Fast LEDs for polymer optical fiber communication at 650nm

Abstract

Data rates above 250 MBit/s via polymer optical fiber (POF) require specially designed light emitting diode (LED) chips. Because of the absorption minimum of the POF, the red wavelength region around 650 nm is of special interest. LED chips in this region comprise active regions out of the AlGaInP material system. To achieve low rise and fall times in the optical output, the current density has to be increased to levels about 400A/cm 2 . Hence the chip design needs ways to confine the current injection to a region significantly smaller than the chip itself. Conventional methods use epitaxially grown layers to ensure the lateral current spreading over the active region. But to confine the current to this region, the current spreading has to be eliminated locally. Typically, this is achieved by ion-implantation, mesa etching or selective oxidation of an AlGaAs layer of high Al-content. In this paper we present a new, planar, and very cost effective chip design for data rates around 250 MBit/s. No current spreading layer is included in the epitaxial growth, but is supplied during chip process using a transparent conductive oxide. Optical power around 2 mW at 20 mA without epoxy encapsulation, and rise and fall times around 2.5 ns have been reached.