It is known that the best way to correct spherical aberrations is the use of aspheric microlenses in optical systems, where a single aspheric microlens can be employed to replace a compound of spherical microlenses in a compact design. However the fabrication of aspheric microlenses is often complex because expensive high-energy beam-sensitive (HEBS) gray scale mask is needed in the fabrication process. In this paper, we reported a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft lithography replication method, to fabricate hyperboloid refractive microlens arrays (MLAs) in the inorganic-organic hybrid SiO2-ZrO2 sol-gel material. The fabrication procedures involved two basic steps. Firstly, a master of hyperboloid MLA was made in photoresist by the sample-inverted reflow technique. Secondly, a negative mold of the master was built by casting polydimethylsiloxane (PDMS) to a silicone elastomer against the master, and then the profile was impressed onto the sol-gel glass. As a result, the fabricated sol-gel MLAs have been obtained with excellent smooth profiles, having negligible discrepancies from the profiles of the ideal hyperboloid MLAs. The root-mean-square roughness values (Rq) of the surface of MLA were measured as 1.2 nm in the central areas and 2.1 nm in the outskirts of the lens. In an application of coupling a laser diode (LD) to a single-mode fibre (SMF), we proposed a two-MLA coupling scheme where two revolved-hyperboloid MLAs were back to back introduced between the LD and the SMF. In this configuration, the coupling efficiency has achieved 83.4% (-0.79 dB).
An improved synthesis of inorganic-organic hybrid silica-zirconia sol-gel material has been developed, and it has controllable refractive index and can form ten-micron-thick film in a single spin coating process. The novel synthesis was realized by uniform hydrolysis and subsequent copolymerization of [3-(methacryloxy) propyl] trimethoxysilane and zirconium propoxide. The optical properties of the prepared sol-gel material was studied and characterized by a
series of experiments. Compared with the sol-gel films reported before, the sol-gel film had good internal homogeneity and surface uniformity due to single layer structure. We employed the hybrid silica-zirconia sol-gel film in the singlestep fabrication of a dielectric channel waveguide on a quartz substrate. In the fabrication process, the sol-gel film was exposed to UV through a binary mask, and the exposed zone within the film formed a channel waveguide core because of its refractive index increase. The channel waveguide core was then covered again with a layer of the same kind of
sol-gel film, and the unexposed zone within the sol-gel film, along with the new cover layer, formed the cladding of final dielectric channel waveguide. The novel sol synthesis enabled a precise control of the geometrical and optical parameters of the channel waveguide. In the 1.55 μm telecommunication window, the fundamental modes TE00 and TM00 in the channel waveguide had acceptable transmission losses of 1.20 ± 0.06 dB / cm and 1.79 ± 0.06 dB / cm, respectively.
Optical trapping and manipulation are based on three types of the force and momentum, in the range of pN, to grab, lift and rotate microparticles due to the light intensity or phase distribution. In the first type, particles are trapped in the highest intensity region of the beam due to optical gradient force for high refractive index particles with respective to its surrounding medium. Secondly, orbital angular momentum (OAM) of a beam can be transferred to a particle due to phase singularity within a beam. Thirdly, spin angular momentum (SAM) can be transferred to the particles due to the circular polarization of the beam. In recent years, microfabricated optical elements have been used to modulate the amplitude and phase of the optical beam to create new generation of optical tweezers with additional manipulation dimensions. In this paper, a review of our recent discoveries of optical trapping and manipulation using micro-beam shaping and micro-optical elements will be presented.
A simple reflow technique and reactive-ion etching are employed 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 characteristics of the monolithic device to be improved greatly when compared 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.
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.
256x290 diffractive microlens arrays have been designed by considering the correlative optical and processing parameters for PtSi focal plane array. The microlens arrays were designed to operate at (lambda) equals4micrometers , with a lens size of 50micrometers x33micrometers and the lens speed f/2.1 located on the backside of PtSi focal plane array chip. The diffractive microlens arrays have been fabricated on the backside of PtSi focal plane array chip by successive photolithography and Ar+ ion-beam etching technique. The alignment of microlens arrays with PtSi focal plane array was completed by a backside aligner with IR light source. The practical processes and fabrication method are discussed. The optical characteristics and performance parameters of PtSi FPA with diffractive microlens arrays are presented.
For the first time, diffractive rectangle-based multilevel steps Si microlens arrays are fabricated by a new method, named part etching. The new method proposed can increase focal length of diffractive microlenses arrays. The 256x256 element microlens arrays are designed for a center wavelength of 4micrometers , with 40micrometers (Horizontal) x 30micrometers (Vertical) quadrate pixel dimension and a speed (F number) of F/2.53 (in air). The focal length of the microlens array is 400micrometers in Si material, much longer than focal length of the microlens arrays of the same size fabricated by conventional binary optics method. The method also includes photolithography and ion beam milling process. The 256x256 element microlens arrays and the same 256x256 element PtSi IR Focal Plan Arrays (FPAs) are monolithic integrated on the same wafer. The IR response characteristics of the integration device are improved greatly.
The IR spectrum from 3 to 5micrometers has numerous applications in both military and civil industries. High performance at high operating temperature is often important in these applications. Conventional Focal Plane Arrays (FPAs) without integration with concentrator such as microlens have poor sensitivity and low signal-to-noise ratio because of their lower fill factor. The binary optics microlens arrays reported in this paper are designed for integration with FPAs. Thus, the FPAs' fill factor, sensitivity, and signal- to-noise ratio can be improved while retaining a given image resolution and optical collection area. In the paper, we discussed the 256(Horizontal)x290(Vertical) microlens arrays designed for a center wavelength of 4micrometers , with 50micrometers (Horizontalx33micrometers (Vertical) quadrate pixel dimension and a speed (F number) of F/1.96. PtSi FPAs were fabricated on the front side of a 400-micrometers -thick Si substrate. The designed diffractive microlens arrays will be etched on the back side of the same wafer in a register fashion and it will be reported in other paper. Considering the diffraction efficiency, 8-phase-level approximation is enough. For the diffraction efficiency of 8-phase-level diffractive microlens reaches 95%. The process only need three mask-level, so we designed and fabricated three masks with the same dimension 4'x4'. Also, a set of fine verniers was designed and fabricated on each mask to allow accurate alignment during the fabrication process. Through a computer simulation, the microlens arrays are nearly diffraction limited, with the diffraction efficiency of 93%, a bit lower than the theoretical value of 95%. Introduction of microlens arrays has the ability to increase the FPAs' fill factor to 100%, while it is only about 21.6% without microlens. To our knowledge, this is the first trial of integration large area microlens arrays with FPAs at home.
A silicon refractive microlens array mounted on a 128- X 128-element PtSi IR CCD focal-plane architecture is fabricated using a multiple-process, including photolithography, heat treatment, and argon ion beam etching techniques. The optical filling factor of PtSi IR CCD with refractive microlens array is more than 95 percent. The focal length of the square-base arch silicon microlens is about 90 micrometer. Both the scanning electron microscope and the surface style measurement are carried out to determine the dimensions and the surface morphology of silicon refractive microlens. The matching properties between the preshaped photoresist mask and silicon substrate during argon ion beam etching are given. The techniques utilized can be applied to fabricate microtips array and microplateforms (circle microtips) array.
A relatively simple and effective method to fabricate 128- X 128-element emission microtips array on the surface of silicon substrate is proposed. The method mainly involves photolithographic process and argon ion beam etching. Typical center-to-center spacing of microtips fabricated is 50 micrometer, typical height is about 11 micrometer, and typical sharpness is about 9 sr. The scanning electron microscope analysis and the surface style measurement are presented for the surface morphology of two kinds of silicon emitters microtips (square-based pyramidal microtips and circle-based cone microtips) and circle microtips array. The experiments show that the technique used can be applied to fabricate silicon emitter microtips array and circle microtips array of larger area.
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