1,720,977 research outputs found
Integrated photonics approach to radio-frequency self-interference cancellation
Full text linkAn integrated photonics based scheme for radio-frequency self-interference cancella-tion is proposed and demonstrated. It is achieved using a dual-parallel Mach-Zehnder modulator that eliminates the interference signal in the optical domain. The output of the modulator is a carrier suppressed double-sideband waveform that contains only the signal of interest. Finally, the signal of interest is recovered by combining the modulator output with a local optical carrier and detecting it at a high-speed photodetector. We present a detailed theoretical analysis and derive the optimal condition for self-interference cancellation for small modulation indices. The modulators were designed and fabricated on IMEC's Silicon-on-Insulator iSiPP50G platform. Using this technique, we experimentally obtain a cancellation depth of 30 dB and a signal to interference ratio of 25 dB for frequencies up to 20 GHz, limited only by the equipment used. This is the first demonstration of self-interference cancellation on a silicon photonics platform and a further expansion of the functionalities offered by integrated microwave photonics.(c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen
Nonreciprocal light propagation in a cascaded all-silicon microring modulator
No full textOptical isolators and circulators are critical building blocks for large-scale photonic integrated circuits. Among the several methods proposed to realize such nonreciprocal devices, including heterogeneous integration with garnet-based materials or using nonlinearities, dynamic modulation of the waveguide properties is a potentially practical and easily accessible method. However, most proposals relying on this method rely on modulators with a very large footprint, limiting their practical applicability. This paper overcomes this issue by presenting a method to achieve nonreciprocal optical transmission taking advantage of compact ring modulators. We use a cascaded system of microring modulators with a footprint as small as 15 mu m x 220 mu m and propose that, by tuning the relative time delay between the RF driving signals and the optical delay between the modulators, nonreciprocal transmission can be achieved. We present a detailed theoretical analysis of our design and investigate the origin of the asymmetric transmission. The modulators were designed and fabricated on IMEC's Silicon-on-Insulator platform iSiPP50G. We achieve a 16 dB difference between forward and backward optical signals at a driving voltage (V-pp) of 8 V at 6 GHz. Moreover, we analyze the impact of fabrication imperfections on the device performance. Our work leads to a significant reduction in device footprint compared to formerly explored solutions using dynamic modulation and is well suited for monolithic integration with photonic integrated circuits
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Mode Engineering in Micro Ring Resonators and Their Application
No full textSilicon Photonics (SiP) has emerged as the prominent platform for Photonic
Integrated Circuits (PICs). CMOS technology compatible fabrication processes,
high index contrast of the waveguide core-cladding leading to sharp bends, and low
propagation loss are the key advantageous features of SiP circuits in Silicon on
Insulator (SOI). Various functional units are already in their mature stage where
Micro Ring Resonators (MRRs) have been widely used to realize wavelength
selective devices in a PIC. Compact design, high Q-Factor, scalable spectral
properties, and the ability to create complex higher-order signal processing
architectures are some of its basic advantages. Due to these benefits of MRR, it has
found a wide range of applications ranging from sensors, optical communication,
and filters.
MRRs resonate at particular resonance wavelengths dictated by the interference
condition. However, fabrication imperfections and parasitic coupling at various
interfaces in MRR excite undesirable degenerate cavity modes that can lead to
unpredictable resonance splitting. The extent of splitting and the shape of split
resonances are uncontrollable and unpredictable within a reasonable degree of
accuracy and are only identified during the device characterization stage. Such split
response limits the use of MRR, otherwise a versatile component in PIC. In this
work, we attempted to tackle the resonance splitting problem by engineering mode
interaction within the cavity. We proposed and demonstrated a unique Self-Coupled
MRR (SCMRR) that provides a predictable and controllable resonance split by
regulating the excitation of the degenerate cavity mode. We also worked over
multiple cavity systems like loaded MRR and quadruple resonance split MRR to
gain control over not only the extent of splitting but also the resonance shape.
Finally, the proposed devices were exploited for applications in three different
domains i.e. sensing, optical communication and RF signal processing using
photonics.
Optical Communication: we demonstrated four channel multicasting at 48Gbps (4 x12 Gbps) by selectively splitting the MRR resonance into four notches. Multicasting
is achieved using Two Photon Absorption (TPA) induced Free Carrier Dispersion
(FCD) in Silicon. To the best of our knowledge, we achieved the highest data
rate/channel of 12 Gbps using a MRR based device.
Sensing: we demonstrated an on-chip self-calibrated sensor interrogator. In this
patented technique, we used SCMRR as an interrogator to scan the shift in FBG
sensor spectrum that can automatically calibrate the system performance against
the natural decay of the SCMRR thermal tuners and fluctuations in the ambient
environment. Unlike a single MRR, SCMRR interrogator response certain spectral
characteristics that can be processed to identify the change in FBG spectrum as
well as the SCMRR resonance split. The SCMRR split is then fed back to the
system to calibrate the thermal tuners for SCMRR.
RF signal processing using photonics: we proposed a RF Phase Shifter (PS) and
generation of on-chip Single SideBand with carrier (SSB+C) for Radio over Fiber
(RoF) based applications. In PS, we achieved continuous tuning of RF phase from
00 to 1800 with a record low power penalty of sub-1dB for a wide bandwidth RF (8
GHz-43 GHz). In RoF, we proposed a method of generating SSB+C signal by
suppressing one of the sidebands of a Double SideBand with Carrier (DSB+C)
signal. We achieved a tunable suppression ratio, high dynamic range, and almost
zero dispersion-based power penalty, unlike DSB+C signals, over a transmission
length of 43 Km and a frequency range of 1 GHz-20 GHz. The suppression is
achieved using DSB+C signal from bulk modulator as well as an on-chip modulato
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