Optimized Mechatronics for Silicon Photonics Alignments

By Justin Bressi
Aerotech, Inc.

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In the rapidly growing realm of silicon photonics, precision alignment of optical components is a crucial part of the fabrication process. If a fiber-optic component is misaligned, this misalignment can prevent the device from functioning properly. Signal strength can be reduced by multiple dBs with just a single micron of misalignment, so having equipment capable of quickly and consistently performing high-precision alignments is critical for manufacturers of fiber optics and silicon photonics devices. Linear alignments are typically the most crucial in these processes, but angular alignment precision can also be very important.

When performing these alignments, a wide variety of precision motion control products can be used with varying levels of performance and capabilities. For lower precision applications and applications with low throughput requirements, manual positioners are often used. For higher precision alignment applications, motorized stages are commonplace, including hexapods, piezo-drive stages, ball-screw driven stages, and direct-drive stages. Combinations of these types of mechanical stages are also used. The optimal system type is often highly dependent on the requirements and acceptable error tolerances of the application, as well as the available error budget for a system.

For the most demanding applications, a linear motor or piezo-based system is typically the best solution because of the kinematic structure of the system. The serialized kinematics of a linear motor or piezo-based system allow for single nanometer minimum incremental linear motion in a specific axis direction with very limited angular and off-axis errors. With a parallel kinematic system such as a hexapod, making such small steps becomes much more challenging because errors are being introduced by all axes of the system rather than just the desired axis of motion. For many applications parallel kinematic systems may be the ideal solution, but in the case of applications requiring single nanometer step sizes with minimal off-axis error, a direct-drive or piezo-driven solution will typically achieve the highest levels of performance.

Fiber Max HP

One such solution for the most demanding applications is Aerotech’s FiberMaxHP, based on their award-winning ANT stages - the flagship product in Aerotech’s family of direct-drive servomotor nanopositioners. The FiberMaxHP platform, available in various configurations ranging from 3D linear motion in a ZXY stack to a 6 degrees-of-freedom ZXYTPR system, is designed specifically with the most demanding alignment applications in mind. Simultaneously capable of both 2 nanometer minimum incremental steps and speeds in the hundreds of millimeters per second over a 50 mm x 50 mm x 3 mm linear travel envelope, the FiberMaxHP is ready to meet the demands of any alignment application. Axes are modular and customizable such that different parts of the motion platform can be configured into separate assemblies depending on the requirements of the alignment process. For example, a 6 DOF system can be built as a single assembly with a single coincident center of rotation, or a 3 DOF ZXY assembly can be constructed next to a tip/tilt assembly to allow for independent movement of the components being aligned. This flexibility allows the FiberMaxHP to adapt to the requirements of virtually any alignment process. The FiberMaxHP can also be customized to accommodate larger travel ranges for applications that need an expanded work envelope.

For applications requiring micron-level travels in a smaller package size, Aerotech also offers piezo-based solutions, such as the QNP-XY stage and the QNP2-XYA stage with a centered aperture. These stages can achieve up to 0.007% linearity over full range of travel, single nanometer step sizes, and have off-axis errors of less than 10 nm. Aerotech’s powerful A3200 controller can simultaneously control piezo stages and linear-motor-based systems, making it the perfect solution for an application requiring both types of axes.

The A3200 controller comes packaged with a variety of tools built specifically to increase the throughput of high-precision alignment processes. The fiber alignment algorithms included with the A3200 controller make programming automatic first-light and optimization alignments an extremely streamlined process and can eliminate weeks of programming and setup time. By configuring a few predetermined parameters, the fiber alignment algorithms can be utilized to meet the specific needs of a particular alignment application without the hassle of manually programming hundreds of lines of code. Aerotech’s fiber alignment algorithms employ an analog feedback signal to measure the signal power associated with a given position of the motion system, and use this information to automatically determine the optimized position to eliminate coupling power loss. This allows the system to automatically align optical components in seconds, a process that can take significantly longer using other methods.

Virtual Pivot Point -Hi Res
Another valuable feature of the A3200 controller is its ability to utilize a virtual pivot point during positioning. By using pre-configured kinematic transformations native to the A3200 controller, a user can define offsets and relative axis positioning and then send commands in virtual polar coordinates. When a command is sent in the virtual coordinate system, the controller automatically determines which axes need to move in order for the system to pivot around the defined virtual point. This is extremely helpful when performing angular alignments because it allows the user to keep a specific point of their component in the same place while rotating about that point. Using the kinematic transformations with the alignment algorithms allows the user to perform complex multi-channel alignments. Once the first channel is aligned, a virtual pivot-point can be defined so that this channel remains in place while the system moves angularly to align the rest of the channels.

When combined with a 6 DOF system such as the FiberMaxHP, Aerotech’s A3200 controller is capable of performing complex nanometer-level photonics alignments in mere seconds. Available customization of the hardware and software platforms allows Aerotech systems to adapt to the specific needs of any alignment application. Regardless of the application challenges, Aerotech’s motion systems are up to the task.

For videos of these alignment algorithms and virtual pivot point in action, please visit /product-catalog/industry-solutions/fiber-optics/fibermaxhp.aspx. For more information on the programming and implementation of Aerotech’s alignment algorithms in the A3200 control platform, go to /industries-and-applications/fiber-optics-and-silicon-photonics/fiber-and-photonics-alignment-algorithms.aspx. For more general information about Aerotech’s alignment system capabilities and other inquiries, please visit our website at www.aerotech.com, or call 1.412.963.7470.

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