Patricia F. Mead

Axial and angular displacement fiber-optic sensor

An intensity-based fiber-optic sensor for measuring axial and angular displacement has been designed and tested in a controlled laboratory environment. In addition, a mathematical model allowing the simultaneous calculation of the three desired parameters needed to characterize the tilt and the position of a surface under investigation is described. Preliminary tests show good agreement between the theory and the experimental results and show the sensors potential for application in the manufacturing industry for position and vibration control. The sensor shows significant improvement in angular range over previously reported methods. An axial displacement range of 2 mm, with an accuracy of 40 mum, and an angular displacement range of 40 mrad, with an accuracy of 0.5 mrad, are demonstrated. Suggestions for further improvement of the range and the sensitivity of the sensor are also described.

Rapid Cure Of Liquid Encapsulants And Structural Adhesives For Electronics Packaging Using Variable Frequency Microwave (Vfm) Energy

This paper reports on the use of an emerging process technique for curing of polymer encapsulants as used in the electronic packaging industry. Previous work performed in the area of materials processing has demonstrated the usefulness of sweeping operating frequencies in order to achieve high levels of electric field uniformity and process control. The use of controlled variable frequency microwave energy has been evaluated as a process technique compatible with electronic packaging requirements. The heating of a series of integrated circuits (ICs) and their subsequent characterization was performed. IC integrity was investigated using X‐Ray, Acoustic Microscopy, Decapsulation and Bond Pull. Processing of liquid encapsulants, underfills and glob‐tops, used in Flip Chip and Chip On Board (COB) applications, was performed. Differential Scanning Calorimetry was used to study cure extent. Further studies show that variable frequency microwave processing leads to fast curing of encapsulants. A reduction in cycle times from 15 to 20 times over conventional curing has been observed. Also, results have showed a reduction in the stresses induced by mismatches in coefficient of thermal expansion.

In-fiber strain characterization of fiber-optic connector assemblies by Bragg grating sensors

In-fiber Bragg grating sensors were used to study mechanical strain in optical fibers that were terminated in standard-termination and ribbon connectors. Our findings indicate that terminated sensors experience a compressive strain whose magnitude depends on the cure profile of the epoxy encapsulant used in these connectors. Anneal treatments on these connectors generally reduce the mechanical stress by inducing stress relaxation in the encapsulant layer. These experiments demonstrate the viability of in-fiber sensors to characterize fiber-optic connector assemblies during and following termination.

Procedure for evaluation of thermal management requirements in a laser diode structure

Temperature is either a direct catalyst or a precipitating factor in several common laser diode degradation mechanisms including dark-line defects, catastrophic optical destruction, metal diffusion and electrode delamination. This strong correlation between device temperature and performance degradation demonstrates the need for an efficient thermal management strategy. We have adopted a commonly used heat generation model to perform a finite element analysis to compute steady-state and transient thermal profiles for a laser diode structure. The flexibility of the FE model is utilized in performing a parametric study of selected variables affecting temperature in the structure. Taguchi principles are used in the set-up and analysis of this model, and quantitative correlations between the selected variables and temperature are derived. The combined interaction expression is then modeled as an optimization function that may be applied in thermal management analysis. The approach demonstrated here conforms to a general methodology for the development of physics of failure models for degradation in optoelectronic devices.

Single-mode operation of diode-pumped Nd:YAG lasers by pump-beam focusing

We present a theoretical study of the maximum single frequency power that can be obtained from a simple coaxially end-pumped Nd:YAG laser. The approach is general for four-level solid-state laser systems. It is shown that careful control of the pump beam geometry, cavity length, and crystal length can enhance single frequency performance. >

Strain evaluation of epoxy-cured fiber-optic connectors

Optical fiber connectors are passive components used to link two fiber links or a fiber link to a photonic device. One widely used type of fiber connector, a design that uses a thermally cured epoxy adhesive, has been evaluated via Bragg grating-based fiber strain sensors. Strain sensors were used to evaluate the strain incurred by the optical fiber as a result of installation and subsequent environmental testing. Preliminary mechanical modeling and a strain analysis using Bragg grating-based strain sensors are discussed. Since the strain sensors were not exposed to uniaxial loading, mechanical modeling was used to determine the optimum placement of the sensors and the expected response. Also discussed are ongoing studies to evaluate the viscoelastic behavior of the epoxy and its effect on the strain state of the connector assembly.

Experimental and numerical studies in the evaluation of epoxy-cured fiber optic connectors

The fiber optic connector (FOC) is a passive optical component that is used in many applications and whose function is to physically and optically link two fiber joints. It is important for the reliability of fiber optic infrastructure to identify the mechanisms of degradation and failure of these components. This paper reviews work at the University of Maryland CALCE Center to accomplish this, including experimental strain analysis utilizing fiber sensors and calculations and models to predict the stresses in FOCs and their effect on the response of the sensors used. In-fiber Bragg grating sensors have been used to study the mechanical strain state in optical fibers that have been terminated in ST connectors. Our findings indicate that terminated sensors experience a compressive strain whose magnitude depends on the cure profile of the epoxy encapsulant used in these connectors. Specifically, we have found that room temperature cures result in lower strain as compared to thermally cured samples. The measured strain magnitude is also believed to be sensitive to the position of the sensor along the axis of the connector. It is believed that to adequately account for such phenomena to occur and predict failure and degradation of the connector, the behavior and response of the epoxy encapsulant is a key consideration.

Optical fiber strain in epoxy-cured fiber optic connectors

Fiber optic connectors are passive optical components made up of various materials and used in harsh and benign environments. This paper presents the results of a project to evaluate the mechanical response of an optical fiber terminated in an optical fiber connector. This work is conducted via in-situ strain sensors based on optical fiber Bragg grating technology. These sensors assess the strain state of the optical fibers as a result of termination and subsequent environmental testing. Previous results and recent findings are reviewed and discussed. A design of experiments methodology is used to ascertain the significance of particular factors in the strain state of the fiber. Of primary interest are the connectors optical loss and strain in the fiber. In addition, there is interest in the role of the epoxy in the mechanical behavior of the connector assembly and accurate modeling of the sensor response. Modeling the response of the Bragg grating sensor when exposed to nonuniform and transverse strains is addressed.

Fiber connector reliability using fiber optic strain sensing

In-fiber Bragg grating sensors have been used to study mechanical strain in optical fibers that have been terminated in ST connectors. Our findings indicate that terminated sensors experience a compressive strain whose magnitude depends on the cure profile of the epoxy encapsulant used in these connectors. These experiments demonstrate the viability of using in-fiber sensors to characterize fiber optic connector assemblies during and following termination. However, the stain state of the sensing environment is a complex one, so there is the challenge of reading out the correct strain from the sensor response. To address this problem, the T-matrix formalism is being utilized. A review of this method and examples of its use will also be presented.