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1.
  • Dely, H., et al. (creator_code:aut_t)
  • High bitrate data transmission in the 8-14 µm atmospheric window using an external Stark-effect modulator with digital equalization
  • 2023
  • record:In_t: Optics Express. - : Optica Publishing Group (formerly OSA). - 1094-4087. ; 31:5, s. 7259-7264
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • High bitrate mid-infrared links using simple (NRZ) and multi-level (PAM-4) data coding schemes have been realized in the 8 µm to 14 µm atmospheric transparency window. The free space optics system is composed of unipolar quantum optoelectronic devices, namely a continuous wave quantum cascade laser, an external Stark-effect modulator and a quantum cascade detector, all operating at room-temperature. Pre- and post-processing are implemented to get enhanced bitrates, especially for PAM-4 where inter-symbol interference and noise are particularly detrimental to symbol demodulation. By exploiting these equalization procedures, our system, with a full frequency cutoff of 2 GHz, has reached transmission bitrates of 12 Gbit/s NRZ and 11 Gbit/s PAM-4 fulfilling the 6.25 % overhead hard-decision forward error correction threshold, limited only by the low signal-to-noise ratio of our detector. 
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2.
  • Gyger, Samuel, et al. (creator_code:aut_t)
  • Reconfigurable frequency coding of triggered single photons in the telecom C–band
  • 2019
  • record:In_t: Optics Express. - : OSA. - 1094-4087. ; 27:10, s. 14400-14406
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • In this work, we demonstrate reconfigurable frequency manipulation of quantum states of light in the telecom C–band. Triggered single photons are encoded in a superposition state of three channels using sidebands up to 53 GHz created by an off-the-shelf phase modulator. The single photons are emitted by an InAs/GaAs quantum dot grown by metal-organic vapor-phase epitaxy within the transparency window of the backbone fiber optical network. A cross-correlation measurement of the sidebands demonstrates the preservation of the single photon nature; an important prerequisite for future quantum technology applications using the existing telecommunication fiber network.
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3.
  • Han, Mengyao, et al. (creator_code:aut_t)
  • Simultaneous modulation format identification and OSNR monitoring based on optoelectronic reservoir computing
  • 2022
  • record:In_t: Optics Express. - : Optica Publishing Group (formerly OSA). - 1094-4087. ; 30:26, s. 47515-47527
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • An approach for simultaneous modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) monitoring in digital coherent optical communications is proposed based on optoelectronic reservoir computing (RC) and the signal’s amplitude histograms (AHs) obtained after the adaptive post-equalization. The optoelectronic RC is implemented using a Mach-Zehnder modulator and optoelectronic delay feedback loop. We investigate the performance of the proposed model with the number of symbols, bins of AHs and the hyperparameters of optoelectronic RC. The results show that 100% MFI accuracy can be achieved simultaneously with accurate OSNR estimation for different modulation formats under study. The lowest achievable OSNR estimation mean absolute errors for the dual-polarization (DP)-quadrature phase-shift keying signal, the DP-16-ary quadrature amplitude modulation (16QAM) signal, and the DP-64QAM signal are 0.2 dB, 0.32 dB and 0.53 dB, respectively. The robustness of the proposed scheme is also evaluated when the optoelectronic RC is in presence of additive white Gaussian noises. Then, a proof of concept experiment is demonstrated to further verify our proposed method. The proposed approach offers a potential solution for next-generation intelligent optical performance monitoring in the physical layer.
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4.
  • Iyer, Srinivasan, et al. (creator_code:aut_t)
  • Impact of apexes on the resonance shift in double hole nanocavities
  • 2010
  • record:In_t: Optics Express. - 1094-4087. ; 18:1, s. 193-203
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • The transmission of light through metallic films with periodic double nanoholes is studied using vectorial three-dimensional finite element method. Special emphasis is given on understanding different transmission resonances arising in gold and silver films with periodic sub-wavelength holes of different shapes. The spectral shift of the hole-shape resonance resulting from a variation of the hole refractive index is analyzed for a double nanohole geometry in the transmission mode using numerical simulations. Specifically, the role of field enhancement at the apexes of the double nanohole in the sensing of medium within the hole cavity is pointed out and discussed. The presence of sharp apexes within the double nanoholes significantly improves the resonance sensitivity as compared to rectangular holes of comparable area. Impact of possible manufacturing errors on the overall sensitivity is also characterized. Robustness and a relatively simple fabrication procedure make these kinds of refractive index sensors practically attractive.
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5.
  • Iyer, Srinivasan, et al. (creator_code:aut_t)
  • Transmission resonances in periodic U-shaped metallic nanostructures
  • 2010
  • record:In_t: Optics Express. - 1094-4087. ; 18:17, s. 17719-17728
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • The spectral response of crescent-like metallic nanostructures, a sub-class of U-shaped split-ring resonators, on a glass substrate at normal incidence is studied numerically. Also, the interpretation of transmission resonances arising from periodic conventional standard split-ring resonators with rectangular edges (SSRR) at normal incidence is revisited. In particular, we focus on one specific transmission resonance which is present for nano-crescents (NC) but absent in the case of SSRRs used for metamaterials. It is proposed that for a U-shaped metallic structure of arbitrary geometry, coupling of plasmonic eigen modes at all the surfaces of the three-dimensional structure is essential to be considered. The manner in which the coupling takes place between plasmonic modes at all the surfaces of the three-dimensional structure is what completely characterizes transmission resonances, and it is unique for each given resonance. (C) 2010 Optical Society of America
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6.
  • Jacobsen, Gunnar, et al. (creator_code:aut_t)
  • EEPN and CD study for coherent optical nPSK and nQAM systems with RF pilot based phase noise compensation
  • 2012
  • record:In_t: Optics Express. - 1094-4087. ; 20:8, s. 8862-8870
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A radio frequency (RF) carrier can be used to mitigate the phase noise impact in n-level PSK and QAM systems. The systems performance is influenced by the use of an RF pilot carrier to accomplish phase noise compensation through complex multiplication in combination with discrete filters to compensate for the chromatic dispersion (CD). We perform a detailed study comparing two filters for the CD compensation namely the fixed frequency domain equalizer (FDE) filter and the adaptive least-mean-square (LMS) filter. The study provides important novel physical insight into the equalization enhanced phase noise (EEPN) influence on the system bit-error-rate (BER) versus optical signal-to-noise-ratio (OSNR) performance. Important results of the analysis are that the FDE filter position relative to the RF carrier phase noise compensation module provides a possibility for choosing whether the EEPN from the Tx or the LO laser influences the system quality. The LMS filter works very inefficiently when placed prior to the RF phase noise compensation stage of the Rx whereas it works much more efficiently and gives almost the same performance as the FDE filter when placed after the RF phase noise compensation stage.
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7.
  • Jacobsen, Gunnar, et al. (creator_code:aut_t)
  • Receiver implemented RF pilot tone phase noise mitigation in coherent optical nPSK and nQAM systems
  • 2011
  • record:In_t: Optics Express. - 1094-4087. ; 19:15, s. 14487-14494
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • In this paper, a novel method for extracting an RF pilot carrier signal in the coherent receiver is presented. The RF carrier is used to mitigate the phase noise influence in n-level PSK and QAM systems. The performance is compared to the use of an (ideal) optically transmitted RF pilot tone. As expected an electronically generated RF carrier provides less efficient phase noise mitigation than the optical RF. However, the electronically generated RF carrier still improves the phase noise tolerance by about one order of magnitude in bit error rate (BER) compared to using no RF pilot tone. It is also found, as a novel study result, that equalization enhanced phase noise - which appears as correlated pure phase noise, amplitude noise and time jitter - cannot be efficiently mitigated by the use of an (optically or electrically generated) RF pilot tone.
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8.
  • Jacobsen, Gunnar, et al. (creator_code:aut_t)
  • Study of EEPN mitigation using modified RF pilot and Viterbi-Viterbi based phase noise compensation
  • 2013
  • record:In_t: Optics Express. - : Optical Society of American (OSA). - 1094-4087. ; 21:10, s. 12351-12362
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • We propose - as a modification of the optical (RF) pilot scheme -a balanced phase modulation between two polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations. The method is applicable for n-level PSK system. The EEPN can be compensated, the carrier phase extracted and the nPSK signal regenerated by complex conjugation and multiplication in the receiver. The method is tested by system simulations in a single channel QPSK system at 56 Gb/s system rate. It is found that the conjugation and multiplication scheme in the Rx can mitigate the EEPN to within 1/2 orders of magnitude. Results are compared to using the Viterbi-Viterbi algorithm to mitigate the EEPN. The latter method improves the sensitivity more than two orders of magnitude. Important novel insight into the statistical properties of EEPN is identified and discussed in the paper.
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9.
  • Kakkar, Aditya, et al. (creator_code:aut_t)
  • Impact of local oscillator frequency noise on coherent optical systems with electronic dispersion compensation
  • 2015
  • record:In_t: Optics Express. - 1094-4087. ; 23:9, s. 11221-11226
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator. Hence, elimination of the frequency noise below a certain cut-off frequency significantly reduces the transmission penalty, even when frequency noise would otherwise cause an error floor. The required cut-off frequency increases linearly with the white frequency noise level and hence the linewidth of the local oscillator laser, but is virtually independent of the symbol rate and the accumulated dispersion.
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10.
  • Koivurova, Matias, et al. (creator_code:aut_t)
  • Complete spatial coherence characterization of quasi-random laser emission from dye doped transparent wood
  • 2018
  • record:In_t: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 26:10, s. 13474-13482
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • We report on the experimental determination of the complete two coordinate spatial coherence function of light emitted by a quasi-random laser, implemented on recently introduced dye-doped transparent wood. The spatial coherence was measured by means of a double grating interferometer, which has some advantages over the standard Young's interferometer. Analysis of the spatial coherence reveals that emission from such a material can be considered as a superposition of several spatial modes produced by individual emitters within semi-ordered scattering medium. The overall degree of coherence, (gamma)over-bar, for this quasi-random laser was found to be 0.16 +/- 0.01, having possible applications in speckle free laser imaging and illumination.
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