Full frequency-domain approach to reciprocal microlasers and nanolasers-perspective from Lorentz reciprocity

Excitation of surface plasmon mode in bulk semiconductor lasers

We propose a realistic process for the excitation of surface plasmon polariton (SPP) modes in a silicon photonic waveguide (WG). The process involves the placement of buried oxide (BOX) composed of silica between a WG and silicon substrate. When the BOX thickness is manipulated, different amounts of modal power leak toward the BOX into the substrate and simultaneously acquire compensation from a semiconductor located on the WG. The compensation related to the leakage can be used to infer transparency gain. Similar to the case for a semiconductor laser cavity, the lowest transparency gain among WG modes can be favored; thus, only one mode can survive in the WG, and it is in the region with the specified BOX thickness. Finally, we propose a credible mechanism suitable for demonstrating the region requirements of the existence of SPP modes.

Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature

Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and −1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations.

Chiral Light-Matter Interaction in Optical Resonators

The Purcell effect explains the modification of the spontaneous decay rate of quantum emitters in a resonant cavity. For quantum emitters such as chiral molecules, however, the cavity modification of the spontaneous decay rate has been little known. Here we extend Purcell's work to the chiral light-matter interaction in optical resonators and find the differential spontaneous decay rate of chiral molecules coupled to left and right circularly polarized resonator modes. We determine the chiral Purcell factor, which characterizes the ability of optical resonators to enhance chiroptical signals, by the quality factor and the chiral mode volume of a resonator, representing, respectively, the temporal confinement of light and the spatial confinement of the helicity of light. We show that the chiral Purcell effect can be applied to chiroptical spectroscopy. Specifically, we propose a realistic scheme to achieve resonator enhanced chiroptical spectroscopy that uses the double fishnet structure as a nanoscale cuvette supporting the chiral Purcell effect.

Design of metal-dielectric grating lasers only supporting surface-wave-like modes

We present a prototype of semiconductor lasers with plasmonic periodic structures that only support transverse-magnetic modes at telecommunication wavelengths. The structure does not sustain transverse-electric guided modes which are irrelevant to surface-wave-enhanced applications, and lasing modes must be surface-wave-like. With thin low-index dielectric buffers near the metal surface, the threshold gain is kept at a decent level around the photonic band edge. Thin windows are then opened on the metal surface to let out significant surface fields. This facilitates usages of surface waves for the spectroscopy and sensing.

Optical cavity modes of a single crystalline zinc oxide microsphere

A detailed study on the optical cavity modes of zinc oxide microspheres under the optical excitation is presented. The zinc oxide microspheres with diameters ranging from 1.5 to 3.0 µm are prepared using hydrothermal growth technique. The photoluminescence measurement of a single microsphere shows prominent resonances of whispering gallery modes at room temperature. The experimentally observed whispering gallery modes in the photoluminescence spectrum are compared with theoretical calculations using analytical and finite element methods in order to clarify resonance properties of these modes. The comparison between theoretical analysis and experiment suggests that the dielectric constant of the ZnO microsphere is somewhat different from that for bulk ZnO. The sharp resonances of whispering gallery modes in zinc oxide microspheres cover the entire visible window. They may be utilized in realizations of optical resonators, light emitting devices, and lasers for future chip integrations with micro/nano optoelectronic circuits, and developments of optical biosensors.

Frequency-domain formulation of photonic crystals using sources and gain

We present a formulation to analyze photonic periodic structures from viewpoints of sources and gain. The approach is based on a generalized eigenvalue problem and mode expansions of sources which sustain optical fields with phase boundary conditions. Using this scheme, we calculate power spectra, dispersion relations, and quality factors of Bloch modes in one-dimensional periodic structures consisting of dielectrics or metals. We also compare the results calculated from this scheme with those from the complex-frequency method. The outcomes of these two approaches generally agree well and only deviate slightly in the regime of low quality factors.

Intra-cavity stimulated emissions of photons in almost pure spin states without imposed nonreciprocity

We propose a chiral Fabry-Perot cavity in which only the cavity modes in almost pure spin (circular polarization) states lase in the presence of gain. In absence of imposed nonreciprocal environments and time-reversal symmetry breaking of emitter states to favor the emission of circularly-polarized photons, only the resonance of modes with a specific spin orientation remains in the cavity. We demonstrate a prototype of the cavity using distributed Bragg reflectors and cholesteric liquid crystals. This reciprocal cavity may provide a method to control the angular momentum state of emitters based on stimulated emissions.