<title>Design of high-power superluminescent diodes with low spectral modulation</title>

Abstract

Superluminescent diodes (SLD) are high gain optical amplifiers whose output is the amplified spontaneous emission (ASE) of a current-pumped semiconductor laser gain medium. Because of the high gain (&gt;40 dB), it is very important to reduce facet reflections to 10<SUP>-6</SUP> or lower in order to maintain spectral modulation due to feedback from facet reflection below a few percents. Tilting the SLD waveguide at an angle with respect to the facets is an effective way to reduce facet reflection. However, the angle cannot be chosen arbitrarily, because the facet reflection does not decrease monotonically with angle. This is due to the geometry of the mode profile, which is a trigonometric function inside the waveguide and a decaying exponential in the outside of the region. It also depends on the stripe width and lateral index contrast of the structure. This paper will discuss the design criteria for achieving low spectral modulation in ordinary index-guided structures and will describe several applications of SLDs. It will also discuss the design of SLDs with output power of several hundred milliwatts using the so-called diamond or inverse bow-tie waveguide structure.