Efficient Er-related photo-, cathodo-, and electroluminescence at 1539 nm was detected from Er and O co-implanted n-type GaN on sapphire substrates. Several combinations of Er and O implants and postimplant annealing conditions were studied. The Er doses were in the range (0.01-5)ϫ10 15 ions/cm 2 and O doses (0.1-1)ϫ10 16 ions/cm 2 . GaN films implanted with 2ϫ10 15 Er 2ϩ /cm 2 at 350 keV and co-implanted with 10 16 O ϩ /cm 2 at 80 keV yielded the strongest photoluminescence intensity at 1539 nm. The annealing condition yielding the strongest Er-related photoluminescence intensity was a single anneal at 800°C ͑45 min͒ or at 900°C ͑30 min͒ in flowing NH 3 . The optimum O:Er ratio was found to be between 5:1 and 10:1. Co-implanting the GaN:Er films with F was also found to optically activate the Er, with slightly ͑20%͒ less photoluminescence intensity at 1539 nm compared to equivalent GaN:Er,O films. The Er-related luminescence lifetime at 1539 nm was found to depend on the excitation mechanism. Luminescence lifetimes as long as 2.95Ϯ0.15 ms were measured at 77 K under direct excitation with an InGaAs laser diode at 983 nm. At room temperature the luminescence lifetimes were 2.35Ϯ0.12, 2.15Ϯ0.11, and 1.74Ϯ0.08 ms using below-band-gap excitation, above-band-gap excitation, and impact excitation ͑reverse biased light emitting diode͒, respectively. The cross sections for Er in GaN were estimated to be 4.8ϫ10 Ϫ21 cm 2 for direct optical excitation at 983 nm and 4.8ϫ10 Ϫ16 cm 2 for impact excitation. The cross-section values are believed to be within a factor of 2-4.

Room temperature operation of erbium and oxygen coimplanted GaN m-i-n (metal–insulator–n-type) diodes is demonstrated. Erbium related electroluminescence at λ=1.54 μm was detected under reverse bias after a postimplant anneal at 800°C for 45 min in flowing NH3. The integrated light emission intensity showed a linear dependence on applied reverse drive current.

The problem of doping optical quality polymers with chelated Nd3+ has been studied. A number of material systems were evaluated. The best results in terms of optical quality at a high Nd3+ concentration were achieved by doping a fluorinated polyimide with fluorinated neodymium chelate. Slab and channel waveguides were fabricated in this material system. Optical absorption and luminescence studies were carried out.

The cathodoluminescence (CL) of erbium and oxygen coimplanted GaN (GaN:Er:O) and sapphire (sapphire:Er:O) was studied as a function of temperature. Following annealing, the 1.54 μm intra-4f-shell emission line was observed in the temperature range of 6–380 K. As the temperature increased from 6 K to room temperature, the integrated intensity of the infrared peak decreased by less than 5% for GaN:Er:O, while it decreased by 18% for sapphire:Er:O. The observation of minimal thermal quenching by CL suggests that Er and O doped GaN is a promising material for electrically pumped room-temperature optical devices emitting at 1.54 μm.

We describe the design and implementation of a bit-serial, four-bit, binary optical counter. The counter was designed and simulated using a digital optical simulation program developed for this purpose. It consists of five switches, a 4-bit fiber loop memory to store the count, four splitters, and fibers to interconnect the components. The counter is presently limited to a clock rate of 50 MHz because of the propagation delay in the single-bit time feedback loop. As designed, the same hardware may be used to count any even number of bits simply by changing the lengths of two fiber loops. The counter is unique in that it does not employ latches or other synchronizing memory elements, rather relying on a time-of-flight architecture. We describe the system issues involved in construction of the counter as well as the novel requirements on the switch drive electronics. We then outline the issues still to be addressed for the current counter and conclude with suggested design alternatives to improve its operation and increase its clock rate.