光器件封装设计
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We address the large shortcomming in placement accuracy of microelectronic tools through precise self-alignment structures designed into the assembly.  

Our first demonstration of this direction is in a mechanically compliant polymer interface between standard single-mode fibers and nanophotonic waveguides. This concept is described here. In addition to the advantages expressed above, its compliance mechanically decouples the silicon chip from the optical connector resulting in the expectation of much improved thermo-mechanical cycling reliability than rigid connections such as direct fiber-to-chip attachment.


We will be updating this website regularly with exciting results as they can be made public.

The compliant polymer interface between standard optical fibers and nanophotonic waveguides is illustrated below. It includes a standard removal fiber interface, integrated flexible polymer waveguides, and a mechanically compliant extension interfacing with the nanophotonic die. A 12x1 MT fiber mechanical interface is shown here but other fiber connector standards could be used as well. In the MT standard, the large holes in the compliant interface interact mechanically with matching metal pins to provide self-alignment between fibers and mode-matched polymer waveguides. 

 

Silicon Nanophotonic Packaging


Concept

The compliant polymer interface between standard optical fibers and nanophotonic waveguides is illustrated below. It includes a standard removal fiber interface, integrated flexible polymer waveguides, and a mechanically compliant extension interfacing with the nanophotonic die. A 12x1 MT fiber mechanical interface is shown here but other fiber connector standards could be used as well. In the MT standard, the large holes in the compliant interface interact mechanically with matching metal pins to provide self-alignment between fibers and mode-matched polymer waveguides. 

The optical path in the compliant interface is drawn below. Standard single-mode optical fibers are butt-coupled to mode-matched polymer waveguides. The cross-section of the polymer waveguide is then adiabatically transformed from a fiber coupler to a higher confinement waveguide for routing. The routing in the compliant interface can be in principle arbitrary. A simple pitch conversion is shown here but more involved schemes including 90 degree bent die interface and port shuffles are possible. The polymer waveguides are then adiabatically coupled to nanophotonic waveguides on the photonic die. 

 

The compliant interface can be assembled to nanophotonic dies using standard high-volume, low-cost microelectronic packaging equipment. To bridge the gap between the typical +/- 10 um accuracy of high-throughput pick and place tools and the required +/- 2 um accuracy for optimal optical perfromance, we use matching sets of lithographycally defined self-alignment structures as shown in the cross-sectional sketch below. Alignment ridges are defined on the compliant interface with matching slanted grooves on the nanophotonic die. 

 

Implementation

Our first implementation of the compliant interface is shown below. It employs a flexible polymer ribbon with lithographically defined waveguides assembled to an injection-molded ferrule to create a standardized interface to single-mode optical fibers. A ferrule lid is also employed to symmetrize the thermo-mechanical properties at the fiber interface. 

 

The ferrule and the polymer ribbon are assembled first. Matching self-alignment structures are precisely defined on the injection-molded ferrule and the lithographically patterned polymer ribbon. These allow for accurate alignment between ribbon and ferrule with low-accuracy, high-throuput assembly tools. Accurate alignment between the ferrule and the ribbon is required for accurate alignment between the polymer waveguides and optical fibers as the fiber connector alignment structures are located on the ferrule while the waveguides are on the ribbon.

Once the ferrule lid is placed and the ferrule/ribbon/lid assembly front-polished to MT specifications, the compliant interface is assembled to a nanophotonic die using standard microelectronic tools as part of a typical microelectronic chip packaging flow. 


 

Demonstration

Pictures of the compliant interface and of an assembly to a silicon nanophotonic chip are shown below.

 

Our self-alignment strategy is central to the low-cost manufacturability of the compliant interface. Hence, this was our first focus of experimental demonstration. We have reported at ECTC 2014 that we achieve self-alignment to 1-2 um accuracy while starting from +/- 10 um purposeful misalignment. Hence, the self alignment structures provide the required alignment for optimal optical perfromance (+/- 2 um) despite large initial misalignment (+/- 10 um) corresponding to the accuracy of standard high-throughput pick and place tools.

Additionally, we have recently published a comprehensive feasibility study of the optical perfromance of the compliant interface. We have performed an exhaustive tolerance analysis using real-word fabrication and assembly uncertainties consitent with low-cost manufacturing. We found that the full optical loss from fiber to integrated silicon nanophotonic waveguide are expected to fall between 1.0 and 2.9 dB for all polarizations (depending on fabrication, assembly, and propagation loss). The optical bandwidth of the structure is very large with a wavelength sensitivity not exceeding a 0.1 dB penalty over a 200 nm bandwidth centered at 1.55 um. We have acquired experimental optical data of full assemblies and will report on this soon.



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