Research

Research topics

Dynamics of semiconductor nano structures

We study dynamical properties of semiconductor nano structures, mainly quantum dot and quantum dash lasers and amplifiers. We concentrate on three aspects:

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Modulation characteristics. We have developed advanced spatially resolved models for quantum dot lasers which are used to design ultrafast lasers and to analyze experimental results. We have achieved record modulation speeds for InP based quantum dot lasers of 22 Gbit/s.

Simulation                                                        Measurement

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We have also studied tunneling injection quantum dot lasers.

Ultrafast spectroscopy of quantum dot and quantum dash gain media

We have developed several unique experimental and simulation tools to study the intricate details of semiconductor devices based on nano structured gain media.

  • Multi wavelength pump probe characterization where we pump with a 100 fs pulse at 1550 nm and probe with a tunable CW lasers everywhere within the gain spectrum of an optical amplifier. The set up enable to characterize the  dynamics of the inhomogeneously broadened gain and also led to the demonstration of a unique instantaneous gain response stemming from two photon induced gain.

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  • XFROG characterization. We have developed FROG and XFROG systems with a temporal resolution of single fs to study ultrafast phenomena on the time scale of the 100 fs pulse. The most important result obtained with the X-FROG system is a direct observation of Rabi oscillations in a room temperature, electrically driven laser amplifier. This opens the way to many practical implementation of quantum mechanical principles for quantum communication and information processing.

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  • Maxwell – Schrödinger FDTD model. We have developed a powerful numerical simulation tool for coherent effects in quantum dot gain media. The simulation is very general and can accommodate any structure and all possible dynamical phenomena.

Rabi oscillations in a laser amplifier

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Coherent control in room temperature quantum dot amplifiers

Using a two pulse X-Frog system in a pump probe configuration, the evolution of decoherence can be mapped out. A pump probe X-FROG system is shown in the figure below. It enables ultra-high resolution (I fs which is less than a fifth of one optical cycle) tuning of the delay between pulses. Both pulses propagate through the amplifier and are characterized at the output by the X-FROG technique.

The first pulse is delay independent both in its amplitude and instantaneous frequency profiles. The second pulse shows a significant change in the chirp profile. A 2 fs change in delay amounts to approximately a π phase shift which causes the second pulse to sense how the system to turns from absorption to the gain regime.

Nonlinear Photonic Crystal Waveguides

We are studying nonlinear photonic crystal waveguides based on GaInP membranes.

GaInP has a wide bandgap – 1.9 eV and therefore suffers no two photon absorption.

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  • Parametric processes. We have studied four wave mixing and parametric gain in conventional W1 as well as dispersion engineered waveguides. We have demonstrated a 1.3 mm parametric amplifier with 11 dB gain pumped with less than 800 mW.
  • We have developed a unique simulation tool based on a procedure called multiple split step Fourier transform which accounts for the dispersive nature of all linear and nonlinear propagation parameters in a photonic crystal waveguide and is also extremely efficient for signals whiose spectrum is sparse.

Nonlinear fiber devices

We are studying various aspects of nonlinear fiber devices concentrating mainly on narrow band four wave mixing. This process was invented at Technion for the purpose of performing slow light experiments but is mainly used for amplifiers and oscillators at unconventional wavelengths.

  • Tunable parametric oscillator for the 2 mm range

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  • Phase sensitive narrow band parametric amplifier

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Optically sensitive nonvolatile memories

We have developed a series of specialized optoelectronic memory cells based on metal nano particles embedded within high-k dielectric films. These memory cells exhibit extremely large hysteresis and are very sensitive to light illumination namely, the memory state can be written using light and then read electronically.

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The memory cells take on the form of capacitors or CMOS transistors where the gate stack comprises the metal nano particles.

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Optically sensitive memory cells use SOI substrates. Light illumination can be from the substrate side or from a top optical port. The opticsal sensitivity of the device can be characterized by the photocurrent or by the spectral dependence of the shift of the flat band voltage

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High sensitivity broad band MIS photodetectors and optically controlled varactors

The memory capacitors can be voltage stressed by applying a forward bias voltage of a magnitude which is close but below the catastrophic damage threshold. The stress causes filaments in the dielectric stack which form in turn conductive paths. This leads to ultra-sensitive photodetectors as well as optically controlled capacitors.

The general structure and the spectral response of the detectors are shown below.

 

 

 

The optical bandwidth is very wide reaching deep into the UV and up to almost 950 nm on the MIR side.

 

 

 

The varactor is described below

Optical meterology lab

student project in optical clocks