Simultaneous Mode and Polarization Conversions Via Periodic Grating Engraved on Strip Waveguide

• Published in: Journal of lightwave technology Vol. 39; no. 23; pp. 7486 - 7494
• Main Authors: Elzahaby, Eman A., Fath Elbab, Ahmed M. R., Shalaby, Hossam M. H.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acceptable noise levels; Bragg grating; Bragg gratings; Conversion; Converters; Coupled modes; coupled-mode theory; Couplings; Crosstalk; Engraving; Gratings; Insertion loss; integrated optics devices; mode chart; mode-division multiplexers; Multiplexing; optical converters; Perturbation; Polarization; polarization rotators; polarization-division multiplexers; Refractive index; Silicon; silicon-on-insulator; Stability analysis; Strip; Strips; Structural stability; Waveguides
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2021.3115410

A converter that manipulates the energy exchange between two arbitrary guided modes having different mode orders and polarization states is proposed. This objective is achieved through engraving a periodic grating on a strip waveguide. Theoretical analysis, based on the coupled-mode theory, is developed to match the proposed structure. In addition, coupling analysis is addressed to provide a comprehensive view regarding the various couplings that can be achieved, including acceptable margins for perturbation designing parameters and their optimum values for each coupling. Moreover, our converter is implemented via both 3D-FDTD simulation and computational solution to examine the validity of the proposed approach and verify the coupling analysis through performing two conversions, namely TM<inline-formula><tex-math notation="LaTeX">_{\boldsymbol{1}}</tex-math></inline-formula>-to-TE<inline-formula><tex-math notation="LaTeX">_{\boldsymbol{0}}</tex-math></inline-formula> and TM<inline-formula><tex-math notation="LaTeX">_{\boldsymbol{1}}</tex-math></inline-formula>-to-TE<inline-formula><tex-math notation="LaTeX">_{\boldsymbol{3}}</tex-math></inline-formula>. The first conversion is obtained with an insertion loss of <inline-formula><tex-math notation="LaTeX">\boldsymbol{-1}\,</tex-math></inline-formula> dB and a crosstalk lower than <inline-formula><tex-math notation="LaTeX">\boldsymbol{-17.5}\,</tex-math></inline-formula>dB at a conversion length of <inline-formula><tex-math notation="LaTeX">\boldsymbol{9.15\,\mu }</tex-math></inline-formula>m. The second is executed with an insertion loss of <inline-formula><tex-math notation="LaTeX">\boldsymbol{-1.5}\,</tex-math></inline-formula>dB and a crosstalk lower than <inline-formula><tex-math notation="LaTeX">\boldsymbol{-15}\,</tex-math></inline-formula>dB at a conversion length of <inline-formula><tex-math notation="LaTeX">\boldsymbol{16.937\,\mu }</tex-math></inline-formula>m. Furthermore, tolerance fabrication analysis is implemented to confirm the degree of stability that the proposed structure can achieve. Finally, the findings reveal that the proposed design achieved its function at a compact length and without being restricted by the hybridization approach.