Dimitri Geskus
Royal Institute of Technology
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Dimitri Geskus.
Journal of The Optical Society of America B-optical Physics | 2010
Jonathan D. B. Bradley; Laura Agazzi; Dimitri Geskus; Feridun Ay; Kerstin Worhoff; Markus Pollnau
Erbium-doped aluminum oxide integrated optical amplifiers were fabricated on silicon substrates, and their characteristics were investigated for Er concentrations ranging from 0.27 to 4.2×1020 cm−3. Background losses below 0.3 dB/cm at 1320 nm were measured. For optimum Er concentrations in the range of 1 to 2×1020 cm−3, an internal net gain was obtained over a wavelength range of 80 nm(1500-1580 nm), and a peak gain of 2.0 dB/cm was measured at 1533 nm. The broadband and high peak gain are attributed to an optimized fabrication process, improved waveguide design, and pumping at 977 nm as opposed to 1480 nm. In a 5.4-cm-long amplifier, a total internal net gain of up to 9.3 dB was measured. By use of a rate-equation model, an internal net gain of 33 dB at the 1533 nm gain peak and more than 20 dB for all wavelengths within the telecom C-band (1525-1565 nm) are predicted for a launched signal power of 1 μW when launching 100 mW of pump power into a 24-cm-long amplifier. The high optical gain demonstrates that Al2O3:Er3+ is a competitive technology for active integrated optics.
IEEE Journal of Quantum Electronics | 2009
Kerstin Worhoff; Jonathan D. B. Bradley; Feridun Ay; Dimitri Geskus; Tom Blauwendraat; Markus Pollnau
A reliable and reproducible deposition process for the fabrication of Al<sub>2</sub>O<sub>3</sub> waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm<sup>2</sup> area and no detectable OH<sup>-</sup> incorporation. For applications of the Al<sub>2</sub>O<sub>3</sub> films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al<sub>2</sub>O<sub>3</sub> layer growth. Dopant levels between 0.2-5times10<sup>20</sup> cm<sup>-3</sup> are studied. At Er<sup>3+</sup> concentrations of interest for optical amplification, a lifetime of the <sup>4</sup>I<sub>13/2</sub> level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al<sub>2</sub>O<sub>3</sub>:Er<sup>3+</sup> channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.
Advanced Materials | 2012
Dimitri Geskus; S. Aravazhi; Sonia M. García-Blanco; Markus Pollnau
Modal gain per unit length versus launched pump power is predicted and measured in a 47.5 at.% Yb(3+) -doped potassium double tungstate channel waveguide. The highest measured gain exceeds values previously reported for rare-earth-ion-doped materials by two orders of magnitude.
Optics Express | 2010
Dimitri Geskus; S. Aravazhi; Kerstin Worhoff; Markus Pollnau
In KGd(1-x)Lu(x)(WO(4))(2):Yb(3+) channel waveguides grown onto KY(WO(4))(2) substrates by liquid phase epitaxy and microstructured by Ar+ beam etching, we produced 418 mW of continuous-wave output power at 1023 nm with a slope efficiency of 71% and a threshold of 40 mW of launched pump power at 981 nm. The degree of output coupling was 70%. By grating tuning in an extended cavity and pumping at 930 nm, we demonstrated laser operation from 980 nm to 1045 nm. When pumping at 973 nm, lasing at 980 nm with a record-low quantum defect of 0.7% was achieved.
Optics Express | 2010
Dimitri Geskus; S. Aravazhi; C. Grivas; Kerstin Worhoff; Markus Pollnau
Epitaxially grown, 2.4-microm-thin layers of KY(WO(4))(2):Gd(3+), Lu(3+), Yb(3+), which exhibit a high refractive index contrast with respect to the undoped KY(WO(4))(2) substrate, have been microstructured by Ar beam milling, providing 1.4-microm-deep ridge channel waveguides of 2 to 7 microm width, and overgrown by an undoped KY(WO(4))(2) layer. Channel waveguide laser operation was achieved with a launched pump power threshold of only 5 mW, a slope efficiency of 62% versus launched pump power, and 76 mW output power.
IEEE Journal of Quantum Electronics | 2009
Kerstin Worhoff; Jonathan D. B. Bradley; Feridun Ay; Dimitri Geskus; Tom Blauwendraat; Markus Pollnau
A reliable and reproducible deposition process for the fabrication of Al<sub>2</sub>O<sub>3</sub> waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm<sup>2</sup> area and no detectable OH<sup>-</sup> incorporation. For applications of the Al<sub>2</sub>O<sub>3</sub> films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al<sub>2</sub>O<sub>3</sub> layer growth. Dopant levels between 0.2-5times10<sup>20</sup> cm<sup>-3</sup> are studied. At Er<sup>3+</sup> concentrations of interest for optical amplification, a lifetime of the <sup>4</sup>I<sub>13/2</sub> level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al<sub>2</sub>O<sub>3</sub>:Er<sup>3+</sup> channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.
Optics Express | 2013
Dimitri Geskus; E. H. Bernhardi; K. van Dalfsen; S. Aravazhi; Markus Pollnau
Channel waveguide lasers operating at 981 nm are demonstrated in KY(1-x-y)Gd(x)Lu(y)(WO4)2:Yb3+ waveguides grown by liquid phase epitaxy onto undoped KY(WO4)2 substrates and microstructured by Ar+ beam etching. Under pumping at 934 nm of samples with different waveguide geometry and outcoupling degree, a record-high slope efficiency of 76% versus absorbed pump power and a record-high output power of 650 mW for rare-earth-ion-doped microstructured channel waveguide lasers is achieved. The laser performance is compared to that of the same devices when pumping at 981 nm and lasing near 1025 nm.
Optics Express | 2011
K. van Dalfsen; S. Aravazhi; Dimitri Geskus; Kerstin Worhoff; Markus Pollnau
Laser experiments on 1.5at.%, 5at.%, and 8at.% thulium-gadolinium-lutetium-yttrium co-doped, buried, ridge-type channel waveguides in a monoclinic potassium double tungstate demonstrate a maximum slope efficiency of 70% and output powers of 300 mW at ~1.9 μm.
Optics Express | 2016
Nur Ismail; Cristine Calil Kores; Dimitri Geskus; Markus Pollnau
We systematically characterize the Fabry-Pérot resonator. We derive the generic Airy distribution of a Fabry-Pérot resonator, which equals the internal resonance enhancement factor, and show that all related Airy distributions are obtained by simple scaling factors. We analyze the textbook approaches to the Fabry-Pérot resonator and point out various misconceptions. We verify that the sum of the mode profiles of all longitudinal modes is the fundamental physical function that characterizes the Fabry-Pérot resonator and generates the Airy distribution. Consequently, the resonator losses are quantified by the linewidths of the underlying Lorentzian lines and not by the measured Airy linewidth. Therefore, we introduce the Lorentzian finesse which provides the spectral resolution of the Lorentzian lines, whereas the usually considered Airy finesse only quantifies the performance of the Fabry-Pérot resonator as a scanning spectrometer. We also point out that the concepts of linewidth and finesse of the Airy distribution of a Fabry-Pérot resonator break down at low reflectivity. Furthermore, we show that a Fabry-Pérot resonator has no cut-off resonance wavelength. Finally, we investigate the influence of frequency-dependent mirror reflectivities, allowing for the direct calculation of its deformed mode profiles.
IEEE Journal of Quantum Electronics | 2009
Kerstin Worhoff; J. Bradley; Feridun Ay; Dimitri Geskus; Tom Blauwendraat; Markus Pollnau
A reliable and reproducible deposition process for the fabrication of Al<sub>2</sub>O<sub>3</sub> waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm<sup>2</sup> area and no detectable OH<sup>-</sup> incorporation. For applications of the Al<sub>2</sub>O<sub>3</sub> films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al<sub>2</sub>O<sub>3</sub> layer growth. Dopant levels between 0.2-5times10<sup>20</sup> cm<sup>-3</sup> are studied. At Er<sup>3+</sup> concentrations of interest for optical amplification, a lifetime of the <sup>4</sup>I<sub>13/2</sub> level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al<sub>2</sub>O<sub>3</sub>:Er<sup>3+</sup> channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.