Abstract: All-optical modulation occurs in crystalline organic semiconductor waveguides (10a) grown by the ultrahigh vacuum process of organic molecular-beam deposition onto substrates (10b). Two light beams with wavelengths of 1.06 and 0.514 .mu.m from a first source (12) and a second source (34), respectively, may be used as the guided and the pump light sources, respectively. A resonant non-linear coefficient at room temperature of 5.4.times.10.sup.-5 cm.sup.2 /W at 1.06 .mu.occurs at a pump intensity of 1.0 W/cm.sup.2. This large non-linear effect is attributed to free electron-hole pairs produced by the dissociation of excitons generated by the short wavelength beam. A carrier lifetime of (17.+-.1) us, which determines the modulator switching time, is in good agreement with theoretical predictions. This appears to be the first observation of free-carrier-induced index modulation in crystalline organic waveguides.

Abstract: A passive control network for connection between a pair of load output level setting terminals, as on a ballast for a dimmable fluorescent lamp in a lighting system, to provide a required variable impedance, where the magnitude of the impedance establishes the load output level. The passive control network includes an isolation transformer for coupling a periodic waveform at the load input terminals to the variable impedance component, the magnitude of which impedance is reflected through the transformer to provide the load level-setting impedance.