Showing papers by "Nils Weimann published in 2007"
TL;DR: In this article, the authors review different optical techniques for generating arbitrary waveforms and present their latest results using a time-domain approach using a single-input single-out (SISO) approach.
Abstract: Optical means for generating arbitrary waveforms have attracted renewed interest because of the wide bandwidth. We will review different optical techniques for generating arbitrary waveforms and will present our latest results using a time-domain approach.
88 citations
03 Jun 2007
TL;DR: In this paper, an integrated push-push oscillator, achieving high output power at 210, 235 and 287 GHz, was realized in a 0.5 mum emitter double-heterojunction InGaAs/InP HBT (D-HBT) technology with a maximum oscillation frequency fmax of 335 GHz and a breakdown voltage (Vbceo) of 4 V.
Abstract: Integrated push-push oscillators, achieving high output power at 210, 235 and 287 GHz, were realized in a 0.5 mum emitter double-heterojunction InGaAs/InP HBT (D-HBT) technology with a maximum oscillation frequency fmax of 335 GHz and a breakdown voltage (Vbceo) of 4 V. The oscillators are based on a balanced Colpitts topology in which a strong second harmonic signal is generated by combining the differential signals at the collector and by reactively tuning the output impedance of the oscillator using a shorted stub. Three oscillators were realized using this topology. A high-power output signal of more then 0 dBm is obtained for oscillators operating at 210 and 232 GHz, an improvement of 5 dB compared to the output power measured on an identical push-push oscillator without 2nd harmonic tuning. Close to -3 dBm output power is obtained at an output frequency of 280 GHz by further reducing the resonator length. By reducing the current, a maximum output frequency of 287 GHz is obtained.
28 citations
19 Nov 2007
TL;DR: In this paper, a single-ended InP transimpedance amplifier (TIA) for next generation high-bandwidth optical fiber communication systems is presented, which exhibits 48 dB-Omega transimpingance and has a 3-dB bandwidth of 92 GHz.
Abstract: A single-ended InP transimpedance amplifier (TIA) for next generation high-bandwidth optical fiber communication systems is presented. The TIA exhibits 48 dB-Omega transimpedance and has a 3-dB bandwidth of 92 GHz. The input-referred current noise is 20 pA/radicHz and the transimpedance group delay is below 10 ps over the entire measured frequency range.
10 citations
TL;DR: In this paper, the Schottky-i-n waveguide structure on InP-based material was used to reduce the switching voltage and the excess loss, while maintaining high modulation efficiencies.
Abstract: An InP-based high-speed optical modulator is presented. The Schottky-i-n waveguide structure on InP-based material was used to reduce the switching voltage Vpi and the excess loss, while maintaining high-modulation efficiencies. To minimize residual amplitude modulation and to improve power handling capability, the bulk electrooptic effect in InGaAlAs was utilized for phase shifting. As a result, a simple structure InAlAs-InGaAlAs Mach-Zehnder optical modulator with traveling-wave electrodes was fabricated and characterized. This device achieved a switching voltage Vpi of 3.6 V, extinction ratio (>23 dB) and high-speed operation at 1.55-mum wavelength
8 citations
23 Jul 2007
TL;DR: This paper reports on the recent progress in using photonic digital-analog converters for arbitrary waveform generation using a time-domain approach based on an interfere metric modulator device.
Abstract: In this paper we report on our recent progress in using photonic digital-analog converters for arbitrary waveform generation. Optical arbitrary waveforms are generated using a time-domain approach based on an interfere metric modulator device.
4 citations
08 Feb 2007
TL;DR: In this article, the authors demonstrate high-reflectivity crack-free Al 0.18 Ga 0.82 N/Al 0.2 N distributed Bragg reflectors (DBR) and monolithic microcavities grown by molecular beam epitaxy on thick c-axis GaN templates.
Abstract: We demonstrate high-reflectivity crack-free Al 0.18 Ga 0.82 N/Al 0.8 Ga 0.2 N distributed Bragg reflectors (DBR) and monolithic microcavities grown by molecular beam epitaxy on thick c-axis GaN templates. The elastic strain energy in the epilayer is minimized by compensating the compressive and tensile stress in every period of the DBR structure. A 25 period DBR mirror provides a 26nm-wide stop band centered at 347 nm with the maximum reflectivity higher than 99%. The high-reflectivity DBRs can be used to form high Q -factor monolithic AlGaN/AlGaN microcavities. INTRODUCTION High-reflectivity distributed Bragg reflect ors (DBR) in the ultraviolet region ar e essential for the development of GaN-based optical devices. In particular, the region around 350 nm is important for devices containing pure GaN as an active medium. The growth of DBRs remains challenging in the nitrid e system. The difficulty lies in maintaining the structural integrity of a relatively thick structure that contains materials with a large lattice constant mismatch and different thermal expansion coefficients. Only a few groups have reported high-reflectivity Al
4 citations
Patent•
21 Dec 2007TL;DR: In this paper, a light detector includes a substrate with a planar surface and an array of photodiodes located along the planar surfaces, each photodiode has a sequence of different semiconductor layers stacked vertically over the surface.
Abstract: An apparatus includes a light detector. The light detector includes a substrate with a planar surface and an array of photodiodes located along the planar surface. Each photodiode has a sequence of different semiconductor layers stacked vertically over the planar surface. The photodiodes are electrically connected in series.