Vera Gorfinkel

Control of surface‐emitting laser diodes by modulating the distributed Bragg mirror reflectivity: Small‐signal analysis

Cavity‐loss control of surface emitting distributed Bragg reflector lasers by electro‐optic modulation of the Bragg mirror reflectivity is shown to be more efficient at high frequencies than the conventional control by current modulation. Combining both means of control offers additional possibilities, such as the elimination of relaxation oscillations and the achievement of a pure frequency‐modulation regime.

A family of novel DNA sequencing instruments based on single-photon detection

We have developed a family of high‐performance capillary DNA sequencing instruments based on a novel multicolor fluorescent detection technology. This technology is based on two technical innovations: the multilaser excitation of fluorescence of labeled DNA fragments and the “color‐blind” single‐photon detection of modulated fluorescence. Our machines employ modern digital and broadband techniques that are essential for achieving superior instrument performance. We discuss the design and testing results for several versions of the automated single lane DNA sequencers, as well as our approach to scaling up to multilane instruments.

High‐frequency modulation and suppression of chirp in semiconductor lasers

We propose a new method for modulating laser radiation by controlling simultaneously the pumping current and the optical gain in the active region. The latter can be independently varied by modulating the effective carrier temperature. The method allows to eliminate the relaxation oscillations and enhance the modulation frequency to 50 GHz. It also allows to suppress the wavelength chirping in optical communication systems operating at pulse repetition rates of 10 Gb/s.

Optoelectronic microwave-range frequency mixing in semiconductor lasers

Optoelectronic mixing of very high-frequency amplitude-modulated signals using a semiconductor laser simultaneously as a local oscillator and a mixer is proposed, Three possible constructions of a monolithically integrated up-or down-converter are considered theoretically: a four-terminal semiconductor laser with dual pumping current/modal gain control, and both a passively mode-locked and a passively Q-switched semiconductor laser monolithically integrated with an electroabsorption pumping current modulator. Experimental verification of the feasibility of the laser-mixer concept is presented. >

Heterostructure bipolar transistor with enhanced forward diffusion of minority carriers

We consider the minority transport in a heterostructure bipolar transistor whose base band gap narrows down toward the collector in N discontinuous steps. Assuming that the potential energy drop at each step is sufficiently large to prevent the reverse flow of minority carriers, we show that the total base propagation delay τ is shorter by a factor of N compared to the diffusive delay in a flat base of the same width. Moreover, if the length of each step is sufficiently narrow, then for large N the magnitude ‖α‖ of the base transport factor α=‖α‖exp(−iωτ) decreases so slowly with increasing frequency ω that it becomes feasible to obtain an active behavior of the transistor above its own conventional cutoff frequencies.

Dual modulation of semiconductor lasers

Large signal analysis of dual modulation of semiconductor lasers (by a simultaneous high-frequency control of the pumping current I and an additional intrinsic parameter) shows that the method allows suppressing the relaxation oscillations for an arbitrary shape of the pumping current signal I(t). Because of that, the rate of information coding can be enhanced to about 80 Gbit/sec. Moreover, we demonstrate that dual modulation allows us to maintain a linear relationship between I(t) and the output optical power in a wide frequency band.

Rapid modulation of interband optical properties of quantum wells by intersubband absorption

Intersubband absorption of radiation by a two‐dimensional electron gas can be used to control the electron temperature and effect a significant modulation of the interband optical properties of the semiconductor in the quantum well. We discuss the implementation of a fast modulator of infrared radiation for fiber‐optical communications as well as the formation of powerful and short single‐mode infrared pulses.

High-frequency modulation of a QW diode laser by dual modal gain and pumping current control

A novel dual modulation technique is proposed and realized for a new four terminal QW diode laser structure. The simultaneous output modulation by modal gain and pumping current density (G&J) control was investigated experimentally. Applying a step-like electric signal with a 20 ps rise-time to the side contacts resulted in the laser switching-off time of the same value. The dynamic laser parameters were extracted from RF measurements, and simulation of the laser response to the dual G&J modulation was carried out. A 3dB bandwidth as broad as 60 GHz has been obtained at moderate laser output powers. In millimeterwave region the laser output response decays as 1spl omega/.<<ETX>>

Fast Data Coding Using Modulation of Interband Optical Properties by Intersubband Absorption in Quantum Wells

Intersubband absorption of radiation by a two-dimensional electron gas can be used to control the electron temperature and effect a significant modulation of the interband optical properties of the semiconductor in the quantum well. We discuss the implementation of a fast modulator of infrared radiation for fiber-optical communications as well as the formation of powerful and short single-mode infrared pulses. The method can also be used to modulate laser radiation by controlling simultaneously the pumping current and the optical gain in the active region. The dual modulation method allows to eliminate the relaxation oscillations and suppress the wavelength chirping in optical communication systems operating at high pulse repetition rates.

Analysis of DNA sequencing systems based on capillary electrophoresis

A method for characterization and optimization of DNA sequencing systems based on capillary electrophoresis is proposed. A model is developed that relates the read length of a sequencing run and the parameters of DNA sequencing systems such as the properties of the separation medium, capillary length, injection time, concentration of the injected DNA sample, detection sensitivity, system noise, and the illumination power. The optimization of DNA sequencing systems will allow determination of optimum regimes for preparation, injection, and separation of DNA samples needed for achieving a read length required. The method proposed is applied to the characterization of capillary-electrophoretic DNA sequencing systems based on single-photon detection.