Biomedical subjects

Xiaocong Yuan

Publications and source records attributed to Xiaocong Yuan.

13 recordsLinked to original sources

PubMed2006

Adjustable refractive index modulation for a waveguide with SU-8 photoresist by dual-UV exposure lithography.

We present a new fabrication technique based on a two-step UV exposure lithographic process to marginally modulate the refractive index in commercial SU-8 photoresist. This technique achieves refractive index modulation as different regions undergo different thermal densification prior to UV-induced polymerization. A small refractive index contrast of 0.0008 or lower can be achieved, and this is especially useful for fabricating waveguides with a low level of propagation modes. This technique may be extended to other UV-curable epoxy photoresists and can easily be applied in the fabrication of optical elements such as optical interconnects and integrated optical sensors without the development process.

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PubMed2006

Photothermally enabled lithography for refractive-index modulation in SU-8 photoresist.

We present a new lithographic technique based on a hybrid photothermal process to modulate the refractive index in commercial SU-8 photoresist. Owing to a difference in cross-linking, the refractive index of unexposed SU-8 cross-linked by thermally induced polymerization is 0.0072 higher than that of SU-8 cross-linked by UV exposure and postbaking. Making use of this property, we fabricated two thick, flat-topped index-modulated diffractive optical elements (DOEs) that contain different phase distributions and measured their wavefront reconstruction. The good experimental reconstructions of the index DOEs demonstrate the potential to extend the refractive-index modulation technique for the fabrication of three-dimensional optical elements without needing a development step.

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PubMed2006

Synthesis of multiple collinear helical modes generated by a phase-only element.

Phase-only elements are generally more desirable than complex-amplitude-modulated elements not only because of the higher diffraction efficiency but the readier implementation and fabrication. A novel iterative algorithm is proposed for generating multiple helical modes by a single phase-only element. A superposition of four helical modes is demonstrated experimentally by using a spatial light modulator.

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PubMed2005

Self-processing solgel material for one-step fabrication of micrometer-period sinusoidal phase gratings using the Lloyd's mirror scheme.

A novel self-processing silica-zirconia hybrid solgel material has been developed and employed in one-step fabrication of micrometer-period sinusoidal phase gratings. In the process, the gratings with a sinusoidal profile were corrugated on the surface of the solgel film by UV exposure using the Lloyd's mirror setup. No further development or etching step is needed to reveal the sinusoidal profile because the corrugation is formed due to the self-processing property of the solgel material, which is robust enough to be used as an end product. The period, amplitude, diffraction efficiency of the +/-1 order, and surface roughness of one of the fabricated gratings are 0.99 microm, 330 nm, 30.56%, and 1.27 nm, respectively. The new self-processing material is practical and promising for fabrication of micro-optical elements.

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PubMed2005

Hybrid sample-inverted reflow and soft-lithography technique for fabrication of conicoid microlens arrays.

We report a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft-lithography replication method, to fabricate conicoid refractive microlens arrays (MLAs), including hyperboloid, paraboloid, and ellipsoid MLAs in inorganic-organic hybrid SiO2-ZrO2 solgel material. The fabrication procedures involve two basic steps. First, a master of the conicoid MLA was made in photoresist by the sample-inverted reflow technique. Second, we built a negative mold of the master by casting polydimethylsiloxane (PDMS) onto a silicone elastomer against the master, and then the profile was imprinted onto the solgel glass. As a result, the fabricated solgel MLAs have been obtained with excellent smooth profiles, having negligible discrepancies from the profiles of ideal conicoid MLAs.

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PubMed2005

Reflowed solgel spherical microlens for high-efficiency optical coupling between a laser diode and a single-mode fiber.

To improve the coupling efficiency between a laser diode and a single-mode fiber, we propose a two-microlens coupling scheme that uses two solgel spherical microlenses for high coupling efficiency. The conventional reflow technique was employed and extended to the inorganic-organic hybrid SiO2/ZrO2 solgel material to form the microlenses. Preliminary results show that the coupling efficiency was increased to--1.28 dB (74.5%) by the proposed scheme, compared with a coupling efficiency of--10.13 dB (9.7%) by the butt-joint method. The proposed fabrication technique demonstrates that use of a reflowed solgel spherical microlens is a cost-effective mass-production approach to application of micro-optical elements in optical communication.

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PubMed2004

Sample-inverted reflow technique for fabrication of a revolved-hyperboloid microlens array in hybrid solgel glass.

We propose a novel fabrication method, which is referred to as the sample-inverted reflow technique, to fabricate a refractive microlens array (MLA) with a revolved-hyperboloid profile in a solgel material. The fabricated solgel MLA demonstrates an excellent smooth profile with a fabrication error much less than the difference between the revolved hyperboloid and the spherical surface. In an application of coupling a laser diode (LD) to a single-mode fiber (SMF), we propose a two-MLA coupling scheme in which two revolved-hyperboloid MLAs are used between the LD and the SMF. In this configuration the coupling efficiency achieves 81.7% (-0.88 dB).

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PubMed2004

Fabrication of concave refractive microlens arrays in solgel glass by a simple proximity-effect-assisted reflow technique.

We report a simple method for fabricating a concave refractive microlens array (MLA) in solgel glass by using a proximity-effect-assisted reflow technique. The solgel concave refractive MLA that we fabricated had excellent surface smoothness; good dimensional conformity, with an 8.23% nonuniformity of the microlens elements; and structural perfection, with a biggest deviation of 1% from a perfect concave spherical crown. The relative error between the measured and the designed values of the concave MLA's focal length was only 1.83%. Compared with the conventional fabrication techniques for concave MLAs, the proposed method has significant advantages including simplicity, low cost, good element conformity, and smooth device surface.

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PubMed2004

Practical implementation of the phase-quantization technique in an iterative Fourier-transform algorithm.

Implementation of the phase-quantization method in the design of computer-generated holograms (CGHs), especially binary CGHs, is a major influence on the diffraction efficiency of the CGHs. We describe the use of various quantization methods in the various steps of an iterative Fourier-transform algorithm and compare the root-mean-square (RMS) errors of the CGHs. As a result of the practical quantization technique, the most effective RMS value of a binary CGH should be decreased by at least 13% to retain maximum diffraction efficiency.

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PubMed2004

Localized self-volume growth in hybrid sol-gel glass induced by ultraviolet radiation with a gray-scale mask.

UV-induced self-volume growth of the hybrid sol-gel glass was investigated for fabrication of an arbitrary-surface relief structure with a user-defined gray scale mask. The gray scale mask was generated through exposure of a high-energy beam-sensitive glass under an electron beam. Saw-tooth gratings of different periods were fabricated by a simple UV exposure through the gray-scale mask. Experimental results showed that the smaller the period is, the shallower the depth obtained owing to the self-volume growth effect is.

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PubMed2004

Experimental study of holographic generation of fractional Bessel beams.

We demonstrate the experimental generation of a fractional Bessel beam by holographic means. Such fractional modes of Bessel beams possess an intrinsic opening gap across concentric intensity rings on propagation. We also show that the opening gaps within the fractional modes are diffraction free for a working distance while a fractional helical wave front is maintained.

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PubMed2004

Self-reconstruction property of fractional Bessel beams.

We study the self-reconstruction property of a fractional Bessel beam (FBB), where the FBB is described in terms of a Bessel beam of a fractional order for both amplitude and azimuthal phase components. The simulation and experimental results show that the FBB can overcome a block of obstacles and regenerate itself after a characteristic distance. As a comparison, the propagation of a Gaussian beam and an integer-order Bessel beam (IBB) through the same obstacles are also studied.

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PubMed2003

Reflow technique for the fabrication of an elliptical microlens array in sol-gel material.

A simple reflow technique is employed for the fabrication of elliptical refractive microlens arrays (MLAs) on a low-cost inorganic-organic SiO2/ZrO2 sol-gel glass. The measured results show that the fabricated elliptical microlenses in a 256 x 512 array have excellent surface and dimensional qualities in terms of smoothness and uniformity. It is also shown that the optical parameters of the MLAs, such as the focal length and aperture dimension, can be accurately controlled. The proposed technique requires only an ordinary binary photomask for pattern transfer. Furthermore, the sol-gel material is found to be feasible for high-volume production, because the fabrication of MLAs can be implemented by use of cheap sol-gel materials without an etching step.

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