U-L-M photonics GmbH has been set up to develop next-generation vertical-cavity surface-emitting laser (VCSEL) products and to exploit the full potential of these industry-leading devices in terms of performance and application areas. Reliability is important for all application areas for VCSELs. This paper presents the excellent reliability characteristics of U-L-M’s VCSEL technology. Accumulation of all advantageous properties VCSELs are famous for, like low power consumption, circular low divergent beam profile, high modulation bandwidth, and scalability of monolithic arrangements, results in two-dimensional (2D) VCSEL arrays that appear as key components to reach highest aggregate bandwidths of tomorrow’s parallel optical transceivers. We report on 2D VCSEL arrays, substrate emitting although operating at 850 nm and prepared for flip-chip bonding, that are well suited for the customer’s needs in terms of speed, power consumption, and compact integration. Up to now, in most single channel transceivers, the VCSEL is packaged in a TO can and connected to the driver via a printed circuit board. We investigate the performance of a high speed VCSEL in a TO 46 package and demonstrate 10 Gbps transmission. The potential of VCSEL technology in other areas of application than datacom or telecom is just going to be exploited. We present a 760 nm single-mode VCSELs for gas monitoring applications.

Parallel optical interconnects based on vertical-cavity surface-emitting lasers are being widely deployed today in switching and routing systems. Almost all of the major OEMs today are using parallel optics in their flagship products to solve interconnect problems where they are most relevant: at the bay-to-bay, shelf-to-shelf, and card-to-card levels. The density and capacity of these systems are already being constrained by the capacity of these one-dimensional links. We expect that next generations of systems will need high-density 2D parallelinks to further improve the performance-cost metric. Ultimately, we believe this metric can be optimized by directly integrating interconnect together with data processing and switching circuitry.

High data-rate communication links are placing increasing demands on the performance and cost of semiconductor-laser diodes. Vertical-cavity surface-emitting lasers (VCSELs) are ideal light sources for 10 Gbit/s applications. At Avalon Photonics Ltd., high-performance multimode VCSELs and VCSEL arrays are developed and fabricated for applications in low-cost fiber-optic communication links. An overview of static and dynamic characteristics of oxide-confined 850 nm VCSELs with data rates of 10 Gbit/s is presented. These 10 Gbit/s VCSELs are developed for the next generation 10 Gigabit Ethernet standard. Results show low threshold, high temperature operation, high modulation efficiency, short rise and fall times, and well-open eye-diagrams at different temperatures. Transmission over 600 m high-bandwidth multimode fiber at 10 Gbit/s is demonstrated. Mainly due to their low noise level and high linearity, these state-of-the-art devices are also well suited for transparent fiber-optic links using subcarrier multiplexed modulation schemes. Spurious-free dynamic ranges greater than 100 dBHz2/3 are reported.

In this paper, a novel way for the fabrication of opto-electronic transceiver modules is proposed. These modules are characterized by the use of MT-RJ connectors, low-cost fabrication tools, highly efficient opto-electronic components such as VCSELs and CMOS integrated detectors, and an easy fabrication scheme. The module is based on the direct alignment technique; this means that the fiber and the photon detector and laser diode are self and directly aligned with respect to each other, without the need for optical lenses. Cost are expected to be low, since the transceiver module can be fabricated using existing mass volume fabrication technqiues.

Here we present an optical transceiver concept for a reflective star bus system, showing favorable properties in respect to coupling efficiency and packaging. It is based on a hot embossed polymer substrate with two integrated micro-mirrors and a waveguide. On top of the substrate, above the mirrors, a vertical-cavity surface-emitting laser diode (VCSEL) and a photodiode chip are mounted with a flip-chip technique. At the end face of the waveguide a Polymer Clad Silica (PCS) fiber with a core diameter of 200 μm is attached in a groove. Thus an easy assembly of the individual components and a compact package is achieved. To evaluate and optimize the efficiency of the transceiver module we performed extended ray tracing calculations. Included are coupling efficiency between fiber and planar waveguide as well as coupling efficiencies between VCSEL and waveguide and between waveguide and photodiode, respectively. For a realistic estimation we took the transverse mode emission behavior of VCSELs at different supply currents and temperatures into account. Therefore we measured far-fields of VCSEL chips mounted on a heat sink for temperatures up to 85 °C and included the results in the simulations. The calculations indicate that the temperature dependant output power of the VCSEL is partly compensated by the variation in coupling efficiency. Measured VCSEL to fiber coupling efficiencies of about 60 % and out-coupling efficiencies to the photodiode of 70 % are achieved, in good agreement with calculations. Therefore our compact and low-cost concept shows at least 2 dB lower insertion losses compared to conventional 3 dB coupler solutions.

Robust, high speed optical data bus systems are increasingly required in automobiles, not only for entertainment applications within the passenger compartment but also for engine management systems and safety sensor networks. Optoelectronic components and modules intended to be used in cars have to withstand harsh environmental conditions, e.g. they have to be operational within a wide temperature range of up to - 55 °C to +1 25 °C for several thousand hours and at the same time they have to be of very low-cost. In this paper we describe a 500 MBit/s transmitter module based on a commercial available 850 nm vertical-cavity surface-emitting laser and a bias-T driving circuit. The optical output power of the module varies only by -0.5 dBm ± 1dB in the required temperature range without active temperature control. In addition we describe a packaging solution for the VCSEL transmitters allowing the operation of the module even in an extreme engine compartment environment, where short term temperature peaks above 125 °C appear.

We present an experimental and rate-equation based theoretical study of the current-driven polarization modulation properties of VCSELs. In some VCSELs abrupt polarization switching (PS) between two polarization modes is observed at a particular value of the pump current. We investigate the dynamics and the associated dominating time scales of PS as these features are strongly linked with the underlying physical mechanism causing the PS. To this end we measure both for gain- and index-guided VCSELs the critical modulation amplitude necessary to steadily force PS back and forth across the PS point as a function of the modulation frequency. This yields the current-driven polarization modulation frequency response, which we compare with the thermal frequency response of the studied devices. The dynamic behavior turns out to be strikingly different for the different VCSEL types. Thermal effects only play a minor role in the PS in our index-guided VCSELs, while they really seem to lie at the origin of PS in the gain-guided VCSELs. By implementing this in a rate-equation based theoretical model of the current-driven polarization modulation properties of VCSELs we are able to explain the peculiarities of the measured response curves and to reproduce the experimental findings.

We have investigated the potential of asymmetric current injection for polarization switching in GaAs-based intra-cavity contacted vertical cavity surface emitting lasers using two sets of p- and n-contacts per device. We simulated the current paths in both symmetric and asymmetric contacted devices. A large lateral current component is present in the asymmetric case; this induces a certain anisotropy in comparison to the symmetric case, possibly able to stabilize the polarization in one direction. Intra-cavity devices are processed on a standard air-post VCSEL wafer. When using the contacts set along the [1-10] direction, the polarization was set along [110] while using the contacts along [110] the polarization switches from the direction along [110] to a direction making an angle of 25° to 90° towards [110]. This peculiar result can be explained by the fact that the used VCSEL structure is not designed for intra-cavity contacting.

The polarization dynamics of vertical-cavity surface-emitting lasers operating close to threshold is investigated experimentally. For free-running devices a characterization of the dynamics is given for a scenario when two modes are excited at threshold due to a small net gain anisotropy. The polarization dynamics in this regime are found to be governed by the relaxation oscillations and to exhibit an anticorrelation of the two modes. The level of anticorrelation is strongly depending on the injection current. If isotropic feedback by a distant reflector is added, the dynamics are governed by the external cavity round-trip time scale and low frequency fluctuations are observed for both modes. These are shown to occur also for large net gain anisotropy, but without excitation of polarization degrees of freedom.

We report on new dynamics in vertical-cavity surface-emitting lasers (VCSELs), which is induced by a polarization preserving optical feedback. Our solitary VCSEL, i.e. without feedback, emits in a single linearly polarized (LP) and fundamental transverse mode. Optical feedback induces multiple polarization switchings in the L-I curve. When the injection current is set close to one of the multiple polarization switching points, the laser system exhibits a random anticorrelated hopping of the two orthogonal LP fundamental modes. Of particular interest is the observation of antiphase oscillations in the two LP modes that occur with a period corresponding to the delay time, and which complement the slow mode-hopping. Moreover, the LP-resolved optical spectra show random frequency hops between ECMs. The laser system is therefore not only bistable between the LP modes, but also multistable between ECMs. A theoretical rate equation approach yields a good qualitative agreement with our experiment. We report similar delay-periodic oscillations complementing a mode hopping in a scalar delay differential equation modeling the motion of a particle in a double well potential. Such a model was recently investigated by Tsimring and Pikovsky, in a very general context. Our results in VCSELs yield the first experimental evidence of delay-periodic oscillations in a bistable physical system with noise, and are therefore thought to be of general interest for many other processes in biology, medicine, etc. that exhibit interaction of noise, delay and bistability.

We present an experimental study of a Vertical-Cavity Surface-Emitting laser with polarized optical feedback. The system displays single-mode Low Frequency Fluctuations (LFF) for a wide range of pump current. Above the solitary laser threshold we observe a new kind of couple-mode dynamics with a leading LFF behavior in one polarization and an induced pulsed emission in the orthogonal one.

Vertical cavity surface emitting lasers (VCSEL) exhibit self-pulsations in the polarization-resolved light output at certain bias currents, where the dominant polarization direction suffers a transition from one direction to its orthogonal direction. This pulsation in the polarization resolved output could be controlled by an external optical injection in a master-slave configuration with VCSEL used as slave laser. Experimentally it has been demonstrated that the stabilization linear polarization directions preferred in the solitary VCSEL. The exact frequency of the optical injection to effect stabilization is dependent on the injection power and polarization.

A nearly single mode vertical cavity surface emitting laser (VCSEL) subject to optical injection have been investigated experimentally. It is found that regions of polarization-resolved chaotic behavior exist for both positive and negative detuning from the stable injection locking regime. Outside the chaos regimes, several nonlinear dynamical phenomena including frequency pushing, nearly degenerate four-wave mixing, injection locking, limit cycle and period doubling, were also observed.

We compare GaInNAs and highly strained InGaAs quantum-wells (QWs) for applications in metal-organic vapor-phase epitaxy (MOVPE)-grown GaAs-based 1300-nm vertical-cavity lasers (VCLs). While the peak wavelength of InGaAs QWs can be extended by a small fraction of N, the luminescence efficiency degrades strongly with wavelength. On the other hand, using highly strained InGaAs QWs in combination with a large VCL detuning it is also possible to push the emission wavelength towards 1.3 μm. The optimized MOVPE growth conditions for such QW and VCL structures are discussed in some detail. It is noted that GaInNAs and InGaAs QWs preferably are grown at low temperature, but with quite different V/III ratios and growth rates. We also point out the importance of reduced doping concentration and growth temperature of the n-doped bottom DBR to minimize optical loss and for compatibility with GaInNAs QWs. InGaAs VCLs with emission wavelength beyond 1260 nm is demonstrated. This includes mW-range output power, mA-range threshold current and 10 Gb/s data transmission.

Long wavelength vertical cavity surface emitting lasers (VCSELs) are ideally suited for applications in Metro networks which are currently dominated by 1.3 μm distributed feedback (DFB) and 1.3 μm Fabry-Perot laser diodes. 1.3 μm GaInNAs/AlGaAs VCSELs have been first to satisfy requirements of OC-48 standards and can also play a role in the 10Gb/E technology for medium reach transmission. The high temperature performance of 1.5 μm VCSELs still needs to be improved before challenging the positions of 1.5 μm un-cooled DFB lasers. With the introduction of agile, reconfigurable WDM systems, tunable optically pumped 1.5 μm VCSELs may have a considerable play in Metro networks.

We have derived and implemented a simplified dynamical multi-mode model for vertical-cavity surface-emitting lasers (VCSELs) requiring minimal computing resources while remaining realistic. A set of spatially independent rate equations with a minimum of parameters is extracted from the general spatially resolved equations and reduced to dimensionless form to expose its essentials. The shape of the carrier density distribution is approximated with a linear sum of the modal shapes which are considered to be bias independent for index-guided devices. Despite this simplification the model, which can be extended to any number of laser modes, includes important effects like spatial hole burning (SHB), carrier diffusion and inhomogeneous injection and shows good agreement with spatially resolved models. We describe the reduction and nondimensionalization of the general spatially resolved equations. The implementation inside a C++ rate-equation framework is discussed and shown to provide a powerful and flexible environment to efficiently study the contribution of different factors. The effect of spatial hole burning (SHB) and mode competition on the small signal modulation response is investigated in three basic cases. The comparison between a single mode VCSEL without SHB, a single mode VCSEL including SHB and two mode VCSEL including SHB enables us to pinpoint which contributions are due to SHB and which are due to the modal competition. Finally,the possibility of using this approach to model polarization switching in VCSELs is discussed. The unavoidable small birefringence (with elasto-optic and electro-optic contributions) present in all VCSELs leads to a doubling of each mode into two orthogonal polarization states which are almost degenerate. Although small, the birefringence causes gain differences: part of which are due to frequency dependent gain and loss of the materials and part of which are due to slightly different transverse modal shapes. As these gain differences depend on the injected current, they can be one of the causes of polarization switching.

Relative intensity noise spectra of weakly index guided VCSELs in a multi--transverse mode regime are analytically obtained. Analytical expressions incorporate the spatial dependence of electrical field and carrier density profiles. Expressions are derived for single and two-mode operation. We show that single-mode noise spectrum depends on the spatial mode profile through a modal effective volume. Two-mode noise spectra also incorporate the dependence on the degree of spatial overlapping between the modes. Two resonance peaks appear in the noise spectra of the individual modes and total power of the two-mode VCSEL. We analytically show that those peaks appear at frequencies that correspond to the relaxation oscillation frequencies of the multimode laser.

We present a detailed study of oxide-confined, vertical-cavity surface-emitting lasers (VCSELs), where the reflectivity of the top mirror has been patterned by means of a metal grid, which at the same time acts also as an electrode. Owing to their features, these kind of devices are commonly referred to as phase-coupled VCSEL arrays. The anlaysis is based on a joint experimental and theoretical effort: the former is devoted to a complete characterization of the emission properites, while the latter is based on a comprehensive fully vectorial model for the structure eigenmodes with the details of their complex structure. The detected characteristics make them quite attractive for various applications and the comparison of their modal properties with the model is proven to be essential for a deep understanding of these lasers. In particular we explain for the first time, a characteristic behavior of the lasing array, which displays spatially inhomogeneous polarization characteristics with symmetry properties with respect to the array diagonals. The good matching between theory and experiment opens new perspectives for optimized devices.

Photonic crystal microcavity lasers are potentially attractive optical sources for future communication systems. They operate at lithographically defined wavelengths and because of their small volumes they are expected to exhibit low operating powers. Much work remains to be done, however, in order for these sources to find mainstream applications. In this presentation we will report on our work on optically pumped photonic crystal lasers. Finite-difference time-domain and finite element simulations will be presented as part of a discussion of the resonant cavity design. The trade-offs in the design of photonic lattice hole radius and membrane thickness will also be included, and we will discuss strategies for minimizing the optical loss in these cavities. The photonic crystal laser cavities reported here are defined by electron beam lithography in pmma. The pmma is subsequently used as a mask to transfer the pattern into a Cr/Au layer in an ion beam milling step. This patterned metal layer is then used as a mask for a reactive ion etch that patterns a silicon nitride layer. Finally this layer is used as a mask to transfer the lattice into the InGaAsP semiconductor using an ECR etching step. Suspended membranes are formed by chemically undercutting the lattice. This provides strong optical confinement at the semiconductor/air interfaces at the top and bottom of the cavity. We have demonstrated pulsed, optically pumped lasing at and above room temperature in these resonant cavities using a semiconductor diode laser as the pump. The resonant cavity in our demonstration is formed by removing 19 holes from a triangular lattice and is about 2.6 mm across. Incident threshold pump powers for this cavity size as low as 0.5 mW have been demonstrated at room temperature. The peak output power collected through an optical fiber is approximately 2 mW. Lasing is seen for pump pulses as long as 200 ns. We have also demonstrated lasing in these cavities at elevated substrate temperatures. This demonstration was done using an 860 nm top emitting VCSEL as the pumping source because we expect it to provide a direction towards monolithic, electrically addressable lasers. Input power versus output power lasing characteristics for substrate temperatures up to 50 °C have been obtained. We will also report on our work on lithographic fine-tuning of the lasing wavelength. This wavelength can be defined through the lattice constant or the hole radius. This feature of photonic crystal lasers allows the definition of multiwavelength arrays. We have built and characterized arrays in which the lattice constant varies 2 nm steps across the array. The lasing wavelength redshifts with increasing lattice constant with an average separation between adjacent lasing wavelengths of 4.6 nm. The lasing wavelength tunes through the gain spectrum before the laser mode hops. Finally, we will present data on the optical loss in these cavities obtained by varying the number of lattice periods. We observed a reduction in incident threshold pump powers with increasing number of lattice periods at least through 11 periods.

Vertical-cavity surface-emitting lasers (VCSELs) are uniquely suited for massively parallel interconnects and scannerless imaging applications due to their small size, high efficiency and amiability to formation of high-density 2-dimensional arrays. We have successfully fabricated 4096 element arrays (64×64) containing alternating rows of selectively-oxidized 850 nm VCSELs and resonant-cavity photodetectors (RCPDs) on a 55 micron pitch monolithically integrated on semi-insulating GaAs substrates. We employ a matrix addressable architecture to reduce the input and output electrical connections to the array, where all the VCSELs (or RCPDs) in each row are connected by a common metal trace at the base of their mesas. The columns are connected by metal traces that bridge from mesa top to mesa top, connecting every other row (i.e., only VCSELs or only RCPDs). The design, fabrication and performance of these arrays is discussed.

This work aims at defining the marks that optoelectronic solutions will have to beat for replacing electric interconnects at chip level. Thus, we first anlayze the communication performance of future electrical interconnects considering the reduction of the lithographic feature size λ from 0.7 to 0.05 μm. We mostly analyze the results with reduced units: Lengths are calculated in multiples of λ times are compared to the chip clock cycle Tc that we estimate from the foreseeable evolution of the processor operation frequency. From our simulations, we conclude that: 1) it does not seem necessary to consider the integration of optical interconnects (OI) over distance shorter than 1000λ, because the performacne of electric interconnects is sufficient; 2) The penetration of IOs between blocks separated by more than 10λ could be envisaged provided that the present performence of OIs could be dramatically improved to beat electric solutions at chip level. New generations of low-threshold high-effieincy VCSELs and ultra-fast high-efficiency photodiode are needed; 3) The first possible application of OIs in chips is likely not for inter-block communication but for clock distribution as the energy constaints are weaker and because the clock tree is an extremely long interconnect.

Next-generation high-end data processing systems such as Internet switches or servers are approaching aggregate bandwidths in excess of 1 Terabit per second. In the case of Internet switches, the increase of fiber bandwidth that is caused by the introduction of Dense Wavelength Division Multiplexing leads to an increase of system size from single-shelf to multi-rack configurations. Intra-system interconnects will therefore span from centimeters (on-board) up to tens of meters (rack-to-rack). The task of providing hundreds of individual links at speeds in excess of 10 Gigabit per second over these distances becomes increasingly difficult for conventional copper-based technology. Using a packet switch system as an example application, we define a set of interconnect requirements for future large-scale systems. Distinguishing three interconnect classes (on-board, card-to-card over a backplane, rack-to-rack), we study the expected limits of copper-based solutions from an application point of view. After an overview of the state of the art in optical interconnect technology, we compare available technologies with the initially defined requirements. From this, we deduct key focus areas for future optical interconnect research. Finally, we present some of our recent activities in the field of waveguide and free-space based board-to-board interconnects.

In highly parallel computer systems, reconfigurable interconnect network topologies can improve the performance by adaptively increasing the communication bandwidth where it is most needed. In electrical reconfigurable interconnect networks (e.g. crossbars or multi-stage networks), a high reconfigurability can only be achieved at the cost of both chip area and network latency. The facts that short-distance optical link latencies are rapidly decreasing and that new technologies allow optical reconfigurability, make optical interconnects an interesting alternative to overcome these interconnection issues. Optical interconnection technologies indeed offer several possibilities to increase network connectivity without drastically increasing the chip area and the delay costs. In this paper we study the bandwidth and latency requirements of inter-processor and processor-memory interconnect for shared-memory parallel computers when the processor clock increases up to 10 GHz. We also investigate new enabling technologies and discuss their potential use in architectures based on reconfigurable optical interconnects.

In order to satisfy the increasing demand for interchip interconnect bandwidth, a number of current research projects are concentrating on the use of waveguided optical interconnect arrays to span PCB-range distances. To accelerate system design and technology development, CAD tools for the design and the simulation of the interconnects are indispensable. We are developing a design methodology for optical inter-chip interconnects, to produce a tool for assisting system designers on deciding on product and parameter options for the different interconnect building blocks. A mandatory first step in this methodology development concerns the investigation of the combined impact of individual product and parameter variations on system-level interconnect system properties. Accurately predicting some interconnect properties requires analog simulation of the full electrical-optical-electrical links. Detailed models for the link building blocks involving geometrical calculations are much too slow for this purpose. Circuit-level simulation tools, with appropriate model descriptions, are much more suitable. In this paper, we describe our framework for the joint simulation of the entire optical interconnect with a mixed analog/digital system. We discuss in detail a number of issues that are involved with the implementation of circuit-level simulation models in the analog modelling language Verilog-AMS, and show a link simulation example.

As a result of the increasing complexity of electronic chips, the bandwidths required for inter- and intra-chip communication are rapidly increasing. As optoelectronics provides high-bandwidth and high-density interconnection it is considered as a candidate for short-range interconnection. For such interconnections, situated at a low level in the systems hierarchy, the interconnect latency is extremely critical for the systems performance. This paper describes some methods for mesochronous synchronization, needed for such interconnections. It will be shown that it can be beneficial to use an additional optical link to transfer a synchronization signal. Such a reference signal can be used efficiently for phase detection, provided that the data skew is sufficiently small, and result in a decrease of the cost-per-link.

As a result of the constant improvement of performances and reliability of VCSEL-fabrication, parallel short distance optical interconnections are becoming more and more important. Integrating optical interconnections on a board level, covering distances from a few centimeters to a few meters, is however very challenging as the optical interconnection and mounting technology has to be integrated in existing printed circuit board manufacturing technology. Fiber based interconnections, using technologies as Fiber-In-Board and Fiber-based optical backpanels are already available, but new solutions for integrating a guided-wave based optical interconnection layer in a standard FR4-based electrical printed circuit board are emerging. These technologies are based on either organic materials or glass sheets integrated in the FR4-stack. Examples of both technologies will be presented and optical interconnections showing the feasibility of both technologies will be described. The interconnections will be realized using VCSEL-arrays and photodetector arrays which are flip-chip, mounted on the printed circuit boards. The coupling of light in and out of the optical layer in the FR4-stack is done using deflecting micro-optics realized in the optical layer, e.g. using laser-ablation.

For coupling of light into and out of the optical layer in electric-optical printed circuit boards (PCBs) a scheme for a perpendicular coupling of the light with respect to the waveguide layer is presented. The required 90° light deflection is accomplished by integrated silver-coated 45° micro mirrors which are moulded into polymer substrate together with the waveguide grooves. Exact alignment of the optoelectronic modules with respect to the mirrors is obtained by holes in the waveguide layer and MT pins in the OE-modules.

This paper focuses on the implementation of a an optoelectronic switching fabric, which is distributed as compared to centralized, as historically deployed. In an attempt to overcome the limitations of centralized switching, a distributed architecture implemented with GaAs based bidirectional optoelectronic structures is presented. The switching technology is composed of two areas - components and architecture. The components discussion will focus on the bidirectional structures required to implement the distributed architectures. Three architectural types - N², N³, and N⁴ are presented. N² represents a matrix/vector Boolean multiplier architecture, N³ represents a matrix/matrix Boolean multiplier, and N⁴ represents a tensor/matrix Boolean multiplier implementation. Each provides increased power and benefit with respect to switching and fault tolerance.

Several thousand glass optical fibers fused together is routinely used as fiber image guides for medical and other image remoting applications. Fiber image guides also offer possibility for flexible optical interconnect links with potentially thousands of bi-directional parallel channels with data rates as high as 10 Gbps per channel, leading to more than Tera bits per second aggregate data transfer rates. A fair number of fiber image guide based link demonstrations using vertical cavity surface emitting lasers have been reported. However, little is known about designable parameters and optimization paradigms for applications to massively parallel optical interconnects. This paper discusses critical optical parameters that characterize a massively parallel link. Experimental characterizations were carried out to explore some of the fundamental interactions between single-mode 850 nm VCSELs and fiber image guides having different numerical apertures, 0.25, 0.55 and 1.00. Preliminary optical simulation results are given. Finally, potential directions for further experimental and analytical explorations, and for applicability into designable link systems are suggested.

New AlOx VCSELs are very interesting for dual-purpose applications, since the emitting aperture, which guide the current lines, may be reduced to a few microns; in parallel, the ALOx diaphragm is transparent to near IR radiations. Thus, with such devices, we can get a detective area greater than the emissive one. We present in this paper our first results for an experimental numerical optical link between two linear AlOx VCSEL arrays. We first give the characteristics of the VCSEL arrays used in our experiment and describe the associated electronics. Then we present the results obtained on our test link and the problem encountered in transmission at a data rate greater than 50 Mbits/s. Finally, we tried to explain this limitation by characterizing the bandwidths of the electronics and testing all the elements on a network analyzer.

We introduce a model for a clustered free-space optical interconnect and use this to determine the maximum array density which can be achieved, together with the optimal cluster lens size which maximizes this density. We assume that the sources are multimode vertical cavity surface emitting lasers and that refractive microlenses are used to collimate the VCSEL beams. We also assume that the relay lenses are diffractive lenses with a quadratic phase profile. We find that for short interconnect distances, the maximum channel density is limited by the speed of the relay lenses, but that as the interconnect distance increases, geometric aberrations become the limiting factor. We also determine the interconnect distance below which a micro-channel relay is more suitable and the distance above which a single lens solution is adequate.

We fabricated and replicated in semiconductor compatible plastics a multi-channel free-space optical interconnection module designed to establish intra-chip interconnections on an Opto-Electronic Field Programmable Gate Array (OE-FPGA). The micro-optical component is an assembly of a refractive lenslet-array and a high-quality microprism. Both components were prototyped using deep lithography with protons and were monolithically integrated using a vacuum casting replication technique. The resulting 16 channel module shows optical transfer efficiencies of 50% and inter-channel cross-talks as low as 22 dB. These characteristics are sufficient to establish multi-channel intra-chip interconnects with OE-FPGA's. The OE-FPGA we used was designed within a European co-founded MEL-ARI consortium, working towards a manufacturable solution for optical interconnects between CMOS IC's. The optoelectronic chip combines fully functional FPGA digital logic with the drivers, receivers and flip-chipped optoelectronic components. With a careful alignment of the micro-optical free-space module above the OE-VLSI chip, we demonstrated for the first time to our knowledge multi-channel free-space intra-chip optical interconnections. Data-communication was achieved with 4 simultaneous channels working at 10Mb/s. The bitrate was limited by the chiptester. Furthermore we investigated the possibilities of a more advanced interconnection module prototyped by combining an in-house fabricated baseplate with microlenses and a commercially available micro 3D glass prism. With this approach the channel count is no longer limited by the thickness of the prism we can fabricate with deep lithography with protons. To conclude we report on the integration of this glass prism and our baseplate and on the first results obtained with this interconnection module.

In this paper we shall describe the design and successful operation of an optoelectronic Hopfield network demonstrator system. This demonstrator system, based around a free-space diffractive optical interconnect, was designed to perform a range of optimisation tasks, in particular those associated with the scheduling of packets through different switching topologies. Experimental optimisation of the neural network throughput, for both a crossbar and Banyan switch topology, allows the neural network parameters (e.g. neuron bias, neuron weighting) to be tuned to ensure optimal operation of the network for a particular switch topology. The weighted interconnections in this optoelectronic system are provided by a diffractive optical element/lens combination whilst the neurons are implemented electronically. The transition between the electronic and optical domains is handled by an 8×8 VCSEL array for the electronic-optic interface, and an 8×8 Si photodetector array for the optic-electronic interface. The VCSEL array, supplied by Avalon Photonics, is an oxide-confined near-infrared GaAs device capable of 250MHz modulation at a wavelength of 960nm. The diffractive optical interconnect is designed using simulated annealing optimization and fabricated using VLSI photolithography. Using these techniques it is possible to create interconnects with a total efficiency of ~70% and a uniformity of < 1%.

We show that vertical-cavity surface-emitting lasers (VCSEL) subject to a polarization preserving optical feedback from a long external cavity may exhibit two different types of low-frequency fluctuations (LFF) regime. In both types, the total intensity shows random drops and then recovers gradually to its original value. But the two LFF types are clearly distinguished by the behavior of the x- and y-linearly polarized (LP) modes. Type I LFF is characterized by the fact that the x- and y-LP modes compete with nearly equal power, while type II LFF is characterized by intensity dropouts in the dominant polarization mode and intensity bursts in the depressed mode. We analyze the parameter regions in which these different LFF occur and characterize them further. Our numerical results suggest that a transition from one LFF type to the other may be experimentally observed by modifying the frequency difference and/or the gain-to-loss ratio of the two LP modes. The LFF we present is an example of vectorial chaos, which may be of use for multichannel secure communication systems using chaotic light.

The increasing interest for high-speed, compact and low cost devices for optoelectronic applications such as bi-directional optical interconnects, optical imaging or telemetry has recently led to focus on the ability for the vertical-cavity surface-emitting lasers to be used as resonant cavity enhanced photodetectors for dual-purpose applications. Here we present results on design, fabrication and characterization of an oxide-confined 830nm top-emitting laser for self-aligned emission and photodetection. In this single-cavity GaAs-based device, submitted alternatively to forward and reverse bias, the oxide layer is not only used to obtain a single mode emission but also to enable decoupling between a small surface emission and a large surface detection. However the optical path is observed to change because of the refractive index difference between the oxidized and non-oxidized zones of the structure. This leads to a detrimental blue-shift on the wavelength of the Fabry-Perot cavity mode. In this work, we demonstrate this effect in photodetection by the means of spatially localized photocurrent and reflectance spectra measurements. These results show that the photocurrent is correctly collected in the whole device despite of the presence of an oxide layer. The results obtained on selective etching for optimisation of this dual-purpose device are presented.

We report a novel three-contact coupled-vertical-cavity surface-emitting laser (VCSEL) for use in polarizaiton-sensitive optical applications. The device consists in two vertical cavities, coupled by a common semitransparent mirror. We demonstrate that one can independenlty choose both the power of the output beam - through the current in the first cavity - and the polarization state - through the bias aplied to the second cavity. The control of the polarization state is performed with a control of voltage required in the range-2V to 0V. Within this interval the structure exhibits a bistable behavior with respect to the bottom cavity bias. Several physical mechanisms to explain the polarization switch are discussed.

We study the potentialities of three dimensional micro-optical pathway blocks combining refractive microlens arrays, reflective micro-prisms and diffractive fan-out elements, to enhance the functionalities of short-distance intra-chip optical interconnects. As an example, we demonstrate the possibility to enhance the point-to-point interconnection functionality to that of broadcasting data over a chip. We also investigate the limitations imposed by the physical dimensions of the refractive and diffractive micro-optical components. We then illustrate this example by a quantitatively elaborated design of a fan-out element from a VCSEL array to a detector array with a 1 to 9 signal broadcasting for every source. Furthermore we show that with the use of DOE’s we can achieve a broadcasting functionality that can lead towards reconfigurable optical interconnects, with the aid of wavelength sensitive resonant cavity detectors and WDM-inspired interconnection schemes.

We have developed novel electrically pumped, surface-emitting lasers emitting at 980 nm with an extended coupled cavity. The concept is scalable from monolithic low power devices all the way to high power extended cavity lasers. The latter have demonstrated 1W cw multi-mode and 0.5 W cw in a TEM₀₀ mode and a single frequency, with 90% coupling efficiency into a single-mode fiber. By inserting a nonlinear optical medium in the external cavity, efficient and compact frequency doubling has been achieved with CW output powers 5-40 mW demonstrated at 490 nm. The latter devices are especially noteworthy due to their very low noise, sub 10 μrad beam pointing stability combined with small size, low power consumption and high efficiency.