Studies on low-cost sol–gel spin-coated TiO2 thin film with high refractive index (HRI), which may be used as an intermediate layer to enhance the light extraction efficiency (LEE) of a typical bottom-emitting organic light emitting diode (OLED), are reported. The TiO2 solution is prepared using titanium tetra iso-propoxide, acetic acid, and ethanol. Spin coating method is used to deposit TiO2 thin films on glass substrate. Different optical characterizations of as-deposited and annealed (150°C, 300°C, and 450°C) TiO2 thin films on glass substrate are done, from which different properties of the film are derived. Ellipsometric measurement shows shrinkage in the thickness of the as-deposited TiO2 films after annealing at different temperatures. X-ray diffraction reveals amorphous TiO2 formation for all the samples. The RI of the coated film increases with the increase in annealing temperatures. Its value at 633 nm wavelength for the as-deposited film is found to be 2.1, which is quite high and it is seen that this RI can be further increased to 2.78 by annealing the samples at 450°C. This value is comparatively high compared to several other reported values of other researchers. The as-deposited sample reveals highest porosity, which further decreases with rise in annealing temperature. Our calculation of LEE for a typical OLED with the intermediate layer of this HRI as-deposited TiO2 film shows improvement of the LEE. However for annealed films, the experimentally obtained thicknesses are not adequate for this improvement, but it is shown that by increasing the film thickness, further improvement of LEE is possible.
A compact, dielectric–metal–dielectric surface plasmon polariton (SPP) waveguide is designed that can have propagation lengths as high as several thousand microns. The dielectric layers surrounding the metal waveguide are actually periodic layers of different nanometer-sized dielectric pairs. By proper selection of the surrounding layer widths, a device with a controllable effective index and increased compactness can be designed. It can have a propagation loss <1 dB / cm, which is much less than any conventional SPP waveguide. Introduction of a metallic layer outside the dielectric layer of this structure results in a hybrid Tamm plasmon polariton (TPP), which can be used for sensing applications. Its sensitivity and the figure of merit are reported at different operating wavelengths. It is seen that the proposed hybrid TPP structure can be used to detect a larger refractive index range with comparable or better sensitivity than other plasmonic sensors. Determination of different optical parameters required for the design is done using a semianalytical approach. All the necessary steps of the present analysis are discussed and the calculated results are matched and compared with similar results of the other researchers whenever required.
Horizontal spot size converter required for horizontal light coupling and vertical bridge structure required for vertical integration are designed on high index contrast SOI platform in order to form more compact integrated photonic circuits. Both the structures are based on the concept of multimode interference. The spot size converter can be realized by successive integration of multimode interference structures with reducing dimension on horizontal plane, whereas the optical bridge structure consists of a number of vertical multimode interference structure connected by single mode sections. The spot size converter can be modified to a spot profile converter when the final single mode waveguide is replaced by a slot waveguide. Analysis have shown that by using three multimode sections in a spot size converter, an Gaussian input having spot diameter of 2.51 μm can be converted to a spot diameter of 0.25 μm. If the output single mode section is replaced by a slot waveguide, this input profile can be converted to a flat top profile of width 50 nm. Similarly, vertical displacement of 8μm is possible by using a combination of two multimode sections and three single mode sections in the vertical bridge structure. The analyses of these two structures are carried out for both TE and TM modes at 1550 nm wavelength using the semi analytical matrix method which is simple and fast in computation time and memory. This work shows that the matrix method is equally applicable for analysis of horizontally as well as vertically integrated photonic circuit.
A photonic crystal (PhC)-based structure is designed to achieve subdiffraction imaging over the entire visible wavelength range. The designed structure is a two-dimensional triangular lattice PhC formed by making circular holes in a 100-nm film of electro-optic lithium niobate (LiNbO3) grown on indium tin oxide. The analysis is done by using MEEP and MPB softwares. This shows that by applying a voltage within ±460 V, equal frequency contour can be obtained for specific values of frequencies, which corresponds to wavelength (λ) in visible range (389 to 757 nm). This indicates that the designed structure will have effective negative refraction and hence subdiffraction imaging over the entire visible wavelength (frequency) range. By placing this type of PhC structure in front of the objective, the resolution of the conventional imaging system can be increased.
A narrowband tunable transmission filter suitable for wavelength division multiplexing is designed. The basic structure is a one-dimensional Fabry–Perot structure formed by layers of dielectric magnesium fluoride and electro-optic lithium niobate, which act as low and high refractive index material layers, respectively. A narrowband phase shifted transmission peak occurs within the stopband of the reflectance spectra of the structure by introducing the defect of a low-index material at a suitable position in the structure. The bandwidth of the peak depends on the number of bilayers and also on the operating wavelength. The phase shift of the transmission peak is linearly related to the wavelength under consideration. By adjusting the defect layer width, this shift of the transmission peak from the operating wavelength can be avoided. The device dimensions are so chosen that such a structure can be fabricated and used with presently available technology. A linear transmission peak tunability of 4 nm/10 V is achieved for this device by varying the refractive index of the electro-optic lithium niobate layer with externally applied voltage along its z axis. All the simulations have been carried out using the finite difference time domain method in a MATLAB® environment.
Multimode Interference (MMI) based on self imaging phenomenon is investigated using matrix
approach. Experimentally MMI is verified using singlemode-multimode-singlemode and multimodesinglemode
structures of optical fiber. The results obtained are also verified by BPM technique.
Vertical 2D PhC having a T-type three port channel on top of InGaAs/GaAs broadband IR LED is considered. Top PhC
is created by 2D periodic repetation of InAs rods in air. T-Channel is created by replacing some solid rods by air. Light
from LED is focussed within the channel. Part of LED light having wavelength out side the PhC bandgap will pass
normally and wavelength within PhC will be guided by the channel. By introducing two different defects in the two arms
of ‘T’ channel tuning of two demultiplexed narrowband sources is obtained.
The translational symmetry of the periodicity in a photonic crystal can be disturbed by introducing a controlled defect in
its periodicity. The photon localization causes a pass band in the photonic bandgap. Based on this concept, we are proposing
the design of a tunable narrow band filter for multiple wavelengths used for coarse wave length division multiplexing
(CWDM) system. To achieve that, a multiple stack Fabry Perot structure with suitable stack materials and controllable
defect is considered. The proposed Fabry Perot structure consists of periodic layers of electro optic material Lithium
Niobate (nH) and Magnesium Fluoride (nL). The optical length of each such layer is their corresponding quarter wave
length width at the design wavelength λ0 (1.55 μm). The reflection band of the quarter wavelength multilayer structure is
formed due to the periodic repetition of the (LH)NL, where L and H are the quarter wavelength width of the nL and nH
material respectively and N is the number of bilayers. A quarter wave layer L is then inserted between the groups of (LH)N
and (HL)N to form the Fabry Perot resonator structure which can be used for narrow band transmission filter. The
simulation has been carried out in both FDTD and TMM method and compared. As the refractive index of the Lithium
Niobate can be tuned electro-optically, the filter can also be made tunable.
A mathematical model to study the phase difference introduced between the two orthogonal components of light wave
due to electro-optic effect in a trapezoidal shaped lithium niobate single crystal has been made. Here, the electrodes are
placed on the two opposite non-parallel faces such that the field is nearly perpendicular to the light beam direction. It is
found that for the said geometry of the device structure, the maximum phase difference is a function of oblique angle
between the two non-parallel faces, which has a critical value. Using random optimization technique based on genetic
algorithm, the device parameters can be optimized for any required phase change between the two components of light
wave. The phase difference between the two orthogonal components of light can be made tunable by using a multi-strip
electrode structure. The advantage of this technique is that tunability can be obtained with a constant voltage source.
Multimode Interference devices are analyzed semi-analytically using matrix approach. The propagation constant and
mode profile of different modes of a multimode waveguide are determined. The field intensity for the combination of all
the modes at different propagation distance is also obtained. The results are in accordance to the theory. The method can
be extended to a singlemode-multimode-singlemode device where the concept of overlap integral is introduced at their
interface. As this method consists of multiplication of 2X2 matrices, it is simple and computationally fast
A simple interferometric technique for measurement of the internal field (IF) in a ferroelectric crystal has been proposed. This technique has several advantages over the other methods used previously for evaluation of IFs in ferroelectric crystals. Here, the electro-optic property of lithium niobate is exploited for quantitative analysis of its IF. The strength of IF obtained using this technique lies within the range given in the literature. However, at frustrated domain inversion state, the measured value of IF shows a reduced value. A possible reason for this reduction based on the defect model has been discussed.
High-index contrast slab and slot optical waveguides have a high index variation both along the lateral and vertical interfaces and are usually analyzed numerically, requiring large computer memory and time. In this article, their analysis is done semianalytically using an effective-index based matrix method. This method, which is computationally very fast, was earlier used successfully for low-index profile waveguide structures only and is now suitably modified for use in high-index contrast structures. The electric field profile of the waveguide structures is plotted and the effective refractive index at different wavelengths is calculated. The results are compared with results obtained from numerical techniques like finite element method, finite-difference time-domain, and beam propagation method and they match very well. The dependence of their different optical characteristics with the waveguide parameters is also studied. These studies will help in obtaining improved sensitivity of slot waveguides for sensing applications.
Experimental work on the study of erbium (Er) diffusion and the characterisation of Er-diffused layers required to form waveguide amplifiers in LiNbO3 substrate is presented. The presence of active Er in the lattice of LiNbO3 is investigated using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) measurement, and spectroscopic reflectometry. The shift of XPS peaks confirms the oxidized state of Er. The PL spectrum shows a sharp peak at 1530-nm wavelength, indicating the 4I15/24I13/2 lasing transition of Er3+. The reflectance spectrum indicates absorption at ~980 and ~1500 nm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.