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  • 1. da Silva, Edson P.
    et al.
    Borkowski, Robert
    Preussler, Stefan
    Schwartau, Fabian
    Gaiarin, Simone
    Olmedo, Miguel I.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Vedadi, Armand
    Piels, Molly
    Galili, Michael
    Guan, Pengyu
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Bres, Camille-Sophie
    Schneider, Thomas
    Oxenlowe, Leif K.
    Zibar, Darko
    Combined Optical and Electrical Spectrum Shaping for High-Baud-Rate Nyquist-WDM Transceivers2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 8, no 1, article id 7801411Article in journal (Refereed)
    Abstract [en]

    We discuss the benefits and limitations of optical time-division multiplexing (OTDM) techniques based on the optical generation of a periodic train of sinc pulses for wavelength-division multiplexing (WDM) transmission at high baud rates. It is shown how the modulated OTDM spectrum bandwidth is related to the optical comb parameters and the pulse shaping of the modulating waveforms in the electrical domain. Such dependence may result in broadening of the modulated spectra, which can degrade the performance of Nyquist-WDM systems due to interchannel crosstalk penalties. However, it is shown and experimentally demonstrated that the same technique of optical pulse train generation can be allied with digital pulse shaping to improve the confinement of the modulated spectrum toward the Nyquist limit independently of the number of OTDM tributaries used. To investigate the benefits of the proposed approach, we demonstrate the first WDM Nyquist-OTDM signal generation based on the periodic train of sinc pulses and electrical spectrum shaping. Straight line transmission of five 112.5-Gbd Nyquist-OTDM dual-polarization quadrature phase-shift keying (QPSK) channels is demonstrated over a dispersion uncompensated link up to 640 km, with full-field coherent detection at the receiver. It is shown that such a design strategy effectively improves the spectral confinement of the modulated OTDM signal, providing a minimum intercarrier crosstalk penalty of 1.5 dB in baud-rate-spaced Nyquist-WDM systems.

  • 2.
    Elshaari, Ali W.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Delft Univ Technol, Kavli Inst Nanosci, Netherlands.
    Zadeh, Iman Esmaeil
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Delft Univ Technol, Kavli Inst Nanosci, Netherlands.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Thermo-Optic Characterization of Silicon Nitride Resonators for Cryogenic Photonic Circuits2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 8, no 3, article id 2701009Article in journal (Refereed)
    Abstract [en]

    In this paper, we characterize the Thermo-optic properties of silicon nitride ring resonators between 18 and 300 K. The Thermo-optic coefficients of the silicon nitride core and the oxide cladding are measured by studying the temperature dependence of the resonance wavelengths. The resonant modes show low temperature dependence at cryogenic temperatures and higher dependence as the temperature increases. We find the Thermo-optic coefficients of PECVD silicon nitride and silicon oxide to be 2.51 +/- 0.08 E-5 K-1 and 0.96 +/- 0.09 E-5 K-1 at room temperature while decreasing by an order of magnitude when cooling to 18 K. To show the effect of variations in the thermo-optic coefficients on device performance, we study the tuning of a fully integrated electrically tunable filter as a function of voltage for different temperatures. The presented results provide new practical guidelines in designing photonic circuits for studying low-temperature optical phenomena.

  • 3. Gong, H.
    et al.
    Chen, Xi
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qu, Y.
    Li, Q.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, M.
    Photothermal Switching Based on Silicon Mach-Zehnder Interferometer Integrated with Light Absorber2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 8, no 2, article id 7456199Article in journal (Refereed)
    Abstract [en]

    We present an all-optical switch based on photothermal effects in a silicon Mach-Zehnder interferometer (MZI) integrated with a light absorber. The metal-insulator-metal light absorber located near the longer arm of the asymmetric MZI efficiently converts infrared light to heat. Pumped by a continuous-wave 1064-nm laser, the spectral transmittance of the fully etched strip waveguide (half-etched rib waveguide) MZI can be tuned with an efficiency of 38 pm/mW (98.5 pm/mW). Dynamic switching experiments show that the rise/fall time constant of the output probe light is 11.45/10.98 μs (8.25/7.13 μs) for the fully etched (half-etched) MZI.

  • 4.
    Jiang, Tao
    et al.
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Tang, Ming
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Lin, Rui
    KTH, School of Information and Communication Technology (ICT). Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Feng, Zhenhua
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Chen, Xi
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Deng, Lei
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Fu, Songnian
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Li, Xiang
    Wuhan Res Inst Posts & Telecommun, State Key Lab Opt Commun Technol & Networks, Wuhan 430074, Hubei, Peoples R China..
    Liu, Wu
    Wuhan Res Inst Posts & Telecommun, State Key Lab Opt Commun Technol & Networks, Wuhan 430074, Hubei, Peoples R China..
    Liu, Deming
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan Natl Lab Optoelect, Wuhan 430074, Hubei, Peoples R China.;Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan 430074, Hubei, Peoples R China..
    Investigation of DC-Biased Optical OFDM With Precoding Matrix for Visible Light Communications: Theory, Simulations, and Experiments2018In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 10, no 5, article id 7906916Article in journal (Refereed)
    Abstract [en]

    Orthogonal frequency-division-multiplexing (OFDM) technology is widely used in visible light communication (VLC) to achieve high data rate transmission. However, the traditional direct-current (DC)-biased optical OFDM (DCO-OFDM) VLC systems suffer from the high peak-to-average power ratio (PAPR) which causes signal clipping distortion, and, thus, performance degradation. Furthermore, severe high-frequency fading due to the limited system bandwidth results in poor bit error rate (BER) performance. Precoding matrix (PM) techniques have been proposed to enhance the performance of VLC OFDM transmission, but a little or no work has been carried out in investigating the theory of PM used in OFDM VLC systems. In this paper, we aim to reveal the theory of PM-DCO-OFDM for a VLC system. To figure out the intrinsic laws of a PM method, we investigate the principles of PAPR reduction, clipping distortion optimization, and signal-to-noise ratio (SNR) distribution equalization. Based on the analysis of PAPR, we theoretically proved the simplicity of PM as a method to reduce the possibility of high PAPR by improving the autocorrelation performance of input symbols. The clipping distortion could be improved due to the reduction of high PAPR. Moreover, the relatively uniform SNR distribution can be achieved by PM through equalizing the clipping and channel noise, which is beneficial to improve the BER performance in high-frequency constrained systems. However, the PM method used in a DCO-OFDM VLC system should consider the transmitting power, modulation format, and transmission distance as a whole to achieve the transmission performance improvement. The simulation results demonstrate the complementary cumulative distribution function of PAPR can be reduced similar to 3 dB, while the performance of clipping distortion power and clipping error probability are significantly improved. Furthermore, experiment is carried out with results showing that the PM method can improve the BER performance in the case that VLC OFDM transmission has enough transmitting power, but with the low transmitting power, the PM also can damage the BER performance. The simulation and experiment results are consistent with our theoretical analysis.

  • 5.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Bernhardi, Edward H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Accumulation of Distributed Phase Shift in Distributed-Feedback Resonators2019In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 11, no 1, article id 1500109Article in journal (Refereed)
    Abstract [en]

    Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum linewidth. The required pi/2 phase shift is often introduced by a distributed change in effective refractive index, e.g., by widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed wavelength. Even when thermally induced chirp or fabrication errors are negligible, this deviation is still present. Here, we show theoretically and experimentally that this deviation is of fundamental nature. The decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to reflection by the periodic grating and the refractive index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Considering the overlap integral between the distributed phase shift and light intensity in the design provides the desired performance.

  • 6.
    Lin, Rui
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. Huazhong University of Sci&Tech (HUST), China.
    Szczerba, Kraysztof
    Agrell, Erik
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Tang, Ming
    Liu, Deming
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Scalability Analysis of Coupler Based Optical InterconnectsIn: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655Article in journal (Other academic)
  • 7.
    Lin, Rui
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Scalability Analysis Methodology for Passive OpticalInterconnects in Data Center Networks Using PAM2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655Article in journal (Other academic)
  • 8.
    Liu, Shih-Chia
    et al.
    Univ Texas Arlington, Dept Elect Engn, Arlington, TX 76019 USA..
    Zhao, Deyin
    Univ Texas Arlington, Dept Elect Engn, Arlington, TX 76019 USA..
    Ge, Xiaochen
    Univ Texas Arlington, Dept Elect Engn, Arlington, TX 76019 USA..
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT).
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT).
    Fan, Shanhui
    Stanford Univ, Dept Elect Engn, Stanford, CA 94305 USA..
    Ma, Zhenqiang
    Univ Wisconsin, Dept Elect & Comp Engn, Madison, WI 53706 USA..
    Zhou, Weidong
    Univ Texas Arlington, Dept Elect Engn, Arlington, TX 76019 USA..
    Size Scaling of Photonic Crystal Surface Emitting Lasers on Silicon Substrates2018In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 10, no 3, article id 4500506Article in journal (Refereed)
    Abstract [en]

    We report here the lateral cavity size scaling and confinement effects on the lasing performance in defect-free photonic crystal surface-emitting lasers (PCSEL) on silicon substrates Hybrid PCSELs with different lateral cavity sizes and different lateral confinement geometries have been fabricated using transfer printing technology and controlled selective etching The measured lasing properties show a strong dependence on the lateral cavity size below 100 mu m. In particular, the finite lateral dimension significantly affects the laser threshold and side mode suppression ratio (SMSR) of the PCSEL devices On the other hand, by controlling the lateral confinement using vertical etching, a reduction of the laser threshold is observed The experimental results agree well with theoretical predictions The work presented here can lead to ultra-compact PCSELs for on-chip integration with excellent energy efficiency.

  • 9. Menon, L.
    et al.
    Yang, H.
    Cho, S. J.
    Mikael, S.
    Ma, Z.
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhou, W.
    Heterogeneously Integrated InGaAs and Si Membrane Four-Color Photodetector Arrays2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 8, no 2, article id 7445929Article in journal (Refereed)
    Abstract [en]

    We report the design and fabrication of heterogeneously integrated silicon and InGaAs membrane photodetector arrays. Visible and near-infrared (NIR) detection can be achieved by transfer printing a silicon membrane on InGaAs substrate. Based on the penetration-depth-dependent absorption of different wavelengths, filter-free visible color detection can be obtained via three-junction photocurrent measurement for silicon, and NIR can be detected by InGaAs. The measurements show good agreement with the optical behavior predicted by the design and simulation.

  • 10.
    Pang, Xiaodan
    et al.
    RISE ACREO AB; Technical University of Denmark.
    Caballero, Antonio
    Dogadaev, Anton
    Arlunno, Valeria
    Deng, Lei
    Borkowski, Robert
    Pedersen, Jesper S
    Zibar, Darko
    Yu, Xianbin
    Tafur Monroy, Idelfonso
    25 Gbit/s QPSK Hybrid Fiber-Wireless Transmission in the W-Band (75–110 GHz) With Remote Antenna Unit for In-Building Wireless Networks2012In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 4, no 3, p. 691-698Article in journal (Refereed)
    Abstract [en]

    In this paper, we demonstrate a photonic up-converted 25 Gbit/s fiber-wireless quadrature phase shift-keying (QPSK) data transmission link at the W-band (75-110 GHz). By launching two free-running lasers spaced at 87.5 GHz into a standard single-mode fiber (SSMF) at the central office, a W-band radio-over-fiber (RoF) signal is generated and distributed to the remote antenna unit (RAU). One laser carries 12.5 Gbaud optical baseband QPSK data, and the other acts as a carrier frequency generating laser. The two signals are heterodyne mixed at a photodetector in the RAU, and the baseband QPSK signal is transparently up-converted to the W-band. After the wireless transmission, the received signal is first down-converted to an intermediate frequency (IF) at 13.5 GHz at an electrical balanced mixer before being sampled and converted to the digital domain. A digital-signal-processing (DSP)-based receiver is employed for offline digital down-conversion and signal demodulation. We successfully demonstrate a 25 Gbit/s QPSK wireless data transmission link over a 22.8 km SSMF plus up to 2.13 m air distance with a bit-error-rate performance below the 2 x 10(-3) forward error correction (FEC) limit. The proposed system may have the potential for the integration of the in-building wireless networks with the fiber access networks, e. g., fiber-to-the-building (FTTB).

  • 11. Soares, Francisco M.
    et al.
    Fontaine, Nicolas K.
    Scott, Ryan P.
    Baek, J. H.
    Zhou, X.
    Su, T.
    Cheung, S.
    Wang, Y.
    Junesand, Carl
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Liou, K. Y.
    Hamm, R. A.
    Wang, W.
    Patel, B.
    Gruezke, L. A.
    Tsang, W. T.
    Heritage, Jonathan P.
    Yoo, S. J. B.
    Monolithic InP 100-Channel X 10-GHz Device for Optical Arbitrary Waveform Generation2011In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 3, no 6, p. 975-985Article in journal (Refereed)
    Abstract [en]

    We demonstrate monolithic integration of a 100-channel arrayed-waveguide grating (AWG) with 10-GHz channel spacing and 100 optically controlled Michelson-interferometer-based phase and amplitude modulators. The high-resolution AWG showed better than -15-dB crosstalk, and the modulator extinction ratio was better than 20 dB with either electrical or optical modulation control. The twin-integrated devices comprise a 50-mm diameter InP wafer with 1200 independent optoelectronic components.

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