MANUFACTURING
Active alignment for precise photonic device assembly
Warren Harvard, Country Manager UK, and Scott Jordan, Head of Photonics, Physik Instrumente
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he rate of innovation in optical communication over the past six decades has continued to rise, resulting in ever- smaller silicon microchips that boast greater processing power. This has been achieved through an exponential increase in the density of integrated circuit (IC) transistors, the size of which can only be reduced to certain dimensional limits before their function will be influenced by quantum effects. Thankfully, photonics has circumnavigated these obstacles, allowing the integration of miniaturised optical devices into applications ranging from sensors in wearable devices to LiDAR and ADAS cameras in driverless vehicles. Photonics can leapfrog conventional electronics and manual techniques at the required assembly tolerances for device miniaturisation, leading to a revolution of the telecommunications sector. Identifying the lingering challenges in photonic device manufacturing is crucial for this growth to continue, and further automation solutions, particularly those that can ensure the perfect alignment of components, are needed to keep up with future demand.
Bottlenecks in manual device assembly
The assembly of photonic devices involves the precise alignment, gluing and curing of a combination of light sources, fibres, lenses, and chips. Each of these individual components must be precisely positioned to ensure the intended functionality of the final product, since even the smallest misalignment can have dramatic negative impacts on the efficiency of a device. The majority of manufacturers still rely on manual techniques for alignment, either using shims to compensate for errors or holding hardware in place with retaining rings. On top of the time-intensive nature of these methods, they typically require specialised labour that is both expensive and hard to find. It can take up to 20 minutes to manually assemble particularly complex devices, leading to a significant production bottleneck at the component positioning step. Furthermore, assembly shims and jigs simply cannot satisfy the increasingly tight tolerances required to manufacture some modern devices. An
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alternative alignment strategy is needed that can more precisely indicate the positioning of components.
Photonic feedback to guide alignment
An inherent advantage of photonic devices is that their efficiency is directly related to the alignment of their individual components, meaning that the strength of their output will fluctuate in real time as the positions of components are changed. The subsequent variation in magnitude of signal strength can guide an iterative process of positional adjustment, resulting in an assembly that is perfectly aligned. Component drift can also be assessed by tracking the variation in photonic output strength during the gluing and curing process. However, this method is unfeasible to perform manually on complex devices that have numerous inputs and outputs, since any movement during the optimisation of one connection will result in a shift to the alignment of others, requiring constant re-optimisation to reach a global consensus. An automated solution is required to solve this problem in the pursuit of a practical production process that avoids the need for time-consuming sequences of back-and-forth adjustments.
Automation by active alignment One way of automating the adjustment process is by closing the feedback loop between device output and positioning hardware, leaving intelligent software solutions and control modules to do the fine tuning. Such systems rely on areal scan algorithms to characterise the assembly and locate the approximate location of peak photonic output, resulting in multiple gradient searches to precisely identify the global optimum. The components can then be guided into perfect alignment using specialised piezo nanopositioners that can adjust several connections at once, in an innovative process known as active alignment. Integrated features, such as compensation factors, can eliminate the need for constant reiterative readjustment. There are now complete modular solutions available that can vastly reduce photonic device manufacturing times, while maintaining
DECEMBER/JANUARY 2024 | ELECTRONICS FOR ENGINEERS
sub-micron precision. For example, Physik Instrumente’s Fast Multichannel Photonic Alignment (FMPA) technology can perform multiple alignments in parallel, reducing assembly time by a factor of 100 or more.
Futureproofing with modular solutions
The photonics market is moving at great pace, and the number of sectors using this technology is predicted to rapidly grow over the next decade. These devices could soon contain hundreds, or thousands, of individual components and connections that require parallel optimisation, making active alignment the only choice for manufacturers to keep up with production demands. Moreover, as photonic devices continue to be adopted by more sectors, increasingly specialised devices are being developed, each of which necessitates a bespoke production process. Flexible combinations of hardware and software that can easily be reconfigured are needed by manufacturers wishing to retain a competitive edge and flexibly adapt to future demands. This is where modular alignment solutions undeniably excel, offering the flexibility and scalability needed for production operations to keep up with market demand and position themselves for continued success.
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