Crystal Refractive Index Research Articles

Design and Synthesis of CdWO4:Sb3+ Phosphor Based on sp Energy Level Regularities of Sb3+ Ion

Sb3+‐activated CdWO4 phosphors were designed according to sp energy levels regularities of Sb3+ ion in some inorganic compounds. The sp energy levels regularities of Sb3+ in dozens of compounds were established with the aid of the dielectric theory of the chemical bond for complex crystals: EA = 6.2187−1.7584he, EB = 7.019−1.957he, EC = 7.259−1.964he. Environmental factor he of Cd site was calculated to be 1.6583 with the refined crystal structure and refractive index of CdWO4:Sb3+. Sb3+‐doped CdWO4 was synthesized through a precipitation method and its structure was refined with the General Structure Analysis System. The transition energy of A band of Sb3+ in CdWO4 can be predicted to be 3.312 eV (374 nm), according to the relationship equation between EA and environmental factor he. By monitoring the 521 nm emission band, the excitation spectrum gives a weak excitation band peaking at 355 nm, which was assigned to the 1S0–3P1 transition of Sb3+ according to our prediction. Thus, Sb3+‐doped CdWO4 phosphor was designed and synthesized successfully based on sp energy levels regularities of Sb3+ ion. This work is a great help to understand the spectroscopy of Sb3+ ion and will be useful for the design and development of Sb3+‐doped phosphors for applications.

Growth and optical properties of a new CGG-type laser crystal Nd^3+:CNGS

A novel CGG-type laser crystal of Nd3+:CNGS is characterized, including crystal growth, structure, refractive index, spectroscopic and laser performance. For Nd3+:CNGS crystal, the unit-cell parameters are a = 0.88897 ( ± 8.89 × 10−5) nm, c = 0.497998 ( ± 4.85 × 10−5) nm and V = 0.28219 nm3. The refractive index no and ne of Nd3+:CNGS were calculated to be 1.772 and 1.854 respectively at 1065 nm. The transmittance spectra of Nd3+:CNGS were measured, four main absorption peaks were located at 586 nm, 748 nm, 804 nm and 804 nm respectively. The absorption cross-section in z-axis is 6.08 × 10−20 cm2 around 804nm. The strongest emission peak of the fluorescence spectra was located at 1064 nm with the emission cross-section of 6.81 × 10−20 cm2 for E//x polarization and the fluorescence lifetime was 255.6 μs. Moreover, the continuous-wave laser at 1065 nm was obtained with the maximum output power of 1.43 W in the z-cut sample for the first time to the best of our knowledge, the optical conversion efficiency was 29.3% and the slope efficiency was 31.0%, which indicated that Nd3+:CNGS crystal should be a promising gain material.

D-shaped photonic crystal fiber refractive index and temperature sensor based on surface plasmon resonance and directional coupling

The photonic crystal fiber has received the widespread attention in the sensing field because of its flexible structure and unique features. A refractive index and temperature sensor based on the D-shaped photonic crystal fiber is designed and analyzed. In the side section of the D-shaped photonic crystal fiber, a coat with a gold film is used as a surface plasmon resonance (SPR) sensing channel for measuring the refractive index of liquid determinand. Temperature sensitive liquid-toluene is filled in an air hole A as a directional coupling sensing channel to realize the temperature measurement. When the SPR mode and guided mode satisfy the phase matching condition, the SPR effect is produced. Most of the core energy is transferred to the metal film layer in the surface, and then the loss of guided mode in the fiber core will grow. Therefore, the shift of the SPR peak position can be used to measure the refractive index of the determinand indirectly. When the wave mode in the thermosensitive liquid-toluene can achieve phase matching with the guided mode, the directional coupling effect occurs, and then the wavelength of the absorption peak position can be used to measure the change of temperature indirectly. Based on further numerical simulation, the peak position of directional coupling is not changed by the refractive index of the determinand, and the SPR peak position is not shifted by the temperature change either. As these two sensing mechanisms can be distinguished easily, the refractive index and temperature sensing are simultaneously realized. The characteristics of the sensor are simulated numerically by using a full vector finite element method under the boundary condition of anisotropic perfectly matched layer. From the analysis of the D-shaped photonic crystal fiber structure parameters, we find that the diameter d of air hole plays an important role in the directional coupling absorption peak position and temperature sensitivity. For the SPR peak, its position is only affected by the thickness t of gold film, and its relative intensity is changed with the diameter d of air hole and grinding depth d1. The results show that when the temperature ranges from -10 ℃ to 80 ℃, the temperature sensitivity reaches 11.6 nm/℃, and when the refractive index is in a range from 1.32 to 1.44, its sensitivity reaches 26000 nm/RIU.

Terahertz polarization splitter based on an asymmetric dual-core photonic crystal fiber

By employing the liquid crystal refractive index changes induced by applied electric field, a novel terahertz polarization splitter with tunable the operating frequency and bandwidths has been proposed and theoretically analyzed. It possesses an extinction ratio as high as the polarization splitters based on the two-dimensional photonic crystal waveguides. These distinguished features ensure its important applications in the integrated optical systems.

Fabrication of optical element from unidirectional grown imidazole–imidazolium picrate monohydrate (IIP) organic crystals for nonlinear optical applications

Nonlinear optical bulk single crystal of Imidazole–imidazolium picrate monohydrate (IIP) has been grown by Sankaranarayanan–Ramasamy (SR) method using acetonitrile as solvent. First time we report the bulk growth of IIP crystal by SR method. The transparent IIP single crystal of maximum diameter 21 mm and length 46 mm was obtained by employing SR method. The grown crystal was subjected to high resolution X-ray diffraction, UV–vis–NIR transmittance, refractive index, hardness, dielectric and laser damage threshold studies. The crystalline perfection of the grown crystal was analyzed using HRXRD. Cut off wavelength and optical transmission window of the crystal was assessed by UV–vis–NIR and the refractive index of the crystal was found. The mechanical property of the crystal was estimated by Vicker׳s hardness test. The dielectric property of the crystal was measured as a function of frequency. The laser damage threshold value was determined. The particle size dependent second harmonic generation efficiency for IIP was evaluated with standard reference material potassium dihydrogen phosphate (KDP) by Kurtz–Perry powder method using Nd:YAG laser, which established the existence of phase matching. The second harmonic generation (SHG) of IIP crystal was investigated by the SHG Maker fringes technique. The mechanism of growth is revealed by carrying out chemical etching using acetonitrile as etchant. • SR method grown bulk IIP crystal of 46 mm length, 21 mm diameter. • The refractive index of IIP crystal by solid prism method is 1.738. • The full width at half maximum of the diffraction curves is 49.25″. • The laser damage threshold of SR method IIP crystal is 0.252 GW/ cm 2 .

A new method of anti-jamming ability improvement for Michelson Interferometer

In order to improve anti-jamming capability of Michelson interferometer system, replace the traditional structure of the moving mirror scanning was replaced, an interference system based on electro-optic modulation of crystal refractive index was designed to achieve optical path scanning. The system modulated voltage signal on the variable refractive crystal, to generate cyclical changes, changed the refractive index to control optical path difference in the original optical path system. Using electronic scanning to replace of mechanical scanning, improved the system's noise immunity was improved. In the electro-optic modulation process, computed the maximum optical path difference of the system was computed, and analyzed of the crystal thickness and crystal diffraction efficiency of the modulation process were analyzed. The simulation experiment shows that, with the modulation voltage range increasing, the available range of the optical path is also increased, and the system spectrum resolving power will also increase accordingly. Meanwhile, in the modulation process set the modulation range was set to make the energy of diffraction energy losses less than 10% of the total energy, so as to ensure a better signal to noise ratio. Experimental results show that, as the modulation voltage changes, interference fringes occurred continuously moved. When the voltage is further increased, the nonlinear error appears. After non-linear error correction for the system, spectrum resolution reached to 7. 2 cm-1, slightly lower than the original system. But its anti-jamming capability is greatly enhanced, as in the absence of experimental platform for seismic conditions, conventional interferometer relative error is more than 20%, while the relative error of the system is less than 5%, in line with the design requirements. It was proved that the anti-jamming capability of the system was enhanced greatly, when the static electro-optical modulation was used.

Enhanced detection limit by dark mode perturbation in 2D photonic crystal slab refractive index sensors

We demonstrate for the first time a 300nm thick, 300μm × 300μm 2D dielectric photonic crystal slab membrane with a quality factor of 10,600 by coupling light to slightly perturbed dark modes through alternating nano-hole sizes. The newly created fundamental guided resonances greatly reduce nano-fabrication accuracy requirements. Moreover, we created a new layer architecture resulting in electric field enhancement at the interface between the slab and sensing regions, and spectral sensitivity of >800 nm/RIU, that is, >0.8 of the single-mode theoretical upper limit of spectral sensitivity.

Role of Sputtering Power on the Structural and Optical Properties of ZnO/SiO<sub>2</sub> Films Deposited by Radio Frequency Magnetron Sputtering

In the present work, we investigated the effect of sputtering power on the structural and optical properties of ZnO films by radio frequency (rf) magnetron sputtering. Atom force microscopy (AFM), X-ray diffraction (XRD) and Prism coupling method were adopted to investigate the structure and optical properties of ZnO thin films deposited by sputtering powers in the range from 100~150W. XRD and AFM results shown that ZnO films with high c-axis preferred orientation crystalline structures have been successfully deposited under higher sputtering power condition. Moreover, it was also found that the indexes refractive of the films obtained by higher sputtering power are less than that of the bulk ZnO materials, which is closer to Crystal Refractive index.

<i></i>Annealing and Deposition Parameters Influence on the Performance of AlN Thin Films

Using the radio frequency magnetron sputtering that directly bombardment A1N target under different sputtering-power and total pressure to deposit the A1N thin films. The crystal structure, composition, surface and refractive index of the thin films were studied by XRD, SEM, AFM and elliptical polarization instrument. The results show that the surface and refractive of the thin films strongly depends on the sputtering-power and total pressure,the good uniformity and smoothness is found at 225 W, Ar flow ratio 5.0 LAr/sccm, substrate temperature 100°Cand 1.2 Pa. All film thickness are from 60 to 80nm, and the highest N/Al mole ratio reach to 0.83.The crystal structure of the as-deposited thin-films is amorphous，then it transforms from blende structure to wurtzite structure as the rapid thermal annealing(RTA) temperature changes from 600 to 1200°C. The refractive index also increases with the RTA temperature it is increasing significantly from 800 to 1000°C. When the Annealing temperature at 1000°C, we get the best uniformity and smoothness of the surface of the film.

Surfactant-Free, Cationic Latices of Poly(BMA-co-MMA) Using AIBA Initiator

When polymer particles come into use, especially, for photonic crystal applications, their diameter, dispersivity, and refractive indices become very important. Poly(benzyl methacrylate) is known to be a kind of high refracive materials (n = 1.57) compared to poly(methyl methacrylate) (n = 1.49). Not many work was concerned for surfactant-free emulsion polymerization of benzyl methacrylate or its copolymerization using cationic initiators. Narrowly dispersed cationic poly(BMA-co-MMA) and PBMA latices were synthesized successfully by surfactant-free emulsion polymerization with AIBA. The influences of BMA/MMA ratio, BMA/MMA monomer and initiator concentrations, addition of DVB/EGDMA crosslink agent, and polymerization temperature on the kinetics and on the particle size and molecular weight were studied. Monodisperse cationic charged PBMA and poly(BMA-coMMA) latices with particle diameters varying between 160-494 nm and polymer molecular weights of the order 1.25 x 10(4) to 7.55 x 10(4) g/mol were prepared. The rate of polymerization increased with increasing MMA concentration in BMA/MMA ratio, AIBA concentration, DVB crosslink agent, and polymerization temperature. The particle diameter increased with BMA concentration in BMA/MMA ratio, AIBA concentration, and BMA/MMA monomer concentration. The molecular weight increased with BMA concentration in BMA/MMA ratio and BMA/MMA monomer concentration. The glass transition temperature of the latex copolymers decreased with increasing amount of BMA from 375 K for PMMA to 321 K for PBMA. It was, thus, found that the particle diameter and rate of polymerization as well as the polymer molecular weight for surfactant-free emulsion polymerization of BMA and MMA can be controlled easily by controlling the BMA/MMA ratio, BMA/MMA monomer concentration, AIBA concentration, and polymerization temperature.

Design of simultaneous high-Q and high-sensitivity photonic crystal refractive index sensors

Sensitivities (S) and quality factors (Q) have been trade-offs in label-free optical resonator sensors, and optimal geometry that maximizes both factors is under active development. In this paper, we demonstrate that the nanoslotted parallel multibeam cavity possesses unexplored high S and high Q. We achieve S>800  nm/RIU (refractive index unit) and Q>107 in liquid at telecom wavelength range when absorption is neglected. To the best of our knowledge, this is the first geometry that features both high S and Q factors, and thus is potentially an ideal platform for refractive index-based biochemical sensing.

Numerical analysis of a photonic crystal fiber based on two polarized modes for biosensing applications

This paper presents a theoretical study on a photonic crystal fiber plasmonic refractive index biosensor. The proposed photonic crystal fiber sensor introduces the concept of simultaneous detection with the linearly polarized and radially polarized modes because the sensing performance of the sensor based on both modes is relatively high, which will be useful for selecting the modes to make the detection accurately. The sharp single resonant peaks of the linearly polarized mode and radially polarized mode, are stronger and more sensitive to the variation of analyte refractive index than that of any other polarized mode in this kind of photonic crystal fiber. For linearly polarized mode and radially polarized mode, the maximum sensitivities of 10448.5 nm per refractive index unit and 8230.7 nm per refractive index unit can be obtained, as well as 949.8 and 791.4 for figure of merits in the sensing range of 1.33–1.45, respectively. Compared with the conventional Au-metalized surface plasmon resonance sensors, our device is better and can be applied as a biosensor.

Preparation and Character Measurements of AlN Films for RF Magnetron Sputtering

AlN dielectric thin films were deposited on N type Si(100) substrate by reactive radio frequency magnetron sputtering that directly bombardment AlN target under different sputtering-power and total pressure. The crystal structure,composition,surface and refractive index of the thin films were studied by XRD, SEM, AFM and elliptical polarization instrument. The results show that the surface and refractive of the thin films strongly depends on the sputtering-power and total pressure,the good uniformity and smoothness is found at 230 W, Ar flow ratio 5.0 LAr/sccm, substrate temperature 100°Cand 1.2 Pa. The crystal structure of the as-deposited thin-films is amorphous，then it transforms from blende structure to wurtzite structure as the rapid thermal annealing(RTA) temperature changes from 600 to 1200°C. The refractive index also increases with the RTA temperature it is increasing significantly from 800 to 1000°C．

The Defect Modes Property Controlled by Temperature in One Dimensional Photonic Crystal with Liquid Crystal Defect Layer

The 5CB liquid crystal as defects will be introduced to one dimensional photonic crystal, taking advantage of temperature property of liquid crystal refractive index, the transmission spectrum of one dimensional liquid crystal defect photonic crystal defect modes was researched by the transfer matrix method(TMM). The numerical results indicated that when the temperature went up, one dimensional liquid crystal defect photonic crystal defect modes removed towards the long wavelength. When the temperature increased from 273k to 320k, the defect modes wavelength from 5121nm drifted to 5508nm, the wavelength shift was 387nm and the maximum of temperature sensitivity was 10.85nm/K, it was also observed that the temperature sensitivity decreased as the temperature increased.

Dynamical diffraction theory of waves in photonic crystals built from anisotropically scattering elements

Analyzing scattering of electromagnetic waves in a two-dimensional photonic crystal from the viewpoint of scattering theory, we come to the conclusion that multiple rescattering of waves by the centers (wires) composing the crystal significantly affects the imaginary part of the crystal refractive index. As a result, it appears that, in the case of crystals, the classical expression relating the refractive index of a random medium to the amplitude of scattering by a single center has limited application, because it does not properly describe the attenuation of waves. We derive an expression that, unlike the classical one, includes the effective amplitude of scattering by a wire in a crystal, instead of the amplitude of scattering by a single wire in vacuum. The same effective amplitude must appear in the equation describing the dynamical diffraction of waves in crystals. We also derive the expression for the effective amplitude in the case when scattering by a single center is anisotropic. Because a most general approach is applied to the description of the scattering process, the results are valid for a wide range of cases without being restricted to either electromagnetic waves or crystals built from wires.

Photonic crystal fiber refractive index sensor based on a fiber Bragg grating demodulation

A refractive index (RI) sensor is proposed which consists of a combination of an intermodal photonic crystal fiber (PCF) interferometer as a sensing head and a fiber Bragg grating (FBG) as a demodulating element. The intermodal PCF interferometer is formed by using a short PCF which is spliced with two single-mode fibers (SMFs) at both ends. The air-holes in the splice regions are fully collapsed and it forms the intermodal PCF interferometer. The corresponding interference phenomenon is found to be sensitive to the change of external RI. A FBG is connected serially after the intermodal PCF interferometer which is used to reflect the optical power at the Bragg wavelength of the interference transmission spectrum. With different external RI values, the corresponding reflective power of the FBG will change, which is resulted from the shift on the interference spectrum of the intermodal PCF interferometer. The resolution of the proposed RI sensor can be obtained as high as 1.5×10−5 at around RI of 1.360 with a combination of a 2.5cm length intermodal PCF interferometer and a FBG at 1566.8nm with 99% reflectivity. Due to a temperature compensation between the FBG and the intermodal PCF interferometer, the proposed RI sensor has a low temperature sensitivity and it is suitable for practical applications.

Photonic-crystal-waveguide based Mach-Zehnder interferometer for terahertz switch and modulator

We propose a novel tunable photonic crystal (PC) waveguide Mach-Zehnder interferometer (MZI) based on nematic liquid crystals (LCs) 5CB and investigate its interference properties numerically by using the finite-difference time-domain method. We can change the refractive index of LC by rotating the directors of the LC molecules. The line defect modes of the PC waveguide with different liquid crystal refractive indices are analyzed by using the plane wave expansion method. Owing to the slow group velocity region of the line defect mode, when the index of 5CB changes from 1.53 to 1.63, the variation of the effective index of the line defect mode arrives at 0.168. This property helps to significantly control the phase of light propagation in a PC waveguide MZI. The novel interferometer can be used as either an optically controlled on-off switch or an amplitude modulator in optical circuits.

Photonic crystal refractive index sensing based on sandwich structure

An ultracompact refractive index sensing based on the sandwich structure of photonic crystal is presented and demonstrated with solutions of water, methylsilicone and silicone. The performances of the sensor are analyzed theoretically by using Fabry–Perot cavity mode, the change in opposite direction between the transmission of the refractive index sensing and its quality factor is derived. The experimental results are consistent with the results of theoretical analysis.

Integrated Bragg reflectors in low-index media: enabling strategies for wavelength tunability in electro-optic liquid crystals

This paper reports two configurations of Bragg reflectors based on liquid crystals confined between two small glass plates. Both approaches employ the efficient electro-optic effect in liquid crystals, which allows tunability of the reflectors by using low voltages. The molecular reorientation induced by an applied electric field implies a refractive index modulation seen by polarized light propagating into the liquid crystal. We show design criteria and profile optimization of the electrodes to induce a liquid crystal refractive index periodic modulation, providing a wavelength selective propagation of confined light in the liquid crystal. The two proposed device configurations differ for the top-bottom electrode configuration in one case and coplanar electrodes in the other case. Modeling of both configurations has been carried by calculating the applied electric field distribution and its interaction with the liquid crystal elastic properties taking into account the boundary conditions due to the alignment layer on the inner faces of the glass substrates. The calculated performance in terms of high wavelength selectivity and ultrawide spectral tuning range indicate that the two designed structures can be proposed for both optical filtering and to produce novel low power integrated distributed feedback resonators in dense wavelength division multiplexed fiber optic systems.

Highly sensitive miniature photonic crystal fiber refractive index sensor based on mode field excitation

A highly sensitive miniature photonic crystal fiber refractive index sensor based on field mode excitation is presented. The sensor is fabricated by melting one end of a photonic crystal fiber into a rounded tip and splicing and collapsing the other end with a single-mode fiber. The rounded tip is able to induce cladding mode excitation, which resulted in an additional phase delay. Linear response of 262.28 nm/refractive index unit in the refractive index range of 1.337 to 1.395 is obtained for the physical length of a 953 μm sensor. The sensor is also shown to be insensitive to environmental temperature.