Abstract: Devices, such as node and network elements for use in communications systems, which include a plurality of ports, each having an input and an output, a plurality of splitters corresponding to the port inputs, a plurality of combiners corresponding to the port outputs, a plurality of signal paths between the splitters and the combiners, wherein each of the signal paths includes a signal varying device, and a plurality of protection devices connected between the splitters and the combiners, wherein each of the plurality of protection devices includes a signal varying device and provides a protection path corresponding to a plurality of the signal paths, and wherein at least one splitter has at least one unused output after the signal paths and the protection paths are connected, and wherein at least one combiner has at least one unused input after the signal paths and the protection paths are connected.

Abstract: Devices, such as node and network elements for use in communications systems, which include a plurality of ports, each having an input and an output, a plurality of splitters corresponding to the port inputs, a plurality of combiners corresponding to the port outputs, a plurality of signal paths between the splitters and the combiners, wherein each of the signal paths includes a signal varying device, and a plurality of protection devices connected between the splitters and the combiners, wherein each of the plurality of protection devices includes a signal varying device and provides a protection path corresponding to a plurality of the signal paths, and wherein at least one splitter has at least one unused output after the signal paths and the protection paths are connected, and wherein at least one combiner has at least one unused input after the signal paths and the protection paths are connected.

Abstract: The negative effects of kinking in the L-I characteristics of laser diode operation with respect to feedback control for laser diode current control is suppressed by either (1) combining the output of a plurality of laser diodes together or (2) by imparting a current modulation superimposed on the direct driving current of the laser diode in conjunction with a limited feedback bandwidth, or a combination of both approaches (1) and (2).

Abstract: Apparatus for providing a laser source optically coupled to an optical waveguide, such as an optical fiber, having a reflective grating positioned from the output facet of the laser source a distance equal to or greater than the coherence length of the laser source providing a portion of reflective feedback into the laser source optical cavity to maintain wavelength operation of the laser source in spite of changes in the laser operating temperature or drive current based upon coherence collapse in the laser operation. In cases where the fiber grating is positioned in the fiber within the coherence length of the laser source, intermittent coherence collapse, as opposed to continuous coherence collapse, is unavoidable. In cases where such a laser source is a pumping source for a solid state gain medium, such as an optical amplifier or laser having an active gain element, e.g.

Abstract: A laser absorption sensor system for performing optical measurements on a sample is described. The sensor system includes a tunable laser, capable of being tuned at rates exceeding 1 KHZ, and with a tuning range approaching 1 GHz. The laser beam is modulated at a modulation frequency between 1 and 100 KHz. Modulation in this frequency range is termed wavelength modulation. The beam is split into two beams, a signal beam and a reference beam. The signal beam traverses the sample where characteristic absorption takes place and is incident on a signal photodetector. The reference beam is incident directly on a reference photodetector. A noise cancellation circuit combines signal and reference photo-currents from signal and reference photodetectors reducing signal noise and increasing system sensitivity. The combination of wavelength modulation and the noise cancellation scheme provide a highly sensitive simple, rugged, low cost laser absorption sensor system.