Weiwei Zhang

Experimental GVD engineering in slow light slot photonic crystal waveguides

The use in silicon photonics of the new optical materials developed in soft matter science (e.g. polymers, liquids) is delicate because their low refractive index weakens the confinement of light and prevents an efficient control of the dispersion properties through the geometry. We experimentally demonstrate that such materials can be incorporated in 700u2009μm long slot photonic crystal waveguides, and hence can benefit from both slow-light field enhancement effect and slot-induced ultra-small effective areas. Additionally, we show that their dispersion can be engineered from anomalous to normal regions, along with the presence of multiple zero group velocity dispersion (ZGVD) points exhibiting Normalized Delay Bandwidth Product as high as 0.156. The reported results provide experimental evidence for an accurate control of the dispersion properties of fillable periodical slotted structures in silicon photonics, which is of direct interest for on-chip all-optical data treatment using nonlinear optical effects in hybrid-on-silicon technologies.

Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures

The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters. These typically require corrugation widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, to the best of our knowledge, on the realization of SOI Bragg filters based on sub-wavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints. Based on this concept, we experimentally demonstrate a single-etch, 220 nm thick, Si Bragg filter featuring a corrugation width of 150 nm, a rejection bandwidth of 1.1 nm, and an extinction ratio exceeding 40 dB. This represents a 10-fold width increase, compared to conventional single-periodicity, single-etch counterparts with similar bandwidths.

High-gain polymer optical waveguide amplifiers based on core-shell NaYF 4 /NaLuF 4 : Yb 3+ , Er 3+ NPs-PMMA covalent-linking nanocomposites

Waveguide amplifiers have always been significant key components for optical communication. Unfortunately, the low concentration of rare earth ions doped in the host material and the inadequate optimization of the waveguide structure have been the common bottleneck limitations. Here, a novel material, NaYF4/NaLuF4: 20% Yb3+, 2% Er3+ nanoparticle-Polymeric Methyl Methacrylate covalent-linking nanocomposite, was synthesized. The concentrations of Er3+ and Yb3+ doping increased an order of magnitude. Under a 980u2009nm laser excitation, highly efficient emission at 1.53u2009μm was obtained. The characteristic parameters of the single mode waveguide were carefully designed and optimized by using a finite difference method. A formulized iteration method is presented for solving the rate equations and the propagation equations of the EYCDWA, and both the steady state behavior and the gain were numerically simulated. The optimal Er3+ and Yb3+ concentrations are 2.8u2009×u20091026u2009m−3 and 2.8u2009×u20091027u2009m−3, and the optimal waveguide length is 1.3u2009cm. Both theoretical and experimental results indicated that, for an input signal power of 0.1u2009mW and a pump power of 400u2009mW, a net gain of 15.1u2009dB at 1530u2009nm is demonstrated. This result is the highest gain ever reported in polymer-based waveguide amplifiers doped with inorganic Er3+-Yb3+ codoped nanocrystals.

Tailoring carbon nanotubes optical properties through chirality-wise silicon ring resonators

Semiconducting single walled carbon nanotubes (s-SWNT) have an immense potential for the development of active optoelectronic functionalities in ultra-compact hybrid photonic circuits. Specifically, s-SWNT have been identified as a very promising solution to implement light sources in the silicon photonics platform. Still, two major challenges remain to fully exploit the potential of this hybrid technology: the limited interaction between s-SWNTs and Si waveguides and the low quantum efficiency of s-SWNTs emission. Silicon micro-ring resonators have the potential capability to overcome these limitations, by providing enhanced light s-SWNT interaction through resonant light recirculation. Here, we demonstrate that Si ring resonators provide SWNT chirality-wise photoluminescence resonance enhancement, releasing a new degree of freedom to tailor s-SWNT optical properties. Specifically, we show that judicious design of the micro-ring geometry allows selectively promoting the emission enhancement of either (8,6) or (8,7) SWNT chiralities present in a high-purity polymer-sorted s-SWNT solution. In addition, we present an analysis of nanometric-sized silicon-on-insulator waveguides that predicts stronger light s-SWNT interaction for transverse-magnetic (TM) modes than for conventionally used transverse-electric (TE) modes.

Hybrid integration of carbon nanotube emitters into silicon photonic nanoresonators (Conference Presentation)

Research of integrated light sources into the silicon platform has been extremely active for the past decades. Solutions such as the integration of III / V materials and components on silicon have been developed in a context of pre-industrial research, devices and systems intending very close to the market applications. The germanium(-tin) route has also demonstrated remarkable breakthroughs. The rationales of this research are the realization of optical interconnects. In parallel with these approaches, another interesting research field is the integration of nano-emitters, with the perspective of the realization of classical light sources but also of single photon and photon pair sources, in particular for quantum-on-chip communications.nIn this context, we propose the use of carbon nanotubes (CNTs) for the integration into silicon photonics towards novel optoelectronic devices. Indeed, CNTs are nanomaterials of particular interest in photonics thanks to their fundamental optical properties including near-IR luminescence, Stark effect, Kerr effect and absorption. Here, we report on the study of the light emission coupling from CNTs into optical nanobeam cavities implemented on the SOI platform. A wide range of situations have been studied by varying the deposition conditions of CNT-doped PFO polymer layers but also by considering different possible geometries of nanobeam cavities. Under optical pumping, we observe a very efficient coupling of the photoluminescence of the nanotubes with the modes of the nanocavities as well as a spectral narrowing of the photoluminescence spectra as a function of the optical power of the pump. These results contribute to the future realization of CNTs lasers, single photon and photon pair sources integrated on silicon.nThe authors thank the support of the European Commissions FP7-Cartoon project.

All-silicon carrier accumulation modulator based on a lateral MOS-capacitor

In silicon photonics, the carrier depletion scheme has been the most commonly used mechanism for demonstrating high speed electro-optic modulation. However, in terms of phase modulation efficiency, carrier accumulation based devices potentially offer almost an order of magnitude improvement over those based on carrier depletion. Previously reported accumulation modulator designs only considered vertical metal-oxide-semiconductor (MOS)-capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, for the first time we report experimental demonstration of an all-silicon accumulation phase modulator based on a lateral MOS-capacitor. Using a Mach-Zehnder interferometer (MZI) modulator with a 500-µm-long phase-shifter, we demonstrate high speed modulation up to 25 Gbit/s with a modulation efficiency (VπLπ) of 1.53 V-cm.

Subwavelength Si photonics for near- and mid-infrared applications (Conference Presentation)

We report our advances in development of subwavelength engineered silicon photonic devices for near- and mid-infrared applications. By periodically patterning Si with a pitch small enough to suppress diffraction, we synthesize an effective photonic medium with refractive index between those of Si and the cladding material. This technique releases new degrees of freedom in engineering of light-matter interaction, chromatic dispersion and light propagation in Si photonic waveguides. We present an overview of our recent results in the realization of novel devices including filters and waveguides for near- and mid-infrared wavelength range.

Raw data for "High speed all-silicon carrier accumulation modulator based on a lateral MOS-capacitor"

This dataset contains the raw data used for the figures in the paper Kapil Debnath, David J. Thomson, Weiwei Zhang, Ali Z Khokhar, Callum Littlejohns, James Byers, Lorenzo Mastronardi, Muhammad K. Husain, Fredric Y. Gardes, Graham T. Reed, and Shinichi Saito High speed all-silicon carrier accumulation modulator based on a lateral MOS-capacitorAbstract: In silicon photonics, primarily carrier depletion scheme has been used for demonstrating high speed electro-optic modulation. However, in terms of phase modulation efficiency, carrier accumulation process offers almost an order of magnitude improvement over carrier depletion process. Due to fabrication restriction, previously reported accumulation modulator designs only considered vertical metal-oxide-semiconductor (MOS)-capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, we design and experimentally demonstrate an all-silicon accumulation phase modulator based on a lateral MOS-capacitor. Using a Mach-Zehnder interferometer (MZI) modulator with a 500-µm-long phase-shifter, we demonstrate high speed modulation up to 25 Gbit-s-1 with a modulation efficiency (VπLπ) of 1.53 V-cm.

Raw data for "20Gbps silicon lateral MOS-Capacitor electro-optic modulator"

This dataset contains the raw data used for the figures in the paper Kapil Debnath, David J. Thomson, Weiwei Zhang, Ali Z Khokhar, Callum Littlejohns, James Byers, Lorenzo Mastronardi, Muhammad K. Husain, Fredric Y. Gardes, Graham T. Reed, and Shinichi Saito 20Gbps silicon lateral MOS-Capacitor electro-optic modulator in CLEO Laser Science to Photonic Applications 2018. Conference on Lasers and Electro-optics 2018, San Jose, United States, 13-18 May.Abstract: This work presents an experimental demonstration of a 500µm long MZI carrier accumulation type modulator based on lateral MOS-capacitor integration on a silicon platform. A modulation efficiency (VπLπ) of 1.53V-cm, moderate modulation speed of 20Gbit-s-1 and extinction ratio of 3.65dB have been obtained.

Efficient excitation of silicon photonic cavity modes from carbon nanotube photoluminescence

Semiconducting single wall carbon nanotubes (s-SWCNTs) are promising room-temperature telecom-band nano-emitters that could be integrated in silicon photonic circuits for the realization of on-chip optical sources. We report here the integration of a large quantity of s-SWCNTs as an active cladding layer on top of silicon micro/nano cavities. The gathered results show that the luminescence of the SCNTs can be efficiently coupled into the considered photonic crystal cavity modes, which exhibits a clear spectral narrowing as a function of the pump power. These results constitute an important step towards the realization of a carbon nanotube optical source integrated into the silicon platform.