Sarfaraz Baig

Vacuum-Assisted Microfluidic Technique for Fabrication of Guided Wave Devices

We report on a novel vacuum-assisted microfluidic (VAM) technique for guided wave device fabrication. Ultraviolet curable resins were used to demonstrate the effective VAM waveguide fabrication. Comparisons to a conventional soft molding technique demonstrate that the VAM approach results in lower propagation losses, lower crosstalk, and improved waveguide structures. More importantly, microscope analysis portrays improved device formation, sidewall edges, and the elimination of the polymer background residue inherent to traditional soft molding fabrication techniques. As a low-cost rapid prototyping technique, the VAM soft lithographic method allows guided wave devices to be implemented rapidly and inexpensively.

Nanoscale optical reinforcement for enhanced reversible holography

We demonstrate a nanoscale optical reinforcement concept for reversible holographic recording. The bone-muscle-like mechanism enables enhancement of holographic grating formation due to the collective alignment of liquid crystal (LC) molecules nearby photo-reconfigurable polymer backbones. The LC fluidity facilitates the ease of polymer chain transformation during the holographic recording while the polymer network stabilizes the LC collective orientation and the consequential optical enhancement after the recording. As such, the holographic recording possesses both long-term persistence and real-time rewritability.

Flexible Polymer Waveguides With Integrated Mirrors Fabricated by Soft Lithography for Optical Interconnection

Flexible polymer waveguides with integrated 45 ° mirrors to support surface normal optical coupling for optical interconnection were fabricated using a vacuum assisted microfluidic (VAM) soft lithographic technique. Waveguide array structures with slanted surfaces of the SU-8 master were realized by prism-assisted inclined UV lithography. The internal surface reflected UV light was utilized to eliminate undercut structures and to form the inclined surfaces on both ends of the straight waveguide structure via one-step UV exposure. Varying the inclined surface depth can result in different needed light coupling efficiency. A polydimethylsiloxane (PDMS) mold was subsequently created. The use of UV curable resins in the VAM fabrication resulted in the polymer waveguides with 45° integrated mirrors, demonstrating a coupling efficiency of 75% for full mirrors and 38% for half mirrors.

Soft lithography fabricated polymer waveguides and 45° inclined mirrors for card-to-backplane optical interconnects

Polymer waveguides with 45° mirrors are fabricated by vacuum assisted microfluidic (VAM) soft lithographic technique for card-to-backplane optical interconnect applications. Waveguide array structures with inclined surfaces in SU-8 photoresist for PDMS mold are fabricated by prism assisted UV exposure. Sample surface reflected UV light is utilized to eliminate undercut structures and to accomplish the inclined mirror surfaces on both ends of the straight waveguide segments by one-step UV exposure. Polymer waveguides with 45° embedded mirrors demonstrated about 0.49 dB/cm propagation loss and 67% mirror coupling efficiency.

Integrated optical coherence tomography and reflectometry system for ocular anterior segment imaging and tear film thickness evaluation

Abstract. We report an integrated optical coherence tomography (OCT) and reflectometry system for ophthalmology imaging. The dual-functional device provides a complementary high-resolution tear film evaluation by reflectometry and anterior segment imaging by OCT, offering a more comprehensive anterior segment examination. The imaging measurement capabilities have been demonstrated on a human eye as well as on a model eye. The minimum measured tear film thickness is 0.3 μm with measurement resolution of less than ±0.58% of film thickness yet the OCT anterior segment offers a depth resolution of 7 μm with a 45-nm bandwidth superluminescent light source at 840-nm center wavelength. The integrated system has demonstrated the capability for three-dimensional imaging in the anterior segment of the eye.

Enhanced non-volatile and updatable holography using a polymer composite system

Updatable holography is considered as the ultimate technique for true 3D information recording and display. However, there is no practical solution to preserve the required features of both non-volatility and reversibility which conflict with each other when the reading has the same wavelength as the recording. We demonstrate a non-volatile and updatable holographic approach by exploiting new features of molecular transformations in a polymer recording system. In addition, by using a new composite recording film containing photo-reconfigurable liquid-crystal (LC) polymer, the holographic recording is enhanced due to the collective reorientation of LC molecules around the reconfigured polymer chains.

Planar concave grating with flattened spectral response for wavelength demultiplexing optical interconnection

A 4-channel planar concave grating device with a flattened spectral response based on SU-8 polymer is presented. The flattened spectral response is accomplished by using an optimized multi-mode interference coupler as the input aperture of the device for spectrally separated channels. The mode field distribution in the input plane is controlled by adjusting the width of input taper coupled to the multi-mode interference coupler. The effects of the input taper width on the flattened spectral response are demonstrated in detail through simulation results. The devices are realized by using an SU-8 polymer strip waveguide with a UV lithography technology. Experimental results show that the flattened spectral response can be easily controlled by adjusting the taper width.

Polymer waveguide with tunable optofluidic couplers for card-to-backplane optical interconnects

Polymeric waveguides with tunable optofluidic couplers are fabricated by the vacuum assisted microfluidic technique for card-to-backplane optical interconnect applications. The optofluidic coupler on a backplane consists of polymer waveguides and a perpendicular microfluidic channel with inclined sidewalls. An index matching liquid and air bubbles are located in the microfluidic hollow channel. The activation or deactivation of the surface normal coupling of the optofluidic coupler is accomplished by setting air bubbles or index matching liquid to be in contact with the waveguide mirrors. 10 Gbps eye diagrams of the card-to-backplane optical interconnect link have been demonstrated showing the high performance of the interconnect system.

Tunable Optofluidic Couplers for Dynamic Card-to-Backplane Optical Interconnect

Polymer waveguides with tunable optofluidic couplers are fabricated by the vacuum assisted microfluidic technique for dynamic card-to-backplane optical interconnect applications. The backplane optofluidic coupler consists of polymer waveguides with 45° integrated waveguide mirrors and perpendicular microfluidic channel structures for translational movement of index matching liquid and air bubbles. Controlled positioning of the air bubble or index matching liquid in contact with the integrated mirror can effectively turn on or off each optofluidic coupler for surface normal coupling in card-to-backplane optical interconnection. Experimental results demonstrated about 23 dB on/off surface normal interconnect signal change for both 1/3 and half size waveguide mirrors of the optofluidic couplers. 10 Gbps card-to-backplane optical interconnect eye diagrams have been demonstrated showing the effectiveness of the interconnect structure.

Fabrication of two kinds of eight-fold photonic quasi-crystals assisted by a specially designed prism

We demonstrate that two kinds of 2D eight-fold photonic quasi-crystals (PQCs) can be fabricated by a specially designed prism via single-exposure holographic lithography. The prism with five continuous side surfaces out of common eight symmetrical side surfaces, plus a top surface, is well designed for PQC fabrication. Compared with the traditional method of setting up eight free-space beams in the half-space for an eight-fold PQC fabrication, our specially designed prism reduces the number of beams, avoids the differences of beam-to-beam phases, and simplifies the fabrication process. The theory and computer simulation confirm the patterns of two kinds of PQCs by a single prism illumination recording. Further, these quasi-crystal patterns are successfully verified by experimental results under a scanning electron microscope. In addition, these samples show some good properties, such as uniformity over large area, the implementation of a single defect by underexposure, and symmetry break of the eight dots. Our special prism-assisted holographic lithography technique provides a base for further investigating the optical properties of these novel structures.