Research topics

We have proposed a high-speed optical free-space modulator with a silicon-organic-hybrid metasurface. By exploiting a unique resonance structure with a dimerized grating, surface-normal light is efficiently trapped and modulated via an external voltage. Using a fabricated device, we demonstrated efficient modulation with a record-low driving voltage and high-speed data modulation at up to 1.6 Gbit/s for the first time.

Related Publication
[1] G. Soma, K. Ariu, S. Karakida, Y. Tsubai, and T. Tanemura, "Subvolt high-speed free-space modulator with electro-optic metasurface," arXiv[physics.optics] 2503.17986 (2025). (Accepted in Nature Nanotechnology.)

We have proposed a high-speed optical free-space receiver that integrates a silicon metasurface and InGaAs/InP membrane photodetector array on both sides of a SiO2 substrate. Using a fabricated compact chip, we demonstrated high-speed signal detection, including 320-Gbps multi-channel signals and a 240-Gbps coherent signal.

Related Publication
[1] G. Soma, T. Akazawa, E. Kato, M. Takenaka, Y. Nakano, and T. Tanemura, "Ultrafast one-chip optical receiver with functional metasurface," arXiv[physics.optics] 2503.02264 (2025). 

We have proposed a metasurface-based polarization splitter that splits the input lightwave into four non-orthogonal polarizations and focuses them on four sensors. Unlike the conventional approach that employs polarization filtering, our metasurface realizes low-loss full-Stokes polarimetry with the minimum number of sensors, which enables high-sensitivity and high-resolution polarimetric imaging.

Related Publication
[1] G. Soma, K. Komatsu, C. Ren, Y. Nakano, and T. Tanemura, "Metasurface-enabled non-orthogonal four-output polarization splitter for non-redundant full-Stokes imaging," Opt. Express 32(20), 34207-34222 (2024). DOI: 10.1364/OE.529389. (2024). 

We have proposed universal vectorial mode converters using multi-layer metasurfaces that can transform an orthogonal set of multiple input vector beams into another orthogonal set of vector beams in a unitary manner. We demonstrated our method by applying it to distinctive devices for optical communication and holographic imaging systems.
Moreover, we experimentally demonstrated polarization and spatial mode multiplexing using a fabricated metasurface device.

Related Publication
[1] G. Soma, K. Komatsu, Y. Nakano, and T. Tanemura, "Complete vectorial optical mode converter using multi-layer metasurface," Nat. Commun. 16, 7744 (2025). DOI: 10.1038/s41467-025-62401-w. [press release] [Preprint: arXiv[physics.optics] 2401.05127]
[2] G. Soma, K. Komatsu, Y. Nakano, and T. Tanemura, "Spatial and Polarization Mode Multiplexer using a Reflective Metasurface Chip," in Optical Fiber Communication Conference (OFC) 2025, M1D. (Refereed / Oral)

We have proposed a surface-normal Stokes-vector receiver using a metasurface for the polarimetric self-coherent systems. We fabricated a Si-based metasurface and successfully demonstrated the 25-km self-coherent transmission of 40GBd QPSK signals. Our device can be realized with a compact receiver module, which has a comparable size and complexity to conventional IM-DD receivers. Moreover, it can easily be extended to receive spatially multiplexed channels owing to the surface-normal configuration.

Related Publication
[1]  G. Soma, Y. Nomoto, T. Umezawa, Y.Yoshida, Y. Nakano, and T. Tanemura, "Compact and scalable polarimetric self-coherent receiver using a dielectric metasurface," Optica 10(5), 604 (2023). DOI: 10.1364/optica.484318.
[2] G. Soma, Y. Nomoto, T. Umezawa, Y. Yoshida, Y. Nakano, and T. Tanemura, “Self-Coherent Transmission Using Metasurface-based Stokes-Vector Receiver,”  Optical Fiber Communication Conference (OFC) 2023, M2E.2.
[3] G. Soma, Y. Nomoto, Y. Nakano, and T. Tanemura, “Surface-Normal Stokes Vector Receiver based on Superimposed Metasurface,” Optical Fiber Communication Conference (OFC) 2022, M4J.5. 

We have proposed a surface-normal coherent receiver using a wire-grid-integrated photodetector array. We fabricated an InP-based photodetector array with gold wire-grid polarizers and successfully demodulated high-speed IQ signals such as 64GBd QPSK and 50GBd 16QAM signals. Since the signal is surface-normally incident to the device in our proposed configuration, our receiver has large scalability and can detect highly parallelized coherent signals. 

Related Publication
[1]  G. Soma, W. Yanwachirakul, T. Miyazaki, E. Kato, B. Onodera, R. Tanomura, T. Fukui, S. Ishimura, M. Sugiyama, Y. Nakano, and T. Tanemura, “Ultra-broadband surface-normal coherent optical receiver with nanometallic polarizers,” ACS Photonics 9(8), 2842-2849 (2022). DOI: 10.1021/acsphotonics.2c00759.
[2] G. Soma, W. Yanwachirakul, T. Miyazaki, E. Kato, B. Onodera, R. Tanomura, T. Fukui, S. Ishimura, M. Sugiyama, Y. Nakano, and T. Tanemura, “Compact Surface-Normal Coherent Receiver with Wire-Grid Polarizers,” Conference on Lasers and Electro-Optics (CLEO) 2023, SM4I.3.

We have proposed a new dual-polarization coherent receiver. It does not require a polarization-splitter-rotator, which is difficult to integrate on InP and thick-Si platforms, and enables the monolithic integration of all necessary optical components. As a proof of concept,  we fabricated the passive device on an InP substrate and successfully demodulated dual-polarization QPSK signals.

Related Publication
[1]  G. Soma, S. Ishimura,  R. Tanomura, T. Fukui, M. Ito, Y. Nakano, and T. Tanemura, "Integrated Dual-Polarization Coherent Receiver without Polarization Splitter-Rotator, " Opt. Express 29(2), 1711-1721 (2021). DOI: 10.1364/OE.413310.
[2] G. Soma, S. Ishimura, R. Tanomura, T. Fukui, M. Ito, Y. Nakano, and T. Tanemura, “Polarization-Splitter-Rotator-Free Dual-Polarization Coherent Receiver with a Single Optical Hybrid,” Conference on Lasers and Electro-Optics (CLEO) 2021, STu2B.4.