310 research outputs found
Parity-Time Anti-Symmetric Parametric Amplifier
We describe the process of parametric amplification in a directional coupler
of quadratically nonlinear and lossy waveguides, which belong to a class of
optical systems with spatial parity-time (PT) symmetry in the linear regime. We
identify a distinct spectral parity-time anti-symmetry associated with optical
parametric interactions, and show that pump-controlled symmetry breaking can
facilitate spectrally selective mode amplification in analogy with PT lasers.
We also establish a connection between breaking of spectral and spatial mode
symmetries, revealing the potential to implement unconventional regimes of
spatial light switching through ultrafast control of PT breaking by pump
pulses.Comment: 5 pages, 5 figure
Metallic Coaxial Nanolasers
The last two decades have witnessed tremendous advancements in the area of
nanophotonics and plasmonics. Undoubtedly, the introduction of metallic
structures has opened a path towards light confinement and manipulation at the
subwavelength scale { a regime that was previously thought to be out of reach
in optics. Of central importance is to devise efficient light sources to power
up the future nanoscale optical circuits. Coaxial resonators can provide a
platform to implement such subwavelength sources. They support ultrasmall
cavity modes and offer large mode-emitter overlap as well as multifold
scalability. Given their large modulation bandwidth, they hold promise for high
speed optical interconnects { where they can be used for light generation and
modulation simultaneously. In addition, the possibility of thresholdless
operation in such devices may have implications in developing the next
generation of efficient lighting systems. In this review article, the physics
and applications of coaxial nanolasers will be discussed
Nonlinear reversal of PT symmetric phase transition in a system of coupled semiconductor micro-ring resonators
A system of two coupled semiconductor-based resonators is studied when lasing
around an exceptional point. We show that the presence of nonlinear saturation
effects can have important ramifications on the transition behavior of this
system. In sharp contrast with linear PT-symmetric configurations, nonlinear
processes are capable of reversing the order in which the symmetry breaking
occurs. Yet, even in the nonlinear regime, the resulting non-Hermitian states
still retain the structural form of the corresponding linear eigenvectors
expected above and below the phase transition point. The conclusions of our
analysis are in agreement with experimental data.Comment: 9 pages, 8 figure
Integrable nonlinear parity-time symmetric optical oscillator
The nonlinear dynamics of a balanced parity-time symmetric optical microring
arrangement are analytically investigated. By considering gain and loss
saturation effects, the pertinent conservation laws are explicitly obtained in
the Stokes domain-thus establishing integrability. Our analysis indicates the
existence of two regimes of oscillatory dynamics and frequency locking, both of
which are analogous to those expected in linear parity-time symmetric systems.
Unlike other saturable parity time symmetric systems considered before, the
model studied in this work first operates in the symmetric regime and then
enters the broken parity-time phase.Comment: 6 pages, 5 figures, accepted for publicatio
Novel Photonic Resonance Arrangements Using Non-Hermitian Exceptional Points
In recent years, non-Hermitian degeneracies also known as exceptional points (EPs) have emerged as a new paradigm for engineering the response of optical systems. EPs can appear in a wide class of open non-Hermitian configurations. Among different types of non-conservative photonic systems, parity-time (PT) symmetric arrangements are of particular interest since they provide an excellent platform to explore the physics of exceptional points. In this work, the intriguing properties of exceptional points are utilized to address two of the long standing challenges in the field of integrated photonics- enforcing single mode lasing in intrinsically multimode cavities and enhancing the sensitivity of micro-resonators. In the first part of this work, I will describe how stable single mode lasing can be readily achieved in longitudinally and transversely multi-moded microring cavities through the systematic utilization of abrupt phase transitions at exceptional points. This technique will be first demonstrated in a parity-time laser that is comprised of a gain cavity coupled to an identical but lossy counterpart. A detailed study of the behavior of this system around the exceptional point will be presented. Furthermore, we report the first experimental realization of a dark state laser in which by strategically designing the spectral locations of exceptional points, widely tunable single-mode lasing can be attained even at high pump levels. Despite the presence of loss in such open laser systems, the slope efficiency remains virtually intact. Our results demonstrate the potential of exceptional points as a versatile design tool for mode management in on-chip laser configurations. In the second part of my dissertation, I will show how the exceptional points and their underlying degeneracies can be used to significantly boost the intrinsic sensitivity of microcavities. I will demonstrate the enhanced sensitivity in a binary PT-symmetric coupled cavity arrangement that is biased at an exceptional point. Then I will report the first observation of higher-order exceptional points in a ternary parity-time symmetric microring laser system with a judiciously tailored gain-loss distribution. The enhanced response associated with this ternary system follows a cubic root dependence on externally introduced perturbation, which can in turn be detected in the spectral domain. Using such arrangements, more than one order of magnitude enhancement in the sensitivity is observed experimentally. These results can pave the way towards improving the performance of current on-chip micro-cavity sensors
A single additive for 3D printing of highly-concentrated iron oxide inks
A single additive, a grafted copolymer, is designed to prepare highly-loaded suspensions of iron oxide nanoparticles (IOPs) and to facilitate the extrusion-based 3D printing of these stable suspensions. This poly (ethylene glycol) (PEG)-grafted copolymer of N- [3(dimethylamino)propyl]methacrylamide (DMAPMA) and acrylic acid (AA) harnesses both electrostatic and steric repulsion to realize an optimum formulation for 3D printing of IOP inks. With the use of 1.15 wt. % (by the weight of IOPs), the suspension attains ~81 wt. % solid loading—96% of the theoretical limit as calculated by the Krieger-Dougherty equation. We fabricated rectangular, thick-walled toroidal, and thin-walled toroidal magnetic cores and a porous lattice structure to demonstrate the utilization of this ink for 3D printing. The electrical and magnetic properties of the magnetic cores were characterized through impedance spectroscopy (IS) and vibrating sample magnetometry (VSM), respectively. The IS indicated the possibility of utilizing wire-wound 3D printed cores as the inductive coils. The VSM confirmed the magnetic properties of IOPs before and after the ink formulation were kept almost unchanged due to the low loading of the additive. This particle-targeted approach for the formulation of 3D printing inks realizes the embodiment of a fully aqueous system with utmost target material content
Effects of polyethylene glycols on intestinal efflux pump expression and activity in Caco-2 cells
The present study was planned to investigate the influence of polyethylene glycols (PEGs) on the activity and expression of P-glycoprotein (P-gp). Sub-toxic concentrations of PEGs in Caco-2 cells were determined using the MTT test assay. Then the measurement of Rhodamine-123 (Rho-123) uptake, a P-gp fluorescence substrate, in Caco-2 cells confronting PEG 400 (1% and 2% w/v), PEG 4000 (2% and 4% w/v), PEG 6000 (2% and 4% w/v), PEG 10000 (2% and 4% w/v), PEG 15000 (1% and 2% w/v), and PEG 35000 (2% and 4% w/v) overnight was taken to elucidate whether non-toxic concentrations of PEGs are able to impact P-gp activity. Furthermore, western blotting was carried out to investigate P-gp protein expression. The results showed that PEG 400 at concentrations of 1% (w/v) and 2% (w/v) and PEG 6000 at the concentration of 4% (w/v) are notably capable of blocking P-gp. Based on the obtained results it is concluded that the mentioned excipients could be used to obstruct P-gp efflux transporter in order to increase the bioavailability of co-administered substrate drug.O presente estudo foi planejado para investigar a influência de polietileno glicóis sobre a atividade e expressão da P- glicoproteína (P-gp) . Concentrações sub-tóxicas de PGPs e em células Caco-2 foram determinadas por meio do ensaio de MTT. Em seguida, efetuou-se a a medida de captura de Rodamina-123 (Rho-123), um substrato fluorescente de P-gp, em células Caco-2, confrontando com PEG 400 (1% e 2% m/v), PEG 4000 (2% e 4% m/v) e PEG 6000 (2% e 4% m /v), PEG 10000 (2% e 4% w/v), PEG 15000 (1% e 2% m/v), e PEG 35000 (2% e 4% m/v). Essa medida foi efetuada durante a noite, para saber se as concentrações não tóxicas de excipientes são capazes de influenciar a actividade da P-gp. Além disso, realizou-se o western blotting para investigar a expressão da proteína P-gp. Os resultados mostraram que o PEG 400, nas concentrações de 1% (m/v) e 2% (m/v), e PEG 6000, na concentração de 4% (m/v) são capazes de bloquear P-gp. Com base nos resultados conclui-se que os excipientes mencionados poderiam ser utilizados para obstruir o efluxo por P-gp, a fim de aumentar a biodisponibilidade de do fármaco co-administrado
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