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  1. Article ; Online: Ultralinear 140-GHz FMCW signal generation with optical parametric wideband frequency modulation enabling 1-mm range resolution.

    Ishimura, Shota / Kan, Takashi / Takahashi, Hidenori / Tsuritani, Takehiro / Suzuki, Masatoshi

    Optics express

    2023  Volume 31, Issue 8, Page(s) 13384–13392

    Abstract: We demonstrate ultralinear and ultrawideband frequency-modulated continuous-wave (FMCW) signal generation using an optical parametric wideband frequency modulation (OPWBFM) method. The OPWBFM method optically expands the bandwidths of FMCW signals beyond ...

    Abstract We demonstrate ultralinear and ultrawideband frequency-modulated continuous-wave (FMCW) signal generation using an optical parametric wideband frequency modulation (OPWBFM) method. The OPWBFM method optically expands the bandwidths of FMCW signals beyond the electrical bandwidths of optical modulators via a cascaded four-wave mixing (FWM) process. Compared to the conventional direct modulation approach, the OPWBFM method simultaneously achieves high linearity and a short measurement time of the frequency sweep. On the other hand, it is also known that the OPWBFM method expands the phase noise of idlers as well as their bandwidths if an input conjugate pair has different phase noise. To avoid this phase noise expansion, it is crucial to synchronize the phase of an input complex conjugate pair of an FMCW signal using an optical frequency comb. For demonstration, we successfully generated an ultralinear 140-GHz FMCW signal by using the OPWBFM method. Moreover, we employ a frequency comb in the conjugate pair generation process, leading to the mitigation of phase noise expansion. By using a 140-GHz FMCW signal, we achieve a range resolution of ∼1 mm through fiber-based distance measurement. The results show the feasibility of an ultralinear and ultrawideband FMCW system with a sufficiently short measurement time.
    Language English
    Publishing date 2023-05-08
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1491859-6
    ISSN 1094-4087 ; 1094-4087
    ISSN (online) 1094-4087
    ISSN 1094-4087
    DOI 10.1364/OE.485140
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Broadband injection-locked homodyne receiver for digital coherent transmission using a low Q Fabry-Perot LD.

    Kasai, Keisuke / Kan, Takashi / Yoshida, Masato / Hirooka, Toshihiko / Nakazawa, Masataka

    Optics express

    2022  Volume 30, Issue 8, Page(s) 13345–13355

    Abstract: We describe the broadband injection-locking performance of a Fabry-Perot laser diode (FP-LD) for digital coherent transmission. The dynamic locking bandwidth of the FP-LD was as wide as 28.8 GHz, which makes it possible to achieve precise carrier-phase ... ...

    Abstract We describe the broadband injection-locking performance of a Fabry-Perot laser diode (FP-LD) for digital coherent transmission. The dynamic locking bandwidth of the FP-LD was as wide as 28.8 GHz, which makes it possible to achieve precise carrier-phase synchronization with extremely low phase noise over a wide frequency range. By applying the FP-LD as an LO in an injection-locked homodyne receiver for digital coherent quadrature amplitude modulation (QAM) transmission, we demonstrate, for the first time, the precise demodulation of 3, 10 and 20 Gbaud 256 QAM signals even when using a widely and randomly phase-modulated transmitter laser. This is attributed to the excellent wideband dynamic injection-locking characteristics of the FP-LD.
    Language English
    Publishing date 2022-04-26
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1491859-6
    ISSN 1094-4087 ; 1094-4087
    ISSN (online) 1094-4087
    ISSN 1094-4087
    DOI 10.1364/OE.456327
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Injection-locked 256 QAM WDM coherent transmissions in the C- and L-bands.

    Kan, Takashi / Kasai, Keisuke / Yoshida, Masato / Hirooka, Toshihiko / Nakazawa, Masataka

    Optics express

    2020  Volume 28, Issue 23, Page(s) 34665–34676

    Abstract: We demonstrate WDM 256 QAM coherent transmissions with injection locking in the C- and L-bands and compare the transmission performance in the two bands. Although four-wave mixing (FWM) is more significant in an L-band EDFA than in a C-band EDFA, the FWM ...

    Abstract We demonstrate WDM 256 QAM coherent transmissions with injection locking in the C- and L-bands and compare the transmission performance in the two bands. Although four-wave mixing (FWM) is more significant in an L-band EDFA than in a C-band EDFA, the FWM did not accumulate through the transmission and the FWM components were hidden by the ASE noise level. Since the FWM was weakened by the decorrelation of the WDM signals during the transmission, the transmission performance in the L-band was the same as that in the C-band. The injection locking circuit enabled precise carrier-phase synchronization between a data signal and a local oscillator regardless of the transmission band. By using this circuit, we successfully transmitted 58.2 and 57.6 Tbit/s 256 QAM WDM signals over 160 km with a spectral efficiency of 12 bit/s/Hz in the C- and L-bands, respectively.
    Language English
    Publishing date 2020-11-10
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1491859-6
    ISSN 1094-4087 ; 1094-4087
    ISSN (online) 1094-4087
    ISSN 1094-4087
    DOI 10.1364/OE.404786
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Chromatic dispersion dependence of GAWBS phase noise compensation with pilot tone.

    Sato, Kozo / Kan, Takashi / Yoshida, Masato / Kasai, Keisuke / Hirooka, Toshihiko / Nakazawa, Masataka

    Optics express

    2021  Volume 29, Issue 7, Page(s) 10676–10687

    Abstract: We describe experimental and numerical results regarding the influence of chromatic dispersion in optical fibers on guided acoustic-wave Brillouin scattering (GAWBS) phase noise compensation with a pilot tone (PT). We compared the compensation ... ...

    Abstract We describe experimental and numerical results regarding the influence of chromatic dispersion in optical fibers on guided acoustic-wave Brillouin scattering (GAWBS) phase noise compensation with a pilot tone (PT). We compared the compensation performance for GAWBS phase noise generated in an ultra-large-area fiber (ULAF) where DULAF = 21 ps/nm/km with that in a dispersion-shifted fiber (DSF) where DDSF = -1.3 ps/nm/km and found that the performance depends strongly on chromatic dispersion. The numerical analysis shows that the group delay between the signal and PT caused by chromatic dispersion reduces the GAWBS noise correlation between them, which degrades the compensation performance for GAWBS phase noise. It is clarified that a condition for effective GAWBS compensation is that the group delay between the signal and PT should be less than half the period of the GAWBS phase noise component.
    Language English
    Publishing date 2021-04-06
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1491859-6
    ISSN 1094-4087 ; 1094-4087
    ISSN (online) 1094-4087
    ISSN 1094-4087
    DOI 10.1364/OE.418891
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Spectrally efficient pilot tone-based compensation of inter-channel cross-phase modulation noise in a WDM coherent transmission using injection locking.

    Kan, Takashi / Sato, Kozo / Yoshida, Masato / Hirooka, Toshihiko / Kasai, Keisuke / Nakazawa, Masataka

    Optics express

    2021  Volume 29, Issue 2, Page(s) 1454–1469

    Abstract: We propose the precise and wideband compensation of the nonlinear phase noise caused by cross-phase modulation (XPM) among WDM channels using a pilot tone (PT) and injection locking for short-reach, higher-order QAM transmission. A high spectral ... ...

    Abstract We propose the precise and wideband compensation of the nonlinear phase noise caused by cross-phase modulation (XPM) among WDM channels using a pilot tone (PT) and injection locking for short-reach, higher-order QAM transmission. A high spectral efficiency is maintained by sharing a single PT among multiple channels. We describe a 60 ch, 3 Gbaud PDM-256 QAM transmission over 160 km, where the bit error rate was improved from 6 × 10
    Language English
    Publishing date 2021-01-18
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1491859-6
    ISSN 1094-4087 ; 1094-4087
    ISSN (online) 1094-4087
    ISSN 1094-4087
    DOI 10.1364/OE.414381
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Article ; Online: 42.3 Tbit/s, 18 Gbaud 64 QAM WDM coherent transmission over 160 km in the C-band using an injection-locked homodyne receiver with a spectral efficiency of 9 bit/s/Hz.

    Kan, Takashi / Kasai, Keisuke / Yoshida, Masato / Nakazawa, Masataka

    Optics express

    2017  Volume 25, Issue 19, Page(s) 22726–22737

    Abstract: We demonstrate a 235-channel wavelength division multiplexing (WDM), polarization-multiplexed (pol-mux) 18-Gbaud 64 QAM coherent transmission of 160 km over the full C-band. By applying an injection-locked homodyne detection circuit to WDM coherent ... ...

    Abstract We demonstrate a 235-channel wavelength division multiplexing (WDM), polarization-multiplexed (pol-mux) 18-Gbaud 64 QAM coherent transmission of 160 km over the full C-band. By applying an injection-locked homodyne detection circuit to WDM coherent transmission, we have achieved low noise optical carrier-phase locking between transmitted data and a local oscillator over the full C-band range. As a result, a potential capacity of 42.3 Tbit/s data with a spectral efficiency of 9 bit/s/Hz was transmitted.
    Language English
    Publishing date 2017-09-18
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1491859-6
    ISSN 1094-4087 ; 1094-4087
    ISSN (online) 1094-4087
    ISSN 1094-4087
    DOI 10.1364/OE.25.022726
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article: Interaction with DNA polymerase eta is required for nuclear accumulation of REV1 and suppression of spontaneous mutations in human cells.

    Akagi, Jun-Ichi / Masutani, Chikahide / Kataoka, Yuki / Kan, Takashi / Ohashi, Eiji / Mori, Toshio / Ohmori, Haruo / Hanaoka, Fumio

    DNA repair

    2009  Volume 8, Issue 5, Page(s) 585–599

    Abstract: Defects in the gene encoding human Poleta result in xeroderma pigmentosum variant (XP-V), an inherited cancer-prone syndrome. Poleta catalyzes efficient and accurate translesion DNA synthesis (TLS) past UV-induced lesions. In addition to Poleta, human ... ...

    Abstract Defects in the gene encoding human Poleta result in xeroderma pigmentosum variant (XP-V), an inherited cancer-prone syndrome. Poleta catalyzes efficient and accurate translesion DNA synthesis (TLS) past UV-induced lesions. In addition to Poleta, human cells have multiple TLS polymerases such as Poliota, Polkappa, Polzeta and REV1. REV1 physically interacts with other TLS polymerases, but the physiological relevance of the interaction remains unclear. Here we developed an antibody that detects the endogenous REV1 protein and found that human cells contain about 60,000 of REV1 molecules per cell as well as Poleta. In un-irradiated cells, formation of nuclear foci by ectopically expressed REV1 was enhanced by the co-expression of Poleta. Importantly, the endogenous REV1 protein accumulated at the UV-irradiated areas of nuclei in Poleta-expressing cells but not in Poleta-deficient XP-V cells. UV-irradiation induced nuclear foci of REV1 and Poleta proteins in both S-phase and G1 cells, suggesting that these proteins may function both during and outside S phase. We reconstituted XP-V cells with wild-type Poleta or with Poleta mutants harboring substitutions in phenylalanine residues critical for interaction with REV1. The REV1-interaction-deficient Poleta mutant failed to promote REV1 accumulation at sites of UV-irradiation, yet (similar to wild-type Poleta) corrected the UV sensitivity of XP-V cells and suppressed UV-induced mutations. Interestingly however, spontaneous mutations of XP-V cells were only partially suppressed by the REV1-interaction deficient mutant of Poleta. Thus, Poleta-REV1 interactions prevent spontaneous mutations, probably by promoting accurate TLS past endogenous DNA lesions, while the interaction is dispensable for accurate Poleta-mediated TLS of UV-induced lesions.
    MeSH term(s) Blotting, Western ; Cell Nucleus/genetics ; Cell Nucleus/metabolism ; Cell Nucleus/radiation effects ; DNA Damage/radiation effects ; DNA Repair ; DNA Replication ; DNA-Directed DNA Polymerase/genetics ; DNA-Directed DNA Polymerase/metabolism ; Fibroblasts/cytology ; Fibroblasts/metabolism ; Fibroblasts/radiation effects ; Fluorescent Antibody Technique ; G1 Phase ; HeLa Cells ; Humans ; Immunoprecipitation ; Mutation/genetics ; Nuclear Proteins/genetics ; Nuclear Proteins/metabolism ; Nucleic Acid Synthesis Inhibitors ; Nucleotidyltransferases/genetics ; Nucleotidyltransferases/metabolism ; RNA, Small Interfering/pharmacology ; S Phase ; Ultraviolet Rays
    Chemical Substances Nuclear Proteins ; Nucleic Acid Synthesis Inhibitors ; RNA, Small Interfering ; Nucleotidyltransferases (EC 2.7.7.-) ; REV1 protein, human (EC 2.7.7.-) ; DNA-Directed DNA Polymerase (EC 2.7.7.7) ; Rad30 protein (EC 2.7.7.7)
    Language English
    Publishing date 2009-05-01
    Publishing country Netherlands
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2071608-4
    ISSN 1568-7856 ; 1568-7864
    ISSN (online) 1568-7856
    ISSN 1568-7864
    DOI 10.1016/j.dnarep.2008.12.006
    Database MEDical Literature Analysis and Retrieval System OnLINE

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