Equilibrium mode distribution

About: Equilibrium mode distribution is a research topic. Over the lifetime, 928 publications have been published within this topic receiving 14939 citations.

Transverse waveguide design for high-brightness laser diodes

Abstract: We describe a new approach to achieving high brightness emission from laser diodes using a compound waveguide containing an unusual high order mode. This mode is predominantly single lobed and unusually localized in the low index region of the waveguide. To examine the utility of this mode we calculated the single-mode fiber butt coupling efficiency for an AlGaAs/GaAs compound waveguide of 61 micrometer aperture width, emitting at a wavelength of (lambda) equals 980 nm. Our results show a 2.3 times enhancement of the fiber coupling efficiency when compared with a simple broad area waveguide. Furthermore the coupling efficiency is still almost a factor of two greater than the coupling efficiency of the emission from a single mode ridge waveguide.

Measurement of complex mode amplitudes in multimode fiber

Abstract: A simple optical technique is described for the measurement of complex mode amplitudes in multimode fibers. The technique used in this experiment involves launching a laser beam into the core of low moded optical fiber, exciting a mixture of normal modes. The emerging mode patterns are stored in microcomputer. The complex modes are then extracted from these recoded intensities with help of modified version of Gerchberg-Saxton algorithm. Many experimental results are recorded in photographic form and comparison with computer analyzed pattern is made. The evaluation of complex mode amplitudes in multimode fiber can yield useful information about the mode filling of such fiber.

1.55-μm mode expander using single epitaxial growth

Abstract: We report on two techniques developed at the University of Maryland, College Park for fabricating expanded mode laser arrays. Both of these techniques use single epitaxial growth and conventional fabrication techniques. The first of these techniques is based on adiabatic mode transformation from a tightly confined active waveguide to a loosely confined large underlying passive waveguide over a mode transmission region 500 micrometers long. The devices butt couple to a standard single mode fiber with a coupling loss of 3.6 dB and reduced farfield divergence angles of 22 degree(s) and 9 degree(s) in the transverse and lateral directions respectively. The excess mode transformation loss is 1.3 dB. The second device is based on a novel resonant coupling scheme between two waveguides of different dimensions and refractive indices. The mode is transformed over a taper length of 200 micrometers with excess mode transformation loss of 0.6 dB. Butt coupling efficiencies of 41% (3.8 dB coupling loss) is achieved to a standard single mode fiber. The farfield divergence angles achieved are 24 degree(s) and 13 degree(s) in the transverse and lateral directions respectively.

Basic studies of fluctuations, transport and their control

Abstract: The first experimental study of a mixed slab - toroidal ITG (ion temperature gradient) driven mode in the Columbia linear machine (CLM) is reported. The effects of the modest levels of magnetic curvature are seen to be further destabilization and reduction of the real frequency of the mode. However, with a further increase in the mirror ratio, the mode amplitude decreased. The mode has the appearance of a hybrid ITG-dissipative trapped electron mode. We have measured the reduction of anomalous fluctuation driven particle transport due to feedback via cross-correlation of Langmuir probe and capacitive probe data for a centrifugal mode driven by E×B rotation of the plasma column. The particle flux is obtained from cross power spectra of density and potential fluctuation. The resulting diffusion coefficient clearly indicates that feedback can reduce the transport by up to a factor of three. To investigate the question of non-linear saturation of the mode we have performed a bispectral analysis of fluctuation data. The results clearly indicate strong mode coupling in the spectral width of the mode. Furthermore, we resolve the spectral width to reveal that it is composed of radial harmonics. These observations suggest that the nonlinear mode coupling between these radial harmonics is the saturation mechanism of the instability, as well as the underlying cause of the consequent anomalous transport.

Observation of mode instability and coherence collapse in a single-frequency polarization-maintaining fiber ring laser

Abstract: Mode instability acts as a common feature in single-frequency fiber ring lasers. The mechanism of coherence collapse by mode instability is theoretically analyzed and demonstrated with an unbalanced fiber Michelson interferometer utilizing phase modulation, which is illuminated by a single-frequency erbium-doped fiber ring laser. Multiform mode instability phenomena accompanied with coherence collapse are observed and discussed in detail by tracing the dynamics of the interference fringe visibility. The results show that mode instability would introduce extra phase noises like a false alarm to interferometric fiber optic sensing systems.