Anatoly Frenkel

Optical response of nongranular high‐Tc Y1Ba2Cu3O7−x superconducting thin films

We have investigated the optical response of c‐axis oriented crystalline Y1Ba2Cu3O7−x thin films (bridge and meander devices) on strontium titanate and MgO substrates. cw optical response to a He‐Ne laser radiation (wavelength of 0.63 μm) was primarily bolometric. The pulsed optical response was studied with Q‐switched and mode‐locked Q‐switched short pulses from a Nd:YAG laser at the wavelength of 1.06 μm. We identify two distinct components contributing to the pulsed optical response: a nonbolometric (as fast as 1 ns) and a bolometric component (several ns). The bolometric component is strong at temperatures in the vicinity of the transition region to the normal state. The nonbolometric component is dominant at temperatures below the transition region showing weak temperature dependence and a linear dependence on the bias current. These results are discussed using the flux motion model and also electron‐phonon scattering relaxation dynamics of nonequilibrium superconductors based on the theory of Bardee...

Observation of fast nonbolometric optical response of nongranular high Tc Y1Ba2Cu3O7−x superconducting thin films

We report fast optical response measurements in predominantly c‐axis oriented crystalline Y1Ba2Cu3O7−x superconducting thin films at the wavelength of 1.06 μm. We identify two distinct components contributing to the optical response: a nonbolometric (as fast as 1 ns) and a bolometric component (several ns). The bolometric component is stronger at temperatures in the vicinity of the transition region to the normal state. The nonbolometric component is dominant at temperatures below the transition region showing weak temperature dependence and a linear dependence on the bias current. This nonbolometric component may be evidence for nonequilibrium effects (e.g., breaking of Cooper pairs and generation of quasiparticles or other mechanisms). These results suggest that with proper optimization of device parameters (its geometry, critical current density, etc.) high‐speed detectors with reasonable sensitivity covering a broad electromagnetic spectrum (visible and infrared) may be developed.

Angle-tuned etalon filters for optical channel selection in high density wavelength division multiplexed systems

Applications are discussed for angle-tuned in-line Fabry-Perot etalons for optical channel selection in a high-density wavelength division multiplexed (WDM) direct-detection fiber system. A typical WDM application (LAMBDANET type) was described. Different demultiplexing techniques and their relative advantages were considered. Design guidelines are given for determining the etalon parameters, the minimum channel spacing and the maximum number of channels for a single etalon and multiple etalons, including stacked identical etalons and stacked nonidentical etalons. Experimental results on using these etalons for optical channel tuning in a multiwavelength WDM optical communication system are presented. >

High Tc superconducting film as a fast nonlinear switch for noise discrimination in digital circuits

Measurements of fast nonlinear switching of a high Tc superconducting thin film at 70 K between the dissipative state (induced by an electrical current) and superconducting state are reported. System rise and fall times are measured to be about 1 ns and are limited by the parasitic components of the electrical circuitry. A novel scheme for noise discrimination in digital circuits using this switching has been proposed and experimentally demonstrated for speeds exceeding 200 Mb/s. This method allows significant reduction of amplitude noise and improvement of signal‐to‐noise ratio in digital circuits.

Dynamic electrical response of Y1Ba2Cu3O7−x

We studied the dynamic electrical properties of epitaxial Y1Ba2Cu3O7−x superconducting thin films on strontium titanate and MgO substrates. A fast nonlinear switching of a high‐Tc film between the dissipative and superconducting states has been demonstrated. These measurements show that the rise and the fall times of these transitions are faster than 250 ps (which are presumably limited by the speed of the measurement electronics). This fast nonlinear switching may lead to opportunities for new high‐frequency electronic devices including, for example, fast logic gates or threshold devices. We have proposed and demonstrated the application of such a nonlinear switching in a novel noise discrimination scheme for speeds of several hundred MHz. The proposed method is simple and effective in the enhancement of signal‐to‐noise ratio in digital electronic circuits.

Multiple angle-tuned étalon filters for optical channel selection in wavelength-division multiplexed and optical frequency-division multiplexed direct-detection transmission systems

We propose and demonstrate the use of multiple angle-tuned in-line Fabry-Perot etalon filters for tunable optical channel selection in wavelength-division multiplexed and optical frequency-division multiplexed direct-direction fiber transmission systems. Feasibility is experimentally demonstrated with two stacked identical etalons [free spectral range (FSR) of 74 nm with a finesse of 50 for each etalon] and with two stacked nonidentical etalons (FSR of 8 and 2 nm, respectively, with a finesse of 76 for both etalons). The stacked etalons are used to select the individual modes of a multilongitudinal-mode semiconductor laser output in the 1550-nm region. The method allows the selection of tens or possibly hundreds of closely spaced optical channels, because the reduction of channel spacing to much less than 1 mm is feasible, and the resultant FSR of stacked nonidentical etalons can be made much larger than their individual FSR’s.