Self-oscillating dimmable electronic ballast

This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out.     

Transient response of ARROW VCSELs under external optical feedback

The effect of external optical feedback on the transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is studied. It can be shown that the proper design of ARROW can suppress the excitation of high-order transverse leaky mode as well as increase the critical feedback strength so that stable high-power single-mode operation of VCSELs can be obtained even under the influence of strong external optical feedback.     

Estimation and Optimization of the Principal H-Maser Parameters

The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics.     

Robust dual-quantisation multibit sigma-delta modulator

A new dual-quantisation sigma-delta modulator is proposed, which introduces an additional feedback path in the input of the second integrator. In this way, unlike other dual-quantisation architectures, larger signal-to-noise ratios can be obtained by means of aggressive noise-shaping, like in a conventional multibit modulator. The proposed modulator is also shown to be more robust against non-idealities than other dual-quantisation architectures.     

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes.     

An optical instrumentation using a sensor with a sensordummyagainst noises on sensor and transmission line

This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance     

1/f noise sources

This survey deals with 1/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an α value with a magnitude in the order of 10^-4. Damaging the crystal has a strong influence on α, α may increase by orders of magnitude. Some theoretical models are briefly discussed none of them can explain all experimental results. The α values of several semiconductors are given. These values can be used in calculations of 1/f noise in devices     

Metal diffraction gratings as laser power or energy dividers

The authors survey published results on the application of metal diffraction gratings as laser power or energy dividers when the laser beam is split into two approximately equal pans. The normal incidence of laser radiation on metal diffraction gratings of various profiles in the case of three propagating diffraction orders n=0, ±1 is discussed, along with the case of oblique incidence with only two propagating diffraction orders n=0 and n =–1.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 22–26, February, 1994.