Abstract-In multisection laser diodes, the amplitude or frequency modulation (AM or FM) efficiency can be improved using the gain lever effect. To study gain lever, InGaAs double quantum well (DQW) edge emitting lasers have been fabricated with integrated passive waveguides and dual sections providing a range of split ratios from 1:1 to 9:1. Both the electrical and the optical gain lever have been examined. An electrical gain lever with greater than 7 dB enhancement of AM efficiency was achieved within the range of appropriate DC biasing currents, but this gain dropped rapidly outside this range. We observed a 4 dB gain in the optical AM efficiency under non-ideal biasing conditions. This value agreed with the measured gain for the electrical AM efficiency under similar conditions. We also examined the gain lever effect under large signal modulation for digital logic switching applications. To get a useful gain lever for optical gain quenched logic, a long control section is needed to preserve the gain lever strength and a long interaction length between the input optical signal and the lasing field of the diode must be provided. The gain lever parameter space has been fully characterized and validated against numerical simulations of a semi-3D hybrid beam propagation method (BPM) model for the coupled electron-photon rate equation. We find that the optical gain lever can be treated using the electrical injection model, once the absorption in the sample is known.
A Marx configured avalanche transistor string and a pulse rise-time peaking diode are used to generate pulses of >1000 V into a 50-Ω load with rise times of less than 300 ps. The trigger delay of this circuit is about 7–10 ns, with jitter <100 ps. This circuit has been used to generate pulses at a repetition rate up to 5 kHz.
Abstruct-Photoconductive switches are one of the few devices that allow the generation of high-voltage electrical pulses with subnanosecond rise time. We are exploring high-voltage, fast-pulse generation using GaAs photoconductive switches. We have been able to generate 35-kV pulses with rise times as short as 135 ps using 5-mm gap switches and have achieved electric field hold-off of greater than 100 kV/cm. We have also been able to generate an approximately 500-ps FWHM onloff electrical pulse with an amplitude of approximately 3 kV using neutron-irradiated GaAs having short carrier life times. This paper describes our experimental results and discusses fabrication of switches and the diagnostics used to measure these fast signals. We also describe our experience with the nonlinear lock-on and avalanche modes of operation observed in GaAs.
The defect-free photonic crystal (PC) slab geometry was explored for size-selective detection of bio-organism simulants. Through feedback between finite-difference time-domain simulations and experiments, we generated a conservative limit of detection estimate for randomized pore filling of a two-dimensional PC slab, and predict that random binding affords the label-free PC-based optical detection of low numbers (of the order of 10) of biological particles.
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