Challenging Established Notions: A Novel Approach in Photonics Expands the Field’s Limits

Challenging Established Notions: A Novel Approach in Photonics Expands the Field’s Limits

Graphic representation highlights the absence of crosstalk during light transmission in the waveguide array enabled by the newly developed metamaterial-based optical semiconductor. Attribution: Korea Advanced Institute of Science and Technology (KAIST) Integrated Metaphotonics Group

In a departure from conventional understanding, researchers have uncovered an innovative coupling process that employs leaky mode, an element historically deemed unsuitable for high-density inclusion in photonic circuits.

This groundbreaking revelation holds significant implications for the enhancement of photonic integration density, thereby revolutionizing the scope and scalability of photonic chips in various applications. These include optical computing, quantum communications, Light Detection and Ranging (LiDAR), optical measurement techniques, and biochemical sensors.

A study recently published in the journal Light Science & Application by Sangsik Kim, an associate professor of electrical engineering at the Korea Advanced Institute of Science and Technology (KAIST), along with scholars from Texas Tech University, showed that anisotropic leaky waves could achieve zero crosstalk among closely packed identical waveguides, facilitated by subwavelength grating (SWG) metamaterials. This unexpected finding substantially lengthens the coupling distance of the transverse-magnetic (TM) mode, which has traditionally faced challenges due to its low level of confinement.

Building on earlier work focused on SWG metamaterials for the mitigation of optical crosstalk, the research team has controlled factors such as the skin depth of evanescent waves and attained remarkable coupling in anisotropic guided modes. SWGs have recently marked considerable progress in the field of photonics, facilitating high-performance Photonic Integrated Circuit (PIC) components. Nevertheless, the TM mode, characterized by a crosstalk approximately 100 times greater than its transverse-electric (TE) counterpart, continued to obstruct high-density chip integration.

Kim elucidated, “We have investigated SWGs for high-density photonic integration and achieved significant advancements. However, previous methods were confined to TE polarization. Photonic chips also involve another orthogonal polarization, TM, which can potentially double the chip’s capacity. TM polarization is often more challenging to densely integrate due to its lower confinement and aspect ratio of the waveguide’s width-to-height.”

Initially skeptical about the feasibility of crosstalk reduction via SWGs, the researchers turned their attention to the possibilities of anisotropic perturbation combined with leaky mode, speculating that cross-cancellation could be achievable. They applied coupled-mode analysis to the characteristics of leaky SWG modes and discovered a unique anisotropic perturbation with a leaky-like characteristic that resulted in zero crosstalk between identical, closely spaced SWG waveguides. Utilizing Floquet boundary simulations, they crafted practically deployable SWG waveguides on a standard Silicon-on-Insulator (SOI) platform, showcasing exceptional crosstalk reduction and an over two-fold increase in coupling lengths as compared to conventional strip waveguides.

This advancement notably decreases noise levels within PICs, offering further potential applications in quantum communication, optical metrology, and biochemical sensing. The study emphasizes the broader ramifications of this discovery, suggesting that such innovative coupling mechanisms could be adapted to other photonic integration platforms and wavelength regimes, spanning from the visible to mid-infrared and terahertz spectrums.

This unanticipated coupling technique has broadened the horizons for dense photonic integration, challenging established theories and advancing the domain’s frontiers. Ongoing research in the field of photonics is anticipated to steer the industry toward more compact, less noisy, and more efficient PIC technologies.

Reference: “Anisotropic leaky-like perturbation with subwavelength gratings enables zero crosstalk” by Md Faiyaz Kabir, Md Borhan Mia, Ishtiaque Ahmed, Nafiz Jaidye, Syed Z. Ahmed, and Sangsik Kim, published on June 2, 2023, in Light: Science & Applications. DOI: 10.1038/s41377-023-01184-5.

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