<title>Longitudinally resolved measurements of carrier concentration and gain in 980-nm InGaAs/GaAs high-power quantum well lasers</title>

Abstract

Measurements of longitudinal variation in critical laser parameters such as gain and carrier concentration are invaluable in understanding and diagnosing device performance and failure mechanisms. However, traditional frontfacet measurements cannot reveal the variation of these parameters along the length of the laser. Other methods require physical modifications to the laser itself, such as the fabrication of a top window, and are thus invasive.We describe a new experimental technique based on analysis of side spontaneous emission. A tapered optical fiber translated along the side of the laser using a micropositioner collects spontaneous emission from the active region, allowing spatially-resolved gain and carrier concentration measurements to be made. Such measurements can be used to track the evolution of dark lines caused by defects where non-radiative recombination is dominant.We applied this method to a 980nm high power laser with an In02Ga8As, 80 A SQW and facets of 90%/1O% reflectivity. It was predicted through a one-dimensional rate equation model that the carrier concentration would increase near the high-reflectivity mirror, due to lower optical field intensities. Using the bimolecular recombination equation to determine the carrier density, this expectation was confirmed. The peak modal gain also increased with proximity to the high-reflectivity mirror, and modulations in the gain peak profile attributed to spatial hole burning were observed.

Spatial hole burning in high-power edge-emitting lasers: A simple analytical model and the effect on laser performance

“…where the pumping constant a ¼ C a i v g ewd a (6) has been introduced. Moreover, modern high-power lasers are designed to have built-in internal losses (those due to waveguide imperfections and absorption due to doping in claddings) at least an order of magnitude smaller than the outcoupling losses, 12 even for long laser cavities, which allows us to neglect the corresponding term in Eq.…”

“…[1][2][3][4][5][6][7][8] The effect consists in the inhomogeneous distribution of carrier density, and therefore optical gain, along the laser axis, caused by the inhomogeneous lasing light intensity distribution in the longitudinal direction. [1][2][3][4][5][6][7][8] The effect consists in the inhomogeneous distribution of carrier density, and therefore optical gain, along the laser axis, caused by the inhomogeneous lasing light intensity distribution in the longitudinal direction.…”

“…4,6 Either way, it is difficult to get a generic view of the magnitude of the effect and its dependence on laser parameters, and the conclusions reached in the literature are thus limited to a particular laser construction and operating parameter range. 4,6 Either way, it is difficult to get a generic view of the magnitude of the effect and its dependence on laser parameters, and the conclusions reached in the literature are thus limited to a particular laser construction and operating parameter range.…”

Effect of spatial hole burning on output characteristics of high power edge emitting semiconductor lasers: A universal analytical estimate and numerical analysis

“…The effect of (long-range) longitudinal spatial hole burning (LSHB) in edge emitting semiconductor lasers has been intensely investigated throughout the history of semiconductor laser technology. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The LSHB effect consists of the inhomogeneous distribution of carrier density, and therefore optical gain, along the laser axis, caused by the inhomogeneous lasing light intensity distribution in the longitudinal direction. [1][2][3][4][5][6][7][8][9][10] It is in practice most pronounced in lasers of an asymmetric design, where one mirror is antireflection (AR) coated and the other mirror is high-reflection (HR) coated.…”

“…Most theoretical approaches to LSHB presented in the literature used either numerical methods of various degrees of complexity 2,7,8 or semi-analytical approaches resulting in complex transcendental formulas that give the spatial dependences of photon and carrier densities in a parametric form. 4,6 Either way, it is not easy to get a generic view of the magnitude of the effect and its dependence on laser parameters, which restricts the conclusions of the analysis to a particular laser construction and operating parameter range. Some analytical progress was made in Refs.…”