Multiplexing Elements Research Articles

Dual-Beam Near-Infrared Hadamard Spectrophotometer

A dual-beam Hadamard multiplexed spectrophotometer is described. The instrument is intended to work in the near-infrared region of the electromagnetic spectrum (900–1800 nm) and is based on the use of a linear Hadamard mask containing 255 multiplexing elements. Simple symmetric Czerny–Turner optics were employed based on 10 cm diameter, 20 cm focus spherical mirrors and a plane grating containing 295 grooves mm−1. The dual-path system employs the multiplexed beam exiting from the mask, which can then be split by using either an integrating sphere, a bifurcated optical bundle, or a beamsplitter. Two cooled PbS or InAs detectors were employed to collect the 255 multiplexed intensities in about 8 s. Signal was obtained by linear displacement of the mask, which was controlled by software written in VisualBasic 4.0. Spectral data were demultiplexed with a program written in the same language. The instrument can successfully correct for the drift of the light source intensity. The wavelength precision is 0.4 nm, while the average standard deviation for absorbance measurements taken from 900 to 1800 nm is 1.5 × 10−3 absorbance units, a value that is about three times lower than that obtained for the single-beam multiplexed approach. The instrument has been applied to the determination of water in fuel ethanol with the use of partial least-squares modeling. The absolute standard error of prediction was 0.07% (w/w).

Multiwavelength highway photonic switches using wavelength-sorting elements-design

We propose multiwavelength highway photonic switch architectures for cross-connects using the wavelength routing function of the waveguide-array-grating demultiplexer. The wavelength router is used as wavelength-sorting elements. The wavelength division multiplexed (WDM) optical signals from multiple input ports are routed to group of output ports with certain combination of wavelengths. This enables multiport WDM systems to be configured using the reduced number of wavelength demultiplexing and multiplexing elements.

Systems with optical aperture synthesis and their application

The spectrum of an optical image was actively stutied for the first time in 1873, when E. Abbe experirnenta~y verified his theory on image formation in a microscope and studied the limits of its applicability [1]. These investigations were further refined when coherent light sources were created, which resulted in elaboration of spatial filtering of images and optical processing of information. The wide use of optical systems in information and measuring devices is responsible for the development of the informational approach to formation and analysis of optical images. Thus, e.g., a direct connection was found between the resolving power of an optical system and the amount of information contained in the image formed. High-resolution optical systems are necessary when solving various practical problems, e.g., in the control of geometrical parameters of products, in noncontact diagnostics, high-resolution photography, optical storage of information, etc. The resolution of conventional optical systems is determined, mainly, by the relative aperture (the ratio of the aperture diameter to the focal length); therefore it is customary to maximize the latter. However, technological and economical reasons may prevent one from doing this. In addition, in certain cases the large relative aperture may hinder the operating characteristics of the device as a whole. Thus, e.g., in order to provide high accuracy (determined by the objective depth of focus) in measuring linear dimensions by a precise focusing technique, the maximum value of relative aperture is preferable, which, because of technological restrictions, requires short-focus objectives to be employed and, hence, considerably reduces the measurement range. The aperture synthesis approach [2], in particular, optical aperture synthesis [3, 4], is one of the superresolution (i.e., resolution that exceeds the Rayleigh classical limit) methods in optics. Optical aperture synthesis (OAS) is realized by introducing into the object space of a conventional optical system a multiplexing optical element (e.g., a diffraction grating or raster lenses), which causes the diffracted beam whose spatial frequency of object spectrum is beyond the limits of the system aperture to decline in such a way that it fits the aperture. In order to reconstruct the beams and to form a "superresolved" image in the image space, an additional multiplexing element is introduced that is optically conjugate to the first one. Mathematical analysis of such a system with OAS shows that the resolving power of the optical system is increased at the expense of its reduced visual field [5] and the resolution is determined by the product of the Fourier transform of the exit pupil and the autocorrelation function of amplitude transmittance of the multiplexing element. If the autocorrelation length is shorter than the diffraction image size of a point object, then the resolving power of the system with OAS exceeds the diffraction limit. Let us consider image formation of a point source in a conventional optical system and in a system with a synthesized aperture. In Fig. 1, the point source is located in the object plane 1. In a conventional optical system (Fig. la), the spatial frequency band is limited by the width Ak ° due to the restricted aperture of the objective 2. It is obvious that at a smaller aperture of the objective 2 the sma~er part of the spherical wave passes into the image space and less information is ava~able about the wave-front curvature and point source location along the axis of the optical system. This uncertainty is manifested in the degree of diffraction image blurring in the plane 3 that can be estimated from the diameter of the Airy disk.

Channel expansion and tolerance analysis of waveguide manifold multiplexers

A computer-aided optimization procedure is introduced to enable the addition of extra channels to an already existing waveguide manifold multiplexer, without changing any of the existing multiplexer elements. The process provides the important advantage of the ability to expand the number of channels as required, a property which was only feasible before for channel dropping type multiplexers. The process is illustrated by practical examples that show its validity. Analysis of the effect of mechanical tolerances on the multiplexer performance is also presented to provide guidelines for the tolerance ranges in manifold multiplexer fabrication.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Narrow-band resonant optical reflectors and resonant optical transformers for laser stabilization and wavelength division multiplexing

We propose a new way of making highly resonant integrated optical circuits based on weak side-by-side coupling between waveguides and high Q distributed Bragg resonators. This method can be used to design a resonant optical reflector which, when used as a feedback element to a laser, will result in a compact structure that has both extremely narrow line width and very low chirp. By coupling the resonator to two waveguides, one on either side, an optical analog of the resonant transformer can be made. This device can be used for wavelength division multiplexing. Such multiplexer elements will both resonantly transform optical power from the laser to a common output channel and also provide feedback which locks the laser to the channel wavelength.

A Decomposition Chart Technique to Aid in Realizations with Multiplexers

Boolean functions can be realized using multiplexer elements by exploiting Shannon's expansion theorem. The cost of the realization often depends on the choice of the expansion variables versus the residue variables. A method employing Ashenhurst's decomposition charts [6] is described which assists in visualizing the residue functions. The method is effective for six variable functions or less.