Silicon Photonics; Ring Modulator Transmitters

The depletion-type Si ring modulator (RM) is of great interest among many Si photonic devices for optical interconnect applications because it has a small size, low power consumption, and large modulation bandwidth. Although the major application of the Si RM are digital optical interconnect systems, there is another application of importance, namely microwave photonics in which the modulation linearity is a key performance parameter. We investigate the modulation linearity performance in terms of spurious-free dynamic range (SFDR) of a RM device fabricated by IHP Si PIC foundry. The device has 8-um radius, 290-nm coupling gap and the nominal peak doping concentration of 7×1017 cm−3 for p-region and 3×1018 cm−3 for n-region. The measured SFDR is 78.7 dB·Hz2/3. The major sources of non-linearity of this device are the nonlinear free-carrier plasma dispersion effect in PN junction as well as the nonlinear resonance characteristics. We also perform the numerical simulation of RM SFDR using key device parameters extracted from measurement. The simulation results match well with the measurement results. With this numerical model, we are able to identify the exact cause of RM nonlinearity and come up with suggestions for improving RM linearity.

We design and analyze a novel high-speed directly-modulated laser combining a pair of push-pull ring modulators. The mechanism of push-pull modulators makes the laser immune to phase-change induced wavelength chirp and other cavity-related modulation penalties.

This study is an experimental research on non-linear effects occurring in vibro-acoustic modulation tests. The work focuses on the analysis of the modulation type. The modulation of the response signal is due to interaction between low- and high-frequency excitation and damage surfaces, which results in the formation of higher harmonics and sidebands. The analysis of the sidebands is an extremely important issue. Their presence may indicate damage in structure. In many cases, the sidebands can be used to determine the damage index. However, not always, the distribution of the sidebands and their evaluation with excitation amplitude allow for an unambiguous interpretation. This may be the result of various damage-related non-linearity sources, which depend on the amplitude of the excitation. Because different types of non-linearities are manifested in different ways, the change in non-linearity type can cause, for example, the disappearance of odd sidebands and/or even harmonics or change in modulation type. To analyse the indicated issues, the sample with prepared contact surfaces was tested in experimental works. Two excitation types, low and high frequencies, are introduced into the structure via electromagnetic shaker and piezoelectric transducer, respectively, to produce contact-related non-linear effects. The contact surfaces are driven to move relative to each other. For a given scenario, the analysis of modulation sidebands is performed based on signal response. The instantaneous frequency approach is used to evaluate modulation type. The results show that the changes in the amplitude of the excitation change the modulation type of response signal. The probable causes of this phenomenon are given.

The unique optical and electronic properties of graphene make possible the fabrication of novel optoelectronic devices. One of the most exciting graphene characteristics is the tunability by gating which allows one to realize active optical devices. While several types of graphene-based photonic modulators have already been demonstrated, the potential of combining the versatility of graphene with subwavelength field confinement of plasmonic waveguides remains largely unexplored. Here we report fabrication and study of hybrid graphene–plasmonic waveguide modulators. We consider several types of modulators and identify the most promising one for telecom applications. The modulator working at the telecom range is demonstrated, showing a modulation depth of >0.03 dB μm−1 at low gating voltages for an active device area of just 10 μm2, characteristics which are already comparable to those of silicon-based waveguide modulators while retaining the benefit of further device miniaturization. Our proof-of-concept results pave the way towards on-chip realization of efficient graphene-based active plasmonic waveguide devices for optical communications.

The aim of the present study was to design and fabricate polyglycolic acid (PGA) modules on the basis of the Raschig ring as a tissue element for bottom–top tissue engineering to increase the feasibility of cellular-assembly technology. Three types of modules, namely, cylindrical, Raschig ring, and transverse-pore modules, with different numbers and orientations of canals, were designed and fabricated by modified selective-laser-sintering (SLS) technology. These modules maintained their structure in a flowing culture environment, and degradation did not create an acidic environment, hence promoting their ability to scale up to highly functional tissue. The modules were seeded with human hepatoma Hep G2 cells and cultured for 10 days. The transverse-pore modules were found to have the highest glucose consumption, albumin production, and cell viability among the three tested modules. Our study showed that the proposed module design provided better mass transfer and possessed the required mechanical strength to enable use in the construction of large tissue.

The electronic, optical, and magnetic properties of H(2)Ti(3)O(7) are investigated by first-principles density function theory calculations, and also the modifications of these properties by metal intercalation in H2Ti3O7. It is shown that the band gap of H(2)Ti(3)O(7) may be significantly reduced by Fe or Ni intercalation, and that the intercalated Fe or Ni may form a one-dimensional (1D) channel via overlapping 3d orbitals along the [010] direction in the interlayer region. These overlapping 3d orbitals result in an extended band within the band gap region of H(2)Ti(3)O(7) and below its Fermi level, and this band in turn results in a low effective mass for hole transport along the 1D channel and a large magnetic moment for the Fe or Ni intercalated material.

Swift heavy ion irradiation is performed on 5% Ag doped Ge2Sb2Te5 (GST) thin films to observe the changes in structural and optical properties. The thin films have been irradiated with Ag9+ ions having 120 MeV energy. It has been observed that irradiation does not leads to phase change and the red shift observed in Raman spectra indicates the weakening of bond strength. Moreover, reduction in bandgap is also observed as an effect of increasing irradiation dose. These results indicate that the irradiation with high energy ions introduces defects in the thin films which may lead to local generation of crystal nuclei. These crystal nuclei may be responsible for the modification of optical and electrical properties in these films.

Spatially periodic temperature modulation of a compressible fluid

The fundamental properties of an optical modulator are theoretically examined in this research using simulation models. The device under study is an active component of integrated optics; it has an interferometer with parallel waveguides and couplers in an S-Bend as its structural components.The Beamprob simulator incorporated into the Rsoft program is employed to continue the performance evaluation of the MZI (Mach Zehnder Inteferometer). Following the application of the polarization voltage, the material in one of the waveguides' arms' nonlinear effects causes a phase shift.The influence of several parameters, such as the length of the arms, the gap (inter-electrode distance), and the coefficient of non-linearity, was presented.We examined how the different output intensities fluctuated in order to use this device for optical modulation so that the area where the signal was most utilized could be identified.

An exact solution to the steady-state dynamics of a microring modulator with simultaneous index and loss modulation is derived. We experimentally validate the theory by demonstrating the generation of an optical frequency comb from a carrier depletion-based ring modulator on silicon.

We demonstrate both the amplitude and bi-phase modulation of ultrawideband (UWB) monocycle pulses using silicon microring modulator. The integrated silicon ring modulator generates the monocycle pulse train and modulates it simultaneously. By applying different driving voltages, the amplitude and phase-modulated UWB signal with a data rate of 2.5 Gb/s are achieved. The ring modulator can be thermally tuned for a free spectral range with a ~50-mW power consumption.

Present report deals with the synthesis of nanocrystalline cadmium oxide (CdO) using low-cost acetate precursor based modified sol–gel technique. Final product was sintered at different temperatures and studied for their structural, optical and electrical properties. In this present work, we report the sintering temperature-dependent structural, optical and electrical properties of nanocrystalline cadmium oxide (CdO) grown by cost effective sol–gel method. Structural properties of CdO materials were investigated by X–ray diffraction (XRD) which reveals the crystalline phase of the samples without any detectable impurity within the range of measurements. Crystallite size (CS), calculated using Scherer’s formula, is found in the range of nanometer (<100 nm) and increases with increasing sintering temperature. Average crystallite size of all CdO nanocrystals were estimated using the William–Hall (W–H) plots from XRD patterns. Furthermore, transmission electron microscopy (TEM) images were captured to check the crystallinity and particle growth of the samples. The optical properties of nanocrystalline CdO were studied by using UV–Visible (UV–Vis) absorption spectrum. High absorption has been observed for nanocrystalline CdO sintered at lower temperatures. The band gap of nanocrystalline CdO was calculated by using Tauc’s law where band gap increases with increasing sintering temperature. The electrical properties of the samples were studied by performing dielectric and AC conductivity measurements. It is observed that dielectric constant decreases with increase in frequency and sintering temperature. Variation in AC conductivity with light and sintering temperature has been discussed in detail.

Two-dimensional (2D) heterostructures composed of transition metal dichalcogenides (TMDCs) are promising materials for next-generation electronics and optoelectronics due to their unique electronic and optical properties. Although 2D TMDC heterostructures with coexisting vertical and lateral junctions are highly desirable for both fundamental research and technological applications, they have rarely been explored. Here, we report for the first time the synthesis of 2D heterostructures with coexisting vertical and lateral junctions composed of MoSe2 and WSe2. Monolayer MoSe2 is first synthesized on a substrate due to its lower thermodynamic formation energy followed by the growth of monolayer WSe2 on both the basal plane and edges of MoSe2, thereby forming MoSe2-WSe2 heterostructures with coexisting vertical and lateral junctions. These heterostructures are characterized using various analytical techniques. We investigated nonlinear optical (NLO) properties using harmonic generation measurements to determine the crystal orientation of star-shaped MoSe2-WSe2 heterostructures. In addition, we investigated the junction geometry-dependent NLO responses of the vertical and lateral heterojunctions over a broad spectral range to demonstrate their resonant features and interlayer coupling effects. Furthermore, we fabricated electronic devices using these heterostructures and compared the diode characteristics of the vertical and lateral p-n junctions. These MoSe2-WSe2 heterostructures with coexisting vertical and lateral junctions are advanced materials for 2D electronics, optoelectronics, and nonlinear optical applications.

A series of donor–acceptor molecules that incorporate N,N-dimethylaniline or carbazole as the common electron donor and 3-phenyl-5-isoxazolone as the electron acceptor moiety have been synthesized and their structural and optical properties and self-assembly behaviors were investigated. All these compounds showed the property of aggregation induced emission (AIE). These compounds with different donors and different conjugation could be self-assembled into different superstructures such as ribbon-like architectures, hollow nanospheres, multilayer plates or rhombic microplates by phase transfer methodology or solvent-vapor techniques. Furthermore, the nonlinear optical (NLO) properties of the four D–A molecules were studied by the Z-scan technique and all of these compounds exhibited third-order nonlinear absorption effects.

Titanium oxide thin films obtained with physical and chemical vapour deposition methods for optical biosensing purposes