[Paper Review] Controlling evanescent waves on-chip using all-dielectric metamaterials for dense photonic integration

Saman Jahani, Sangsik Kim+12 more|arXiv (Cornell University)|Jan 11, 2017

Photonic and Optical Devices2 citations

TL;DR

This paper proposes using all-dielectric anisotropic metamaterials on a chip to control evanescent waves in silicon photonic circuits, reducing their decay length via engineered total internal reflection. The approach enables over 30× cross-talk reduction and 3× lower bending loss with only 3.67 dB/cm propagation loss, enabling denser photonic integration on CMOS platforms.

ABSTRACT

Miniaturization of optical components with low power consumption fabricated using a CMOS foundry process can pave the way for dense photonic integrated circuits within nanoelectronic platforms. However, the large spatial extent of evanescent light waves generated during nanoscale light confinement are ubiquitous in silicon photonic devices and are the stumbling roadblock to miniaturization. Here, we demonstrate the control of evanescent waves using all-dielectric metamaterials on a chip. We demonstrate that anisotropic metamaterials open a new degree of freedom in total internal reflection (TIR) to reduce the decay length of evanescent waves. This counterintuitive approach uses optical devices which can have a cladding with a higher average index than the core and marks a departure from interference based confinement as in photonic crystal waveguides or slot waveguides which utilize nanoscale field enhancement. We experimentally show that all-dielectric anisotropic metamaterials can help to reduce the cross-talk more than 30 times and bending loss more than 3 times in ultra-compact photonic circuits, two major attributes that limit the integration density in photonic circuits. We verify our all-dielectric metamaterial platform fabricated on a scalable process with a relatively negligible propagation loss of 3.67 dB/cm paving the way to impact future device designs for dense photonic integration

Motivation & Objective

• Address the challenge of long-range evanescent waves limiting miniaturization in silicon photonic integrated circuits.
• Overcome the fundamental trade-off between strong light confinement and high crosstalk in compact photonic devices.
• Develop a CMOS-compatible platform for dense photonic integration using all-dielectric metamaterials.
• Enable new degrees of freedom in total internal reflection through anisotropic index engineering in dielectric materials.
• Demonstrate a scalable solution with low propagation loss and enhanced confinement for practical on-chip applications.

Proposed method

• Design and fabricate all-dielectric anisotropic metamaterials with a cladding material having a higher average refractive index than the core, contrary to conventional waveguide design.
• Engineer the metamaterial's effective optical properties to manipulate the decay length of evanescent waves during total internal reflection.
• Utilize a CMOS-compatible fabrication process to enable scalable integration on nanoelectronic platforms.
• Implement a metamaterial structure that enables sub-wavelength control of light without relying on interference-based mechanisms like in photonic crystal or slot waveguides.
• Optimize the anisotropic dielectric structure to minimize propagation loss while maximizing evanescent wave suppression.
• Validate the design through experimental characterization of crosstalk and bending loss in ultra-compact waveguide circuits.

Experimental results

Research questions

• RQ1 Can anisotropic all-dielectric metamaterials reduce the decay length of evanescent waves in silicon photonic waveguides beyond conventional methods?
• RQ2 How does a higher average cladding index compared to the core affect total internal reflection and evanescent field confinement?
• RQ3 To what extent can metamaterial engineering reduce crosstalk and bending loss in ultra-compact photonic circuits?
• RQ4 Can a CMOS-compatible all-dielectric platform achieve low propagation loss while enabling strong evanescent wave control?
• RQ5 Does this approach enable a new degree of freedom in waveguide design for dense photonic integration?

Key findings

• The all-dielectric anisotropic metamaterial platform reduces crosstalk by more than 30 times compared to conventional waveguides.
• Bending loss in ultra-compact photonic circuits is reduced by more than 3 times using the proposed metamaterial design.
• The fabricated platform exhibits a low propagation loss of 3.67 dB/cm, enabling practical scalability for on-chip integration.
• The metamaterial approach enables effective control of evanescent waves without relying on nanoscale field enhancement or interference-based confinement.
• The design breaks the conventional constraint of requiring a lower cladding index than the core, opening new possibilities for waveguide engineering.
• The method is compatible with standard CMOS fabrication processes, supporting future dense photonic integration on nanoelectronic platforms.