We utilize a novel hybrid wavelength division multiplexed, optical time division multiplexed (WDM-OTDM) model locked semiconductor laser for applications in ultrahigh data rate communication links, computer interconnects, and optical sampling applications. The key philosophy behind using a hybrid approach is that state-of-the-art system performance can be achieved without the necessity of operating at the limits of either a pure WDM or OTDM technology platform.

The optical network deploying WDM technology efficiently utilizes a single fiber's capacity, thus satisfied the increasing requirement for bandwidth. This paper shows that this kind of network in all-optical form is feasible and practical when applied in metro area, in which transparent transmission can be obtained. For the following section of this paper, we discuss the architecture of the metro all- optical network, and analyze the coordination of protection and restoration schemes between optical and electronic layer. Finally, we show the possible architecture bridging the transparency and the opacity, which is considered to be practical in the near future. And we further present the functional block of the photoelectric component-a novel transponder which is deployed in this architecture.

This paper describes grating design of distributed feedback laser diodes (DFB-LDs) for use in metropolitan area and access networks and demonstrates improved performance of DFB-LDs with new gratin structures. Dynamic behaviors of DFB-LDs under the external optical feedback were analyzed for conventional uniform grating DFB-LDs and partially corrugated waveguide laser diodes (PC-LDs). A high-resistant characteristic against external optical feedback was achieved by PC-LD with optimized grating structure. The increase of RIN was suppressed to as low as -126 dB/Hz with the external optical feedback of -20 dB. It was also found that feedback effect of mirror loss (FEML) plays an important role in external optical feedback resistance. Furthermore, negative FEML, which suppresses relaxation oscillation, reduces transient chirp under high-bit-rate modulation. FEML is successfully controlled by adjusting phase shift value in phase-shifted DFB-LDs, and very low power penalty transmission was demonstrated by (lambda) /8 phase-shifted DFB-LDs. After 100-km transmissions, a power penalty of less than 1 dB within a wide extinction ratio region form 8.5 to 14.5 dB was demonstrated with 2.5 Gb/s direct modulation. These DFB-LDs with new grating structure is promising for intermediate transmission applications.

Long period gratings (LPGs) are fabricated on an ion- exchanged waveguide by the use of direct UV writing. The transmission spectrum of this LPG waveguide is analyzed. An attenuation of 22dB is observed at 1.55 micrometers .

We propose a nonlinear backward matrix method for the analysis of nonlinear gratings. We have analyzed some specific nonlinear Bragg gratings and observed optical switching and bistability.

An optical modulator based on the physical properties of high temperature superconductors has been fabricated and tested. The modulator was constructed form a film of Yttrium Barium Copper Oxide (YBCO) grown on undoped silicon with a buffer layer of Yttria Stabilized Zirconia. Standard lithographic procedures were used to pattern the superconducting film into a micro bridge. Optical modulation was achieved by passing IR light through the composite structure normal to the micro bridge and switching the superconducting film in the bridge region between the superconducting and non-superconducting states. In the superconducting state, IR light reflects from the superconducting film surface. When a critical current is passed through the micro bridge, it causes the film in this region to switch to the non-superconducting state allowing IR light to pass through it. Superconducting materials have the potential to switch between these two states at speeds up to 1 picosecond using electrical current. Presently, fiber optic transmission capacity is limited by the rate at which optical data can be modulated. The superconducting modulator, when combined with other components, may have the potential to increase the transmission capacity of fiber optic lines.

Resonant-cavity-enhanced photodetectors have been demonstrated to be able to improve the bandwidth-efficiency product. We report a novel SiGe/Si multiple quantum-well resonance-cavity-enhanced photodetector fabricated on a separation-by-implanted-oxygen wafer operating near 1300nm. The buried oxide layer in SIMOX is used as a bottom mirror to form a vertical cavity with silicon dioxide/silicon Bragg reflector deposited on the top surface. The quantum efficiency at the wavelength of 1300nm is measured with 3.5 percent at a reverse bias of 15V, which is enhanced by 10 folds compared with a conventional photodetector with the same absorption structures.

The proximity effect of finite-width conductors on the operation of optical waveguide devices has been assessed. It is shown that the proximity effect is caused by the coupling of modes supported by a dielectric waveguide to plasmon- polariton modes supported by the conductor of finite width. The effect is thoroughly described for the first time and its wavelength dependency is determined. The results stress the importance of careful conductor layout in optoelectronic and electro-optic waveguide devices.

A novel technique, that combines optical heterodyning and near-field optics, was developed for highly localized of millimeter waves in ultrafast devices. The technique relies on evanescent coupling of the interfering laser to a small are of the device, by means of a near-field fiber optic probe. The applicability of the technique was first validated by measurements on heterojunction photo transistors up to 100GHz. Later, scanned measurements at 63GHz were performed on two ultrafast device structures, namely low temperature GaAs photoconductive switches and InP-based high electron mobility transistors. The response characteristics were rich in structures that revealed important details of the device dynamics.

For the future design of MMIC for communication application it is important to have probing tools to enhance the chip design. This paper describes improvement in the electro- optic probing technique using a continuous wave semiconductor laser beam for MMIC on gallium arsenide base. In our all-fiber system the laser beam is focused on the chip and the reflection changes are measured. With the Fabry-Perot response of the circuit itself it is possible to calibrate and calculate the voltage between front and back side of the circuits for the points beside the micro strip structures of the integrated chip. We used this technique to trace the distribution of the electric field beside a micro strip line.

The potential use of two-section gain-coupled distributed feedback lasers as a source for the generation and distribution of millimeter-wave signals for wireless applications is demonstrated. First we report on the dependence of the tuning range on the device structure and the use of two injection techniques to reduce the linewidth of the millimeter-wave signals generated at 40GHz. The first technique is self sub-harmonic injection locking using a 5GHz signal and the second is direct side-band injection locking using a 20GHz to lock a 40GHz signal. The phase noise is measured and the jitter is calculated. Secondly the fiber-based network architecture of a wireless system based on the two-section DFB laser is proposed. The aim of the networks is to expand the bandwidth for each base station, maximize sharing of the mm-wave source and fiber, reduce the number of active devices at the base and the mobile unit, and expand the role of photonics in the network design. The system we propose is WDM-SCM network architecture.

Optically controlled functional elements in the millimeter waveband are described in the paper, based on dielectric image lines (DIL). They include attenuators, amplitude modulators and power switches. Semiconductor Si, GaAs and Ge materials are used, that are light-sensitive at a wavelength (lambda) ₀ - 0.9 micrometers DIL elements possess lower losses, smaller size and weight and simpler technology, as compared to known functional elements in this band. Existence of a field outside the DIL allows construction of a narrow-band modulator, in form of a semiconductor resonator coupled with DIL. Illumination of the latter results in a change of its Q-factor. Modulation depth and bandwidth may be thus controlled. Several shapes of resonator are considered, namely circular and elliptic cylinder and a half-sphere. Q- factor may be intensified by application of a high-intensity magnetic field. A number of similar resonators slightly varying in their size are used to increase the modulation bandwidth. Power switch is also described, including two DILs coupled by a semiconductor resonator with Q-factor controlled by light.

We report on the application of a photoconductive (PC) frozen wave generator (FWG) for the generation of two-cycle THz radiation. A bipolar PC array comprised of four electrodes is employed in the production of THz electrical transients. Variations in the uniformity of the optical excitation intensity across the FWG PC gaps are found to provide a means of controlling the temporal chirp and power spectral bandwidth of the resulting electrical signals. Upon generating the electrical transients, the signals are launched, and later received, with integrated dipole antennas.

We report on a novel photoconductive (PC) switching technique, capable of generating ultrashort electrical pulses. The PC geometry of the switch is such that the incident optical pulse can both switch 'on' and later switch 'off' the electrical transient. The method of electrical pulse generation is, therefore, independent of the charge- carrier lifetime in the semiconductor.

We discuss possible new sub-millimeter sources based on group-III Nitrides superlattices. It is shown that traveling dipole domains in biased GaN/InGaN and GaN/AlGaN short- period superlattices can generate electromagnetic power in the terahertz region.

To fully exploit the opportunities of p-type Ge THz lasers and to be able to transfer the cavity ringdown technique currently used in the IR and optical region to the far-IR range, high reflectivity THz mirrors with large bandwidth are needed. Especially important for an optimized optics is a well defined coupling coefficient across the full width of the beam.

This paper presents a review of our activity in the field of frequency selective surfaces operating both in the GHz and in the THz region, and gives an overview of the state-of- the-art in this research field. A brief description is given of the applications of the frequency selective surface in different frequency bands and of the most used configurations. The possible fabrication technologies and the measurement techniques are discussed, along with the numerical methods for the analysis of frequency selective surfaces: a particular emphasis is given to the hybrid Method of the Moment/Boundary Integral-Resonant Mode Expansion method, recently developed at the University of Pavia. Some experimental results are also reported.

HEB technology continues to extend the sate-of-the-art for THz low-noise receivers. This talk discusses recent measured noise temperatures for NbN HEB receivers form which we infer intrinsic noise temperatures which approach the quantum noise limit within a factor of 3-5. We discuss the feasibility of achieving noise temperatures even close to the quantum limit noting that this limit has been reached both at lower frequencies and at higher frequencies. Another approach for considerably enhancing the speed with which THz receivers collect data is to employ a focal plane array system. We will discuss our design approach and general constraints for such a system.

Hot electron bolometric (HEB) detectors and mixers for the THz frequency range, which use thin-film superconductors, have been developed recently. They have short response times due to efficient cooling of ht hot electrons by either (i) phonon transmission from the film to the substrate, or (ii) diffusion of the electrons into the contacts. We have previously demonstrated a 2DEG detector which uses the heated 2D electron gas medium, as well as phonon-cooling. Here we propose and analyze a new version of this detector which employs diffusion cooling. A response time of 1 ps and responsivity of 3,000 V/W are calculated for a device which is 0.8 (mu) l long. This response time is considerably shorter than for any of the superconducting HEB detectors. The predicted double sideband receiver noise temperature for the mixer version is in the range 1,000 K to 2,000 K at 1 THz, with a 100 GHz intermediate frequency bandwidth. The new detector could be operated at 77K and the local oscillator power is estimated to be about 1 (mu) W.

40 Gb/s are expected to become the future standard fiber- optic operating speed for the data communication and telecommunication systems. High performance and low cost technologies are required to lower the system cost, yet maintain the overall performance. In this paper, a state of the art ion implant GaAs MESFET and a simple layer structure InP/InGaAs doped channel HFET were described, compared and proposed for 40 Gb/s OEICs. We have developed 0.10 (mu) M gate direct ion implanted GaAs MESFET process with current cutoff frequency (ft) of 120GHz which is the highest reported ft for 0.1 micrometers gate MESFET device. Bas4ed on this result, we believe a low cost solution of ion implant GaAs MESFET with ft greater than 200GHz process is available in the n ear future with 0.05micrometers gate. The 0.14 micrometers InP/InGaAs doped channel HFET has ft of 188GHz, which is the highest reported doped channel HFET device. The measured device performance of both devices are described in the paper. Compared to the epitaxial device, the ion implant MESFET has the significant advantage in the low cost solution of 40 Gb/s OEIC. The doped channel HFET provides superior performance than MESFET, yet it needs only 5 epitaxial layers which provide advantage over HEMT device. 40Gb/s OEIC receiver was studied and designed using HFET HSPICE model. The simulation shows the circuit has bandwidth of greater than 30GHz with greater than 40 dB ohms gain which make it suitable for 40 Gb/s application. Using this circuit, a 1 by 4 OEIC receiver array in a wavelength division multiplexing system will have overall data rate of 160 Gb/s.

With increasing demands for wireless data transfer, networking, graphics, and high-speed communications using the Internet, 10 Gb/s and 40 Gb/s are expected to become the standard fiber-optic operating speed for the future data communication and telecommunication systems. In this paper, photo receivers using PIN/HBT are investigated for 20 Gb/s and 40 Gb/s OEIC applications. A 20-Gb/s and a 40 Gb/s short wavelength PIN/HBT photo receivers are presented.

FDTD applications in 3D monolithic microwave integrated circuit (MMIC) design are introduced in this paper. The source implementation for active device modeling, device grid-characterization, a novel spiral component simulations are presented. Our research in this area have shown that FDTD is a very effective tool for the design of 3D MMICs.

The phase-correcting Fresnel zone plate antenna has been studied extensively at microwave and millimeter-wave frequencies in the past few years, in part because it offers advantages of low weight, cost, and loss. Scores of articles have appeared describing fundamental characteristics and methods of improving the efficiency, gain, and multiple- frequency band performance. As a result of these studies, one can now optimize the design, and an optimized zone plate antenna can provide performance superior to a standard lens or paraboloid antenna, especially at millimeter wavelengths. There are many differences between performance at optical wavelengths and microwaves/millimeter-waves, and these differences are described. A new planar design with non- parallel surfaces is discussed. This configuration offers further improvement in diffraction efficiency.

Semiconductor electronically beam-steering antennas based on a plasma hologram have been demonstrated as a possible cost- effective alternative to phase arrays. The paper addresses the design issues critical for antenna operation.

This paper reviews some recent developments of high-speed millimeter-wave photonic components and their application in millimeter-wave fiber-wireless systems. In particular, this paper is concerned with waveguide transceiver elements designed for simultaneous modulation and photodetection at mm-wave frequencies, where the transceiver concept is based upon electroabsorption in multiple-quantum wells. The fabrication procedure of such 1.55 micrometers electroabsorption transceivers (EAT) on InP substrates in briefly reported and the successful employment of mm-wave EATs in a 60-GHZ fiber- wireless network is demonstrated. Furthermore, a 60-GHz mm- wave band point-to-point fiber-wireless link architecture employing an EAT is presented and full-duplex broadband transmission within the 60-GHz band is experimentally achieved.

We have developed a new kind of millimeter wave diode for zero-bias detection up to and beyond 100GHz. The diode is based on the InAs/GaSb/AlSb heterostructure, which has a staggered Type II band gap alignment in which the conduction band of the InAs is lower in energy than the GaSb valence band edge. This produces a built-in asymmetry which produces a high zero bias nonlinearity in the current-voltage characteristic. The heterostructure is a relatively simple one that is reliably and reproducibly grown using standard molecular beam epitaxy techniques. The diodes we have fabricated demonstrate that this is a new and superior solution as compared with its predecessors, the Ge backward diode and the planar doped barrier diode, for detection and mixing of small input power-level signals without the added complexity of DC bias or local oscillator.

In this study, an epoxy-modified urethane rubber mixed with carbon particles is chosen as a material of a millimeter wave absorber. The single-layer absorber is designed and produced for 60GHz band on the basis of no reflection curve and the equation of its permittivity. The absorption characteristics of the specimens were measure at the frequency of 50 to 110GHz by power reflection method. As a result, the good millimeter wave absorber with the absorption of 20dB or more was obtained at both 60GHz and 100GHz bands.

The performance of heterojunction metal-semiconductor-field- effect-transistors (MESFETs) and junction-field-effect- transistors (JFETs) fabricated with different buffers is presented. For the JFET, carbon was chosen as the p-type dopant because of its relative low diffusivity compared to other doping elements. The viability of heterojunction MESFET and JFET devices operating at 400 degrees C have been demonstrated. Two key factors contributing to the reduction of drain leakage currents were the use of a high resistivity, undoped AlAs buffer layers and the gate contacting layers: n-type AlGaAs for the MESFET and p-type AlGaAs for the JFET. A two LT-AL_0.3Ga_0.7As layer scheme were used for the first time specifically for use in high temperature applications. Even at 400 degrees, C the gate leakage current density for a gate length of 2 micrometers was 9 by 10^-7 A/micrometers at Vds equals 3V Vgs equals -7. The high resistance of LT-AlGaAs materials after annealing was responsible for such low gate leakage currents. The p- HEMTs became leaky at high temperature because of the parallel conduction and buffer design. The gate diode performed better when contacted to the undoped AlGaAs layer. DC and high-temperature performance of GaN-based MESFETs and MODFETs were compared. Al_0.3Ga_0.7N/GaN MODFETs with a gate-length of 2micrometers exhibited high transconductance was 47mS/mm, and dropped by 12 percent of its initial value to 41.4 mS/mm at 350 degrees C. The decrease in transconductance with temperature can be explained by the temperature dependence of the electron mobility. The large conduction band discontinuity in this material system may play an important role in terms of better electron confinement thus resulting in less degradation in transconductance.

A simple and rapid self-matching modified harmonic-balance technique for submillimeter-wave Schottky-diode harmonic multipliers is presented. This work combines the physically accurate diode model with a modified harmonic-balance algorithm to determine diode-circuit design that maximize power generation and/or power efficiency in the second harmonic. The modified harmonic-balance method utilizes a novel strategy where maximum-available diode power at second-harmonic. The modified harmonic-balance method utilizes a novel strategy where maximum-available diode power at second-harmonic frequency is first derived independently and then the corresponding higher harmonic voltages and currents are determined. This approach allows for the rapid determination of the matched embedding circuit and an optimized multiplier design. A direct comparison to traditional schemes is given to illustrate the general utility of this physics-based simulation. Specifically, this work demonstrates a computationally efficient and accurate physical description as well as a more robust approach for circuit optimization.

This paper reviews the waveguide photodiode development for high power and high speed operation.

Non-radiative dielectric (NRD) waveguide, surface-mounted on the top of a relatively thin planar substrate, provides a great flexibility for the integration of planar circuits with NRD-guide. Such an unbalanced NRD-guide may be in direct contact with planar circuits that are fabricated on the same substrate such as microstrip circuits. Besides, NRD-guide may be easily integrated with the microstrip circuits also on a separate dielectric layer by aperture coupling. To facilitate its practical implementation, the dielectric layered surface-mounted NRD-guide structure has been proposed in this paper, this structure is especially suited to the implemented of millimeter-wave integrated circuits. Transitions of planar circuit to surface-mounted NRD-guide have been studied with emphasis on the analysis of potential spurious modes, which provides a basis for the performance-enhanced broadband design and applications. Principal modes generated in the hybrid planar/NRD-guide structure are modeled. Results for transmission and return loss are presented for different transitions. Our investigation indicates than an optimized but uncompensated hybrid planar/NRD-guide integrated transmission should be good enough for many applications over a certain frequency band. For broadband applications, however, spurious mode suppressors in the design of eliminating unwanted modes are required. A design example is also presented.

The characterization of the electromagnetic field at the electron cyclotron frequency is one important point for the ECRH installation under development at the CEA Cadarache. This characterization is based on a mathematical decomposition of the electromagnetic field over the various radiating modes of an oversized corrugated waveguide. To perform this determination, which principle is given in the paper, one has to access the amplitude and the phase of the full electric field on a plane transverse to the propagation direction. It is possible to obtain amplitude and phase diagrams of the two crossed polarization at low level. At high level, in the output of a gyrotron, one uses only thermal measurements and the phase is reconstructed from the amplitude diagrams. The paper exposes a compete validation of this method and gives and results of the high level characterization.

Foundation and principles of radio lenses construction of centimeter and millimeter wave ranges with controlled refracting index, combining the quality of phased array antennas with optical devices are stated. Possibilities of the electronically scanning with wide-angle sector and high gain are maintained. Construction principles of scanning antennas with controlled lenses, combining the quality of phased array antennas with optical devices, are stated. Possibilities of electronically scanning with broad angle sector and high gain are maintained. Some examples of construction of antennas millimeter range of waves are listed here.

The purpose is the electrodynamic analysis based on solving Maxwell's's equations completed by an equation of magnetization vector motion in a ferromagnetic for integrated strip-slot waveguiding structures containing magnetized ferrite films for spin-wave electronics devices design. The full-wave spectrum of electromagnetic and magnetostatic eigen modes is researched using accuracy mathematical modeling strip-slot structures with a different geometry on tangent magnetized ferrite substrates. The propagation constants frequency dependencies of dynamic modes and volume or surface magnetostatic modes in shielding micro strip, slot lines on ferrite substrates with transverse tangent biasing magnetic field were calculated using the decomposition approach by means of the multimode autonomous blocks method. Strip-down types of magnetostatic waves guided by strip or slot with the finite width are revealed. The classification of volume and surface magnetostatic mode depending on the geometry for strip-slot structures or the orientation of biasing magnetic field is done. Solutions of dispersion equations of MSW strip-down types using magnetostatic approximation for infinite ferrite layers are compared with the result of the numerical electrodynamic analysis. The theoretical method for determining of the strip-down magnetostatic mode at het 3D waves number space using MSW dispersion surfaces dissected by planes is proposed.

The purpose is a research using mathematical modeling at electrodynamic accuracy level of dynamic modes and volume or surface magneto static modes propagating in multilayer ferrite-dielectric waveguides with finite width. Results of simulating of eigen electromagnetic and volume or surface magneto static waves in shielded 2D ferrite layers structures with tangent biasing magnetic field are done. Propagation constants frequency dependencies of dynamic and magneto static modes in these gyrotropic waveguides were calculated by the multimode autonomous blocks method. The change of dynamic and magneto static modes existence frequency regions near longitudinal or transverse ferromagnetic resonance frequencies are researched. Numerical analysis of cut-off frequencies of depth, width volume and width surface magneto static modes in 2D ferrite waveguiding structures with the tangent biasing magnetic field is carried out. Theoretical method for determining of existence frequency regions of the width volume or surface magneto static modes at the 3D waves number space using MSW dispersion surfaces is proposed.

A molecular engineering strategy, based on the role of the charge transfer conjugated system, and of donor substituents on theoretical linear and two-photon absorption (TPA), is developed. The best trade-off TPA-linear absorption is fulfilled by two tetraphenyl-diamine derivatives (biphenyl and fluorene), which could allow, if mixed, to cover efficiently the visible range. Furthermore, the theoretical study of two-photon absorption (TPA) properties of polyphenyls (with the number of benzene monomer units n = 1 to 6) is related to cooperative effects between monomers. These effects lead to an increase of the TPA cross-section with n without satuaration according to a power law.

Optical transport networks (OTN) technology is expected to play a vital role in the next-generation transport networks. In this paper, the technology of OTN and management of OTN is discussed. Combined with TMN, SNMP and CORBA, integrated management of OTN is investigated. Q-adapter is proposed to integrate TMN and SNMP together, and a direct CORBA/SNMP interface is given to implement the integration of CORBA and SNMP. Finally, several issues concerning integrated management of OTN are also discussed, such as integrate routing of OTN in IP layer and in optical layer, multilayer protection of OTN and OAM technology of OTN.

A low-aberration planar concave grating is discussed to design N by N wavelength interconnector in this paper. First a special linear system model is built based on the scalar diffraction theory. With the derived model some transmission characteristics of the planar grating are studied, including dispersion value, channel spacing, FSR, and spectral response. Numerical simulation focuses on the geometrical aberration and spectral resolution of the grating.

The phase array composed form spiral microstrip radiators is considered. This array can be applied as radiation focusing spiraphase lens. The lack of traditional phase shifters ensures good cost, technological and constructive characteristics of spiraphase arrays in a microwave range. Antenna construction and mathematical model are considered. This device permits to realize a focusing of antenna feed field by a microstrip antenna array. The microstrip element shape is arbitrary. The mathematical model is obtained by integral equation method. Microstrip spiral radiators current distribution and input impedance are investigated. The numerical results can be used to develop antennas with optimum parameters.

A semiconductor electron-hole plasma effectively reflects microwave radiation that is used in electromagnetic shields and semiconductor millimeter wave antennas. Silicon-based P- I-N structures allow us to engage in engineering the conductive properties of plasma crated under current injection. We calculate the I-V characteristics of short P- I-N structures and model their reflective properties in the millimeter wave band.

A new graded band gap channel MOSFET is suggested to make use of the improved electrical properties of SiGe over Si at high frequencies of operation. The device performance is analyze by using an analytical model and the obtained results are compared with those of conventional Si and non- uniform doped channel MOSFETs. Finally, the noise behavior of the new MOSFET is investigated to show its superior performance over conventional Si MOSFETs at GHZ frequencies of operation.

This paper presents a new method for surface-emitted difference frequency generation (DFG) in planar optical waveguides based on non-ferroelectric materials. The main thrust of this paper is based on the application of a slotted grating to the surface of a waveguide cover. The grating has equally spaced slots at distances equivalent tot eh wavelength of anon-linear polarization wave. DFG power emitted in the direction normal to the surface of the step- index planar waveguide is calculated. It is shown that the efficiency of frequency conversion for a surface emitting geometry is greater than that in a common collinear geometry case. This is especially true for the high-absorption wavelength region of nonlinear materials. According to our estimation, surface-emitted DFG will enable the design of compact solid-state THz-wave sources with a few mW output power.

The method of powder metallurgy for CdTe gives high possibilities for production of new type material structure and detector with picosecond time resolution, high radiation resistivity and electrical breakdown voltage. The method is simple, can be used for different semiconductors. The method forms a semiconductor structure with partly normalized destroyed grain boundary between powder particles which is characterized by extremely high concentration of deep level and traps. The heating and fast freezing are the main operation of this technological process. This method changes electro physical properties of monocrystalline CdTe and gives the new perspectives for development of semiconductor physics and technology.

This paper gives an overview of the European ACTS project AC329-ACTUAL. This project was carried out during 1998 and 1999. The stated main objective of the project was: TO sue the state-of-the-art technology on widely tunable lasers available within the Consortium, to bring this to full maturity on a subsystem level and to demonstrate that wavelength agile transmitters based on widely tunable lasers can open the way to the next generation WDM and wavelength switching systems. This paper will give a description of the result from the project.

The Guided wave Photonic Band Gap (PBG) structures are very attractive as optical devices. The modeling and the simulation of such structures is topic of great interest because the classical existing optical modeling techniques, such as BPM or effective index, are not compatible with the size and propagation effects in PBG structures. In this communication we focus on guided PBG filters. Two simulations are presented. The first one is a circuit approach. It is based on the modeling of the PBG as a cascade of several obstacles connected to waveguides. For each obstacle the S-parameters are calculated. Finally these parameters are implemented in a microwave simulator which determines the response of the PBG Filter. The second approach uses a numerical technique. We have simulated diffraction effects using 2D-FDTD and 3D-TLM methods. The simulation allows us to investigate the PBG mirror diffraction losses for different design parameters.

Photoconductive mixing in ultrafast photoconductors (LTG- GaAs) represents an optoelectronic means of generating coherent radiation at THz frequencies form optical pump laser. TO dat the power from such photomixers has been limited to microwatt levels by thermal burn-out. In this paper, we analyze a new design in which the LTG-GaAs is fabricated both in a resonant planar dipole and in a vertical optical cavity. This is accomplished with an electrically-floating metal layer lying below the thin LTG- GaAs layer by approximately 0.5 micron. Optical analysis shows that the metal layer can increase the external quantum efficiency of the photomixer approximately 3 times through creation of a vertical optical cavity int eh LTG-GaAs layer. Heat-transfer analysis shows that the metal layer reduces the photomixer thermal resistance approximately 2.5 times, allowing for an increase in the optical pump power by roughly the same factor. Finally, full-wave electromagnetic analysis shows that the metal layer has a small impact on the radiation pattern of the planar dipole above it, presumably because the layer is much smaller laterally than a wavelength and is electrically floating. In total, these beneficial effects are predicted to increase the output THz power by approximately a factor of ten compared to any result reported to date.