We present a new photomask technology capable of forming a continuous rotationally symmetric microstructure in thick photoresist. This technique eliminates many of the drawbacks of grayscale and half-tone masking technology. A binary phase grating of pi phase depth on a transparent quartz mask plate is fabricated in PMMA resist using an e-beam direct writing technique. When the phase mask is used in the stepper, an analog intensity profile is created on the wafer. The period is constrained, allowing for control of the zero-order in the stepper. The duty cycle of the phase gratings can be varied in such a way to provide the proper analog intensity profile for a wide range of micro-optics on the photoresist. The design, analysis, and fabrication procedures of this technique are discussed. This processing technique can be applied to many MOEMS devices that require refractive elements for optical processing. The method greatly simplifies the device process, reducing the cost and improving the device yield.
Trihedral corner cube arrays are efficient retro-reflectors. They are integral parts in numerous imaging and sensing applications. However, the fabrication of these trihedral arrays can prove to be both difficult and cost prohibitive. Using a phase-only mask, we have fabricated an array of analog reflectors which can then be tiled using a photolithographic stepper. The elements are designed using a fixed period and varying fill factor to create the analog slope of each side wall. The overall depth of the array can be controlled by both the exposure and etching processes to ultimately create the desired effect. After etching, a single coating of metal finishes the process, and the elements can then be diced out and integrated into each specific application. The etched arrays may alternatively be used as a mold to create high volumes of the desired element. The design and fabrication parameters for trihedral corner cube arrays will be discussed in detail. The advantages and limitations will then be discussed.
In this paper, we present a new photo-mask technology capable of forming a continuous relief micro-optic profile on thick photo-resist. This technique eliminates many of the drawbacks of gray-scale and half-tone masking technology. An optical stepper is used to fabricate binary phase gratings of pi phase depth on a transparent quartz reticle. When the phase reticle is used in the stepper an analog intensity profile is created on the wafer. The period is constrained allowing for control of the 0th order in the stepper. The duty cycle of the phase gratings can be varied in such a way to provide the proper analog intensity profile for a wide range of micro-optics on the photo-resist. The design, analysis, and fabrication procedures of this technique will be discussed.
Micro-Optics have begun to play a key role in micro-photonic systems and devices. This is largely due to the fact that semiconductor processing has enabled one to incorporate complex optical functions and integration features into the actual optical substrates. In this paper, key application areas of micro-optics are demonstrated for mode matching, gain equalization, and spectral filtering.
This paper investigates methods to launch high modes propagating along helix paths into a graded index fiber. These techniques may be particularly useful to avoid the central dip problem due to defects located in the center of the index profile of multimode fibers. Light was coupled into a graded index multimode fiber using the flat surface of side-polished or D-shaped fiber. The fibers were polished down to a few microns close to the core on a distance of about 3mm. The first method, active, is based on coupling the light from a D-shaped single mode fiber to a D-shaped graded index fiber. The two fibers are in contact through a film of index matching fluid and the coupling may be thought as the leakage from a fiber to a slab waveguide. The launching angle of the skew rays in the multimode fiber is controlled by the tilt between the fibers. Simulations using beam propagation method are presented. Analytical equations for the path of the skew rays in graded index fiber are also used for a parabolic index profile. The second method, passive, consists of etching a tilted grating on a side polished multimode fiber by means of focused-ion beam (FIB) technology. We discuss the fabrication of such a grating and the possibility of using FIB technology to etch diffractive elements on fused silica waveguides.
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