Mahesh Pitchumani

Selective excitation of the TE/sub 01/ mode in hollow-glass waveguide using a subwavelength grating

In this work we demonstrate, for the first time to our knowledge, a novel subwavelength optical element for the selective excitation of the TE/sub 01/ mode inside a 300-/spl mu/m bore diameter hollow-glass waveguide (HGW) in order to reduce the transmission loss. The device consists of form birefringent gratings, where each section is oriented in a different direction so as to convert a linearly polarized input light to a rotating polarized one matching the TE/sub 01/ mode. Using this polarization converting element, we measured a 1.65-dB decrease in the transmission loss in the HGW at a wavelength of 1.55 /spl mu/m.

Additive lithography for fabrication of diffractive optics

An innovative fabrication technique is introduced that is based on multiple-exposure techniques for micro-optics fabrication. This method utilizes various exposure times and combinations of binary and analog photo masks to sculpture complex photoresist profiles. It also demonstrates the fabrication of analog structures from the multilevel structures thus formed by using resist reflow.

Selective excitation of the LP11 mode in step index fiber using a phase mask

We present a novel mode selective coupling technique for step index fiber. This technique utilizes phase matching for excitation of higher-order modes while suppressing the fundamental mode. Using this technique, a phase element is fabricated and tested to demonstrate the high coupling efficiency to the LP11 mode. In addition, we derive an analytical expression of the coupling efficiency of the LP11 using a single

Aberration measurement of photolithographic lenses by use of hybrid diffractive photomasks

In optical lithography the degradation of image quality due to aberrations present in the exposure tool is a serious problem. Therefore it is desirable to establish a reliable aberration measurement procedure based on the analysis of printed images in the photoresist. We present what is to our knowledge a new method for characterizing the aberrations of an exposure tool using a hybrid diffractive photomask. By utilizing each different impact on the aberrated image from each diffracted illumination, we were able to extract the aberration present in the stepper system. We experimentally verified this method with a G-line stepper and verified its spherical aberration astigmatism.

Analog micro-optics fabrication by use of a binary phase grating mask

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.

Polarization-independent on-axis light coupler for surface plasmon resonance using a concentric chirped grating

A novel on-axis one-element polarization-independent light in- and out-coupling mechanism for surface plasmon resonance (SPR) is proposed. The system utilizes an integrated high-NA concentric chirped grating to both focus the incident light on the metallic film and collimate the reflected beam onto a CCD array to extract the SPR signal. With NA up to 1.47, a broad sensing dynamic range from n=1 to 1.35 can be achieved. An analytical model is implemented to demonstrate the dependency of the radial location of the resonances on the detecting substance and its sensitivity to the change of the refractive index. The model shows a trend similar to rigorous ray-tracing calculations.

Micro-optic fabrication with subdomain masking

An innovative fabrication technique is introduced that is based on multiple-exposure techniques for micro-optics fabrication. This approach is compatible with conventional lithography systems used in integrated circuit manufacturing and can be applied to thick and thin photoresists and is based on additive lithographic techniques introduced elsewhere [Appl. Opt. 41, 6176 (2002)]. We chose a simple subdomain basis set to transform the two-dimensional basis patterns into a family of various three-dimensional micro-optic elements using exposure control to modulate the third dimension. We demonstrate the capability to sculpt the photoresist into a variety of three-dimensional micro-optic elements by performing multiple exposures using elements from the subdomain basis set, without resorting to multiple etching steps.

Additive lithography for refractive micro-optics

An innovative fabrication technique is introduced that is based on multiple exposure techniques for micro-optics fabrication. This approach is compatible with conventional lithography systems used in Integrated Circuit manufacturing and can be applied to thick and thin photoresists. The additive concept is centered on the idea of using multiple exposures to remove the desired amount of resist without resorting to multiple etching steps. This presentation will explain how the additive technique, used with thin and thick resists, will revolutionize our capability to efficiently form refractive lenses and micro-optics for optical beam shaping and transforming. The quality and reproducibility of these elements will also be discussed.

Polarization converting element for minimizing the losses in cylindrical hollow waveguides

Bending loss is the biggest drawback to hollow waveguides used for light delivery applications such as laser ablation. One way to overcome this limitation without changing the fiber design or fabrication is to engineer the input light to excite specific modes with better optical properties. Our first order calculations of the transmission and bending losses inside the cylindrical hollow waveguides showed that the TE01 mode suffers the least amount of losses. To selectively excite this mode, it is desired to design an optical component that converts incident linearly polarized light into a rotating wave similar to the TE01 mode. This work focuses on the design and fabrication of a subwavelength structure that converts the input polarization into that of the TE01 mode.

Presculpting of photoresists using additive lithography

In this paper we present the fabrication of refractive micro optical elements by additive sculpting of the photoresist using binary amplitude masking techniques. We also present the fabrication of micro optical elements by pre sculpting the photoresist before reflow. This enables the use of fewer masking patterns while allowing us to obtain smooth profiles on the resist. The resist can be pre sculpted into any shape by using a set of binary patterns thus allowing us to fabricate refractive beam shaping elements.