Photoinduced Refractive Index Change Research Articles

Extraordinary stability of anisotropic femtosecond direct-written structures embedded in silica glass

In this letter we report the different response to temperature displayed by isotropic femtosecond written structures (type I_fs), and anisotropic ones (type II_fs), which are characterized by the presence of a self-assembled subwavelength periodic structure within the irradiated volume. We observe that the anisotropic structures display an extraordinary annealing behavior, namely, their photoinduced change in refractive index increases with the annealing temperature. We explain our experimental results with a theoretical model.

Optical-stopping effect of As2S8 channel waveguide fabricated by method of photoinduced refractive index changes

The photorefractive phenomenon of As2S8 film is reported in this paper. An ultraviolet irradiation technique is presented and applied successfully to As2S8 channel waveguide preparation on the basis of analyzing these experimental data. This channel waveguide of As2S8 displays good characteristics of a waveguide using a guided mode excitation. It is found that the optical stopping effect of As2S8 channel waveguide has the rotential application owing to its switching function with the photo-optical effect.

Ultrafast photoresponsive materials and molecular photonics applications by guided wave mode geometry

Molecular photonics, information processing based on strong interactions of photons and molecules, has attracted much attention, since it can fully utilize many superior properties of both photons and molecules. We have developed polymeric materials showing ultrafast absorption changes in the visible to near-infrared regions including the telecommunication wavelength by photoinduced electron transfer and reverse reactions between substituted pyridinium and its counter anion. By selecting the counter anion we succeeded in making steady and ultrafast absorption changes. Time-resolved absorption and fluorescence spectroscopy upon femtosecond laser excitation revealed reaction mechanism and ultrafast dynamics. In order to fully utilize such photoresponses in molecular photonics, we proposed guided wave mode (GWM) device composed of a prism, a low refractive index polymer film, and a photoresponsive polymer film. The reflectance in this GWM is controlled by many factors such as thickness values and complex refractive indices of two polymer layers as well as an incident angle and wavelength. We successfully achieved sensitive, all optical, and very fast control of reflectance by means of photoinduced complex refractive index changes upon femtosecond laser excitation.

Evaluation of photoinduced change in refractive index of a polymer film doped with an azobenzene liquid crystal by means of a prism-coupling method

The photoinduced change in refractive index of poly(methyl methacrylate) films doped with an azobenzene liquid crystal was measured by the prism-coupling method. Upon irradiation of the film with a high-pressure mercury lamp at 366nm, the coupling angles shifted and then recovered to the initial position by turning off the light. The change in refractive index was found to be 2×10−3, which is attributed to the reversible photoisomerization of the azobenzene moieties.

Photo-induced refractive index change of bismuth-based silicate glass

We report the ultraviolet laser-induced absorption spectra and refractive index changes in bismuth-based silicate glass. A positive maximum refractive index change of 6 × 10−4 has been observed in bismuth-based silicate glass upon exposure to a pulsed 248 nm KrF excimer laser. It is also seen that the changes in the absorbance and refractive index are strongly dependent on glass melting conditions.

Metal mask fabrication with an inkjet printer for AWG phase trimming using a photosensitive refractive index change

We report a simple method for fabricating a metal mask with wet etching designed to reduce the adjacent crosstalk of arrayed-waveguide gratings (AWGs) by using a photoinduced refractive index change. This process utilizes a commercially available inkjet printer and a copy machine, and so the resolution of the fabricated window pattern is not very high. However, the fabricated mask enables us to achieve a great reduction in adjacent crosstalk because it depends solely on a slowly varying component in the phase error distribution of an AWG.

Influence of UV-irradiation on the structure and optical properties of polycarbonate films

Abstract Polycarbonate films were prepared by casting technique. The absorption spectral analysis showed that the unirradiated PC has no absorption bands, while the irradiated films have two shoulder bands. This suggests that PC undergoes a photo-degradation process. The absorption coefficient and the optical energy gap ( E opt ) have been obtained from indirect allowed transitions in K-space. It was found that, E g decreases with increasing the irradiation time. The width of the tail of localized states in the band gap (Δ E ) was evaluated using the Urbach edge method. The refractive index ( n ) was determined from the analysis of the transmittance data. Analysis of the refractive index ( n ) yields the values of the long wavelength dielectric constant ( e ∞ ), the average oscillator wavelength ( λ o ), average oscillator strength ( S o ), average oscillator energy ( E o ), the refractive index dispersion parameters ( E o / S o ) and the dispersion energy ( E d ). The dependence of refractive index on irradiation time has been discussed. It was found that the photo-induced refractive index changes are very large. These changes suggest the applicability of PC films in optical devices.

Photoinduced Changes in Sn-Doped Sol-Gel Silica Glass Films

Sn-doped SiO2 thin films were fabricated on Si substrates by the Sol-Gel method. Permanent refractive index change was found using ultraviolet (UV) laser radiation at 248 nm. The photoinduced refractive index change increased after radiation and variety in the contents of Tin. The optical and surface properties of the films were characterized using X-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry (VASE).

PREPARATION OF MEROCYANINE SALTS BY TREATMENT OF ACIDS ON SPIROPYRANS AND INVESTIGATION ON THEIR PHOTOCHROMIC BEHAVIORS

Merocyanine salts were prepared and their photochromic behavior investigated. The salts were prepared from a solution of spiropyrans in the presence of acids such as toluenesulfonic acid and dodecylbenzene sulfonic acid under irradiation of UV light and heat. The 1H NMR spectrum confirmed the chemical structure of the merocyanine salts. The salt showed an absorption peak at 422 nm, which was blue-shifted as compared with the absorption peak at 578 nm of the merocyanine form of spiropyran. The salt form was quite stable and virtually exhibited a negative photochromism. The salt showed better fatigue resistance than the spiropyran. The photoinduced refractive index change for the salt films by a prism coupler method was estimated to be as large as 0.0055.

PHOTOINDUCED TRANSMISSION CHANGE IN BACTERIORHODOPSIN EMBEDDED PHOTONIC CRYSTAL SLAB

We investigate the transmission properties and its photoinduced change in a one-dimensional photonic crystal slab. This periodic waveguide consist of quartz grating substrate and a thin polymer film containing a photosensitive protein bacteriorhodopsin. We propose a scheme to achieve light-controlled optical switching using the photoinduced refractive index change of bacteriorhodopsin.

E′center in Ge-dopedSiO2glass

The $\mathrm{Ge}\text{\penalty1000-\hskip0pt}{E}^{\ensuremath{'}}$ centers generated by ultraviolet irradiation in Ge-doped amorphous $(a\text{\penalty1000-\hskip0pt})$ $\mathrm{Si}{\mathrm{O}}_{2}$ are considered to be closely related to the photoinduced refractive-index changes of this material. We have examined the structural stability of a Ge-related oxygen deficient center (Ge-ODC) using the first-principles pseudopotential method. We have found that the puckered configuration with an unpaired paradiamagnetic electron is more stable than the dimer one for a positively charged state. Our results provide strong theoretical support to a model of the photoinduced transformation of the neutral Ge-ODC into the $\mathrm{Ge}\text{\penalty1000-\hskip0pt}{E}^{\ensuremath{'}}$ center, as proposed in $\ensuremath{\alpha}$-quartz and $a\text{\penalty1000-\hskip0pt}\mathrm{Si}{\mathrm{O}}_{2}$. The origin of the photoinduced refractive changes of Ge-doped $a\text{\penalty1000-\hskip0pt}\mathrm{Si}{\mathrm{O}}_{2}$ is discussed.

Periodic precipitation of crystalline Ge nanoparticles in Ge–B–SiO2 thin glass films

Crystalline 20- to 40-nm-diam Ge nanoparticles were precipitated periodically in Ge–B–SiO2 thin glass films fabricated by the plasma-enhanced chemical vapor deposition method. Such a periodic structure was created by exposure to an interference pattern with a KrF excimer laser (248nm wavelength) and successive annealing at 600°C. Nanoparticles were precipitated predominantly in the unirradiated region after photoinduced refractive index change was erased completely after annealing up to 500°C.

Photoinduced absorption and refraction in azo dye doped PMMA films: the aging effect

We report the nonlinear interferometric and spectral studies of photoinduced changes of the complex refractive index in azo dye doped polymers. A simple theoretical analysis is used that describes rather well the experimental results when a dominant nonlinearity due to the photoexcitation mechanism, is present. The approach is used to study the behavior of chromophores in different aging stages of the host.

광섬유-평면도파로 결합기를 이용한 광변색성 디아릴에텐 유도체의 광유도 굴절률 변화에 관한 연구

광섬유와 평면도파로 결합기의 소산장 결합을 이용하여 디아릴에텐 유도체 DM-BTE(1,2-bis[2,5-dimethylthio-phen-3-yl]-hexafluorocyclopentene)의 광유도 굴절률 변화(photo-induced refractive index change)에 관하여 그 특성을 평가하였다. DM-BTE가 분산된 평면도 파로는 자외선과 가시광선(λ＞450 nm)의 조사에 의해 광변색 반응이 가역적으로 진행되었으며 굴절률변화에 의한 공명 파장 또한 가역적으로 이동하였다. 광변색 반응이 진행되는 동안 평면도 파로의 결정상태(crystal shape)는 일정한 형태를 유지하였으며, 자외선 조사시간에 대한 소자의 파장응답은 0.057 nm/sec 이었고 포화시간은 60 sec로 나타났으며, 가시광선이 다시 조사될 때의 공명파장의 변화는 0.028 nm/sec 이었고, 복귀시간은 140 sec로 측정되었다. We have manufactured and characterized the fiber-to-Planar Waveguide Coupler for analysis of the photo-induced refractive index change of DM-BTE .(l,2-bis[2,5-dimethylthio-phen-3-yl]-hexafluorocyclopentene) When irradiated with ultraviolet light, the colorless diarylethene(DM-BTE)-crystal turned red while keeping the crystal shape. The red color was bleached by irradiation with visible light(λ＞450 nm). The resonant wavelength was shifted and recovered owing to the refractive index variation of the planar waveguide because of its photo-functional properties on exposure to UV and visible light. The wavelength responses of this switch by UV exposure were measured as 0.057 nm/sec with saturation time of 60 seconds. and when illuminated by visible light, resonance wavelength variations were measured as 0.028 nm/sec, with recovery time of 140 seconds.

Trans-4-stilbenemethanol-doped photosensitive polymer fibers and gratings.

We report the development of photosensitive polymeric optical fibers for gratings. The fiber is made of a copolymer of methyl methacrylate and butyl methacrylate, and its core is made of a copolymer of methyl methacrylate, ethyl methacrylate, and benzyl methacrylate (90/4/6 molar ratio) doped with trans-4-stilbenemethanol. Ultraviolet absorption and photoinduced refractive-index change of the doped core system are presented, and its photosensitivity is demonstrated by fabrication of Bragg gratings in the core of the fiber by use of a pulse laser at 325 nm.

Large Photoinduced Densification in Organically Modified Germanosilicate Glasses

Organically modified germanosilicate (ORMOGSIL) glasses prepared by a sol-gel method showed a large refractive index change on ultraviolet exposure. The large photoinduced refractive index change in the ORMOGSIL glasses is mainly due to the structural densification caused by ultraviolet irradiation. The shifts in frequency of the Raman bands measured at room temperature reveal structural densification by reduction of the average intertetrahedral bonding angle θ in the ORMOGSIL glasses. Surface relief patterns by photoinduced densification were directly inscribed on the ORMOGSIL glasses.

Long-period fibre grating fabrication with femtosecond pulse radiation at different wavelengths

The fabrication of long-period fibre gratings (LPFGs) in optical fibres by femtosecond pulses at different wavelengths is reported. Several types of fibres were used and it was found that LPFGs with strong attenuation peaks (more than 20 dB) can be induced in hydrogen-loaded germanosilicate fibres using the second harmonic of a femtosecond Ti:sapphire laser without the use of an amplifier (400 nm, 70 fs and 2.5 nJ) and amplified, frequency-quadrupled pulses from a Nd:glass laser (264 nm, 220 fs and 0.4 mJ). Low ‘out-of-band’ losses and results of isochronal annealing for the fabricated gratings suggest that the photoinduced refractive index change is not accompanied by damage to irradiated fibres.

Two-component model for photo-induced refractive index change in hydrogen-loaded phosphosilicate glass

In wireline optical networks, planar lightwave circuits are next generation components capable of performing enhanced optical functions. Ultraviolet (UV) photoinduced refractive index increase at 193 nm was obtained experimentally in hydrogen-loaded doped silica glasses (P 2O 5 ∼ 1.5 mol% and B 2O 3 ∼ 9 mol% codoped, and phosphorus-doped P 2O 5 ∼ 8 mol%) used to realize channel waveguides. Refractive index variations (up to 9 × 10 −3) were measured using the prism-coupling technique and a two-component model is proposed to interpolate the experimental data of Δ n against total UV exposure fluence (kJ/cm 2).

Photorefractivity in nanostructured tin-silicate glass ceramics: a radiation-induced nanocluster size effect.

The possibility of obtaining permanent photoinduced refractive index changes, up to -10(-3), in nanostructured silica-based composites has been demonstrated in SiO(2):SnO(2) optical-grade glass ceramics exposed to ultraviolet radiation. Optical and electron paramagnetic resonance data suggest that the negative refractive index change involves a modification at the surface of the SnO2 nanoclusters, leading to a reduction of their crystalline size.

Photoinduced Refractive Index Change of Polymer Films Containing Mesoionic Sulfur‐Substituted Phenyloxatriazolones

AbstractWe measured photoinduced refractive index changes (see Figure) of polymer films containing various sulfur‐containing mesoionic compounds. PMMA films containing 30 wt.‐% of 3‐phenyl‐1,2,3,4‐thiatriazole‐5‐thione (3PTTT) showed refractive index changes of −0.036 during photoirradiation, at a wavelength far from the resonant region. An increase in the number of sulfur atoms in the mesoionic compounds doped in PMMA films resulted in the increase in refractive index changes during photoirradiation. The estimation and comparison of the changes in specific refraction and densities of the systems suggest that the change in electronic structure mainly contributes to the refractive index changes of the film in the case of 3PTTT, while the changes in both electronic structure and density equally contribute to the refractive index change in the film with 3‐phenyl‐1,2,3,4‐oxatriazole‐5‐thione (3POTT). Refractive indices, n, of PMMA films containing various weight fractions of 3POTT (square) and 3PTTT (circle). Open symbols are for n before photoirradiation, filled ones are for n after photoirradiation.magnified imageRefractive indices, n, of PMMA films containing various weight fractions of 3POTT (square) and 3PTTT (circle). Open symbols are for n before photoirradiation, filled ones are for n after photoirradiation.