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.

One of the most efficient ways to prepare nonlinear optical polymer channel waveguides is by photobleaching. To control the index profile precisely and to design and improve the performance of active electro-optical devices, modeling of the photobleaching process is important. We report our phenomenological bleaching model, which uses a stretched exponential time dependency technique that predicts the index profile for polymer channel waveguides and present design rules for active optical switches and modulators. One way to verify the bleaching model is to calculate the effective index and compare this with our measured effective index obtained with prism-coupling techniques. The bleaching model shows good agreement with experiments.

A systematic study of photoluminescence (PL) of Er and O ion implanted and annealed n-type GaN grown on R-plane sapphire (A12O3) was performed. The Er implants ranged from 2 × 1013 to 1 × 1015 Er++/cm2, and the O co-implants ranged from 1014 to 1016 O+/cm2. The resulting nine different combinations of GaN:Er,O were annealed at 600 °C (4 hrs. in N2), 700 °C (1.5 hrs. in N2), 800 °C (0.75 hr. in NH3), and 900 °C (0.5 hr. in NH3) Following each annealing step, the Er3 -related PL at 1.54 μm was measured from each sample at 77K, when pumped directly with 135 mW of power at 980 nm. The three samples with the highest dose of Er (1 × 1015 Er++/ cm 2), regardless of O co-dopant dose, yielded the strongest PL peak intensity at 1.54 μm after all the anneals. The integrated PL from 1.52 to 1.58 μm was reduced by 62 % when going from 77 K to room temperature (RT).

We have constructed what is to our knowledge the first speed-of-light 100-MHz digital optical counter using directional coupler switches and single-mode fibers. The counter has operated with both 4- and 6-bit counts, with the use of two different counter designs. In addition, we have demonstrated operation of two simultaneous and independent 4-bit counters running on the same hardware by time-division multiplexing the hardware. This approach allows effective clock rates many times the individual machine clock rate and is limited only by the switching speed. For large latency systems, this approach offers the promise of gigahertz clock rates for digital optical computers.