Prism Coupling Technique Research Articles

Refractive index profile in titanium-diffused congruent lithium tantalate optical waveguide

Titanium-diffused lithium tantalate (Ti:LT) multimode planar waveguide was produced by in-diffusion of titanium thin-film deposited onto a Z-cut congruent LT substrate. Titanium concentration (CTi) in the titanium-diffused layer was profiled by secondary-ion-mass-spectrometry. Modes guided in the waveguide were characterized by prism coupling technique. Refractive index in the waveguide is profiled on the basis of the measured mode indices, and is related to the CTi profile. The results show that both the refractive index and the CTi profiles obey to a Gaussian function. The profiles of titanium-induced extraordinary and ordinary index changes are almost identical, implying that the index change in the Ti:LT waveguide has a small anisotropy and the confinement to the mode field is polarization-insensitive. The ordinary and extraordinary index changes reveal a similar exponential dependence on the CTi with a power index of ∼0.8.

Diffusion processes for planar waveguides fabrication in soda-lime glasses

This paper reports about the fabrication of planar waveguides made of the ion-exchanged technique on a soda-lime glass. The process of the ion-exchanged from molten salt AgNO3+KNO3. Fabrication is conducted at 70 mol% of KNO3 and 30 mol% of an AgNO3 melt takes place for the realization of planar waveguides. The duration of ion-exchanged has been varied in the range of 25-900 minutes at the temperature of 315°C and 350°C to diffusion processes. The purpose of our experiments is especially to study the effect temperature and duration of the ion-exchange process to the main parameters used to characterized optical waveguides. The refractive index change, the number of modes waveguides, and diffusion depth had been investigated. The m-lines spectroscopy with standard prism-coupling technique at 632.8 nm was used to measure the number of modes and depth of waveguides. Refractive index was measured with refractometer ABBE. The Ocean Optics USB4000 Spectrometer is used to obtain absorption spectra. The values of penetration depth from glass surface increased with increasing ion-exchange temperature and time.

Refractive index change in Ti-diffused near-stoichiometric LiTaO3 waveguide and its relation to Ti-concentration

Ti-diffused near-stoichiometric(NS) LiTaO3 multimode planar waveguide was fabricated by diffusion of Ti-film coated onto a congruent LiTaO3 substrate and post Li-rich vapor transport equilibration process. The crystalline phase in the Ti-diffused layer was analyzed by powder x-ray diffraction and the Li2O-content was evaluated from the measured birefringence. The Ti-concentration profile was analyzed by secondary ion mass spectrometry. The modes guided in the planar waveguide were characterized by prism-coupling technique. The refractive index profile was constructed from the measured mode indices, and correlated with the Ti-concentration profile. The results show that the waveguide retains the LiTaO3 phase and is in an NS composition environment. Both the refractive index and Ti-concentration follow Gaussian profile. The extraordinary and ordinary index change profiles are almost same, implying that the electric field profile of the mode guided in the NS Ti:LiTaO3 waveguide would be polarization-insensitive. The ordinary and extraordinary index changes and the Ti-concentration follow a similar exponential relationship with a power index ∼1.3. Comparison shows that the Ti:LiTaO3 waveguide shows considerable differences from the Ti:LiNbO3 in Ti diffusivity, index change profile and its relation to Ti-concentration, and polarization dependence of guided mode.

Experimental Demonstration of Tunable Directional Scattering of Visible Light from All-Dielectric Asymmetric Dimers

Due to the presence of strong magnetic resonances, high refractive index dielectric nanoantennnas have shown the ability to expand the methods available for controlling electromagnetic waves in the subwavelength region. In this work, we experimentally demonstrate that an asymmetric dielectric dimer made of silicon can lead to highly directional scattering depending on the excitation wavelength, due to the interference of the excited magnetic resonances. A back focal plane imaging system combined with a prism coupling technique enables us to explore the scattering profile parallel to the substrate. The directivity of scattering along the substrate is high enough to produce selective guiding of light along the substrate. These results showing tunable control of directional scattering will encourage the realization of novel optical applications, such as optical nanocircuitry.

The evaluation of the refractive indices of bulk and thick polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers by the prism coupling technique

This paper presents the study of the optical properties of bulk and thin-film samples made from polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers. The chemical structures of the prepared elastomer samples were characterised by infrared spectroscopy. Also their transmission spectra were measured in the visible and infrared regions. The refractive indices of the samples were measured by the prism coupling technique using dark mode spectroscopy for five wavelengths (473, 632.8, 964, 1311 and 1552 nm). Particular focus was placed on the effect of the dependence of refractive index on the conditions of deposition. It has been found that the changes of refractive indices can be achieved by the modification of deposition conditions (hardening temperature and/or A:B mixed agent ratios). In order to obtain more significant changes of the refractive indices, we recommend using polydimethyl-diphenylsiloxane elastomer as a waveguide layer because of it content of phenyl groups, which lead to an increase in the value of the refractive index.

Visible and near-infrared optical properties of Nd:CLNGG crystal waveguides formed by proton implantation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11405041 and 61177084), the Nanjing University of Posts and Telecommunications Scientific Foundation (NUPTSF), China (Grant No. NY214159), and the RCOCET, China (Grant No. ZSF0401).

A Nd:CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H+ ion implantation with a dose of 1.0×1017 protons/cm2. Its propagating modes at 632.8 nm and 1539 nm were measured by the well-known prism coupling technique. The refractive index profile at either 632.8-nm wavelength or 1539-nm wavelength was optical barrier type in the proton-implanted Nd:CLNGG crystal optical waveguide, which was calculated by using the reflectivity calculation method. The near-field light intensity distributions were also simulated by the finite-difference beam propagation method in the visible and near-infrared bands.

Third order optical non-linear (Z-scan), birefringence, photoluminescence, mechanical and etching studies on melaminium levulinate monohydrate (MLM) single crystal for optical device applications

Z-scan studies on the grown crystal was investigated by diode-pumped Nd; YAG laser. Nonlinear refractive index (n2) and third-order nonlinear optical susceptibility (χ3) values of MLM were found to be −1.0 × 10−8 cm2/W and 1.36 × 10−6 esu respectively. Powder X-ray diffraction analysis depicted that the crystal belongs to monoclinic system with space group P21/c. Birefringence study revealed the optical dispersion behavior of MLM crystal. Linear refractive index on (10-1) plane was measured by prism coupling technique and was estimated to be 1.4705. Hardness study was carried out along three different planes which exhibit hardness anisotropy of 41.11%. Meyer's index values of the grown crystal for the (10-1), (010) and (111) planes were found to be 2.39, 2.61 and 2.04 respectively. Etching studies on the prominent (10-1) growth plane was explained by two dimensional layer growth mechanisms. Photoluminescence study was performed on MLM crystal to explore its efficacy towards optical device fabrications.

Optical waveguides in Er3+/Yb3+-codoped silicate glasses fabricated by proton implantation

In this work, a planar waveguide was fabricated by proton implantation in Er3+/Yb3+-codoped silicate glasses with energies of (500 + 550) keV and fluences of (1 + 2) × 1016 ions/cm2. The end-face coupling method was employed to determine whether the light could be confined in the waveguide or not. The prism coupling technique was applied to measure the guided mode spectrum and the intensity calculation method was used to construct the refractive index profile. With the profile, a near-field intensity distribution was calculated by the finite difference beam propagation method. The obtained results may be helpful in developing integrated optical devices.

Visible to near-infrared refractive properties of freshly-excised human-liver tissues: marking hepatic malignancies.

The refractive index is an optical constant that plays a significant role in the description of light-matter interactions. When it comes to biological media, refraction is understudied despite recent advances in the field of bio-optics. In the present article, we report on the measurement of the refractive properties of freshly excised healthy and cancerous human liver samples, by use of a prism-coupling technique covering the visible and near-infrared spectral range. Novel data on the wavelength-dependent complex refractive index of human liver tissues are presented. The magnitude of the real and imaginary part of the refractive index is correlated with hepatic pathology. Notably, the real index contrast is pointed out as a marker of discrimination between normal liver tissue and hepatic metastases. In view of the current progress in optical biosensor technologies, our findings may be exploited for the development of novel surgical and endoscopic tools.

Surface plasmon resonance study on the optical sensing properties of tin oxide (SnO2) films to NH3 gas

Surface plasmon resonance (SPR) technique is an easy and reliable method for detecting very low concentration of toxic gases at room temperature using a gas sensitive thin film layer. In the present work, a room temperature operated NH3 gas sensor has been developed using a laboratory assembled SPR measurement setup utilising a p-polarized He-Ne laser and prism coupling technique. A semiconducting gas sensitive tin oxide (SnO2) layer has been deposited under varying growth conditions (i.e., by varying deposition pressure) over the gold coated prism (BK-7) to excite the surface plasmon modes in Kretschmann configuration. The SPR reflectance curves for prism/Au/SnO2/air system for SnO2 thin films prepared at different sputtering pressure were measured, and the SnO2 film deposited at 10 mT pressure is found to exhibit a sharp SPR reflectance curve with minimum reflectance (0.32) at the resonance angle of 44.7° which is further used for sensing NH3 gas of different concentration at room temperature. The SPR reflectance curve shows a significant shift in resonance angle from 45.05° to 58.55° on interacting with NH3. The prepared sensor is found to give high sensing response (0.11) with high selectivity towards very low concentration of NH3 (0.5 ppm) and quick response time at room temperature.

Properties of Siloxane Based Optical Waveguides Deposited on Transparent Paper and Foil

In this paper, we present the properties of flexi- ble planar optical waveguides made of siloxane-based polymer deposited on Xerox transparent paper and PLEXI- GLAS foil substrate. Measurement of optical properties such as the waveguiding properties and refractive index is carried out by the prism coupling technique for five wave- lengths (473, 632.8, 964, 1311 and 1552 nm) and propa- gation optical loss were measured by the fiber probe tech- nique at a wavelength of 632.8 nm (He-Ne laser). The measurement proved waveguiding properties for all meas- ured wavelengths and the losses generally did not exceed 0.40 dB·cm -1 ; the best samples had optical losses around 0.24 dB·cm -1 .

Diffusivity, solubility and thermodynamic modelling of diffusion growth of Ga3+-doped LiTaO3 thin film for integrated optics

A thermodynamic study was performed on diffusion growth of Ga3+-doped LiTaO3(LT) thin film for integrated optics. Some Ga3+-doped LT thin films were grown on LT surface by in-diffusion of homogeneously coated Ga2O3 film at the temperature range of (1273 to 1473)K. After growth, the refractive indices at Ga3+-doped and un-doped surface parts were measured by prism coupling technique and Li composition there was evaluated from the measured refractive indices. The results show that Ga3+ dopant has small effect on the LT index. Li2O out-diffusion is not measurable. The Ga3+ profile in the grown thin film was analysed by secondary ion mass spectrometry. It is found that the grown Ga3+ ions follow a complementary error function profile. A thermodynamic model for Ga3+ diffusion growth is suggested and verified experimentally. From the measured Ga3+ profiles, some thermodynamic parameters were obtained. These include diffusivity, diffusion constant, chemical activation energy, solubility, solubility constant and enthalpy of solution. These parameters are crucial to design and growth of a desired Ga3+-doped LT thin film for integrated optics. Comparison shows that Ga3+ grows in LT two orders faster than Ti4+ because of its smaller radius. Ga3+ diffusivity/solubility in LT is one order/1.5-fold lower than in LiNbO3 because Ta has a larger atomic mass and hence a lower mobility than Nb.

Er3+ diffusion in LiTaO3 crystal

Some Er3+-doped LiTaO3 plates were prepared by in-diffusion of Er-metal film locally coated onto congruent Z-cut substrate in air at a wide temperature range from 1000 to 1500°C. After diffusion, Er3+-doping effect on LiTaO3 refractive index and Li2O out-diffusion arising from Er3+ in-diffusion were studied at first. Refractive indices at the doped and undoped surface parts were measured by prism coupling technique and the surface composition was estimated. The results show that Er3+ dopant has small contribution to the LiTaO3 index. Li2O out-diffusion is slight (Li2O content loss <0.3mol%) for the temperature below 1300°C while is moderate (Li2O content loss <0.6mol%) for the temperature above 1400°C. The Er3+ profile was studied by secondary ion mass spectrometry. The study shows that the diffused Er3+ ions follow either a complementary error function or a Gaussian profile. Characteristic parameters including diffusivity, diffusion constant, activation energy, solubility, solubility constant and heat of solution were obtained and compared with the LiNbO3 case. The comparison shows that the diffusivity and solubility in LiTaO3 are considerably smaller than in LiNbO3 because of the difference of Ta and Nb in atomic weight.

Investigation of optical properties of multilayer dielectric structures using prism-coupling technique

A method based on resonant excitation of waveguide modes with a prism coupler is proposed for measuring the thickness and refractive index of thin-film layers in multilayer dielectric structures. The peculiarities of reflection of TE- and TM-polarised light beams from a structure comprising eleven alternating layers of zinc sulfide (ZnS) and magnesium barium fluoride , whose thicknesses are much less than the wavelength of light, are investigated. Using the mathematical model developed, we have calculated the coefficients of reflection of collimated TE and TM light beams from a multilayer structure and determined the optical constants and thicknesses of the structure layers. The refractive indices of the layers, obtained for TE and TM polarisation of incident light, are in good agreement. The thicknesses of ZnS and layers, found for different polarisations, coincide with an accuracy of . Thus, we have demonstrated for the first time that the prism-coupling technique allows one to determine the optical properties of thin-film structures when the number of layers in the structure exceeds ten layers.

Doped with DR13 molecules TiO2/organically modified silane organic–inorganic hybrid materials with low propagation loss and ultrafast optical response

Disperse red 13 (DR13) azoaromatic chromophores were incorporated into sol-gel derived TiO 2 /organically modified silane matrix to achieve a hybrid material with low propagation loss and ultrafast optical response. The planar waveguide and nonlinear optical properties of the as-derived hybrid films were studied by a prism coupling technique and an optical Kerr shutter technique with an 800-nm femtosecond laser, respectively. Results indicate that the response time of the bulk sample doped with 0.1% DR13 molecules is less than 208 fs, and the third-order nonlinear refractive index is estimated at about 1.141×10 −15 cm 2 /W . The planar waveguide film with a low propagation loss less than 1 dB/cm for both transverse electric and transverse magnetic modes at a wavelength of 1312 nm can be easily obtained by a spin-coating process. It can be concluded from the above results that the as-prepared hybrid materials under present conditions are expected to have potential in ultrafast optical applications.

Control of scandium diffusion in LiNbO3 single crystal by co-diffusion of titanium

The mutual influence of co-diffused Ti4+ and Sc3+ in LiNbO3 single-crystal was studied. Sc3+/Ti4+ co-doped LN plates were prepared by annealing (at 1060 °C in wet O2) Z-cut congruent LiNbO3 substrates coated with stacked Sc2O3 and Ti films, which have different thicknesses and coating sequences. After the annealing, the refractive index and composition at the undoped and Sc3+-only doped surface parts were characterized by prism coupling technique. The Sc3+ and Ti4+ profiles were analyzed by secondary ion mass spectrometry. The results show that the Sc3+-doping has little contribution to the LiNbO3 refractive index. Li2O out-diffusion is not measurable. In the only diffusion case, the Sc3+ diffuses five times slower than the Ti4+. In the Sc3+/Ti4+ co-diffusion case, the Ti4+ assists and controls the Sc3+ diffusion. The Sc3+ diffusivity increases linearly with the initial Ti-metal thickness. In contrast, the Sc3+ affects the Ti4+ diffusion little. Neither the Sc2O3 film thickness nor the coating sequence influences the diffusivity of the two ions. The co-diffusion features are explained. A model for the co-diffusion system is suggested and verified experimentally. The Ti:Sc:LiNbO3 planar and strip waveguide are optically characterized. The results show that the Sc3+ presence does not affect the waveguide characteristics and the waveguide is optical-damage-resistant.

Effect of heat treatment on optical properties of crosslinkable Azo Chromophore doped in poly amic acid

In this work, we have studied the optical properties of a crosslinkable poly amic acid containing Disperse Red 1. The thin films were cured at 130, 160 and 195°C. The structural and optical properties of the doped films were investigated by using UV-VIS spectra, and Prism Coupling techniques. The composite crosslinks during poling rendering it totally insoluble. A r33 of 1.5 pm/v was obtained after poling.

Sol-gel Preparation and Optical Properties of TiO2/Organically Modified Silane Hybrid Material Containing DR13

Disperse red 13 (DR13) azoaromatic chromophores were incorporated into sol-gel derived TiO2/organically modified silane matrix to achieve a hybrid material doped with dye molecules. Nonlinear optical properties of the asprepared hybrid material were investigated by an optical Kerr shutter technique with an 800-nm femtosecond laser. It is obtained that the response time of the bulk sample doped with 0.1% DR13 molecules is less than 208 fs and the third-order nonlinear refractive index is estimated at about 1.141×10-15 cm2/W. It is also found that the sample of material with higher DR13 content could be with higher third-order nonlinear susceptibility. The linear refractive index and the thickness of the hybrid films derived by a spin-coating process were also studied by a prism coupling technique. It is found that with an increasing of the baking temperature, both the refractive index and the thickness of the hybrid films decrease. Absorption spectra, microstructural and morphological properties of the hybrid films were also characterized by UV–Vis absorption spectroscopy, thermal gravimetric analysis, Fourier-transform infrared spectroscopy and atomic force microscopy. Results indicate that the as-prepared hybrid material is expected to be potential in ultrafast photonic applications.

Influence of phosphorous precursors on spectroscopic properties of Er3+-activated SiO2-HfO2-P2O5 planar waveguides

(70-x)SiO2-30HfO2 -xP2O5 (x= 5, 10 mol %) glass planar waveguides activated by 0.5 mol% Er3+ ions were prepared by sol-gel route. Several phosphorous precursors have been investigated for the synthesis of a dielectric stable sol useful for the realization of planar waveguides. The waveguides were investigated by different diagnostic techniques. The optical properties such as refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 632.8 and 543.5 nm by prism coupling technique. Transmission measurements were carried out in order to assess the transparency of the deposited films. Photoluminescence measurements and lifetime decay curves of the Er3+ transition (4I13/2 → 4I15/2) were performed in order to investigate the role of P2O5.

Zr4+/Ti4+ Codiffusion Characteristics in Lithium Niobate

Zr4+/Ti4+‐codoped LiNbO3 plates were prepared by local codiffusion of stacked ZrO2 and Ti metal films coated onto Z‐cut congruent LiNbO3 substrates in wet O2 at 1060°C. The metal and oxide films have different thicknesses and coating sequences. After diffusion, the Zr4+ doping effect on the refractive index of LiNbO3 and the Li2O out‐diffusion issue were studied by the prism coupling technique. The codiffusion characteristics of Zr4+ and Ti4+ were studied by secondary ion mass spectrometry. The results show that the Zr4+ doping has little contribution to the refractive index of the crystal. Li2O out‐diffusion is not measurable. In the Zr4+‐only diffusion case, the diffusivity of Zr4+ is four times smaller than that of Ti4+. In the Zr4+/Ti4+ codiffusion case, the Ti4+ codiffusion assists the Zr4+ diffusion. The Zr4+ diffusivity increases linearly by two more times with the increase in initial Ti film thickness from 0 to 200 nm. On the other hand, the Zr4+ affects the Ti4+ diffusion little. Neither the ZrO2 film thickness nor the coating sequence of Ti metal and ZrO2 oxide films influences the diffusivity of the two ions. All the codiffusion characteristics are explained. A Zr4+/Ti4+ codiffusion model is suggested that consists of two independent diffusion equations with a Zr4+ diffusivity dependent of Ti4+ concentration and a constant Ti4+ diffusivity. In addition, the existence of a waveguide in the Zr4+/Ti4+‐codoped layer is verified experimentally, and the optical‐damage‐resistant feature of the waveguide is verified by two‐beam hologram recording experimental results.