Efficient vertical coupling of photodiodes to InGaAsP rib waveguides

Abstract

Monolithic optoelectronics requires optical linkage between waveguides and photodiodes. Vertical coupling offers the advantages of single-step epi-growth and ease of junction placement.1,2 Its drawback is weak coupling, resulting in long detector lengths L and high capacitance. thinner guides can reduce L,1,2 but increase input coupling difficulty. We recently demonstrated than an optical "matching layer' introduced between a thick n-/n^+ InP waveguide and an InGaAs absorber significantly enhances vertical coupling.3 Here we show that this approach provides efficient coupling between InGaAs detectors and InGaAsP waveguides of the type currently employed in photonic integration.