Micro-optical Elements Research Articles

Determining the micro-optical element surfaces profiles using transmission deflectometry with liquids

We propose a method for simultaneously measuring the front and back surface profiles of transparent optical components. The proposed method combines dual wavelength transmission deflectometry with liquids to record distorted phases at different wavelengths, and then numerically reconstructs the three-dimensional phase information to image the front and back surfaces of the lens. We propose a theoretical model to determine the surface information, and the imaging of achromatic lenses is experimentally demonstrated. Unlike conventional transmission deflectometry, our proposed method supports direct observation of the front and back surface profiles of the optical elements. Compared with other techniques such as interferometry, the proposed setup is simpler to align, has lower cost, and does not require coherent illumination. The proposed method can be applied to normal transmission deflectometry for determining the three-dimensional surface profiles of optical components.

3D micro-optical elements for generation of tightly focused vortex beams

Orbital angular momentum carrying light beams are usedfor optical trapping and manipulation. This emerging trend provides new challenges involving device miniaturization for improved performance and enhanced functionality at the microscale. Here we discus a new fabrication method based on combining the additive 3D structuring capability laser photopolymerization and the substractive sub-wavelength resolution patterning of focused ion beam lithography to produce micro-optical elements capable of compound functionality. As a case in point of this approach binary spiral zone pattern based high numerical aperture micro-lenses capable of generating topological charge carrying tightly focused vortex beams in a single wavefront transformation step are presented. The devices were modelled using finite-difference time-domain simulations, and the theoretical predictions were verified by optically characterizing the propagation properties of light transmitted through the fabricated structures. The resulting devices had focal lengths close to the predicted values of f = 18 µm and f = 13 µm as well as topological charge l dependent vortex focal spot sizes of ~ 1:3 µm and ~ 2:0 µm for l = 1 and l = 2 respectively.

Optimization of the Optical Microelements Using High-Performance Computer Systems

We present a numerical analysis of the laser beam diffraction by a two-zone binary microlens for different focal lengths. Characteristics and features of diffraction of the Gaussian beam and the (0,1) Gauss–Laguerre mode with linear and circular polarizations by the considered element are studied.

Producing optical microelements from glasses by means of extrusion

This communication generalizes a research cycle devoted to the development of the technology and methods for forming optical microelements (microlenses, aspheric components of microobjectives, and raster systems) by extruding glasses in the softened state through cylindrical channels. The studies were carried out at the S. I. Vavilov State Optical Institute.

Optical polymers with tunable refractive index for nanoimprint technologies

In order to realize a versatile high throughput production of micro-optical elements, UV-curable polymer composites containing titanium dioxide nanoparticles were prepared and characterized. The composites are based on an industrial prototype epoxy polymer. Titanium dioxide nanoparticles smaller than 10 nm were synthesized by the nonaqueous sol method and in situ sterically stabilized by three different organic surfactants. The composites exhibit high transparency. Distinct alteration of optical transmission properties for visible light and near IR wavelength range could be avoided by adaption of the stabilizing organic surfactant. Most importantly, the refractive index (RI) of the composites that depends on the fraction of incorporated inorganic nanoparticles could be directly tuned. E.g. the RI at a wavelength of 635 nm of a composite containing 23 wt% titanium dioxide nanoparticles is increased to 1.626, with respect to a value of 1.542 for the pure polymer. Furthermore, it could be demonstrated that the prepared inorganic–organic nanocomposites are well suited for the direct fabrication of low-cost micro-optical elements by nanoimprint lithography. A low response of the optical composite properties to temperature treatment up to 220 °C with a shrinkage of only about 4% ensures its application for integrated micro-optical elements in industrial production.

Determining Two-Sided Surface Profiles of Micro-Optical Elements Using a Dual-Wavelength Digital Holographic Microscope With Liquids

In this paper, a method is proposed for simultaneously measuring the front and back surface profiles of transparent micro-optical components. The proposed method combines a dual-wavelength digital holographic microscope with liquids to record holograms at different wavelengths, and then numerically reconstructs the three-dimensional phase information to image the front and back sides of the sample. A theoretical model is proposed to determine the surface information, and imaging of an achromatic lens is demonstrated experimentally. Unlike conventional interferometry, our proposed method supports nondestructive measurement and direct observation of both front and back profiles of micro-optical elements.

Enhancing photovoltaic output power by 3-band spectrum-splitting and concentration using a diffractive micro-optic.

We report the enhancement of photovoltaic output power by separating the incident spectrum into 3 bands, and concentrating these bands onto 3 different photovoltaic cells. The spectrum-splitting and concentration is achieved via a thin, planar micro-optical element that demonstrates high optical efficiency over the entire spectrum of interest. The optic (which we call a polychromat) was designed using a modified version of the direct-binary-search algorithm. The polychromat was fabricated using grayscale lithography. Rigorous optical characterization demonstrates excellent agreement with simulation results. Electrical characterization of the solar cells made from GaInP, GaAs and Si indicate increase in the peak output power density of 43.63%, 30.84% and 30.86%, respectively when compared to normal operation without the polychromat. This represents an overall increase of 35.52% in output power density. The potential for cost-effective large-area manufacturing and for high system efficiencies makes our approach a strong candidate for low cost solar power.

A gating tunable planar lens based on graphene

Graphene is regarded as the ideal platform for propagating a surface plasmon polariton wave in THz and infrared frequency bands. We proposed a graphene-based planar lens with variable focal length. The proposed lens structure is composed of a single flake of graphene, a set of polysilicon DC gating pads, and a dielectric layer grown over a silicon substrate. The designed lens is realized by applying a gating voltage between the polysilicon DC gating pads and silicon substrate. By dynamically controlling the gating voltage, the lens is capable of focusing and collimating a surface plasmon polariton wave according to different focal lengths, such as 150, 200, 250, and 300 nm. The performance of the proposed lens is evaluated versus different focal lengths and chemical potentials. The correlation filtering system can be simulated by the lenses with different focal lengths. Numerical simulations demonstrated that the results were nearly consistent with our design methodology. The designed planar lens can be used as Micro-Optics elements and opens a new way to achieve plasmonic optics devices.

Flexible mask illumination setup for serial multipatterning in Talbot lithography

A flexible illumination system for Talbot lithography is presented, in which the Talbot mask is illuminated by discrete but variable incidence angles. Changing the illumination angle stepwise in combination with different exposure doses for different angles offers the possibility to generate periodic continuous surface relief structures. To demonstrate the capability of this approach, two exemplary micro-optical structures were manufactured. The first example is a blazed grating with a stepsize of 1.5 μm. The second element is a specific beam splitter with parabolic-shaped grating grooves. The quality of the manufacturing process is evaluated on the basis of the optical performance of the resulting micro-optical elements.

Improvement of the Fabrication Accuracy of Fiber Tip Microoptical Components via Mode Field Expansion

A novel method to overcome the problem of accurately centering microoptical components built by direct laser writing on the tip of a single mode optical fiber is presented, and it includes employing mode field expansion. A hybrid microoptical component consisting of an aspherical and a conical lens integrated into a single monolithic element has been fabricated at the end-face of a fiber using the technique of direct laser writing of photopolymers. The optical performance of the fabricated microstructures has been measured experimentally. We show that optical properties of Gaussian and Bessel beams can be easily tuned by adjusting the geometrical parameters of fiber-tip microoptical elements. In addition, we experimentally demonstrate the increase of propagation distance of a Bessel beam five-fold, using the fabricated microoptical element. This improvement in the fabrication method of fiber-tip microoptical elements can be used in the manufacturing of integrated micro-optical devices for optical tweezing, laser micromachining and long focal depth optical systems.

Soft glasses for photonic crystal fibers and microstructured optical components

Thermally stable tellurite, lead-bismuth-gallium oxides based boron-silicate and lead-silicate glasses dedicated for multiple thermal processing are presented. The glasses are successfully used for the development of photonic crystal fibers, nanostructured gradient index lenses, all-solid microstructured fibers as well as refractive or diffractive micro-optical elements with ultra-broadband transmission.

Fabrication of micro-optical elements on curved substrates by electrostatic induced lithography

This article reports the fabrication and characterization of polymeric micro-optical elements on curved substrates using electrostatic induced lithography.

Sharp focusing of a mixture of radially and linearly polarized beams using a binary microlens

Using a binary microlens of diameter 14 µm and focal length 532 nm (numerical aperture NA = 0.997), we focus a 633-nm laser beam composed of a mixture of radially and linearly polarized waves obtained by reflection of a linearly polarized Gaussian beam from a gold-coated subwavelength binary four-zone diffractive optical microelement (micropolarizer) of size 100×100 µm to a near-surface, near-circular focal spot of size (0.37±0.02)λ and (0.39±0.02)λ, where λ is wavelength. A linearly polarized light beam forms an elliptical focal spot with diameters (0.35±0.02)λ and (0.41±0.02)λ. Both focal spots have the area of 0.133λ². Subwavelength focusing using two microoptical components (a binary microlens and a micropolarizer) is suggested for the first time.

Monolithic generators of pseudo-nondiffracting optical vortex beams at the microscale

We report on the fabrication and characterization of micro-optical elements with typical size of 100 μm, which enable the production of pseudo-nondiffracting optical vortex beams of arbitrary order. This is made possible from the monolithic integration of spiral phase plates and axicons into helical axicons by direct laser writing using femtosecond laser nanopolymerization. The optical performances of the fabricated three-dimensional singular microstructures are experimentally measured and compared with their expected theoretical behavior, both in intensity and phase. The proposed approach thus represents an attempt to merge the field of singular integrated optics with that of nondiffracting light fields.

Fabrication and characterization of microlenses made of tellurite and heavy metal oxide glass developed with hot embossing technology

In this paper we describe the work on application of hot embossing process to fabrication of micro-optical elements transmitting in the visible, near infrared and mid-infrared part of spectrum, using multi-component soft glasses as starting materials. Description of used hot embossing (HE) process is provided, followed by discussion of rheological and viscosity properties of several glass types considered for demonstrator fabrication experiment. Demonstrator microlenses were fabricated from lead-bismuth-gallium oxide (PBG08) and tellurite glasses (TWPN/I/6), with transmission windows extending from the visible up to the mid-infrared (up to around \(6.5\,\upmu {m}\)). Fabricated elements, which included diffractive and refractive lenses and lens arrays, were examined in context of homogeneity (quality of pattern replication) and obtained optical properties (\( {M}^{2}\), focal length, resolution). A demonstrator microscope objective was constructed using refractive plano-concave, plano-convex and biconvex lenses fabricated with the HE setup and its optical characteristics were provided.

Fabrication of continuous relief micro-optic elements using real-time maskless lithography technique based on DMD

Abstract A novel method is proposed to fabricate continuous relief micro-optic elements using real-time maskless lithography technique based on digital mirror device (DMD). To evaluate the method, aspheric and spheric micro-lens array was fabricated by following the proposed principle. Firstly distribution of the required exposure dose of lens array was obtained and sliced into a number of contours of equal proportions. Then the contour planes instead of virtual masks were converted into binary image. On the lithography system, the dose accumulated over multiple exposures and the required exposure dose profiles were reconstructed. Finally in the photoresist layer, virtual profiles of lens array were formed, consistent with the original designed elements. The method is feasible and reliable for the fabrication of arbitrary continuous relief micro-optic elements.

Manipulation of cross-linked micro/nanopatterns on ZnO by adjusting the femtosecond-laser polarizations of four-beam interference

We report the fabrication of cross-linked micro/nanopatterns on ZnO by adjusting the femtosecond-laser polarizations of four-beam interference. The micro/nanopatterns are composed of two types of patterns with vertically oriented and horizontally oriented ripples, respectively. The relative locations, ablation depths and the nanoripple distributions of the two patterns can be manipulated by adjusting the laser polarizations. Theoretical calculations of the interference patterns indicate clearly that the micropatterns are determined by the interferential intensity patterns, while the nanopatterns depend on the interferential polarization patterns. The micro/nanopatterns have potential applications in micro-optical polarization diffraction elements by virtue of femtosecond-laser-induced anisotropy.

Optimization of hot embossing method for development of soft glass microcomponents for infrared optics

Abstract Hot embossing is an attractive alternative to other micro-replication methods, since its cost effectiveness makes it suitable for mass-fabrication of wide range of elements. In this work, hot embossing is presented in context of fabrication of micro-optical elements made of soft glasses for near and mid infrared spectral region. Particular attention is given to the selection of suitable materials from which the mold is prepared, in order to minimize sticking and degradation of the embossing stamps. Refractive lens and diffractive gratings are successfully developed with the proposed approach.

Shape‐Memory Polymers: Deformable, Programmable, and Shape‐Memorizing Micro‐Optics (Adv. Funct. Mater. 26/2013)

Micro-optical elements with micro- and nanoscale surface features prepared from an optically transparent shape-memory elastomer via replica molding at high precision are reported by Tao Xie, John A. Rogers, and co-workers on page 3299. Through shape-memory programming, the surface features and corresponding optical functions can be manipulated both globally and locally in a controlled manner. The image illustrates that a flattened microlens array loses the capability to focus light and only those completely recovered microlenses (coupled with a circular indium tin oxide heater) are able to project the letter “A” after thermal activating.

Development of silicate and germanate glasses based on lead, bismuth and gallium oxides for midIR microstructured fibers and microoptical elements

Three component PbO–Bi2O3–Ga2O3 glasses are characterized by high midIR transmittance, with a large susceptibility to crystallization. In this paper we investigate the increase in the thermal stability of these glasses by the addition of oxides such as GeO2, SiO2, Tl2O, CdO, Nb2O5. The resulting multicomponent glasses are well suited for the fabrication of microstructured fibers and micro-optical elements. The increased thermal stability of the modified multi-component glasses resulted in the IR absorption cut-off shifting to shorter wavelengths.