J. Blondelle

High efficiency planar microcavity LED's: comparison of design and experiment

This paper describes the design of substrate emitting microcavity LEDs and a comparison of experimental results with modeling results. The modeling is based on a simulation tool which accounts for guided modes, quantum well reabsorption and photon recycling. The overall quantum efficiencies of /spl lambda//2 and /spl lambda/ cavities both with a 60% and a 90% reflecting DBR mirror are compared and a good qualitative correspondence is found between theory and experiment. The maximum theoretical overall quantum efficiency for the considered structures is expected to be around 14%, whereas the best experimental value amounts to 10.2%.<<ETX>>

III-V semiconductor waveguiding devices using adiabatic tapers

Abstract In the past few years much effort has been put into the fabrication and optimization of III–V semiconductor waveguiding devices with integrated adiabatic mode size converters (tapers). By integrating a taper with a waveguide device, one wants to reduce the coupling losses and the packaging cost of OEICs in future optical communication systems. This paper gives an overview of different taper designs, their performance and the technological approaches used in realizing such tapered devices.

Monolithic integration of diffractive lenses with LED-arrays for board-to-board free space optical interconnect

Since optical interconnections can severely reduce problems associated with electrical interconnect technology (including bandwidth limitations, electromagnetic cross talk, signal delay and EMI aspects), the development of suitable electrooptic components is of crucial importance for implementation of optical interconnects in future computer systems. This paper addresses the design, modeling, fabrication as well as experimental assessment of LED-arrays, with diffractive lenses etched into the rear side of the LED-substrate. The suitability of such optical sources for board-to-board optical interconnections will be demonstrated. >

Planar substrate-emitting-microcavity light-emitting diodes with 20% external QE

The external QE of microcavity light emitting diodes strongly depends on the device size and operational current density. Our experiments reveal that spectral broadening of the optical spectrum emitted by the three InGaAs QWs as well as photon originally emitted into the guided mode of the cavity can explain these differences. An optimized microcavity layer design yields external QEs of 20 percent for substrate emitting light emitting diodes with diameters of 1.5 mm.

Resonant Cavity LED’s

Light Emitting Diodes (LED’s) suffer from poor external quantum efficiencies because most light is coupling to modes confined within the semiconductor. With the use of optically small structures it is possible to channel more light into the radiation modes thus increasing the quantum efficiency of the device. In this contribution we will discuss and demonstrate the potential of planar microcavity LED’s.

Microcavity LEDs with an overall efficiency of 4% into a numerical aperture of 0.5

Summary form only given. Microcavity LEDs were optimised for optical interconnect requirements. Overall quantum efficiency of up to 4.3% into a numerical aperture of 0.5 and a FWHM beam divergence angle of 105 degrees at a drive current of 1 mA was achieved. Microcavity LEDs with one gold and one GaAs-AlAs DBR-mirror have been optimized for efficiency into a limited NA of 0.5. Simulations indicate that an efficiency of 8% can be achieved. Experimental devices give a best value of 3.7%.

High Efficiency Microcavity LEDs

The work described here was aimed towards high efficiency light emitting diodes (LEDs), thereby compromising on directionality and narrow spectrum. At present our efforts have yielded devices which have an external quantum efficiency (QE) of over 22%. This is believed to be a record QE for planar LEDs. This result relies on both careful design and material growth. For the design we developed a simulation tool which proves useful in selecting interesting structures and interpreting experimental results. The theoretical analysis includes the guided modes, reabsorption of light by the active material and subsequent photon recycling. The material is grown with MOVPE, which yields high quality material as well as allowing excellent control over layer thickness and composition. In the first part we highlight the main characteristics of the theoretical model and deal with some key issues in the design of high efficiency microcavity LEDs (MCLEDs). In part two the main experimental results are discussed. (6 pages)

Emitters for optical interconnection

In order to provide cost effective solutions for different applications in optical interconnection, different approaches are needed. Cost and reliability are important considerations. The wavelength region between 900 nm and 1000 nm is very attractive since cheap Si-detectors can be used, the GaAs substrate is transparent and the fabricated Qw laserdiodes and LEDs have high performances and high reliability. Parallel optical interconnects require high performance (low threshold, high yield), densely packed laser arrays using fiber ribbon. For long distance communication, more emphasis is laid on the power budget and coupling efficiencies. If in parallel optical interconnect the very high modulation speed of laserdiodes is not really needed, InAlGaAs LED-arrays may be used, because of their stability, robustness and the possibility to integrate diffractive lenses on the backside of the component, which makes the component suitable for free-space optical interconnect. The better performances of microcavity LEDs will enhance this option even more.