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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: Multi-IF-over-fiber transmission using a commercial TOSA for analog fronthaul networks aiming beyond 5G.

    Ishimura, Shota / Kao, Hsuan-Yun / Tanaka, Kazuki / Nishimura, Kosuke / Inohara, Ryo / Suzuki, Masatoshi

    Optics express

    2021  Volume 29, Issue 2, Page(s) 2270–2278

    Abstract: An IF-over-fiber (IFoF)-based analog transport technology for mobile fronthaul applications has recently attracted significant attention. However, most previous studies have employed discrete optical components. For the analog transport technology to be ... ...

    Abstract An IF-over-fiber (IFoF)-based analog transport technology for mobile fronthaul applications has recently attracted significant attention. However, most previous studies have employed discrete optical components. For the analog transport technology to be a more cost-effective and power-efficient solution, it is necessary to utilize existing integrated optical transceivers. In this paper, we demonstrate IFoF transmission using a commercial off-the-shelf transmitter optical sub-assembly (TOSA). Although the TOSA was developed for a digital system employing non-return-to-zero (NRZ) signals, we show that it is also possible for the TOSA to support high-capacity analog transmission. As a demonstration, by using the TOSA, we could successfully transmit 64- and 256-ary quadrature-amplitude-modulated (64/256QAM) orthogonal-frequency-division-multiplexed (OFDM) signals with net bit rates of 54.74 and 36.49 Gbps per wavelength, respectively. Since the TOSA has four wavelength channels, the total capacities are 218.94 and 145.98 Gbps, respectively. To the best of our knowledge, these rates are the highest among all the demonstrations using analog transport technology.
    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.414714
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Integrated dual-polarization coherent receiver without a polarization splitter-rotator.

    Soma, Go / Ishimura, Shota / Tanomura, Ryota / Fukui, Taichiro / Ito, Maiko / Nakano, Yoshiaki / Tanemura, Takuo

    Optics express

    2021  Volume 29, Issue 2, Page(s) 1711–1721

    Abstract: We propose and demonstrate a simple integrated dual-polarization (DP) coherent receiver that does not require a polarization splitter-rotator (PSR). Based on a novel concept, a DP coherent signal is mixed with the local-oscillator (LO) waves inside a ... ...

    Abstract We propose and demonstrate a simple integrated dual-polarization (DP) coherent receiver that does not require a polarization splitter-rotator (PSR). Based on a novel concept, a DP coherent signal is mixed with the local-oscillator (LO) waves inside a single interferometer and detected by five single-ended photodetectors. The signal-signal and LO-LO beat noises are eliminated through differential detection. We design and fabricate a proof-of-concept device on InP and experimentally demonstrate complete retrieval of DP quadrature phase-shift keyed signals. Requiring minimal number of optical components without a PSR, the demonstrated scheme would be attractive particularly for the InP and thick-silicon photonic platforms due to its significantly reduced footprint and ease of fabrication.
    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.413310
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Eight-state trellis-coded optical modulation with signal constellations of four-dimensional M-ary quadrature-amplitude modulation.

    Ishimura, Shota / Kikuchi, Kazuro

    Optics express

    2015  Volume 23, Issue 5, Page(s) 6692–6704

    Abstract: We apply the eight-state trellis-coded modulation (TCM) using signal constellations of four-dimensional M-ary quadrature-amplitude modulation (4D-MQAM) to optical communication systems for the first time to our knowledge. In the TCM scheme, the free ... ...

    Abstract We apply the eight-state trellis-coded modulation (TCM) using signal constellations of four-dimensional M-ary quadrature-amplitude modulation (4D-MQAM) to optical communication systems for the first time to our knowledge. In the TCM scheme, the free distance of the trellis diagram is equal to the minimum distance between constellation points in partitioned subsets, which enlarges the coding gain effectively. In fact, its asymptotic power efficiency is 3-dB larger than that of the set-partitioned 4D-MQAM (SP-4D-MQAM) format, while their spectral efficiencies are the same. Such theoretical predictions are confirmed through computer simulations on eight-state TCM with constellations of 4D-4QAM (i.e., 4D quadrature phase-shift keying: 4D-QPSK) and 4D-16QAM. In particular, eight-state TCM with 4D-QPSK constellations is practically important because of its simple encoder structure, relatively low computational cost, and high coding gain against dual-polarization QPSK (DP-QPSK) and SP-4D-QPSK. Through measurements of its bit-error rate (BER) performance, we confirm that the coding gain against DP-QPSK is about 3 dB at BER=10(-3).
    Language English
    Publishing date 2015-03-09
    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.23.006692
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Multi-dimensional permutation-modulation format for coherent optical communications.

    Ishimura, Shota / Kikuchi, Kazuro

    Optics express

    2015  Volume 23, Issue 12, Page(s) 15587–15597

    Abstract: We introduce the multi-dimensional permutation-modulation format in coherent optical communication systems and analyze its performance, focusing on the power efficiency and the spectral efficiency. In the case of four-dimensional (4D) modulation, the ... ...

    Abstract We introduce the multi-dimensional permutation-modulation format in coherent optical communication systems and analyze its performance, focusing on the power efficiency and the spectral efficiency. In the case of four-dimensional (4D) modulation, the polarization-switched quadrature phase-shift keying (PS-QPSK) modulation format and the polarization quadrature-amplitude modulation (POL-QAM) format can be classified into the permutation modulation format. Other than these well-known modulation formats, we find novel modulation formats trading-off between the power efficiency and the spectral efficiency. With the increase in the dimension, the spectral efficiency can more closely approach the channel capacity predicted from the Shannon's theory. We verify these theoretical characteristics through computer simulations of the symbol-error rate (SER) and bit-error rate (BER) performances. For example, the newly-found eight-dimensional (8D) permutation-modulation format can improve the spectral efficiency up to 2.75 bit/s/Hz/pol/channel, while the power penalty against QPSK is about 1 dB at BER=10(-3).
    Language English
    Publishing date 2015-06-15
    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.23.015587
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Article ; Online: Complete retrieval of multi-level Stokes vector signal by an InP-based photonic integrated circuit.

    Ghosh, Samir / Suganuma, Takahiro / Ishimura, Shota / Nakano, Yoshiaki / Tanemura, Takuo

    Optics express

    2019  Volume 27, Issue 25, Page(s) 36449–36458

    Abstract: An integrated Stokes vector receiver (SVR) that can retrieve state of polarization of light in the three-dimensional (3D) Stokes space has widespread applications, such as short-reach communication links, polarization-sensitive imaging, and sensing. ... ...

    Abstract An integrated Stokes vector receiver (SVR) that can retrieve state of polarization of light in the three-dimensional (3D) Stokes space has widespread applications, such as short-reach communication links, polarization-sensitive imaging, and sensing. While various approaches have been demonstrated to date, monolithic integration of polarization components on InP has been a challenging issue. In this paper, we develop a novel 4-port SVR circuit integrated on a compact InP chip to retrieve complete Stokes parameters of incoming light with various intensity and degree-of-polarization. By judiciously designing the lengths and positions of asymmetric waveguide sections, we demonstrate that the SV of signal can be projected onto four vertices of a regular tetrahedron inscribed in the Poincaré sphere. Additionally, we employ this device in decoding 10-Gbaud 4-ary and 8-ary Stokes-vector-modulated signals in the 3D Stokes space.
    Language English
    Publishing date 2019-12-23
    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.27.036449
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article ; Online: Photonic Armstrong method enabled by direct detection for wideband electrical PM generation.

    Ishimura, Shota / Kao, Hsuan-Yun / Tanaka, Kazuki / Nishimura, Kosuke / Inohara, Ryo / Tsuritani, Takehiro / Suzuki, Masatoshi

    Optics express

    2021  Volume 29, Issue 3, Page(s) 4721–4732

    Abstract: Wideband signal generation using frequency/phase modulation (FM/PM) is the key fundamental function for various applications such as radar and analog communication systems. It is well known that analog FM/PM communication systems can dramatically improve ...

    Abstract Wideband signal generation using frequency/phase modulation (FM/PM) is the key fundamental function for various applications such as radar and analog communication systems. It is well known that analog FM/PM communication systems can dramatically improve signal quality by spectral expansion. In classical communication theories, the Armstrong indirect method is one of the most popular methods for bandwidth expansion of FM signals. In the Armstrong method, a narrowband signal is converted to a broadband signal with the help of a nonlinear frequency multiplier. In this paper, we propose a photonic Armstrong method enabled by direct detection. By utilizing the nonlinearity caused by direct detection, we can increase bandwidth so that it is double that of the original signal in the photonic Armstrong method. Also, it completely eliminates signal-to-signal beat interference (SSBI) at the same time. We conducted an experiment to verify the concept and confirmed these advantages experimentally.
    Language English
    Publishing date 2021-02-01
    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.417640
    Database MEDical Literature Analysis and Retrieval System OnLINE

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