Hybrid Optical Elements Research Articles

Enhanced imaging with binary circular Dammann Fresnel zone plate

We introduce a novel approach in optical engineering by combining Dammann gratings with binary Fresnel zone plates to create a unique hybrid optical element with enhanced energetic efficiency of its focal spots. Traditionally, binary Fresnel zone plates focus light at multiple points with varying intensities, while Dammann gratings are renowned for their efficient and uniform light splitting capabilities. Our innovation lies in merging these two elements and generating a binary circular Dammann (varying along the radial direction) Fresnel zone plate that concentrates most of the incident light into a small and desired number of focused points with equal intensities, rather than distributing light’s energy non-equally across multiple points. This novel design significantly enhances the efficiency and precision of light manipulation. It opens new possibilities in applications requiring high-intensity focal points, such as in advanced medical imaging and in accurate scientific measurements. By redefining the conventional roles of these optical elements, our research contributes an advancement to the field, paving the way for innovative solutions in various optical applications.

Novel fabrication and designs for hybrid optical elements with wider angle field of view by using integrated direct laser lithographic system

Hybrid optical elements, which are diffraction pattern arrays fabricated on curved refractive optical elements, have the ability to widen the field of view angle, and improve optical performance, by combining refraction and diffraction. As such, they have high potential in next-generation optical devices. However, manufacturing a high resolution diffraction pattern array that fully covers the curve of the refracted optical surface, so that the normal vectors of every pattern are perpendicular to the tangent plane of the refractive lens surface, is challenging. Furthermore, the lack of diffractive pattern designs corresponding to the curvature makes it difficult to replace curved microlens arrays with hybrid optics. In this study, a direct laser lithographic system combined with an auto-focus system and high accuracy rotational system was built to fabricate the diffractive patterns array on a cylindrical lens. This approach provides a method to manufacture hybrid optical elements with wider field of view. In addition, we proposed novel designs of a linear zone plate (LZP) and elliptical zone plate (EZP) on a cylindrical lens that can be used for focusing light beam into lines and points, respectively. These hybrid optics exhibit superior performance in both diffraction efficiency and resolution, 25% better than traditional diffractive optical elements. An array of two types of zone plates were fabricated fully along the curve of the cylindrical lens using the proposed system, giving a 20° angle field of view, which acts like a curved cylindrical lens array and 1D curved microlens array. The performance of these hybrid optical elements were evaluated by optical verification system and simulation.

Refractive-diffractive hybrid optics array: comparative analysis of simulation and experiments

Hybrid optical elements, which combine refractive and diffractive optical components to enhance optical performance by taking advantage of the optical characteristics of the individual components, have enormous potential for next-generation optical devices. However, there have not been many reports on the simulation methodology to characterize such hybrid optical systems. Here, we present a method for simulating a hybrid optical element realized by attaching an ultra-thin, flexible diffractive optics array onto a refractive optical element. The ultra-thin diffractive optical element is fabricated by direct-laser-writing using a femtosecond pulsed laser as the light source. A systematic investigation of the proposed simulation method, which does not require extensive hardware resources or computational time, but retains resolution and accuracy, is presented. The proposed scheme is validated by comparing simulation and experimental results. The simulation and experimental results on the spot size and focal length for the diffractive Fresnel zone plate (FZP) match well, with typical errors of less than 6%. The aspect ratio of the focal spot sizes at the compound and FZP focal planes of the hybrid optical system from the simulation and experiment also match quite well, with typical errors below 7%. This simulation scheme will expedite the designs for novel hybrid optical systems with optimal optical performances for specific applications, such as microfluidics and aberration-controlled optics.

Grating/microlens arrays fabricated by hot-melting, self-assembly and replication

This paper reports a convenient method to fabricate hybrid optical element of grating/microlens array (GMA) by hot-melting, self-assembly and replication on the same surface. The polydimethylsiloxane (PDMS) microlens array with lens diameters of 700 μm and effective focal length of 3.7 mm is replicated twice from the photoresist microlens array by hot-melting. And the self-assembly gratings with groove density of 886 lines/mm are fabricated on the surface of stretching microlens array by oxygen plasma. A single part of GMA operates across a wavelength spectrum from 450 nm to 650 nm with a maximum resolution of 6.9 nm at 450 nm.

Hybrid refractive-diffractive microlenses in glass by focused Xe ion beam

The combination of refractive and diffractive components in a single optical element provides miniaturization of optical systems and enhancement of their performance. Thus, hybrid singlet lenses with diffractive structures added on top of the refractive curved surface were shown to have reduced chromatic and spherical aberration. Optical systems based on such hybrid lenses have reduced dimensions as they require fewer lenses for aberrations-correction. Diffractive elements provide additional possibilities of light manipulation and enable the realization of miniaturized multifocal systems, spectrometers, and other devices. Glass hybrid lenses are typically realized by diamond turning or glass moulding. These techniques, however, are not applicable for the fabrication of lenses in brittle materials or microlenses (hundreds of micrometers in diameter or less). On the other hand, direct writing techniques, such as focused ion beam (FIB) milling (typically Ga), offer a high resolution and flexibility of patterning on curved lens surfaces made of a great variety of materials. The disadvantages of FIB milling are its slow speed and Ga implantation that may alter or degrade the optical performance of fabricated components. FIB systems based on high brightness plasma ion sources provide more than an order of magnitude increase in milling rates with noble gas ions (e.g., Xe) compared with Ga FIBs. Here, the authors demonstrate the feasibility of rapid, direct milling of hybrid refractive-diffractive microlenses in glass using >60 nA of Xe ion current. Microlenses with up to 300-μm diameter were milled and diffraction gratings were realized on top of their curved surfaces. The performance of the lenses was characterized by mapping the transmitted intensity at different positions. Due to the introduction of diffraction gratings on the surface of the lenses, their optical performance is modified with the emergence of additional focal spots spatially separated by distances consistent with the theoretical and simulated values. The results indicate the applicability of the plasma focused ion beam systems for rapid fabrication of high-quality hybrid optical elements directly in hard substrates.

Optical system design of four-channel dual-band infrared panoramic imaging

In order to reduce the volume of a panoramic optical system, a four-channel infrared dual-band panoramic imager was designed using spatial multicamera image mosaicking. Each optical system of the imaging channel was designed in a double imaging configuration with an F-number of 2, working bands of MWIR 3 to 5 μm and LWIR 8 to 12 μm, and a full field of view (FOV) of 122 deg. By adopting refractive-diffractive hybrid optical elements and introducing aspheric designs, the system was made to achieve temperature compensation from −40 ° C to 60°C by means of optical passive athermalization. Results indicate that the system attained almost 100% cold stop efficiency. At the Nyquist frequency of 18 lp/mm, the modulation-transfer-function (MTF) of the MWIR system was higher than 0.70 at the edges of the FOV, whereas the MTF of LWIR system was greater than 0.35 for the same condition, both approaching the diffraction limit.

Hybrid micro-optical elements by laser-based fabrication of Fresnel lenses on the end face of gradient index lenses.

Fresnel lenses are fabricated directly upon the end face of gradient index (GRIN) lenses by F2-laser machining at 157 nm wavelength. The employed laser processing technique combines a mask projection configuration at 25-x demagnification with a rotation of the structured lens. The ablation characteristics of the GRIN materials require very high pulse fluences with typical values above 7 J/cm2. Topography measurements on the Fresnel lenses reveal a good contour accuracy with residual deviations from the design profile well below 100 nm. Such hybrid optical elements, combining GRIN lenses with diffractive lenses in one element, can serve as the basis for high-performance micro-optical imaging systems with diameters up to 2 mm. Examples of possible applications include imaging sensors like proximity sensors or color-corrected microscope objectives with high numerical aperture for endoscopy applications.

Design of refractive/diffractive hybrid optical elements for beam shaping with large diffraction pattern

Diffractive optics is an important technique for beam shaping with high light efficiency and strong diffraction pattern flexibility. Since the diffraction angle is limited by the unit size of the diffractive optical element (DOE), the size of the required diffraction pattern is always rather small. In this Letter, refractive/diffractive hybrid optical elements (RDHOEs) consisting of a DOE and a lens are used to realize beam shaping for a large diffraction pattern. The lens, as the component of the RDHOEs, can not only be concave but also convex, and the double sampling Fresnel diffraction algorithm is developed for the design of these two types of RDHOEs. The simulation and experimental results provide solid evidence to demonstrate the proposed method with the pure phase spatial light modulator.

Gaussian laser beam transformation into an optical vortex beam by helical lens

In this article, we investigate the Fresnel diffraction characteristics of the hybrid optical element which is a combination of a spiral phase plate (SPP) with topological charge p and a thin lens with focal length f, named the helical lens (HL). As incident a Gaussian laser beam is treated, having its waist a distance ζ from the HL plane and its axis passing through the centre of the HL. It is shown that the SPP introduces a phase singularity of pth order to the incident beam, while the lens transforms the beam characteristic parameters. The output light beam is analyzed in detail: its characteristic parameters and focusing properties, amplitude and intensity distributions and the vortex rings profiles, and radii, at any z distance behind the HL plane, as well as in the near and far field.

Rosette gratings as generators of nondiverging intensity patterns

In this paper we present and investigate binary phase diffraction gratings whose phase reliefs have form of rosettes-the so-called rosette gratings. They are constructed by the equiphase lines of the cosine-profiled phase Siemens star axicon-a hybrid optical element consisting of an axicon and a phase optical element with azimuthal cosine profile. It is shown that the rosette gratings transform the incident Gaussian laser beam into a sum of odd-diffraction orders beams, nondiverging in defined propagation intervals. The amplitude and intensity distributions of the separate diffraction orders, as well as the interference between them are studied. Under certain conditions these gratings can act as suitable substitutes for the cosine-profiled phase Siemens star axicons in their applications.

Integration of rotated 3-D structures into pre-patterned PMMA substrate using step & stamp nanoimprint lithography

In this work, we fabricated hybrid micron-scale blazed grating structures on top of linear nanoscale gratings by superimposing thermal nanoimprint process. A poly(methyl methacrylate) (PMMA) substrate was at first pre-patterned with a nanoscale binary line grating by thermal NIL. The second imprint was added into the linear surface-gratings by sequential thermal imprinting using a stamp with micron-scale blazed gratings. The rotation controlled patterning was realized by Step and Stamp Imprint Lithography (SSIL) using NPS300 nanoimprinting stepper with a rotation imprint head with ability to control X/Y positioning and angular orientation of the stamp. In this paper, we demonstrate the potential of the hybrid imprint process for fabrication of e.g. hybrid bio devices or optical elements with arbitrary orientation.

Refractive-diffractive hybrid optical element for true beam smoothing

A refractive-diffractive hybrid optical element for true beam smoothing is designed with the precise design method. The intensity of any point on the focal plane is fully filled with the required demand, besides the sampling points used in the optimization. An aspheric refrac- tive surface gives a good initial intensity distribution on the focal plane and can decrease the phase depth of the diffractive surface. After the optimization, the phase depth of the diffractive surface is smaller than 1.1p, which is correspondingly easy to fabricate. © 2003 Society of Photo-

Design of hybrid micro optical elements with coded gray-tone mask

A new method to fabricate hybrid micro-optical elements in one-step lithography is proposed in this paper. A gray-tone coding method has been developed to achieve one step photolithography of achromatic hybrid micro-optical elements. Design and simulation of hybrid lens with grey-tone mask are presented. The aberrations of optical elements are pre-corrected in the lithography process. The operating range of the hybrid optical element is in infrared band (8.0∼12.0 μm) with the central wavelength at 10.6 μm.

Design Example for the Use of Hybrid Optical Elements in the Infrared

<p>The Petzval objective is an effective design form for IR camera systems. It has excellent performance characteristics for high-aperture applications. Its field coverage is limited to a few degrees by the uncorrected Petzval sum.</p><p>Using a hybrid aspheric/diffractive front element, it is possible to achieve broadband color correction over the 3-5 µm or 8-12 µm region using only one lens material. For the long wavelength region, Germanium is typically used (except when the application environment is expected to exceed 60° C where Ge becomes opaque). This hybrid combination allows for the correction of the spherical and chromatic aberrations.</p><p>The advantage of the high precision obtainable with diamond turning makes it possible to generate simultaneously the diffractive phase profile superimposed on the aspheric surface. To protect the diffractive profile from the environment, it is placed on the rear surface of the first element.</p>