Telecommunication Frequency Bands Research Articles

Utilizing polarization-selective mode shaping by chalcogenide thin film to enhance the performance of graphene-based integrated optical devices

High refractive index (RI) thin films are capable of pulling waveguide mode profiles towards themselves. In this study, it is shown that by applying high RI coatings with specific thicknesses on the side of optical waveguides, significantly different mode profiles for orthogonal polarizations can be achieved. This phenomenon, that we call it polarization-selective mode shaping, can be extensively used in the enhancement of polarization-dependent integrated optical devices. As an illustrating application, a tri-layer structure consisting of poly(methyl methacrylate)/graphene/chalcogenide on a side-polished fiber is designed to realize an extremely high extinction ratio polarizer. This structure changes the mode profiles in a way that the attenuation of TE mode is maximized, while the power carried by the TM mode remains relatively constant. Simulations and experimental characterizations confirm that polarization-selective mode shaping coordinates four loss mechanisms to maximize the extinction ratio and minimize the insertion loss of the polarizer. The fabricated polarizer is examined in the O, C, and L telecommunication frequency bands. This configuration achieves the high extinction ratio of 51.3 dB and its maximum insertion loss in the tested wavelengths is 1.79 dB. The proposed polarizer has been compared with other state-of-the-art polarizers in the conclusion section which shows its superiority.

Towards integrated metatronics: a holistic approach on precise optical and electrical properties of Indium Tin Oxide

The class of transparent conductive oxides includes the material indium tin oxide (ITO) and has become a widely used material of modern every-day life such as in touch screens of smart phones and watches, but also used as an optically transparent low electrically-resistive contract in the photovoltaics industry. More recently ITO has shown epsilon-near-zero (ENZ) behavior in the telecommunication frequency band enabling both strong index modulation and other optically-exotic applications such as metatronics. However, the ability to precisely obtain targeted electrical and optical material properties in ITO is still challenging due to complex intrinsic effects in ITO and as such no integrated metatronic platform has been demonstrated to-date. Here we deliver an extensive and accurate description process parameter of RF-sputtering, showing a holistic control of the quality of ITO thin films in the visible and particularly near-infrared spectral region. We are able to custom-engineer the ENZ point across the telecommunication band by explicitly controlling the sputtering process conditions. Exploiting this control, we design a functional sub-wavelength-scale filter based on lumped circuit-elements, towards the realization of integrated metatronic devices and circuits.

On-chip magnetic-free optical multi-port circulator based on a locally linear parity–time symmetric system

This paper introduces a new type of magnetic-free optical circulator without utilizing a Faraday rotator, polarization beam splitter, and magneto-optic material for the first time, to the best of our knowledge. The designed circulator operates linearly and relies on the parity-time symmetric (PTS) system. The property of the non-Hermitian system (the linear PTS system) plays the key role in the suggested optical circulator so that it can simultaneously support N-ports. The proposed device is integrated, broadband, and operates in the optical telecommunication frequency band. A great value of isolation rate of 47dB is achieved. The proposed circulator can pave the way for optical integrated circuits and optical networks.

A Multi-Band Body-Worn Distributed Radio-Frequency Exposure Meter: Design, On-Body Calibration and Study of Body Morphology

A multi-band Body-Worn Distributed exposure Meter (BWDM) calibrated for simultaneous measurement of the incident power density in 11 telecommunication frequency bands, is proposed. The BDWM consists of 22 textile antennas integrated in a garment and is calibrated on six human subjects in an anechoic chamber to assess its measurement uncertainty in terms of 68% confidence interval of the on-body antenna aperture. It is shown that by using multiple antennas in each frequency band, the uncertainty of the BWDM is 22 dB improved with respect to single nodes on the front and back of the torso and variations are decreased to maximum 8.8 dB. Moreover, deploying single antennas for different body morphologies results in a variation up to 9.3 dB, which is reduced to 3.6 dB using multiple antennas for six subjects with various body mass index values. The designed BWDM, has an improved uncertainty of up to 9.6 dB in comparison to commercially available personal exposure meters calibrated on body. As an application, an average incident power density in the range of 26.7–90.8 μW·m is measured in Ghent, Belgium. The measurements show that commercial personal exposure meters underestimate the actual exposure by a factor of up to 20.6.

TELECOMMUNICATION FREQUENCY BAND SPECTRUM OCCUPANCY IN KAMPALA UGANDA

The Effective utilization of the radiofrequency electromagnetic spectrum is paramount for wireless communication systems especially in telecommunication. This paper presents measurements and analysis of spectrum occupancy in the telecommunication frequency bands performed in Kampala, Uganda in March 2015. The telecommunication bands considered in this study are GSM900, GSM1800, UMTS2100 and LTE2600. Occupancy measurements have been carried out in an outdoor setting using the Aaronia Hyperlog 70600 antenna and the Spectran HF-6065 V4.The analysis shows that the licensed telecommunication spectrum bands are not fully utilized. Highest spectrum occupancy of 52.4% was observed in the GSM900 Downlink telecommunication band while the lowest occupancy of approximately 0% was observed in the LTE2600 band.

GSM/DCS/UMTS low-profile metamaterial-based microwave antenna

We present the design and characterization of a triband low-profile antenna based on the use of artificial magnetic conductor (AMC) surfaces. The engineered double AMC substrate allows reducing the separation between the radiating element and the ground plane. The radiating element is a wide band microstrip elliptical dipole and is associated to the double AMC substrate to cover the (790–860 MHz) GSM, the (1710–1880 MHz) DCS and the (1920–2170 MHz) UMTS telecommunication frequency bands. The whole antenna system presents a reduced level of backward radiation and is intended to be inserted in the back of a jacket. Presented experimental performances agree qualitatively with the numerical ones. The fabricated prototype demonstrates the feasibility of a triband antenna with a substantial reduction of the thickness through the use of AMC surfaces. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:737–741, 2015

Spatially Localized Enhancement of Evanescent Coupling to Whispering-Gallery Modes at 1550 nm Due to Surface Plasmon Resonances of Au Nanowires

We demonstrate a highly localized enhancement of evanescent coupling between a tapered optical fiber and a high-Q dielectric microresonator owing to the resonant evanescent excitation of localized surface plasmons of a gold nanowire placed on the microresonator's surface. This localized enhancement, at 1550 nm, is due to nanowire fragments that are confined to specific regions of the surface. The enhancement (of photon-tunneling probability) is measured by comparing properties of the whispering-gallery modes' throughput dips before and after deposition of the nanowire. The experimental results presented here show coupling enhancement by a factor of 10-700, depending on the position of fiber-microresonator contact in relation to the nanowire. These Au-nanowire-coated microresonators could provide enhanced sensitivity in various types of surface-plasmon-based gas, chemical, and biological-sensing applications within the telecommunication frequency bands.

Designing of omni-directional high reflectors by using one-dimensional modified hybrid Fibonacci/Cantor band-gap structures at optical telecommunication wavelength band

By studying the reflection spectra of one-dimensional modified hybrid quasi-periodic Fibonacci/Cantor structures at the optical telecommunication frequency band for any incident simulator and for both parallel (P) and orthogonal (S) polarizations, reflection bands covering the three wavelengths of telecommunication were obtained, where the propagation of light is forbidden in this region for all incident angles and for S polarization. The broad extension of the stop band explains that strong light localization occurs in this region. The modification law of the stacks was introduced by applying the following rule , where x j is the position of the beginning of the jth layer, y j is the position of the beginning of the jth layer after modification and where k represents the coefficient defining the modification degree. The reflection spectra are determined by using a theoretical model based on the transfer matrix method (TMM).

이동통신주파수 대역에서 순철 분말-고무 복합체 Sheet의 전파흡수특성

이동통신주파수 대역에서 박형의 전파흡수체를 제작하기 위해 순철 분말을 흡수 충진재로 사용한 고무 복합체의 고주파 특성(복소투자율, 복소유전율) 및 전파흡수특성에 대해 조사하였다. 주요 실험변수는 순철 분말의 초기입도와 형상(구형, 압분체) 변화였다. Attrition milling에 의해 두께가 표피두께보다 작은 순철 압분체를 제작함으로써 임피던스정합 조건에 근접하는 고투자율과 고유전율을 동시에 얻을 수 있었다. 이는 milling에 의해 구형에서 평판상으로 모양이 바뀜에 따라 와전류 손실이 감소하고(복소투자율의 증가), 압분체 간의 정전용량이 증가한 것(복소유전율의 증가)에 기인한다. 초기입도가 10<TEX>$\mu\textrm{m}$</TEX>인 순철 압분체를 흡수 충진재로 사용함으로써 이동통신주파수 대역(0.8-2.0㎓)에서 반사손실이 -5㏈(70% 전력흡수율), 두께가 0.7mm 수준인 박형의 전파흡수체를 제안할 수 있었다. For the aim of thin electromagnetic wave absorbers used in mobile telecommunication frequency band (0.8-2.0㎓), we investigate high-frequency magnetic, dielectric and microwave absorbing properties of iron particles dispersed in rubber matrix in this study. The major experimental variables are particle shape (sphere and flake) and initial particle size (in the range 5-70 <TEX>$\mu\textrm{m}$</TEX>) of iron powders. High value of magnetic permeability and dielectric permittivity can be obtained in the composites containing thin plate-shape (flake) iron particles (of which thickness is less than skin depth in ㎓frequency), which can be produced by mechanical forging of spherical iron powders using an attrition mill. This result is attributed to the reduction of eddy current loss (increase of permeability) and the increase of space charge polarization (increase of permeability). The optimum initial particle size is found to be about 10 <TEX>$\mu\textrm{m}$</TEX> for the attainment of the material parameters (particularly, real part of complex permeability) satisfying the wave impedance matching. With the iron powders controlled in size and shape as absorbent fillers in rubber matrix, the thickness can be reduced to about 0.7mm with respect to -5㏈ reflection loss (70% power absorption) in mobile telecommunication frequency band.

Diffractionless optical networking in an inverse opal photonic band gap micro-chip

We present a design for a photonic crystal (PC) all-optical micro-chip based on a three-dimensional (3D) inverse opal heterostructure intercalated with a two-dimensional (2D) triangular lattice photonic crystal slab. Within the 2D micro-chip layer, we demonstrate single-mode (diffractionless) waveguiding of light in air, throughout a bandwidth of more than 70 nm near 1.55 μm. This suggests that inverse opal photonic band gap (PBG) materials can facilitate on-chip optical networking functions over the telecommunication frequency band used in current-day optical fibers.

Design and Fabrication of thin Microwave Absorbers of ITO/Dielectric Structures Used for Mobile Telecommunucation Frequency Bands

For the aim of thin microwave absorbers used in mobile telecommunication frequency band, this study proposed a high permittivity dielectrics(λ/4 spacer) coated with ITO thin films of 377 /sq(impedance transformer). High frequency dielectric properties of ferroelectric ceramics, electrical properties of ITO thin films and microwave absorbing properties of ITO/dielectrics were investigated. Ferroelectric materials including (BT), 0.9Pb(3/Nb3/)-0.1 (PMN-PT), 0.8 Pb (Mg3/3/)-0.2 Pb(33/)(PMN-PZN) were prepared by ceramic processing for high permittivity dielectrics,. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave frequency range. The microwave absorbance (at 2 ㎓) of BT, 0.9PMN-0.1PT, and 0.8PMN-0.2PZN were found to be 60%(at a thickness of 3.5 mm), 20% (2.5 mm), and 30% (2.5 mm), respectively. By coating the ITO thin films on the ferroelectric substrates with λ/4 thickness, the microwave absorbance is greatly improved. Particularly, when the surface resistance of ITO films is closed of 377 /sq, the reflection loss is reduced to -20 ㏈(99% absorbance). This is attributed to the wave impedance matching controlled by ITO thin films at a given thickness of high permittivity dielectrics of λ/4 (3.5 mm for BT, 2.5 mm for PMN-PT and PMN-PZN at 2 ㎓). It is, therefore, successfully proposed that the ITO/ferroelectric materials with controlled surface resistance and high dielectric constant can be useful as a thin microwave absorbers in mobile telecommunication frequency band.

Fabrication and Properties of Thin Microwave Absorbers of Ferroelectric Materials Used in Mobile Telecommunication Frequency Bands

High-frequency dielectric and microwave absorbing properties have been investigated in ferroelectric materials (BaTiO(BT), (1-x)Pb)O-xPbTiO(PMN-PT), (1-x)PbO-xPb(Zn_{\frac{1}{3}}Nb_{\frac{2}{3}}$)O(PMN-PZN) for the aim of thin microwave absorbers in the frequency range of mobile telecommunication. The specimenns are prepared by conventional ceramic processing and complex permittivity has been measured by transmission/reflection method. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave range and their domiant loss mechanism is considered to be domain wall relaxation. The microwave absorbance of BT 0.9PMN-0.1PT, and 0.8PMN-0.2PZN specimen (determined at 2) are found to be 99.5% (at a thickness of 4.5 mm), 50% (2.5 mm), and 30% (2.5 mm), respectively. It is suggested that PMN-PT or PMN-PZN ferroelectrics are good candidate materials for the spacer of λ/4 absorber. The use of ferroelectric materials is effective in reducing the thickness of absorber with their advantage of high dielectric constant.