Patterning of graphene on silicon-on-insulator waveguides through laser ablation and plasma etching

We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to be 0.132 dB/μm

Mode-field matching design, 3D fabrication and characterization of down-tapers on single-mode optical fiber tips for coupling to photonic integrated circuits

Photonic Integrated Circuits have made it possible to decrease the footprint of traditionally bulky optical systems and they create opportunities for various new and fascinating applications. One of the limiting factors for the widespread adaption of PICs is their connection to the outside world. As the mode field diameter of optical modes in waveguides tends to be an order of magnitude smaller than in their fiber counterparts, creating an efficient, robust and alignmenttolerant fiber-to-chip interface remains a challenge. In this work, we investigate the optimization of the fiber-side of the optical interface, whereas the chip itself remains untouched and makes use of spot-size convertors. Optical fiber tips can be functionalized using two-photon polymerization-based 3D nanoprinting technology, which offers full 3D design freedom and sub-micrometer resolution. We present a down-taper design strategy to match the mode-field diameter of single-mode optical fibers to the modefield diameter of waveguides with spot-size converters on PICs. The 3D printed down-tapers are characterized towards their geometry and mode shape, and we experimentally demonstrate their use for coupling towards a Silicon-On-Insulator chip with spot-size convertors. Furthermore, the performance of these down-tapered fibers is compared to conventional lensed fibers in terms of optical coupling efficiency

Designer Descemet membranes containing PDLLA and functionalized gelatins as corneal endothelial scaffold

Corneal blindness is the fourth leading cause of visual impairment. Of specific interest is blindness due to a dysfunctional corneal endothelium which can only be treated by transplanting healthy tissue from a deceased donor. Unfortunately, corneal supply does not meet the demand with only one donor for every 70 patients. Therefore, there is a huge interest in tissue engineering of grafts consisting of an ultra-thin scaffold seeded with cultured endothelial cells. The present research describes the fabrication of such artificial Descemet membranes based on the combination of a biodegradable amorphous polyester (poly (d,l-lactic acid)) and crosslinkable gelatins. Four different crosslinkable gelatin derivatives are compared in terms of processing, membrane quality, and function, as well as biological performance in the presence of corneal endothelial cells. The membranes are fabricated through multi-step spincoating, including a sacrificial layer to allow for straightforward membrane detachment after production. As a consequence, ultrathin (90%), semi-permeable membranes could be obtained with high biological potential. The membranes supported the characteristic morphology and correct phenotype of corneal endothelial cells while exhibiting similar proliferation rates as the positive control. As a consequence, the proposed membranes prove to be a promising synthetic alternative to donor tissue

Single parameter optimization for simultaneous automatic compensation of multiple orders of dispersion for a 1.28 Tbaud signal

We report the demonstration of automatic higher-order dispersion compensation for the transmission of 275 fs pulses associated with a Tbaud Optical Time Division Multiplexed (OTDM) signal. Our approach achieves simultaneous automatic compensation for 2nd, 3rd and 4th order dispersion using an LCOS spectral pulse shaper (SPS) as a tunable dispersion compensator and a dispersion monitor made of a photonic-chip-based all-optical RF-spectrum analyzer. The monitoring approach uses a single parameter measurement extracted from the RF-spectrum to drive a multidimensional optimization algorithm. Because these pulses are highly sensitive to fluctuations in the GVD and higher orders of chromatic dispersion, this work represents a key result towards practical transmission of ultrashort optical pulses. The dispersion can be adapted on-the-fly for a 1.28 Tbaud signal at any place in the transmission line using a black box approach

Two photon polymerization: the 'masterkey' to microfabrication?

The present work aims to demonstrate the potential of two photon polymerization for the production of ultraprecise microstructures. The technique benefits from the two photon absorption principle where two photons with half the energy required for excitation can result in a local polymerization reaction when absorbed simultaneously by a suitable photo-initiator (PI). In order to render the probability for simultaneous absorption sufficiently high to enable reproducible polymerization, a tightly focused femtosecond pulsed laser source is applied. As a consequence of tight focusing, a very small voxel originates where the photon density is large enough to make it statistically possible for an initiator molecule to simultaneously absorb two photons. As a result, a 3D structure can be ‘recorded’ simply by moving the focal spot within a photo-crosslinkable solution, leaving a path of polymerized material behind. Consequently, this technique is the only rapid prototyping technique which enables ‘true’ 3D structuring without the necessity to work in a layer by layer fashion. This unique feature results in nearly no structural limitations with respect to the design of the produced structures.[1] Furthermore, polymerization only occurs at the voxel around the focal spot inside the solution, so no typical struggles encountered during conventional stereolithography occur (e.g.; resolution abberations because of surface tension, need for support structures, oxygen inhibition).[1] In the present work, suitable materials for 2PP have been examined for their processing parameters and compared with commercially available dedicated 2PP resists. The applied laser source was a pulsed erbium doped femtosecond fiber laser with a center wavelenght of 780 nm. As a consequence, Irgacure 819 was selected as PI, because of its suitable absorbance spectrum. Using this photo-initiation system, several crosslinkable substances have succesfully been processed into very precise microstructures (see Figure 1). The obtained structures were examined both via optical microscopy as well as scanning electron microscopy to determine the optimal processing parameters. In a next step, the optimal processing parameters were compared to commercially available 2PP resins, namely IP-L 780 and IP-Dip 780. The results illustrated that although the commercially available resins enabled far higher writing speeds, the investigated materials could still be processed in a sufficiently reproducible manner via 2PP. Furthermore, the applied materials can be developed using only isopropanol, whereas the commercial resins require development using propyleneglycolmonomethyletheracetate (PGMEA) and isopropanol. This feature makes it possible to print the applied materials onto polymeric substrates (eg. PMMA) for ultraprecise surface modification without the risk of substrate dissolution during development. References [1] J. Torgersen, A. Ovsianikov, V. Mironov, N. Pucher, X. Qin, Z. Li, K. Cicha, T. Machacek, R. Liska, V. Jantsch, and J. Stampfl, “Photo-sensitive hydrogels for three-dimensional laser microfabrication in the presence of whole organisms.,” J. Biomed. Opt., vol. 17, no. 10, p. 105008, Oct. 2012. [2] A. Ovsianikov, S. Mühleder, J. Torgersen, Z. Li, X.-H. Qin, S. Van Vlierberghe, P. Dubruel, W. Holnthoner, H. Redl, R. Liska, and J. Stampfl, “Laser photofabrication of cell-containing hydrogel constructs.,” Langmuir, vol. 30, no. 13, pp. 3787–94, Apr. 2014

Prototyping micro-optical components with integrated out-of-plane coupling structures using deep lithography with protons: art. no. 618504

We present Deep Lithography with Protons (DLP) as a rapid prototyping technology to fabricate waveguide-based micro-optical components with monolithically integrated 45 degrees micro-mirrors acting as out-of-plane couplers, splitting the optical signal in 3 separated paths. For the first time, two different proton beam sizes are used during one irradiation and a 20 mu m collimating aperture is chosen to accurately define the out-of-plane coupling structures. We fully optimized the DLP process for this 20 mu m proton beam and we measured the surface roughness (R-q=27.5nm) and the flatness (R-t=3.17 mu m) of the realized components. Finally, we experimentally measured the optical transmission efficiency of the micro-optical splitter component. The results are in excellent agreement with non-sequential ray-tracing simulations performed for the design. Above that, we present a pluggable out-of-plane coupler incorporating a single micro-mirror for the 90 degrees coupling of light to or from polymer multimode waveguides integrated on a printed circuit board (PCB). This millimeter-sized mass-reproducible component can then be readily inserted into laser ablated cavities. Non-sequential ray-tracing simulations are performed to predict the optical performance of the component, showing coupling efficiencies up to 78%. These results are then experimentally verified using piezo-motorized positioning equipment with submicron accuracy in a multimode fiber-to-fiber coupling scheme, showing coupling efficiencies up to 56%. The fabricated coupling components are suitable for low-cost mass production since our micro-optical prototyping technology is compatible with standard replication techniques, such as hot embossing and injection molding, has been shown before

Characterization of the optical parameters of high aspect ratio polymer micro-optical components

International audienc

Proof-of-concept demonstration of a miniaturized multi-resolution refocusing imaging system using an electrically tunable lens

Refocusing multi-channel imaging systems are nowadays commercially available only in bulky and expensive designs. Compact wafer-level multi-channel imaging systems have until now only been published without refocusing mechanisms, since classical refocusing concepts could not be integrated in a miniaturized configuration. This lack of refocusing capabilities limits the depth-of-field of these imaging designs and therefore their application in practical systems. We designed and characterized a wafer-level two-channel multi-resolution refocusing imaging system, based on an electrically tunable liquid lens and a design that can be realized with wafer-level mass-manufacturing techniques. One wide field-of-view channel (2x40°) gives a general image of the surroundings with a lower angular resolution (0.078°), whereas the high angular resolution channel (0.0098°) provides a detailed image of a small region of interest with a much narrower field-of-view (2x7.57°). The latter high resolution imaging channel contains the tunable lens and therefore the refocusing capability. The performances of this high resolution imaging channel were experimentally characterized in a proof-of-concept demonstrator. The experimental and simulated depth-of-field and resolving power correspond well. Moreover, we are able to obtain a depth-of-field from 0.25m until infinity, which is a significant improvement of the current state-of-the-art static multi-channel imaging systems, which show a depth-of-field from 9m until infinity. Both the high resolution and wide field-of-view imaging channels show a diffraction-limited image quality. The designed wafer-level two-channel imaging system can form the basis of an advanced three-dimensional stacked image sensor, where different image processing algorithms can be simultaneously applied to the different images on the image sensor.status: publishe

Optofluidic chip for single-beam optical trapping of particles enabling confocal Raman measurements

We present an optofluidic chip in polymethyl methacrylate (PMMA) that combines optical trapping of single particles with confocal Raman spectroscopy. We introduce the design of the optofluidic chip and the ray-tracing simulations combined with mathematical calculations used to determine the optical forces exerted on the particles and to model the excitation and collection of Raman scattering. The optical trapping is done using a single-beam gradient trap realized by a high numerical aperture free-form reflector, monolithically embedded in the optofluidic chip. The focused beam functions both as the excitation beam as well as the trapping beam. The embedded freeform reflector is also used to collect the Raman scattered light generated from the trapped particle. We discuss the fabrication process for the prototyping of the chip, which consists of an ultraprecision diamond turning step and a sealing step. Finally, we demonstrate the functionality of the optofluidic chip in a proof-of-concept experimental setup and trap polystyrene beads with diameters from 6 to 15m. We characterize the maximal transverse optical trap strength in the sample flow direction using the drag force method, measuring average efficiencies that lie between 0.11 and 0.36, and perform confocal Raman measurements of these particles