High Refractive Index Change Research Articles

Thermal diffusivity of lead-free solders measured by photothermal beam deflection. Effect of the surrounding media

The search for lead-free alloys has increased markedly in recent years, as new environmental regulations have been approved. In particular, traditional solders used in the microelectronics industry are now being gradually replaced by new lead-free materials. In this work, we report measurements of the thermal properties of new Sn-based alloys with varying contents of Bi, Al, Ag and Cu, which have been developed as alternatives to the traditional lead-based solders used in microelectronic assemblies. Measurements of thermal diffusivity were performed using the photothermal beam deflection [1] (PBD) technique. We tested the influence of the surrounding media in the quality of the measurements. We found out that the sensitivity can be greatly improved using as surrounding medium fluids with very low thermal diffusivities and high refractive index change with temperature ( ∂ n / ∂ T ). Although a more general physical characterisation of the lead-free alloys, concerning measurements of electrical resistivity, mechanical properties and structural characterisation, is still under way, these thermal measurements combined with information about the electrical resistivity show that these alloys can be good alternatives for soldering applications.

Controlled Refractive Index Polymers: Polyphosphazenes with Chlorinated- and Fluorinated-, Aryloxy- and Alkoxy- Side-Groups

A series of novel halogenated alkoxy and aryloxy polyphosphazenes have been synthesized via macromolecular substitution reactions carried out on poly(dichlorophosphazene). These polymers showed good film-forming properties and tunability of refractive index. Moreover, several examples combined low glass transition temperatures with high refractive index changes as a function of temperature − a prerequisite for optical switching applications. The refractive indices could be controlled over the range of 1.3889−1.5610 by alterations to the side-groups or side-group ratios. The birefringence (nTE − nTM) of these polyphosphazenes was shown to be highly dependent on the amount of aryloxy side-group attached to the polyphosphazene backbone. They showed evidence of thermal stability up to 400 °C. These properties, combined with the tailorability of the polyphosphazene system make chlorinated- and fluorinated-, alkoxy- and aryloxy-substituted polyphosphazenes possible candidates for optical waveguide and optical s...

Photochromic Sol-Gel Films Containing Dithienylethene and Azobenzene Derivatives: From the Design of Optical Components to the Optical Data Storage

This work is devoted to photoresponsive hybrid organic-inorganic materials prepared by the sol-gel method, using dithienylethene or azobenzene as photosensitive chromophores. These photochromic units were covalently attached to the silica backbone as part of the main-chain and as a side group respectively. The electrocyclization of dithienylethene or the isomerization of azobenzene under irradiation cause local modifications of the optical properties of the host sol-gel polymers We took advantage of either high refractive index changes (>10−2) or material deformation of the sol-gel films to design optical components and to store information.

Active erbium-doped organic–inorganic waveguide

The existence of optical amplification at 1550 nm wavelength in channel waveguides using erbium doping and 980 nm laser pump involves as low a OH group quantity as possible. Moreover, a high refractive index variation between the guide and the cladding is necessary to induce a maximum confinement and then increase the doping efficiency. This field is now limited to pure inorganic materials or semiconductors. We propose to extend this field to hybrid organic–inorganic materials. In such a way, we have developed a new composition based on hydrophobic sol–gel precursors to reduce the OH quantity, and on a diacrylate monomer whose reactivity allows a high refractive index change under UV light exposure. Signal enhancement is observed for the first time in a hybrid organic–inorganic channel waveguide.

Fabrication of Erbium-Doped Channel Waveguides by a Combination of Ion Exchange and Sol-Gel Techniques

Erbium-doped germano-silicate thin films of good optical quality were produced by the sol-gel technique. High refractive index changes of up to 0.018 were obtained by sodium-silver ion exchange. Monomode optical waveguides with Gaussian mode profile were fabricated by this technique. It is shown that, if the ion exchange process parameters are well chosen, the influence of the waveguide fabrication on the active properties of the material is negligible.

Large photoinduced refractive index changes in pulsed-laser-deposited lead germanate glass waveguides with controllable refractive index sign change

A study of the photosensitivity of lead germanate glasses grown by pulsed laser deposition is presented. Lead germanate films were grown from stoichiometric bulk targets, on borosilicate glass substrates in an oxygen atmosphere, to form optical waveguides. The films grown exhibited high absorption in the ultra violet spectral area (around 240 nm) which indicated the possibility of high photosensitivity. The photosensitivity of the materials was examined by phase mask and interferometric grating recording over a wide ultra violet spectral region (325nm-193nm) using various continuous and pulsed laser sources. Very high refractive index changes (up to 1%) have been observed along with variable sign of the refractive index change depending on the oxygen background pressure used during growth and recording intensity

Ultrafast All-Optical Switch with an Operational Speed Unlimited by the Slow Relaxation of a High Efficiency Nonlinear Refractive Index Change.

We experimentally demonstrate that the switching speed of a novel symmetric Mach-Zehnder (SMZ) all-optical switch, proposed by the present authors, is unrestricted by normally slow relaxation times of highly efficient, incoherent nonlinear refractions. A cross-correlation trace with a full-width at half-maximum of 2 ps was achieved, which is corresponding to nearly full-switching at 1.5 ps. To our best knowledge, this is the fastest switching experiment with incoherent and thus realistic nonlinearities. We also demonstrate that a repetition rate much faster than that implied by the relaxation time of the utilized optical nonlinearity is also possible with the SMZ all-optical switch. We will explain an experimental result under excitation by packets of four control pulses with a pulse interval of 100ps. We point out that the well-known figure of merit for optical nonlinear materials is no longer applicable to the present device and discuss how it is modified to take full advantage of the present device. We also note that a square-like, contrary to the exponential-like, switching characteristic is quite important in practice and show that such square-like modulation is possible with the SMZ all-optical switch.

Extraordinary versus ordinary refractive index change in planar LiNbO3:Ti waveguides

Various planar waveguides are fabricated by indiffussion of one or two titanium layers into y-cut LiNbO3 substrates. The effective indices of guided TE- and TM-modes are measured for red, green, and blue light. The refractive index profiles are reconstructed by a new reliable inverse WKB procedure. Despite of widely differing profiles there is, for each wavelength, a one to one relationship between the changes Δno of the ordinary and Δne of the extraordinary refractive index. For low and for high refractive index changes Δne and Δno grow proportionally, but their ratios differ appreciably. The results support recent findings that the LiNbO3:Ti system exists in two distinct phases. Verschiedene planare Wellenleiter werden durch Eindiffusion von einer oder zwei Titanschichten in y-geschnittene LiNbO3-Substrate hergestellt. Die effektiven Indizes der geführten TE- und TM-Moden werden für rotes, grünes und blaues Licht gemessen. Mit einem neuen zuverlässigen inversen WKB-Verfahren werden die Brechungsindexprofile rekonstruiert. Trotz stark unterschiedlicher Profile existiert für jede Wellenlänge eine eins-zu-eins-Beziehung zwischen den Änderungen Δno des ordentlichen und Δne des außerordentlichen Brechungsindexes. Für niedrige und hohe Brechungsindexänderungen wachsen Δno und Δne proportional, jedoch unterscheiden sich ihre Verhältnisse beträchtlich. Die Ergebnisse bestätigen die kürzlich gemachte Entdeckung, daß das LiNbO3:Ti-System in zwei unterschiedlichen Phasen existiert.

Polymer thin film optical waveguide

AbstractPolymers that are suitable for thin films are also used as materials for hybrid optical IC's; however, it is not easy in general to get a high refractive index change in the waveguide using these materials. To remove this difficulty, we have used copolymers of glycidyl methacrylic acid and methyl methacrylic acid, doped with cinnamic acid; this acid was directly photolocked, by ultraviolet exposure, to the epoxy rings of glycidyl methacrylic acid. Eventually, a refractive index change as large as 2% was achieved. Single‐mode optical waveguides with various widths were fabricated by means of the present method, and the dependence of the loss on the waveguide width and the loss in a bend were measured.

Radiation damage and refractive index of ion-implanted LiNbO 3

The formation of radiation damage in LiNbO 3 crystals implanted at room temperature with N +, O + and Ne + ions, was analyzed by RBS, density and refractive index measurements. We have found that there are two steps in the dose dependence: 1) Formation of point defects and simple defect clusters connected with a remarkably high refractive index change in the low dose region. 2) “Amorphization” of the implanted surface layer in a narrow dose range around 10 15 cm −2 followed by the saturation of volume expansion ( ΔV max/ V = 0.10 ± 0.02) and refractive index change (− Δn 0 max = 0.165 ± 0.015, − Δn e max = 0.105 ± 0.015 at 0.6328 μm).