Biomedical subjects

Waleed Mohammed

Publications and source records attributed to Waleed Mohammed.

4 recordsLinked to original sources

PubMed2006

Full vectorial modal analysis of specialty fibers and their Bragg grating characterization.

Optical fibers and specialty waveguides are the bases of the majority of today's telecommunication, biomedical, sensing, and light-delivery applications. Modal analysis plays an important role in optimizing the optical performance of these fibers when they are integrated with optical systems. We present a full vectorial modal theoretical analysis of specialty cylindrical symmetric fibers with arbitrary index profiles, using a staircase approximation and scattering matrix approach with no constraints on the refractive index profile. We demonstrate the generality of this method by investigating the modal characteristics of two specialty fibers: graded-index fiber and concentric-shell multicore fiber. The calculated modal effective indices for the graded-index fiber are compared with those calculated by the WKB method, stressing the main differences between the scalar and vectorial approaches. Using the same approach, we calculate the Bragg grating response of a holographic grating written in the guiding regions of a concentric-shell fiber and compared them with experimental measurements.

Journal Article↗

PubMed2004

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.

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PubMed2003

Monolithic integration of dual-layer optics into broad-area semiconductor laser diodes.

A broad-area semiconductor laser diode with two monolithically integrated optical elements is presented. A 275-nm period detuned second-order diffraction grating on the p-doped side layer is combined with a refractive lens transferred into the GaAs substrate so that outcoupling and beam-shaping functions are decoupled. The high-power device produces a circular spot and demonstrates the potential of dual optics integration in broad-area semiconductor diodes.

Journal Article↗

PubMed2002

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.

Journal Article↗