We demonstrate the fabrication of binary, multilevel, and blazed diffractive structures by a fast and flexible direct-write process by using an excimer-laser-based tabletop micromachining workstation with an integrated optical surface profiler.

A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces.The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements.

The thermal properties of lenses play an important role in the performance of optical systems. We discuss the effects of uniform temperature changes and thermal gradients on diffractive lens performance. Comparisons are made between the thermal sensitivity of refractive and diffractive lenses. Useful design equations are presented that describe focal length, phase coefficients, and diffraction efficiency as functions of temperature. We present important thermal data for a number of lens materials. The optothermal expansion coefficient is used to design athermalized lenses that combine refractive and diffractive surfaces.

We describe a computational imaging technique to extend the depth-of-field of a 94-GHz imaging system. The technique uses a cubic phase element in the pupil plane of the system to render system operation relatively insensitive to object distance. However, the cubic phase element also introduces aberrations but, since these are fixed and known, we remove them using post-detection signal processing. We present experimental results that validate system performance and indicate a greater than four-fold increase in depth-of-field from 17" to greater than 68".Index Terms-Computational imaging, extended depth of field, millimeter wave imaging.