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Optoelectronic system based on photonic integrated circuits to miniaturize spectral domain OCT
(2023)
We present a miniaturized optical coherence tomography (OCT) setup based on photonic integrated circuits (PIC) for the 850 nm range. We designed a 512-channel arrayed waveguide grating (AWG) on a PIC for spectral domain OCT (SD-OCT) that is co-integrated with PIN-photodiodes and analog-to-digital-converters on one single chip. This image sensor is combined with all the necessary electronics to act as a camera. It is integrated into a fiber-based OCT system, achieving a sensitivity of >80dB and various samples are imaged. This optoelectronic system will allow building small and cost-effective OCT systems to monitor retinal diseases.
Signatures of the optical stark effect on entangled photon pairs from resonantly-pumped quantum dots
(2023)
Two-photon resonant excitation of the biexciton-exciton cascade in a quantum dot generates highly polarization-entangled photon pairs in a near-deterministic way. However, the ultimate level of achievable entanglement is still debated. Here, we observe the impact of the laser-induced ac-Stark effect on the quantum dot emission spectra and on entanglement. For increasing pulse-duration-to-lifetime ratios and pump powers, decreasing values of concurrence are recorded. Nonetheless, additional contributions are still required to fully account for the observed below-unity concurrence.
Combining parallel pattern generation of electrohydrodynamic lithography with serial addressing
(2018)
Design of low loss 1x64 y-branch splitter having symmetric splitting ratio and small footprint
(2014)
Progress in integrated photonics enables development of integrated photonics circuits with new unique properties, circuits of the future, and overcomes current limits in information and communication technologies. The packaging of photonic integrated circuits is necessary for taking them out of research laboratories into real implementation in the information and communication technology applications.
Telecom optical fibers are still being the best transmission medium of digital data and analogue signals for long distance applications. The effective coupling of optical radiation between telecom optical fiber with ten microns core dimension and photonic integrated circuits optical waveguides with submicron dimensions are necessary. To address these challenges, we present our concept of photonics integrated circuit packaging with radio frequency, direct current and fiber array ports with automated active alignment system.
SiN is a suitable material for fabricating of photonic integrated circuits with middle refractive index contrast for the visible and near infrared spectral region with ultra-low propagation losses. The paper deals with the design and simulation of fiber to SiN chip butt coupler with single step fabrication process without thickness tapering. Coupler is designed for 850 nm band for coupling between strip 0.25 μm × 1.00 μm waveguide and Nufern's 780-OCT single mode optical fiber with core diameter 4.4 μm. The coupling losses simulation results of the two simulation methods finite-difference beam propagation techniques and eigenmode expansion method are compared.
A Telecom optical fibers are still being the best transmission medium of digital data and analogue signals for long distance applications. Progress in integrated photonics enables development of photonic chips with new unique properties, circuits of the future, and overcomes current limits in information and communication technologies. The packaging of photonic chips is necessary for taking them out of research laboratories into real implementation in the information and communication technology applications. One important step of packaging is effective coupling of optical radiation between telecom optical fiber with ten microns core dimension and photonic chip optical waveguide with submicron dimensions. For complex photonic chips, it is necessary to couple not one optical fiber but several optical fibers, which are arranged in fiber arrays. In this case, it is necessary to use a 6D positioning system, which allows to optimally adjust the relative position of the photonic chip and the fiber arrays. After setting the optimal relative position of the photonic chip and the fiber array, the process of their fixation follows. One possibility of fixation is gluing with an adhesive in the optical path between the photonic chip and an array of optical fibers with a refractive index close to the refractive index of the optical fiber core. This paper is focused on the experimental test set-up for the temperature characterization of fiber array to photonics chip butt coupling at 1310 nm and 1550 nm wavelengths fixed themselves by UV adhesive in the optical path. The main aims of this works are selection of better adhesive from two types for gluing of photonic chip and fiber array in packaging process of photonics chips and validation of gluing process developing. The coupling and alignment of fiber arrays to photonics chip were done by automated active alignments system and they were fixed themselves by curable epoxy adhesive. Temperature changes of coupling insertion losses are measured and investigated for two different UV adhesives during three temperature cycles from -40 °C to 80 °C in climatic chamber according to Telcordia. Spectral dependence of insertion losses were measured and compared before and after three temperature cycles for 1530 nm to 1570 nm spectral range at room temperature.
This work was supported by the Slovak Research and Development Agency under the contracts APVV-17-0662 and SK-AT-20-0017 and by the COST Action “European Network for High Performance Integrated Microwave Photonics” (EUIMWP) CA16220.
The main aims of this work are the validation of the developed process of gluing a single-mode optical fiber array with a photonic chip and the selection of a more suitable adhesive from the two adhesives being compared. An active alignment system was used for adjusting the two optical fiber arrays to a photonics chip. The gluing was done by two compared UV curable adhesives applied in the optical path. The insertion losses of glued coupling were measured and investigated at two discrete wavelengths 1310 nm and 1550 nm during temperature testing in the climatic chamber according to Telcordia GR_1209_Corei04 [3]. The measurement, investigation, and comparison of insertion losses of the glued coupling at the spectral band from 1530 nm to 1570 nm were done immediately after gluing process and after three temperature cycles in the climatic chamber with one month delay.
In this paper we report on the experimental test set-up for the temperature characterization of fiber array to photonics chip butt coupling at 1310 nm and 1550 nm wavelengths. The alignment and gluing of fiber arrays to photonics chip were done by automated active alignments system and they were fixed themselves by UV curable epoxy adhesive. Temperature changes of coupling insertion losses are measured and investigated for two different UV adhesives during three temperature cycles from -40 °C to 80 °C in climatic chamber. Spectral dependence of insertion losses was measured and compared before and after three temperature cycles for 1530 nm to 1570 nm spectral range at room temperature.
The paper deals with designing and numerical modelling a 2 x 2 optical switch for photonic integrated circuits based on 2 x 2 MMI elements and phase modulators. The 2 x 2 optical switch was modelled in the RsoftCAD with the simulation tool BeamPROP. The 2 x 2 optical switch is a common element for creating more complex 1 x N or N x N optical switches in all-optical signal processing.
The paper deals with the optimization of 2x2 optical switch for photonic integrated circuits based on two 2x2 MMI splitters and two phase-modulators. The optical switch was modelled in the RSoftCAD with the simulation tool BeamPROP. The optimization was done to minimise the insertion losses and broaden the spectral band at 1550 nm by using linear tapers in a 2x2 MMI splitter topology. The 2x2 optical switch is a common element for creating more complex 1xN or NxN optical switches in all-optical signal processing.
Compression of ultrashort laser pulses via gated multiphoton intrapulse interference phase scans
(2014)
In this work, parametric excitation is introduced in a fully balanced flexible rotor mounted on two identical active gas foil bearings. The active gas foil bearings change the top foil shape harmonically with a specific amplitude and frequency. The deformable foil shape is approximated by an analytical function, while the gas pressure distribution is evaluated by the numerical solution of the Reynolds equation for compressible flow. The harmonic variation of the foil shape generates a respective variation in the bearings’ stiffness and damping properties and the system experiences parametric resonances and antiresonances in specific excitation frequencies. The nonlinear gas bearing forces generate bifurcations in the solutions of the system at certain rotating speeds and excitation frequencies; period doubling and Neimark-Sacker bifurcations are noticed in the examined system, and their progress is evaluated as the two bifurcation parameters (rotating speed and parametric excitation frequency) are changed, though a codimension-2 numerical continuation of limit cycles. It is found that at specific range of excitation frequency there are parametric anti-resonances and the bifurcations collide and vanish. Therefore, a bifurcation-free operating range is established and the system can operate stable at a wide speed range.