value corresponds to a d33 coefficient of 18.9 pm/V and a r33 value of 4.7 pm/V.

Nonlinear optical characterization of LiNbO_3 I Theoretical analysis of Maker fringe patterns for x-cut wafers

Maker fringe analysis was adapted to x-cut LiNbO3 wafers to examine variations in birefringence, thickness, and photoelastic strain. The pump beam was polarized parallel to the crystalline y axis and produced e- and o-polarized Maker fringes, owing to d31 and d22, respectively, by rotation of the sample about the y axis. Fitting our model to the o-polarized data enabled computation of the sample thickness to an uncertainty of approximately ±0.01 μm. The accuracy was limited by an implicit ±2×10-4 uncertainty in no that exists in the commonly used Sellmeier equation of G. J. Edwards M. Lawrence , Opt. Quantum Electron. 16, 373 (1984). For a pump wavelength λp=1064 nm, fitting the model to the e-polarized fringes revealed that ne at 532 nm deviated from the Sellmeier result by typically -1.58×10-4. The uniformity of ne over a wafer 10 cm in diameter was approximately ±4×10-5. This result is consistent with that expected from compositional variations. Our model included multiple passes of the pump and second-harmonic waves. The effects of photoelastic strain in producing perturbations and mixing of the e- and o-polarized fringes was investigated. This was restricted to two experimentally motivated cases that suggested that strains produce rotations of the optic axis by typically ±0.05° about the x axis and y axis with the former assigned to an indeterminant combination of S1,S2, and S4 and the latter to an indeterminant combination of S5 and S6. In both cases the magnitude of the collective strains is of the order of 10-4. The birefringence variations that are due to strain are of the same magnitude as those expected from compositional variations. The formalism developed here is used in the subsequent mapping study of x-cut wafers.

Synthesis and characterization of polymers containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 3. Poly(p‐chloromethylstyrene) derivatives

AbstractPoly[p‐(4′‐cyanobiphenyl‐4‐yloxymethyl)styrene]s (PCBMS) were prepared by chemical modification of poly(p‐chloromethylstyrene) with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl or free radical polymerization of p‐(4′‐cyanobiphenyl‐4‐yloxymethyl)‐styrene (CBMS). The latter method appeared to be a good one for the preparation of polymers with high glass transition temperature and high chromophore content if performed in dimethyl sulfoxide. There was no real evidence for liquid crystal properties in the resulting polymers, which resemble typical amorphous isotropic polymers. This indicates that these polymers should be considered to be polyethylene containing the benzyl ether of 4‐cyano‐4′‐hydroxybiphenyl as the mesogenic group attached directly to the backbone, and not as polystyrenes containing the cyanobiphenyl group attached to the backbone through a OCH2spacer. Some preliminary Corona poling experiments were performed, and the second harmonic generation coefficients d31 and d33, were measured by Maker fringe analysis. Interestingly, the ratio of d33 to d31 was found to be 6, which is much larger than the value of 3 predicted by the molecular statistical model for electric field poling of isotropic systems. This was attributed to conformational constraints on chromophore ordering as expected in such polymers containing no flexible spacer.

Generation of noncentrosymmetric structures in glassy liquid crystalline siloxanes

AbstractPhotoisomerization has been used to induce polar order in azo‐dye‐containing polymeric liquid crystalline oligosiloxanes at room temperature. The extent of the induced polar order was probed using a Maker fringe analysis at 1064 and 1542 nm. All samples studied at 1064 nm gave asymmetric fringe maxima, which was ascribed to a gradient in the induced polar order. The benefits of this poling mechanism, which operates on the combined effect of both light and static electric fields, was highlighted via poling of a defined area of the liquid crystal. This ability to selectively write polar structures into the liquid crystals may lead to electro‐optic diffractive devices.

Synthesis and characterization of polyoxetanes containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 1. Chemical modification of poly[3,3‐bis(chloromethyl)oxetane]with sodium 4‐cyano‐4′‐biphenyl oxide

AbstractTwo copolyethers were prepared by chemical modification of poly[3,3‐bis(chloromethyl)oxetane] with sodium 4‐cyano‐4′‐biphenyl oxide, employing the concept of having the cyanobiphenyl species serve concomitantly as both the nonlinear optical chromophore and the mesogenic moiety in the polymer. Their thermal behavior was established by means of DSC and optical microscopy. Some preliminary Corona poling experiments were performed, and the second harmonic generation coefficients d31 and d33 were measured by Maker fringe analysis. The results showed that liquid crystallinity enhances field‐induced polar ordering. The ratio d33/d31 was found to be much larger than 3, in agreement with the theoretical models for electric field poling of liquid crystalline polymers where hyperpolarizable chromophores are attached as side groups to a polymer backbone.

Side chain liquid crystalline polymers: Electric field effects and nonlinear properties

AbstractSide chain liquid crystalline polymers offer unique advantages as a new class of organic materials with potential for nonlinear optical response. Synthesis of a number of cyanobiphenyl‐based side chain polymers was carried out employing the concept of having the cyanobiphenyl species serve concomitantly as both the linear optical chromophore and the mesogenic moiety in the polymer. The thermal behavior of these polymers was studied by DSC, optical microscopy and X‐ray diffraction. Thin polymeric films were spin coated and electric field poling measurements were carried out as a function of temperature. The second harmonic (SH) coefficients d33 and d31 were measured by Maker fringe analysis and compared with the values predicted by molecular statistical models. The results showed that one can gain in net polar ordering by starting with a liquid crystalline system. The enhancement in d33 when < P<2 > = 0,6 was found to be a factor of 2,3‐3,3 over the isotropic case ( P<2 > = 0). The relaxation process was investigated. Both the presence of liquid crystal character in the material and the temperature at which the films were stored below Tg appeared important in determining the thermal stability of the SH coefficients.

Second-order nonlinear optical measurements in guest-host and side-chain polymers

The second harmonic generation (SHG) coefficients dij of several corona-poled guest-host and side-chain polymers have been measured and studied over time using a new Maker Fringe analysis. The electro-optic coefficient r33 and scattering losses have also been measured in thin-film waveguides, on silicon and glass substrates, made from some of the polymers. Kleinman symmetry (d15=d31) was not valid for near-resonant SHG in these materials and d15/d31 was determined. Stable values of d33, for a fundamental of 1.064 μm, were as high as 40 pm/V for one of the side-chain polymers. Optical waveguide losses determined from scattering measurements were as low as 0.4 dB/cm at 1.06 μm.

Nonlinear Optical Properties of PBT in Nematic Solutions

ABSTRACTThird-order nonlinear optical properties of lyotropic liquid crystal poly(1,4-phenylene-2,6-benzobisthiazole), PBT, solutions are studied by third harmonic generation measurements. Besides the enhancement observed for this coefficient with respect to the pure PBT, coupling is observed between the mean filed nematic director n and the incident fundamental polarization B0. Different geometries, with respect to the relative orientation of B0 and n, provided different harmonic Maker Fringe Patterns. These data are compared using refractive index measurements, independently achieved on these materials, and necessary for Maker Fringe analysis.