M. Haridim

Theoretical analysis of gain-recovery time and chirp in QD-SOA

We present a theoretical analysis of the gain recovery and chirp characteristics of quantum-dot semiconductor optical amplifier (QD-SOA). We have derived an analytical expression for the frequency chirp in QD-SOA. The values of chirp and gain recovery time (GRT) for various signal power levels are calculated by numerical solution of the rate equations. The simulation results show that the chirp value in QD-SOA is approximately one order of magnitude lower than that in a bulk SOA. The dependences of the GRT and the chirp on the pump power level are studied.

Ultrafast All-Optical Processor Based on Quantum-Dot Semiconductor Optical Amplifiers

We have developed a theoretical model of an ultra- fast all-optical signal processor based on the Mach-Zehnder interferometer with quantum-dot semiconductor optical amplifiers in both its arms. It is shown that such a processor under different conditions may realize wavelength conversion, XOR logic operation, and optical 3R regeneration.

Acceleration of gain recovery and dynamics of electrons in QD-SOA

We propose a new method for reducing the patterning effect in quantum-dot semiconductor optical amplifier (QD-SOA) by using an additional light beam. A detailed theoretical analysis of the carrier dynamics in QD-SOA is presented. It is shown that the increase of the bias current only partially improves the QD-SOA temporal behavior. The additional light beam drastically reduces the patterning effect.

Proposal for All-Optical Generation of Ultra-Wideband Impulse Radio Signals in Mach–Zehnder Interferometer With Quantum-Dot Optical Amplifier

We developed a theoretical analysis of a novel method of ultra-wideband impulse radio signals all-optical generation based on cross-phase modulation and cross-gain modulation in a nonsymmetric integrated Mach-Zehnder interferometer (MZI) containing quantum-dot semiconductor optical amplifier. The proposed method is promising due to the advantages of compact, easily controlled, and low energy integrated MZI structures as compared to optical fiber systems.

All-Optical AGC of EDFA Based on SOA

We propose a novel all-optical method for automatic gain controlling of transients in erbium-doped fiber amplifiers (EDFAs) using a semiconductor optical amplifier (SOA)-based negative feedback loop for adjusting the EDFA pump power. A dynamic model for the EDFA-SOA system is developed and used for numerical simulation of the transient behavior of this system. Simulation results for EDFA-SOA performance of the proposed method are presented. It is shown that using this method, it is possible to significantly reduce the transient effects, without producing power oscillations on the surviving channels

Up-Conversion of Triple-Band OFDM UWB Signals by a Multimode VCSEL

We present novel experimental results for the all-optical up-conversion of the triple-band orthogonal frequency-division-multiplexing ultra-wideband radio signals from lower frequency band group 1 up to higher frequency band groups 2 or 3 based on the vertical-cavity surface-emitting laser optical second- and third-order nonlinearities. Low conversion losses and error vector magnitude values, respectively, for low bias currents have been demonstrated.

Optical Transmission of OFDM Ultra-wideband Signals beyond 40 Gb/s (Invited Paper)

We for the fi rst time propose the highly eff icient method of RF and optical signal mixing based on two different architectures: the parallel-RF/serial-optics architecture charac- terized by all-optical mixing for sub-carrier multiplexing, and the parallel-RF/parallel-optics architecture based on the array of 12x10 GHz components with directly modulated VCSELs and 12 multimode optical fibers. The main advantages of the both architectures are simplicity and low-cost implementation. We have carried out numerical simulations of ultra-wideband signals propagation in the proposed systems and proved the high efficiency and feasibility of the proposed method.

Cellular Phone Antenna with a Small Irradiation of the Human Head

A compensation method for reducing the irradiation of the head of a cellular phone user without degradation of the far field is analyzed. This method uses two radiators that are located in the near region of each other, and create a weak field area in this region. The impacts of the mutual coupling between closely located radiators on the input impedance, current distribution, and fields of the radiators are studied. It is shown that the structure of two closely spaced monopoles is equivalent to the superposition of two basic structures: a two-wire open-ended line, and a single monopole. The shape and dimensions of the dark spots and the irradiation-reduction factor are determined. To facilitate the field calculations in the near zone of the antennas, a method based on replacing a piecewise-homogenous medium by an equivalent homogenous medium is used. The calculations and the experimental results in the presence of the head qualitatively agreed.

Dark spot shift along a vertical line

Use of compensation method for creation of weak field area located above an antenna feed point is considered. Structure comprising two additional radiators, which are placed symmetrically with respect to the straight line passing through a main radiator feed point and a dark spot center and create the same fields, is presented.

A monopole with raised feed point

The field of a finite length monopole whose feed point is raised (sleeve antenna) is calculated. Its behavior is similar to a dipole with two feed points. The mutual coupling between closely located radiators of this type, when used in the compensation method, is considered.