TE Polarization Modes Research Articles

Contrast Analysis of Polarization in Three-Beam Interference Lithography

This paper analyzes the effect of polarization and the incident angle on the contrasts of interference patterns in three-beam interference lithography. A non-coplanar laser interference system was set up to simulate the relationship between contrast, beam polarization, and the incident angle. Different pattern periods require different incident angles, which means different contrast losses in interference lithography. Two different polarization modes were presented to study the effects of polarization with different incident angles based on theoretical analysis simulations. In the case of the co-directional component TE polarization mode, it was demonstrated that the pattern contrast decreases with the increase in the incident angle and the contrast loss caused by the polarization angle error also grew rapidly. By changing the mode to azimuthal (TE-TE-TE) polarization, the contrast of the interference pattern can be ensured to remain above 0.97 even though the incident angle is large. In addition, TE-TE-TE mode can accept larger polarization angle errors. This conclusion provides a theoretical basis for the generation of high-contrast light fields at different incident angles, and the conclusion is also applicable to multi-beam interference lithography.

Optimized Omnidirectional High-Reflectance Using Octonacci Photonic Crystal for Thermographic Sensing Applications

The transmittance of waves through one-dimensional periodic and Octonacci photonic structures was studied using the theoretical transfer matrix method for both wave-polarization-modes. The first structures were made up of the SiO2 and TiO2 materials. The objective here was to obtain a broad omnidirectional high reflector covering the infrared spectrum of a thermographic camera [1–14µm] and, especially, to prevent the transmission of emitted human body peak radiation λmax = 9.341 µm. By comparing the periodic and Octonacci structures, we found that the last structure presented a main and wide photonic band gap near this human radiation. For that, we kept only the Octonacci structure for the rest of the study. The first structure did not give the aspired objective; thus, we replaced the TiO2 layers with yttrium barium copper oxide material, and a significant enhancement of the omnidirectional photonic band gap was found for both TE and TM polarization modes. It was shown that the width of this band was sensitive to the Octonacci iteration number and the optical thickness (by changing the reference wavelength), but it was not affected by the ambient temperature. The number of layers and the thickness of the structure was optimized while improving the omnidirectional high reflector properties.

Sensitivity enhancement of a difference interferometer refractive index sensor based on a silicon-on-insulator hybrid plasmonic waveguide

A refractive index (RI) sensor using a silicon-on-insulator hybrid plasmonic waveguide (HPWG) difference interferometer is proposed. We first provide a rigorous analysis that enables the construction of the modal characteristic equations of the TM- and TE-polarized modes in a HPWG. These equations are solved to get the modes’ complex effective indices in addition to their electromagnetic power distributions. The feature of polarization spatial diversity in HPWGs is then exploited to design a difference interferometer with a superior sensing capability. Our results reveal that the proposed device has a lower limit of detection of 1.32 × 10 − 6 refractive index unit (RIU) and a sensitivity of 756.2 π r a d / R I U at a wavelength of 1550 nm, accounting for a greater than 50% improvement to the sensitivities of recently published all-dielectric interferometers. Moreover, the sensing interactive length in this work is shown to be 1396 µm, acquiring more than a threefold reduction compared to those reported in the literature. In addition, the propagation loss is reduced by more than 5 × 10 2 times compared to its value in the case of a surface plasmon interferometer, which is found to enhance the detectable power level by 13.6 dB. Furthermore, the proposed HPWG difference interferometer is investigated with a broadband interrogation. Our findings come out with a high density of local extrema of the light interference intensity, for a short sensing interactive length, in the spectral range of interest (from 1490 to 1610 nm), which is favorable for accurate statistical analysis of the interference intensity signal.

Prism coupling technique investigation of optical and thermo-optical properties of polyvinyl alcohol and polyvinyl alcohol/silica nanocomposite films

In this paper, the optical and thermo-optical properties of polyvinyl alcohol (PVA) and polyvinyl alcohol/silica (PVA/SiO 2) nanocomposite films were characterized by using the prism coupler technique. The polymer films were deposited by solution casting method at room temperature. The refractive indices of TE polarization mode, nTE, of all samples were measured at 444 nm, 633 nm, 829 nm, and 1308 nm, respectively. The wavelength dependence of the refractive index is well described by Cauchy’s equation. The effect of polymer molecular weights and the concentration of silica nanoparticles on the optical properties of PVA films was also investigated and discussed. The refractive index of the PVA films was found to increase with molecular weight, whereas it decreases with the concentration of SiO 2 in PVA matrix. The variation of the refractive index of neat PVA and PVA/SiO 2 nanocomposite films with temperature in the range of 30 to 70 °C was determined. Both PVA and PVA/SiO 2 nanocomposites show negative thermo-optic coefficients (dn∕dT) of the order of 10−4 °C−1. Moreover, it was found that the addition of silica in the PVA affect thermo-optic coefficients of the films. The obtained results suggest that PVA is a material with tunable refractive indices and it is suitable for use in optical devices such as optical temperature sensors.

Design and simulation of polarization-insensitive ring resonator based on subwavelength grating and sandwiched structure

Ring resonator fabricated on a silicon-on-insulator is versatile in optical integration, which can be used to realize filters, modulators and switches. However, silicon-on-insulator is difficult to control the polarization dependence, and thus its application is greatly limited. The polarization dependence of the ring resonator is caused mainly by two factors: the coupling coefficients of the coupling region at the same wavelength for the two orthogonal polarization modes are different, and the birefringence effect of curved waveguide results in the different resonant wavelengths of TE and TM polarization modes. When the coupling region polarization independence and the resonant wavelength polarization independence are simultaneously satisfied, the polarization independence of the ring resonator can be realized. In this paper, a new type of polarization-insensitive ring resonator on a silicon-on-insulator is designed based on subwavelength grating and sandwiched structure. Firstly, by adjusting the duty cycle of the subwavelength grating and the refractive index of SiN<i><sub>x</sub></i> in the coupling region, polarization independence of the coupling region is achieved. Secondly, the refractive index of SiN<i><sub>x</sub></i> in curved waveguides is designed to make the resonance wavelengths for orthogonal polarization modes equal. Thirdly, the parameters of the coupling region are optimized to reduce the insertion loss. The three-dimensional finite-difference time-domain method is used for simulation. The results show that the radius of the ring is only 10 μm, the 3-dB bandwidth of the device is less than 0.8 nm, and the insertion loss is lower than 0.8 dB. It has potential applications in the future dense wavelength division multiplexing systems.

Dielectric properties and electromagnetic wave transmission performance of aluminium silicate fibreboard at 915 MHz and 2450 MHz

Refractory lining is an important part of microwave heating equipment, and its wave-transparent effect significantly influences microwave heating efficiency. The complex dielectric constant of the material is the main factor determining its wave-transparent properties. In this study, with aluminium silicate fibreboard (ASF) as the study object, the complex dielectric constant of this material was investigated at temperatures ranging from 25 °C to 1000 °C at 915 MHz and 2450 MHz, respectively. Based on the theory of transmission lines, the wave-transparent properties of the material during the entire microwave heating process were calculated and analysed. It has been found that the dielectric constant and loss factor at both frequencies increase significantly when the temperature exceeds 700 °C; the wave-transparent properties of this material decrease with increasing temperature and present a fluctuating trend as the material thickness increases, with maximum and minimum values; in TM polarization mode, there is an optimal angle of incidence for total transmission, which contributes to a better overall wave-transparent effect of the material in TM polarization mode than that in TE polarization mode. Finally, this study provides the preferred thickness values at different working frequencies and temperatures under vertical incidence of electromagnetic waves for reference. This study is of certain theoretical significance to the research on the change mechanism of the material's dielectric and wave-transparent properties and has practical guidance on the optimization of microwave heating equipment and the selection of the technological parameters of furnace linings.

A Novel All-Optical Sensor Design Based on a Tunable Resonant Nanocavity in Photonic Crystal Microstructure Applicable in MEMS Accelerometers

In view of the large scientific and technical interest in the MEMS accelerometer sensor and the limitations of capacitive, resistive piezo, and piezoelectric methods, we focus on the measurement of the seismic mass displacement using a novel design of the all-optical sensor (AOS). The proposed AOS consists of two waveguides and a ring resonator in a two-dimensional rod-based photonic crystal (PhC) microstructure, and a holder which connects the central rod of a nanocavity to a proof mass. The photonic band structure of the AOS is calculated with the plane-wave expansion approach for TE and TM polarization modes, and the light wave propagation inside the sensor is analyzed by solving Maxwell’s equations using the finite-difference time-domain method. The results of our simulations demonstrate that the fundamental PhC has a free spectral range of about 730 nm covering the optical communication wavelength-bands. Simulations also show that the AOS has the resonant peak of 0.8 at 1.644µm, quality factor of 3288, full width at half maximum of 0.5nm, and figure of merit of 0.97. Furthermore, for the maximum 200nm nanocavity displacements in the x- or y-direction, the resonant wavelengths shift to 1.618µm and 1.547µm, respectively. We also calculate all characteristics of the nanocavity displacement in positive and negative directions of the x-axis and y-axis. The small area of 104.35 µm2 and short propagation time of the AOS make it an interesting sensor for various applications, especially in the vehicle navigation systems and aviation safety tools.

In-fiber comb-like linear polarizer with leaky mode resonances

Leaky mode resonance (LeMR) has been proven as a promising high-performance and effective technology for fiber-optic devices. Here, we propose and theoretically demonstrate an in-fiber comb-like linear polarizer based on enhanced LeMR (eLeMR) in tilted fiber grating (TFG) with indium tin oxide (ITO) nanocoating. The ITO nanocoating induces the guidance of TE-polarized leaky modes, and hence greatly enhances the mode coupling with the core guided mode, which leads to the excitation of dense comb-like TE eLeMRs. By optimizing the ITO thickness and grating length, the results show that the eLeMRs can be designed to realize a novel in-fiber comb-like linear polarizer with remarkable polarization extinction ratio (PER) up to 57dBand ultra-narrow bandwidth (full width at half maximum, FWHM) smaller than 0.5nm, together with wavelength separation between adjacent bands equal to 3.1nm, in a broad wavelength range. Moreover, the operating wavelength of the polarizer can be further tuned by tailoring the grating parameters, like the period and tilt angle of the TFG. The designed polarizer will cover a wide range of applications including multi-wavelength fiber lasers, dense wavelength-division-multiplexed (DWDM) systems, optical spectrometers, and fiber-optic sensing systems.

Multimode silicon photonic waveguide corner-bend.

An ultra-sharp multimode waveguide bend (MWB) based on a multimode waveguide corner-bend (MWCB) is proposed and realized. With the present MWCB, total internal reflection (TIR) happens and the light propagation direction of all the mode-channels can be modified with low excess losses (ELs) and low inter-mode crosstalk (CT) in the optical communication bands from 1260 nm to 1680 nm. For the MWCB designed for the TE0 and TE1 modes, the ELs are less than 0.18 dB and the inter-mode CTs are less than -36 dB in the wavelength range of 1260-1680 nm. The measurement results show the fabricated MWCB works very well as predicted by the theory. It is very flexible to extend the present MWCB for more mode-channels by simply adjusting the core width. For example, the MWCB designed with a 35 µm-wide core has an EL less than 0.54 dB and inter-mode CT less than -24 dB for the ten TE-polarization modes (i.e., TE0∼TE9) in the wavelength-band of 1260-1680 nm. For the present MWCB, the fabrication is also very convenient because no tiny nano-structure and no additional fabrication steps are needed. It also shows that the present MWCB is not sensitive to the sidewall angles even when the angle is up to 8°. The proposed MWCB is promising for multimode silicon photonics because of the simple structure, easy design, easy fabrication as well as excellent performances in an ultra-broad wavelength-band.

Polarization-independent hybrid plasmonic coupler based on T-shaped slot waveguide

In this paper, a novel polarization-independent hybrid plasmonic coupler based on a T-shaped slot waveguide is proposed and investigated by numerical simulations using the finite element method. The structure supports both the TE-polarized slot waveguide mode and the TM-polarized plasmonic mode, offering a greater possibility to achieve the polarization-independent operation. The simulation results show that with proper structural parameters, the waveguide coupler with high extinction ratios of 31.2 dB (TE) and 30 dB (TM) and low insertion losses of 0.38 dB (TE) and 2.04 dB (TM) can be achieved at a telecommunication wavelength of 1550 nm. An investigation of the influence of structural perturbations indicates that the proposed coupler also has a good tolerance to fabrication errors. The proposed structure has potential applications in the field of subwavelength integrated photonic circuits.

Lossy mode resonance generated by titanium dioxide nanoarray: a comprehensive theoretical research

The lossy mode resonance (LMR)-based optical fiber waveguide based on titanium dioxide nanoarrays was discovered and researched for the first time in this paper. Two kinds of waveguide coating structures, titanium dioxide nanoarrays and nanofilms-nanoarrays systems, were researched using finite element method, where the localized field distribution, the mode transmission characteristics and measurement sensitivities of surrounding refractive index were researched in detail. In the former structure, there exists a localized electromagnetic field that can be generated by both TE and TM polarization modes around nanoarrays. By increasing the diameters of nanoparticles and decreasing the intervals of nanoarrays, the resonance wavelength will redshift and the measurement sensitivity will be enhanced. In the latter structure, the localized electromagnetic field can be obviously enhanced due to the mode coupling between nanofilms and nanoarrays. In addition, the measurement sensitivity of refractive index was 5179 nm/RIU in the range of 1.333–1.343, which is two times higher than that of the structure without TiO2 nanoarrays. This paper opened up a door to study the LMR generated by semiconductor nanoparticles, which is useful in the research of electromagnetic resonance-based sensors in nanoscales.

Ultra-Sharp Multimode Waveguide Bends with Dual Polarizations

A silicon-based on-chip ultra-sharp multimode waveguide bend (MWB) is proposed to work for dual polarizations by introducing modified Euler-curves and shallowly-etched non-uniform subwavelength-gratings (SWGs). For the designed 90° MWB with a core width of 1.01 μm and an effective bending radius as small as 10 μm, the excess losses are less than 0.23 dB and the inter-mode crosstalk is lower than <−26.5 dB over a broad band from 1500 nm to 1600 nm for six mode-channels, including three TE-polarization modes and three TM-polarization modes. It shows a great improvement compared to a regular 90° arc-bend.

Polarization-stabilized tunable VCSEL with internal-cavity sub-wavelength grating.

In this paper, a tunable VCSEL with internal-cavity sub-wavelength grating structure at 850nm was demonstrated. Utilizing the birefringence and anti-reflection characteristics of the sub-wavelength grating, the tunable VCSEL with wide wavelength tuning range and stable TE polarization mode was achieved. The relationships between the parameters of sub-wavelength grating and the transmittance/effective index of two polarization modes were analyzed. The tuning efficiency, polarization mode and wavelength tuning range of the tunable VCSEL with internal-cavity sub-wavelength structure were studied. Simultaneously, the MEMS cantilever structure with 'bowknot' shape on the end of the cantilever was designed, which can effectively avoid the concentration of stress distribution and reduce the maximum stress. The results show that the wavelength tuning range is 22.7nm, the peak output power is 1.6mW at 20°C, and the polarization suppression ratio is more than 20dB.

Polarization-Independent Perfect Optical Metamaterial Absorber as a Glucose Sensor in Food Industry Applications.

Perfect optical metamaterial absorbers (POMMA) utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. In all the reported absorbers, the absorption occurs only at a single wavelength or dual/multi-band wavelengths where plasmon resonances are ex-cited in the nanostructure. Here we not only show a single-band perfect absorber but also demonstrate that our proposed design has the ability to be multi-band absorber at the same structure. Furthermore, we numerically demonstrate the proposed POMMA can be utilized as a glucose sensor for refractive index sensing which has more than 225 nm/RIU sensitivity at the infrared frequency regime which is good value. Its polarization-independent absorbance is about 100% at normal incidence for both TE and TM polarization modes. The proposed optical glucose sensor offers great potential to maintain the performance of localized surface plasmon (LSP) sensors in nanostructures in food industry applications.

Optical properties of GaN/Er:GaN/GaN core–cladding planar waveguides

Erbium-doped GaN (Er:GaN) possesses superior optical, mechanical and thermal properties and is a very promising material as a gain medium for solid-state high-energy lasers. We report here the optical properties of GaN/Er:GaN/GaN core–cladding planar waveguides (PWGs). Optical confinement in the core layer has been investigated. The measured optical loss coefficients of Er:GaN PWGs at 1.54 μm are 1.0 cm−1 for the TE polarization mode and 1.2 cm−1 for the TM polarization mode. Approaches to further reduce optical loss and the optimal configuration for resonantly pumped GaN/Er:GaN/GaN PWGs for achieving amplification near 1.5 μm have been identified.

Broadband on-chip polarization mode splitters in lithium niobate integrated adiabatic couplers.

We report, to the best of our knowledge, the first broadband polarization mode splitter (PMS) based on the adiabatic light passage mechanism in the lithium niobate (LiNbO3) waveguide platform. A broad bandwidth of ~140 nm spanning telecom S, C, and L bands at polarization-extinction ratios (PER) of >20 dB and >18 dB for the TE and TM polarization modes, respectively, is found in a five-waveguide adiabatic coupler scheme whose structure is optimized by an adiabaticity engineering process in titanium-diffused LiNbO3 waveguides. When the five-waveguide PMS is integrated with a three-waveguide "shortcut to adiabaticity" structure, we realize a broadband, high splitting-ratio (ηc) mode splitter for spatial separation of TE- (H-) polarized pump (700-850 nm for ηc>99%), TM- (V-) polarized signal (1510-1630 nm for ηc>97%), and TE- (H-) polarized idler (1480-1650 nm for ηc>97%) modes. Such a unique integrated-optical device is of potential for facilitating the on-chip implementation of a pump-filtered, broadband tunable entangled quantum-state generator.

Analytical theory on electromagnetic shielding effectiveness of infinite conductor plate with periodic aperture array under plane wave illumination

Penetration of a plane electromagnetic wave through the apertures on a perfectly conducting flat plate is a classical electromagnetic problem. In some practical applications like electromagnetic shielding, where only the fields far from the apertures are concerned and the aperture sizes are small compared with a wavelength, the role of apertures can be represented by the equivalent electric and magnetic dipoles located in the centers of the apertures. In principle, the penetration field can be expressed as the superposition of the radiation fields of the dipoles. However, the direct superposition leads to a double series with complex form and poor convergence. On the other hand, this problem may also be solved by full wave numerical simulations. Even so, finding analytical solutions is still desirable considering that it is clear in physical significance and easy to implement. In this paper, the analytical formula of the penetration fields are derived for both TE and TM polarization mode with different angles of incidence. The derivation is carried out firstly by averagely distributing each dipole moment within each periodic unit. As a result, the dipole array is replaced with a flat sheet with uniform magnetization and polarization intensity. Then, the equivalent surface current and charge distributions are obtained directly from the polarization intensity. Finally, the penetration fields are treated as the radiation fields of the surface sources. It is shown that the amplitude of the penetration field is proportional to aperture magnetic polarization coefficient and wave frequency, and it is inversely proportional to the area of a periodic unit. In regard to the effect of the incidence angle, the amplitude of the penetration field is proportional to the cosine of the incidence angle for TE polarization. However, for the TM polarization, the relationship is a little complicated due to the coexistence of electric and magnetic dipoles: the field is not rigorously inversely proportional to the cosine of the incidence angle due to the existence of a correction term involving both the polarization coefficient and the sine of the angle. The formula is used to calculate the shielding effectiveness for several different aperture shapes and different incidence angles. The results are in good agreement with those from the full wave simulation software.

On-chip polarization beam splitter with multimode operation in a SOI waveguide

The polarization beam splitter (PBS) based on the directional coupler is numerically investigated to operate transverse-electric (TE) and transverse-magnetic (TM) modes including high-order modes. Based on the phase-matching condition, all TM-polarization modes are switched from the bus waveguide to the adjacent waveguide without changing the spatial profile of the electric field and mode order while all TE-polarization modes go along the bus waveguide without significant coupling. The results show a low cross talk characteristic (>20 dB at 1.55 μm) and big fabrication tolerance (δw = ±20 nm). It becomes an essential supplement for polarization splitting with multimode operation in photonics integrated circuits.

Polarization-independent and super broadband flat lens composed of graded index annular photonic crystals

Abstract In this paper, we propose two types of all-dielectric polarization-independent graded index annular flat lens with a wide operating frequency range. The lenses are composed of two-dimensional triangular and square lattice photonic crystals with circular silica ( S i O 2 ) rods in the air. We assume in both square and triangular structures, the lenses are obtained by making air holes within each dielectric rod and we consider that the outer radius of the created annular rods is maintained constant while the size of the inner air holes varies along the transverse direction whose the air holes variation follow two types of linear and parabolic function. The graded structures are made in such a way that the modulus of the refractive index is biggest at the centre and decreases towards the edges. The optical properties and the physical background of the polarization-independent focusing mechanism are studied in frequency and spatial domains, using plane wave expansion and finite-difference time-domain methods. Our numerical results show that, through an appropriate set of design, the designed lenses are able to focus the light regardless of polarization for a wide frequency range into approximately same focal length in which difference between the focal distance of TE and TM polarization modes stays below λ 4 . Compared to previously polarization-independent designed photonic crystal based lenses, our proposed structures work under much wider frequency range. Also, in contrast with most of the graded structures, our graded lens are made without altering the lattice constant along the optical axis or transverse to the optical axis. Moreover, the design approach is restricted to the use of silica and non-use of more complicate materials such as liquid crystals, plasma, and the like. Thus, the designed systems can be constructed easier relative to the previously designed lenses.

High-Q resonances supported by a single dielectric ridge on the surface of a slab waveguide

Diffraction of slab waveguide modes on a dielectric ridge located on the waveguide surface is studied. Calculations, based on aperiodic rigorous coupled-wave analysis, demonstrate the existence of sharp resonant features in the reflectance and the transmittance spectra occurring at oblique incidence of TE-polarized waveguide mode on the ridge. Angular widths of the resonant peaks and dips vary from units to less than a thousandth of a degree. Using the effective index method, we explain the resonances by the excitation of cross-polarized modes of the ridge. The existence of high-Q resonances makes this structure promising for filtering, sensing and all-optical signal processing.