Anjan K. Ghosh

Package design for low-cost optical liquid-level sensors

Design and packaging of simple, low-cost, noncontact optical sensors for continuous liquid-level measurements are discussed. The sensors considered consist of only a source and a photoreceptor placed in a cylindrical tube containing the liquid. Selection of the sizes of various devices and placement of these devices in a compact package while maintaining suitable distances between them are considered. Various parameters of the possible packages are selected through diffraction calculations.

ALIGNMENT CONSIDERATIONS IN EXTRINSIC FIBER-OPTIC SENSORS

The performance of a fiber-optic sensor and its overall cost depend on the packaging of the sensor. Alignment of different optical, optoelectronic, and mechanical components is a key problem in the package design of a fiber-optic sensor. An intensity based fiber-optic sensor that can be used as a refractive-index or displacement sensor is considered as a case study in analyzing the effects of alignment on the performance of a fiber-optic sensor. Alignability of this sensor package is defined and calculated, taking into account the coupling efficiency and effects of various misalignments. Guidelines for making the package so that the fiber-optic sensor works more efficiently are developed from our calculations.

Effects of misalignments in packaging of array-based optical interconnects and processors

Parallel optical interconnections which replace metallic transmission lines with optical fibers or free space channels pro-vide high throughput, easy system integration, and low latency. These systems are used in making multiprocessor based supercomputers, telecommunication exchange switches and terminals, optical information processors and computers. A first-order model for the decrease in coupling efficiency between elements of two linear arrays of a free-space, parallel optical interconnect owing to misalignments or offsets in packaging is developed. Such an array interconnect consists of an array of optical sources, such as, optical fibers or VCSELs and an array of photo-receptors, such as, optical fibers, micromirrors or photodetectors. The coupling efficiency between source and receptor elements is modeled in terms of the sizes of the array elements, inter-element spacing and distances. The coupling efficiency is subject to degrading in-fluence of six varieties of random offsets, which may occur during the alignment, and fixing of the two arrays in a pack-age. We then determine first order approximations of the effects of these offsets. Our paper presents simple analytical formulas useful for a quick design of array-based parallel optical system packages and estimation of overall system per-formances. The formulas developed are useful for design and packaging of any optoelectronic processing system.

Low-cost optical liquid level sensors

Design of simple, low cost optical sensors for continuous liquid level measurements is discussed. The sensor consists of only a source and a photo-receptor placed in a cylindrical tube containing the liquid. Various parameters of this simple package are selected through diffraction calculations.

Performance Analysis of Acousto-optic Digital Signal Processors using the Describing Function Approach

Usually the amplitude of the electrical signal fed to an acousto-optic cell is kept low so that the acousto-optic diffraction becomes approximately linear with respect to the input amplitude. In this paper the approach of describing functions is used to analyze and quantify the nonlinear dependence of acousto-optic diffraction on the input signal amplitude. As a case study the performance of digital filter realizations using acousto-optic cells is analyzed. Acousto-optic digital filters can be used for real time processing of discrete time signals with high sampling rates (> 106 per sec). The advantages of the acousto-optics based realization are high throughput rate, high speed and compact size. These filters can be used in adaptive or non-adaptive signal processing applications in the areas such as radar signal processing and video communication systems. Analytical results are obtained using the describing function approach to study the effects of nonlinearity in the acousto-optic Bragg diffraction on t...

Describing functions for nonlinear optical systems.

The concept of describing functions is useful for analyzing and designing nonlinear systems. A proposal for using the idea of describing functions for studying the behavior of a nonlinear optical processing system is given. The describing function can be used in the same way that a coherent transfer function or optical transfer function is used to characterize linear, shift-invariant optical processors. Two coherent optical systems for measuring the magnitude of the describing function of nonlinear optical processors are suggested.

Optimal actuation of microcantilevers by a laser beam

Singly-clamped micron-sized cantilevers actuated by optical radiation pressure exerted by a laser are analyzed. An expression for optimum point of actuation giving the maximum amount of deflection is obtained.

Design and calibration of low-cost fiber optic sensors for refractive index measurement of turbid liquids

An optical fiber, stripped partially out of its cladding is used to sense refractive index of a liquid to a precision to fifth place of decimal. The dependence of the light output of the sensor on the refractive index of the test liquid is nonlinear. The light output of the sensor depends on the thickness to which the cladding is stripped. It shows both positive and negative slope with increasing refractive index of the test liquid. The slope of the plot of sensor output against liquid refractive index shows a change of sign at around the fiber refractive index. The sensor is unaffected by the presence of absorption and is insensitive to the chemical nature of the solute. The sensor is sensitive in the whole of the tested range of refractive indices 1.33 to 1.52. Experiments that show the significance of cladding modes in sensing are described.

Optical processing of signals in surface-plasmon-resonance-based optical biosensors

Surface plasmon resonance based optical sensors can be realized in integrated planar optical system on a glass substrate using mirrors and diffractive optical elements etched on the surfaces. Such a realization gives new capabilities for interrogating the sensor and for enhancing the response through multiple interactions and new possibilities for all-optical processing of the optical signals in the sensor.

The Radiation of Light from Laser Machined Taps on Optical Fibers

Micron-scale radiative taps can be made on optical fibers by etching a cut on the cladding using the CO2 laser ablative chemical etching process. Such taps can be used for making varieties of optical signal processors, fiber optic sensors and communication networks. The propagation of the optical fields along the fiber and their scattering at the discontinuity introduced by the tap are simulated using the finite-difference time-domain technique. The change in the radiated fields are studied for various values of tap shapes and tap sizes. The optical field visualization package is of great help in designing a tap for an application that requires a radiated beam of a specific pattern and a given amount of radiated power.