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Personne :
Jafari, Omid

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Jafari

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Omid

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Université Laval. Faculté des sciences et de génie

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ncf11921344

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Résultats de recherche

Voici les éléments 1 - 10 sur 10
  • PublicationAccès libre
    High-efficiency silicon photonic modulator using coupled Bragg grating resonators
    (Institute of Electrical and Electronics Engineers, 2019-02-05) Jafari, Omid; Sepehrian, Hassan; LaRochelle, Sophie; Shi, Wei
    We propose a novel design of a silicon photonic modulator that has a high modulation efficiency and that is tolerant to temperature variations. A series of phase-shifted Bragg gratings are placed in each arm of a Mach-Zehnder interferometer in order to provide enhanced phase modulation. The slow light effect in these ultra-compact coupled resonators improves phase modulation efficiency compared to conventional silicon phase shifters. These Bragg grating cavities are designed such that the optical bandwidth is increased compared to other coupled resonators such as micro-rings. This improved bandwidth reduces the temperature sensitivity of the devices. We present in detail how to optimize these modulators considering properties such as modulation efficiency (Vπ×L), optical modulation amplitude (OMA), and optical bandwidth (𝛥λBW); the latter property determining the operating temperature range (𝛥T). As examples, we present two designs that meet different target specifications for short-reach or long-haul applications. We further provide a model, based on coupled mode theory, to investigate the dynamic response of the proposed modulators. A large signal analysis is performed using finite difference time domain (FDTD) in order to simulate on/off keying (OOK) modulation and eye diagrams up to 110 Gb/s.
  • PublicationAccès libre
    Mach-Zehnder silicon photonic modulator assisted by phase-shifted Bragg gratings
    (Institute of Electrical and Electronics Engineers, 2020-03-05) Jafari, Omid; LaRochelle, Sophie; Shi, Wei
    We experimentally demonstrate a silicon photonic Mach-Zehnder modulator (MZM) assisted by phase-shifted Bragg gratings. Coupled resonators are inserted in the Bragg grating structure to significantly enhance the phase modulation efficiency, while maintaining a wide optical bandwidth compared to other resonator-based modulators. Fabricated using a CMOS-compatible foundry process, the device achieved a small-signal Vπ× L of 0.18 V.cm, which is seven times lower than a conventional silicon MZM fabricated with the same process. The device has a compact footprint, with a length of only 162 μm , and shows a modulation bandwidth of 28 GHz at a reverse bias of 1 V. Non-return-to-zero modulation is demonstrated at 30 Gb/s with a bit-error-rate (BER) below the 7%-overhead forward error correction (FEC) threshold over a bandwidth of 3.5 nm. This bandwidth should translate into an operating temperature range greater than 40 0 C.
  • PublicationAccès libre
    Silicon photonic modulator loaded by NPN junctions
    (Institute of electrical and electronics engineers, 2020-08-17) Jafari, Omid; LaRochelle, Sophie; Shi, Wei
    We experimentally demonstrate an asymmetric Bragg grating modulator with a phase shifter length of 240 μm, loaded by p-n junctions. The mode conversion by the asymmetric sidewall grating allows us to operate a Bragg modulator in reflection without a circulator. Simulation results show that there is room for improving the modulator efficiency and footprint by exploiting NPN junctions instead of p-n junctions.
  • PublicationAccès libre
    Silicon photonic modulator based on coupled Bragg grating resonators used as phase shifters
    (Optical Society of America, 2018-03-11) Jafari, Omid; Sepehrian, Hassan; LaRochelle, Sophie; Shi, Wei
    Bragg gratings with phase-shifts are inserted in a Mach-Zehnder modulator to enhance phase modulation, reduce device length and improve efficiency (Vπ×L=0.28 Vcm). Simulations show 3 nm optical bandwidth corresponding to 50 K operating temperature range.
  • PublicationAccès libre
    Efficiency-speed tradeoff in slow-light silicon photonic modulators
    (IEEE, 2020-11-06) Jafari, Omid; LaRochelle, Sophie; Shi, Wei
    he purpose of this paper is twofold. First, we discuss the efficiency-speed tradeoff in slow-light (SL) silicon photonic (SiP) modulators. For this, a comprehensive model for the electro-optic (EO) response of lumped-electrode SL Mach-Zehnder modulators (SL-MZMs) is presented. The model accuracy is verified by comparing it to experiments. Our analysis shows that slowing down the optical wave helps to enhance efficiency by increasing the interaction time between the optical wave and the uniform voltage across lumped electrodes, but at the cost of limiting the EO bandwidth. Then, we investigate SL-MZMs with traveling-wave (TW) electrodes whose dynamic interaction is predicted using a distributed circuit model. Having been solved by the finite-difference time-domain (FDTD) method, the model shows that TW SL-MZMs are capable of improving both efficiency and speed under an optimized SL effect. We also compare SL-MZMs with conventional MZMs (C-MZM) considering a figure of merit (FOM) that combines key parameters such as efficiency, loss, and EO bandwidth. We show that the additional loss of SL waveguides significantly impacts the preferred modulator choice at different baudrates. The second aim of this paper is to examine different design strategies to reduce Vπ of C-MZMs in order to meet the requirement of COMS driver using 1) a longer phase shifter, 2) higher doping densities, and 3) the SL effect. It is shown that the SL effect provides the best overall performance among the three. Indeed, only the SL effect offers simultaneous improvement in Vπ, footprint, and EO bandwidth; the other approaches provide Vπ reduction but at the cost of reduced speed or enlarged footprint (or even both).
  • PublicationAccès libre
    Silicon photonic modulator using mode conversion with asymmetric sidewall bragg gratings
    (IEEE, 2018-10-04) Jafari, Omid; LaRochelle, Sophie; Shi, Wei
    An asymmetric sidewall grating allows to operate a Bragg modulator in reflection without circulator and with less than 1.5 dB on-chip loss. An asymmetric Y-branch directs the incident TE0 mode to the grating, while the reflected TE1 mode is guided to the drop port.
  • PublicationAccès libre
    A model for electro-optic response of lumped slow-light silicon photonic modulators
    (IEEE, 2020-11-16) Jafari, Omid; LaRochelle, Sophie; Shi, Wei
    We model the electro-optic bandwidth of lumped slow-light modulators. In agreement with experiments, the model shows that modulators speed is determined by the RC constant and the interaction time in the slow light Brag structure.
  • PublicationRestreint
    Mode-conversion-based silicon photonic modulator using asymmetric Bragg grating and Y-branch
    (2019-09-22) Lin, Jiachuan; Jafari, Omid; LaRochelle, Sophie; Shi, Wei
    We experimentally demonstrate a Bragg-grating-based modulator operating in reflection with low loss and without a circulator by using mode conversion and an asymmetric Y-branch. With a compact footprint of 240μm, we demonstrate OOK up to 30 Gbit/s with an estimated switching energy of 150 fJ/bit.
  • PublicationRestreint
    Silicon photonic modulator loaded by a combination of lateral and interleaved p-n junctions
    (OSA, 2020-07-16) Jafari, Omid; Zhalehpour, Sasan; LaRochelle, Sophie; Shi, Wei
    We experimentally demonstrate a silicon photonic modulator loaded by lateral and interleaved p-n junctions simultaneously. Operated in reflection without a circulator, we demonstrate OOK up to 45Gbit/s with a short phase shifter length of 290µm.
  • PublicationAccès libre
    Mode-conversion-based silicon photonic modulator loaded by a combination of lateral and interleaved p-n junctions
    (Optical Society of America, 2021-03-19) Jafari, Omid; Zhalehpour, Sasan; LaRochelle, Sophie; Shi, Wei
    We experimentally demonstrate a silicon photonic modulator that can be loaded with a combination of lateral and interleaved p-n junctions to enhance its phase modulation. We use an asymmetric Bragg grating to introduce mode conversion in the active area, allowing the modulator to operate in reflection without introducing additional on-chip loss. With a compact footprint (phase shifter length of 290 μm), the modulator demonstrates a modulation speed up to 45 Gb/s with a bit error rate below the 7% forward-error-correction (FEC) threshold (up to 55 Gb/s with 20% FEC), and a low power consumption of 226 fJ/bit.