Polarization- and wavelength-agnostic nanophotonic beam splitter

Abstract

High-performance optical beam splitters are of fundamental importance for the development of advanced silicon photonics integrated circuits. However, due to the high refractive index contrast of silicon-on-insulator platforms, state-of-the-art nanophotonic splitters are hampered by trade-offs in bandwidth, polarization dependence and sensitivity to fabrication errors. Here, we present a new strategy that exploits modal engineering in slotted waveguides to overcome these limitations, enabling ultra-broadband polarization-insensitive optical power splitters with relaxed fabrication tolerances. The proposed splitter design relies on a single-mode slot waveguide that is gradually transformed into two strip waveguides by a symmetric taper, yielding equal power splitting. Based on this concept, we experimentally demonstrate −3 ± 0.5 dB polarization-independent transmission for an unprecedented 390 nm bandwidth (1260–1650 nm), even in the presence of waveguide width deviations as large as ±25 nm.

Metamaterial-Engineered Silicon Beam Splitter Fabricated with Deep UV Immersion Lithography

“…Experimental results for L MMI = 18 µm are shown in Figure 3a-c with orange solid lines. Excess losses (Figure 3a), power imbalance (Figure 3b) and phase error (Figure 3c) were determined using the asymmetric Mach-Zehnder interferometers and a reference waveguide for transmission normalization [34][35][36]. The experimental results are in good agreement with 3D FDTD simulations and confirm high device performance.…”

Scaling Up Silicon Photonic-based Accelerators: Challenges and Opportunities

“…For an input vector size of N, light passes through log 2 N splitters before modulation, resulting in a total insertion loss of 10log 10 N + EL splitter • log 2 N dB, where EL splitter is the estimated excess loss for a single splitter and ranges between 0.01 dB to 0.5 dB [42][43][44][45][46] . The estimated excess loss for beam splitters and combiners in this study is 0.01 dB.…”

High-Performance On-Chip Silicon Beamsplitter Based on Subwavelength Metamaterials for Enhanced Fabrication Tolerance

“…State-of-the-art power division structures such as directional couplers, multimode interference (MMI) devices or power splitters based on slot and adiabatic waveguides entail shortcomings in terms of reduced operational bandwidth, high sensitivity to fabrication deviations or large footprints [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Directional couplers [ 14 ], despite a significant improvement in their manufacturing tolerances through geometrical optimization [ 15 ] and phase control sections [ 16 ], still present comparatively limited operational bandwidth.…”

“…While bent directional couplers [ 17 ] have achieved a broadband response, they are affected by a strong sensitivity to manufacturing deviations. Slot waveguides [ 18 ] and adiabatic couplers [ 19 ] have demonstrated good performance over a wide bandwidth; however, these devices have considerably larger footprints. Similarly, MMI couplers offer numerous advantages, such as relatively small size and relaxed manufacturing tolerances [ 20 ], but their bandwidth is limited by the strong modal dispersion in multimode SOI waveguides.…”

“…The transition between the stem and arms is nearly lossless and wavelength independent for small enough branching angles and a perfectly sharp junction tip between said branches [ 28 ]. However, the latter condition is hindered in real scenarios by the finite resolution of fabrication processes, hence requiring the application of more complex structures and optimization algorithms, such as slotted Y-junctions [ 18 ] or particle swarm optimization (PSO) [ 33 ]. This is particularly stringent in deep-ultraviolet (UV) lithography [ 34 ], with a substantially larger minimum feature size (MFS) compared to electron-beam (e-beam) technology.…”