Fabrication and assembly technologies for high-speed board-to-board optical interconnect (B²OI) systems are presented. In the system architecture, the transmitters and receivers are placed on the linecards and the optical signals are routed to the optically passive backplane through the optical jumpers with MTP connectors. The backplane contains an optical layer with embedded polymer waveguides and 45° reflector micromirrors. The waveguides are fabricated by direct lithographic patterning and have propagation losses as low as 0.05 dB/cm at 850 nm. Hot-embossing is also evaluated for the waveguide fabrication demonstrating the waveguide propagation losses in the range of 0.06-0.1 dB/cm but rather poor channel-to-channel uniformity. The wedge dicing technology is developed for fabrication of the 45° reflector micromirrors with 0.5 dB losses. The pluggable optical connectors with microlens adaptors are used to couple the light from the optical jumpers into the backplane waveguides. The fabricated prototype optical interconnect modules with integrated channel waveguides, mirrors, and assembled connectors demonstrate insertion losses of 5-6 dB. The modules successfully pass high-speed transmission tests at data rates up to 11 Gb/s.

Deep UV-induced modification of the refractive index of polymers is a useful technique for low cost realization of integrated optical circuits for telecommunication und sensor applications. The combination with replication techniques like injection molding and hot embossing give the capability of a monolithic integration of these waveguide structures in optical or fluidic microsystems. In addition the hybrid integration of these integrated optofluidic microsystems with organic or inorganic photodiodes will open up the possibility to development novel, cheap, disposable integrated optical sensors for environmental, chemical and biological monitoring.

Laser ablation is presented as a versatile technology that can be used for the definition of arrays of multimode waveguides and coupling structures in a stacked two layer optical structure, integrated on a printed circuit board (PCB). The optical material, Truemode Backplane^TM Polymer, is fully compatible with standard PCB manufacturing and shows excellent ablation properties. A KrF excimer laser is used for the ablation of both waveguides and coupling structures into the optical layer. The stacking of individual optical layers containing waveguides, that guide the light in the plane of the optical layer, and coupling structures, that provide out-of-plane coupling and coupling between different optical layers, is very interesting since it allows us to increase the integration density and routing possibilities and limit the number of passive components that imply a certain loss. Experimental results are presented, and surface roughness and profile measurements are performed on the structured elements for further characterization. Numerical simulations are presented on the tolerance on the angle of the coupling structures and the influence of tapering on the coupling efficiency of the waveguides.

We present Deep Lithography with Protons (DLP) as a rapid prototyping technology to fabricate waveguide-based micro-optical components with monolithically integrated 45° micro-mirrors acting as out-of-plane couplers, splitting the optical signal in 3 separated paths. For the first time, two different proton beam sizes are used during one irradiation and a 20μm collimating aperture is chosen to accurately define the out-of-plane coupling structures. We fully optimized the DLP process for this 20μm proton beam and we measured the surface roughness (R_q=27.5nm) and the flatness (R_t=3.17μm) of the realized components. Finally, we experimentally measured the optical transmission efficiency of the micro-optical splitter component. The results are in excellent agreement with non-sequential ray-tracing simulations performed for the design. Above that, we present a pluggable out-of-plane coupler incorporating a single micro-mirror for the 90° coupling of light to or from polymer multimode waveguides integrated on a printed circuit board (PCB). This millimeter-sized mass-reproducible component can then be readily inserted into laser ablated cavities. Nonsequential ray-tracing simulations are performed to predict the optical performance of the component, showing coupling efficiencies up to 78%. These results are then experimentally verified using piezo-motorized positioning equipment with submicron accuracy in a multimode fiber-to-fiber coupling scheme, showing coupling efficiencies up to 56%. The fabricated coupling components are suitable for low-cost mass production since our micro-optical prototyping technology is compatible with standard replication techniques, such as hot embossing and injection molding, has been shown before.

The use of organic optoelectronic devices such as organic light-emitting diodes and organic photodiodes in micro-optical systems is discussed. Potential applications like optical interconnects and optical sensor systems are examined. Device characteristics including emission spectra, I-V-curves and the dynamic behaviour are analysed. In the combination with a polymeric optical fibre (POF) a transmission line comprising a organic light emitting diodes and organic photodiodes is demonstrated. An important step towards integration is realized by coupling the amplified spontaneous emission of an organic semiconductor material into a single-mode polymethylmethacrylate (PMMA) waveguide.

Optical interconnections integrated on a flexible substrate combine the advantages of optical data transmissions (high bandwidth, no electromagnetic disturbance and low power consumption) and those of flexible substrates (compact, ease of assembly...). Especially the flexible character of the substrates can significantly lower the assembly cost and leads to more compact modules. Especially in automotive-, avionic-, biomedical and sensing applications there is a great potential for these flexible optical interconnections because of the increasing data-rates, increasing use of optical sensors and requirement for smaller size and weight. The research concentrates on the integration of commercially available polymer optical layers (Truemode Backplane^TM Polymer, Ormocer®) on a flexible Polyimide film, the fabrication of waveguides and out-of plane deflecting 45° mirrors, the characterization of the optical losses due to the bending of the substrate, and the fabrication of a proof-of-principal demonstrator. The resulting optical structures should be compatible with the standard fabrication of flexible printed circuit boards.

We present a fabrication technology for integrating polymer waveguides and 45° micromirror couplers into standard electrical printed circuit boards (PCBs). The most critical point that is being addressed is the low-cost manufacturing and the compatibility with current PCB production. The latter refers to the processes as well as material compatibility. In the fist part the waveguide fabrication technology is discussed, both photo lithography and laser ablation are proposed. It is shown that a frequency tripled Nd-YAG laser (355 nm) offers a lot of potential for defining single mode interconnections. Emphasis is on multimode waveguides, defined by KrF excimer laser (248 nm) ablation using acrylate polymers. The first conclusion out of loss spectrum measurements is a 'yellowing effect' of laser ablated waveguides, leading to an increased loss at shorter wavelengths. The second important conclusion is a potential low loss at a wavelength of 850 nm, 980 nm and 1310 nm. This is verified at 850 nm by cut-back measurements on 10-cm-long waveguides showing an average propagation loss of 0.13 dB/cm. Photo lithographically defined waveguides using inorganic-organic hybrid polymers show an attenuation loss of 0.15 dB/cm at 850 nm. The generation of debris and the presence of microstructures are two main concerns for KrF excimer laser ablation of hybrid polymers. In the second part a process for embedding metal coated 45° micromirrors in optical waveguiding layers is described. Mirrors are selectively metallized using a lift-off process. Filling up the angled via without the presence of air bubbles and providing a flat surface above the mirror is only possible by enhancing the cladding deposition process with ultrasound agitation. Initial loss measurements indicate an excess mirror loss of 1.5 dB.

The use of conventional fabrication techniques for the fabrication of polymer based photonic integrated waveguide circuits is a necessary step to reduce costs. The replication of rib waveguides is presented using nickel shims. Results of replicated waveguides and 1 x 2 multimode interference (MMI) couplers are shown.

Laser beam soldering as a longterm and temperature stable joining alternative to adhesive bonding for optoelectronical systems is introduced. Using a solder alloy that can be processed fluxless (e.g. 80Au20Sn) more functionality than pure position securing, for instance electrical connections and heat sinks for laseroptics, can be incorporated into the joint. Along with smart system platforms, made from ceramics and composites, providing the right interfaces for such functional joints a dense integration of optical and heat generating electrooptical components becomes possible.

The design and fabrication of a demonstration kit (EduKit) for secondary school students is described. We present the final iteration of the layout of the EduKit and outline some of the simple experiments which the kit is intended to show. The mass replication techniques used in the production of this project are described and the final educational outcomes of the project are discussed.

Fill-factor of microlens arrays (MLAs) is one of the most important performance criteria of microlens arrays (MLA), especially in imaging applications. Low fill-factor lenses suffer greatly from spurious light and diffraction affects and result in low contrast in a beam steering system. Contrast ratio of low fill-factor circular shaped microlens arrays is nearly one-fourth of that of the system with high fill-factor square shaped microlens arrays. In this study performance of various types of nearly 100% fill-factor spherical MLAs in beam steering applications are compared. Design and fabrication of the MLAs are studied. A new hybrid method for design and fabrication of 100% fill-factor MLAs--by combining refractive-diffractive lenses, is suggested and tested.

We present a genetic algorithm with small population sizes for the design of diffraction gratings in the rigorous domain. A general crossover and mutation scheme is defined, forming fifteen offspring from 3 parents, which enables the algorithm to be used for designing gratings with diverse optical properties by careful definition of the merit function. The initial parents are randomly selected and the parents of the subsequent generations are selected by survival of the fittest. The performance of the algorithm is demonstrated by designing diffraction gratings with specific application to high power laser beam lines. Gratings are designed that act as beam deflectors, polarisers, polarising beam splitters, harmonic separation gratings and pulse compression gratings. By imposing fabrication constraints within the design process, we determine which of these elements have true potential for application within high power laser beam lines.

As the use of DOEs has become ever more popular, there has been a concurrent increase in the development of the design algorithms used to optimise their phase profiles. The earliest design methods claimed efficiencies of around 75% and an image spot intensity variation of ±15%. Methods used today can give efficiency percentages in the high 90s and non-uniformities below 2%. As developments made in the design algorithms continue it increasingly becomes the case that the major factor contributing to losses in efficiency and increases in non-uniformity are not the ability of the algorithm to optimise the phase profile but the errors introduced by the fabrication process. In this paper we simulate the effects of misalignment and feature rounding on the quality of the output intensity of 7 different fan-out gratings. From these simulations we observe that the affect of misalignment on efficiency is generally greater for masks with deeper etches, although the extent of the drop in efficiency can be influenced by the direction of misalignment. Nonuniformity is less consistently affected, in some cases the π level is dominant, in others it is the π/2 level and there is often strong asymmetry between negative and positive misalignment. Study of feature rounding produces results which, as one might expect, indicate levels with deeper etches have a greater influence on the drop in efficiency and increased non-uniformity.

We present a fine-grain parallel processor architecture which considers particularly the requirements defined by future 3-dimensional (3D) stacked optoelectronic devices. The architecture concept is well-suited for novel detector arrays which are exploited in data communication applications based on high-speed VCSEL photonic interconnects as well as for optical sensing applications in smart CMOS camera chips. We assume the presence of a two-dimensional optoelectronic interface mounted on top of the stacked device. Such a vertical communication scheme is perfect for the realization of very compact and fast working devices in embedded systems, e.g. in gripper arms of robots.

A series of electronic models, both analog and digital, have been developed to simulate the behaviour of a field programmable gate array chip with optoelectronics providing access to an optical interconnect fabric. The minimum latency of a 320Mbits^-1 system was found to be 158.5ns.

Nowadays, multiprocessor systems are reaching their limits due to the large interconnection bottleneck between chips, but recent advances in the development of optical interconnect technologies can allow the use of low cost, scalable and reconfigurable networks to resolve the problem. In this paper, we make an initial evaluation of the performance gain on general network reconfigurability. In a next stage, we propose an optical system concept and describe a passive optical broadcasting component to be used as the key element in a broadcast-and-select reconfigurable network. We also discuss the available opto-electronic components and the restrictions they impose on network performance. Through detailed simulations of benchmark executions, we show that the proposed system architecture can provide a significant speedup for shared-memory machines, even when taking into account the limitations imposed by the opto-electronics and the presented optical broadcast component.

This paper presents results of our work on the design, fabrication ad integration of a generic form of optical printed circuit boards (O-PCBs) by lamination of an optical layer board and an electrical layer board. This is a part of our ongoing work on the micro/nano-scale design, fabrication and integration of optical waveguide arrays and devices for optical printed circuit board (O-PCBs) and VLSI micro/nano-photonic integrated circuit application. The optical layer consists of planar optical integrated circuits and arrays of waveguides and photonic devices of various dimensions and characteristics to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards. The electrical layer consists of electrical wires and circuits of various functions to drive the light sources, photondetectors, modulators, and others to assist the optical functions. We use lamination technique to assemble the two layers to form an O-PCB. The advantages of lamination include the processing simplification, cost reduction, fabrication of compact devices, and the reduction of alignment problem among others. VLSI micro/nano-photonic integrated circuits can be realized by using photonic crystals and plasmonic structures to perform the optical functions on a chip scale. We describe design approaches to generic and application specific O-PCBs and lamination process as a way of integrating and assembling an optical printed circuit board as a platform for VLSI photonic chip.

The use of standard telecommunication components for optical communication over very short ranges (<2 m) on and between printed circuit boards (PCB) is restricted due to their comparatively large dimensions and high price. For this reason efforts are made to reduce the size of the electrooptic and optoelectronic converters and to integrate optical waveguides into the board like common PCB tracks. In this paper we present a novel board level optical interconnect, based on standard multimode glass fibers, which are embedded into a multilayer PCB. The fibers are accessed through cavities inside the PCB by novel optoelectronic coupling elements. These elements combine laser- or photodiodes with coupling structures to achieve as a new feature a solely passive alignment. The objective is the automatic mounting of the components with common pick-and-place systems.

A packaged high speed reflective electroabsorption transceivers for radio-over-fiber applications is demonstrated. The transceiver, an AFPMD (Asymmetric vertically addressed Fabry-Perot Modulator/Detector), is successfully packaged into a standard module, originally intended for 10 Gbit/s Ethernet detectors. The packaging process and the electrical, optical and thermal performance of the packaged component are presented. A bandwidth of 6 GHz, a total reflective optical coupling loss of 7.1 dB and a responsitivity of 0.14 mA/mW are accomplished. By optimizing the operation optical wavelength and bias voltage, fifth-order nonlinearity dominates the intermodulation distortion and a spurious free dynamic range (SFDR) of 101dB^.Hz^4/5 at 5.554GHz can be achieved experimentally.

A hermetic fibre pigtailed laser module utilizing passive device alignment on a low temperature co-fired ceramics (LTCC) substrate is demonstrated. The 3-dimensional shape of the laminated and fired ceramic substrate provides the necessary alignment structures including holes, grooves and cavities for the laser to fibre coupling. The achieved passive alignment accuracy allows high coupling efficiency realizations of multi-mode fibre pigtailed laser modules. The ceramic substrate is intrinsically hermetic and it opens up a possibility to produce cost efficient hermetic packaging. In our concept hermetic sealing is produced by utilizing Kovar frame, which is soldered to an LTCC substrate. Kovar frame has a hole for fibre feed-trough and a hermetic glass-metal sealing between fibre and frame is processed using glass preform. The heart of the module is a power laser diode chip, which can produce several watts of continuous power. The module, however, can be finally used as a transmitter in a laser pulse time-of-flight distance sensor and in this application it can be overdriven by a factor of 10. This means that the peak optical power in the pulses can be several tens of watts. The laser chip allows this kind of overdriving due to the fact that the duty factor in the operation is only 0.0001 at 2 kHz pulsing frequency. Optical coupling efficiency of the multi-mode laser system was simulated using optical systems simulation software. The nominal coupling efficiency between 210 μm x 1μm stripe laser and 200/220 μm step index fibre (NA=0.22) was 0.65. The simulated coupling efficiency was verified by prototype realization and characterization. The measured average coupling efficiency of the hermetically sealed prototypes was 0.39. The coupling efficiencies of prototypes varied from 0.14 to 0.64. Leak rate of 1 x 10^-7 [atm x cm³/s] was measured in the helium leak tests for the final prototype module, when the module was tested according to MIL-STD-883D method 1014.9 specification. Leak rate for the module using a buffer stripper fibre without a rubber guard tube was 3 x 10^-9 [atm x cm³/s]. The background helium level before and after the tests was less than 3 x 10^-10 [atm x cm³/s]. This clearly higher leak rate in the final module leak measurement is mainly due to the absorbed helium to the fibre polymer buffer layer and rubber guard tube in the pressurization process. Measurements show that the implemented module is hermetic. Cost-of-ownership modelling was performed starting from low production volume up to production of 10 million good modules per year. Module production cost was estimated through COO modelling. Modelling forecasted that the module production can be lower than 10 EUR in high volume production.

Technologies to design and fabricate high-bit-rate chip-to-chip optical interconnects on printed wiring boards (PWB) are studied. The aim is to interconnect surface-mounted component packages or modules using board-embedded optical waveguides. In order to demonstrate the developed technologies, a parallel optical interconnect was integrated on a standard FR4-based PWB. It consists of 4-channel BGA-mounted transmitter and receiver modules as well as of four polymer multimode waveguides fabricated on top of the PWB using lithographic patterning. The transmitters and receivers built on low-temperature co-fired ceramic (LTCC) substrates include flip-chip mounted VCSEL or photodiode array and 4x10 Gb/s driver or receiver IC. Two microlens arrays and a surface-mounted micro-mirror enable optical coupling between the optoelectronic device and the waveguide array. The optical alignment is based on the marks and structures fabricated in both the LTCC and optical waveguide processes. The structures were optimized and studied by the use of optical tolerance analyses based on ray tracing. The characterized optical alignment tolerances are in the limits of the accuracy of the surface-mount technology.

In this paper we give an overview of the fabrication and assembly induced performance degradation of an intra-multi-chip-module free-space optical interconnect, integrating micro-lenses and a deflection prism above a dense opto-electronic chip. The proposed component is used to demonstrate the capabilities of an accurate micro-optical rapid prototype technique, namely the Deep Proton Writing (DPW). To evaluate the accuracy of DPW and to assess whether our assembly scheme will provide us with a reasonable process yield, we have built a simulation framework combining mechanical Monte Carlo analysis with optical simulations. Both the technological requirements to ensure a high process yield, and the specifications of our in-house DPW technology are discussed. Therefore, we first conduct a sensitivity analysis and we subsequently simulate the effect of combined errors using a Monte Carlo simulation. We are able to investigate the effect of a technology accuracy enhancement on the fabrication and assembly yield by scaling the standard deviation of the errors proportionally to each sensitivity interval. We estimate that 40% of the systems fabricated with DPW will show an optical transmission efficiency above -4.32 dB, which is -3 dB below the theoretical obtainable value. We also discuss our efforts to implement an opto-mechanical Monte Carlo simulator. It enables us to address specific issues not directly related with the micro-optical or DPW components, such as the influence of glueing layers and structures that allow for self-alignment, by combining mechanical tolerancing algorithms with optical simulation software. More in particular we determined that DPW provides ample accuracy to meet the requirements to obtain a high manufacturing yield. Finally, we shortly highlight the basic layout of a completed demonstrator. The adhesive bonding of opto-electronic devices in their package is subject to further improvement to enhance the tilt accuracy of the devices with respect to the optical interconnect modules.

We report on the design, fabrication and test results of monolithically integrated transceiver chips consisting of GaAs metal-semiconductor-metal photodiodes and 850nm wavelength vertical-cavity surface-emitting lasers. These chips are well suited for low-cost and compact bidirectional optical interconnection at Gbit/s data rates in mobile systems and industrial or home networks employing large core size multimode fibers.

D-Lightsys considers free space optical links for intermediate communication distances ranging from a few centimeters to one or two meters. In this paper, we present the initial simulations and the first experimental characterizations of a VCSEL-based point-to-point free space interconnect on distances ranging from 16cm to 40cm targeting bit rates up to 2.5Gbps.

The design of hybrid electro-optical systems needs to address the issue of signal integrity. In the area of electrical interconnects the input/output buffer information specification was introduced. To define a similar specification for optical interconnects an analytical model for vertical cavity surface emitting lasers is developed. It is based on the known solution of the Lotka-Volterra differential equations, which are related to the rate equations describing the behavior of lasers. The parameters of this analytical model directly describe the dynamic behavior of vertical cavity surface emitting lasers and they share many features with the input/output buffer information specification as they can be provided in a tabulated form and are partly accessible to measurement.

Very short range (VSR) high bit rate optical fiber communications are an emerging market dedicated to local area networks, digital displays or board to board interconnects within real time calculators. In this technology, a very fast way to exchange data with high noise immunity and low-cost is needed. Optical multimode graded index fibers are used here because they have electrical noise immunity and are easier to handle than monomode fibers. 850 nm VCSEL are used in VSR communications because of their low cost, direct on-wafer tests, and the possibility of manufacturing VCSEL arrays very easily compared to classical optical transceivers using edge-emitting laser diodes. Although much research has been carried out in temperature modeling on VCSEL emitters, few studies have been devoted to characterizations over a very broad range of temperatures. Nowadays, VCSEL VSR communications tend to be used in severe environments such as space, avionics and military equipments. Therefore, a simple way to characterize VCSEL emitters over a broad range of temperature is required. In this paper, we propose a complete characterization of the emitter part of 2.5 Gb/s opto-electrical transceiver modules operating from -40°C to +120°C using 850 nm VCSELs. Our method uses simple and semi-automatic measurements of a given set of chosen device parameters in order to make fast and efficient simulations.

In the context of optical interconnection applications, we report on results obtained on strained InGaAs quantum well Vertical Cavity Surface Emitting Lasers (VCSELs). Our devices are top p-type DBR oxide-confined VCSEL, grown by metalorganic vapour-phase epitaxy (MOVPE). These lasers exhibit low threshold currents and deliver up to 1.77 mW in continuous wave operation at room temperature. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm at room temperature is reached for a 4 μm oxide diameter VCSEL. The particular design of the active layer based on a large detuning between the gain maximum and the cavity resonance gives our devices a very specific thermal and modal behaviour. Therefore, we study the spectral and spatial distributions of the transverse modes by near field scanning optical microscopy using a micropolymer tip at the end of an optical fibre.

We present flip-chip attached high-speed VCSELs in 2-D arrays with record-high intra-cell packing densities. The advances of VCSEL array technology toward improved thermal performance and more efficient fabrication are reviewed, and the introduction of self-aligned features to these devices is pointed out. The structure of close-spaced wedge-shaped VCSELs is discussed and their static and dynamic characteristics are presented including an examination of the modal structure by near-field measurements. The lasers flip-chip bonded to a silicon-based test platform exhibit 3-dB and 10-dB bandwidths of 7.7 GHz and 9.8 GHz, respectively. Open 12.5 Gbit/s two-level eye patterns are demonstrated. We discuss the uses of high packing densities for the increase of the total amount of data throughput an array can deliver in the course of its life. One such approach is to provide up to two backup VCSELs per fiber channel that can extend the lifetimes of parallel transmitters through redundancy of light sources. Another is to increase the information density by using multiple VCSELs per 50 μm core diameter multimode fiber to generate more complex signals. A novel scheme using three butt-coupled VCSELs per fiber for the generation of four-level signals in the optical domain is proposed. First experiments are demonstrated using two VCSELs butt-coupled to the same standard glass fiber, each modulated with two-level signals to produce four-level signals at the photoreceiver. A four-level direct modulation of one VCSEL within a triple of devices produced first 20.6 Gbit/s (10.3 Gsymbols/s) four-level eyes, leaving two VCSELs as backup sources.

We present a new approach to achieve tunability on a 1.55 μm vertical cavity surface emitting laser (VCSEL). Tunability is achieved thanks to an electro-optic index modulator. This electro-optic material consists in a n-PDLC phase layer introduced inside the VCSEL cavity. N-PDLC comprises nematic liquid crystal dispersed in a polymer material. This first VCSEL exhibits a 10 nm tuning range and an excellent side-mode suppression ratio higher than 20 dB over the whole spectral range. The device is formed by a conventional InP-based active region with an epitaxial and a dielectric Bragg mirror. The n-PDLC layer length, close to 6 μm, is in agreement with a tunable laser emission without mode-hopping. Another decisive advantage, compared to mechanical solutions, is the tuning response time which is close to a few 10 μs to scan the full spectral range, making this device appropriate for some access network functions. Voltage values are the main limiting factor, 170 Volts have been required to obtain 10 nm tunability, but material engineering is in progress to improve this point. We presented a first version of the device optically pumped, the next version will be electrically pumped as required for access network applications targeted here.

High-performance vertical-cavity surface-emitting lasers (VCSELs) with an emission wavelength of approximately 764 nm are demonstrated. This wavelength is very attractive for oxygen sensing. Low threshold currents, high optical output power, single-mode operation, and stable polarization are obtained. Using the surface relief technique and in particular the grating relief technique, we have increased the single-mode output power to more than 2.5mW averaged over a large device quantity. The laser structure was grown by molecular beam epitaxy (MBE) on GaAs (100)-oriented substrates. The devices are entirely based on the AlGaAs mixed compound semiconductor material system. The growth process, the investigations of the epitaxial material together with the device fabrication and characterization are discussed in detail.

We present a new three dimensional, fully vectorial optical modeling of oxide confined as well as shallow relief vertical-cavity surface-emitting laser. Our model is based on the combination of the plane wave expansion method with the method of lines resulting in a fast and accurate computational technique. We carry out hereby a comparison between the Plane Wave Admittance Method (PWAM) and other numerical approaches for VCSEL optical modeling and show very good agreement. Furthermore, this procedure makes it possible to find optimal basic computational parameters for the PWAM in the case of VCSELs.

We numerically investigate how polarization properties of vertical cavity surface emitting lasers (VCSELs) are affected by optical feedback from an extremely short external cavity. In order to do it we use a two modes rate equation model that accounts for infinite round trips in the external cavity. With it we perform maps of bistability finding out a modulation of the polarization switching currents when increasing the external cavity length with a period equal to half the wavelength of operation of the device. When the external mirror reflectivity is high enough there is a region within each period of modulation where the VCSEL polarization is stable at any injected current within the operation range. Moreover, using polarized feedback the map of bistability is channelled and the bistable region is almost suppressed. A preliminar study of the effects of temperature variations on the map of bistability is also carried out and presents polarized feedback as a more robust technic to obtain polarization stabilization. An experimentally obtained map of bistability supports the model showing very good agreement with it.

We report on the design and the fabrication of refractive microlenses using a polymer droplet deposition microsystem. The principle of this original technique consists in monomer droplets deposition using a robotized silicon-microcantilevers array. The advantages of this technique rely on the control of droplets dimensions and the positioning accuracy. Microlenses have been first modelled to optimize their geometrical parameters for VCSEL collimation. Results of lens optimization as well as the influence of the fabrication parameters fluctuations on the final divergence are detailed. First results on droplets deposition are presented, demonstrating the technique feasibility. Finally, the possibility of the modification of the surface energy to obtain the most suited contact angle before deposition is also discussed.

In this paper we present the fabrication of optical mode field adaptors at the end of single mode and multimode optical fibers, which act as a micro lens, for fiber optical communications devices, capable up to 40Gbit/s data. The mode field adaptors were used to focus the optical output field (1550nm wavelength) of the fiber to receiver and transmitter OEICs. Based on the measurement of a singlemode fiber in accordance with ITU Recommendation G.652 the optical mode fields are measured in a new set-up, which is demonstrated and discussed in comparison to conventional methods. The work was performed in cooperation with the Heinrich-Hertz-Institute in Berlin.

This paper describes a modification of the standard MIMIC technology, solving its main drawbacks, to define arrays of spherical or ellipsoidal microlenses. Perfectly symmetrical meniscuses have been obtained by using a XP SU-8 NO-2 layer beneath the PDMS mold. Moreover, the photostructurable properties of this polymer allow obtaining self-alignment structures for adequate fiber optics positioning. Microchannels ended with these meniscuses have been filled with standard SU-8 to obtain 3D microlenses. Agreement between theory and experimental results allows confirming the validity of the proposed technology.

We design two different types of lens-based fibre connectors and perform a tolerance study on these connectors through optical simulations. Next, we assemble these connectors and we measure experimentally the coupling efficiency. To obtain a better agreement between the experimental results and the results from the simulations, we measure the exact surface profiles of the micro-lenses and implement these real surface profiles in the simulation models. Finally, we repeat the tolerance analysis using the real lens surface profiles in the simulation.

The optical properties of plano-convex refractive microlenses with low Fresnel Number (Typically FN < 10) are investigated. Diffraction effects at the lens stop limit the range of the effective focal length. The upper limit of the focal length is determined by the diffraction pattern of a pinhole with equal diameter. Refraction and diffraction have antagonist effects on the focal length when changing the wavelength of illumination. Diffraction effects at the lens stop are used to balance dispersion and to design microlens achromats. Gaussian beam propagation method has been used for simulation. The presented results are of relevance for applications like Shack Hartmann wavefront sensors or confocal microscopes, where microlenses with small apertures and long focal lengths are widely used.

The correspondence between the linear integral transform and the ray-transfer matrix of a diffraction-free first-order optical system is used to describe the ray trajectory and to study the point spread function (PSF) in an active GRIN microlens characterized by a complex refractive index. The results show that the active microlens is regarded as a lossless microlens with a Gaussian mask induced by the complex refractive index. Comparison between light propagation effects in passive and active GRIN microlens is outlined.

A novel rectangular shape microlens array having high sag for solid-state lighting is presented. Suggested microlens array which have high sag is realized using photoresist reflow and replication technique. Applying to the light-emitting-diode (LED) packaging, the rectangular shape of proposed microlens can maximize the fill factor of silicon based LED packaging and minimize the optical loss through the reduction of unnecessary reflection at the same time. Microlens, which has high sag, over 375 μm and large diameter, over 3 mm can enormously enhance output optical extraction efficiency. Moreover wafer level packaging technology is used to improve the aligning accuracy and mass production of LED packaging. This wafer level microlens array can be directly fabricated on LED packaging using replication method. It has many advantages in optical properties, low cost, high aligning accuracy, and mass production. Therefore wafer level LED packaging method adopts high sag rectangular microlens array demonstrates only improved optical performance but also mass production capability.

With our in-house technology, Deep Proton Writing (DPW) we fabricate, apart from other components, spherical refractive microlenses. Till now, the fabrication of cylindrical microlenses was an unexplored field within our technology. In this paper we will show how we can use Deep Proton Writing as an effective technology for the fabrication of cylindrical microlenses and microlens arrays with specific design parameters. We will explain the adjustments we made to our standard fabrication process as well as the investigation procedure we followed to fulfill our goal.

A fast 2x2 free-space photonic switch based on ferroelectric liquid crystal (FLC) is demonstrated with switching times of order of microseconds. An examination of the insertion loss and crosstalk properties of the switch reveals an average loss and crosstalk of < 0.45 dB and -33 dB, respectively. Such low-loss and low-crosstalk properties indicate that the switch is suitable for a larger-scale matrix switch design. We discuss incorporation of the demonstrated switch into a multistage network configuration and the properties of optical components required for achieving up to 1000 channel matrix switches.

Different methods of fabrication of micro-optical devices for the Infra-Red (I.R.) such as micro-lens, micro-prism, micro-mirror arrays and Fresnel lenses based on the use of chalcogenide photoresists are described. In chalcogenide photoresists, two photoinduced phenomena are observed: photoinduced structural transformations and photoinduced diffusion of some metals, primarily, silver, and both phenomena enabled the development of new types of I.R micro-optical devices. The use of a new three-component As-S-Se photoresist and a new efficient amine-based selective developer allows for the realization of soft contrast characteristics of the photolithographic process with a Xe-source of light. Recent progress in the development of devices using photostructural transformations based on these two innovations will be described. Devices using the photoinduced silver diffusion are based on the different dissolution rate (in selective etchants) of the non-doped and silver-doped chalcogenide films. Parameters and characteristics of several micro-optical devices made using this effect are compared and discussed.

We have approximated with second-order polynomials the frequency tuning curves of long-wavelength single-mode VCSELs operating near 1654 and 1512 nm. Fitting coefficients were calculated using experimental data on injection currents and heat sink temperatures required to tune lasers to frequency markers generated by gas absorption lines. To measure temperature tuning rates, we tuned the lasers by temperature sequentially to pairs of absorption lines with known frequency separations. To determine fitting coefficients associated with linear and non-linear frequency tuning, we varied the laser injection currents and temperatures simultaneously in such a way that made a laser emit exactly the same frequency. Linear and non-linear tuning coefficients were then calculated from the data on effects of relatively small and large variation of laser operation parameters on laser frequency. Lasers were calibrated by tuning them on narrow absorption lines with frequencies accurately known from previous studies. The simulated tuning curves were demonstrated to fit frequency markers generated over spectral intervals up to 40 cm^-1 with an accuracy of ± 0.10 cm^-1(1654-nm laser) and ± 0.15 cm^-1 (1512-nm laser). A temperature dependence of injection current tuning rates of the 1654-nm laser was determined from the best fits of simulated tuning curves to a series of CO₂ absorption lines in the whole operation temperature range of the laser (0 - 50 °C). A simple and accurate method developed to describe tuning properties of long-wavelength VCSELs can be applied to quantitatively characterize any narrow-linewidth tunable laser.

We present the laser backwriting process on glass by laser ablation of metal targets, in order to fabricate waveguides on pyrex glasses. An horizontal position of the sample and the plate was found suitable to improve the effect of the plume in the sample with respect to the alternative vertical arrangement. We have analysed the longitudinal and transversal profiles, using a profilometer and have compared the results for the different laser sources used, speeds and metal targets. We have analyzed the refractive index profile of the samples obtained, in order to evaluate the change in the substrate due to the metal ablation. A cleaning of the surface and a heat treatment of the glass has been made in order to improve the results.

In this paper we describe the direct laser writing of complex structures in a multifunctional acrylate polymer system using fan-out and grey-scale diffractive optical elements (DOE). The effective writing speed of waveguides was successfully increased using a fan-out DOE element. The DOEs to produce greyscale outputs (such as an intensity ramp) and other complex outputs (such as Heriot-Watt University logo) were used to fabricate greyscale and complex structures in polymer. Quantitative fabrication results of these structures are presented in this paper.

This work concerns the fabrication, optical characterization and potential applications of two types of microstructures manufactured in congruent lithium niobate. The first type consists of a simple 2D hexagonal lattice of inverted ferroelectric domains fabricated by standard electric field poling at room temperature. The second structure is the chemically etched version of the first one. Long etching in hot HF acid results in differential etching of opposite ferroelectric domain faces. In this way obtain a 3D structure is obtained in which the hexagonal domain array becomes an array of truncated pyramids. Both these structures are characterized through a digital interferometric analysis. The samples are inserted in the arm of a Mach-Zenhder interferometer and the digital holograms acquired are used to numerically reconstruct both the amplitude and the phase of the wavefront transmitted by the sample. Finally, we report on the possible applications of the fabricated structures. The hexagonally poled structure can be used as a variable binary phase array. In fact both sides of the poled sample are covered with a thin conductive layer (ITO), which acts as transparent electrode. By applying an external electric field it is possible to change the difference between the two phase levels, via the linear electro-optic effect, and, consequently, the distribution of light intensity in the diffracted orders. On the other hand, the 3D structured etched sample can be used as an micrometer size integral imaging system.

In this paper, laser ablation (at UGent), deep proton writing (at VUB) and laser direct writing (at HWU) are presented as versatile technologies that can be used for the fabrication of coupling structures for optical interconnections integrated on a printed circuit board (PCB). The optical layer, a highly cross-linked acrylate based polymer, is applied on an FR4 substrate. Both laser ablation and laser direct writing are used for the definition of arrays of multimode optical waveguides, which guide the light in the plane of the optical layer. In order to couple light vertically in/out of the plane of the optical waveguides, coupling structures have to be integrated into the optical layer. Out-of-plane turning mirrors, that deflect the light beam over 90°, are used for this purpose. The surface roughness and angle of three mirror configurations are evaluated: a laser ablated one that is integrated into the optical waveguide, a laser direct written one that is also directly written onto the waveguide and a DPW insert that is plugged into a cavity into the waveguiding layer.

The device presented in this paper is designed for coupling a free space optical wave under quasi-normal incidence in and out of a highly multimode waveguide with high efficiency. It uses two resonant diffraction gratings at the substrate-waveguide interface that are made of a shallow metal grating, covered with a high refractive index layer. It is shown that the resonant structure can theoretically diffract up to 90% of the incident energy in and out of the waveguiding layer. The geometrical parameters of the structure and the tolerances can easily be achieved by conventional technology means.

There are several technologies for cheap mass fabrication of microelements. One of them is deep proton lithography, used for the fabrication of elements of high structural depth. In this technology, accelerated protons are usually focused or formed by a mask to light a target. The energy of the proton beam is enough for all the protons to get through the target, losing only a part of their kinesthetic energy. Protons leaving the target are counted in various ways, thanks to which it is possible to estimate the energy deposed inside the target. In the next step chemical development is used to get rid of the radiated part of the target. With the use of this method, various 2D microelements can be obtained and the proton beam plays the role of a knife, cutting out the required shapes from the material. However, in order to make elements of modified surface (2.5D surface) it is necessary to change the energy of the proton beam or to change the dose deposed inside the material. The current article presents a proposal of creating simple 2.5D structures with the use of the method modifying the deposed does. This entails the modification of the deep proton lithography setup, which results moving the part for measuring the deposed dose of energy before the target. Additionally, the new deep proton lithography setup operates in the air. This article presents the results of simulations, as well as experimental results for such a setup built for the tandem accelerator in Erlangen, Germany.