Design and fabrication of embedded micro-mirror inserts for out-of-plane coupling in PCB-level optical interconnections (original) (raw)
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. Several technologies have been proposed for the fabrication of 45 • reflector micro-mirrors directly into waveguides. Alternatively, it is possible to make use of discrete coupling components which have to be inserted into cavities formed in the PCB-integrated waveguides. In this paper, we present a hybrid approach where we try to combine the advantages of integrated and discrete coupling mirrors, i.e. low coupling loss and maintenance of the planararity of the top surface of the optical layer, allowing the lamination of additional layers or the mounting of optoelectronic devices. The micro-mirror inserts are designed through non-sequential ray tracing simulations, including a tolerance analysis, and subsequently prototyped with Deep Proton Writing (DPW). The DPW prototypes are compatible with mass fabrication at low cost in a wide variety of high-tech plastics. The DPW micro-mirror insert is metallized and inserted in a laser ablated cavity in the optical layer and in a next step covered with cladding material. Surface roughness measurements confirm the excellent quality of the mirror facet. An average mirror loss of 0.35-dB was measured in a receiver scheme, which is the most stringent configuration. Finally, the configuration is robust, since the mirror is embedded and thus protected from environmental contamination, like dust or moisture adsorption, which makes them interesting candidates for out-of-plane coupling in high-end boards.
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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.
Embedded Micromirror Inserts for Optical Printed Circuit Boards
IEEE Photonics Technology Letters, 2008
We present the use of an embedded 45 micromirror, which is patterned in polymer photoresist using deep proton writing. The micromirror is metallized and inserted in a laser ablated cavity in the optical layer and in a next step covered with cladding material. Surface roughness measurements confirm the excellent quality of the mirror facet. Loss measurements have been carried out to evaluate the behavior of the embedded micromirror. These measurements indicate an average loss below 0.35 dB, measured in a receiver scheme, which is the most stringent configuration.
Discrete Out-of-Plane Coupling Components for Printed Circuit Board-Level Optical Interconnections
IEEE Photonics Technology Letters, 2000
We propose discrete out-of-plane coupling components as a versatile alternative to current approaches used to couple light in and out of the propagation plane in waveguide-based printed circuit board (PCB)-level optical interconnections. The out-of-plane couplers feature a 45 micromirror and are fabricated using deep proton writing as a rapid prototyping technology. Their fabrication is compatible with replication techniques and shows all the potential of low-cost mass fabrication. In a first configuration, we use the component in a fiber-to-fiber coupling scheme. Coupling losses as small as 0.77 dB were achieved. In a second configuration, the out-of-plane coupler is plugged into a laser ablated cavity in optical waveguides integrated on a PCB. Here a total link loss between out-of-plane fiber and in-plane fiber of 3.00 dB was achieved when using it at the transmitter side and 5.69 dB when using it at the receiver side.
Optical interconnect modules with fully integrated reflector mirrors
IEEE Photonics Technology Letters, 2005
A robust and cost-effective technology for integration of 45 reflector mirrors and polymer waveguides (WGs) into optical interconnect (OI) substrates is developed. The planar WGs are formed from photopatternable polymers with propagation losses as low as 0.05 dB/cm. The mirrors with losses of 0.5-0.8 dB are fabricated by the microdicing technique allowing lateral and vertical positioning of the mirror plane within several microns. A prototype OI module with integrated channel WGs, mirrors, and assembled connectors is fabricated and successfully tested at 10-Gb/s transmission rate.
Integration of optical interconnections on circuit board (invited paper)
2007
Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate optoelectronic interconnects. The target is communication between surface-mounted integrated circuit packages on printed circuit board through embedded optical waveguides. Different kinds of optical elements for coupling between transmitters/receivers and waveguides are studied, including microlens arrays, microlenses integrated on VCSELs, surface-mountable beam deflecting elements, optical pillar structures, and waveguide structures patterned by laser ablation. Integration experiments by the use of ceramic packaging substrate as well as results of the coupling efficiency and alignment tolerance characterizations are presented.
Integration of Optical Interconnects on Circuit Board
Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate optoelectronic interconnects. The target is communication between surface-mounted integrated circuit packages on printed circuit board through embedded optical waveguides. Different kinds of optical elements for coupling between transmitters/receivers and waveguides are studied, including microlens arrays, microlenses integrated on VCSELs, surface-mountable beam deflecting elements, optical pillar structures, and waveguide structures patterned by laser ablation. Integration experiments by the use of ceramic packaging substrate as well as results of the coupling efficiency and alignment tolerance characterizations are presented.
Integration of optical interconnections on circuit board
2007
Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate optoelectronic interconnects. The target is communication between surface-mounted integrated circuit packages on printed circuit board through embedded optical waveguides. Different kinds of optical elements for coupling between transmitters/receivers and waveguides are studied, including microlens arrays, microlenses integrated on VCSELs, surface-mountable beam deflecting elements, optical pillar structures, and waveguide structures patterned by laser ablation. Integration experiments by the use of ceramic packaging substrate as well as results of the coupling efficiency and alignment tolerance characterizations are presented.
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.
Circuit World, 2012
PurposeThe purpose of this paper is to present the need, and a potential solution, for in‐plane routing of optical signals for optical‐enabled circuit boards.Design/methodology/approachMultimode waveguides and integrated 45° in‐plane mirror structures were made in a low loss acrylate‐based photopolymer using excimer laser ablation. The fabrication of multimode waveguides and mirrors was carried out in a single laser system which minimised alignment issues.FindingsIt was established that in‐plane mirror fabrication using laser ablation can be achieved and can potentially be used to define mirrors in waveguides made by other methods such as photolithography.Research limitations/implicationsWhile the concept (integrated in‐plane mirror) was demonstrated, the viability of its deployment will depend on the results of optical loss measurements for which further research is required.Originality/valueThe paper gives an overview of the design concept and fabrication steps for an in‐plane emb...
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