Category: Manufacturing

Products Used:

• LabVIEW 6i


• NI PCI-6503 Digital I/O card


• NI PCI-GPIB card


• NI PCI-CAN card


• NI PCI 7344 Motion Control card

Challenge: Technicians, using micrometer driven stages, were manually aligning lasers to fibers. This process took 90 minutes and occasionally the technician could not align the laser and fiber at all. The challenge was to automate alignment and reduce alignment time by a factor of 10.

Solution: Emergent developed an automated precision alignment solution featuring an intuitive pull-down menu-driven front panel that integrated the customer's existing motorized stages and instrumentation. The software reduced the alignment time to 3 minutes, far exceeding design goals. The program also stores the alignment and power data to disk for post processing analysis.

Searching for Light -- the Challenge

The recent growth of the fiber optics industry has been phenomenal. Glass fiber cables are being laid on seabeds across the oceans to residential doorsteps. This has ignited an exponential growth in demand for components to support this expanding glass network.

One of the key components of this infrastructure is the laser to fiber assembly, or pigtail, as it is referred to in the industry. (The picture shows glass fibers yet to be aligned to lasers.) When producing these assemblies it is essential that the fiber be aligned exactly at the laser's focal point for transmission of maximum optical power and to minimize signal loss. The fibers range in size from four microns (4 millionths of a meter) to a few hundred microns, smaller in diameter than a human hair. Because of the incredibly small size of these fibers, aligning them to lasers has been compared to trying to find a few specific blades of grass on a football field. Engineers and scientists have been aligning pigtails in the laboratory by hand using micrometers for several years. However, it is a time consuming, laborious process, which does not lend itself to high volume production.

Searching for Light -- the Solution

A leading manufacturer of electro-optical components had to improve its production throughput capabilities to meet customer demands. Using their existing techniques, technicians were producing about five assemblies per day, provided, that is, when they could achieve alignment.

Emergent Information Technologies, Inc. was contracted to develop an automated alignment solution for the customer's pigtail production line. There were two steps to this process. The first was to correctly position the fiber in a retaining ferule as part of a pre-alignment process. The next step was to position the pre-aligned fiber assembly at the laser's focal point. This required movement in the vertical, lateral, and along the optical axes. This second process, an alignment that required movement in three axes, was taking technicians, as stated above, up to 90 minutes to complete, and they were not always successful in aligning the devices.

For the pre-alignment phase of the assembly, Emergent used the NI PCI 7344 Motion Control Card to control; a commercial, off the shelf amplifier; and servo motor stage. The LabVIEW application gave the user a pop-up control panel that allowed intuitive submicron control of the positioning process. This automated approach dramatically improved pre-alignment accuracy and repeatability. Pre-alignment user interface is pictured here.

To automate the laser fiber alignment phase of the assembly process, Emergent developed a system to control three micro-stepper motor driven stages and two piezoelectric stages. The National Instruments hardware consisted of a PCI CAN Bus Card, a PCI GPIB Card, and a PCI DIO Card. Emergent's LabVIEW software featured a multi-tiered menu-driven user interface. When started, the software presents the user with a single menu pull-down with three menu options: auto align, supervisor, and exit. The auto align option automatically sequences through the steps to align pigtail assemblies. The software prompts the operator to mount the laser and fiber on the stages, controls the laser, monitors the laser power meter, aligns the fiber in front of the laser, separates the stages for adhesive application, repositions the fiber at the peak power position, and prompts the operator to remove the assembly after the adhesive has cured. (The pictures show two steps in the automated aligmnent process.)

Using the manual system, the technician had to record the laser identification, serial number, laser power, coupling loss, and alignment position by hand. Then another person, doing data entry, entered it into a database. The Emergent's automated system stores all the information directly into the database, saving up to 10 minutes per assembly and eliminating the possibility of errors in the data.

When the supervisor mode is selected, a dialog box pops up and prompts the user for a password. After successfully logging into the supervisor mode, it offers the user three menu bar pull-downs featuring utilities for homing and moving the stages, laser and power meter control functions, several alignment options, and the auto align function.

All laser alignment systems must define a region of interest to search for the laser power. These regions are scanned using a variety of search methods. Several of the popular methods utilize raster or spiral searches or variations of the two. These methods spend much of the scan time searching areas where there is not any light. Other algorithms find power and search for a peak; this search method is prone to find false and lower power peaks rather than the peak focal point power. For this project Emergent developed a Modified Raster Algorithm that greatly reduced search times, ignored false laser low power peaks, and found the true peak laser power focal point without scanning areas devoid of any laser light. (Picture shows automated X and Z plot of laser power.)

Searching for Light -- the Results

Emergent's alignment solution yielded not only a 30 fold reduction in alignment time, it also produced an improvement in pre-alignment accuracy, and thereby optical coupling, by a factor of 28. The automated data storage routine eliminated an additional 10 minutes of overhead time and removed the possibility of transcription errors.

The manual pre-alignment of the fiber in the ferule was producing an error of up to 7 microns off the desired position. The automated Emergent solution consistently produced assemblies with less than 0.5 microns (500 nanometers) from the peak power position.

Finally, the automated pigtail alignment system eliminated the occurrences of the pigtails that could not be aligned by hand. The benefits were achieved by making expert use of the inherent connectivity and scalability of the NI hardware and software. The customer has since proceeded with automating several other alignment and test processes, and continues to build on the LabVIEW platform using other National Instruments components.