It has been quite some time since the motion control industry has seen an emerging market demand new motion technology. While the semiconductor industry continues to drive the performance of existing technology, the telecommunications industry has driven the need for completely new technology to support fiber optic applications. The emergence of fiber optics has not only created a need for repackaged products, but more importantly, a need for new operating characteristics of drives.
As the telecommunications industry looks to develop fiber optic networks and digital switches across the US and the world, there are an abundance of motion control applications in the manufacture of MEMs, optical components, and the integration of fiber optic wire to various components. In the manufacture of these components, some unique motion requirements involve exceptionally high position resolution and absolute stability.
Align and Attach
A fiber optic network depends on the ability to attach small diameter (as small as 5 microns) glass fiber to components such as laser diodes, attenuators, couplers, and other devices. In manufacturing these components, the process requires the ability to provide light through the fiber optic cable and measure the percentage of alignment. With an objective to get as high a percentage as possible, misalignment of light causes back-reflections and limited signal capacity that slows or corrupts a transmitted signal.
Alignment systems must have the ability to move the fiber (or component) in increments of 50 to 100 nanometers, to generate the proper alignment, and then remain absolutely stable during an attachment process. Whether the alignment is to a laser diode or other component, the device is tested, light is measured, and ultimately secured. These requirements have created the need for motion systems to integrate drives that can not only move with high resolution, but eliminate the traditional servo dither (or hunting).
Component Manufacturing
Separate from the alignment applications, there is a host of applications from placing a chamfer on a fiber for ferrule insertion, to mirror assemblies used in switches. These applications have very similar motion requirements, as small incremental steps are necessary to calibrate and set directional mirrors. Once set, there is a time-consuming process to fix the mirror in place, often between 6 to 10 minutes. During this process, the positioning system must be absolutely stable.
New Motion Technology
The nature of these applications precludes the use of rotary step and servo motor, as couplings drive screws make it virtually impossible to transmit very small moves. Brushless linear motors have been applied in these types of applications, but typically require an encoder resolution of 20nm or less to avoid the effects of servo dither. A newer and more appropriate drive mechanism, based on piezo elements, provides excellent performance characteristics and can be easily applied to linear and rotary motion stages.
Piezo devices from manufacturers such as EDO, Burleigh, or Nanomotion, based on traditional or a reversed piezo effect, provide exceptional resolution and the ability to hold position, without servo dither. Several piezo drives could be considered friction drives, as they push or force a linear or rotary device. As a 'friction' drive, they possess the stability to hold position in a vertical or horizontal position while an attachment process takes place.
The "Photonics Series" from Bayside Motion Group, illustrated here, features a family of linear and rotary positioning devices designed specifically for high resolution/position stable fiber optic applications.
These stages are used for fiber alignment of laser diodes, manufacture of MEMs, and the manufacture/calibration of mirrors, used in optical network switches
The Motion System
While the drive mechanisms require unique characteristics, the overall motion system must have the ability to move in extremely small increments. Actuating a stage in 50nm to 100nm increments is no trivial task and there are few bearing structures that provide the stiffness and smoothness to achieve this. Today's air bearing technology certainly has the operating characteristics to support the motion requirements; however, most fiber optic applications dictate exceptionally small work areas. Air bearings depend on a large puck size to provide bearing stiffness, making it too large and bulky for the majority of applications.
Crossed rollers, providing high stiffness with very low friction, can be made suitable for these applications. While traditional mechanical bearing stages face issues related to the bearing roundness and compliance, which would limit the ability to move in such small increments, Bayside's closely matched hollow rollers and patented Autoflex preload provides the bearing smoothness necessary to make such small moves.
Crossed roller bearing stage, as illustrated, can be packaged in an exceptionally small operating envelope, integrating the necessary feedback and drive technology to support fiber optic applications. While some applications require travels of 50mm to 100mm for load and unload positions, the majority of work is done in a very small area. The assembly shown provides 5mm travel in X/Y and Z directions with 50nm resolution and the ability to repeat position to 100 nanometers.
In addition to the mechanical motion system, the testing process of fiber optic components often dictates that the motion controller have a network interface for data acquisition. This requires the motion controller to support TCPIP or GPIB interfaces to receive and transmit data, to support SPC in the test process, particularly in 'young' fiber optic processes that are faced with high failure rates. As well as the network interface, the controls are often integrated into 19 in. racks that support the entire test equipment necessary for testing the fiber optic components. This requires high end motion controllers to be packaged in 3U formats, housed in a 19 in. rack.
Summary
As the telecommunications industry continues to drive the use of optical networks, the need for fiber optic components continues to grow. At present, the manufacturing technologies and capacities are insufficient to produce the required components. The fiber optic companies need to convert previous manual processes to automated processes with the ability to produce a high volume of components.
It is doubtful that the future applications will continue to push the resolution much further than the present needs. But as testing processes improve in efficiency and manufacturing processes mature, it is expected that the same motion characteristics will be required, at higher speeds. Ultimately, the name of the game is throughput.
