Controlling the directionality of spontaneous emission by evanescent wave coupling

We report an approach toward controlling the directionality of spontaneous emissions by employing the evanescent wave coupling effect in a subwavelength-sized ridge or truncated cone structure. An InGaAs/GaAs light-emitting diode in which a stripe-shaped InGaAs/GaAs quantum well with a stripe width of about 100 nm is embedded at the center of a subwavelength-sized GaAs ridge (of width ∼520 nm) is fabricated by micro processing and epitaxial regrowth techniques. Strong directionalities characterized by a half-intensity angle of 43° are observed in planes perpendicular to the ridge axis. The directionality is found to be almost independent of operating conditions.