Publications

Press release

• NTT Press Release, “World’s first and most accurate field demonstration of end-to-end visualization of fiber-optic link without measuring equipment —Enables fast optical connection and maintenance through the realization of the digital twin of optical network—” 2024.

Journal articles

• T. Sasai, S. Y. Set, and S. Yamashita, “Design of Fiber-Longitudinal Optical Power Monitor,” Journal of Lightwave Technology, 2024.(early access).
• K. Suzuki, M. Ota, Y. Morimoto, K. Yamaguchi, O. Moriwaki, F. Hamaoka, S. Sugawara, T. Sasai, T. Kobayashi, M. Nakamura, Y. Miyamoto, S. Katayose, T. Umeki, D. Ogawa, M. Takeshita, M. Fukutoku, Y. Ma, S. Camatel, “Multi-granular switching node and enabling devices,” Journal of Lightwave Technology, 2024.(early access).
• F. Hamaoka, M. Nakamura, T. Sasai, S. Sugawara, T. Kobayashi, Y. Miyamoto, and E. Yamazaki, “Long-Haul >100-Tb/s Transmission over >1000 km with High-Symbol-Rate Triple-Band WDM Signals,” Journal of Lightwave Technology, 2024.(early access).
• H. Nishizawa, G. Borraccini, T. Sasai, Y.-K. Huang, T. Mano, K. Anazawa, M. Namiki, S. Usui, T. Matsumura, Y. Sone, Z. Wang, S. Okamoto, T. Inoue, E. Ip, A. D’Amico, T. Chen, V. Curri, T. Wang, K. Asahi, and K. Takasugi, “Semi-automatic line-system provisioning with an integrated physical-parameter-aware methodology: field verification and operational feasibility,” Journal of Optical Communications and Networking, 16, pp.894-904, 2024.
• T. Sasai, “Digital Longitudinal Monitoring of Fiber-optic Link Using Coherent Receiver,” NTT Technical Review, 22(9), pp. 73–78, 2024.
• D. Wang, Y. Song, Y. Zhang, X. Jiang, J. Dong, F.N. Khan, T. Sasai, S. Huang, A.P.T. Lau, M. Tornatore, M. Zhang, “Digital Twin of Optical Networks: A Review of Recent Advances and Future Trends,” Journal of Lightwave Technology, 42(12), pp. 4233-4259, 2024.
• M. Takahashi, T. Sasai, E. Yamazaki and Y. Kisaka, “Monitoring PDL Value and Location Using DSP-Based Longitudinal Power Profile Estimation,” Journal of Lightwave Technology, 42(17), pp. 5866-5873, 2024.
• A. Kawai, M. Nakamura, T. Kobayashi, M. Nagatani, H. Yamazaki, T. Sasai, F. Hamaoka, Y. Miyamoto, “Digital Inverse Multiplexing for Transmitters with Symbol Rates over DAC Bandwidth Limit,” Journal of Lightwave Technology, 42(11), pp. 4076-4085, 2024.
• T. Sasai, M. Takahashi, M. Nakamura, E. Yamazaki, and Y. Kisaka, “Linear Least Squares Estimation of Fiber-Longitudinal Optical Power Profile,” Journal of Lightwave Technology, 42(6), pp.1955-1965, 2024.
• (Invited)T. Sasai, E. Yamazaki, and Y. Kisaka, “Performance Limit of Fiber-Longitudinal Power Profile Estimation Methods,” Journal of Lightwave Technology, 41(11), pp.3278-3289, 2023.
• H. Nishizawa, T. Sasai, T. Inoue et al., “Dynamic Optical Path Provisioning for Alien Access Links: Architecture, Demonstration, and Challenges,” IEEE Communications Magazine, 61(4), pp.136-142, 2023.
• F. Hamaoka, K. Saito, A. Masuda,
  H. Taniguchi, T. Sasai, M. Nakamura, T. Kobayashi, and Y. Kisaka, “Over 100-Tbit/s Ultra-wideband Wavelength Division Multiplexed Transmission Technologies for Future Optical Transport Network Systems,” NTT Technical Review, 21(3), pp. 27–33, 2023.
• (Invited)T. Sasai, M. Nakamura, E. Yamazaki, S. Yamamoto, H. Nishizawa, and Y. Kisaka, “Digital Longitudinal Monitoring of Optical Fiber Communication Link,” Journal of Lightwave Technology, 40(8), pp.2390-2408, 2022.
• (Invited)T. Sasai, “Physics-Oriented Learning of Nonlinear Schrödinger Equation for Digital Longitudinal Monitoring of Optical Transmission Systems,” Laser reviews, 49(12), pp.653-659, 2021.
• H. Nishizawa, W. Ishida, Y. Sone, T. Tanaka, S. Kuwabara, T. Inui, T. Sasai, and M. Tomizawa, “Open whitebox architecture for smart integration of optical networking and data center technology,” Journal of Optical Communications and Networking, 13, pp.A78 – A87, 2021.
• F. Hamaoka, T. Sasai, K. Saito, T. Kobayashi, A. Matsushita, M. Nakamura, H. Taniguchi, S. Kuwahara, H. Kawahara, T. Seki, J. Ozaki, Y. Ogiso, H. Maeda, Y. Kisaka, and M. Tomizawa, “Dual-Carrier 1-Tb/s Transmission Over Field-Deployed G.654.E Fiber Link Using Real-Time Transponder,” IEIEC Transactions on Communications, E103-B(11), pp.1183-1189, 2020.
• H. Maeda, K. Saito, H. Kawahara, T. Seki, T. Sasai and F. Hamaoka, “High Spectral Efficiency Real-Time 500-Gb/s/carrier Long-Haul Transmission Over Field-Installed Fibers,” Journal of Lightwave Technology, 39(4), pp. 933-939, 2021
• H. Maeda, K. Saito, T. Sasai, F. Hamaoka, H. Kawahara, T. Seki, T. Kawasaki, J. Kani, “Real-time 400 Gbps/carrier WDM transmission over 2,000 km of field-installed G.654.E fiber,” Optics Express 28(2), 1640-1646, 2020.
• T. Sasai, M. Nakamura, E. Yamazaki, A.Matsushita, S. Okamoto, K. Horikoshi, Y. Kisaka, “Wiener-Hammerstein Model and Its Learning for Nonlinear Digital Pre-distortion of Optical Transmitter,” Optics Express, 28(21), pp.30952-30963, 2020.
• (Invited)T. Sasai, A. Matsushita, M.Nakamura, S. Okamoto, F. Hamaoka, and Y. Kisaka, “Laser Phase Noise Tolerance of Uniform and Probabilistically Shaped QAM Signals for High Spectral Efficiency Systems,” Journal of Lightwave Technology, 38(2), pp.439-446, 2020.
• F. Hamaoka et al., “Ultra-Wideband WDM Transmission in S-, C-, and L-Bands Using Signal Power Optimization Scheme,” in Journal of Lightwave Technology, vol. 37, no. 8, pp. 1764-1771, 15 April15, 2019.

Conference

• (Invited paper)T. Sasai, “Digital Longituidinal Monitoring: Advanced Physical Layer Monitoring for Network Automation,” Optical Fiber Communications Conference and Exhibition (OFC) 2025, San Diego, USA, 2025.
• (Invited paper)T. Sasai, “Fiber-optic link tomography enabled by optics-informed machine learning,” Photonics West 2025, San Francisco, USA, 13375-68, 2025.
• (Invited paper)T. Sasai, “Digital Longitudinal Monitoring for Digital Twin Operation of Optical Network,” Asia Communications and Photonics Conference (ACP), Workshop “Digital Twin of Optical Communication Systems”, Beijing, China, 2024.
• (Top-scored paper)T. Sasai, M. Takahashi, M. Nakamura, E. Yamazaki, and Y. Kisaka, “On the Signal Pattern Effect on Fiber-Longitudinal Power Monitor,” European Conference on Optical Communication (ECOC) 2024, Frankfurt, Germany, M3E.1, 2024.
• (Top-scored paper)M. Nakamura, H. Wakita, M. Nagatani, Y. Ogiso, F. Hamaoka, Y. Shiratori, T. Sasai, H. Takahashi, T. Kobayashi, and Y. Miyamoto, “46.4-Tb/s Full C-band 246-km Transmission with Net >2-Tb/s/λ WDM Signals Using >100-GHz-BW InP-based Tx Front-end,” European Conference on Optical Communication (ECOC) 2024, Frankfurt, Germany, Tu4B.5, 2024.
• M. Takahashi, T. Sasai, M. Nakamura, and E. Yamazaki, “Experimental Investigation of Longitudinal Power Profile Estimation Accuracy in Fibre Links with Large Effective Core Area,” European Conference on Optical Communication (ECOC) 2024, Frankfurt, Germany, W2A.105, 2024.
• R. Kaneko, T. Sasai, M. Takahashi, M. Nakamura, and E. Yamazaki, “Accuracy Comparison between Forward- or Backward-based Implementation of Longitudinal Power Profile Estimation,” European Conference on Optical Communication (ECOC) 2024, Frankfurt, Germany, M3E.3, 2024.
• M. Takahashi, T. Sasai, E. Yamazaki, “Experimental Investigation of the Impact of Transceiver Imperfections on Longitudinal Power Profile Estimation,” Opto-Electronics and Communications Conference(OECC), 219, Melbourne, Australia, 2024.
• (Post-deadline paper)T. Sasai, G. Borraccini, Y. K. Huang, H. Nishizawa, Z. Wang, T. Chen, Y. Sone, T. Matsumura, M. Nakamura, E. Yamazaki, Y. Kisaka, “4D Optical Link Tomography: First Field Demonstration of Autonomous Transponder Capable of Distance, Time, Frequency, and Polarization-Resolved Monitoring,” Optical Fiber Communications Conference and Exhibition (OFC) 2024, San Diego, USA, Th4B.7, 2024.
• (Invited)T. Sasai, “Recent Advances in Digital Longitudinal Monitoring of Fiber-Optic Link,” Optical Fiber Communications Conference and Exhibition (OFC) 2024, San Diego, USA, W1B.3, 2024.
• (Invited)T. Sasai, “Digital Longitudinal Monitoring of Fiber-Optic Link,” at Workshop “Neural Networks for Optical Fiber Transmission: Hype or Hope?,” Optical Fiber Communications Conference and Exhibition (OFC) 2024, San Diego, USA, 2024.
• R. Kaneko, T. Sasai, F. Hamaoka, M. Nakamura, and E. Yamazaki,”Fiber Longitudinal Monitoring of Inter-band-SRS-induced Power Transition in S+C+L WDM Transmission,” Optical Fiber Communications Conference and Exhibition (OFC) 2024, San Diego, USA, W1B.4, 2024.
• K. Suzuki, M. Ota, Y. Morimoto, K. Yamaguchi, F. Hamaoka, S. Sugawara, T. Sasai, T. Kobayashi, M. Nakamura, S. Katayose, T. Umeki, D. Ogawa, Y. Ma, S. Camatel, M. Fukutoku, Y. Miyamoto, and O. Moriwaki”Double-decker CDC-ROADM node for multi-band network with wavelength band granularity,”Optical Fiber Communications Conference and Exhibition (OFC) 2024, San Diego, USA, 2024.
• F. Hamaoka, M. Nakamura, T. Sasai, S. Sugawara, T. Kobayashi, Y. Miyamoto, and E. Yamazaki”110.7-Tb/s Single-Mode-Fiber Transmission over 1040 km with High-Symbol-Rate 144-GBaud PDM-PCS-QAM Signals,” Optical Fiber Communications Conference and Exhibition (OFC) 2024, San Diego, USA, 2024.
• (Invited)T. Sasai, “Digital Longitudinal Monitoring of Fiber-Optic Link,” in Photonics West 2024, San Francisco, USA, 12894-20, 2024.
• T. Sasai, Y. Sone, E. Yamazaki, M. Nakamura and Y. Kisaka, “A Generalized Method for Fiber-longitudinal Power Profile Estimation,” in European Conference on Optical Communication (ECOC) 2023, Glasgow, Scotland, Tu.A.2.6, 2023.
• M. Takahashi, T. Sasai, E. Yamazaki, and Y. Kisaka, “Experimental Demonstration of Monitoring PDL Value and Location Using DSP-Based Longitudinal Power Estimation with Linear Least Squares,” in European Conference on Optical Communication (ECOC) 2023, Glasgow, Scotland, P14, 2023.
• M. Nakamura, T. Sasai, F. Hamaoka, M. Nagatani, H. Yamazaki, T. Jyo, M. Mutou, Y. Shiratori, H. Wakita, T. Kobayashi, H. Takahashi, Y. Kisaka, Y. Miyamoto, “High symbol rate 200-GBd PDM-QPSK Transmission over 3520 km Using Ultra-broadband InP-DHBT Analogue Multiplexer,” in European Conference on Optical Communication (ECOC) 2023, Glasgow, Scotland, We.D.5.4, 2023.
• F. Hamaoka, M. Nakamura, T. Sasai, T. Kobayashi, Y. Kisaka, and Y. Miyamoto, “Net Bitrate of >1.3-Tb/s/λ Transmission over 80 km with Transmitter-side Semiconductor Optical Amplifier,” in European Conference on Optical Communication (ECOC) 2023, Glasgow, Scotland, P12, 2023.
• (Best paper)A. Kawai, M. Nakamura, T. Kobayashi, M. Nagatani, H. Yamazaki, T. Sasai, F. Hamaoka, and Y. Miyamoto, “Digital Inverse Multiplexing-based Pre-distortion for Analog Multiplexed Broadband Transmitter,” in European Conference on Optical Communication (ECOC) 2023, Glasgow, Scotland, We.D.3.2
• M. Takahashi, T. Sasai, E. Yamazaki, and Y. Kisaka, “DSP-based PDL Estimation and Localization in Multi-Span Optical Link Using Least Squares-based Longitudinal Power Monitoring,” in Opto-Electronics and Communications Conference(OECC) 2023, Shanghai, China, OECC2023-0317-21, 2023.
• R. Kaneko, T. Sasai, M. Takahashi, E. Yamazaki, and Y. Kisaka, “Experimental Performance Evaluation of Rx DSP-based Fiber-longitudinal Power Profile Estimation,” in Opto-Electronics and Communications Conference(OECC) 2023, Shanghai, China, OECC2023-0320-74, 2023.
• (Invited)T. Sasai, “Digital Longitudinal Monitoring for Optical Networks,” Advanced Photonics Congress, Workshop “AI and Digital Twin for Transforming Optical Networks: What They Can and Cannot Do?”, Busan, Korea, 2023.
• T. Sasai et al., “0.77-dB Anomaly Loss Localization Based on DSP-Based Fiber-Longitudinal Power Estimation Using Linear Least Squares,” in Optical Fiber Communications Conference and Exhibition (OFC) 2023, San Diego, USA, W1H.4, 2023.
• T. Sasai et al., “Closed-Form Expressions for Fiber-Nonlinearity-Based Longitudinal Power Profile Estimation Methods,” in European Conference on Optical Communication (ECOC) 2022, Basel, Switzerland, Tu1D.6, 2022.
• (Invited)T. Sasai et al., “Digital Longitudinal Monitoring of Optical Transmission Link,” in European Conference on Optical Communication (ECOC) 2022, Basel, Switzerland, Th1D.1, 2022.
• T. Sasai et al., “Proposal of Linear Least Squares for Fiber-Nonlinearity-Based Longitudinal Power Monitoring in Multi-Span Link,” in OptElectronics and Communications Conference/ International Conference on Photonics in Switching and Computing (OECC/PSC) 2022, Toyama, Japan, WB3-1, 2022.
• F. Hamaoka et al., “112.8-Tb/s Real-Time Transmission over 101 km in 16.95-THz Triple-Band (S, C, and L Bands) WDM Configuration,” in OptElectronics and Communications Conference/ International Conference on Photonics in Switching and Computing (OECC/PSC) 2022, Toyama, Japan, 2022.
• T. Sasai et al., “Precise Longitudinal Power Monitoring over 2,080 km Enabled by Step Size Selection of Split Step Fourier Method,” in Optical Fiber Communications Conference and Exhibition (OFC) 2022, San Diego, USA, Th1C.4, 2022.
• M. Nakamura et al., “1.0-Tb/s/λ 3840-km and 1.2-Tb/s/λ 1280-km Transmissions with 168-GBaud PCS-QAM Signals Based on AMUX Integrated Frontend Module,” in Optical Fiber Communications Conference and Exhibition (OFC) 2022, San Diego, USA, 2022.
• K. Saito et al., “Impact of Local Oscillator Phase Noise on Long-Haul Transmission of 120-Gbaud Digital Sub-Carrier Signals,” in Optical Fiber Communications Conference and Exhibition (OFC) 2022, San Diego, USA, 2022.
• T. Sasai et al., “Revealing Raman-amplified Power Profile and Raman Gain Spectra with Digital Backpropagation,” in Optical Fiber Communications Conference and Exhibition (OFC) 2021, San Francisco, USA, M3I.5, 2021.
• K. Anazawa et al., “Automatic Modulation-Format Selection with White-box Transponders: Design and Field Trial,” in OptElectronics and Communications Conference (OECC) 2021, HongKong, 2021.
• (Extended paper)T. Sasai et al., “Digital Backpropagation for Optical Path Monitoring: Loss Profile and Passband Narrowing Estimation,” in European Conference on Optical Communications(ECOC) 2020, Brussels, Belgium, Tu2D-1, 2020.
• T. Sasai, M. Nakamura, S. Okamoto, F. Hamaoka, S. Yamamoto, E. Yamazaki, A. Matsushita, H. Nishizawa, and Y. Kisaka, “Simultaneous Detection of Anomaly Points and Fiber types in Multi-span Transmission Links Only by Receiver-side Digital Signal Processing,” in Optical Fiber Communications Conference and Exhibition(OFC) 2020, San Diego, CA, USA, Th1F.1, 2020
• H. Maeda, H. Kawahara, K. Saito, T. Seki, T. Sasai and F. Hamaoka, “Real-Time Demonstration of 500-Gbps/Lambda and 600-Gbps/Lambda WDM Transmission on Field-Installed Fibers,” Optical Fiber Communications Conference and Exhibition (OFC), San Diego, CA, USA, 2020.
• K. Saito, T. Sasai, F. Hamaoka, H. Kawahara, T. Seki and H. Maeda, “High spectral efficiency real-time 500-Gb/s/carrier transmission over field-installed G.654.E fiber link using forward and backward distributed Raman amplification,” Optical Fiber Communications Conference and Exhibition (OFC), San Diego, CA, USA, 2020.
• K. Minoguchi, F. Hamaoka, S. Okamoto, T. Sasai, K. Horikoshi, A. Matsushita, M. Nakamura, E. Yamazaki, Y. Kisaka, “Beyond 100-Tb/s ultra-wideband transmission in S, C, and L bands over single-mode fiber,” Photonics West, 2020.
• F. Hamaoka et al., “Dual-Carrier 1-Tb/s Transmission Over Field-Deployed Large-Core Pure-Silica-Core Fiber Link Using Real-Time Transponder,” 2019 24th OptoElectronics and Communications Conference (OECC) and 2019 International Conference on Photonics in Switching and Computing (PSC), Fukuoka, Japan, 2019.
• (Top-Scored paper)T. Sasai, A. Matsushita, M. Nakamura, S. Okamoto, F. Hamaoka, and Y. Kisaka, “Experimental Analysis of Laser Phase Noise Tolerance of Uniform 256QAM and Probabilistically Shaped 1024QAM,” in Optical Fiber Communications Conference and Exhibition(OFC) OFC2019, San Diego, CA, USA, W1D.5, 2019.
• F. Hamaoka et al., “150.3-Tb/s Ultra-Wideband (S, C, and L Bands) Single-Mode Fibre Transmission over 40-km Using >519Gb/s/A PDM-128QAM Signals,” 2018 European Conference on Optical Communication (ECOC), Rome, Italy, 2018.
• T. Sasai, F. Hamaoka, A. Matsushita, M. Nakamura, H. Kawakami, and Y. Kisaka, “Experimental Investigation of Laser Linewidth Tolerance of 32-GBaud DP-256QAM Optical Coherent System,” in Opto-Electronics and Communications Conference(OECC) 2018, Jeju Island, Korea (South), 6D2-1, 2018.
• T. Sasai, M. Kishi, and K. Hotate, “Enhancement of Spatial Resolution in Distributed Measurement of Brillouin Dynamic Grating Spectrum by Optical Correlation Domain Analysis,” in Conference on Lasers and Electro-Optics(CLEO)2016, San Jose, CA, USA, SM3P.6, 2016

Domestic conference (Japan) / 国内学会

• 笹井健生, セットジイヨン, 山下真司 “光リンクトモグラフィの雑音解析” 第71回光波センシング研究会, LST-06, 2024.
• 笹井健生, “［招待講演］コヒーレント受信器を用いた光ファイバ伝送路の長手方向モニタリング技術” OCS研究会、2024.
• 笹井健生, “非線形シュレディンガー方程式の逆解析による光伝送路モニタリング” at “光ソリトン通信50周年記念シンポジウム ファイバ非線形性への挑戦” レーザ学会学術講演会第44回年次大会、2024.
• 笹井健生, “非線形シュレディンガー方程式の機械学習とその応用,” OCSサマースクール, 2023.
• 笹井健生, “光伝送システムの長軸方向モニタリング技術”, 光ネットワーク産業技術研究会，オンライン, 2022.
• 笹井健生 他, “非線形シュレディンガー方程式の学習による光伝送システムの長軸方向モニタリング技術”, 電子情報通信学会 OCS研究会 OCSシンポジウム, オンライン, P02, 2021.
• 笹井健生, “高多値デジタルコヒーレント光通信におけるレーザ位相雑音の影響”, 電子情報通信学会 ソサエティ大会2021, オンライン, CI-2-1, 2021.
• 笹井健生 他, “非線形シュレディンガー方程式の学習: 損失分布とPassband narrowingの推定”, 電子情報通信学会 総合大会2021, オンライン, B-10-11, 2021.
• Takeo Sasai et al., “Digital backpropagation for optical path monitoring — Loss and Dispersion profile estimation,” IEICE Tech. Rep., vol. 120, no. 309, OCS2020-39, pp. 61-64, Jan. 2021.
• 笹井健生 他, “光伝送路モニタリング技術としてのDigital backpropagation:損失/分散分布の推定”, 電子情報通信学会 ソサエティ大会2020, オンライン, B-10-12, 2020.
• 笹井健生, 岸眞人, 保立和夫, “光相関領域法によるブリルアンダイナミックグレーティングスペクトラムの分布測定におけるポンプ・リード間光路長差の影響”, 応用物理学会春季学術講演会, パシフィコ横浜, 16a-316-4, 2017.
• 笹井健生, 岸眞人, 保立和夫, “ブリルアンダイナミックグレーティングを用いた光相関領域法による温度・歪の分離分布測定の高空間分解能化に関する研究”, 応用物理学会春季学術講演会, 東京工業大学, 20p-H116-16, 2016.

General magazine

• Takeo Sasai, “How did the data propagate?” Research Outreach, issue 119, pp.106-109, 2020
• 笹井健生, “非線形シュレディンガー方程式の学習によるマルチスパン光伝送路モニタリング技術” ビジネスコミュニケーション, 58(6), 2021.

Preprint

• T. Sasai, S. Y. Set, and S. Yamashita, “Design of Fiber-Longitudinal Optical Power Monitor,” arXiv preprint, arXiv:2410.12602, 2024.
• T. Sasai, M. Takahashi, M. Nakamura, E. Yamazaki, and Y. Kisaka, “Linear Least Squares Estimation of Fiber-Longitudinal Optical Power Profile,” arXiv preprint, arXiv:2310.04936, 2023.
• T. Sasai, E. Yamazaki, and Y. Kisaka, “Performance limit of Fiber-Longitudinal Power Profile Estimation Methods,” arXiv preprint, arXiv:2211.08128, 2022.
• T. Sasai, M. Nakamura, E. Yamazaki, S. Yamamoto, H. Nishizawa, Y. Kisaka, “Physics-oriented learning of nonlinear Schrödinger equation: optical fiber loss and dispersion profile identification,” arXiv preprint, arXiv:2104.05890, 2021.
• T. Sasai, M. Nakamura, E. Yamazaki, A.Matsushita, S. Okamoto, K. Horikoshi, Y. Kisaka, “Wiener-Hammerstein model and its learning for nonlinear digital pre-distortion of optical transmitters,” arXiv preprint, arXiv:2012.08046, 2020.
• T. Sasai, A. Matsushita, M.Nakamura, S. Okamoto, F. Hamaoka, and Y. Kisaka, “Laser Phase Noise Tolerance of Uniform and Probabilistically-shaped QAM Signals for High Spectral Efficiency Systems,” arXiv preprint, arXiv:2012.08078, 2020.