Erasable diffractive grating couplers in silicon on insulator for wafer scale testing

Abstract

Test points are essential in allowing optical circuits on a wafer to be autonomously tested after selected manufacturing steps, hence allowing poor performance or device failures to be detected early and to be either repaired using direct write methods, or a cessation of further processing to reduce fabrication costs.Grating couplers are a commonly used method for efficiently coupling light from an optical fibre to a silicon waveguide. They are relatively easy to fabricate and they allow light to be coupled into/out from any location on the device without the need for polishing, making them good candidates for an optical test point.A fixed test point can be added for this purpose, although traditionally these grating devices are fabricated by etching the silicon waveguide, and hence this permanently adds loss and leads to a poor performing device when placed into use after testing. We demonstrate a similar device utilising a refractive index change induced by lattice disorder. Raman data collected suggests this lattice damage is reversible, allowing a laser to subsequently erase the grating coupler.

Drive-noise tolerant optical switching inspired by composite pulses

“…Options to achieve this include weakly coupled integrated detectors, "taps" to route some of the light to external detectors or frequency selective Bragg gratings [62]. To avoid increased losses, these taps could be made using a process which allows for them to be removed [63]. Alternatively, a modular construction [64,65] would allow for each stage to be calibrated individually.…”

Ge Ion Implanted Photonic Devices and Annealing for Emerging Applications

“…Results from our previous study revealed that the difference in residual insertion loss between the crystalline silicon and annealed silicon devices is negligible. The resultant peak concentration of Ge ions in the silicon waveguides is less than 0.3%, compared with a silicon concentration in the same volume [18,34,45,50], indicating that the creation of a SiGe alloy is not a concern.…”

“…The ion implantation process was carried out at the Ion Beam Centre at the University of Surrey. An ion energy value of 130 keV and a dose of 1 × 10 15 ions/cm 2 were used in order to efficiently implant Ge into silicon and create deeper implantation in the silicon waveguides, based on our previous studies [50].…”

“…The implanted sections of these devices can be annealed by laser or electrical heaters, with the latter being a more feasible choice for commercial silicon photonic chips with high volume production and large-scale integration, as thermal heaters can be activated even in packaged devices. Tapers with a length of at least 700 µm are required for each erasable grating coupler, to minimise residual loss after annealing and to facilitate straightforward alignment within a commercial wafer prober, whereas erasable directional couplers can be much smaller [50]. A smaller insertion loss should be potentially achieved if a shorter implanted waveguide is used.…”