Aligning fibers to devices demands precision

Kamran Mobarhan

As novel commercial fiberoptic components evolve, so must new techniques and machines for precise, high-volume alignment and attachment of optical fibers to devices.

For years, researchers have used a variety of micropositioning and stage subassemblies to align fibers to other fibers or to waveguide structures. Many of these applications require submicron tolerances and are typically performed on an optical table in the laboratory by a skilled engineer or research scientist. This extensive research effort has resulted in many novel fiberoptic components that are rapidly finding their way into high-volume production. The tools and techniques of alignment have evolved in response to these changing requirements of the industry.

MANUAL ALIGNMENT SUBASSEMBLIES
Planar waveguide devices constitute a significant family of fiberoptic components that requires high-precision stages for alignment of the optical fibers to the device. Planar waveguide devices can range from a simple one-by-two switch to a complex arrayed waveguide grating for multiplexing and demultiplexing applications. In the research laboratory, these waveguides are typically aligned manually with stage systems that should offer high precision, exceptional stability, and a wide variety of configurations and accessories (see Fig. 1).

One key requirement in manual stage design is the m.odularity of stage components to be able to effectively address novel fiberoptic applications. Many users of these stages demand simple components that can be used like bulidng blocks to construct complex positioning structures.

AUTOMATIC ALIGNMENTMany of the fiberoptic components used in optical telecommunication networks are some sort of passive optical waveguide structure. In this type of device, one of the key manufacturing challenges is the alignment and attachment of an optical fiber (or an array of optical fibers) to a waveguide structure. To perform this alignment and attachment process, it is crucial that the device and the fibers are held securely and moved with respect to each other along the various linear and rotational axes without incurring any damage. Safe handling of the device is not much of an issue when an experienced research scientist is developing and testing the device in the laboratory. In an industrial factory setting, however, the handling of fiberoptic components is typically the largest yield problem because optical fibers attached to fiberoptic devices are extremely fragile and quite cumbersome.

Many fiberoptic component manufacturers are still using manual techniques to assemble their products. Each time a technician must handle the device, the opportunity exists for damage or error. Compounding the problem, the typical production floor of a factory that produces passive waveguides has dozens or even hundreds of technicians working at different assembly workstations. As the number of technicians and workstations increases, the problems associated with repeatability become exponentially more complicated. When the process becomes operator dependent, manufacturing throughput and yield fall significantly.

The key to economical high-volume production of fiberoptic components is to define new automation strategies and machine platforms that minimize the influence of the operator on the process and thus facilitate repeatability. This concept can be applied to cottage-industry style factories in which hundreds of workers sit at workstations manually assembling parts, as well as to automatic machines that produce many devices per hour.

In automated systems, pneumatically actuated tweezers can be used to grip, position, and align the fibers (see Fig. 2). A specialized kinematic gripping fixture is used to hold the planar waveguide structure. In automatic assembly platforms, the gripping fixture is the interface between the device and the automatic assembly system. The adjustable and interchangeable components of this fixture allow the tool to be used with devices of various sizes. The tooling itself is also modular and can be removed from the machine and replaced with a different tooling. In this way, it is possible to have the machine reconfigured for different applications.

In many situations, such as planar waveguide device assemblies, arrays of fibers need to be aligned and attached to the waveguide. Often these arrays are encapsulated in rectangular-shaped metallic or glass fiber ferrules. The same style of machine tooling fixture can hold the fiber arrays as well as the waveguide device itself. The input fiber, the device, and the output fiber array are each held in place by a dedicated gripper fixture, which ensures precise and repeatable positioning of the components within the assembly machine platform (see Fig. 3). The fixtures holding the input and output fiber arrays are mounted on precision stages that make it possible to move the fibers with respect to the device along x, y, and z axes. It is also possible to adjust the pitch, roll, and yaw of the fiber arrays.

NEXT-GENERATION FIBER-ALIGNMENT MACHINESAutomating production to accommodate high yields with minimal interference by an operator is a critical consideration (see Fig. 4). A device designed without high-volume manufacturing in mind will not easily adapt to automated production and will become very difficult and expensive to produce in large numbers.

The time-to-market of new products in fiberoptic component manufacturing industry has accelerated and is now only a matter of months. Consequently, engineers don't have time to redesign the device, or its manufacturing process, when it is time to move the product from the laboratory to the manufacturing floor. As a result, more R&D engineers and research scientists now must consider manufacturing issues from the very beginning. Equipment suppliers that make the tools and the machines used to assemble and test fiberoptic devices are also affected by this early planning, and need to be well-positioned to provide engineering support to the manufacturer early in the design phase of the product, and to assist in their development and transition from concept, to prototype, through pilot-production, and eventually to high-volume manufacturing.

Kamran Mobarhan is marketing manager of technology and applications in the Fiber Optics and Photonics Division of Newport Corporation, 1791 Deere Avenue, Irvine, CA 92606; e-mail: [email protected].