On radiating-zone boundaries of short, /spl lambda//2, and /spl lambda/ dipoles

This article presents a critical analysis of the classical definitions of the radiation regions for the particular case of short, /spl lambda//2, or /spl lambda/ dipole antennas, regions which we have revisited. We worked out a definition of radiation zones from consistent criteria directly linked with radiation characteristics: radiated field, wavefront, wave impedance, and radiated power. The "far-field zone" boundary is then defined as the distance beyond which the radiated wave is spherical and the radial component of the fields is negligible compared to the transverse component. Next, we consider the "near-field-reactive or very-near-field zone" to be the region wherein the wave impedance is different from Z/sub 0/ =120/spl pi/, and wherein the reactive power is not negligible when compared to the active power. In this paper, the short dipole case is first studied. Dipoles of length up to /spl lambda/ are also treated, considering diameters from 0 up to /spl lambda//20. The results obtained lead us to accurately set the boundaries of the radiation zones of dipoles without the need for the restrictive hypotheses of the classical definitions.     

Broadband 180/spl deg/ bit phase shifter using a /spl lambda//2 coupled line and parallel /spl lambda//8 stubs

In this paper, a broadband 180/spl deg/ bit phase shifter using a new switched-network was presented. The new network is composed of a /spl lambda//2 coupled line and parallel /spl lambda//8 open and short stubs, which are shunted at the edge points of a coupled line, respectively. According to a desired phase shift, it provides a controllable phase dispersive characteristic by the proper determination of Z/sub m/,Z/sub s/, and R values. The 180/spl deg/ bit phase shifter operated at 3 GHz was fabricated and experimented using design graphs which provide the required Z/sub m/,Z/sub s/ values, and I/O match and phase bandwidths. The experimental performances showed broadband characteristics.     

Thin-film /spl lambda//spl sim/3.7 /spl mu/m 'W' laser released from InAs substrate

A mid-infrared type-II 'W' laser fabricated by releasing the epitaxial film from its original InAs substrate is reported. The process exploits the extreme selectivity between GaSb and InAs when etched by hydrochloric acid. The detached film is coated with an Si/sub 3/N/sub 4/ optical cladding layer, grafted to a foreign GaAs substrate, and cleaved into laser bars. For epitaxial-side-up mounting, the device operates to 70 K, with a low threshold (/spl sime/150 W/cm/sup 2/) when pumped with the maximum available CW power of 320 mW from a 980 nm laser diode.     

Short wavelength (/spl lambda//spl sim/4.3 /spl mu/m) high-performance continuous-wave quantum-cascade lasers

We report continuous-wave (CW) operation of a 4.3-/spl mu/m quantum-cascade laser from 80 K to 313 K. For a high-reflectivity-coated 11-/spl mu/m-wide and 4-mm-long laser, CW output powers of 1.34 W at 80 K and 26 mW at 313 K are achieved. At 298 K, the CW threshold current density of 1.5 kA/cm/sup 2/ is observed with a CW output power of 166 mW and maximum wall-plug efficiency of 1.47%. The CW emission wavelength varies from 4.15 /spl mu/m at 80 K to 4.34 /spl mu/m at 298 K, corresponding to a temperature-tuning rate of 0.87 nm/K. The beam full-width at half-maximum values for the parallel and the perpendicular far-field patterns are 26/spl deg/ and 49/spl deg/ in CW mode, respectively.     

Thermo-optical modulation at /spl lambda/=1.5 /spl mu/m in an /spl alpha/-SiC-/spl alpha/-Si-/spl alpha/-SiC planar guided-wave structure

A planar waveguide based on an amorphous silicon-amorphous silicon carbide heterostructure is proposed for the realization of passive and active optical components at the wavelengths /spl lambda/=1.3-1.5 /spl mu/m. The waveguide has been realized by low temperature plasma enhanced chemical vapor deposition and is compatible with the standard microelectronic technologies. Thermo-optical induced modulation at /spl lambda/=1.5 /spl mu/m is demonstrated in this waveguide. Numerical simulations predict that operation frequencies of about 3 MHz are possible. The measurements have also allowed the determination of the previously unknown thermo-optical coefficient of undoped amorphous silicon at this wavelength.     

Resonant-phonon terahertz quantum-cascade laser operating at 2.1 THz (/spl lambda//spl sime/141 /spl mu/m)

The development of quantum-cascade lasers (QCLs) at 2.1 THz (/spl lambda//spl sime/141 /spl mu/m), which is the longest wavelength QCL to date without the assistance of magnetic fields, is reported. This laser uses a structure based on resonant-phonon depopulation, and a metal-metal waveguide to obtain high modal confinement with low waveguide losses. Lasing was observed up to a heatsink temperature of 72 K in pulsed mode and 40 K in continuous-wave (CW) mode, and 1.2 mW of power was obtained in CW mode at 17 K.     

High-power room temperature emission quantum cascade lasers at /spl lambda/=9 /spl mu/m

We present two different techniques for processing InP-based /spl lambda/=9 /spl mu/m quantum cascade lasers which improve the thermal dissipation in the device. The first process is based on hydrogen implantation creating an insulating layer to inject current selectively in one part of the active region. The second process uses a thick electroplated gold layer on the laser ridge to efficiently remove the heat produced in the active region. Each process is designed to improve heat evacuation leading to higher performances of the lasers and will be compared to a standard ridge structure from the same wafer. We give evidence that the process of proton implantation, efficient in GaAs based structures, is not directly applicable to InP based devices and we present a detailed analysis of the thermal properties of devices with an electroplated gold thick layer. With these lasers, an average power of 174 mW at a duty cycle of 40% has been measured at 10/spl deg/C.     

Interband cascade laser operating to 269 K at /spl lambda/=4.05 /spl mu/m

A ten-stage interband cascade laser with 13 mum-wide, 4 mm-long ridge waveguide and Au electroplating for improved epitaxial-side-up heatsinking operates CW to a temperature of 269 K, where the emission wavelength is 4.05 mum. Maximum CW output powers are 130 mW at 78 K, 58 mW at 200 K, and 9 mW at 260 K, and the threshold current density at T=260 K is 660 A/cm²     

Traffic grooming in WDM networks

The emergence of wavelength-division multiplexing technology has led to a tremendous increase In the available transmission capacity in wide area networks. Consequently, these networks may no longer be limited by the transmission bandwidth, but rather by the processing capability of electronic switches, routers, and multiplexers in the network. This realization has led to a new wave of research aimed at overcoming the electronic bottleneck by providing optical bypass at the WDM layer. Traffic grooming can be used as a bypass mechanism by which low-rate circuits are assigned to wavelengths in order to minimize the amount of electronic multiplexing equipment. This topic has received a significant amount of attention in both the research and commercial arenas. We give an overview of the traffic grooming problem and survey some representative work in this area. While most work has focused on grooming in SONET rings, grooming traffic in general mesh networks is an important emerging problem     

Improved GaAs-based quantum cascade laser (/spl lambda//spl sim/11 /spl mu/m) using high-reflectivity metal facet coating

By applying a high-reflectivity metal coating to the rear facet of a GaAs-based quantum cascade laser operating at /spl lambda//spl sim/11.5 /spl mu/m, the threshold current has been reduced by 11% at 260 K and pulsed operation of the epilayer-up mounted device was extended from 283 to 294 K.     

Short wavelength (/spl lambda/ =3.5?3.65 /spl mu/m) InAs/AlSb quantum cascade lasers

InAs/AlSb quantum cascade lasers emitting at 3.5-3.65 mum are demonstrated. The lasers employ a plasmon enhanced waveguide consisting of heavily doped n-InAs cladding layers and low doped InAs spacers. The maximum operation temperature is 200 and 140 K for lasers emitting near 3.65 and 3.5 mum, respectively. The present lasers' performances are limited by interband absorption in narrow gap InAs spacers     

Pulsed operation of long-wavelength (/spl lambda//spl sime/11.3 /spl mu/m) MOVPE-grown quantum cascade lasers up to 350 K

Pulsed laser action above room temperature at /spl lambda//spl sime/11.3 /spl mu/m has been achieved in quantum cascade devices grown by metal organic vapour phase epitaxy (MOVPE). The emission wavelength (/spl lambda//spl sime/11.3 /spl mu/m) is the longest reported for QC lasers grown with this technique. The peak output power at 77 K is approximately 315 mW, decreasing to /spl sime/100 mW at room temperature. The devices display laser operation up to at least 350 K.     

WDM光网络中的业务量疏导

波分复用（WDM）技术在主干传送网中巳广泛应用，WDM光网络的研究进展也非常迅速，光网络中的业务量疏导定义为复用、解复用和交换低速率业务流到大容量的光路中的行为。介绍了WDM光网络的业务量疏导的重要性，研究方法及其最新研究进展情况。     

Elimination of PD-/spl lambda/ at all output ports of silica-based AWG

It is shown that the polarisation dependent wavelength shift (PD-/spl lambda/) of a silica-based arrayed waveguide grating (AWG) is proportional to its output port location as a result of the birefringence in a slab waveguide. This PD-/spl lambda/ was eliminated to less than 0.01 nm by inserting a half waveplate across the slab waveguide.     

RF HBT oscillators with low-phase noise and high-power performance utilizing a (/spl lambda//4/spl plusmn//spl delta/) open-stubs resonator

This paper presents a new type of transmission-line resonator and its application to RF (microwave and millimeter-wave) heterojunction bipolar transistor (HBT) oscillators. The resonator is a parallel combination of two open stubs having length of /spl lambda//4/spl plusmn//spl delta/(/spl delta//spl Lt//spl lambda/), where /spl lambda/ is a wavelength at a resonant frequency. The most important feature of this resonator is that the coupling coefficient (/spl beta//sub C/) can be controlled by changing /spl delta/ while maintaining unloaded Q-factor (Q/sub u/) constant. Choosing a small value of /spl delta/ allows us to reduce /spl beta//sub C/ or equivalently to increase loaded Q-factor (Q/sub L/). Since coupling elements such as capacitors or electromagnetic gaps are not needed, /spl beta//sub C/ and Q/sub L/ can be precisely controlled based on mature lithography technology. This feature of the resonator proves useful in reducing phase noise and also in enhancing output power of microwave oscillators. The proposed resonator is applied to 18-GHz and 38-GHz HBT oscillators, leading to the phase noise of -96-dBc/Hz at 100-kHz offset with 10.3-dBm output power (18-GHz oscillator) and -104-dBc/Hz at 1-MHz offset with 11.9 dBm (38-GHz oscillator). These performances are comparable to or better than state-of-the-art values for GaAs- or InP-based planar-circuit fundamental-frequency oscillators at the same frequency bands.     

Quantum cascade lasers emitting at lambda greater than 100 /spl mu/m

Quantum-cascade lasers based on a bound-to-continuum transition and emitting at /spl lambda//spl sim/106 /spl mu/m (2.8 THz) are reported. They produce peak output powers of a few milliwatt and can be operated up to a heatsink temperature of 65 K. The devices demonstrate the feasibility of this technology for frequencies below 3 THz.     

Measurement technique for the quotient of cross sections /spl sigma//sub e/(/spl lambda//sub s/)//spl sigma//sub a/(/spl lambda//sub s/) of erbium-doped fibers

A method for the measurement of the quotient of the emission and absorption cross section of erbium-doped fibers is presented which utilizes the spontaneous emission perpendicular to the fiber axis. The maximum population of the first excited state achievable through illumination by signal light (/spl lambda//sub s/=1530 nm) is fixed by the quotient of the absorption and the emission cross section. This fact is used to determine the desired quotient. First measurements show that this method is very simple and highly accurate.<>     

A miniaturized net-type microstrip bandpass filter using /spl lambda//8 resonators

A novel miniaturized three-pole net-type bandpass filter using /spl lambda//8 resonators has been proposed. Asymmetric frequency characteristics of this filter exhibit a single transmission zero on the lower side of the passband at finite frequency, which is attributed to multi-path effect. Full-wave simulator IE3D is used to extract the coupling coefficients and external quality factor in order to determine the physical dimensions of this filter. The measured results are in good agreement with the simulated predictions. The overall size of the filter is only about 0.22/spl lambda//sub g/ by 0.2 /spl lambda//sub g/. As a result, the filter has not only a small size but also a wider upper stopband up to 6.5 f/sub 0/.