Optical control of microwaves by LED-induced DBR structures in silicon coplanar waveguides

An analysis of a periodically photoexcited structure (PPS) in a silicon coplanar waveguide is presented. The numerical results confirm the potential of PPSs to work as optically CW- or pulse-induced tunable filters and reflectors.<>     

Microwave measurements of effective dielectric constant ofsemiconductor waveguides via periodic-structure photoexcitation

In this paper a new method for measurements of the effective dielectric constant of layered or full-substrate semiconductor waveguides at microwave frequencies is presented. The light-induced generation of a photoconductivity grating within the excited waveguide section is utilized. Incoming swept-frequency signals produce a stop-band reflection spectrum which exhibits a dominant major-lobe peak value at the grating center frequency. The effective dielectric constant is calculated from a simple analytical expression by substituting the measured center frequency. Theoretical background, error estimation, and an example are presented     

Grenzfehlerabschätzung für das diffusionsabhängige Impedanz-Stufenprofilmodell von optoelektronischen Wellenleitergittern

Übersicht Das diffusionsabhängige Impedanz-Stufenprofilmodell zur Berechnung des lichtinduzierten Mikrowellenreflexionsfaktors von optoelektronischen Wellenleitergittern basiert auf einer einfachen Approximation der realen Photoleitfähigkeitsverteilung. Die hierdurch verursachten Betrags-und Winkelfehler des Reflexions-faktors als Funktion der Gitterstufenzahl, der Filtermittenfrequenz, der Signalfrequenz und der Strahlungsleistungsdichte sind für die Grenzbedingung einer starken Trägerdiffusion in Wellenausbrei-tungsrichtung ermittelt worden. Der maximale Fehler des Reflexionsfaktors in Bandmitte beträgt 37% im betrag und 11° im Winkel. Für den Fall schwacher bis mäßiger Diffusion hat sich das Stufenprofilmodell aufgrund des drastisch reduzierten numerischen Aufwands bei akzeptablen Fehlerwerten als exzellentes Hilfsmittel bei der Analyse von optoelektronischen Wellenleitergittern erwiesen.

---

Worst-case error estimation of the diffusion-dependent stepped-impedance model of optoelectronic waveguide gratings

Contents The diffusion-dependent stepped-impedance model for the calculation of light-induced microwave reflection coefficient of optoelectronic waveguide gratings is based on a simple approximation of the actual distribution of photoconductivity. The resultant errors concerning magnitude and phase of the reflection coefficient as function of the number of grating elements, centre frequency, signal frequency, and irradiance have been computed for the worst-case condition, i.e. when strong carrier diffusion into the direction of wave propagation occurs. The maximum error of the peak reflection coefficient at centre frequency amounts to 37% in magnitude and 11° in phase. In the case of low or moderate diffusion, the stepped-impedance model has proved to be an excellent tool for the analysis impedance model has proved to be an excellent tool for the analysis of optoelectronic waveguide gratings owing to the drastic reduction of numerical effort along with acceptable errors.

     

Measurement of small optically pulse-modulated reflection coefficients

The letter presents a new method for measuring small pulse modulated complex reflection coefficients of which both phase and magnitude are a rapidly varying function of time. The method is based on a single-point dynamic balance of two differently pulse-modulated signals produced in a modified reflection coefficient bridge. The measuring procedure is described in detail, and the first experimental results are discussed.     

Time Constrained Verification of Analog Circuits using Model-Checking Algorithms

In this contribution we present algorithms for model checking of analog circuits enabling the specification of time constraints. Furthermore, a methodology for defining time-based specifications is introduced. An already known method for model checking of integrated analog circuits has been extended to take into account time constraints. The method will be presented using three industrial circuits. The results of model checking will be compared to verification by simulation.     

Autocollimator for spectroscopy of broad resonances with pulsed lasers

For the application of autocollimation spectroscopy [Z. Phys. D 18, 249-255 (1991)] a pulsed dye laser that is emerging from a focus (diameter, 1 mm; divergence, 30 mrad) has to be reflected back in itself with high precision. The difference Δθ between the mean angles of the counterpropagating laser beams has to be less than 1 × 10(-6) rad. Using a paraxial approximation, we show that a cat's eye fulfills the needs best. An adjustment procedure together with additional calibration equipment (CCD arrays and quadrant diodes) for the device is presented. Accounting for the uncertainties of the adjustment and using ray tracing, we show that Δθ ≤ 5 × 10(-7) rad can be achieved.     

Optimum gapwidth in light-controlled microstrip modulators

The letter describes a simple method for calculating the optimum gapwidth of facing microstrip contacts in light-controlled microstrip switches and modulators using parts of an evaporated, sensitised semiconductor film as integrated radiation sensors.