LIGA, the process sequence of deep lithography, electroforming and molding has been used for the fabrication of polymer waveguide components with passive fiber-to-chip coupling. The variety of 3D structures that can be realized, the high precision that can be achieved and especially the possibility of cost-effective mass production make these components most relevant for telecom, datacom and sensor applications. A novel waveguide design for a singlemode Y- splitter acting as telecommunication wavelengths was developed and realized together with the coupling scheme described above. It shows superior performance to conventional layouts and is ideally adapted to a fabrication using LIGA. Combining LIGA with high precision diamond machining multi-level tools with the complementary waveguide and fiber alignment structures were fabricated. For the first time a very high precision of better than 1 micrometers was achieved for heights and widths of all critical structures. A large number of molded parts was fabricated by hot embossing in PMMA. Detailed investigations proved that a reproducibility of better than 0.5 micrometers for the replicated structures is possible. By filling in a suitable core material into the waveguide prestructures and fixing fibers in the fiber grooves, fully pigtailed Y-splitters have been fabricated. This is an easy passive fiber-to-waveguide alignment with a significant reduction of manufacturing costs. First optical measurements on the samples showed an excess loss of 3.5 dB. Uniformity values were less than 0.6 dB and already meet Bellcore specifications. As another application of this fiber-to-waveguide coupling scheme a novel 4 X 4 star coupler for use in multimode optical bus systems is presented. First samples show an insertion loss of less than 9 dB and a uniformity better than 2 dB.

Understanding the parameters that affect the performance of milliscale and microscale actuators is essential to the development of optimized designs and fabrication processes, as well as the qualification of devices for commercial applications. This paper discusses the development of optical techniques for motion measurements of LIGA fabricated milliengines. LIGA processing permits the fabrication of precision millimeter-sized machine elements that cannot be fabricated by conventional miniature machining techniques because of their small feature sizes. In addition, tolerances of 1 part in 10³ to 10⁴ may be maintained in millimeter sized components with this processing technique. Optical techniques offer a convenient means for measuring long term statistical performance data and transient responses needed to optimize designs and manufacturing techniques. Optical techniques can also be used to provide feedback signals needed for control and sensing of the state of the machine. Optical probe concepts and experimental data obtained using a milliengine developed at Sandia National Laboratories are presented.

Fiber optical switches for telecom and datacom purposes become more and more important with the growth of fiber- based networks. This paper proposes a new principle for manipulating optical light paths through switchable, but non-moving polymeric mirrors in free-space optical interconnects. To achieve this a polymeric body and a thin liquid film are moved within a cavity. By moving the body up and down perpendicular to the light path the cavity wall can be switched from total reflective to transmissive state while the liquid film remains between body and wall due to capillary forces. The body can be moved with integrated electro-magnetic actuators and so the whole concept allows the realization of very compact switching elements. The coupling of single mode optical fibers requires a lateral and angular alignment precision in the micron and millirad range for both direct coupling and expanded beam coupling concepts. To meet these requirements, the LIGA technology provides a promising approach with respect to the high precision and also low-cost fabrication by mass replication processes. The combination of LIGA technology with other precision machining technologies allows the fabrication of miniaturized systems with both micro-optic and micromechanic components which fulfill the required tolerances for optical coupling. First demonstrators of 1 X 2 and 2 X 2 switches with bistable electro-magnetic actuators have been fabricated to show the feasibility of the proposed principle. The measured insertion loss is less than 2 dB at 1300 nm with -40 dB crosstalk. The switching time was measured 100 ms. The capabilities of the proposed non-moving mirror principle can be applied to 1 X 2 repair switches for the access area as well as to FDDI-switching-nodes up to compact N X M cross-connect switches for reconfiguration purposes or parallel interconnects to optical backplanes for the office area.

This paper describes the design and fabrication of optical microelectromechanical systems devices using the Sandia Ultra-planar Multi-level MEMS Technology fabrication process. This state-of-the-art process, offered by Sandia National Laboratories, provides unique and very advantageous features which make it ideal for optical devices such as micromirrors. This enabling process permits the development of micromirror devices with near-ideal characteristics which have previously been unrealizable in standard polysilicon processes. This paper describes many of these characteristics such as elevated address electrodes, various address wiring techniques, planarized mirror surfaces using Chemical Mechanical Polishing, unique post-process metallization, and the best active surface area to date.

This paper presents an overview of the research and development work on packaging and manufacturing different optoelectronic modules and microsystems for spectroscopic applications at VTT Electronics. Four different spectrometer concepts are analyzed: a multiwavelength detector module, an LED array spectrometer module, a PGP-spectrograph and an IR- spectrometer on silicon. The construction, main features, packaging concepts and performance are reviewed.

Rockwell is in the state of technology transfer to manufacturing of a micro-opto-electro-mechanical scan engine with superior scanning performance for bar code reading and factory automation. The scan engine consists of three main components: actuator, mirrors, and control electronics. The first two components are fabricated on a silicon cantilever beam while the control electronics are presently hybrid. The actuator comprises of a bimorph layer covered with two metal layers. The mirror has a large area (several mm²) and it is micromachined with a surface flatness better than (lambda) /2. Actuator scan-angles greater than 22 degree(s) with high repeatability in performance are achieved. The scan engine was integrated with an existing Rockwell commercial bar code reader/decoder and successfully proven to read a two-character code 39 bar code. The system was capable of decoding the 13-mil label at 360 scans per second with a 100% successful read performance. Environmental testing of the device indicates that the scanner can operate at elevated temperatures up to 70 degree(s)C with minor fluctuations in frequency and scan angle. The scanner has also gone through a lifetime cycle test and it has survived more than 8 billion cycles during a period of 18 months. To increase the yield and the performance level of the device, theoretical study as well as dynamic simulation by finite elements modeling have been investigated and will be reported separately.

This paper presents some results from phase-1 research into developing a beam steerer based on micro-mechanical diffractive elements. The position of these elements is electrostatically controlled, to allow dynamic programming of a 2D phase function. Feasibility prototypes were constructed in the MUMPs polysilicon surface micromachine process.

Using technologies such as replication or batch-fabrication, a number of micro-optical elements can be fabricated with low costs. However, as the realization of complex optical functions, for instance beam shaping and beam deflection, often requires several optical components, the mounting effort increases dramatically. It makes sense to emphasize the system aspects already in the design work. With the help of some examples for micro-optical fiber switches and modulators driven by piezoelectric actuators, we demonstrate that the combination of gradient-index optics with planar surfaces and replicated optical elements like micro-prisms, lens arrays on these surfaces can be an important step in the system integration.

A monolithic silicon integrated optical micro-scanner is presented. The device consists of a mirror located on the tip of a thermal bimorph actuator beam. The fabrication process is very simple and compatible with IC fabrication techniques. The device is excited electrothermomechanically at its resonance frequency, enabling large angular deflections at low power consumption. The technological process consists of basic frontside silicon micromachining steps requiring only three mask levels. The moving part is defined by selective silicon bulk etching. The bimorph beam is made of silicon dioxide and a thin film conductor. The residual stress in the two layers is used to achieve a 45 degree(s) out-of-plane rest position of the mirror. This allows optical components (e.g. laser diode, collimating lens) to be placed directly on the silicon substrate. Mirrors of 500*300 and 1000*500 micrometers ² with resonant frequencies at 300 and 100 Hz respectively were realized. Mechanical scan angles of above 90 degree(s) were achieved. The devices are very robust and have run through fatigue tests of billions of cycles at 300 Hz and 90 degree(s) deflection. The power consumption of the device is typically 1 mW for 30 degree(s) mechanical scan angles.

Test equipment for the development and mass production of micromirror array have been devised. Test equipment for the static and dynamic response of a single micromirror consists of HeNe laser, lenses, XY stage, CCD camera, position- sensitive photodiode and PC. It can be used to measure reflectance, tilt angle--input voltage relation, response time and resonant frequency, in the developing stage. It can also check the lifetime and uniformity of mirror quality over the wafer. Test equipment for the evaluation of micromirror array consists of CCD camera, lenses, XY stage, video signal processor and PC. It can classify the error- state of micromirror, generate statistical data and map of the position of abnormal micromirrors. The test results are shown on the monitor as a map that shows the error state, position and statistical data. It takes about 90 seconds to evaluate 50 X 50 micromirror array.

The merging of Microelectromechanical (MEM) devices and optics to create Microoptoelectromechanical (MOEM) systems provides opportunity to create new devices and to expand the functionality and applications of MEMS technology. Planar optical waveguide co-integration with surface micromachined (SMM) structures and inclusion of diffractive optical systems within 3D MEMS chip stack architectures have the potential to enable integrated optical test, metrology, and state feedback functions for complex MEM systems. This paper presents the results of research developing a fabrication process for co-integrating polymer optical waveguides with prefabricated MEMS devices. Multimode air superstrate rectangular optical waveguides have been fabricated using Ultradel optical polyimides over unreleased MEMS dice fabricated using the MultiUser MEMS Process Service (MUMPS) SMM process. These structures serve as the basic building block for exploration of guided wave integrated optical metrology functions for MEMS. Specially designed `split- comb' linear resonator devices enabling coupling of waveguide output to the resonator stage for position measurement are one class of a set of prototype MEMS function MUMPS testbeds under development for both guidance and evaluation of waveguide and free-space IOM efforts. Recently initiated work analytically and experimentally evaluating through-wafer free-space micro-optical systems for IOM will also be outlined.

Optoelectronic devices often make use of detectors or spatial light modulators. These components frequently are integrated with other electronics or devices that limit their fill factor on the substrate to less than unity. A frequently quoted approach to overcoming the fill factor problem is to use microlens arrays in conjunction with the components to increase the fill factor to near unity. However, the effect of the field angle over which the devices must operate is often not considered. In this paper we present results of geometric and physical optic analyses of microlens arrays in conjunction with detectors and modulators. Design equations for the microlens arrays are derived, the effect of field angle is quantified, and expected fill factor improvement is presented. Examples of possible systems applications are also considered.

An intersecting waveguide modulator which utilizes the carrier injection effects is presented and characterized. Using O⁺ implantation to render the implanted region electrically inactive, a well confined injection carrier channel is formed. This area can be driven to function as waveguide or as antiwaveguide. A transversal electrode switches the modulator from the on-state to the off-state or vice versa. At the base of carrier induced refractive index modeling and the finite difference beam propagation method, an optimum design modeling is given out to optimize the switch performance and to obtain the smallest injection current of this modulator.

The near-field scanning optical microscopy is widely applied in obtaining local optical information on the surface structures with subwavelength resolution. In the common illumination-transmission operation mode, the sample is illuminated by a near-field probe formed from an aluminum- coated, tapered optical fiber with subwavelength aperture and the transmitted light is collected by a conventional objective lens. Commonly the aperture tip is modeled according to Bethe's theory as the effective electric and magnetic dipoles whose magnitudes are only related to the incident electromagnetic fields. However, the coupling of the tip with the sample and the extended wafer can not be neglected as the tip is located in the proximity of the sample. In this work we treat the electromagnetic coupling of the tip with the sample and wafer in the real-space self- consistent approach and simplify the coupling of the wafer by the image method. The magnitudes of the effective dipoles are determined by the incident fields above the aperture as well as the perturbed fields reflected from below by the sample and wafer. When the coupling tip-sample-wafer system is solved in self-consistency, the transmitted optical signal collected by the lens can be derived straightforwardly, relating to the effective dipoles and the polarization of the sample. The simulation results show that the signal is sensitive to the polarization character of the incident fields.

Microprisms play an important role in a number of micro- optical systems for beam shaping and beam deflection. The task of the prisms is to deflect a beam selectively in order to bring it into an other optical channel of the system or to redirect a beam in the way that the redirected beam propagates parallel with respect to the optical axis of subsequent optical elements. We derive general requirements for microprisms for these applications and discuss some experimental results.

We give a quick overview of what and where in Europe new MOEMS technologies and products are arriving. We will mainly focus on developments funded by the European Community and especially on Europractice II partners existing products and technologies and particularly on the Competence Center Number 3 whose LETI and the authors are the coordinator.

Monolithically-integrated wavelength-selective receivers are needed for dense wavelength-division multiplex transmission in the 1.55 micrometers wavelength regime. We present a novel concept for tunable optical Fabry-Perot filters with long resonant cavities of about 30 micrometers . III-V semiconductor technology compatible to PIN detector integration is applied to fabricate bulk-micromachined movable membrane Bragg mirrors. The initial membrane curvature as well as the actuation-induced bending are analyzed using a white light interferometer. Continuous filter tuning achieved by thermal or electrostatical actuation is analyzed in the optical as well as in the mechanical regime. Opto-mechanical constraints of the realized filters are discussed in view of novel epitaxial demands and optimum design for micro-opto- electro-mechanical receiver systems.

The advent of micromachining has opened new doors for reducing the size and weight of conventional systems. A significant example is in the area of optics in which the size reduction can be exploited to produce ultra-miniature systems using MEMS device as the sensing or control elements. Using MEMS-based fabrication methods (the MUMPS runs), a series of optical diffraction gratings has been produced to examine limitations on the production methods and explore alternative applications. These devices consist of a variety of structures including single gratings, arrays of gratings and multi-periodic gratings. These devices are based on 3D architectures which can be adjusted in real time using electrostatic attraction from custom segmented electrode structures. The gratings were released and packaged for laboratory tests. Selected packaged devices were equipped with windows and integrated into a compact spectrograph to document spectral quality and performance. Preliminary results of mechanical, optical and electrical tests will be discussed.

We describe and demonstrate what we believe is the first 3- axis MEMS active fiber optic micro-aligner, which will allow for in-package alignment of fiber optic and micro-optic components. The micro-aligner is a wafer level fabricated device, based on a combination of silicon micromachining and LIGA technology. The electrically controllable actuators demonstrate the high force and displacement necessary to overcome fiber optic, counterforce springs, friction, and wirebonds to perform in-package alignment of a fiber optic. We have demonstrated movement of > 20 microns in all three axes in an in-package configuration. The first prototype device are currently small enough (4 X 4 X 0.5 mm³) to fit into a standard 14 pin butterfly package. We will show that future devices with the same forces and displacements can be made smaller than 1 X 1 X 0.5 mm³ thus allowing for multiple single mode fiber optic attachments inside a standard opto-electronic package.

A new concept for the detection of very small changes in the refractive index of a small sample of transparent material is given. The concept is based on measuring the frequency difference between two modes of a laser (possibly a twin- laser), where the evanescent field of one mode is affected by small refractive index changes. Intracavity sensing allows for orders of magnitude greater sensitivity than with external sensing. The frequency difference is obtained by light beating of the two modes. An imbedded diffractive element ensures proper modematching for the light beating. The relative frequency change is equal to the relative change in refractive index properly averaged over the waveguide. The performance of the intracavity system is compared with a system based on a Mach-Zehnder interferometer. The intracavity system may achieve a resolution that is 10⁴ - 10⁶ higher than the sensitivity of a system based on an external interferometer. The effect of thermal instability is investigated and it is discussed how the required very low thermal off-set can be maintained. Injection locking can be a problem. The problem may be solved by either introducing a fixed frequency off- set or by proper design of the cavity structure. An implementation based on III-V materials with a waveguide configuration and Bragg-mirrors is possible with existing technologies. A concept based on a polymer configuration is proposed.

Piezoelectrical elements offer best parameters for high resolution and high dynamic motions. However they can provide only motions in the micrometers range. Using piezoelectrical translation systems in MOEM devices, different systems such as optical fiber switches, intensity modulators and choppers can be developed. These systems have excellent dynamical properties. The integration of piezoelectrical actuators into a special accommodation with solid state hinges provides very compact systems with a high straightness of their motion. By this way the electrical capacitance of the actuating system can be reduced and the system can be minimized in its dimensions. The lower capacitance offers advantages for dynamic work with respect to power consumption. From the mechanical side, each piezoactuator has a certain resonant frequency. The system can be considered as an oscillating system with a high finesse. The excitation of the resonant frequency (by short voltage pulses) leads to parasitic oscillations on the full system. This effect can influence important parameters such as switching time, coupling efficiencies, cross talk behavior etc. The paper presents general aspects for optimizing high dynamic systems. Different methods of reducing parasitic oscillation will be discussed. First demonstration of piezoelectrical MOEM devices will be presented.

Near-field scanning optical microscope (NSOM) system with a bent or a straight optical fiber probe has been successfully developed to perform optical recording on the surface of cyanine (C₃₅H₃₅CIN₂-O₄) dye layer or Ge₂₁Te₂₆Sb₅₃ phase change (PC) thin film. Optical writing bits < 40 nm on the cyanine dye layer of a commercial compact disk-recordable were shown by atomic force microscope images of our tapping mode NSOM. For an vertical reflection mode NSOM, both optical writing and reading can be achieved on Ge₂₁Te₂₆Sb₅₃ PC thin film, and the diameter of 500 nm recording bits are shown.

Microlens array design and fabrication on silicon and quartz substrates for infrared focal plane applications have been described. A 128 X 128 element silicon microlens array with a pixel size of 60 X 45 micrometers for 3 - 5 micron bandwidth was designed using ray tracing and computer simulation program. A photoresist shap with rectangular arch was prepared by milting process and the shap was transferred onto a silicon substrate using ion beam milling. A 2 X 20 element quartz microlens array has also been fabricated using the same method as the manufacture of silicon microlens array. The microlens array structures were characterized by both the scanning electron microscope and the surface stylus. The experimental results show that the microlens arrays can be effectively formed at the temperature of less than 150 degree(s)C. The use of the microlenses to improve the performance of IR detector arrays is described. A photocurrent gain in excess of 2 has been achieved.

For many MEMS devices, silicon including polysilicon so far is the most idea materials, therefore the silicon micromachining technology has been well developed. However, for some MOEMS devices and systems, using other materials such as glasses, quartz, dielectric and ferroelectric crystals or ceramics, compound semiconductors, metals and alloys are also available or unique. As a result, it is necessary to develop the nonsilicon micromachining technology. In this paper, the nonsilicon micromachining process and some devices such as different kinds of micro- hinges will be reported.

The fabrication of surface profile may become an interesting technology in the field of micro optics and micromachining. Recently, surface profiles are known and widely used in optics, especially in diffractive optics. In the last few years the demand on deep and arbitrarily shape profiles increased drastically. Laser beam writing and e-beam writing are technologies suitable for the fabrication of such profiles, but only for a limited range of profile depth. Photolithography is also able to realize surface profiles, much deeper profiles can be realized by combining of different technologies. In this paper we report about a strategy for arbitrary deep profile generation as well as results we achieved by using single and combined technologies of special gray scale masks (based on HEBS glass), e-beam lithography and photolithography.

A new micromotor that is powered by the mechanical rectification of oscillatory motion is conceived, designed and fabricated. Its operational characteristic is quite rich and exhibits various modes of excitations. The idea explored in the design of this novel device is completely different than other micromotors reported in the literature. It consists of a rotor with elastic fins and linear actuators located on its perimeter and it operates as follows. When the actuators move toward the fins, the friction between the actuator edge and the tip of the fins causes them to deform. This deformation applies a force to the rotor that has both tangential and normal components. The tangential components results in a twisting action on the rotor, setting it into rotation. When actuators move away from the fins, the fins are released and allowed to move back to their original position. Continuous rotation is achieved by matching the oscillations of the actuators with the movement of the adjacent fins. The torque of this device is quite large (mN.m for 0.5 micrometers rotor radius) and can be adjusted by the radius of the actuator, the length and elastic properties of the fins, the tilt angle of the fins with respect to the rotor, the force exerted by the actuators, the vibration frequency and the number of fins, and by adjusting the friction between actuators and the fins. Experimental data using a prototype micrometer will be given and various application of the micromotor in optical MEMS and fluidics will be discussed.

Micro-opto-electro-mechanical sensors (MOEMS) where optics are integrated with micro-electro-mechanical systems are logical candidates for sensing flow properties in high temperature and pressure applications. MOEMS offer high frequency response, small size, immunity to electromagnetic interference, and resistance to degradation from exposure to harsh environments. Interfacing MEMS sensors with fiber optics is quite challenging. We are investigating novel transduction and coupling methods based on evanescent field interaction and fiber bending methods. An evanescent field, created when total internal reflection between two dielectric media occurs, is an electromagnetic field in the lower index medium. In the case of fiber optics, the evanescent field decays exponentially away from the fiber core/cladding interface. The decay length depends on refractive indices and incident angles inside the fiber. Bringing a foreign object close to the exposed core introduces a change in the effective index and as a result, the transmitted light output is modified. Sensors can also be designed based on the `touching' and `bending' of the fiber optic. In this case, the output light is affected in a linear manner as opposed to the evanescent mode interaction where the sensitivity is exponential. Experimental results obtained regarding pressure sensors for both of these methods are discussed in terms of sensitivity, temperature effect, design parameters, and fabrication techniques.

The development of micro-opto-electro-mechanical systems (MOEMS) and devices no longer focuses on feasibility studies and expensive demonstrators. On the contrary, fabrication of micro-optical components is already feeding dynamic markets with a large variety of products that are more or less on the verge of inexpensive mass production. A major application area for MOEMS is, without any doubt, tele- and datacommunications, while miniature optical sensors (e.g. spectrometers and interferometers) have a growing part in many kinds of biotechnological, chemical and pharmaceutical applications. In this presentation numerous examples for optical microstructures are given that range from the field of low cost fiberoptic components to polymer waveguide elements, from fiber switches to mass-producible microlenses made of thermoplastics or glass, and from microstructured photonic bandgap materials to optical sensor tips for investigating nanostructures. It is emphasized that for realizing MOEMS very different materials have to be processed while the necessary hybrid integration demands for specific automated assembly methods. In particular, the examples given show now microtechnologies can be adapted and combined with each other to take into account the special requirements of the product.