Antti Tanskanen

Parallel optical interconnect between ceramic BGA packages on FR4 board using embedded waveguides and passive optical alignments

We have studied technologies to design and fabricate high-bit-rate chip-to-chip optical interconnects on printed circuit boards (PCBs) using board-embedded polymer waveguides and surface-mounted component packages or modules. In order to demonstrate the developed technologies, a 4times10 Gb/s optical interconnect was completely integrated on a standard FR4 PCB. The optical link demonstrator consists of 4-channel BGA-mounted transmitter and receiver modules as well as of four parallel multimode optical waveguides fabricated on top of the solder mask of the PCB using lithographic patterning. The transmitters and receivers built on low-temperature co-fired ceramic (LTCC) substrates include 4times10 Gb/s flip-chip mounted VCSEL or photodiode array, wire-bonded driver and receiver ICs, and optical coupling structures. Two microlens arrays and a micro-mirror enable optical coupling between the optoelectronic devices and the waveguide array. The passive optical alignment was based on the marks and structures fabricated both in the LTCC process and in the patterning of the optical layers. The characterized optical alignment tolerances are in the limits of accuracy of the surface-mount technology. The demonstrated technology is suitable for interconnecting CBGA-packaged ICs or multi-chip-modules

Embedded optical interconnect on printed wiring board

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. A modular demonstrator was designed based on three different kind of optical coupling schemes: butt-coupling and couplings based on microlens arrays and on micro ball lenses. The optical front-ends 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. An electrical simulation model was developed for the design of a VCSEL-based transmitter circuit. Polymer waveguides were fabricated on separate FR-4 boards to allow characterization of alignment tolerances with different waveguides. Optical and adhesion properties of several potential waveguide materials were characterized. The simulations and experiments suggest that, with optimized optomechanical structures and with low loss waveguides, it is possible to achieve acceptable total path loss and yield with the accuracy of automated assembly.

Fiber-Optic Transceiver Module for High-Speed Intrasatellite Networks

High-speed intrasatellite networks are needed to interconnect units such as synthetic aperture radars, high-resolution cameras, and fast image-compression processors that produce data beyond gigabits per second. We have developed a fiber-optic link, named SpaceFibre, which operates up to 3.125 Gb/s and is compatible with the existing SpaceWire network. The link provides symmetrical, bidirectional, full-duplex, and point-to-point communication. It employs 850-nm vertical-cavity surface emitting lasers, radiation-hardened laser-optimized 50/125 mum graded-index fibers, and GaAs p-i-n photo diodes. The transceiver electronics is realized using a multilayer-ceramic-substrate technology that enables the passive alignment of optical fibers to active devices. The SpaceFibre link demonstrator was tested to transfer data at 2.5 Gb/s over 100 m with a bit error rate of less than 1.3middot10-14. Fiber-pigtailed modules were stressed with temperature variations from -40degC to +85degC, vibrations up to 30 g, and mechanical shocks up to 3900 g. The test results of 20 modules show that the SpaceFibre link is a promising candidate for the upcoming high-speed intrasatellite networks

Multi channel in-plane and out-of-plane couplers for optical printed circuit boards and optical backplanes

We present multi channel optical interconnects, based on integrated glass fibers, with passively aligned in-plane and 90° out-of-plane couplers for printed circuit boards. The out-of-plane coupler features micro optics, mechanical alignment structures, and a snap-fit system to assemble the complex coupler out of several simple, self aligning parts. Further we present an optical printed circuit board for on-board transmitter and receiver electronics for four channels using 4×10 Gbit/s transmitter and receiver chips.

Parallel optical interconnect between surface-mounted devices on FR4 printed wiring board using embedded waveguides and passive optical alignments

Technologies to design and fabricate high-bit-rate chip-to-chip optical interconnects on printed wiring boards (PWB) are studied. The aim is to interconnect surface-mounted component packages or modules using board-embedded optical waveguides. In order to demonstrate the developed technologies, a parallel optical interconnect was integrated on a standard FR4-based PWB. It consists of 4-channel BGA-mounted transmitter and receiver modules as well as of four polymer multimode waveguides fabricated on top of the PWB using lithographic patterning. The transmitters and receivers built on low-temperature co-fired ceramic (LTCC) substrates include flip-chip mounted VCSEL or photodiode array and 4x10 Gb/s driver or receiver IC. Two microlens arrays and a surface-mounted micro-mirror enable optical coupling between the optoelectronic device and the waveguide array. The optical alignment is based on the marks and structures fabricated in both the LTCC and optical waveguide processes. The structures were optimized and studied by the use of optical tolerance analyses based on ray tracing. The characterized optical alignment tolerances are in the limits of the accuracy of the surface-mount technology.

Optical interconnect on printed wiring board

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 micro-ball 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.

Fiber-optic transceivers for high-speed intra-satellite links

High-bit-rate fiber-optic transmitter and receiver components were developed for intra-satellite data links, which will benefit from reduced EMI and savings in mass and volume. The ceramic-based fiber-optic packages enable robustness for harsh environments. Two kinds of components were introduced: “SpaceFibre” transceivers (>;6 Gbps) and parallel optic transceivers with fiber ribbon cables (4+4 x 10 Gbps), both based on 850-nm VCSEL sources and multimode fibers. The transceivers are expected suitable also for other harsh environment applications.

Optical transceivers for interconnections in satellite payloads

The increasing data rates and processing on board satellites call for the use of photonic interconnects providing high-bitrate performance as well as valuable savings in mass and volume. Therefore, optical transmitter and receiver technology is developed for aerospace applications. The metal-ceramic-packaging with hermetic fiber pigtails enables robustness for the harsh spacecraft environment, while the 850-nm VCSEL-based transceiver technology meets the high bit-rate and low power requirements. The developed components include 6 Gbps SpaceFibre duplex transceivers for intra-satellite data links and 40 Gbps parallel optical transceivers for board-to-board interconnects. Also, integration concept of interchip optical interconnects for onboard processor ICs is presented.

Optical interconnects for satellite payloads: overview of the state-of-the-art

The increased demand of broadband communication services like High Definition Television, Video On Demand, Triple Play, fuels the technologies to enhance the bandwidth of individual users towards service providers and hence the increase of aggregate bandwidths on terrestial networks. Optical solutions clearly leverage the bandwidth appetite easily whereas electrical interconnection schemes require an ever-increasing effort to counteract signal distortions at higher bitrates. Dense wavelength division multiplexing and all-optical signal regeneration and switching solve the bandwidth demands of network trunks. Fiber-to-the-home, and fiber-to-the-desk are trends towards providing individual users with greatly increased bandwidth. Operators in the satellite telecommunication sector face similar challenges fuelled by the same demands as for their terrestial counterparts. Moreover, the limited number of orbital positions for new satellites set the trend for an increase in payload datacommunication capacity using an ever-increasing number of complex multi-beam active antennas and a larger aggregate bandwidth. Only satellites with very large capacity, high computational density and flexible, transparent fully digital payload solutions achieve affordable communication prices. To keep pace with the bandwidth and flexibility requirements, designers have to come up with systems requiring a total digital througput of a few Tb/s resulting in a high power consuming satellite payload. An estimated 90 % of the total power consumption per chip is used for the off-chip communication lines. We have undertaken a study to assess the viability of optical datacommunication solutions to alleviate the demands regarding power consumption and aggregate bandwidth imposed on future satellite communication payloads. The review on optical interconnects given here is especially focussed on the demands of the satellite communication business and the particular environment in which the optics have to perform their functionality: space.

Multichannel VCSEL-based optical transceiver employing multicore fibers at 6x25 Gbps/fiber (Conference Presentation)

Multicore fiber enables a parallel optic data link in a single optical fiber. Thus, it is an attractive approach to increase the aggregate data throughput and the integration density of the interconnection. We developed and demonstrated mid-board optical transceiver modules employing novel multicore fiber pigtails and multicore-optimized optoelectronic engines. The silica fibers having 125 µm diameter and including six graded-index multimode cores enable multi-gigabit interconnects at very short distances. The fiber is compatible with the 850-nm VCSEL technology that has many advantages, such as, the very low power operation and the mature and cost-effective GaAs-based device technology. The transceiver incorporates transmitter and receiver subassemblies that are based on the multicore-optimized 850-nm VCSEL and photodiode array chips as well as on the co-designed multichannel VCSEL driver and TIA receiver ICs. All devices are operating up to 25 Gbps/channel and beyond, thus creating a 150 Gbps full-duplex link with the two 6-core fibers. The active areas on the 6-channel VCSEL and PD chips are arranged in a circular array layout that matches the cross-sectional layout of the fiber cores. This allows butt coupling to the fiber cores. The power consumption of the complete link is below 5 mW/Gbps. The transceiver was developed to be applicable for harsh environmental conditions, including space. Therefore, for instance, hermetic packaging was applied and both the active devices and the integration structure enable very wide operation temperature range of up to approx. 100 °C. This paper will present the technical approach including the basic building blocks and the transceiver module implementation. It will also present the results of the data link performance and some reliability testing.