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1. Emission of R6G dye in Fabry–Perot cavities in weak and strong coupling regimes

   https://doi.org/10.1364/JOSAB.403612  

   Faruk, Md_Omar; Jerop, Nelly; Noginov, Mikhail_A (October 2020, Journal of the Optical Society of America B)

   We have studied spectra and angular distribution of emission in Fabry–Perot cavities formed by two silver mirrors separated by a layer of poly (methyl methacrylate) polymer doped with rhodamine 6G (R6G) dye in low ( $20\mathrm{g}/\mathrm{l}$) and high ( $200\mathrm{g}/\mathrm{l}$) concentrations. The frequency of emission radiated to a cavity mode was larger at large outcoupling angles—the “rainbow” effect. At the same time, the angle of the strongest emission was also determined by the cavity size: the larger the cavity, the larger the angle. The angular distribution of emission is commonly dominated by two symmetrical lobes (located at the intersection of the three-dimensional emission cone with a horizontal plane) pointing to the left and to the right of the normal to the sample. Despite the strong Stokes shift in R6G dye, the branch of the cavity dispersion curve obtained in the emission experiment is positioned above the one obtained in the reflection (extinction) experiment. Some dye molecules are poorly coupled to cavity modes. Their emission has very broad angular distribution with the maximum at $\mathrm{\theta <\#comment/>}=0^{\circ <\#comment/>}$. The signatures of strong cavity–exciton coupling were observed at high dye concentration ( $200\mathrm{g}/\mathrm{l}$) but not at low concentration ( $20\mathrm{g}/\mathrm{l}$). The evidence of the effect of strong coupling on emission is exemplified by a strong difference in the angular distribution of emission in two almost identical cavities, one with and another without strong coupling. Most importantly, we have demonstrated the possibility to control the ground state concentration, the coupling strength, and the dye emission spectra with Q-switched laser pulses. 

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2. Power coupling losses for misaligned and mode-mismatched higher-order Hermite–Gauss modes

   https://doi.org/10.1364/OL.426999  

   Tao, Liu; Kelley-Derzon, Jessica; Green, Anna_C; Fulda, Paul (May 2021, Optics Letters)

   This paper analytically and numerically investigates misalignment and mode-mismatch-induced power coupling coefficients and losses as a function of Hermite–Gauss (HG) mode order. We show that higher-order HG modes are more susceptible to beam perturbations when, for example, coupling into optical cavities: the misalignment and mode-mismatch-induced power coupling losses scale linearly and quadratically with respect to the mode indices, respectively. As a result, the mode-mismatch tolerance for the ${\mathrm{H}\mathrm{G}}_{3,3}$mode is reduced to a factor of 0.28 relative to the currently used ${\mathrm{H}\mathrm{G}}_{0,0}$mode. This is a potential hurdle to using higher-order modes to reduce thermal noise in future gravitational-wave detectors. 

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3. Ultra-thin plasmonic detectors

   https://doi.org/10.1364/OPTICA.438039  

   Nordin, Leland; Petluru, Priyanka; Kamboj, Abhilasha; Muhowski, Aaron_J; Wasserman, Daniel (December 2021, Optica)

   Plasmonic materials, and their ability to enable strong concentration of optical fields, have offered a tantalizing foundation for the demonstration of sub-diffraction-limit photonic devices. However, practical and scalable plasmonic optoelectronics for real world applications remain elusive. In this work, we present an infrared photodetector leveraging a device architecture consisting of a “designer” epitaxial plasmonic metal integrated with a quantum-engineered detector structure, all in a mature III-V semiconductor material system. Incident light is coupled into surface plasmon-polariton modes at the detector/designer metal interface, and the strong confinement of these modes allows for a sub-diffractive ( $\sim <\#comment/>{\mathrm{\lambda <\#comment/>}}_0/33$) detector absorber layer thickness, effectively decoupling the detector’s absorption efficiency and dark current. We demonstrate high-performance detectors operating at non-cryogenic temperatures ( $T=195\mathrm{K}$), without sacrificing external quantum efficiency, and superior to well-established and commercially available detectors. This work provides a practical and scalable plasmonic optoelectronic device architecture with real world mid-infrared applications. 

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4. Mid-IR spectroscopy of Er ³⁺ doped low-phonon CsCdCl ₃ and CsPbCl ₃ crystals

   https://doi.org/10.1364/JOSAB.470152  

   Brown, Ei_Ei; Fleischman, Zackery_D; McKay, Jason; Hommerich, Uwe; Kabir, Al_Amin; Riggins, Jazmine; Trivedi, Sudhir; Dubinskii, Mark (September 2022, Journal of the Optical Society of America B)

   The mid-IR spectroscopic properties of ${\mathrm{E}\mathrm{r}}^{3+}$doped low-phonon ${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$and ${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$crystals grown by the Bridgman technique have been investigated. Using optical excitations at $\sim <\#comment/>800\mathrm{n}\mathrm{m}$and $\sim <\#comment/>660\mathrm{n}\mathrm{m}$, both crystals exhibited IR emissions at $\sim <\#comment/>1.55$, $\sim <\#comment/>2.75$, $\sim <\#comment/>3.5$, and $\sim <\#comment/>4.5\text{µ<\#comment/>}\mathrm{m}$at room temperature. The mid-IR emission at 4.5 µm, originating from the ${}^4{\mathrm{I}}_{9/2}\to <\#comment/>{}^4{\mathrm{I}}_{11/2}$transition, showed a long emission lifetime of $\sim <\#comment/>11.6\mathrm{m}\mathrm{s}$for ${\mathrm{E}\mathrm{r}}^{3+}$doped ${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$, whereas ${\mathrm{E}\mathrm{r}}^{3+}$doped ${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$exhibited a shorter lifetime of $\sim <\#comment/>1.8\mathrm{m}\mathrm{s}$. The measured emission lifetimes of the ${}^4{\mathrm{I}}_{9/2}$state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated emission cross sections for the ${}^4{\mathrm{I}}_{9/2}\to <\#comment/>{}^4{\mathrm{I}}_{11/2}$transition in ${\mathrm{E}\mathrm{r}}^{3+}$doped ${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$and ${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$were determined to be $\sim <\#comment/>0.14\times <\#comment/>{10}^{-<\#comment/>20}{\mathrm{c}\mathrm{m}}^2$and $\sim <\#comment/>0.41\times <\#comment/>{10}^{-<\#comment/>20}{\mathrm{c}\mathrm{m}}^2$, respectively. The results of Judd–Ofelt analysis are presented and discussed. 

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5. Guided-mode resonances in flexible 2D terahertz photonic crystals

   https://doi.org/10.1364/OPTICA.388761  

   Kyaw, Chan; Yahiaoui, Riad; Chase, Zizwe_A; Tran, Viet; Baydin, Andrey; Tay, Fuyang; Kono, Junichiro; Manjappa, Manukumara; Singh, Ranjan; Abeysinghe, Don_C; et al (May 2020, Optica)

   In terahertz (THz) photonics, there is an ongoing effort to develop thin, compact devices such as dielectric photonic crystal (PhC) slabs with desirable light–matter interactions. However, previous works in THz PhC slabs have been limited to rigid substrates with thicknesses $\sim <\#comment/>100\mathrm{s}$of micrometers. Dielectric PhC slabs have been shown to possess in-plane modes that are excited by external radiation to produce sharp guided-mode resonances with minimal absorption for applications in sensors, optics, and lasers. Here we confirm the existence of guided resonances in a membrane-type THz PhC slab with subwavelength ( ${\mathrm{\lambda <\#comment/>}}_0/6-<\#comment/>{\mathrm{\lambda <\#comment/>}}_0/12$) thicknesses of flexible dielectric polyimide films. The transmittance of the guided resonances was measured for different structural parameters of the unit cell. Furthermore, we exploited the flexibility of the samples to modulate the guided modes for a bend angle of $\mathrm{\theta <\#comment/>}\ge <\#comment/>5^{\circ <\#comment/>}$, confirmed experimentally by the suppression of these modes. The mechanical flexibility of the device allows for an additional degree of freedom in system design for high-speed communications, soft wearable photonics, and implantable medical devices. 

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