Telecommunication Frequencies Research Articles

Reconfigurable Add–Drop Optical Filter Based on Arrays of Digital Micromirrors

We demonstrate a universal reconfigurable add-drop optical filter based on arrays of digital micromirrors. Our approach allows for reconfiguration of the device parameters for operation in different sets of channel wavelengths, even or uneven channel-to-channel separation, adjustable channel passband, and dynamic add-drop of optical signals. The proposed device shows insertion loss at the center wavelength in the all-pass configuration of 7.6 dB, extinction ratio of 35 dB, channel isolation better than 24dB, negligible loss ripple, and possibility of reconfiguration time in the order of microseconds. Although designed for demonstration on optical telecommunication frequencies, the high-flexibility features of the proposed add-drop filter allow it to be used for other optical wavelength-based filtering/switching applications.

Surface Plasmon Amplification in Planar Metal Films

The propagation and amplification of surface plasmon polaritons (SPPs) is studied at the interfaces between metals and active media. A permittivity renormalization technique is proposed and developed to obtain an explicit analytic expression for the critical gain required to achieve infinite SPP propagation length. A specific multiple quantum-well (MQW) system is identified as a prospective medium for demonstrating efficient SPP amplification at telecommunication frequencies. The proposed system may have a strong impact on a variety of photonic devices ranging from plasmonic nanocircuits, subwavelength transmission lines and plasmonic cavities to nanosized transducers.

Design and fabrication of segmented, slotted waveguides for electro-optic modulation

Recently, slotted waveguides have been used in conjunction with second order nonlinear optical polymers to provide a platform for electro-optic modulation at telecommunication frequencies. A challenge with these devices is the need to provide high-frequency electrical driving signals to the slots. The silicon resistivity must be high to reduce optical loss, and as a result electrical performance can be severely limited. We have designed and fabricated a class of waveguide that achieves quasicontinuous electrical contact with subwavelength segmentations and has low optical losses of 4dB∕cm, allowing both millimeter-wave and optical fields to be concentrated in the same area.

Slow guided surface plasmons at telecom frequencies

The phenomenon of slow light is interesting not only from a fundamental physics standpoint, but also because it introduces the possibility of new applications in telecommunications1. For a practical slow-light device, the important features are bandwidth, range of wavelength tunability and size, rather than the absolute slowdown factor achieved2. Slow light can be achieved in three main ways: through quantum interference effects3,4,5,6,7,8, which can slow the speed of light down to several metres per second, albeit within a very narrow bandwidth; by using photonic crystals9, which are able to slow light over large bandwidths but with much smaller slowdown factors10,11; and by using stimulated Brillouin or Raman scattering12,13. Surface plasmon polaritons have the advantage that they can overcome the diffraction limit of light in a microchip-sized device14,15,16,17. Increases in the propagation lengths of surface plasmon polaritons18 and the feasibility of all-optical wavelength tunability19 have been reported. Here we report the observation of slow, femtosecond surface-plasmon-polariton wavepackets. We show that a highly compact (55 µm length) plasmonic structure is able to achieve an effective slowdown factor of two over a 4 THz bandwidth. These results will increase the scope of photonic devices based on surface plasmon polaritons.

Magnetic Metamaterials at Telecommunication and Visible Frequencies

Arrays of gold split rings with a 50-nm minimum feature size and with an LC resonance at 200 THz frequency (1.5 microm wavelength) are fabricated. For normal-incidence conditions, they exhibit a pronounced fundamental magnetic mode, arising from a coupling via the electric component of the incident light. For oblique incidence, a coupling via the magnetic component is demonstrated as well. Moreover, we identify a novel higher-order magnetic resonance at around 370 THz (800 nm wavelength) that evolves out of the Mie resonance for oblique incidence. Comparison with theory delivers good agreement and also shows that the structures allow for a negative magnetic permeability.

A frequency-doubled laser system producing ns pulses for rubidium manipulation

We have constructed a pulsed laser system for the manipulation of cold 87Rb atoms. The system combines optical telecommunications components and frequency doubling to generate light at 780 nm. Using a fast, fibre-coupled intensity modulator, we sliced output from a continuous laser diode into pulses with a length between 1.3 and 6.1 ns and a repetition frequency of 5 MHz. These pulses are amplified using an erbium-doped fibre amplifier, and frequency-doubled in a periodically poled lithium niobate crystal, yielding a peak power up to 12 W. Using the resulting light at 780 nm, we demonstrate Rabi oscillations on the F=2,mF=+2↔F′=3, m′ F=+3-transition of a single 87Rb atom.

Experimental demonstration of fiber-accessible metal nanoparticle plasmon waveguides for planar energy guiding and sensing

Experimental evidence of mode-selective evanescent power coupling at telecommunication frequencies with efficiencies up to 75% from a tapered optical fiber to a metal nanoparticle plasmon waveguide is presented. The waveguide consists of a two-dimensional square lattice of lithographically defined Au nanoparticles on an optically thin silicon membrane. The dispersion and attenuation properties of the waveguide are analyzed using the fiber taper. The high efficiency of power transfer into these waveguides solves the coupling problem between conventional optics and plasmonic devices and could lead to the development of highly efficient plasmonic sensors and optical switches.

Square spiral 3D photonic bandgap crystals at telecommunications frequencies

We present evidence of complete, three-dimensional photonic bandgaps in obliquely deposited thin films with a porous microstructure of tetragonally arranged square spirals. We further present a capability to engineer the bandgap center to wavelengths as low as 1.65 mum, with bandgap widths of up to 10.9%. Using new deposition methods that provide detailed control over the photonic crystal dimensions and morphology, this approach allows advanced photonic crystal architectures to be realized over large scales with uncomplicated fabrication technology.

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.

Low-loss fiber accessible plasmon waveguide for planar energy guiding and sensing

A metal nanoparticle plasmon waveguide for electromagnetic energy transport utilizing dispersion engineering to increase lateral energy confinement via a two-dimensional pattern of Au dots on an optically thin Si membrane is described. Using finite-difference time-domain simulations and coupled-mode theory, we show that phase-matched evanescent excitation from conventional fiber tapers is possible with efficiencies &amp;gt;90% for realistic geometries. Energy loss in this waveguide is mainly due to material absorption, allowing for 1/e energy decay distances of about 320 μm for excitation at telecommunication frequencies. This concept can be extended to the visible regime and promises applications in optical energy guiding, optical sensing, and switching.

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.

Digital Communication for Current Differential Protection Schemes

The overwhelming majority of the more than 200,000 differential relays that are in worldwide operation today use pilot cables as their cammunication media. The advances in telecommunications frequency make a change of the complete protection system concept necessary. Modern digital communicatians have entered the substation. Fibre optic cables and enterprise digital communication networks replace more and more traditonal pilot wires. The majority of today’s telephone networks have now been upgraded from analogue to digital, with the result that there are hardly any rentable wire pilot wires available any more for analogue differential relays. This paper deals with the relay requirements on digital communication links and new opportunities for a further enhancement of line differential schemes.

Generation of an amplitude modulated optical wave up to 275 GHz by laser wave mixing for optical component bandwidth measurement

This paper presents a method to achieve an amplitude-modulated optical wave in the range of telecommunication frequencies for optical components bandwidth tests. The principle is based on the optical heterodyning of two free distributed feedback lasers. The frequency tunabil- ity of the modulated wave reaches 275 GHz with high stability. These characteristics constitute the originality of our work. Our laboratory has developed an experimental fusion setup that enables the realization of numerous optical fiber components. Component bandwidth measurement enables their validation for high-rate data transmissions. We present in this paper results obtained for a 57-GHz beat signal in a fast photodiode and we describe bandwidth optical components tests in the 0 to 40 GHz range.

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.

Achieving of an optical very high frequency modulated wave source using heterodyne technique

We describe a method for generating an amplitude modulated optical wave in the range of the telecommunication frequencies. The originality is to guaranty a tunability of the source up to 275 GHz with about 45 MHz spectral width. The principle is based on the optical heterodyne of two DFB laser sources emitting around 1550 nm. After describing various existing methods for optical wave modulation and for millimetric signal generation, we concentrate our interest on the heterodyne technique. We carry out a study concerning the spectral width influence on the spectral purity of the generated signal. Then, the experimental measurement set-up is described, as well as characterization of the spectral width of the lasers. Finally, we present the results obtained in reception of the beat of two identical lasers on a 25 GHz bandwidth photodiode.

Preparation of polymer optical fibers doped with nonlinear optical active organic chromophores

AbstractWe synthesized two novel organic nonlinear optical chromophores—chiral S(+)‐N‐[p‐(4‐nitrostyryl) phenyl] prolinol and non‐chiral [p‐(4‐nitrostyryl) phenyl] piperdine—as potential laser‐active dyes for photonic applications. Both materials show good optical transmittance in the telecommunication frequency region, desirable solubility in acrylic polymer optical fiber matrices, and attractive fluorescence properties that are advantageous for laser‐gain materials and devices. Subsequently, these two chromophores were incorporated into poly(methyl methacrylate) and poly(ethyl methacrylate) and drawn into polymer optical fibers. The relevant properties of these organic dye‐doped fibers have been studied, revealing essential attributes of laser‐active characteristics. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1794–1801, 2001

Femtosecond Laser Micromachining of Si-on-SiO2 for Photonic Band Gap Crystal Fabrication

Femtosecond laser pulses at 387 nm were used to machine Si-on-SiO2 substrates for photonic band gap crystals. With 387 nm ultrashort near-UV pulses, we obtained holes as small as 160 nm, which is smaller than one half of the laser wavelength with only conventional optics. Moreover, a pitch size of 420 nm is also obtained in Si-on-SiO2, which meets the spacing requirement for today's telecommunication frequency -1550 nm. Ultrafast laser micromachining is fast and versatile, thus it is a powerful tool for in-situ microstructure operations such as nanostructuring, repairing, and production industrial applications.

The gravitational lenses of alpha centauri a, b, c and of barnard's star

The gravitational lenses of the three nearest stars, Alpha Centauri A, B and C (Proxima Centauri), are studied in this paper. For each star, the minimal focal distance is found, and turns out to equal 679.263, 563.485 and 112.138 AU, respectively, plus or minus the (large) uncertainties deriving from the uncertainties in the estimates of the star masses and radii. A comparison of these three minimal focal distances against the corresponding value for the Sun (550 AU, or, more correctly, 548.230 AU) is then made, but it is clearly pointed out that all these minimal focal distances are just the theoretical values given by Einstein's deflection formula for the corresponding “naked star”, i.e. the star as if it had no corona around! The study of the true focal distances that follow from taking the corona into account is much more difficult and uncertain, and has to be delayed to further research. For the naked stars, we study the deflection of radio waves for five different frequencies: the hydrogen line at 1.420 GHz, the water maser at 22 GHz, NASA's Interstellar Probe (ISP) telecommunication frequency at 32 GHz (K a band), the Cosmic Microwave Background peak frequency at 160.378 GHz and finally the positronium frequency at 203.385 GHz. For each frequency the antenna patterns of the three naked stars gravitational lenses are given. Finally, all the above data are derived also for the fourth star in increasing distance from the Sun, Barnard's star.

The magnetic applications choice among ferrite ceramics, metallic strips, or metal powder cores

Iron-based metallic strip materials such as iron, silicon-iron, and amorphous metal are used for low frequency (50–60 Hz. line) power applications. Low-loss Nickel-based alloys as high permeability strip or insulated powder cores are the choices for stable, low-level higher frequency applications. Iron-based powder cores offer low cost as power supply filter chokes. Ceramic ferrites combine highest frequency operation with low cost and reduced component size as transformers and chokes in telecommunication and high frequency power supply applications.