A laser and optical amplifier waveguide device with a plurality of layers that
supports a single lowest-order optical mode with gain while higher order modes
radiate and have a net loss. The supported lowest-order mode which has gain, has
a mode cross section which is large compared to the operating optical wavelength
in both the transverse and lateral directions. The contours of constant optical
intensity of such lowest-order can be nearly circular, having an approximately
elliptical shape with a small aspect ratio.
