Michael W. Farn

Binary gratings with increased efficiency

Coupled-wave analysis is used to design binary gratings with high efficiencies (70-80%). The binary designs have grating periods greater than one wavelength but use subwavelength structures within each period in order to achieve high efficiency.

Color separation by use of binary optics

We describe the preliminary design, fabrication, and demonstration of an array of micro-optics that is used to separate colors locally on the focal plane. The 64 x 64 array combines 100 microm x 100 microm, F/2 refractive microlenses with a 17-microm period grating. The microlenses concentrate the incoming radiation, while the grating disperses the radiation according to wavelength. The element, with a minimum feature size of 1 microm and total depth of 8 microm, is fabricated on a silicon wafer (for use in the 8-12-microm band) by means of a nonstandard binary-optics process.

New iterative algorithm for the design of phase-only gratings

We present a new algorithm for the design of phase-only gratings. In general, a successful grating design will shape the relative intensities of the diffracted orders while simultaneously maximizing the light contained in the orders of interest. This iterative algorithm achieves both of these goals. Solutions typically have efficiencies of .90 to 1.00 and can be made arbitrarily close to the desired intensity profile. Convergence to a solution is quick for small numbers of orders (about 20) and the performance of the final solution is fairly independent of the starting point.

Agile beam steering using phased-arraylike binary optics

A method is demonstrated for two-dimensional steering of a laser beam by way of the mechanical translation of two phased-arraylike binary optics elements. The elements are translated over a 320-pum distance, resulting in the steering of a green He-Ne laser (λ = 0.543 µm) over a 6-deg field of view. Both theoretical development and experimental verification are presented.

Quantitative comparison of the general Sweatt model and the grating equation

When using the general Sweatt model for ray tracing diffractive optical elements (binary optics, holographic optical elements, etc.), lens designers must choose an index of refraction that is sufficiently high to avoid significant errors in the ray trace. We derived two new criteria for a sufficiently high index of refraction. To avoid significant errors, the index must satisfy these two new criteria in addition to Sweatts originally suggested criterion. In almost all cases the new criteria require a higher index than Sweatts original criterion.

Dual-sided lithography: a method for evaluating alignment accuracy

We describe a method for measuring the accuracy of aligners used to align lithographic patterns on opposite sides of a substrate (back-to-front aligners). The method, with minor modifications, can also be used as an aid in performing back-to-front alignments. The method is based on interferometric principles, is insensitive to manufacturing errors, and is simple to implement. The version described in this paper is fabricated by using binary optics technology and can measure the accuracy of aligners to +/-0.2 microm.

Microconcentrators for focal plane arrays

Micro-optics can be used to significantly increase the effective fill factor of focal planes. This, in turn, can enhance the overall performance of an imaging system in a number of ways. In this paper, we study the efficiency of different types of micro-concentrators, considering both the imaging and non-imaging varieties. The effective fill factor of a focal plane enhanced by a micro-concentrator is shown to be a function of three parameters: the type of micro- concentrator, the difficulty of the required concentration, and the severity of diffraction effects. For typical focal plane applications, both imaging and non-imaging concentrators are capable of increasing the effective fill factor to almost 100%.