Abstract
Germanium (Ge) ion implantation into silicon waveguides will induce lattice defects in the silicon, which can eventually change the crystal silicon into amorphous silicon and increase the refractive index from 3.48 to 3.96. A subsequent annealing process, either by using an external laser or integrated thermal heaters can partially or completely remove those lattice defects and gradually change the amorphous silicon back into the crystalline form and, therefore, reduce the material’s refractive index. Utilising this change in optical properties, we successfully demonstrated various erasable photonic devices. Those devices can be used to implement a flexible and commercially viable wafer-scale testing method for a silicon photonics fabrication line, which is a key technology to reduce the cost and increase the yield in production. In addition, Ge ion implantation and annealing are also demonstrated to enable post-fabrication trimming of ring resonators and Mach–Zehnder interferometers and to implement nonvolatile programmable photonic circuits.
Highlights
Silicon photonics is currently a commercially established and yet fast-growing technology for communication systems
We demonstrated that Ge ion implantation and annealing can be applied for post-fabrication trimming [34,35,36,37], with some unique advantages over other techniques, such as a large change in refractive index change and easy implementation
After fine-tuning the transmission, the working states of the directional couplers or Mach–Zehnder interferometers (MZIs) are fixed and do not need a continuous electrical power supply to retain the operating point [34]. This will greatly reduce the power consumption, compared with more traditional programmable photonic circuits, implemented with MZI arrays controlled by integrated thermal heaters [39]
Summary
Silicon photonics is currently a commercially established and yet fast-growing technology for communication systems. The optical phase error induced by the variation in waveguide dimensions across the chip will significantly change the device performance. This is one of the major factors affecting the yield of final silicon photonic modules in production [20,21]. In addition to the applications of wafer-scale testing and post-fabrication device trimming, we implemented a proof of principle of nonvolatile programmable photonic circuits with the Ge implantation technology [38]. After fine-tuning the transmission, the working states of the directional couplers or MZIs are fixed and do not need a continuous electrical power supply to retain the operating point [34] This will greatly reduce the power consumption, compared with more traditional programmable photonic circuits, implemented with MZI arrays controlled by integrated thermal heaters [39]
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