David Kudzuma

Integrated waveguide micro-optic elements for 3D routing in board-level optical interconnects

Planar waveguides and embedded microelements such as 45o vertical mirrors, lateral mirrors, bends, and microlenses comprise main building blocks of the waveguide-based optical printed circuit boards (PCB) for board-level optical interconnects (OI). These microelements enable a variety of three dimensional (3D) routing architectures which are required to support high density interconnects in optical boards. Optical polymers have proved to be the materials of choice for large-scale OI modules with propagation dimensions exceeding 100 mm. In order to meet the loss budget available for the integrated OI modules, the polymers are expected to have optical losses less than 0.05 dB/cm. Both channel and slab waveguides can be used to transmit the signals between the input and output ports. In the case of channel waveguides, the critical issues are the waveguide core shaping, propagation losses and ability to form various passive elements such as bends, crossings and reflective mirrors. In the case of slab waveguides, two dimensional waveguide microlenses have to be designed to collimate the light beams for propagation at longer distances with the controllable beam divergences. The 45o micromirrors can be used to couple the light signal in and out of the waveguiding layer and enable 3D routing of the optical signal in the waveguiding layers. In this work, we present the experimental and computational results on the development of different waveguide devices and microelements for the board level OI.

Hybrid integration of optical modules for planar deflector switches

Nonblocking crossconnect photonic switches based on light beam deflection require planar optical modules with hybrid integration of active deflector chips. In this work we present optical modules with two dimensional silica microlens arrays and slab waveguides fabricated on silicon substrates. The 1.55 μm light is launched in the input microlens array, which collimates parallel beams propagating along the module. The slab waveguide vertically confines the light. The output microlenses focus the beams laterally into output fibers. Two chips are inserted in the light path after the input microlens and before the output microlens arrays. The input and output microlenses allow propagation of the light beams through modules up to 100 mm long with a beam width of less than 400 μm. A hybrid integration process flow is developed to place the deflector chips in the light path with high alignment accuracy. The chips are flip-chip bonded to the substrate with submicron accuracy in the vertical positioning. Various contributions can lead to the chip displacements such as, for example, standoff island height variations, aligner tolerances, substrate bow, etc. Experiments are conducted to evaluate the effect of chip displacement on the insertion losses of the hybrid-integrated modules. 100-mm long optical modules with input and output chips are fabricated with less than 4 dB insertion losses. The analysis of loss contributions and possibilities for improvements are discussed.