B. Jalali

Lifetime of photogenerated carriers in silicon-on-insulator rib waveguides

The lifetime of photogenerated carriers in silicon-on-insulator rib waveguides is studied in connection with the optical loss they produce via nonlinear absorption. We present an analytical model as well as two-dimensional numerical simulation of carrier transport to elucidate the dependence of the carrier density on the geometrical features of the waveguide. The results suggest that effective carrier lifetimes of ⩽1ns can be obtained in submicron waveguides resulting in negligible nonlinear absorption. It is also shown that the lifetime and, hence, carrier density can be further reduced by application of a reverse bias pn junction.

Broadening and tuning of spontaneous Raman emission in porous silicon at 1.5μm

In the last three years, the possibility of light generation and/or amplification in silicon, based on Raman emission, has achieved significant results. However, limitations inherent to the physics of silicon have been pointed out, too. In this letter, an approach based on Raman scattering in porous silicon is investigated. Two significant advantages with respect to silicon are proved: the broadening of spontaneous Raman emission and the tuning of the Stokes shift. Finally, we discuss about the prospect of Raman amplifier in porous silicon.

Nondispersive wavelength-division sampling

We propose and demonstrate a new wavelength-division-sampling technique with high temporal resolution. A discrete-time true-time delay generates multiwavelength near-transform-limited pulses from a supercontinuum source. Pulses sample the analog signal in an electro-optic modulator and are subsequently demultiplexed in a wavelength-division-multiplexing filter. A 100-Gsample/s experimental demonstration of this concept is presented.

Comparison of graded and abrupt junction In0.53Ga0.47As heterojunction bipolar transistors

We compare calculated intrinsic forward delay as a function of base thickness and p‐type doping level in n‐p‐n heterojunction bipolar transistors with graded as well as abrupt Al0.48In0.52As/In0.53Ga0.47As and InP/In0.53Ga0.47As emitter‐base junctions. We find that, for a given p‐type concentration and fixed base delay time, an InP/In0.53Ga0.47As abrupt junction design results in high intrinsic speed, low base resistance, and modest power consumption.

Broadband, high-brightness 10-Gbit/s supercontinuum source for A/D conversion

Summary form only given. We demonstrate a broadband (140 nm) supercontinuum (SC) source that has broad flat region (40 nm), high-power spectral density (7.9 dBm/nm), high coherence and potentially high temporal resolution. Compared with other sources used in analog-to-digital (A/D) conversion, short fiber SC simultaneously has quadrupled uniform spectral width, nearly doubled bandwidth and eight times better temporal resolution (/spl sim/5 ps). Based on the parameters of our SC source, we estimate that sampling of continuous signals with <10% pulse-to-pulse variation and up to 400 GSa/s with 1-nm filter spacing is achievable.

30 Gsample/s 4-bit time-stretch analog-to-digital converter

Summary form only given.Photonic time stretch preprocessing (TSP) has been proposed as a means to enhance the performance of electronic ADCs. This concept is based on the premise that if the analog signal can be stretched in time free of distortion, then the effective sampling rate and the input bandwidth of the ADC is increased. The technique is best suited for time-limited analog signals, such as those encountered in pulsed radars. In this paper we demonstrate complete time-stretch ADC with 30 Gsample/s sampling rate, and 4 effective number of bits resolution realized over a 4 GHz bandwidth. The system consists of a photonic TSP and a commercially available electronic digitizer with 8 Gsample/s sampling rate and 1.5 GHz bandwidth.

Spontaneous Raman emission in porous silicon at 1.5 µm and prospects for a Raman amplifier

In the last three years, the possibility of light generation and/or amplification in silicon, based on Raman emission, has achieved significant results. However, limitations inherent to the physics of silicon have also been pointed out. One possible option to overcome these limitations is to consider low dimensional silicon. In this paper, an approach based on Raman scattering in porous silicon is theoretically and experimentally investigated. We prove two significant advantages with respect to silicon: the broadening of the spontaneous Raman emission and the tuning of the Stokes shift. Finally, we discuss the prospect of a Raman amplifier in porous silicon.

Wavelength conversion and light amplification in silicon waveguides

This study demonstrates wavelength conversion and intrinsic Raman amplification. This work shows that phase matching is required to achieve high conversion efficiencies. In addition, reduction of waveguide cross section, while maintaining low propagation loss, is highly desirable for both wavelength conversion and optical amplification. The resulting increase in light intensity enhances the Raman interaction and the reduction in free carrier lifetime diminishes the two-photon absorption-induced free carrier losses.

Time stretch optical header recognition

To overcome the electronic speed limitation, all-optical packet extraction and recognition has been extensively studied. In this paper, we propose and demonstrate a new method named time stretch header recognition technique, where the header is (i) optically extracted and (ii) slowed down so that it can be processed with conventional electronics running at lower speed than the data rate. A 10 Gb/s bit stream is stretched by the factor of around 20 allowing capture and processing by low speed electronics. An optical quality factor of 18 dBQ was achieved for the time-stretched header.

Transferred‐electron induced current instabilities in heterojunction bipolar transistors

Current driven instabilities in the collector of III–V heterojunction bipolar transistors (HBT) are investigated. Numerical simulations indicate that in a modified AlGaAs/GaAs HBT the collector current shows oscillatory behavior due to the transferred‐electron (Gunn–Hilsum) effect. Influence of the Kirk effect as well as conditions for oscillation are discussed.