Jing Bu

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 MLAs 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.

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.

Monolithically integrated refractive microlens array to improve imaging quality of an infrared focal plane array

A simple reflow technique and reactive-ion etching are em- ployed to fabricate and integrate a refractive square-apertured arch Si microlens array (MLA) on the back of an IR focal plane array device (IRFPA), resulting in the formation of a monolithic MLA/IRFPA device. The fabricated on-chip Si MLA behaves as optical concentrators and is used to collect most of the incident light from each pixel area on a smaller photosensitive area of the IRFPA, causing the IR response char- acteristics of the monolithic device to be improved greatly when com- pared with an ordinary IRFPA device without the MLA. The advantages of employing the reflow technique and the reactive-ion etching lie not only in the excellent surface smoothness and dimensional uniformity of the fabricated MLA, but also as a cost-effective and mass production technology.

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).

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.

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.

Two-microlens coupling scheme with revolved hyperboloid sol-gel microlens arrays for high-power-efficiency optical coupling

In lightwave communications, the high-power-efficiency coupling between a laser diode (LD) and a single-mode fiber (SMF) is indispensable. This paper proposes an imaginative two-microlens-array (MLA) coupling scheme whereby two revolved hyperboloid MLAs were used back-to-back between the LD and the SMF, and a coupling efficiency of 83.4% (-0.79 dB) has been achieved. The study also employs a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft lithography replication method, to fabricate revolved hyperboloid MLAs in inorganic-organic hybrid silica-zirconia sol-gel material. As a result, the fabricated MLAs have excellent smooth profiles and negligible discrepancies from the profiles of the ideal hyperboloid MLAs.

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 Lloyds 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.

A high-corrugation-rate self-Processing SiO/sub 2/--ZrO/sub 2/ hybrid sol-gel material for fabrication of microlens array

A novel high-corrugation-rate self-processing SiO/sub 2/--ZrO/sub 2/ hybrid sol-gel material has been developed and employed in single-step fabrication of refractive microlens array (MLA). In the proposed process, the SiO/sub 2/--ZrO/sub 2/ hybrid sol-gel film was exposed to ultraviolet through a binary mask and directly patterned into an MLA, which could be used as an end product with no further development or etching steps. Measurements showed that the surface relief depth could reach 1.32 /spl mu/m, equivalent to 17.1% of the sol-gel film thickness. As expected, the fabricated refractive MLA had excellent surface smoothness, structural and dimensional conformity. The discrepancy between the designed and actual focal length of the MLA was 5.3%. The self-processing, being a true single-step method, was shown to be a practical, cost-effective, and promising fabrication technique for microoptical elements.

Reflowed sol-gel microlens for coupling a laser diode and a single-mode fiber with high efficiency: a cost-effective and high-volume fabrication solution

In optical communications and optical interconnects, high coupling efficiency between a laser diode and a single mode fiber is indispensable, while the coupling loss mainly originates from the mismatch of their numerical apertures. In order to improve the coupling efficiency, it is a practical scheme to introduce a refractive microlens between them. Nevertheless, the fabrication of refractive microlens array (MLA) often required complicated lithographic and etching process. Moreover, structural homogeneity and dimensional uniformity of fabricated MLA were difficult to sustain. In this paper, we extend the application of low-cost inorganic-organic SiO2/ZrO2 sol-gel glass with a simple reflow technique for fabrication of refractive MLA. The intrinsic advantages of hybrid sol-gel material lay not only as an etch-free single-step fabrication material, but also, its uniformity and other excellent optical properties. The adoption of reflow technique in the fabrication of refractive MLA is much more economical and suitable to mass production as expensive high-energy beam-sensitive gray-scale mask, or etching processes is not required. The fabricated refractive MLA have excellent surface smoothness and dimension uniformity, which can provide high coupling efficiency of a laser diode to a single mode fiber. The proposed microlens coupling scheme has the advantages of low coupling loss, low cost and small package volume.