Contrary to popular belief, scientists have discovered a new communication mechanism involving a leakage mode previously thought to be unsuitable for high-density integration in photonic circuits. This remarkable discovery transforms the potential and scalability of photonic chips in areas such as optical computing, quantum communications, light detection and ranging (LiDAR), optical metrology, and biochemical sensing, paving the way for massive photonic integration.

In a recent publication Light Science and Application Sangsik Kim, associate professor in the Department of Electrical Engineering at the Korea Advanced Institute of Science and Technology (KAIST), and his students at Texas Tech University showed that an anisotropic leakage wave can achieve zero crosstalk between closely spaced identical waveguides using subwavelength wavelengths. grids (SWG) metamaterials. This counterintuitive discovery significantly increases the coupling length of the transverse magnetic (TM) mode, which has historically been problematic due to low confinement.

This work builds on previous research on SWG metamaterials for reducing optical crosstalk, including depth control of the evanescent wave skin effect and outstanding coupling in anisotropic directional mode. SWGs have recently made significant progress in the field of photonics, creating a variety of high-performance PIC components. However, integration density issues remain for the TM mode, which exhibits approximately 100 times higher crosstalk than the crossed electric (TE) mode, preventing high-density chip integration.

“Our group has explored SWG for dense photonic integration and achieved significant improvements. However, previous approaches were limited to TE polarization only. In a photonic chip, another orthogonal polarization can be used, which can double the capacity of the chip and is sometimes preferred over TE, for example in instantaneous field measurements.” There is TM. TM is more difficult to tightly integrate than TE because it is generally less confined due to the lower aspect ratio of the waveguide,” Kim explained.

At first, the team thought it was impossible to reduce crosstalk with SWG because they expected the leakage mode to increase coupling between waveguides. However, they focused on the potential for anisotropic leakage mode perturbation and suggested that crossover cancellation could be achieved.

By applying coupled mode analysis to the modal properties of leaky SWG modes, they discovered a unique anisotropic perturbation with a leak-like mode that results in zero crosstalk between closely spaced identical SWG waveguides. Using Floquet limit simulations, they designed practically realized SWG waveguides on a standard silicon-on-insulator (SOI) platform readily available in industry; this showed excellent anti-crosstalk and more than twice the coupling length compared to ribbon waveguides.

This breakthrough also significantly reduces noise in PICs, potentially impacting quantum communications and computing, optical metrology, and biochemical sensing. In addition, the researchers highlighted the broader implications of their work by noting that this new communication mechanism can be extended beyond the telecommunications band to other integrated photonic platforms and wavelength regimes in the visible, mid-infrared, and terahertz bands.

This surprising coupling mechanism has challenged conventional wisdom and pushed the boundaries of the field by expanding the potential for dense photonic integration. As research continues, the photonics industry will likely see a shift towards denser, lower noise, and more efficient PIC technologies.