The design and modeling of micro-optical systems is still a challenging task because classical methods like ray tracing do not take into account diffraction effects and other coherent effects which appear e.g. in the presence of micro-optical array systems. On the other side, there exist scalar or rigorous diffraction theories to model optical systems. But they are also limited in their applications because they either neglect non-paraxial effects or the calculation time is too high for a practical use. In this paper we will therefore give an overview about existing (scalar) theories to model optical systems, especially systems containing micro-optics: a simple paraxial matrix theory, ray tracing, Gaussian beam propagation and the propagation of a wave using the angular spectrum of plane waves. The advantages and disadvantages of these theories will be shown and compared. At the end we will describe a combination of ray tracing and wave propagation methods to give a more realistic simulation of micro-optical systems.
Micro-Optics have begun to play a key role in micro-photonic systems and devices. This is largely due to the fact that semiconductor processing has enabled one to incorporate complex optical functions and integration features into the actual optical substrates. In this paper, key application areas of micro-optics are demonstrated for mode matching, gain equalization, and spectral filtering.
First developed over 30 years ago, gradient index lenses play an important role not only in telecommunications technology, but also in applications such as information interface and biomedical technology. Traditional manufacturing consists of doping a certain ion, A+ into the mother glass, drawing the glass into rods and then immersing the rods into s molten salt bath containing another certain ion B+. During a thermal ion exchange process, the original ion migrates out of the mother glass, and is replaced by the alternate ion, creating a refractive index variation. Current research is being conducted to improve the thermal ion exchange technology, and open new applications. This research includes extending working distances to greater than 100mm, decreasing the lens diameter, increasing the effective radius, and combining the technology with other technologies such as photolithographically etched masks to produce arrays of gradient index lenses. As a result of this ongoing research, the gradient index lens is expected to continue to be the enabling optical technology in the first decade of the new millennium and beyond.
Multilayer micro-optics combines refractive beam shaping with wavelength selective multiple interference. Layer composition and thickness distribution were optimized by advanced simulation software. Components were fabricated by mask-shaded vapor deposition with planetary rotation. Surface profiles were characterized interferometrically. For two-dimensional reflectance mapping, a high-accuracy automated system was developed. Micro-mirror arrays for self-imaging resonators, mode selective mirrors for miniaturized solid-state lasers and angular-adapted graded AR-coatings for microlenses are presented as applications.
We suggest a new technique for fabricating a wide class of continuous refractive optical elements in glass by combining the technique of ion exchange with high precision structuring of metal masks. We call this technique mask structured ion exchange (MSI). We have demonstrated the potential of this method by fabrication of rectangular shaped microlenses with low numerical aperture for Hartmann-Shack wavefront sensing applications. The lenses, positioned on a 400 micrometers raster, had a fill factor of 100 %, a focal length of 33 mm and diffraction limited performance. Due to the special fabrication conditions, the lens shape, position and even the focal length can be varied spatially within one substrate. For realization of a high aperture microlens array by field assisted exchange process we could reduce proximity effects between adjacent mask apertures by MSI.
In order to address an increasing numbers of industrial applications for Diffractive Optical Elements, the development of more efficient ways of designing and fabricating these devices is clearly needed. Among the main applications of these devices are beam shaping, optical interconnects and filtering. In order to reduce the design complexity and increase the performance and robustness, a novel, full complex-amplitude modulation Diffractive Optical Element was designed. This proposed element has the flexibility of allowing full control over both phase and amplitude modulation of whatever optical wave-front. The concept of this element is to bring together the positive characteristics of the high efficient phase modulation Diffractive Optical Element and the characteristics of an amplitude modulation Diffractive Optical Element, to achieve design freedom and fabrication facility, capable of obtaining a high-quality reconstructed image. The phase grating was fabricated in an amorphous hydrogenated carbon thin film, and thereafter an aluminum layer was deposited and patterned to obtain apertures in this reflective film. The use of a reflective layer in the fabrication avoids the risk of laser-induced damage since no absorption is involved in the process. Several devices, such as high-quality holographic displays, can be manufactured with this technique.
Novolak type polymers are the basic material for most commercial photoresists used in microelectronic processes, but are not often used for micro-optic applications. In this work, three types of optical devices were implemented in AR P322 novolak-based resist, which can be used as a positive photoresist and a positive electron resist. Gratings of parabolic divergent microlenses with f-number of 0.5 were fabricated using traditional optical lithography, employing the diffraction characteristics of de-focused light during the photolithographic exposure. The contrast curve of the AR P322 used an electron sensitive resist, was determined and yielded a gamma factor of 3.02. This relatively low contrast allows to obtain structures with well controlled curved walls. Direct write electron beam lithography was employed to manufacture gratings of parabolic convergent microlenses with different diameter and focal length, what enables one to control the intensity of the different orders of the diffracted light. This technique was also used to obtain convergent parabolic microlenses, with different diameters and different heights, allowing the control of the focal length of these lenses. These structures have several applications in the fields of pattern recognition, robotic vision and optical sensors.
Demand for optical components and subsystems has exploded in the last decade. The question directed at component providers by customers is no longer when can you make it? The critical question is now become when can you make it in high volume? Wafer scale manufacturing, developed for the integrated circuit industry, has transitioned into the realm of optical fabrication and assembly. Photonic Chip optical subassemblies are products fabricated using these techniques. To create them, the optical elements are lithographically generated with integrated alignment and bonding features. Wafers of complimentary elements can be aligned and bonded at the wafer level, assembling hundreds of optical systems in parallel with a single operation. Electro-optical components, such as source and detector elements can be assembled into the system at the chip level, using flip-chip die bonding to complete the mechanical and electrical connection. The striking features of this manufacturing method are its parallel assembly techniques, broad use of automation, and very attractive intrinsic cost at high volume.
A novel technique for the realization of guiding structures for passive / automatic alignment is proposed. The technique is based on a recently available special photoresist. This photoresist can be processed by standard lithographic processes and shows a mechanical stability close to glass. Guiding structures may thus be realized in the same process as the functional structures on a substrate. We discuss the material behavior in terms of processing, change of shape due to shrinking or swelling and shear stability. First results of accuracy experiments are shown. As an example we demonstrate fiber ferrules for horizontal and for vertical mounting. We also show alignment structures for fiber/fiber coupling.
The functions of gradient-index (GRIN) rod lenses and opto- mechanical alignments in a thin-film dense wavelength- division multiplexing (DWDM) filter module is analyzed analytically and numerically. Two figures of merit are adopted to characterize the performance of the thin film filter: center wavelength (CWL) shift and coupling efficiency (CEF). For a typical 100 GHz filter with four cavities and 143 stacks of films, the angular alignment tolerance is so tight that meaningful product yield will be difficult to achieve. However, with the deployment of GRIN lenses and active alignments, the angular product yield will be difficult to achieve. However, with the deployment of GRIN lenses and active alignments, the angular alignment tolerance is relaxed by two orders of magnitude. The effects of component tolerances and assembly tolerances on coupling efficiency are also analyzed. The results indicate that while the GRIN lens helps in the alignment of a thin- film filter, and sequence of assembly also plays an important role.
Proc. SPIE 4437, Compact bidirectional photonic circuit employing stacked multilayers of diffractive optical elements for fiber-to-the-home applications, 0000 (13 November 2001); doi: 10.1117/12.448147
In order to introduce optical fibers in the last one mile to the home, the realization of low cost photonic circuit is crucial. We propose a new concept of photonic circuit consisting of stacked multi-layers of diffractive optical elements. Wafer-scale alignment is expected to reduce fabrication cost of each photonic circuit. The first prototype demonstration of the photonic circuit is reviewed. The experimental results required further insertion loss improvement. To fulfill this need, we developed an optical CAD environment specifically targeted on telecommunication applications. The detail of the CAD environment as well as the second prototype experimental results are discussed.
Precision collimators and collimator arrays are increasingly critical components as telecommunication networks increase in bandwidth. In this paper we describe the collimator fabrication process at Corning Rochester Photonics Corporation. We describe replicated and etched collimator arrays and illustrate packaging concepts. Metrology and optical performance data is presented for both individual and arrayed collimators. Microlens surfaces etched into fused silica with surfaces sags of greater than 70micrometers , surface finishes better than 30 Angstroms are presented. Collimator arrays with pointing errors less than 40(mu) Rad, and microlens focal length uniformity error less than +/- 0.5% have been fabricated and the data presented.
There are many applications for micro-optics. Perhaps the most exciting use of micro-optics is in fiber optical communication systems, getting the light signals in and out of the fibers. Other possible uses include data processing, chemical sensing, and spectroscopic applications. In this talk we will describe (mu) ChemLab, the Polychromator, a new spectroscopic gas identification device, a fiberoptic status monitor, and a deep X-ray lithographic technique for fabricating micro-optical systems.
We designed, fabricated and characterized a micro-optical beamshaping device, intended to optimize the coupling of an incoherent, linearly extended high-power diode-laser into a multimode fiber. The device uses two aligned micro-optical elements (DOEs) in combination with conventional optics. With a first prototype we achieved an overall efficiency of 28 %. Straightforward improvements, like antireflective coatings and the use of graytone elements, should lead to an efficiency of about 50 %. The device is compact and the fabrication is suited for mass production at low cost. We applied three different technologies for the fabrication of the micro-optical elements and compared the performance. The technologies were: direct laser writing, multiple projection photolithography in combination with reactive ion etching (RIE) in fused silica, and high-energy-beam-sensitive (HEBS) glass graytone lithography in photoresist. We found that the refractive type elements (graytone) yield better efficiency for large deflection angles, while diffractive elements give intrinsically accurate deflection angles.
This paper presents an innovative architecture where a micro-prism structure performs an in-line and wavelength-dependent extraction of the light injected at the edge of the device. This partial extraction of light is carried out by holographic mirrors coated onto each micro-prism oblique side. Thanks to the fabrication process, customization is possible and the number and the performances of each extractive faces can easily be tailored at will. These devices can be advantageous for any kind of applications where a high spectral selectivity is required or when a discrete extraction of spectral components has to be performed.
The present paper examines the possibility of improving of the resolution of the phase rheological media without losing the unaltered diffraction efficiency by applying of surface- active substances. It is demonstrated that the concentration of the surface-active substances determines the value of the resolution capacity due to the reduction of the coefficient of surface tension of the phase rheological media. The infliction of the surface-active substances in a hyperfine layer on the free surface of the rheological media gives us an opportunity to record the optical information by means of holographic method on the transmitting surface of the multilayer structure. Such a multilayer structure gives us an opportunity to manufacture optical hybrids in the form of arrangements of photothermoplastic lenses with the period of 4-100micrometers and with the transmitting surface in the form of grating with the period of 0.2-1micrometers . It is determined that in case of such multilayer structures the question of proportionality of diffraction efficiency and dimensions of deformation (depth) needs further specification. The thing is that even when deformation is not substantial, the diffraction efficiency may be considerably increased due to the increase of density of deformation. In the process of research a technical plant is elaborated in order to select the mode of recording on the multilayer structures. This technical plant gives us the opportunity to obtain the permanent density of deformation and trace the changes in the relief deformation depth.
Microlenses are being applied widely, especially in fiber- optic components and modules. The lenses are frequently made in arrays which are coupled with fiber arrays to make arrays of collimated laser beams. A back focal length (BFL) that is uniform across the array and a low average insertion loss are critical for many applications. In this paper, we describe interferometric techniques for measuring the BFL and IL of all elements in a microlens array, and we document the measurement precision. The BFL of a lens can be measured interferometrically by illuminating it with a point source that is generated by a converging lens in the test leg of the interferometer. The point source is initially located at the back focal point of the lens under test (i.e., confocal configuration) and a plane mirror reflects the beam back through the lens and into the interferometer. The interferometer is then moved axially to obtain the cat's eye reflection from the back surface of the lens. The BFL is equal to the axial distance between these two points. We report results of measurements of BFL and IL of microlenses having nominal BFL of 3.4 mm. The BFL is measured to a precision of <4micrometers . The precision depends primarily on the test wavelength and the n.a. of the test. part, and these relationships are described. The IL is a function of transmitted wavefront error, and we compare wavefront- derived IL to the directly-measured IL.
In this paper we present the design and characterization of a micro 4f optical imaging system for the purpose of characterizing mesoscopic diffractive optical elements. To this end, we demonstrate the systems' ability to measure very small variation sin diffraction intensity with high resolution. Because the system is illuminated by both coherent and incoherent sources, we characterize the cutoff frequency and modulation transfer function to determine the spatial resolution of the system. The system is validated by comparing measured results to theoretical predictions.
Optical lens of micrometer order diameter for coupling between optical fiber and laser diode were formed by argon ion laser polymerization method at visible light cured resin. Test resin materials consisted of triethylene glycol dimethacrylate for main resin, camphorquinon for photo initiator of visible light area, hydroquinon for inhibitor, and N,N-dimethylmethacrylate for reducing agent. In order to obtain the micro lens of short focal length and small spherical aberration, the use of this technique makes it possible to simultaneously form the polymerized aria on glass plate at the argon ion laser beam irradiation zone. The polmerized aria made a high quality micro lens without using molding pattern. We have verified our claims with visual inspection, ray trajectory calculations for measurement of side long spherical aberration (transverse aberration), Fourier transform infrared spectroscopy for degree of conversion analysis of polymerized resin area, and Duc de Chaulnes method for measurement of lens shape. The lens has a diameter of 300micrometers or more, a focal length of 500micrometers or more with an NA of 0.5, and transverse aberration plot of about 100% of the within the limits of +/- 25micrometers . This method can be applied for producing circular, non-circular, linear, and array micro lenses by scanning or patterning of argon ion laser beam.