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Silicon erasable waveguides and directional couplers by germanium ion implantation for configurable photonic circuits

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A novel technique for realization of configurable/one-time programmable (OTP) silicon photonic circuits is presented. Once the proposed photonic circuit is programmed, its signal routing is retained without the need for additional power consumption. This technology can potentially enable a multi-purpose design of photonic chips for a range of different applications and performance requirements, as it can be programmed for each specific application after chip fabrication. Therefore, the production costs per chip can be reduced because of the increase in production volume, and rapid prototyping of new photonic circuits is enabled. Essential building blocks for the configurable circuits in the form of erasable directional couplers (DCs) were designed and fabricated, using ion implanted waveguides. We demonstrate permanent switching of optical signals between the drop port and through the port of the DCs using a localized post-fabrication laser annealing process. Proof-of-principle demonstrators in the form of generic 1×4 and 2×2 programmable switching circuits were fabricated and subsequently programmed.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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Figures (6)

Fig. 1.
Fig. 1. Structures of the implanted waveguides (WGs) and DCs. (a) Cross sectional view of the erasable DC with a conventional rib waveguide and an ion implanted waveguide. (b) Simulation result for the Ge implanted process using the Silvaco software, the density of damage to the crystal lattice is shown in the figure. (c) Illustration of the single-stage DC. (d) Illustration of the two-stage DC. Optical microscope images of (e) a fabricated single-stage DC and (f) a two-stage DC on a SOI wafer.
Fig. 2.
Fig. 2. (a) Calculated fundamental optical mode for the 500 nm wide silicon waveguide. (b) Calculated fundamental optical mode for the 560 nm wide germanium implanted silicon waveguide. (c) Top view of the simulation result for the optimized two-stage directional coupler.
Fig. 3.
Fig. 3. Measured propagation losses of the implanted waveguides. A linear dotted line was fitted to each device group measured. Each device group includes waveguides from the same silicon chip. The corresponding function equations are shown in the figure. The width of the implanted waveguides are: (a) 360 nm, (b) 560 nm, (c) 760 nm, and (d) 960 nm.
Fig. 4.
Fig. 4. Measured optical transmission of the: (a) single-stage DCs with various coupling lengths, and (b) two-stage DCs with various coupling lengths. Simulated results (dotted line), with a step-index profile assumed for the implanted waveguides, are plotted as a reference. (c) SEM image of a typical opening in the implantation mask after Ge ion implantation. The original designed width of the opening is 500 nm (marked in yellow). However, the width was increased to around 620 - 660 nm after ion implantation.
Fig. 5.
Fig. 5. (a) Illustration of the laser annealing process for the two-stage DCs. (b) Measured results for the two-stage DCs with various coupling lengths after laser annealing. The original coupling length for the directional couplers used for this test are 20 μm. Simulation results (dotted line) were plotted as a reference.
Fig. 6.
Fig. 6. (a) Optical microscope images of a 1×4 programmable photonic switching circuit and (b) a 2×2 photonic switching circuit. Measurement results for the photonic switching circuits. The 1×4 photonic switching circuit was programmed by laser annealing to produce an output at one of the four ports sequentially (c, d, e and f). (c) Measured results when P1 is set to be the output port. (d) Measured results when P2 is set to be the output port. (e) Measured results when P3 is set to be the output port. (f) Measured results when P4 is set to be the output port. The 2×2 switching circuit was programmed to operate in two modes by laser annealing: (g) cross-coupling modes or, (h) through-coupling mode.
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