The benefits of PICs

By consolidating many optical devices into a single device, PICs enable system designers to implement improvements in system size, power consumption, reliability and cost. Photonic integration delivers these benefits in various ways.

For example, integrating multiple devices and functions into a single PIC greatly reduces the number of optical packages required. Since packages and associated assembly dominate total cost of optical components, accounting for at least 50% of total costand up to 80% for more complex devices, the consolidation of dozens of components into a single device creates significant efficiencies. Packaging reductions also save on costs associated with the individual burn-in and testing of many individual components.

Both electronic and photonic integration address the classical problem of "tyranny of numbers". In the electronic case, the wires between transistors represented a significant scaling and reliability problem. In the photonic case, the tyranny of numbers refers to the optical equivalent of wires; fiber couplings. Photonic integration therefore reduces the need for precise and complex sub-micron optical assemblies required to couple light from optical devices into optical fiber, and minimizes the time-consuming manual alignment and/or complex and costly robotic alignment systems required to do this.

In addition, since each fiber coupling is a potential failure point, the use of many fiber- coupled devices in optical transport systems has a negative impact on system reliability. Each fiber coupling must be robust enough to maintain efficient coupling while withstanding the manipulation, mechanical shock, vibration, temperature shifts and temperature extremes expected over the system operating lifetime. Any change to the fiber attachment will reduce the performance of the component, typically by increasing component loss or reducing output power. Because of this, fiber couplings are the dominant failure mode of today's optical components, with approximately 70% of device failures over life being traceable to fiber coupling failures. The ability of photonic integration to significantly reduce the number of fiber couplings in an optical transport system therefore creates flow-through benefits for system reliability.

Another ramification of having many discrete fiber couplings is the impact on cumulative optical loss at each fiber-device interface. Depending upon the mechanics of the fibercoupling, losses can be between 1dB to 3dB (note that a 3 dB loss is a 50% reduction in power). When many devices are cascaded, these losses accumulate and require better upstream performance in order to achieve a given final optical launch power into the network fiber, thereby increasing the cost and complexity of optical component design. Because device reliability increases exponentially with decreasing power levels, and since monolithically integrated DFB lasers in a PIC can be operated at one quarter or less of the power of discretely packaged DFBs for the same system-level performance, this further improves component and system reliability of PIC-based systems.

Finally, with the ability to easily and cost-effectively integrate diagnostic devices in a PIC, functional on-chip testing can be performed at a wafer level. This allows in-situ testing and screening to be performed before incurring downstream costs for device separation, mounting and testing. In comparison, many optical components such as lasers, modulators and detectors fabricated at a wafer level must first be separated and individually mounted on carrier substrates before their performance can be tested. This process adds additional value-added cost to each component even before basic functional screening can be implemented. This creates not only manufacturing inefficiencies but also increases end-to-end device manufacturing time and cost.

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© 2008 Infinera Corporation.