Electrical and optical properties of the four-terminaldouble-heterostructure opto-electronic switch

The authors extend the theory of the three-terminal double-heterostructure opto-electronic switch (DOES) device, in which the third terminal (the injector) makes contact to the bulk section of the active region, to the four-terminal DOES, in which the fourth terminal (the source) accesses the inversion channel at the n-n heterojunction. The source is shown to be capable of initiating switching at lower current densities than the injector. The effects of incident light on the device are also examined, yielding results similar to the injection of carriers at the source and injector. Incomplete ionization of the charge sheet and two-dimensional quantum effects in the channel, which have been neglected in previous DOES models, have been included. These effects are shown to affect significantly the characteristics of the device and to reduce the discrepancy between simulated and experimental results     

Strained layer (1.5 μm) InP/InGaAsP lasing opto-electronicswitch (LOES)

We present for the first time a lasing opto-electronic switch (LOES) fabricated in the InP/InGaAsP system. In this device the active region is composed of four 63 Å compressively strained quantum wells. A lasing threshold of 104 mA, or 6933 A/cm², has been observed at a temperature of 298 K, with an external differential quantum efficiency of 14%. The lasing wavelength is centered at 1.52 μm. The current-voltage characteristics manifest pronounced differential negative resistance, characterized by switching and holding voltages of 6.8 V and 1.6 V, respectively, and a switching current density of 33 A/cm². The OFF and ON state resistances are approximately 150 kΩ and 4 Ω, respectively     

Spontaneous oscillations in the InP-InGaAsP lasing optoelectronicswitch (LOES)

We present the first comprehensive experimental and theoretical analyses of spontaneous electrical and optical oscillations that occur when the InP-InGaAsP lasing optoelectronic switch (LOES) is biased in or near the negative differential resistance region of the device characteristic. For a device with a switching voltage and current of ~7 V and 0.5 mA, respectively, electrical oscillations are observed which result in current spikes of up to 613 mA, with a FWHM of 0.6 μs. The repetition rate varies from 900 Hz to 0.22 MHz, increasing with bias current. Pulses of laser light correlated to the current pulses are emitted from the LOES for some circuit configurations. A lumped circuit element model is presented which agrees well with the experimental results, and illustrates the effects of the bias circuit parameters on the device oscillations     

Basic building units and properties of a fluorescence single plane illumination microscope

The critical issue of all fluorescence microscopes is the efficient use of the fluorophores, i.e., to detect as many photons from the excited fluorophores as possible, as well as to excite only the fluorophores that are in focus. This issue is addressed in EMBL's implementation of a light sheet based microscope [single plane illumination microscope (SPIM)], which illuminates only the fluorophores in the focal plane of the detection objective lens. The light sheet is a beam that is collimated in one and focused in the other direction. Since no fluorophores are excited outside the detectors' focal plane, the method also provides intrinsic optical sectioning. The total number of observable time points can be improved by several orders of magnitude when compared to a confocal fluorescence microscope. The actual improvement factor depends on the number of planes acquired and required to achieve a certain signal to noise ratio. A SPIM consists of five basic units, which address (1) light detection, (2) illumination of the specimen, (3) generation of an appropriate beam of light, (4) translation and rotation of the specimen, and finally (5) control of different mechanical and electronic parts, data collection, and postprocessing of the data. We first describe the basic building units of EMBL's SPIM and its most relevant properties. We then cover the basic principles underlying this instrument and its unique properties such as the efficient usage of the fluorophores, the reduced photo toxic effects, the true optical sectioning capability, and the excellent axial resolution. We also discuss how an isotropic resolution can be achieved. The optical setup, the control hardware, and the control scheme are explained in detail. We also describe some less obvious refinements of the basic setup that result in an improved performance. The properties of the instrument are demonstrated by images of biological samples that were imaged with one of EMBL's SPIMs.