Ultracompact Photonic Structure Design for Strong Light Confinement and Coupling Into Nanowaveguide

• Published in: Journal of lightwave technology Vol. 36; no. 14; pp. 2812 - 2819
• Main Authors: Turduev, Mirbek, Bor, Emre, Latifoglu, Cagri, Giden, Ibrahim Halil, Hanay, Y. Sinan, Kurt, Hamza
• Format: Journal Article
• Language: English
• Published: New York IEEE 15.07.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Artificial intelligence; Compression ratio; Confinement; Coupling; Design; Finite difference method; Finite difference methods; Focusing; Fourier transforms; Incident light; Lenses; Machine learning; Machine learning algorithms; nanophotonics; Optical coupling; Optimization; Performance enhancement; photonic integrated circuits; Photonics; Time domain analysis; Training; Transmission efficiency
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2018.2821361

Different optimization algorithms have recently been utilized to design and improve the performance of many nanophotonic structures. We present the design of a compact photonic structure by an approach based on machine learning. Three-dimensional finite-difference time-domain method is integrated with a machine learning algorithm in order to design a photonic structure. In particular, a subwavelength focusing lens structure that operates at telecom wavelengths is designed to have desired beam properties such as subwavelength full-width at half-maximum value of 0.155 λ and suppressed side-lobe levels at focal point, where λ denotes the wavelength of incident light and equals to 1550 nm. The designed compact lens structure has the footprint of 2 × 1 μm 2 with a slab thickness of 280 nm, which is the smallest photonic lens for subwavelength focusing of light to date comparing to its conventional ones. The focusing mechanism of designed lens structure is explained with the help of applying discrete Fourier transform to the two-dimensional dielectric distribution of the structure. It is also shown that, due to its strong light confinement property, the designed lens structure can be used as a waveguide-to-waveguide optical coupling device with a beamwidth compression ratio of 10:1 by integrating a nanowaveguide with the width of 200 nm to the output surface of lens structure. Normalized transmission efficiency of the optical coupling device is calculated as high as 0.62 at the wavelength of 1550 nm. The outcomes of the presented study show that machine learning can be beneficial for designing efficient compact photonic structures.