In most optical materials the atomic or molecular structure is so fine that the propagation of light within them may be characterized by their refractive indices. When an object has structure which is larger than the wavelength of light, its influence on the propagation of light may be described by the laws of diffraction, refraction and reflection. Between these two extremes is a region in which there is structure that is too fine to give rise to diffraction in the usual sense but is too coarse for the medium to be considered as homogeneous. Recent developments in micro-lithography have extended the possibility of generating sub-wavelength structures and it is now possible to produce materials with remarkable new optical properties.

Several applications in science and industry require a precise measurement of the polarization of the incident light, e.g. the online characterization of textile-fiber birefringency in spinning machines. A promising concept to realize these polarimeters is based on structured polarizers that consist of three polarizing metal stripe gratings, whose spatial orientations are tilted against each other with an angle of 60deg. With such an approach the state of polarization can be determined with a very small device without any moving parts. Here we report on the fabrication of a micro optical polarimeter based on three polarizing metal stripe gratings with a grating period of 300nm and a size of 0.3 mm x 0.3 mm each. To achieve the necessary high aspect ratio we combined electron-beam direct writing with dry etching and metal coating under oblique incidence. The measured polarization contrast of the fabricated micropolarizers is more than 300:1 over a large spectral range (wavelength between 450nm and 1000nm), moreover they have a contrast of even more than 1000:1 if light with a wavelength between 500nm and 600nm is used. Thus, they are well suited for microsensors to detect birefringency.

We have developed a simple, low-cost process for the fabrication of high-quality three-dimensional artificial-opal and inverse-opal photonic crystals. The process is based on the self-assembly of a template from a uniform suspension of polystyrene microspheres, which is sintered for added strength and subsequently back-filled with high-index material. The template formation is assisted by a combination of centrifugation and spin-annealing, which requires relatively short process times and inexpensive laboratory equipment. The process has been used to fabricate polycrystalline photonic crystals with photonic stop gaps in the mid-IR portion of the spectrum. Details of the fabrication process and fabricated samples will be presented. In addition, Fourier-transform IR reflection spectroscopy has been used to characterize the samples; the results are shown to be in excellent agreement with band structure diffraction calculations.

The CSG’s physical performance is decided by its structural parameters, such as width of grating stair, height of grating stair, and the shape of stair edge. Consideration of the practical fabrication process, an error model of CSG’s structure is built to express the relationship between CSG’s performance and its structural parameters. In this model, each structural parameter of CSG is expressed as a variable, and the structural parameter error induced by fabrication process is expressed as minute disturb of relative variable. Through analysis and simulation, we obtained a general estimation standard for the structural parameter errors of CSG, which provides a theoretical direction for CSG’s fabrication and usage.

Multiple beam interference lithography is an efficient method to produce very small periodic surface-relief structures over large surfaces. For a recording wavelength of 413nm, the period of these structures ranges from a few hundreds nanometer to a few micrometers. Applications of these structures range from antireflective surfaces, when the gratings have sub-wavelength periods, to various types of diffractive optical elements. Using a single exposure with two-beam interference, the profile of the obtained structures is sinusoidal. Superimposing, however, several such exposures with increasing spatial frequencies, also non-sinusoidal structures can be obtained. By decomposing the desired profile in its Fourier components, it is possible to obtain virtually any profile of structure, depending only on the number of Fourier components that the optical setup can produce. Various kinds of periodic structures are shown, starting with simple one-dimensional gratings up to more complex two-dimensional structures, such as an array of micro pyramids. Therefore, we gave a demonstration of the great potential of this method for realizing optical components. The advantages of the method are the simultaneous fabrication of relatively large arrays in a quick and simple manner and the accurate control of the periodicity of the structure.

We designed a tunable, oblique incidence resonant grating filter covering the c-band as drop device. Our resonant grating filter consists of a planar waveguide on a glass substrate covered by low index medium that separates the waveguide from the grating on top of it. With these 3 layers we reach a finesse of more than 3000, which would require much more layers in traditional thin film technology. The drop filter can be tuned by tilting the MEMS platform on which the filter will be glued. Tuning over the c-band will require tilt angles of 3° of the MEMS platform in both directions. Measurements indicate a resonance peak shift of 1.2% and a negligible shape change of the resonance peak from 1526nm at 45° angle of incidence to 1573nm at 53° with a full width at half maximum of 0.4nm. In this range the peak wavelength shift is linear with respect to the change of the AOI.

Diffractive optical elements (DOEs) have a great potential in the complete or partial substitution of refractive or reflective optical elements in imaging systems. The greater design flexibility compared to an all-refractive/reflective solution allows a more convenient realization of the optical systems and additionally opens up new possibilities for optimizing the performance or compactness. To demonstrate the opportunities of the hybrid optical concept we discuss different imaging systems for various applications. We present the lens design of a hybrid microscope objective which is especially applicable for wafer inspection technologies. Meeting the requirements for such a system used in the deep-UV regime (248 nm) is very challenging. The short wavelength limits the material selection and demands cement free optical groups. The additional requirement of an autofocus system, working at a wavelength in the near infrared region, is fulfilled by the special combination of two selected and adjusted DOEs. Furthermore, we discuss the opportunities of the hybrid concept c of a slit lamp used for ophthalmologic examinations. The DOEs are the basic elements of this hybrid concept. We demonstrate that holographic lithography is an appropriate technology to realize a wide variety of elements with different profile geometries. We address in particular the additional possibilities of an UV-laser system as an exposure tool. Additionally to the high spatial frequencies, the 266 nm exposure wavelength allows the use of novel photo resists with advantageous development behavior.

We have developed a method for fabricating almost any type of optical surfaces in diamond. The method consists of the following steps: First, a polymer film, spun onto diamond substrates of optical quality, is patterned by lithographic processes. Next, the surface relief is transferred into the underlying diamond by use of inductively coupled plasma dry etching in an oxygen/argon chemistry. Using this technique, we have successfully demonstrated the fabrication of diamond spherical microlenses, blazed gratings, Fresnel lenses, subwavelength gratings and diffractive fan-out elements. The spherical microlenses had apertures of 90 μm and f-number of 4. The phase error, measured with a Twyman-Green interferometer at 633 nm, was found to be less than 31 nm. The diffraction efficiency for the blazed grating was measured to be 68% at 400 nm, with a theoretical maximum of 71%. The subwavelength grating was designed for reducing surface reflections at a wavelength of 10.6 μm. Spectrophotometric results show that the optical transmission was increased from 70%, using a non-structured diamond substrate, to 97%, using our subwavelength structured diamond. Finally, the fan-out element has been tested with a 6 kW carbon-dioxide laser, to microstructure pieces of PMMA. The results are excellent, showing diffraction limited spots.

Optical elements, such as grating, holographic optical element and Fresnel lens, are made on the SiN membrane. The SiN film was deposited on the silicon wafer by low pressure chemical vapor deposition (LPCVD). Its advantages include the high transmission efficiency, light weight, and easy packaging for the Si-based optical pickup head.

We developed the fabrication process of all-plastic cantilever for force controlled atomic force microscope. The force controlled atomic force microscope can prevent damage during the scanning of the soft sample. However it has a drawback in its stability. To stabilize the system the cantilever is required to have small Q factor. The negative photo resist for MEMS (SU-8) has ideal properties, micromachinability and small Q factor, for this purpose. Here we demonstrate the cantilever consists of tip, lever and base with same polyimide. The mold of the probing tip is the pyramidal pit pattern on silicon wafer formed by direct leaser writing and anisotropic etching of silicon. Other elements of the cantilever are formed by contact lithography. The photo mask is also fabricated by direct laser writing. By arranging the dimensions of the cantilever, we can control its spring constant and resonant frequency. For the spring constant of 0.1N/m and the first resonant frequency of 2kHz, the typical dimensions of the cantilever is 1030 x 300 x 7 μm³. The fabrication error in cantilever geometry was 1.5%. The estimated resonant frequency has a good agreement with the designed value.

We report a micro-optical sensor system for the on-line characterization of the textile-fiber birefringence in spinning machines. The measurement set-up is using the method of Senarmont but does not require any moving parts in the optical path. This has been achieved by usage of different micro-optical elements in combination with optical fibers for illumination and signal capturing. One of the key-components is an array of micropolarizers made of subwavelength-period metal-stripe gratings fabricated by e-beam direct writing and ion-beam etching. Having a total height of only 6mm the sensor system is extremely flat and thus applicable also in special spinning equipment.

We have focused on measurement needs for micro-refractive lenses and have developed a flexible and compact micro-interferometer that can be used to measure lens radius of curvature and form errors. Transmitted wavefront and back focal length measurements can be easily added to the instrument. This instrument addresses measurement needs for micro refractive lenses. The interferometer is based on a Mitutoyo metallurgical microscope and operates with a 633 nm helium neon source. The radius of curvature measurement is directly traceable, meaning an external artifact is not required for calibration. This requires a careful mechanical design, a detailed alignment procedure with estimates of alignment uncertainties, and stage error motion characterization with estimates of uncertainties. The instrument can also be used to measure some diffractive components and mold form errors. We describe the instrument in this paper and discuss design goals and measurement specifications.

The use of diamonds to generate precision patterns and precision surfaces on a micrometer or nanometer scale has a history that dates back centuries. Uses of diamond in semi-automated machinery can be traced to ruling machines, pantographs, and ornamental turning with "diamond turning" dating back about a century. Poor behavior in machining more common materials (e.g. ferrous alloys) has limited diamond use in traditional industrial machining. The niche of the single crystal diamond is its edge sharpness and the ability to produce near-optical finish in materials such as aluminum, copper and their alloys; however, due to machine limitations, diamond machining remained a novelty until relatively recently. A convergence of machine technologies developed for both weapons and commercial applications led to modern diamond turning. Current turnkey machines can produce contoured surfaces with surface finish in the range of 5 nm Ra and long range accuracy of micrometers or less. Macroscopic scale, three axis, diamond machining is a well-developed technology; machining of features on a micrometer and submicrometer scale is a new and rapidly developing application of single crystal diamond machining. The role of this technology in micro-optics replication has yet to be fully defined.

In the last years it has been shown that the gray tone lithography (with HEBS-glass masks) is a suitable technology for fabricating arbitrary continuous surface profiles. However, the resolution of this technology is limited and is in the range of some micrometers dependent on the electron energy used for darkening the HEBS glass mask. To overcome this drawback, we suggest to apply two subsequent lithographic steps on the photoresist layer without a second coating. Non-standard gray tone lithography will be used in a first step for fabricating a pre-form and the second lithographic step which can provide the resolution demanded will correct for the residual deviations. This is possible with an alternative method of gray tone lithography which makes use of the absorption and bleaching of the photoresist. Exposure with a sufficiently short time leaves a bottom part of the resist layer unexposed and develop-ment stops at its face. Thus, the remaining resist profile can be exposed in a second lithographic step without a new re-sist coating. With this method it will be possible to fabricate sub-wavelength structures, e.g. for antireflection, on top of arbitrary continuous surface profiles. Moreover, this method can be used for the fabrication of deep profiles by repeated applica-tion of the first lithographic step. In the paper we will discuss the problems of accuracy, resolution and profile depth of this method and present results of optical elements fabricated by this technology.

An optimized coding gray-tone mask method with multi-parameters is presented in this paper. Precise calculations, which are performed on the dead area in the backward reflection of the pyramid prism, demonstrate that the fringe error caused by the coding gray-tone mask has little affect on the performance of the pyramid prisms. This not only greatly reduce the resolution requirement of the coding gray-tone mask, but also reduce the errors produced by the exposure process. A satisfying simulation result is obtained with the designed coding gray-tone mask.

While recent advances in optical integrated circuits and photonic crystal devices have been impressive, there presently exists an unsatisfied need for an efficient means of coupling into these systems from the outside world. To this end, we have developed writing techniques for continuous-tone grayscale masks in high-energy beam sensitive (HEBS) glass, which we subsequently employ in the fabrication of tapered coupling devices. These devices demonstrate efficient coupling of free-space and fiber signals into waveguides fabricated on silicon-on-insulator substrates. This approach significantly reduces losses as compared to standard butt-coupling and end-fire coupling methods, in addition to being inherently broadband. In this paper, we discuss grayscale mask process development, fabrication techniques for the coupling devices, and characterization of device performance.

We report on a new approach in analog photolithography for the manufacturing of optical elements with a continuous profile. It is based on a phase-only mask used in a mask aligner.The advantage of this new approach is that it is contact free, i.e.there is a gap between the mask and the substrate during the exposure. That allows a non-destructive mask lithography.

We report on a novel technique for hardening micro-optical resist elements, like beam-shaping elements or micro lenses, with large profile depths before proportional transfer into the fused silica substrate. This technique allows to harden the resist with only small distorsions of the height profile. For demonstration a refractive beam shaper was designed and fabricated in photo-resist using gray-tone lithography. This element was transfered into fused silica with high etch rates using an optimized set of parameters in an ICP-etcher.

For many high-volume applications of micro-optical elements and systems the most cost-effective fabrication technology is replication in polymer materials with techniques such as UV embossing, hot embossing, and injection molding. Replication significantly reduces the cost in volume production in comparison to silicon-based etched components. However, the temperature and humidity stability of most commercial polymers is not suitable for the application of replicated elements in areas such as telecom or datacom. A process based on UV-replication in chemically durable polymers has been developed. Technologies for all fabrication steps from mastering over tooling to replication on wafer-scale, post-processing and characterization are described. We present results of various projects with double-sided micro-optics for telecom/datacom and various sensor applications.

With respect to the manufacturing of optical elements, facile and effective fabrication method is proposed. It is developed in connection with photo-induced surface relief (PSR)formation phenomenon that occurs on the azobenzene functionalized polymer film. Purely optically inscribed surface relief structures have been used as a plastic mold for manufacturing of its replica. At least a hundred times replication process has been achieved using thermosetting resin without any deterioration. This method has many merits not only from a technical viewpoint but also from a economical efficiency. In this report,first the PSR phenomenon is explained and then several examples for optical component fabrication are demonstrated.

Low-cost micro fabrication technique is indispensable for mass production of micro optical elements. Si very large-scale integration (VLSI) fabrication technology such as electron beam lithography or advanced photo lithography is generally applied to fabricate micro structures, however the production cost is too expensive for mass production of optical elements. To overcome the problem, imprint lithography is one of the promising method to fabricate micro structures at low cost. Various shaped mold is fabricated by semiconductor process technology. Process conditions such as temperature or pressure are designed to avoid fracture of the glass plate. Fine gratings, fine blazed and various shaped structures are successfully achieved on the glass surface without fatal defects. The cross-sectional profile of the imprinted structure is fairly good and surface roughness is less than a few nano meters.

The development of an inexpensive, reproducible and highly accurate method for the production of microlens arrays is of vital importance to the next generation of optics based technologies. Currently there are a large number of companies using many different techniques to produce these arrays, however no single technique has proven itself capable of providing the necessary range of lens properties. One technique that has been used to produce arrays is the reflow of photoresist method first suggested by Popovic et al. in 1988. This technique utilises mature fabrication patterning technology, i.e. photolithography, however when lenses are produced they are often found to have large deviations from the spherical case. This limits the range of f-numbers, f/#, that can be produced. There are a number of polynomial models that have been presented in the literature that are used to model the resulting lens profiles, however these models are not based on the physical nature of the fabrication technique and hence provide no information about the processes involved. One model that attempts to model the profile from a physical basis has been reported in the literature, the Curvature Correction Model, (CCM), by Abe and Sheridan in 1999. This model has been shown to provide qualitative fits to the 1-D case (cylindrical lenses). In this paper we discuss our current work in generalising the model to the 2-D case (spherical lenses).

In this presentation we propose the multi-layer subwavelength structures to realize the polarization-sensitive optical elements. The multi-layer structures are fabricated on such consideration that a periodic relief subwavelength structure (we call the base structure later) with depth D₁ is first prepared in a substrate with refractive index n₁ , then a dielectric material with a refractive index n₂ is directionally coated on it with thickness D₂ . With the above fabrication process the coated dielectric material alternatively covers on the ridges or fills in the grooves of base structure to form the multi-layer structures. The characteristics of the effective indices and the form-birefringence behaved in such structures were investigated. The form-birefringent wave plates and the blazed-binary polarization-selective diffractive optical elements for normal incidence were synthesized with the proposed structures. The optical behaviors included the phase retardation, diffraction efficiencies, and the polarization contrasts were numerically analyzed with rigorous electromagnetic algorithm. A quarter-wave plate for the operating wavelength of He-Ne laser (λ=632.8 nm) was fabricated and the significant optical performances was obtained.

Inductively Coupled Plasma (ICP)can achieve high density plasma in low pressure,so it has a number of significant advantages such as improved etching rates,better profile control,improved uniformity, greatly increased selectivity and a dramatic reduction in radiation damage and contamination. In optics,quartz is an ideal optical material with transmitting spectral range from deep ultraviolet to far infrared.So we systematically studied the etching characteristics of quartz by using a Inductively Coupled Plasma (ICP)etching system.In the xperim nts,the gas was the mixture of CHF₃,O₂ and Ar,and the chamber pressure was about 10 mTorr.Th influences of gas flow rate and the power of the radio frequency on etching rate were optimized. The uniformity and repeatability of the etching technology were also studied. After residue mask material was removed by wet chemical solution, no polymer was observed on the surfaces of samples,and the surfaces of the fabricated quartz elements were smooth and clean. The optimized etching process is important for the fabrication of micro-optical lements based on quartz. Using this etching process, many gratings such as Dammann grating, rectangular groove grating, and optical disk grating can be fabricated successfully.

A new alternative coding method is proposed for the fabrication of circular diffractive optical elements with half tone masks, in which a series of rings with variant widths are used to produce desired gray distribution. Analytical analysis of this coding method is given and illustrated with numerical simulation examples.