Waveguide Measurements Research Articles

Optical waveguide characterization of dielectric films deposited by reactive low-voltage ion plating

We determine the quality of single films of various oxides, which are deposited on thermally oxidized silicon wafers by reactive low-voltage ion plating (RLVIP), by measuring their optical waveguide losses. We use a prism coupler for inserting the radiation of a wavelength-selectable He-Ne laser into the waveguide and a CCD camera for imaging the light scattered from the surface of the films. The waveguide losses of the RLVIP films are typically of the order of 1 to 10 dB/cm. Some data obtained for TiO(2) layers on thermally grown SiO(2) and RLVIP SiO(2) seem to confirm the presence of an absorbing boundary layer between RLVIP SiO(2) and TiO(2) that has been found in SiO(2)-TiO(2) multilayers. The waveguide measurements also reveal unusual index gradients in thick (~ 10 µm) single layers of Al(2)O(3) derived from multimode effective index calculations.

Low- and high-frequency conductivities of RbAg 4I 5 and Ag β″-alumina at low temperatures

The specific ionic conductivities, σ, of polycrystalline RbAg 4I 5 and Ag β″-alumina superionic conductors were determined by two- and four-probe impedance measurements at low frequencies (10 −3Hz≤ƒ≤10 2Hz) and waveguide measurements at high frequencies (18×10 9Hz≤ƒ≤26.5×10 9Hz≡:k-band) in the temperature range 15K≤ T≤298K. Above a transition temperature T t=(90±20)K, the conductivity data represent clearly a silver ion transport process with thermal activation. The activation energies of the α, β, and γ phases of RbAg 4I 5 were determined for the low- and high-frequency ranges. Below T t a nearly temperature-independent conductivity was observed in accordance with previous results. Around T t a long-time relaxation effect is observed in low-frequency EIS measurements, changing α and the dielectric constant ε. The low-temperature conductivity data can be explained neither in terms of the jump-relaxation nor in terms of the two-level tunneling system (TLS) model. A different mechanism which takes into account the influence of inhomogeneities on the ionic conductivity is proposed. This mechanism is obviously valid in a restricted temperature range located between the ion TLS-tunneling and the jump-relaxation regimes.

The design and fabrication of optical filters using organic materials

In the vast majority of cases optical filters have been constructed using inorganic materials, as these are able to provide a wide range of refractive indices and useful mechanical properties. However, for short wavelength (UV/visible) applications, and particularly for rugate optical filters, it is often difficult to accurately control the stack thickness of inorganic materials. The Langmuir-Blodgett (LB) technique enables monomolecular layers of organic materials to be deposited in a highly organised structure with fine control of stack thickness. This work reports the use of organic materials deposited by the LB technique for the fabrication of quarter-wave and rugate optical filters. The materials used in this study were PSA 50 (a partially subsituted side-chain polysiloxane) and ω-TA (a hydrocarbon based carboxylic acid). Estimates for the refractive index and molecular length of each material were made from ellipsometry, reflectometry and waveguiding measurements on bulk layers. These values were then refined by measuring the response of a nine stack quarter-wave filter (530 nm operation) and back modelling to obtain a close fit with the theoretical response. Using these values a three cycle rugate filter was then fabricated for operation at 530 nm. Excellent agreement was obtained between the measured and theoretical response. In addition, data was obtained relating to the inherent low scattering behaviour of these films (less than 0.4% for a film 0.5μm thick) and the tilt angle of ω-TA (26°), the latter in good agreement with literature values.

Fabrication and Measurement of Fiber-Matched InP Rib Waveguides

Fabrication and Measurement of Fiber-Matched InP Rib Waveguides

Microwave modeling of 2-D active grid antenna arrays

A new measurement technique for determining the broadband driving point impedance of large two-dimensional active grid arrays is presented. The active array radiates a plane wave in the broadside direction when all elements are locked in phase. For analysis, the array is reduced to a single unit cell by exploiting the array symmetries. The driving point impedance of the unit cell is determined by using the dielectric waveguide measurement method (DWM). The approximations of the method are discussed, and the method is compared with other measurement techniques. Results are presented for four square arrays: dipole, bow-tie, double-vee and slot array. The measurement method is verified by comparing it to the full-wave theory in the whole range. It is shown that all four antenna arrays can be represented by very simple circuits that use only transmission lines as circuit elements. The bow-tie array is found to represent the best choice for broadband operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Complex dielectric behavior of polyaniline at microwave and millimeter-wave frequencies

A study of the complex dielectric properties at microwave and millimeter-wave frequencies on several polyanilines was performed. The polymers investigated were based on emeraldine salts. The chemically synthesized emeraldine base was protonated with acids of various pH levels. Aqueous HCl (pH range 0.12 to 1.07) and tosylic (pH range 0.22 to 1.13) acids were used. Complex permittivities of the emeraldine base and salts were determined at the X-band and R-band using waveguide measurements. Characterization techniques were developed to reduce the measurement error. This included the electrical determination of the sample holder length and sample position. The real component of the dielectric constant was found to vary from 4 to 131 at X-band and from 3.8 to 1910 at R-band. The dielectric loss spanned three orders of magnitude at X-band and four orders of magnitude at R-band. The frequency dependence was relatively level within each band with a slight decrease in each permittivity component with increasing frequency. The d.c. conductivity ranged from 10 −4 to 10 −1 S/cm for the emeraldine salts. The time dependence of the complex permittivity and d.c. conductivity was examined.

Selective excitation of high-order modes in circular waveguides

The excitation of very high-order modes in circular waveguides has been performed in a cavity with a connected up-taper with a geometry similar to those used in gyrotrons. A Gaussian beam was coupled to the cavity which was made translucent by an array of holes. With the help of a special optics, the amplitude as well as the phase distribution of the beam was matched to the mode to be excited in the resonant cavity. By simple rotation of one mirror to adjust the phase distribution together with the change of frequency to match the resonance condition, a large number of modes could be produced with one experimental set-up. Field measurements in the output waveguide show a high mode purity of the radiation and confirm the calculations. The method can be used for cold tests of electrodynamic systems operating with these modes, e.g. quasi-optical converters for gyrotrons.

Frequency dependence of the FMR linewidth in single crystal barium ferrite platelets

Measurements of the frequency dependence of the room-temperature ferromagnetic resonance (FMR) linewidth have been performed in well-characterized barium hexaferrite single crystals at millimeter-wave frequencies. A shorted waveguide measurement technique was used to obtain very clean FMR profiles in the frequency range of 55 to 90 GHz. FMR field values versus frequency determined from these profiles show good agreement with theoretical values for uniform mode precession. The FMR linewidth increases linearly with frequency at a rate of 0.54+or-.02 Oe/GHz, and has a zero frequency extrapolation close to zero. These data yield a Landau-Lifshitz damping frequency of 4.6*10/sup 6/ rad/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Guided-wave optical properties of sol-gel ferroelectric films

Sol-gel processing methods have been used to prepare thin films of lead titanate, Pb(Zr,Ti)O3, and Pb(Mg1/3Nb2/3)O3 on sapphire and single-crystal strontium titanate substrates. These films have been characterized using x-ray diffraction, optical waveguiding measurements at 633 nm wavelength, and optical transmission measurements. The films, in general, contain a mixture of perovskite and pyrochlore phases, with perovskite formation being favored by higher processing temperatures, by use of the SrTiO3 substrates, and by the addition of excess lead precursor compound to the starting solutions. The films have refractive indices close to, but lower than, those of the corresponding bulk materials. The reduction of the refractive indices from the bulk values is believed to result primarily from incomplete densification. Transmission measurements show that the optical dispersion in the PbTiO3 films is similar to that in the bulk crystal. Although all films showed scattering losses, waveguiding over distances up to 1 cm was observed in some films. For multimode waveguides, conformity of the mode indices to those expected for a uniform guide is suggested as one test of film uniformity as a function of depth.

Optical loss measurement of low-loss thin-film waveguides by photographic analysis

Photographic film was used to measure low intensities of guided light scattered from three different thin-film optical waveguides. The technique is shown to permit measurement of optical loss down to 0.07 dB/cm. The method involves the taking of a photograph of a guided light beam (lambda = 632.8 nm) and the use of a microdensitometer to measure the two-dimensional scattered intensity profile. The sensitivity of the photographic film permits the measurement of low light levels, and the beam profile information permits the evaluation of the uniform scattering assumption. The technique can be adapted to channel waveguide loss by using high-definition photographic film. Additionally, the use of infrared-sensitive film can permit the technique to measure loss in the infrared.

Side-chain dilution effects on the optical properties of poly[3-alkylthiophene

Waveguiding and refractive index measurements were performed at a number of wavelengths in the red and near infrared region of the spectrum by grating coupling into a series of polythiophenes, poly[3-tetradecylthiophene] (PT14), poly[3-decylthiophene] (PT10) and poly[3-hexylthiophene] (PT6) films. The dispersion in the refractive index was compared to the Kramers-Kronig analysis of the absorption spectra. A decrease of the refractive indices with increasing number of side-chains was found due to a volume dilution effect of the optically active main chain.

Complex Permittivity Studies of Polyaniline

ABSTRACTA study of the complex dielectric properties at microwave and millimeterwave frequencies on several polyanilines was performed. The polymers investigated were based on emeraldine salts. The chemically synthesized emeraldine base was protonated with acids of various pH levels. Aqueous HCI (pH range 0.12 to 1.07) and Tosylic (pH range 0.22 to 1.13) were used. Complex permittivities of the emeraldine base and salts were determined at X-band and R-band using waveguide measurements. Characterization techniques were developed to reduce the measurement error. This included the electrical determination of the sample holder length and sample position. The real component of the dielectric constant was found to vary from 4 to 107 at Xband and from 3.8 to 926 at R-band. The dielectric loss spanned 3 orders of magnitude at X-band and 4 orders of magnitude at Rband. The frequency dependence was relatively level within each band with a slight decrease in each permittivity component with increasing frequency. The DC conductivity ranged from 10−4 S/cm to 10−1 S/cm for the emeraldine salts. The time dependence of the complex permittivity and DC conductivity was examined.

Characterization of annealed proton exchanged LiNbO/sub 3/ waveguides for nonlinear frequency conversion

A thorough and detailed characterization of annealed proton-exchanged (APE) waveguides in Z-cut LiNbO/sub 3/ is described. The mode index measurements in planar waveguides as a function of wavelength and annealing time are reported, including useful analytical relations for the refractive index change, its dispersion, and the depth profile as a function of annealing parameters. Analytical expressions for the mode propagation characteristics are presented and experimentally verified with reasonable accuracy. It is shown that the planar waveguide characterization results can be used to model the channel waveguide characteristics accurately. The model provides closed-form expressions for the mode index and the mode field profile, and the theoretical results are in excellent agreement with the measured data. The technique is used to accurately predict the phase mismatch between the fundamental and second harmonic modes in frequency-doubling experiments using APE channel waveguides. An optimum waveguide geometry for which the phase mismatch is relatively insensitive to the waveguide nonuniformity was predicted and verified experimentally.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Accuracy of bicomplex permeability measurements in waveguides using automatic network analyzers

Accuracy of bicomplex permeability measurements in waveguides using automatic network analyzers

Microwave dielectric properties of layered perovskite A 2B 2O 7 single-crystal fibers

Single-crystal fibers of the layered perovskite A 2B 2O 7 (A=La, Nd, Ca, B=Ti, Nb) family were grown by the laser-heated pedestal growth technique. The dielectric constant and loss at 9 GHz were measured by a perturbation waveguide technique. The Nd 2Ti 2O 7 and Ca 2Nb 2O 7 exhibited low losses, below 0.0009. The single-crystal fiber geometry is well suited to the waveguide measurement technique and offers a rapid evaluation of the microwave dielectric properties of a range of materials.

Measurement of nonlinear refractive index and transmission in polydiacetylene waveguides at 1.319 μm

Nonlinear optical measurements in strip-loaded channel waveguides of poly(4-BCMU) at 1.319 μm are reported. Using a pulse-modulated interferometry method, the intensity-dependent refractive index is found to have an electronic contribution, n2=(4.8±2.7)×10−8 cm2/MW, and an estimated thermal contribution, n2=−(7.9±4.5)×10−11 cm2/MW, for 60 pS laser pulses at 76 MHz. The two-photon absorption coefficient β is less than 0.25 cm/GW. Figures-of-merit suggest that poly(4-BCMU) has properties desirable for all-optical devices, but that fabrication losses and thermal effects due to absorption will limit device performance.

Direct comparison of hydrogen depth distributions and refractive index profiles in annealed proton-exchanged z-cut LiNbO3 waveguides

For the first time, to the authors&apos; knowledge, hydrogen distributions in weakly and strongly annealed protonexchanged z-cut LiNbO3 have been measured using modified secondary ion mass spectrometry and correlated with refractive index profiles determined by optical waveguide measurements.

Measurement of permeability and permittivity of ferrites

The dielectric and magnetic properties of some ferrite materials have been measured by four widely different methods. These are measurements in waveguide at 14 GHz using a slotted line approach; measurements in waveguide using S parameter data; the open resonator at 24 GHz (the solution of the equations is presented); and an oblique reflection method at 35 GHz. A successful form of apparatus is described. The results from the methods are contrasted. The open resonator method appears to be a good technique for frequencies above about 30 GHz, but it requires very thin specimens, which are difficult to make. The oblique reflection method is promising and has advantages for lossy materials.

Dielectric properties measurement of substrate and support materials

AbstractIn this paper a fast and straightforward waveguide measurement technique is described for the determination of the dielectric constant and loss tangent of many commercially available materials. These dielectric materials include Cuflon, Teflon, Arlon's polyimides, Lockheed's ceramic foams, and Rogers Duroid materials. The effective dielectric constant and loss tangent of Hexsel's honeycomb material is also measured by this method and is compared to the predicted data obtained using the volume averaging theory. The accuracy and other features of this measurement technique are also discussed.

A novel technique for measurement of the mode indexes of channel waveguides

An accurate technique for measurement of small differences in the mode indexes of channel waveguides is presented and compared with the prism coupler. It has a distinct advantage over the prism coupler method since it allows measurements in buried waveguides as well. The absolute mode index of an individual guide can also be obtained provided a guide near the mode cutoff is available on the same substrate. The technique is expected to be useful with waveguides of high index materials, especially when the prism coupler monitoring the uniformity of optical fibers or measuring the waveguide birefringence.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>