A grand challenge in nanofabrication of large-scale photonic integrated chips is the low yield due to inevitable fabrication errors. These imperfections may sum up and degrade the chip performance. Conventionally, the as-fabricated photonic chips that fail the performance test have to be discarded, resulting in significant cost increase. One approach to compensate the fabrication errors is to introduce active and reconfigurable components. This, however, increases the device complexity and requires additional power consumption.
In this paper, Yu and coauthors propose a static control method to reset the beam splitting ratio of directional couplers, which are essential components of quantum photonic integrated chips. Their experiments demonstrate that the coupling coefficient of the directional coupler can be continuously reconstructed using a femtosecond laser secondary direct writing technique. Hence, the beam splitting ratio of imperfect devices can be reset to any desired value for several times irrespective of its initial state. Such a static control method can find intriguing applications not only in repairing the fabrication errors, but also in reconfiguring the functionalities of photonic integrate chips in both classical and quantum regimes.