A four-frame phase shift method insensitive to phase shifter nonlinearity

A four-frame phase shift method and an associated algorithm using unequal phase steps are presented. The unique advantage of this method is that it becomes insensitive to phase shifter nonlinearity because of the performance of a special procedure, in which the phase shifts are shared out between the reference beam and the object beam. By this means, any phase shifter can work as long as one phase shift is accurately known. On the basis of the technique, a simple calibration method for the linear phase shifter is suggested. The influences of phase shifter miscalibration, detector nonlinearity and random noise on the algorithm are investigated, and the optimal phase shifts are given.

alpha-tocopherol is essential for acquired chill-light tolerance in the cyanobacterium Synechocystis sp strain PCC 6803

Unlike Escherichia coli, the cyanobacterium Synechocystis sp. strain PCC 6803 is insensitive to chill (5 degrees C) in the dark but rapidly losses viability when exposed to chill in the light (100 mu mol photons m(-2) s(-1)). Preconditioning at a low temperature (15 degrees C) greatly enhances the chill-light tolerance of Synechocystis sp. strain PCC 6803. This phenomenon is called acquired chill-light tolerance (ACLT). Preconditioned wild-type cells maintained a substantially higher level of alpha-tocopherol after exposure to chill-light stress. Mutants unable to synthesize alpha-tocopherol, such as slr1736, slr1737, slr0089, and slr0090 mutants, almost completely lost ACLT. When exposed to chill without light, these mutants showed no or a slight difference from the wild type. When complemented, the slr0089 mutant regained its ACLT. Copper-regulated expression of slr0090 from P-petE controlled the level of et-tocopherol and ACLT. We conclude that alpha-tocopherol is essential for ACLT of Synechocystis sp. strain PCC 6803. The role of a-tocopherol in ACLT may be based largely on a nonantioxidant activity that is not possessed by other tocopherols or pathway intermediates.

Residual plastids of bleached mutants of Euglena gracilis and their effects on the expression of nucleus-encoded genes

Bleached mutants of Euglena gracilis were obtained by treatment with ofloxacin (Ofl) and streptomycin (Sm) respectively. As shown by electron microscopy, the residual plastids contain prothylakoids in an Ofl mutant, and the highly developed and tightly stacked membranous structure found in cells of two Sm, mutants. Nine genes of the plastid genome were examined with PCR, showing that ribosomal protein genes and most other plastid genes were lost in all but one Sm mutant. Using differential display and RT-PCR, it was shown that chloroplast degeneration could cause changes in transcription of certain nucleus-encoded genes during heterotrophic growth in darkness.

High-power quantum-dot superluminescent LED with broadband drive current insensitive emission spectra using a tapered active region

High-power and broadband quantum-dot (QD) superluminescent light-emitting diodes are realized by using a combination of self-assembled QDs with a high density, large inhomogeneous broadening, a tapered angled pump region, and etched V groove structure. This broad-area device exhibits greater than 70-nm 3-dB bandwidth and drive current insensitive emission spectra with 100-mW output power under continuous-wave operation. For pulsed operation, greater than 200-mW output power is obtained.

Broadband polarization-insensitive semiconductor optical amplifier gate with tensile InGaAs quasi-bulk and compressively strained InGaAs wells

A novel wideband polarization-insensitive semiconductor optical amplifier (SOA) gate containing compressively strained InGaAs quantum wells and tensile-strained InGaAs quasi-bulk layers is developed. The fabricated SOA gates have a wide 3-dB optical bandwidth of 102 nm, less than 0.8-dB polarization sensitivity, more than 50-dB extinction ratio, and less than 75-mA fiber-to-fiber lossless operating current. (C) 2004 Society of Photo-Optical Instrumentation Engineers.