Silicon (Si) photonics has proven its importance in the recent years for enabling the integration of photonic components, using available complementary metal oxide semiconductor (CMOS) fabrication ...flows. The simultaneous realization of electronics and photonics in the same manufacturing platform allows for the accomplishment of high-performance electronic-photonic integrated circuits (EPICs). Their adoption in optical communication systems meets one essential challenge - the optical interfacing to the transmission links, based on single-mode fibers (SMFs). On the one hand, there is a large mode-field mismatch between the tiny on-chip Si waveguide with an area of about 0.1 µm² and the external SMF with a core diameter of around 10 µm. In addition, there is a severe discrepancy between the polarization natures of both optical modes. While the external SMF supports a mode with two orthogonal, degenerated polarization states, the integrated Si waveguides and remaining components are mostly designed for the fundamental transverse electric (TE) polarization. A Si photonic coupling interface is thus required to deliver polarization handling capabilities as well. A favored component for a simple interfacing is the diffraction grating coupler (GC). In its most basic, one-dimensional implementation, a silicon waveguide mode is laterally enlarged by a taper structure, feeding a periodically etched grating. The latter deflects the light under a small angle with respect to the chip surface's normal. The external SMF is tilted under the same angle and placed at a small distance above the grating. The coupling device in this form allows for mode matching, but not for polarization manipulation. For that reason, its modified form - the two-dimensional grating coupler (2D GC) - is necessary. The latter combines two one-dimensional GCs in such a manner, that both orthogonal SMF polarizations are coupled into two separate Si waveguides, supporting the fundamental TE polarization, and vice versa. This time, the SMF is not only tilted with respect to the vertical, but also oriented towards the grating's symmetry axis between the feeding waveguides. Accordingly, the grating should be able not only to diffract both Si modes in a nearly vertical direction, but also to direct them along the symmetry plane.Although 2D GCs have been known for many years, their efficient and polarization independent design remained very challenging. To overcome this problem, a good basic understanding of the fundamental physical effects in such structures is necessary. This work is entirely dedicated to the investigation and systematization of the physical properties of 2D GCs. The gained theoretical base is used for the 2D GCs' optimization in different aspects. Starting with the theoretical description of the diffraction mechanisms in two dimensions, the interplay between the grating's geometry and coupling angles is demonstrated. Furthermore, an in-depth characterization of the polarization behavior of 2D GCs is presented. New aspects, such as the polarizations' conversion, crosstalk and non-orthogonality are analyzed, tracking their origins back to the in-plane scattering, resulting from the finite size of the grating's perturbing elements with respect to the Si mode. The importance of this physical process in 2D GCs has been underrated until now, and is revealed here as the most determining limitation for the optimal performance of 2D GCs. After this conclusion, several methods for the in-plane scattering's suppression are considered. The feasibility of the proposed approaches is investigated by both numerical simulations and wafer-level experiments. In the end, a novel optimization technique is demonstrated, which allows for the design of efficient 2D GCs with a low polarization crosstalk, low non-orthogonality and low polarization-dependent loss.
In this paper, we report on polarization combining two-dimensional grating couplers (2D GCs) on amorphous Si:H, fabricated in the backend of line of a photonic BiCMOS platform. The 2D GCs can be used ...as an interface of a hybrid silicon photonic coherent transmitter, which can be implemented on bulk Si wafers. The fabricated 2D GCs operate in the telecom C-band and show an experimental coupling efficiency of − 5 dB with a wafer variation of ± 1.2 dB. Possibilities for efficiency enhancement and improved performance stability in future design generations are outlined and extension toward O-band devices is also investigated.
Upcoming generations of coherent intra/inter data center interconnects currently lack a clear path toward a reduction of cost and power consumption, which are the driving factors for these data ...links. In this work, the tradeoffs associated with a transition from coherent C-band to O-band silicon photonics are addressed and evaluated. The discussion includes the fundamental components of coherent data links, namely the optical components, fiber link and transceivers. As a major component of these links, a monolithic silicon photonic BiCMOS O-band coherent receiver is evaluated for its potential performance and compared to an analogous C-band device.
Focusing grating couplers for the excitation of the fundamental transverse-magnetic (TM) mode in integrated silicon photonic waveguides are designed and characterized under the boundary conditions of ...a photonic BiCMOS foundry. Two types of waveguide geometries are considered – a nanowire and a rib waveguide. Wafer-scale experimental results for nanowire TM grating couplers are in excellent agreement with numerical investigations and demonstrate a robust behavior on the wafer. The mean coupling loss and the 3σ interval are -3.9 ± 0.3 dB. The on wafer variation is three times lower than for the fundamental transverse-electric (TE) polarization. Similarly, the coupling in rib waveguides is examined as well. The results indicate that the rib waveguides require a modified geometry when designed for TM. In general, the nanowire waveguide type is more suitable for TM coupling, showing a stable and repeatable performance.
In this work, we present an O-band dual-polarization coherent receiver optical sub-assembly (cROSA), monolithically integrated in a 0.25 <inline-formula><tex-math ...notation="LaTeX">\mu</tex-math></inline-formula>m BiCMOS technology. The receiver features 248 nm deep ultra violet compatible 2-dimensional grating couplers (2D-GRCs), and an adaptive polarization controller, suitable for mitigation of local oscillator induced power fading in self-homodyne transmission systems. The cROSA is evaluated in system experiments at 64 GBd quadrature-phase shift-keying. Experimental results are related to grating coupler induced polarization crosstalk through Monte-Carlo simulations. Second generation 2D-GRCs are proposed.
An arteriogram was performed to provide a road map of the blood supply to the uterus and fibroids from both the left and right uterine arteries. Clinical trials comparing the effect of embolization ...and surgery (hysterectomy or myomectomy) show similar results, regarding clinic, quality of life and prognosis with lower...
Background The aim of our study was to evaluate the efficiency and safety of a minimally invasive procedure for treating uterine fibroids trough brachial access. The early and medium-term (5 years) ...results in recent studies show that uterine embolization is as effective as surgery (hysterectomy or myomectomy) for symptom control...
Silicon photonic two-dimensional grating couplers for C- and O-band dual-polarization coherent transceivers are analyzed with respect to their polarization splitting/combining performance. Due to ...scattered light in the grating's plane, a linear cross-polarization results. The latter is responsible for a limited polarization split ratio and a polarizations' non-orthogonality. The impact of these two quantities is evaluated by system-level simulations with regard to OSNR penalties in coherent systems. For both C- and O-band, a design modification for reduced penalties is proposed.
The focus of this article is the development of Volodymyr Zelensky as an actor with a career spanning over 20 years, mainly concentrated in the field of comedy genres, before he was elected President ...of Ukraine. As a key to the understanding of Zelensky's performance style, Mikhail Chekhov's theory of acting is drawn, insofar as, on the one hand, it is particularly relevant in the context of the post-Soviet artistic scene, and on the other hand, it offers tools for building a stage and screen image, whose effects are visible precisely in the realm of comedy. Zelensky's on-screen presence from the end of the 1990s and the evolution of his team from Studio Kvartal 95 are traced in the context of the question of whether the TV shows and the series „Servant of the People" can be commented on as a political project, especially after the annexation of Crimea in 2014. The role of satire in the process of forming civic consciousness in the audience and even in the process of forming national identity is considered. Ultimately, the observations stress the political functionality of the image of the actor-comedian, who will eventually face the tragedy of war.
We report a case of a high-risk 73-year-old patient with a combined aortic valve disease with predominant severe, symptomatic aortic regurgitation and a history of an end-stage respiratory failure ...with prohibitive surgical risk who was successfully treated using a minimalist approach to implant off-label а self-expandable Medtronic Evolut R prosthesis. This case report demonstrates that the self-expandable prosthesis Medtronic Evolut R might be implanted without tissue damage and migration in a moderate-calcified tricuspid aortic valve with predominant regurgitation and mild stenosis with satisfactory hemodynamic results and improvement in functional class heart failure in a patient with concomitant severe respiratory failure.
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