Ultra-Compact Power Splitters with Low Loss in Arbitrary Direction Based on Inverse Design Method

The power splitter is a device that splits the energy from an input signal into multiple outputs with equal or uneven energy. Recently, the use of algorithms to intelligently design silicon-based photonic devices has attracted widespread attention. Thus, many optimization algorithms, which are called inverse design algorithms, have been proposed. In this paper, we use the Direct Binary Search (DBS) algorithm designed with three 1 × 3 power splitters with arbitrary directions theoretically. They have any direction and can be connected to other devices in any direction, which greatly reduces the space occupied by the optical integrated circuit. Through the simulation that comes about, we are able to get the insertion loss (IL) of the device we designed to be less than 5.55 dB, 5.49 dB, and 5.32 dB, separately. Then, the wavelength is 1530–1560 nm, so it can be used in the optical communication system. To discuss the impact of the footprint on device performance, we also designed another device with the same function as the second one from the above three devices. Its IL is less than 5.40 dB. Although it occupies a larger area, it has an advantage in IL. Through the design results, three 1 × 3 power splitters can be freely combined to realize any direction, multi-channel, ultra-compact power splitters, and can be better connected with different devices to achieve different functions. At the same time, we also show an example of a combination. The IL of each port of the combined 1 × 6 power splitter is less than 8.82 dB.

Digitized subwavelength surface structure on silicon platform for wavelength-/polarization-/charge-diverse optical vortex generation

Optical vortices carrying orbital angular momentum (OAM) have recently attracted increasing interest for providing an additional degree of freedom for capacity scaling in optical communications. The optical vortex generator is an essential component to facilitate OAM-enabled optical communications. Traditional devices face challenges of limited compactness, narrow bandwidth and first-order OAM modes. Here, using the direct-binary search (DBS) optimization algorithm, we design, fabricate and demonstrate a digitized subwavelength surface structure on silicon platform for wavelength-/polarization-/charge-diverse optical vortex generation. It features an ultra-compact footprint (~3.6×3.6 μm 2 ) and ultra-wide bandwidth (1480-1630 nm), supporting two polarizations and high-order OAM modes (OAM +1 , OAM -1 , OAM +2 , OAM -2 ) with high purity of ~90%. The mode crosstalk matrix is measured in the experiment with favorable performance. When generating x-pol. OAM +1 , x-pol. OAM -1 , y-pol. OAM +1 and y-pol. OAM -1 , the crosstalk of the worst case is less than -14 dB. When generating OAM +1 , OAM -1 , OAM +2 and OAM -2 , the crosstalk between any two OAM modes is less than -10 dB, and the lowest crosstalk is about -17 dB. The wavelength-/polarization-/charge-diverse optical vortex generator enables the full access of multiple physical dimensions (wavelength, polarization, space) of lightwaves. The demonstrations may open up new perspectives for chip-scale solutions to multi-dimensional multiplexing optical communications.