Discrete Out-of-Plane Coupling Components for Printed Circuit Board-Level Optical Interconnections (original) (raw)
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Micro-Optics, VCSELs, and Photonic Interconnects II: Fabrication, Packaging, and Integration, 2006
We present Deep Lithography with Protons (DLP) as a rapid prototyping technology to fabricate waveguidebased micro-optical components with monolithically integrated 45 • 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 20µm collimating aperture is chosen to accurately define the out-of-plane coupling structures. We fully optimized the DLP process for this 20µm proton beam and we measured the surface roughness (R q =27.5nm) and the flatness (R t =3.17µm) 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 • 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. Nonsequential 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.
2007
Board-level optical interconnects offer a possible solution to the bandwidth problems that electrical interconnects are facing in the near future. The integration of the optical interconnection to the board level is done by integrating one or more optical layers on a printed circuit board (PCB). We present Deep Proton Writing (DPW) as a generic rapid prototyping technology for the fabrication of a micro-optical coupling component incorporating a 45° micro-mirror that can be readily inserted into a multilayer optical waveguiding structure integrated on a PCB. Micro-cavities are ablated into the optical layers to accommodate the discrete out-of-plane coupler. The advantage of using a discrete component is that micro-lenses can be incorporated to increase the coupling efficiency with a guaranteed perfect alignment of the lens and the micro-mirror. In case lenses are integrated in the coupling component, the layer thickness of top and bottom optical layer has to be in accordance with the designed value and the alignment of the component with respect to the waveguide is critical. In the case the lenses are not used and a metallized mirror facet is used for out-of-plane coupling, there is quite a large tolerance on the thickness of the layers and the alignment accuracy of the component. The surface quality of the fabricated components was characterized and the coupling efficiency of the out-of-plane coupling components was be measured in a fiber-to-fiber coupling scheme. The coupling component is prototyped in PMMA material, which is not compatible with standard PCB manufacturing. This should however not be considered as a limiting factor since the DPW process is compatible with mass replication technologies such as hot embossing or micro-injection moulding and the master as such can be replicated in a variety of hightech plastics.
Applied Optics, 2007
Optical interconnects can provide chip-to-chip data communication with much needed bandwidth as processor speed and density keep growing. Optical waveguides and couplers are essential components for implementing optical interconnections. Techniques for directly dispensing polymer waveguides in laserablated trenches on printed circuit boards and for fabricating optical couplers are presented for quick prototype of optical interconnects. High-quality UV curable polymer waveguides were routinely fabricated. High-efficiency couplers, blazed grating couplers on sloped waveguides, sloped facet metal film couplers, and reflective-undercut facet couplers can be fabricated by using excimer laser ablation.
Optical interconnections have gained interest over the last years, and several approaches have been presented for the integration of optics to the printed circuit board (PCB)-level. The use of a polymer optical waveguide layer appears to be the prevailing solution to route optical signals on the PCB. The most difficult issue is the efficient out-of-plane coupling of light between surface-normal optoelectronic devices (lasers and photodetectors) and PCB-integrated waveguides. The most common approach consists of using 45 • reflecting micro-mirrors. The micro-mirror performance significantly affects the total insertion loss of the optical interconnect system, and hence has a crucial role on the system's bit error rate (BER) characteristics.
Towards low cost coupling structures for short-distance optical interconnections
2007
The performance of short distance optical interconnections in general relies very strongly on coupling structures, since they will determine the overall efficiency of the system to a large extent. Different configurations can be considered and a variety of manufacturing technologies can be used. We present two different discrete and two different integrated coupling components which can be used to deflect the light beam over 90° and can play a crucial role when integrating optical interconnections in printed circuit boards. The fabrication process of the different coupling structures is discussed and experimental results are shown. The main characteristics of the coupling structures are given. The main advantages and disadvantages of the different components are discussed.
Fast fabrication of polymer out-of-plane optical coupler by gray-scale lithography
Optics Express, 2017
We report a fabrication process of a polymer, and mirror-based out-of-plane optical coupler. In the process, a pre-formed mirror blank made of a buffer coat material is reexposed by a laser direct writing tool with low numerical aperture of 0.1. The fabrication process is inherently fast because of the low numerical aperture (NA) process. The surface figure of the mirror is controlled under 0.04 waves in root-mean-square (RMS) at 1.55 μm wavelength, with mirror angle of 45 ± 1 degrees. Nominal insertion loss of 8.5dB of the mirror-based coupler was confirmed with polymer waveguides fabricated simultaneously.
2004
In this communication, the fabrication and characterization results of O/E-PWBs comprising multimode polymer waveguides with optical-I/O-coupling facets are presented. The epoxy-based glycidyl ether derivative of bisphenol-A novolac (SU-8) and its refractive index modified grade (L6100) polymers are used as the optical waveguide core and the cladding, respectively. The waveguides with integrated 45° out-of-plane turning micromirrors are fabricated using ultraviolet (UV) lithography. The surface topography and sloping angle characterization using scanning electron microscopy (SEM) showed that 45-degree nearly rectilinear mirror planes were achieved. Parallel waveguide channels with the total-internal-reflection (TIR) are fabricated as an optical-build-up layer on conventional PWBs for functional evaluation. The waveguide transmission loss of the guides with and without the mirror facets is measured using the cut-hack method.
Embedded optical interconnect on printed wiring board
2004
Integration of high-speed parallel optical interconnects into printed wiring boards (PWB) is studied. The aim is a hybrid optical-electrical board including both electrical wiring and embedded polymer waveguides. Robust optical coupling between the waveguide and the emitter/detector should be achieved by the use of automated pick-and-place assembly. Different coupling schemes were analyzed by combining non-sequential ray tracing with Monte-Carlo tolerance simulation of misalignments. The simulations demonstrate that, with optimized optomechanical structures and with very low loss waveguides, it is possible to achieve acceptable total path loss and yield with the accuracy of automated assembly. A technical demonstrator was designed and realized to allow testing of embedded interconnects based on three different kind of optical coupling schemes: butt-coupling, and couplings based on micro-lens arrays and on microball lenses. They were implemented with PIN and flip-chip-VCSEL arrays as well as 10-Gb/s/channel electronics onto LTCC-based (low-temperature co-fired ceramic) transmitter and receiver modules, which were surface mounted on high-speed PWBs. The polymer waveguides were on separate FR-4 boards to allow testing and characterization of alignment tolerances with different waveguides. With micro-lens array transmitter, the measured tolerances (±10 µm) were dominated by the thickness of the waveguides.
IEEE Photonics Technology Letters, 2000
A high-coupling-efficiency optical interconnection has been demonstrated using a 90 -bent fiber array connector to deflect beams between surface-emitting lasers or surface-receiving photodiodes and optical layers embedded in a board. A 90 -bent fiber array is mounted in a tetragonal body with a millimeter scale size to make it suitable for passive packaging in the board. The bending radius of silica fibers in the connector was controlled to have 1.5 mm resulting in bending loss of about 0.5 dB. An optical link of 2.5-Gb/s signals with a total interconnection loss of 1.3 dB was demonstrated using the connectors and a fiber-embedded board.