Planar Microlens Research Articles

High-throughput and controllable manufacturing of liquid crystal polymer planar microlens array for compact fingerprint imaging.

The microlens array (MLA) with a small geometric footprint and unique performances, is the key enabler to push the development of photonic devices toward miniaturization, multi-function and large-scale integration. However, the realization of 100% fill-factor (FF) MLAs with high controllability and its mass manufacturing without complex steps has always been a difficult issue. Here, we propose an efficient, highly flexible and low-cost manufacturing approach for MLAs with a high FF via snapshot polarization patterning. The digitalized linear polarization pattern was distributed across the photo-alignment layer with both high efficiency and accuracy, enabling large-area liquid crystal MLA with parameter controllability from element to element. The MLA manufacturing process does not involve developing, etching and deposition steps and is suitable for industry up-scaling. We further proposed a novel compact compound-eye imaging system for biometrics with the obtained MLAs. The 100% FF MLA enables high light utilization efficiency and low background crosstalk, yielding compact biometrics indentation with high recognition accuracy. The realization of such planar optics would lead to a plethora of different miniaturized multiaperture imaging systems in the future.

Effect on the Optical Properties of Planar Microlens Arrays with Different Ion-exchange Time

Effect on the Optical Properties of Planar Microlens Arrays with Different Ion-exchange Time

Research on Slow Tool Servo Machining of Complicated Planar Microlens Array

Research on Slow Tool Servo Machining of Complicated Planar Microlens Array

Planar microlenses for near infrared CMOS image sensors

In this paper we present planar microlenses designed to improve the sensitivity of SPAD pixels. We designed diffractive and metasurface planar microlens structures based on rigorous optical simulations. The current melted microlens solution and designed diffractive microlens were implemented on STMicroelectronics 40nm CMOS testchips (32 × 32 SPAD array), and average gains of 1.9 and 1.4 in sensitivity respectively were measured, compared to a SPAD without microlens.

Demonstration of multi-imaging and multifocusing through planar motheye kind of gradient microlens multi-array

We experimentally demonstrate multiple imaging, multifocusing and 3D imaging through motheye kind of dual periodic rhombic-hexagonal and hexagonal-hexagonal gradient microlens multi-array based on photoresist coated glass substrate. FDTD based simulation study presents a bow-shape multifocus for broad spectrum of an unpolarized electromagnetic wave through these planar hexagonally packed microlens array. The multi-imaging and focusing property of the fabricated microlens array is expected to help collect real-time 3D depth information in bio-imaging. The principle of multi-focus is based on the gradient variation of the spatial dimension (diameter) of the micro-lenses leading to a different radius of curvatures and focal length in an array. This planar microlens arrays can be realized through a single step using a cost-effective phase-controlled interference lithography technique.

Ultrathin Planar Microlens Arrays Based on Geometric Metasurface

AbstractAscribing to the properties of two dimensional parallel focusing and imaging, low propagation loss, integration and miniaturization, microlens array has been widely used in imaging, optical communication, organic light emitting devices, adaptive optics, photolithography, biomedical and other applications. However, the existing traditional microlens array suffers from difficulty in fabrication, large‐thickness, curved surface, non‐uniformity of light spots, or requirement of additional discrete components to control the microlens. Herein, a planar microlens array is experimentally demonstrated based on the geometric metasurface. The single microlens is composed of space‐variant subwavelength metallic gratings with high polarization conversion efficiency and thus exhibits gradient phase distribution. The focused spot diameter of 22.5 μm with radius of 350 μm, focal length of 1 cm and the light spots intensity uniformity of 0.9885 (standard deviation 0.0115) at the focal plane are obtained. Moreover, the broadband property of microlens array is also confirmed. The novel design strategy for microlens array would facilitate the miniaturization of optical devices and be easily integrated in the optical interconnected devices.

Subwavelength focus of light by a planar microlens

We numerically show that using a planar gradient-index (GRIN) microlens it is possible to focus coherent light of wavelength λ into a narrow line of width 0.026 λ and length 0.182 λ. The efficiency of focusing amounts to 22%. Replacement of the GRIN lens with a photonic-crystal analogue fabricated in silicon is shown practically not to impair the lens performance. In fact, the replacement is shown to result in decreasing side-lobes in the focal spot, while increasing the efficiency up to 30%.

Planar microlens with front-face angle: design, fabrication, and characterization

This paper studies the effect of microlens front-face angle on the performance of an optical system consisting of a planar-graded refractive index (GRIN) lens pair facing each other separated by a free-space region. The planar silica microlens pairs are designed to facilitate low-loss optical signal propagation in the free-space region between the opposing optical waveguides. The planar lens is fabricated from a 38-μm-thick fluorine-doped silica layer on a silicon substrate. It has a parabolic refractive index profile in the vertical direction, which is achieved by controlled fluorine incorporation in the silica film to collimate the optical beam in the vertical direction. Horizontal beam collimation is achieved by incorporating a horizontal curvature at the front face of the lens defined by deep oxide etch. A generalized 3×3ABCDGH transformation matrix method has been derived to compute the coupling efficiency of such microlens pairs to take front-face angles that may be present due to fabrication variations or limitations and possible input/output optical fiber offset/tilt into considerations. Pairs of such planar GRIN lens with various free-space propagation distances between them ranging from 75 to 2500 μm and with front-face angles of 1.5 deg, 2 deg, and 4 deg have been fabricated and characterized. Beam propagation method simulations have been carried out to substantiate the theoretical and experimental results. The results indicate that the optical loss is reasonably low up to 1.5 deg of front-face angles and increases significantly with further increase in the front-face angle. Analysis shows that for a given system with specific microlens front-face angle, the optical loss can be significantly reduced by properly compensating the vertical position of the input and output fibers.

Broadband Metallic Planar Microlenses in an Array: the Focusing Coupling Effect.

The microlens arrays (MLAs) are widely utilized for various applications. However, when the lens size and the spacing between two adjacent microlenses are of the length scale of the working wavelength, the diffraction effect plays a vital role in the final focusing performance. We suggest a kind of broadband metallic planar microlenses, based on which the ultra-compact microlens arrays are also constructed. The focusing coupling effect revealing for such devices is then investigated in detail by using the finite-difference time-domain (FDTD) method, with the emphasis on the changing spacing between adjacent microlenses, the working wavelength, the diameter of microlenses, and the array size. The results show that a larger spacing, a larger lens size, a shorter wavelength, or a smaller array scale can lead to a weaker focusing coupling effect. This research provides an important technological reference to design an array of metallic planar microlenses with the well-controlled focusing performance.

Single nucleotide polymorphism detection using gold nanoprobes and bio-microfluidic platform with embedded microlenses.

The use of microfluidics platforms combined with the optimal optical properties of gold nanoparticles has found plenty of application in molecular biosensing. This paper describes a bio-microfluidic platform coupled to a non-cross-linking colorimetric gold nanoprobe assay to detect a single nucleotide polymorphism associated with increased risk of obesity fat-mass and obesity-associated (FTO) rs9939609 (Carlos et al., 2014). The system enabled significant discrimination between positive and negative assays using a target DNA concentration of 5 ng/µL below the limit of detection of the conventionally used microplate reader (i.e., 15 ng/µL) with 10 times lower solution volume (i.e., 3 µL). A set of optimization of our previously reported bio-microfluidic platform (Bernacka-Wojcik et al., 2013) resulted in a 160% improvement of colorimetric analysis results. Incorporation of planar microlenses increased 6 times signal-to-loss ratio reaching the output optical fiber improving by 34% the colorimetric analysis of gold nanoparticles, while the implementation of an optoelectronic acquisition system yielded increased accuracy and reduced noise. The microfluidic chip was also integrated with a miniature fiber spectrometer to analyze the assays' colorimetric changes and also the LEDs transmission spectra when illuminating through various solutions. Furthermore, by coupling an optical microscope to a digital camera with a long exposure time (30 s), we could visualise the different scatter intensities of gold nanoparticles within channels following salt addition. These intensities correlate well to the expected difference in aggregation between FTO positive (none to small aggregates) and negative samples (large aggregates).

Fabrication of curved microlens array using a drop-on-demand droplet generator and polydimethylsiloxane replica mold

A simple approach was demonstrated to fabricate the curved microlens array (MLA) using a drop-on-demand (DOD) droplet generator and a polydimethylsiloxane (PDMS) replica mold. The planar microlens array (planar MLA) was fabricated using a simple and cost-effective DOD droplet generator, and then the curved MLA was fabricated by multiple replication processes. The PDMS elastomer membrane mold replicated from the planar MLA was used to transfer the microlenses from a planar substrate onto a spherical surface. The NORLAND65 (NOA65) optical adhesive was chosen to be the material of the curved MLA due to its good optical properties. The curved MLA, whose radii of curvature of the spherical surface were approximately 5.1 and 1.8 mm, was fabricated. The morphology damage during the replication process was avoided by the surface treatment of the PDMS elastomer membrane mold and the deformation of the curved microlens was analyzed and was ranged from 2.1% to 8.5%. The surface quality of the curved microlenses was measured by a white light interferometer and an atomic force microscope and the results showed that the arithmetical mean deviation of the profile R a was 0.54 nm with a 2×2- μ m 2 scanned area, while the resultant surface showed an excellent surface smoothness. The imaging and focus performance of the curved MLA were measured by a projection experiment. The experimental results demonstrated a high potential for curved MLA being applied to scale-invariant processing, robot vision, and fast motion detection.

Focusing with planar microlenses made of two-dimensionally varying high contrast gratings

We report on the focusing performance of reflective two-dimensionally varying high contrast grating lenses based on silicon. The combination of their subwavelength nature and their high refractive index contrast makes it possible to create highly tolerant and planar microlenses. We used a rigorous mathematical code to design the lenses and verified their performance with finite element simulations. We also investigated the effects of grating thickness, angle, and wavelength of incidence in these simulations. Experimentally, we show the evo- lution of the beam profile along the optical axis for a lens with a high (0.37) numerical aperture. We have explored a wide range of numerical apertures (0.1-0.93) and show that the lenses behave as expected across the full range. Our analyses demonstrate the large design flexibility with which these lenses can be made along with ease of fabrication and potential for a number of applications in micro-optics.©2014SocietyofPhoto-Optical Instrumentation

CO2 Laser Manufacturing of Miniaturised Lenses for Lab-on-a-Chip Systems

This article describes the manufacturing and characterisation of plano-convex miniaturised lenses using a CO2 laser engraving process in PMMA substrates. The technique allows for lenses to be fabricated rapidly and in a reproducible manner at depths of over 200 µm and for lens diameters of more than 3 mm. Experimental characterisation of the lens focal lengths shows good correlation with theory. The plano-convex lenses have been successfully embedded into capillary microfluidic systems alongside planar microlenses, allowing for a significant reduction of ancillary optics without a loss of detection sensitivity when performing fluorescence measurements. Such technology provides a significant step forward towards the portability of fluorescence- or luminescence-based systems for biological/chemical analysis.

变折射率方形孔径平面微透镜阵列的聚焦和散焦特性

变折射率方形孔径平面微透镜阵列的聚焦和散焦特性

Study on the Fabrication of RPAS Micro-Lens Array for CCD Integration

The micro-lens array for CCD systems can enhance the utilization efficiency of light energy, then improve its detection sensitivity. This paper firstly researches on the principle of micro-lens array for CCD integration, the lens changing refractive index theory and the mechanism of ionic exchange on glass materials. Then, with reasonable design of the mask and optimization the ionic exchange process parameters, the paper finally produces the Rectangular Plane Arched Shape (RPAS) micro-lens array on the plate glasswith the unit feature size being 22μm x 22μm. The results show that the RPAS micro-lens array’s fill factors could be achieved 93%, and the spectral sensitivity can be improved by 0.3 times. The mask plays a decisive role in micro-lens which is manufactured by ionic exchanged method. The reasonable selection of the mask parameter can eliminate the void that in the circular aperture planar micro-lens array, and enhance the fill factor; in the ionic exchange process, it is easy to obtain the large refractive index by using the ion-pair that have big differences. The ionic exchanged temperature below the glass softening temperature at about 20°C is appropriate.

两种开孔的高填充率GRIN平面微透镜阵列离子扩散特性

两种开孔的高填充率GRIN平面微透镜阵列离子扩散特性

Cylindrical planar microlens based on diffraction of parallel metallic nanowires

We report on the optimization of ultrasmall microlenses based on the diffraction of two parallel metallic nanowires. The Rayleigh–Sommerfeld integral is used in the visible range to simulate the near field diffraction patterns induced by single and paired planar silver wires. We demonstrate that the wire width w affects only the diffraction efficiency and the contrast of the diffraction pattern. The wire interdistance D controls the focal length and the depth of focus, which are equal and vary in the 0.1 to 10 μm range when D/λ increases from 1 to 8. The transversal FWHM increases from 200 to 700 nm, and a normalized intensity greater than 2.2 is obtained at the focal point when w is about 300 nm and D/λ=3. There is excellent agreement between these calculated properties and the experimental results obtained for single and paired parallel silver nanowires. We show that in our microsized geometry, the plasmon contribution is negligible with respect to pure diffraction effect. In addition, these nanowire microlenses have focusing properties similar to those of ideal refractive lenses limited by diffraction.

Kinoform microlenses for focusing into microfluidic channels

Optical detection in microflow cytometry requires a tightly focused light beam within a microfluidic channel for effective microparticle analysis. Integrated planar lenses have demonstrated this function, but their design is usually derived from the conventional spherical lens. Compact, efficient, integrated planar kinoform microlenses are proposed for use in microflow cytometry. A detailed design procedure is given and several designs are simulated. A paraxial kinoform lens integrated with a microfluidic channel was then fabricated in a silicate glass material system and characterized for focal position and spotsize, in comparison with light emerging directly from a channel waveguide. Focal spotsizes of 5.6 μm for kinoform lenses have been measured at foci as far as 56 μm into the microfluidic channel.

Power Coupling Efficiency Enhancement in Multimode Step-Index Fiber Using Refractive and Diffractive Microlenses

A novel study has been undertaken for the coupling efficiency enhancement on planar (refractive and diffractive) microlenses as coupling elements with various geometrical shapes in fibre optics communication. When the dispersion of the planar diffractive microlens is expressed in terms of an Abbe number, it is easy to solve for the refractive and diffractive power coupling efficiency that result in a single material. Coupling loss is reduced with microlens used as coupler even when increasing wavelength of the Gaussian beam. A slight difference of power coupling efficiency is observed with the different direction of electric polarisation for a Gaussian beam of large spot size at its waist due to coupling property has been discussed and shown to agree well with theoretical model.

A simple and effective fabrication method for various 3D microstructures: backside 3D diffuser lithography

This paper describes a simple and effective method to fabricate oblique or curved 3D microstructures with high uniformity and manifold shapes, utilizing backside 3D diffuser lithography. A negative photoresist spin-coated on the metal-patterned glass substrate is exposed from the backside where an optical diffuser is located and used to randomize the incident ultraviolet (UV) light, which creates the self-aligned curved 3D microstructures. The various 3D microstructures can be obtained simply by adjusting the key process parameters of this method such as the type of diffuser, the UV exposure dose, the opening width of the patterned metal on the glass substrate, etc. Through these parameter studies, a microball lens with a sag of 10 µm to 115 µm, a cylindrical microlens, a 3D planar microlens with circular and biconvex structures and an inverse-trapezoidal microstructure having different sidewall angles of 45°, 51°, 56° and 72° were successfully fabricated. The proposed method can be extensively applied for fabrication of micro-optical components due to its simplicity and versatility.