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Whispering gallery mode (WGM) lasers are wellknown for their small sizes, low thresholds, and narrow linewidths, and have been the subject of research and development for more than two decades. However most of the initial reports and studies have focused on near-IR and visible WGM microlasers. Recent advances in the synthesis, doping, and processing of high quality mid-IR transparent glasses have provided the means to extend the wavelengths of these microlasers to the mid-IR range. In this paper, we present a detailed characterization of a compact and low-cost mid-IR spherical WGM microlaser based on heavily doped Er:ZBLAN glass operating near 2.7 μm with an estimated linewidth less than 1.1 MHz. We describe experimental results on observed singlemode and multimode spectra, thermal tuning, and polarization characteristics of such microlasers. Using a simple analysis of spherical microresonator modes and including considerations of pump and laser mode overlap we provide guidelines for optimized microlaser design. [ABSTRACT FROM AUTHOR]

Mode characteristics of AlGaInAs/InP square resonator microlasers laterally confined by a bisbenzocyclobutene layer, with an output waveguide connected to one vertex or the midpoint of one side, are investigated numerically and experimentally. Numerical simulation results indicate that the square resonator with the midpoint output waveguide has a better single-mode property, but a lower mode Q-factor than that with the vertex output waveguide. For a 20-μm-side-length square microlaser with a 1.5-μm-wide vertex output waveguide, lasing spectra with multiple transverse modes are observed with the mode wavelength intervals agreeing with the 2-D-finite difference time domain simulation results. In contrast, single-mode operation with a side-mode suppression ratio of 42 dB is obtained for a 20-μm-side-length square microlaser with a 1.5-μm-wide midpoint output waveguide. The results indicate that output waveguide can result in a mode selection in addition to realizing unidirectional emission. [ABSTRACT FROM AUTHOR]

A high peak power (>MW), passively Q-switched Yb:YAG/Cr:YAG micro-laser end-pumped by fiber-coupled 120-W QCW LDs (Repetition~rate<100~Hz) is developed. The convex output coupler with a curvature of -2~m successfully enlarges the fundamental mode size in the micro-laser cavity, and the output pulse energy increases to 3.6 mJ at a Cr:YAG initial transmission of 89% without optical damage. The TEM00 transverse mode and the single-frequency oscillation are confirmed. The pulse duration is 1.3 ns, and then the peak power is estimated as 2.8 MW. To our knowledge, these are the highest pulse energy and peak power ever reported in Yb:YAG/Cr:YAG micro-lasers. The Yb:YAG rod with 5 at.% Yb concentration and 4.2-mm thickness keeps more than 80% single-pass pump absorption ranging from 15^\circC to 45^\circC in LD temperature. On the other hand, the characteristic temperatures of Yb:YAG/Cr:YAG and Nd:YAG/Cr:YAG lasers were estimated as 110 and 278 K, respectively. This means that the ratio of the increase in threshold pump energy to temperature of a Yb:YAG/Cr:YAG laser is twice or higher than that of a Nd:YAG/Cr:YAG laser due to a quasi-3-level system of Yb:YAG. [ABSTRACT FROM PUBLISHER]

Mode characteristics are analyzed for electrically injected equilateral-triangle-resonator (ETR) semiconductor micro- lasers, which are laterally confined by insulating barrier SiO2 and electrode metals Ti-Au. For the ETR without metal layers, the totally confined mode field patterns are derived based on the reflection phase shifts, and the Q-factors are calculated from the farfield emission of the analytical near field distribution, which are agreement very well with the numerical results of the finite-difference time-domain (FDTD) simulation. The polarization dependence reflections for light rays incident on semiconductor-SiO2 -Ti-Au multi-layer structures are accounted in considering the confinement of TE and TM modes in the ETR with the metal layers. The reflectivity will greatly reduce with a Ti layer between SiO2 and Au for light rays with incident angle less than 30° especially for the TE mode, even the thickness of the Ti layer is only 10 nm. If the ETR is laterally confined by SiO2 -Au layers without the Ti layer, the Fabry-Pérot type modes with an incident angle of zero on one side of the ETR can also have high Q-factor. The FDTD simulation for the ETR confined by metal layers verifies the above analysis based on multi-layer reflections. The output spectra with mode intervals of whispering-gallery modes and Fabry-Pérot type modes are observed from different ETR lasers with side length of 10 μm, respectively. [ABSTRACT FROM AUTHOR]

Equilateral-triangle-resonator (ETR) lasers with an output waveguide jointed at one vertex of the resonator are fabricated on (100) GaInAsP-InP wafers using photolithography and a two-step inductively coupled plasma (ICP) etching technique. Distinct peaks with the mode spacing of longitudinal mode intervals are observed in the luminescence spectra at room temperature. Furthermore, some minor peaks appear in the middle of the main peaks, which can be attributed to the first-order transverse modes as predicted in the theoretical results. CW directional lasing emissions are achieved for ETR lasers with side lengths ranging from 15 to 30 μm up to 200 K. The temperature dependences of the threshold current and lasing wavelength are measured for an ETR laser with the side length of 20 μm from 80 to 200 K. The observed threshold current rapidly increases as temperature increases over 170 K. [ABSTRACT FROM AUTHOR]