Ultra-high-speed photodetectors and printed-circuit antennas construct photonic transmitters. In this letter, we demonstrate a terahertz ͑THz͒ photonic transmitter: edge-coupled membrane photonic transmitters based on metal-semiconductor-metal traveling-wave photodetectors, which are fabricated with low-temperature-grown GaAs photoabsorption layers. With a membrane-based and edge-coupled structure, the demonstrated photonic transmitters can eliminate the requirement of Si lenses and attain an over 20 times higher optical-to-THz power conversion efficiency 2ϫ10 Ϫ4 than vertical illuminated photonic transmitters with Si lenses at the same operation frequency.

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High-output-power and high-bandwidth performances are usually two tradeoff parameters in the design of high-speed photodetectors. In this letter, we report high peak-output-voltage ͑ϳ20 V͒ and peak-output-current ͑ϳ400 mA, 50 ⍀ load͒ together with ultrahigh-speed performances ͑1.5 ps, 220 GHz͒, observed in low-temperature-grown-GaAs ͑LTG-GaAs͒ based metal-semiconductor-metal ͑MSM͒ traveling-wave photodetectors ͑TWPDs͒ at a wavelength of 800 nm. Ultrahigh-peak-output-power and ultrahigh-electrical-bandwidth performances were achieved due to the superior MSM microwave guiding structure and a short carrier trapping time in the LTG-GaAs layer, which reduced the space-charge screening effect and increased the photoabsorption volume without sacrificing electrical bandwidth significantly. We also observed different bias-dependent nonlinear behaviors in MSM TWPDs under high and low illuminated optical power excitations, which are possibly dominated by the space-charge screening and the lifetime increasing effects, respectively.Ultrahigh speed photodetectors ͑PDs͒ attract much attention due to their applications in fiber communication and optical measurement systems. 1 Recently, the development of optical amplifier has created a new demand of high inputoptical power durability in these high-speed PDs. Some receiver circuits use fiber amplifiers as preamplifiers, which relieve or even eliminate the necessity of electrical amplifiers. 1 By utilizing photomixing techniques, microwave photonic systems are expected to generate tunable and highpower microwaves or submillimeter waves under intense optical excitation. 2 However, ultrahigh bandwidth PDs are known to suffer bandwidth degradation problems under intense optical illumination. 3,4 Maximum output current/power and electrical bandwidth performances are usually two tradeoff parameters in the design of high-speed PDs. 1 By properly scaling down the size and photoabsorption volumes of PDs, ultrahigh speed performances can be achieved due to the reduction of parasitic capacitance and resistance in PDs. 5 However, the small photoabsorption volume ͑ϳ1 m 3 ͒ would cause high densities of photogenerated free carriers inducing strong space-charge fields that screen the external applied bias field. The device electrical bandwidth would thus degrade seriously due to the reduction in drift velocities of photogenerated carriers. 3,4 On the other hand, by reducing the optical modal absorption constant and increasing the photoabsorption volume, the output power can be increased significantly at the expense of the electrical bandwidth limited by R-C time constant and high microwave loss in the large-area and long-absorption-length devices. 6,7 There are two major ways to increase the output-saturation-current͑power͒-electrical-bandwidth-product performances. One is to distribute the photocurrents along edge-coupled PDs, such as the velocity match distributed photodetectors ͑VMDPs͒, 8 the other is to increase the carrier velocity using unitraveling carrier PDs ͑UTC-PDs͒. 1 In this letter...

Genotoxicity assessment is carried out on freeze dried powder of cultured probiotics containing Lactobacillus rhamnosus LCR177, Bifidobacterium adolescentis BA286, and Pediococcus acidilactici PA318. Ames tests, in vitro mammalian chromosome aberration assay, and micronucleus tests in mouse peripheral blood are performed. For 5 strains of Salmonella Typhimurium, the Ames tests show no increased reverse mutation upon exposure to the test substance. In CHO cells, the frequency of chromosome aberration does not increase in responding to the treatment of probiotics. Likewise, the frequency of micronucleated reticulocytes in probiotics-fed mice is indistinguishable from that in the negative control group. Taken together, the toxicity assessment studies suggest that the multispecies probiotic mixture does not have mutagenic effects on various organisms.

The effects of incorporating low-temperature-grown GaAs (LT GaAs) into the layer structure of Al0.98Ga0.02As/GaAs are studied. Results show that the structures containing a 300 nm layer of LT GaAs have faster oxidation rates and lower oxidation temperatures compared to reference samples without the LT GaAs layer. This letter will discuss the mechanisms involved in the oxidation rate increase, attributed to the LT GaAs enhancing the transport of As species during the oxidation process.