Hugo Thienpont

Relaxing alignment tolerance in single-mode fiber connections using 3D nanoprinted beam expanders

Optical fiber technology is the driving force behind the ever-increasing data transport and internet usage in today’s connected society. The tight alignment tolerance required when connecting single-mode telecom fibers become even more tight when multiple fiber connectors are being used in the optical link. To alleviate this, we expand the mode field of the fiber and use 3D nanoprinting to print taper structures that can relax alignment tolerances in physical contact expanded beam connectors. We present the design and fabrication of a linear taper which expands the fundamental mode of a single-mode telecom fiber adiabatically with a factor of 3. The taper itself was fabricated on top of a cleaved fiber facet with the two-photon polymerization-based 3D nanoprinting technique, which allows fabrication of high aspect-ratio structures with submicrometer resolution. A proof-of-concept demonstrator was built to measure the obtained misalignment tolerance relaxation. Experimental results for lateral misalignment show excellent agreement with simulated values, but the beam expansion with an air-cladding taper also induces an excess loss of about 0.22 dB compared to a standard physical contact connection without beam expansion. This shows the compromise that has to be made between insertion loss and misalignment tolerance relaxation. The use of additive manufacturing techniques in fiber beam expansion applications makes it possible to fabricate taper structures with full 3D design freedom.

Design of a freeform, luminance spreading illumination lens with a continuous surface

Given the high source luminance of current white LEDs, spreading this luminance in order to avoid glare, is a crucial aspect of effective LED lighting system design. In previous work, a method has been presented to design a rotational symmetric or extruded lens consisting of different freeform segments. These segments are designed in such a way that they spread the incoming rays into multiple overlapping fans of which the combination forms a desired target intensity pattern. The advantage of using freeform lens segments is that these can be precisely tailored to different target intensity patterns, e.g. intensity patterns with a sharp cut-off. The transformation of the incoming intensity distribution to the target intensity distribution can be seen as a linear transformation. If the source and target distributions are discretized into a finite number of bins, it is possible to represent this transformation as a matrix. With an iterative procedure one can quickly generate such transformations for specific source and target distributions. The spreading of light at each point of the optical surface can then be realized with small freeform lens segments. These individual freeform segments can be implemented in two different ways, convex or concave. In this paper, the case is considered in which convex and concave freeform structures are alternated which allows for the creation of a continuous, smooth, oscillating lens surface. This approach can improve both the performance and manufacturability when compared with a discontinuous surface. A drawback of the approach is the fact that one loses control over the overall form factor of the resulting lens. The derived iterative procedure was used to design a luminance spreading illumination lens with smooth, wavy structures on one side and a flat surface on the other side. The lens was designed to generate a specific wide-beam target intensity distribution when combined with a high-brightness LED.

Deep Proton Writing: A Rapid Prototyping Tool for Polymer Micro-Optical and Micro-Mechanical Components

During the last decades, the use of photonics in data communication and numerous other industrial applications brought plenty of prospects for innovation and opened different unexplored market opportunities. Refractive micro-optical and micro-mechanical structures like 2-D arrays of spherical micro-lenses, micro-prisms and cylindrical micro-lenses or mechanical alignment features such as 2-D fiber array holders, are likely to be combined with optoelectronic devices and optical fibers to play a key role in optical interconnection technology, in massive parallel optical sensors or in high-definition display and projection systems. This vast domain of applications is a major driving force for the fabrication of these micro-optical and micro-mechanical structures (MOMS) and their accurate alignment and integration into opto-mechanical modules and systems. Technologies that enable the fabrication of monolithic, robust and replicable modules which integrate these individual micro-opto-mechanical components are scarce however. Indeed, the rapid prototyping of micro-optical structures is a highly challenging task since the surfaces of the resulting structures should have a sufficient optical quality. This means that the surface flatness should be controlled within a sub-micrometer scale and that the resulting surface roughness should be only a fraction of the operating wavelength (e.g. λ/20). By far the most conventional fabrication method that can obtain the required resolution is photolithography, which transfers very fine two-dimensional patterns from a mask into a thin layer of photosensitive material. However, this technique is limited to the patterning of flat surfaces (e.g. to create layers for different transistor parts in micro-electronic circuits). Nevertheless, it is often desirable to create more extensive 3D structures to fabricate micro-optical systems, integrated micro-sensors, micro-fluidic systems or medical devices. Therefore, new technologies are being developed, which enable the micro-structuring of deep geometries. A first technology is laser photoablation, a method in which a sample is exposed to such intense light pulses that some of the material at the surface is being spontaneously evaporated (Mihailov & Lazare, 1993). A second one is the LIGA (German acronym for Lithografie, Galvanoformung und Abformung) technology, in which a polymer substrate is Deep Proton Writing: A Rapid Prototyping Tool for Polymer Micro-Optical and Micro-Mechanical Components 16

Microoptical Components for Information Optics and Photonics

Creating performant communication channels between different parts of digital processing units is more then ever the limiting factor to further digital processing development. The confluence of increased performance of computing chips, huge off-chip interconnectivity requirements, and increasingly high channel speeds together with a looming issue of thermal and power management make that current galvanic links are without any doubt under high strain. It is indeed not unusual for the multigigabyte galvanic board links to require compensation on the high-frequency absorption for as much as 30 to 45 dB of attenuation, while crosstalk, dispersion, and timing issues become more severe with each newly introduced complementary metal oxide semiconductor (CMOS) technology node.nnOptical interconnects have therefore been often cited as a possible route to alleviate the current technology conundrum. Indeed, the use of photons for communication has some clear advantages from a physical point of view compared to its galvanic contenders and is already now the default interconnect choice for link lengths above a few hundred meters. At a shorter distance, optics have also demonstrated their ability to enable high data transmission at a very high bitrate per channel and massive parallelism with single dependent electromagnetic interference (EMI). This has lead to an enormous and successful development in optoelectronic devices and hybridization technologies. Yet, optical interconnect at such length scales have thus far failed to become a mainstream commercial reality mostly because of cost, uncertainties in reliability, and unsatisfying packaging solutions.nnThe incumbent technology, the printed circuit board (PCBs), has moreover relentlessly continued to become a cheaper and more mature technology, aided by the development in signal processing chips and new packaging technologies. Nevertheless, it is unclear with this technology where the future performance increases can be found without trading off too much in cost and complexity.

Rapid Prototyping of Polymer Micro-Opto-Mechanical Components with Deep Proton Writing

We present Deep Proton Writing as a flexible rapid prototyping technology for the fabrication of a wide variety of three dimensional refractive micro-optical components and high-aspect-ratio micro-mechanical structures with applications in telecom, datacom and biophotonics.

The European Network of Excellence in Micro-Optics (NEMO)

We highlight the joint strategy of 30 partners, who teamed up in a European Network of Excellence to structure and integrate their efforts in the multidisciplinary domain of micro-optics, the key-link between photonics and nano-electronics.