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We discuss a novel surface emitting InGaAsP LED with a relatively narrow spectrum obtained by the integral growth of a 2.6 μm thick semiconductor absorbing, or filtering, layer on a conventional double heterostructure device. The full width at half maximum for the filtered LED with peakpower at m is Å (63 meV),compared with an unfiltered LED half width of Å (97 meV). Half width measurements were made at a drive current density of 10 kA/cm2. The optimization of the filtered LED is considered, and it is found that a substantial reduction of the power in the short wavelength spectral tail can be obtained without significantly decreasing the total LED output power. For these reasons, the filtered LED has potential applications for low cost wavelength division multiplexing systems where a low overlap of spectral output between adjacent wavelength channels is required. In addition, the narrow spectrum may prove useful in moderate bit rate (> 100 Mbits/s) multimode transmission systems where the output from broad spectrum, conventional surface emitting LED's leads to unacceptably high levels of signal dispersion.