Tuneable silicon photonic devices and circuits

Abstract

The commercial market for silicon photonics is growing at a rapid pace. Many optical communications companies have developed their own techniques and products based on silicon photonic platforms. The cost is one of the most important factors in industrial production. The cost spent on testing, packaging and masks, and the yield of each manufacturing process, deeply affects the overall cost of each silicon photonics chip. In this project, new methods of wafer-scale testing, post-fabrication trimming, and programmable photonic circuits are proposed, which can be utilized to decrease the cost. Several erasable and tuneable silicon photonic devices are demonstrated, including Mach– Zehnder interferometers, ring resonators and directional couplers. They are all developed by Ge ion implantation and annealing techniques. Ge ion implantation induces lattice damage and disorder in conventional silicon waveguide. The refractive index of implanted silicon waveguides, the effective index of propagating modes in these waveguides and the optical performance of devices are altered. This lattice damage can be altered afterwards via annealing processes, including laser annealing and integrated electrical annealing. The performance of implanted devices can be shifted after annealing. Based on this properties, these implanted devices can be used to realize reliable wafer-scale testing in photonic integrated circuit production. The erasable directional couplers can work as the optical input and output ports in large and complex photonic integrated circuits. The coupling efficiency can be designed from 0% to over 90% for each coupler. In order to avoid permanent parasitic loss, these optical testing points can be permanently removed from the main functional circuits after the testing. After full annealing of the implanted sections, the coupling efficiency of an implanted directional coupler dropped to -18dB or less. This residual insertion loss is negligible for optical transmission. The Ge ion implantation and annealing techniques can also be used to realize CMOS compatible post-fabrication trimming. The shift of optical performance brought by Ge ion implantation is larger than that caused by fabrication variations. The optical performance of implanted devices, such as the resonant wavelength of ring resonators and transmission of Mach–Zehnder interferometers, can be trimmed to the originally designed working points. Over one full-spectral range and 1.5� phase shift is achieved respectively for ring resonators and Mach–Zehnder interferometers in this project. The implanted Mach–Zehnder interferometers and directional couplers can act as the basic building blocks in programmable photonic circuits. The long-term power consumption and thermal crosstalk are no longer issues for programmable photonic circuits developed by Ge ion implantation and integrated electrical annealing, making programmable photonic circuits viable for production for the first time

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