Crossing Waveguides in Silicon-Based Optical Devices

Jimmy Yin


Moore’s Law states that silicon chip performance will double approximately every 18 months. However, as transistor size approaches the physical limits of fabrication, researchers are looking into photonic integrated circuits as the new path forward. Silicon waveguide crosses are an essential component for high-density photonic integrated circuits. The crosses must be highly compact, yet highly efficient. Previous works have proposed low insertion loss and low crosstalk waveguide crossings, however, the crosses remain relatively large at 6x6 microns. A new proposal discussed a waveguide crossing where insertion loss and crosstalk remain low, but the size is greatly reduced to 1x1 microns. The size reduction is achieved by a small, lens-like structure at each terminal of every cross. While simulations show an insertion loss less than 0.18dB and crosstalk less than -30dB, fabricated crosses have not been tested in a laboratory setting. This research attempts to fabricate the proposed devices on a silicon chip using electron beam lithography and take crosstalk and insertion loss measurements. Measurements were performed using a test setup composed of three stages capable of five axis manipulation for fiber and chip alignment, two lens tapered fibers for coupling light onto the chip, a polarization rotator to control polarization of the input light, a tunable light source producing 1550nm light, and an optical spectrum analyzer for measuring power. Insertion loss was measured by using the cutback method, comparing straight waveguides consisting of varying number of waveguide crossings. Preliminary results show an approximate 0.52 dB insertion loss per crossing. The higher than expected loss compared to simulation is likely due to deviations in the lens dimensions related to proximity effect, common to e-beam lithography. Continued work will focus on gathering more data from the current fabricated devices and fabricating additional devices that account for the proximity effect.


Crossing Waveguides; Silicon; Insertion Loss

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