研究者詳細 - 柳　博文

柳　博文（リュウ　ボーウェン）

Liu, Bowen

写真a

所属（所属キャンパス）: 理工学研究科（矢上）

職名: 特任助教（有期）

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Compute-and-transmit photonic convolution using a microcomb-driven 300 GHz wireless link

Kokubu J., Sato K., Yomoda A., Imamura M., Sugano R., Liu B., Tanabe T.

Optics Express 34 （ 10 ） 18704 - 18716 2026年05月

　概要を見る

We demonstrate a comb-based photonic processor that performs temporal convolution in the optical domain and directly converts the analog computation result into a 300 GHz wireless signal. A dissipative Kerr soliton microcomb with a 300-GHz free spectral range provides parallel wavelength channels, in which convolution kernels are encoded as comb-line weights and processed via dispersion-induced delays. The convolution output is optically heterodyned in a uni-traveling-carrier photodiode, generating a 300 GHz carrier whose amplitude envelope represents the convolution result. We experimentally demonstrate real-time optical convolution at 1.2 Gbaud and a successful free-space THz link of the processed signal in the terahertz band. Offloading the convolution to the optical domain reduces the estimated computational cost by 23.1% relative to a purely electronic implementation. A latency estimate further suggests that direct optical-to-terahertz transmission can alleviate the I/O overhead by avoiding local digitization and bus-based data transfer.
- Access to Document (DOI)
Repetition-rate-difference tunable dual-comb fiber laser using bidirectional Lyot filtering

Zhu Y., Liu B., Dai M., Ma Y., Yamashita S., Tanabe T., Set S.Y.

Optics and Laser Technology 194 2026年02月

ISSN 00303992

　概要を見る

Single cavity dual-comb fiber lasers adopting different multiplexing configurations are benefited from the natures of common-mode noise suppression and superior coherence. Particularly, repetition-rate-tunable dual-combs enable non-ambiguous ranging and aliasing-free spectroscopy. However, their sampling rate and spectral resolution are severely restricted by the mechanical delay line (DLL). In a previous work, as rapid as 500 kHz/s tuning rate was realized to address this issue, while the minimum comb-frequency difference remained large under the inaccuracy of mechanical DLL. In this work, a polarization-multiplexing dual-comb fiber laser incorporated with a thermally controlled bidirectional Lyot filter is demonstrated with 870-times enhanced tuning precision compared with mechanical schemes. Linear correlation between temperature and repetition-rate-difference of this tuning mechanism is revealed. We achieve a tuning efficiency of 4.4 Hz/K and a control accuracy of 0.44 Hz, denoting a significant advance in operating Hz-scale differential comb lines. This design offers a robust platform for extending non-ambiguous distance in dead-zone-free dual-comb ranging and eliminating aliasing in spectroscopy.
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Quantifying Phase Noise Tolerance for Single-Carrier M-QAM Terahertz Wireless Communications With Advantages of Photonic Approaches

Liu B., Tanabe T.

Journal of Lightwave Technology 44 （ 6 ） 2223 - 2236 2026年

ISSN 07338724

　概要を見る

Terahertz wireless communications offer abundant untapped spectrum and are regarded as a promising playground for next-generation high-throughput links. Yet oscillator phase noise becomes the dominant impairment at such high frequencies, severely limiting the reliability of high-order QAM transmission. While photonic approaches, such as microcombs, are known to realize ultralow phase noise, the quantitative level of suppression required to sustain reliable high-order QAM transmission has not been clarified. Here, phase noise is reconstructed from measured spectra and embedded into a single-carrier link model to evaluate its impact. Distinct distortion mechanisms are identified, with slow common phase error and instantaneous phase jitter, where the latter remains as the residual impairment after carrier phase recovery. We further adopt a 3×EVM error margin, which maps residual distortions onto the constellation, providing a clear and practical indicator of system robustness. The results indicate that modest improvements in oscillator stability translate into significant BER gains without proportional power increase. These findings provide intuitive tolerance of phase noise in M-QAM systems and emphasize the importance of integrating low-noise photonic oscillators such as microcombs.
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Comb-mode-resolvable narrow-bandwidth polarization-maintaining mode-locked fiber laser with large tunability

Dai M., Liu B., Zhu Y., Ma Y., Set S.Y., Yamashita S.

Optics Letters 50 （ 15 ） 4718 - 4721 2025年08月

ISSN 01469592

　概要を見る

Comb-mode-resolvable fiber lasers output a set of evenly spaced and detectable frequencies, enabling precision applications in frequency metrology and high-resolution spectroscopy. Here, we report a narrow-bandwidth down to GHz level, polarization-maintaining mode-locked fiber laser with comb-mode resolvability. Under narrow-bandwidth filtering, the laser owns a minimum spectral width of 12.1 pm (1.49 GHz) at 1560 nm, with a pulse width of 437 ps and a comb spacing of 21 MHz. The comb spectrum is successfully resolved by using low-bandwidth electronics, owing to the high coherence of the combs. The output bandwidth (12.1 pm–3 nm) and center wavelength (1530 nm–1565 nm) can be easily tuned in a large range by setting the intracavity programmable pulse shaper. Therefore, the laser can operate at a broadband range despite its narrow bandwidth. The proposed widely tunable narrow-bandwidth laser has the potential for precise frequency comb metrology and spectroscopy with only a simple detection end.
- Access to Document (DOI)
GHz fundamental mode-locking of a highly integrated Er-doped all-fiber ring laser

Dai M., Liu B., Ma Y., Yang R., Zhang Z., Set S.Y., Yamashita S.

Optics Express 33 （ 15 ） 32361 - 32373 2025年07月

　概要を見る

High repetition rate ultrafast fiber lasers are essential for both scientific research and industrial applications. Here, we report the first, to the best of our knowledge, all-fiber ring laser with a fundamental repetition rate exceeding 1 GHz, by integrating all necessary functions into one single device with commercial active fiber pigtails. Low-threshold self-starting mode-locking is achieved by using a carbon nanotube (CNT) saturable absorber that directly deposits on the Er-doped fiber connector. The laser operates at 1562 nm, delivering 682 fs pulses with 1.028 GHz fundamental repetition rate with good stability, low intensity/phase noise, and high signal-to-noise ratio. The proposed compact source is promising for high repetition rate applications and provides a reference for fiber lasers with different mode-locking mechanisms or in various wavelength ranges. We also provide in-depth discussions on the key challenges and future directions for fiber lasers mode-locking at GHz rates using real saturable absorbers.
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