E Barry Smalbrugge

Real versus measured surface potentials in scanning Kelvin probe microscopy.

Noncontact potentiometry or scanning Kelvin probe microscopy (SKPM) is a widely used technique to study charge injection and transport in (in)organic devices by measuring a laterally resolved local potential. This technique suffers from the significant drawback that experimentally obtained curves do not generally reflect the true potential profile in the device due to nonlocal coupling between the probing tip and the device. In this work, we quantitatively explain the experimental SKPM response and by doing so directly link theoretical device models to real observables. In particular, the model quantitatively explains the effects of the tip-sample distance and the dependence on the orientation of the probing tip with respect to the device.

Observation of Q-switching and mode-locking in two-section InAs/InP (100) quantum dot lasers around 1.55 µm

First observation of passive mode-locking in two-section quantum-dot lasers operating at wavelengths around 1.55 mum is reported. Pulse generation at 4.6 GHz from a 9 mm long device is verified by background-free autocorrelation, RF-spectra and real-time oscilloscope traces. The output pulses are stretched in time and heavily up-chirped with a value of 20 ps/nm, contrary to what is normally observed in passively mode-locked semiconductor lasers. The complete output spectrum is shown to be coherent over 10 nm. From a 7 mm long device Q-switching is observed over a large operating regime. The lasers have been realized using a fabrication technology that is compatible with further photonic integration. This makes the laser a promising candidate for e.g. a mode-comb generator in a complex photonic chip.

Integrated Tunable Quantum-Dot Laser for Optical Coherence Tomography in the 1.7

In this paper, we present the design and characterization of a monolithically integrated tunable laser for optical coherence tomography in medicine. This laser is the first monolithic photonic integrated circuit containing quantum-dot amplifiers, phase modulators, and passive components. We demonstrate electro-optical tuning capabilities over 60 nm between 1685 and 1745 nm, which is the largest tuning range demonstrated for an arrayed waveguide grating controlled tunable laser. Furthermore, it demonstrates that the active-passive integration technology designed for the 1550 nm telecom wavelength region can also be used in the 1600-1800 nm region. The tunable laser has a 0.11 nm effective linewidth and an approximately 0.1 mW output power. Scanning capabilities of the laser are demonstrated in a free space Michelson interferometer setup where the laser is scanned over the 60 nm in 4000 steps with a 500 Hz scan frequency. Switching between two wavelengths within this 60 nm range is demonstrated to be possible within 500 ns.

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In this paper, we present the design, fabrication, and characterization of two monolithically InP-based integrated electro-optically tunable filters. The combination of these filters can be used to achieve a filter with a narrow passband and a large free spectral range. These filters are designed to be used in an integrated tunable laser source in the 1600-1800 nm wavelength region using active-passive integration technology. The fact that these filters worked successfully shows that this integration technology, originally designed to be used around 1550 nm wavelength, can also be used successfully in the 1600-1800 nm wavelength region without a large penalty in performance. The two filters, a high-resolution arrayed waveguide grating-type filters and a low-resolution multimode interferometer-tree-type filter are made tunable using 5 mm long electro-optic phase modulators in the arms of the waveguide arrays. Measurements show that these filters can be tuned over a wavelength range of more than 100 nm with an accuracy of 0.1 nm (1% of the free spectral range) for the high-resolution filter and an accuracy of 9 nm (4% of the free spectral range) for the low-resolution filter.

Wavelength Region

Organic electronic ratchets rectify time-correlated external driving forces, giving output powers that can drive electronic circuitry. In this work their performance characteristics are investigated using numerical modeling and measurements. It is shown how the characteristic parameters of the time–varying asymmetric potential like length scales and amplitude, as well as the density and mobility of the charge carriers in the device influence the performance characteristics. Various ratchet efficiencies and their relations are discussed. With all settings close to optimum, a ratchet with charge displacement and power efficiencies close to 50% and 7% respectively is obtained.

InP-Based Monolithically Integrated Tunable Wavelength Filters in the 1.6–1.8

In this paper we show that using a DVS-BCB adhesive bonding process compact heterogeneously integrated III-V/silicon single mode lasers can be realized. Two new designs were implemented: in a first design a multimode interferometer coupler (MMI) – ring resonator combination is used to provide a comb-like reflection spectrum, while in a second design a triplet-ring reflector design is used to obtain the same. A broadband silicon Bragg grating reflector is implemented on the other side of the cavity. The III-V optical amplifier is heterogeneously integrated on the 400nm thick silicon waveguide layer, which is compatible with high-performance modulator designs and allows for efficient coupling to a standard 220nm high index contrast silicon waveguide layer. In order to make the optical coupling efficient, both the III-V waveguide and the silicon waveguide are tapered, with a tip width of the III-V waveguide of around 500nm. The III-V thin film optical amplifier is implemented as a 3μm wide mesa etched through to the n-type InP contact layer. In this particular device implementation the amplifier section was 500μm long. mW-level waveguide coupled output power at 20°C and a side mode suppression ratio of more than 40dB is obtained.

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To make an electrically pumped photonic crystal membrane laser is a challenging task. One of the problems is how to avoid short circuiting between the p- and n-doped parts of the laser diode, when the membrane thickness is limited to 200–300nm. We propose to use the oxide of AlInAs to realize a current blocking function. In this way, based on submicron selective area re-growth, we aim for electrically injected photonic crystal lasers with high output power, small threshold currents and low power consumption. Here results are presented on the oxidation of AlInAs. The results show that it is feasible to use the oxide of AlInAs for current blocking in an InP-based membrane photonic crystal laser.

m Wavelength Region for Tunable Laser Purposes

Position-controlled InAs quantum dots (QDs) are integrated into planar InP structures by employing selective area growth of InP pyramids and regrowth by metalorganic vapor-phase epitaxy. A smooth surface morphology is obtained at elevated regrowth temperature due to suppression of three-dimensional growth on the pyramids. The height differences are less than 30 nm after nominal 700 nm InP regrowth at 640 °C. Most important, the integrated QDs maintain good optical quality after regrowth for the realization of integrated nanophotonic devices and circuits operating at telecom wavelengths.

The performance of organic electronic ratchets

We present a method to prepare a mixed resist material composed of a positive electron-beam resist (ZEP520A) and C60 fullerene. The method is modified from previous methods in literatures to achieve an optimized mixing. An improvement of the mixed material on the thermal resistance respect to the same structures fabricated with normal ZEP resist has been demonstrated by fabricating multimode interference couplers and coupling regions of micro-ring resonators. An improvement on the propagation loss of the InP membrane waveguides from 6.6 to 3.3 dB/cm using this mixed material is also shown.

Heterogeneously integrated III-V/Si single mode lasers based on a MMI-ring configuration and triplet-ring reflectors

We have designed and fabricated a monolithically integrated continuously tunable laser source for frequency domain optical coherence tomography (FD-OCT) in the 1.6 to 1.8µm wavelength region. The InP-based laser consists of two 8mm long quantum dot (QD) semiconductor optical amplifiers and two electro-optically (EO) tunable filters in a 43.5 mm long ring laser cavity. An 8mm long output amplifier is used to boost the output signal. A picture of the mask is given in Fig. 1a.