Unlike PT and SUSY lasers, here we show an extra loss-free non-Hermitian laser engineering approach to realize single mode lasing operation for the first time. By selectively enhancing the fundamental mode’s quality factor, we obtain single mode operation with higher output power per cavity since all cavities in this system contribute to the laser output, in contrast to other non-Hermitian approaches. Furthermore, we show that this approach interestingly allows reducing the number of to-be-designed cavities in super-partner array as compared with, for example, the SUSY approach, thus leading to reduced design complexity upon coupled cavity scale up of laser arrays. In summary, the ability to engineer coupled laser systems where each laser cavity contributes to coherent light amplification opens up a new degree of laser-design freedom leading to increased device performance and simultaneous reduced design and fabrication complexity.
Single mode with in-phase operation of the laser arrays is one of the main challenges for engineers to achieve high power in phase far field emission. Recently single mode lasing based on non-Hermitian engineering of the laser is investigated and two scenarios based on parity time (PT) symmetry and super symmetry are presented. Here we present a new method based on Q-enhancing to achieve single mode operation. This design device will satisfy requirement for LIDARs in space applications. The output supports up-to 300 Watts for few integrated coupled cavity lasers.
The light confinement properties of high quality (Q) factor microtoroid whispering-gallery mode (WGM) optical resonators prevent efficient coupling between far-field radiation and the WGM. Instead, light is most commonly evanescently coupled to the WGM using optical fibers that have been tapered to micron-scale thickness. These tapers, however, break easily and are sensitive to environmental vibrations and fluid flow fluctuations. This limits their effectiveness in mass-produced and/or field-portable biochemical sensing applications. Here we present a gold nanorod grating as an experimentally-feasible alternative for robust coupling of free-space light to a microtoroid resonator, and we simulate its performance with a novel finite-element 3D beam envelope method. 3D simulations of the full system are not tractable due to its large size. Previously, simulations of nanostructures on microtoroids have been performed on a thin wedge of the 3D system with perfect electrical conductor (mirror) boundary conditions. While these simulations provided some insight, they do not accurately model typical travelling-wave WGM experiments because they can only simulate standing waves. The standing wave nodes and antinodes significantly alter interactions between the WGM and the nanostructure. In our new method, we use a small wedge domain with custom boundary conditions that accurately simulate the travelling wave and nanophotonic interactions. Using this approach, we have designed and simulated a grating for far-field WGM coupling. With the grating, it is possible to maintain a high Q-factor of 3×10^6. We anticipate that our proposed modeling approach can solve a variety of other nanoparticle-microtoroid coupled systems in the future.
Discovery of TCC-VCSEL done by Dr. Dalir (PI) in 2013 led to new functionalities of VCSEL structure. In principal, a TCC-VCSEL has same vertical structure as conventional VCSEL. A VCSEL is consists of two distributed Bragg reflector (DBR) mirrors parallel to the wafer surface with an active region consisting of one or more quantum wells for the laser light generation in between. The planar DBR-mirrors consist of layers with alternating high and low refractive indices. Each layer has a thickness of a quarter of the laser wavelength in the material, yielding intensity reflectivity’s above 99%. High reflectivity mirrors are required in VCSELs to balance the short axial length of the gain region. Here we assume a TCC-VCSEL with a coupling of K between the cavities. We pump one cavity with a gain of g, while the other cavity has loss of ɣ. It is noted that the lasing frequency is a function of loss and coupling between the cavities. Assuming a constant coupling (K), tunabilty of the TCC-VCSEL will be adjusted by the loss. The three-dimensional simulation of the single mode operation in TCC structure is performed by employing film mode matching method of FIMMWAVE Photon Design Corp. With a coupling of K= 1.5THz, a 19.7 nm wavelength will be swept in the PT regime crucial for lab-on-a-chip integrated bio-sensor applications.
Local field enhancement of plasmonic nanoantennas below the diffraction limit plays an important role in a variety of applications, including surface-enhanced Raman scattering, spontaneous emission enhancement, nanolasing, enhanced nonlinear effects and biosensing. Yet due to the radiation and ohmic loss of these nanocavities, their quality factor (Q) is much smaller than a typical optical microcavity Q factor, such as that of a microsphere or microtoroid. Coupling a nanoantenna to an optical microcavity increases the Q of the hybrid plasmonic-photonic system, however, this dramatically degrades the Q of the original microcavity. Here, we propose a judicious hybridization of a plasmonic dark mode of a gold nanoring and whispering gallery mode (WGM) of a microtoroid. It is shown through finite element simulation that the hybridized WGM and dark mode of the proposed plasmonic gold nanoring solves the aforementioned issues in two ways. First, the small radiation loss of the dark mode minimizes Q degradation and allows the system to maintain its ultra-high Q. Second, the nanoring enhances the field on the microcavity’s surface which in turn increases the interaction between, for example, a biomolecular target and the WGM. We have shown that the proposed system generates larger resonance shifts compared to a microcavity loaded with same volume of conventional linear gold nanoantennas . This results in significant enhancement in the system’s sensitivity. We have repeated the same simulations for different materials and volumes.
Optical whispering gallery mode (WGM) biochemical sensors operate by tracking changes in resonant frequency as materials enter the evanescent near-field of the resonator. To achieve the smallest limit of detection, it is desirable for WGM sensors to exhibit as large a frequency shift as possible for a material of a given size and refractive index, as well as the ability to track as small a frequency shift as possible. Previously, plasmonic nanoantennas have been coupled to WGM resonators to increase the magnitude of resonance shifts via plasmonic enhancement of the electric field, however this approach also results in increased scattering from the WGM, which degrades its quality factor, making it less sensitive to extremely small frequency shifts. This degradation is caused by the ohmic and scattering dissipation caused by metallic nanoantennas. Using simulations, we show here that the precise positioning of nanoantennas coupled to a microtoroid WGM resonator can be used to overcome this drawback and achieve ultrahigh-Q plasmonic cavity modes simultaneously with electric field enhancement. It is shown that a nanoantenna composed of two similarly coupled nanorods supports higher Q modes than a single nanorod antenna. Our results have immediate application in the context of optical sensing.
All optical Schmitt trigger based on Kerr bistability in quasi periodic Thue-Morse
photonic crystals is investigated. Finite difference time domain is used to investigate the Schmitt
trigger operation in one dimensional nonlinear Thue-Morse Photonic crystals.
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