Peter Jänes

Limits on optical pulse compression and delay bandwidth product in electromagnetically induced transparency media

Delay bandwidth products (DBPs) and physical pulselengths obtainable in media exhibiting electromagnetically induced transparency (EIT) are analyzed. The study is performed in stationary media as well as for dynamic storing of light pulses in such media. In the latter case, the dispersion inherent in storage and readout of the pulses is analyzed. It is shown that absorption and the group velocity dispersion (GVD) are limiting factors. Analytical expressions for the minimum compressed pulselength and DBP are derived, and these expressions show good agreement with simulations of pulse propagation in EIT media.

A high-speed intersubband modulator based on quantum interference in double quantum wells

Calculations on a modulator based on quantum interference in AlGaAs/GaAs asymmetric double quantum wells (QWs) are performed. The modulation of the absorption is based on the anti-crossing behavior of the two lowest states in the coupled wells. At anti-crossing, the oscillator strengths of the transitions from these two lowest states to a higher state are changed in opposite directions. The width of the barrier between the wells should be thick enough to allow a large change in oscillator strength with applied field, yet thin enough so that the absorption peaks of the transitions are resolved. The QWs are designed so that one absorption peak has only a small energy shift for the transition used for modulation while the absorption varies rapidly with the applied voltage. A complete structure including a surface plasmon waveguide is proposed enabling calculations of modal absorption. Parameters important for the performance of the modulator are then determined. An extinction ratio of 10 dB at a wavelength of 8.4 /spl mu/m is predicted for a device length of 18 /spl mu/m and a peak-to-peak voltage of 0.9 V. The resistance-capacitance-limited 3-dB bandwidth is 130 GHz. The predicted performance compares very favorably with present interband modulators based on the quantum-confined Stark effect.

Recent developments in high-speed optical modulators

Publisher Summary This chapter reviews the theory of high-speed modulators and practical design approaches, which include a comparison of lumped and traveling-wave designs, and experimental results. The emphasis is on electro-absorption devices based on the Franz–Keldysh effect, the quantum-confined Stark effect, and intersubband absorption. Current high-speed light wave systems make use of electro-optic modulators based on lithium niobate or electro-absorption modulators based on semiconductor materials. In commercial systems, very high-speed lithium niobate devices require a traveling wave structure, while the semiconductor devices are usually lumped. The optical single-mode waveguide-based modulator has emerged as a critical component with rapid development in high data rate communications. This is brought about by the ever-increasing demands from the Internet and requirements for very high-speed computer connections. This growing importance of the modulator has taken place because the external modulator is the only known device that can cope with time division multiplexed signals at 100 Gb/s and beyond—rates that are increasingly required.

GaN/AlN multiple quantum well structures grown by MBE on GaN templates for 1.55 mu m intersubband absorption

We have used MBE to grow MQW structures on MOVPE GaN/sapphire templates. The MQW devices are intended for high speed intersubband electroabsorption modulator devices operating at 1.55-&mgr;m. The GaN/AlN multiple quantum well material was systematically studied regarding the surface morphology, structural characterization and optical property by atomic force microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The intersubband resonance energy was also calculated considering many-body effects in n-type doped structures. The multiple quantum well structure showed superior performance in terms of linewidth when grown on GaN templates as compared on sapphire. GaN quantum well and AlN barriers with a thickness of 3.3 and 4.2 nm respectively resulted in FWHM of the intersubband absorption peak as low as 93 meV at an absorption energy of 700 meV. This is promising for intersubband modulator applications.

Efficient infrared electroabsorption with 1 V applied voltage swing using intersubband transitions

We have demonstrated efficient intersubband electroabsorption in InGaAs/InAlGaAs/InAlAs step quantum wells grown by metal-organic vapor-phase epitaxy. An absorption modulation of 6 dB (Delta alpha= ...

High-speed optical modulator based on intersubband transitions in InGaAs/InAlAs/AlAsSb coupled quantum wells

We investigate theoretically an optical modulator based on intersubband transitions in InGaAs/InAlAs/AlAsSb coupled quantum wells with an operating wavelength of 1.55 /spl mu/m. We show that such a modulator has the potential to outperform conventional electroabsorption and electro-optic modulators with a combination of high speed, moderate voltage swing, negative chirp and high saturation power. The modulator studied here is predicted to have a RC-limited speed of 90 GHz with 10 dB extinction ratio at a peak-to-peak voltage of 2.0 V.

Efficient electroabsorption for mid-infrared wavelengths using intersubband transitions

We have demonstrated efficient intersubband (IS) electroabsorption in InGaAs/InAlGaAs/InAlAs step quantum wells grown by metal-organic vapor phase epitaxy (MOVPE). An absorption modulation of 2300 cm-1 at λ = 5.7 μm due to Stark shift of the IS resonance was achieved with a low applied voltage swing of ± 0.5 V in a multipass waveguide structure. Two useful wavelength ranges of λ≈5.4–5.8 μm and 6.3–6.6 μm were obtained by considering the two flanks of the IS resonance. Based on the experimental results it is estimated that an electroabsorption modulator with a low peak-to-peak voltage of VPP = 0.9 V can yield a modulation speed of f3dB = 120 GHz with the present material by using a strongly confining surface plasmon waveguide of 30 μm length.

Pulse-Distortion in EIT Medium

We analyze pulse-distortion due to propagation through medium exhibiting Electromagnetically Induced Transparency. Separately investigating real and imaginary parts of the susceptibility; the latter being the limiting factor, by analytical and numerical arguments.