ecent advancements in pla-nar optics technology , specifi-cally in the area of optical splitters, switches, modula-tors, and wavelength-divi-sion multiplexers, are driving demand for immediate increas in production
throughput, consistency, and yield.Simultaneously, price pressures on the components are forcing drastic reductions in asmbly and test costs,which still reprent one of the largest portions of the overall packaged com-ponent cost.
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asmble becau
•multiple input and output channels;••in handling.
potential to achieve both improved throughput and enhanced yield—by reducing cycle times, eliminating opera-
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tor dependence, and implementing the statistical process measurement, control,and improvement capabilities required to achieve high-reliability components.The factors provide the highest lever-age for reducing device asmbly costs.Until recently , there has been very little
academic or commercial rearch in the ment efforts funded by the Defen Advanced Rearch Projects Agency or other defen organizations, e.g., differ-ent defen organizations’ Manufactur-ing Technology (MANTECH ) programs,have had a strong military-applications focus, resulting in negligible transfer to
the commercial ctor. More recently , the Take the guesswork out of planar optics pigtailing
R
8, while N designates the number of output channels, which can vary from 1 to 64, depending on the application. UV or thermally curing epoxy is normally ud to bond the components together.
Reprinted from the February 1998 edition of LIGHTWA VE
Copyright 1998 by PennWell
manufacturing as a critical area that could benefit from more-explicit govern-ment funding under the Advanced T echnology Program.
Having identified this lack of basic rearch into photonics packaging automation, Newport Corp. has teamed with veral leading rearch programs at the University of Maryland to more intenly analyze—and subquently optimize—automation algorithms and process for aligning and bonding fibers and fiber arrays to planar optical elements. This work brings together the National Science Foundation-sponsored Center for Opto-Electronic Devices,Interconnects, and Packaging and Newport’s Photonics Packaging Automation Div . in an effort to acceler-ate the fundamental process rearch required to develop and deploy success-ful commercial automation systems.Recently completed rearch has resulted in a fully documented align-ment and bonding process flow for 1 ×N and M ×N waveguide structures (e Fig. 2). Included in the rearch were the development, testing, and automation of advanced optical alignment algorithms and quencing software, which result-ed in extremely reproducible, operator-independent “align-and-attach” process control. Typical load-to-unload asm-bly cycle times on a 1 ×8 fud silica splitter, using pre-asmbled V-groove fiber arrays and ultraviolet (UV) curing epoxy , were under 15 min. Furthermore,the process automation programs have already been implemented on com-mercially available asmbly automa-tion platforms, demonstrating a very rapid product development cycle (e photo).
The asmbly automation process
The asmbly process has been divided into nine discrete steps:
炮手燃魂•Input power measurement—Before you inrt the actual device, you must mea-sure initial power throughput on all input fibers for later reference in quan-tifying inrtion loss, validating opti-mum alignment, or qualifying compo-nent performance. This is typically done using a 90/10 splitter from the
reference source to normalize measure-ments against noi and input source variations.•Device loading—Reproducible, damage-free inrtion of the fibers and fiber arrays and waveguide chips can be accomplished through the u of preci-sion device tooling and high-magnifi-cation video feedback. Spring-loaded or pneumatically controlled grippers work best in bonding applications becau they hold the devices more curely during critical bonding process.•Initial light throughput—In many pla-nar optic structures, more light will propagate through the substrate layers than through the waveguides them-lves if they are misaligned.Therefore, it is often necessary to qual-ify initial light-launch conditions by end-on viewing of the waveguide out-puts to validate proper alignment of the input fiber(s) to the device.•Coar alignment—Coar alignment only requires about 50 nW of through-put to start. This process is defined as the optimization of one of the M input channels and one of the N output chan-nels in x , y , and z directions, to a pa-ration distance of ap
proximately 100microns between the fibers and the waveguide. (Typically the process begins at about 500-micron parations between components.) This is achieved
through a rapid quence of profiling scans, two-dimensional (x-y ), and three-dimensional (x-y-z ) alignment
optimization subroutines. This ensures sufficient coupling to perform sub-quent fine-adjustment and “roll” (Θz )alignment process.
•Alignment optimization—In this quence,fine alignment is completed for one input and one output fiber, followed by coar and fine roll alignments, and finally , fine adjustment of the z -axis positions. This process typically results in parations of less than 10 microns at
fully optimized alignment, depending on the mode-mismatch of the fibers and waveguides. In many cas, index-matching gel or the specified adhesive will be applied during this process to
minimize backreflections and Fabry-Perot interference between the mating surfaces. The effects can often be en, even where the surfaces have been angle-polished to reduce their effects. In addition, the ur may
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choo between having the alignment optimized on one of the channels, or balancing the power among the vari-ous channels by eking a best-fit posi-tion that maximizes throughput while minimizing variations.•Pre-bonding metrology—Before bond
curing is done, a wide variety of
bonding of planar waveguide components. The exact alignment algorithms, adhesive lec-tion, curing parameters, and process quences are highly device- and substrate-material-dependent, but are easily changed or optimized by automation software.
metrology tests can be performed using the automation features of the system. For example, the light throughput on each output channel (channel uniformity) can be measured simply by jogging one of the output fibers (which are connected to the power meter) from one channel to the next. This step-and-read measurement quence is easy to automate and can be programmed for any waveguide paration. All motions and positions are bidirectionally reproducible to less than 50 nm and can be quenced in any order to avoid damage to the devices. Software compensation can also be ud to adjust for angled edges or tilted components.
•Bonding—If adhesive has not already been applied, it is injected via a time-puld or positive-displacement adhe-sive dispenr. Adjustable hard-stops control the position of the epoxy syringe. Calibrated UV radiation is delivered via dual fiber-optic illumina-tors; the delivery of radiation can be programmed for variable intensity during the curing cycle. Both commer-cial-grade and ur-proprietary optical adhesives can be accommodated. For example, Newport has developed bonding process quences for fud silica waveguides (using commercial-grade UV adhesives) that reproducibly achieve extremely small (less than 0.1-dB) curing shifts. Thermally activated device tooling can also be incorporat-ed; however, thermal curing adds sub-stantial time to the overall process cycle. Alignment re-optimization dur-ing the curing cycle is an available fea-ture, although this is typically only required during prolonged thermal curing cycles.
•Post-bonding metrology—After the bond has cured and cooled (about 2 to 5 min for many UV adhesives), final throughput measurements are made to quantify bond shift and validate device quality . All measurements and process results are automatically logged and can be transferred to ur databas via an Ethernet connection.
•Unloading—One of the most expensive yield points is device unloading.Breaking a device or fiber at this point
consumes about 90% of all the added value. Proper tooling and ergonomics (e.g., large access areas for the operator)can facilitate damage-free removal of the asmbly .
Key rearch factors
Although at first glance this asmbly process may em fairly straightfor-ward, many critical elements were investigated to arrive at a widely applicable process that could be com-mercially deployed.
First, the alignment optimization quence compris many parameters and process choices. Developing an optimum formula of scanning, profil-ing, gradient arch, and other numer-ic alignme
nt methods, along with understanding the basic trade-off between process parameter lection,cycle time, and reliability , was no triv-ial task. The software platform ud in this rearch (e Fig. 3) enabled fast testing and validation of different tech-niques, and also permitted easy pro-gramming and asmbling of process subroutines to facilitate test program development.
Second, veral completely new align-ment techniques were developed from
女友生日祝福语the insights gained during the rearch.Among the are multiple approaches to optimizing Θz roll alignment (multiple scanning techniques and adaptive algo-rithm optimization), and channel-bal-ance methods for minimizing through-put variations between channels.
Finally , the company had to develop a comprehensive nomenclature for all device components, channel designa-tions, process variables, and pre-t automation quence positions. Using the, any new ur can fully under-stand the process automation quence and easily manipulate it to suit new applications or device technologies.Future work
In addition to rearching alignment and bonding process, we continue to study veral other key areas of hard-ware and software development that are also critical to a successful automa-tion system solution. The areas include
•vision-aided positioning and gauging (onboard calibrated optical measure-ment),长干寺
•implementation of onboard wavelength testing metrology
,
Automation advances have already begun to appear in commercial systems. The wave-guide workstation automation platform shown here provides complete alignment, imaging,adhesive delivery, and UV curing.
•enhanced tooling/fixturing/parts han-dling systems,•adhesive dispensing/curing process development for various materials,•automated alignment techniques and
algorithms.Rearch will continue to achieve a
more fundamental understanding of the critical asmbly and test process requirements. New techniques should continue to remove the uncertainties in photonics manufacturing and lead to the deployment of cost-effective automation solutions in the photonics industry . x Acknowledgments
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Newport Corp. gratefully acknowl-edges the contributions of our princi-pal rearchers, development
engi-neers, and project sponsors on this project: Daniel Lee and Prof. Y.J. Chen of the University of Maryland/Balti-more County; and Victor Kardos,Howard Fitzer, Gary Rangel-Friedman,James Legget, Trung Nguyen, Curtis McGinty, Nick Mangano, and Soon Jang of Newport Corp.
Randy Heyler is director of the Photonics
Packaging Automation Div. at Newport Corp., Irvine, CA. He is past president of the Lars and Electro-Optics Manufac-turers Association and currently rves as chairman for the Coalition for Photonics
and Optics.
Fig. 3. Software-bad process control systems offer comprehensive process automation and quencing control, enabling fast process optimization and reproducible automation results.心食谱
