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SUMMARY We propose a new set of equations describing a cylindrical vertical cavity surface emitting laser (VCSEL) cavity under CW operation, based on the rate equations including lateral carrier diffusion. The only numerical step in the calculation consists in finding the roots of a polynomial expression. This model enables a quasi-instantaneous calculation of the laser’s light-current characteristic, including such effects as spatial hole burning, current spreading, inhomogeneous optical intensity distribution, and diffusion losses. An analysis of the VCSELs threshold current and differential quantum efficiency is proposed, which illustrates the interplay between injected current profile and diffusion coefficient. Copyright # 2003 John Wiley & Sons, Ltd.

We investigate the influence of oxide aperture size and number of top distributed Bragg reflector pairs on the performance of oxide confined vertical-cavity surface emitting lasers. Several counteracting mechanisms are shown to result in nonmonotonic behavior, which limits the performance of very small cavities. Static, dynamic, and noise behavior are considered. We examine static operation by means of steady-state measurements, whereas dynamic behavior and noise performance are described by the intrinsic relaxation oscillation frequency, damping coefficient, and Schawlow–Townes linewidth. These parameters are extracted from relative intensity noise measurements. Reducing the oxide aperture up to a given optimal diameter is shown to improve the device’s characteristics. We attribute the performance degradation below this value to increased diffraction losses, reduced confinement factor, and enhanced spontaneous emission. Similarly, increasing the number of Bragg reflector pairs first yields better overall performance as a consequence of reduced mirror losses. However, beyond an optimal value, significant reduction of the differential gain is observed that is attributed to gain compression and possibly thermal effects, degrading both the steady-state and high-frequency performance of the device.

We propose a set of transformed two-dimensional (2-D) rate equations, which allow the computation of dynamic gain competition resulting from inhomogeneous field and carrier spatial distributions inside a vertical cavity surface-emitting laser cavity. Any explicit spatial dependency has been removed from the modified equations, reducing the computational time by several orders of magnitude. Resulting 2-D dynamic intensity profiles allow investigating effects related to improper fiber coupling due to transverse misalignment between laser beam and fiber. Although the expected increased relative intensity noise (RIN) levels associated with mode partition noise are observed, other effects might have larger contributions to the total noise under specific conditions. We show that the minimum RIN level is not necessarily reached for zero misalignment, but at positions where modes with broad far-field profiles and low power experience important filtering.

International audience; Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

We present a coherent optical commu nication system for inter-satellite links with a new type of Optical Phase Lock Loop (OPLL). The OPLL requires no residual carrier transmission, although it employs a conventional 180° 3 dB hybrid and an AC-coupled balanced front end.

In analog RF fiber-optic (FO) links with directly modulated multimode laser diodes (LD's), nonlinear distortions of the received modulation signal occur due to fiber dispersion. Using a simple analytical two mode model, we show that the mutual compensation of strong nonlinearities between particular modes breaks down at high-modulation frequencies. The effect can be observed even in 1300-nm links with single-mode (SM) standard fibers. Simulations as well as measurements of intermodulation (IM) illustrate this argument.

A complementary logic circuit with Josephson junctions has been investigated theoretically and experimentally. This paper will discuss a circuit with a measured risetime of 100 ps, a power dissipation of 16.4 μW, with the flip-flop operated with a 1500-MHz input signal.

We have studied tapers that couple light from a conventional ridge waveguide into a planar photonic crystal (PhC) waveguide. Tapering is achieved by changing the PhC waveguide width either in steps or gradually. Lag effects in fabrication provide an additional tapering due to the fact that the hole depths scale with the corresponding hole diameter. Our analysis deals with the out-of-plane loss that arises within such taper sections. The PhC consists of a triangular lattice of air holes introduced into an InGaAsP/InP slab structure. For conceptual studies we use the 2D multiple multipole method (MMP) in conjunction with an extended phenomenological model. This model covers the out-of-plane scattering providing a loss parameter and an effective index correction for the holes under consideration. This realistic 2D model is retrieved from full-wave 3D FDTD simulations and measurements.

Organic two-dimensional photonic bandgap structures (2D PBG) have been fabricated by spin-coating a thin polymer film onto a nano-patterned SiO2 circular-grating surface-emitting distributed Bragg reflectors (CG-SE-DBR). When optically pumped and for certain grating parameters, these structures exhibit a peak inside the stop band that leads to lasing with a reduced threshold. An analytical model based on the transfer-matrix method has been developed to investigate the origin of this peak. The theoretical results are in excellent agreement with the experimental findings.

The design of aperture coupled patch (ACP) antennas for an RFID system in the 2.4 GHz ISM using circular polarization modulation is presented. Due to the requirements of the modulation scheme the ACP antennas are circularly polarized with switchable polarization sense. Four ACP antennas are compared according to their impedance and gain bandwidth, axial ratio, and crosspolarization isolation. Among the presented antennas a novel compact ACP antenna is shown that allows replacement of the conventional quadrature hybrid polarizer by /spl lambda//4 quarter transmission lines.

This survey of European GaAs device activities focuses on GaAs MESFETs, HEMTs, and GaInAs JFETs. In all areas significant progress is noted and attributed to advanced processing methods. In the case of the GaInAs JFET, outstanding device results are cited. It is felt that the technology, however, is presently suited to very simple integrated circuits only and that of tools and processes similar to those for MESFETs are needed similar levels of integration to become feasible. >

The noise temperature dependence on the electric field in an AlInAs/GaInAs HEMT heterostructure has been measured. It was found that the dependence of the noise temperature on the electric field in GaAs MESFETs and in AlInAs/GaInAs HEMTs are remarkably different. For this reason a different model must be used for AlInAs/GaInAs HEMTs. Based on the measured noise temperature dependence on the electric field, am analytic noise model for the AlInAs/GaInAs HEMT has been developed. The noise source parameters were calculated and compared with extracted noise source parameters from noise measurements. >

In this contribution the development of a large signal model describing the electrical behaviour of an InAlAs/InGaAs/InP-HEMT will be discussed. The transistors under question were fabricated at our laboratory. They revealed a transit frequency of 150 GHz, which is, to our knowledge, the best result obtained with a T-gate of 0.25 /spl mu/m footprint. The aim of this project was to develop a model of this transistor for simulating nonlinear circuits with commercial simulator software like HP-MDS or Spice. The procedure results in an easily applicable model which produces very good fits to the measured S-parameters.

We report depletion and enhancement mode InP high electron mobility transistors (HEMTs) fabricated using CH/sub 4//H/sub 2/ selective dry etch gate recess process. Under the etching conditions developed, the process has a In/sub 0.7/Ga/sub 0.3/As to In/sub 0.52/Al/sub 0.48/As selectivity of 130. The dc threshold voltages of the devices fabricated in this way increase from -1.3 V to 0.1 V as a function of dry etch time, with an extrinsic transconductance of 520 mS/mm in the depletion mode and 800 mS/mm in enhancement mode. The devices exhibit an extrapolated cut-off frequencies of 150 GHz. This work demonstrates the potential of the use of dry etching as a gate recess technology for the future development of high frequency InP-based circuits.

A modified GaAs MESFET-model has been developed to improve accuracy over a large bias range, particularly within the linear region. The enhancements consist of a modified Statz equation for the gate charge to improve the modeling of the gate drain capacitance, and an equation for the bias dependent drain source resistance for exact modeling of the dispersive output conductance.

An accurate noise parameter measurement technique is presented that uses an amplifier/attenuator noise source, a multi-octave tuner and a directional coupler for noise injection at all tuner states. The presented concept allows measurements with more than 30 different ENR steps and the ability to calibrate the ENR during system calibration. A system that demonstrates the concept was built for the frequency range from 0.5-6.0 GHz.

We propose a new asymmetric drive scheme for vertical-cavity surface-emitting lasers (VCSELs) that is expected to permit the active compensation of misalignment between laser beam and waveguide. Simulations performed with a VCSEL integrated spatiotemporal advanced simulator simulation tool indicate that driving the laser with two orthogonal, individually addressable contacts may improve coupling efficiency by selective excitation of modes with given azimuthal distributions. Besides improved and more-stable coupling efficiency, significantly lower noise levels that result from reduced mode partition noise are observed, which significantly enhance the performance of digital transmission systems. Such electronic beam shaping from the driver side may drastically reduce the system’s costs by relaxing its fabrication tolerances.

Remote antennas in cellular telephone networks can be supplied by coaxial cable or optical fibre. It is useful to know which of the two technologies is more appropriate with respect to dynamic range and costs. Coaxial and optical fibre links are considered for GSM applications. The link length-dependent costs are compared for two reasonable values of the dynamic range.

In modern low cost RF amplifiers or fibre optic links, it is essential to know the limit of the third order intercept point definition to make accurate intermodulation predictions. The authors present a simple formula to calculate this limit from the data sheet parameters' third order intercept point and 1dB compression point.

The noise temperature dependence on the electric field in an AlInAs/GaInAs-HEMT heterostructure has been measured. It was found that the dependence of the noise temperature on the electric field in GaAs-MESFETs and in AlInAs/GaInAs-HEMTs is remarkably different. For this reason a different model must be used for AlInAs/GaInAs-HEMTs. Based on the measured noise temperature dependence on the electric field, an analytic noise model for the AlInAs/GaInAs HEMT has been developed. The noise source parameters were calculated and compared with extracted noise source parameters from noise measurements.

The small signal and noise equivalent circuit of a microwave transistor is evaluated using an analog simulation model. The noise figure has been determined with the same model as a function of the source admittance and the frequency. The s parameters and noise figures are compared with the results calculated on a digital computer.

During recent years significant progress has been made in GaAs technology and the GaAs Schottky-barrier field-effect transistor now shows outstanding microwave gain and noise properties. Two experimental microwave amplifiers demonstrate that the device is very well suited for broad-band applications and that large bandwidth in the X- and Ku-band can be obtained with simple circuits. The first of the two three-stage amplifiers realized was optimized with respect to noise and a noise figure of 3.8 dB was obtained at 8 GHz; the maximum gain is 17.5 dB at 8.3 GHz and the 3-dB bandwidth is 1.3 GHz. The second amplifier has a maximum gain of 11.5 dB at 11.5 GHz. The gain is greater than 8.5 dB in the range 9.5-14.3 GHz.

The noise behavior of the GaAs Schottky-barrier gate field-effect transistor has been investigated theoretically and experimentally. It has been found that an additional noise source has to be taken into account in GaAs FET's biased in the pinchoff region: the intervalley scattering noise. This noise source has been investigated and a new transistor noise model is proposed. Measured and calculated noise figures show good agreement in the frequency range 2-10 GHz. It is shown that the influence of the intervalley scattering noise can be reduced by reducing the channel thickness, and that such devices show excellent gain and noise properties in the X band.

The noise behavior of a Schottky barrier gate field-effect transistor is investigated by the use of the noise equivalent circuit. The influence of the carrier velocity saturation is estimated. The noise parameters are calculated by taking into account the influence of parasitic resistances. Measured and calculated noise parameters show good agreement in the frequency range 2-8 GHz.

Si and GaAs Schottky-barrier field-effect transistors with gate lengths of 0.5 μm have been experimentally realised. Noise and gain properties were measured in the microwave range up to 20 GHz. When compared with 1 μm-gate f.e.t.s, the devices show considerable improvements in gain and in noise figure. At 10 GHz, the following values were measured: Si m.e.s.f.e.t.: maximum available gain = 5.9 dB, noise figure = 5.8 dB; GaAs m.e.s.f.e.t.: maximum available gain = 12.8 dB, noise figure = 3.7 dB.

This paper will report on two low-power FET amplifiers: 8.2 GHz with 17.5-dB gain and 1.3-GHz bandwidth; 9.5-14.3 GHz with 8.5-dB gain.

We propose a new system-oriented 2D VCSEL model, which takes into account the detailed interactions between the transverse carrier and field distributions. It shows several orders of magnitude improvement in computational efficiency compared to conventional models.

GaAs field-effect transistors with a Schottky-barrier gate have been investigated in the frequency range 12–20 GHz. Measurements of the maximum available gain have shown that the devices have much higher gain in this range than has been expected. A 17 GHz oscillator having an output power of 4mW and a 4-stage 14.9GHz amplifier with 16 dB of power gain have been built using stripline technique.

A logic circuit with Josephson junctions has been developed that operates as logic gate or as a flip-flop. Despite the latching-type characteristic of the Josephson tunnel junction, the complementary logic circuit is nonlatching. The test circuit has a power dissipation of 16.4 μW and a signal risetime of approximately 60 ps has been measured.

An improved silicon MESFET with a 1; gate is described which has a maximum frequency of oscillation of 15 GHz. The improvement over previous MESFET's has been achieved by reducing the influence of the resistance of the gate metallization and by decreasing the gate-pad parasitics. Maximum available gain MAG is now 5 dB at 7 GHz and the optimum noise figure F 0 is 5 dB at 6 GHz. Below about 6 GHz the device is conditionally unstable. Unilateral gain U up to 3 GHz is 20 dB. The investigation indicates that not all parasitics have been removed. If the series resistance of the channel in the source-gate spacing could be decreased, f max should approach 35 GHz the estimated value of the intrinsic transistor.

A GaAs Schottky-barrier f.e.t. (m.e.s.f.e.t.) with a 1 ?m gate has been built, which is suitable for X band and Ku band applications. The unilateral power gain over the X band is above 9 dB and the noise figure is only 5 dB at 10 GHz.