Picosecond time-resolved bleaching dynamics of self-assembled quantum dots

Picosecond bleaching dynamics of vertically stacked self-assembled quantum dots (QDs) is investigated by means of time-resolved pump-probe differential reflection spectroscopy (TRDR) at room temperature (RT). We observe that the absorption spectrum, which represents the QD density of states at RT, is strongly shifted with respect to the photoluminescence spectrum. This shift can not be interpreted by carrier emission and re-trapping alone. TRDR allows us to study the dynamics of the pump generated carriers within the QDs. From the time-resolved measurements, we detect that the bleaching decay time has a strong energy dependence and is dominated by radiative and nonradiative recombination at low energy and by carrier emission at high energy.     

Design, Fabrication and Characterization of an InP-Based Tunable Integrated Optical Pulse Shaper

In this paper a tunable integrated semiconductor optical pulse shaper is presented. The device consists of a pair of arrayed waveguide gratings with an array of electrooptical phase modulators in between. It has been fabricated in InP-InGaAsP material for operation at wavelengths around 1.55 mum. Multimode inputs to the waveguide gratings are used to flatten their optical passband. We have used a new short-pulse characterization technique to fully characterize pulse shaping by the device, i.e., both the power and the phase profile. A fourfold decrease in pulse ringing was observed for the devices with flattened passbands. Moreover these devices showed a 25% increase in pulse peak power. The possibilities for using the device as a dispersion (pre-) compensator have been investigated. Pulse reconstruction could be obtained for dispersion values of up to 0.2 ps/nm. The fabrication technology of the pulse shaper is compatible with the fabrication of integrated mode-locked lasers, which makes further integration of complete arbitrary pulse generators possible.     

Butt joint integrated extended cavity InAs/ InP (100) quantum dot laser emitting around 1.55 μm

The first butt joint integrated extended cavity InAs/InP (100) quantum dot (QD) Fabry-Perot laser emitting around 1.55 mum is demonstrated. Continuous wave lasing at room temperature on the QD ground state transition is achieved. The threshold current is comparable to that of all-active QD lasers. The Butt joint reflectivity for straight waveguides is below -40 dB.     

Self-organized anisotropic strain engineering: a new concept for quantum dot ordering

We have established a new concept for creating ordered arrays of quantum dots by self-organized epitaxy. The concept is based on self-organized anisotropic strain engineering of strained layer templates and is demonstrated for (In,Ga)As/GaAs superlattice structures on GaAs (100) and strain-induced (In,Ga)As growth instability on GaAs (311)B. The well-defined one- and two-dimensional networks of InAs quantum dots grown on top of these templates are of excellent structural and optical quality. This breakthrough, thus, allows for novel fundamental studies and device operation principles based on single and multiple carrier- and photon-, and coherent quantum interference effects.     

Integrated 2 X 2 quantum dot optical crossbar switch in 1.55 μm wavelength range

A highly compact quantum dot semiconductor optical amplifier based crossbar switch is proposed, fabricated and demonstrated at a wavelength of 1550 nm. Power penalty measurements at 10 Gbit/s show minimal path dependence with values of 0.15 to 0.25 dB and an extinction ratio of 24 dB.     

Characterization of a Monolithic Concatenated SOA/SA Waveguide Device for Picosecond Pulse Amplification and Shaping

In this paper, a monolithic waveguide device, named IRIS, is presented. The device consists of an array of concatenated semiconductor optical amplifiers and saturable absorbers. We have fabricated the devices in InP-InGaAsP bulk gain material and we have experimentally investigated picosecond pulse transmission through these devices. Operated as an optical amplifier the IRIS devices show a decreased temporal pulse broadening and decreased amplified spontaneous emission noise generation as compared to a semiconductor optical amplifier of equivalent length. Used as a nonlinear element to increase the optical bandwidth of a picosecond pulse train, the spectra obtained with IRIS devices show an increased broadening and smoothness as compared to a semiconductor optical amplifier. We have set up a theoretical model to describe spectral and temporal pulse shaping by the IRIS device. Agreement between the simulations and the experiments is obtained.     

InAs–InP (1.55- μm Region) Quantum-Dot Microring Lasers

In this letter, we demonstrate electrically pumped continuous-wave lasing at room temperature in microring lasers, which employ a quantum-dot gain medium. Lasing occurs in the important 1.55-mum telecom wavelength range. The 2-mum-wide ring waveguides are made from InGaAsP-InP (100) material suitable for active-passive photonic integrated circuits. Lasing in rings down to 22 mum in diameter is found, with a threshold current of 12.5 mA.     

Lateral Ordering, Position, and Number Control of Self-Organized Quantum Dots: The Key to Future Functional Nanophotonic Devices

Lateral ordering, position, and number control of self-organized epitaxial semiconductor quantum dots (QDs) are demonstrated. Straight linear InAs QD arrays are formed by self- organized anisotropic strain engineering of an InGaAsP/InP (10 0) superlattice template in chemical beam epitaxy. The QD emission wavelength at room temperature is tuned into the important 1.55 mum telecom wavelength region through the insertion of ultrathin GaAs interlayers. Guided self-organized anisotropic strain engineering is demonstrated on shallow- and deep-patterned GaAs (3 1 1)B substrates by molecular beam epitaxy for the formation of complex InGaAs QD arrays. Lateral positioning and number control of InAs QDs, down to a single QD, are demonstrated on truncated InP (100) pyramids by selective-area metal-organic vapor phase epitaxy. Sharp emission around 1.55 mum is observed well above liquid nitrogen temperatures. The regrowth of a passive waveguide structure establishes submicrometer-scale active- passive integration. The demonstrated control over QD formation is the key to future functional nanophotonic devices and paves the way toward the ultimates of photonic-integrated circuits operating at the single and multiple electron and photon level with control of the quantum mechanical and electromagnetic interactions.