Guided Wave Optical Interconnects Research Articles

A technical report on fabrication of SU-8 optical waveguides

Technical considerations of fabrication and optical characterization of SU-8 multimode waveguides are reported. This low cost, simple technology may directly be used for guided-wave MOEMS and optical interconnection.

45° polymer-based total internal reflection coupling mirrors for fully embedded intraboard guided wave optical interconnects

An array of 50μm×50μm polymer waveguides with 45° total internal reflection (TIR) wideband coupling mirrors were fabricated by soft molding to achieve fully embedded boardlevel optoelectronic interconnects. The 45° TIR coupling mirrors were formed at the ends of the waveguides to provide surface normal light coupling between waveguides and optoelectronic devices. Three-dimensional optoelectronic interconnects were replicated in one-step transfer by the soft molding technique. The measured propagation loss of the multimode waveguide was 0.16dB∕cm at 850nm wavelength. The coupling efficiency of the silver-coated 45° micromirrors buried under the top cladding was 92% with low polarization sensitivity.

Routing permutations on baseline networks with node-disjoint paths

Permutation is a frequently-used communication pattern in parallel and distributed computing systems and telecommunication networks. Node-disjoint routing has important applications in guided wave optical interconnects where the optical "crosstalk" between messages passing the same switch should be avoided. In this paper, we consider routing arbitrary permutations on an optical baseline network (or reverse baseline network) with node-disjoint paths. We first prove the equivalence between the set of admissible permutations (or semipermutations) of a baseline network and that of its reverse network based on a step-by-step permutation routing. We then show that an arbitrary permutation can be realized in a baseline network (or a reverse baseline network) with node-disjoint paths in four passes, which beats the existing results [M. Vaez et al., (2000)], [G. Maier et al., (2001)] that a permutation can be realized in an n /spl times/ n banyan network with node-disjoint paths in O(n/sup 1/2/) passes. This represents the currently best-known result for the number of passes required for routing an arbitrary permutation with node-disjoint paths in unique-path multistage networks. Unlike other unique path MINs (such as omega networks or banyan networks), only baseline networks have been found to possess such four-pass routing property. We present routing algorithms in both self-routing style and central-controlled style. Different from the recent work in [Y. Yang et al., (2003)], which also gave a four-pass node-disjoint routing algorithm for permutations, the new algorithm is efficient in transmission time for messages of any length, while the algorithm in [Y. Yang et al., (2003)] can work efficiently only for long messages. Comparisons with previous results demonstrate that routing in a baseline network proposed in this paper could be a better choice for routing permutations due to its lowest hardware cost and near-optimal transmission time.

Fully embedded board-level guided-wave optoelectronic interconnects

A fully embedded board-level guided-wave optical interconnection is presented to solve the packaging compatibility problem. All elements involved in providing high-speed optical communications within one board are demonstrated. Experimental results on a 12-channel linear array of thin-film polyimide waveguides, vertical-cavity surface-emitting lasers (VCSELs) (42 /spl mu/m), and silicon MSM photodetectors (10 /spl mu/m) suitable for a fully embedded implementation are provided. Two types of waveguide couplers, titled gratings and 45/spl deg/ total internal reflection mirrors, are fabricated within the polyimide waveguides. Thirty-five to near 100% coupling efficiencies are experimentally confirmed. By doing so, all the real estate of the PC board surface are occupied by electronics, and therefore one only observes the performance enhancement due to the employment of optical interconnection but does not worry about the interface problem between electronic and optoelectronic components unlike conventional approaches. A high speed 1-48 optical clock signal distribution network for Cray T-90 super computer is demonstrated. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-48 clock signal distribution and for point-to-point interconnects. The feasibility of using polyimide as the interlayer dielectric material to form hybrid three-dimensional interconnects is also demonstrated. Finally, a waveguide bus architecture is presented, which provides a realistic bidirectional broadcasting transmission of optical signals. Such a structure is equivalent to such IEEE standard bus protocols as VME bus and FutureBus.

Volume-consumption comparisons of free-space and guided-wave optical interconnections

We compare volume-consumption characteristics of free-space and guided-wave optical interconnections. System volume consumption is used as a fundamental measure of various point-to-point space-invariant and space-variant interconnections of two-dimensional arrays of N(1/2) x N(1/2) points. We show that, in free-space and space-invariant situations, although volume consumption for macroaperture optics is O1(N(3/2)), where O denotes the order, it is only O2(N) for microaperture optics. For free-space and space-variant operations only microaperture optics is possible without fundamental power losses. The corresponding minimum volume consumption is O3(N3). We show that single microaperture-per-channel implementations of either space-invariant or space-variant operations are, in general, more volume efficient than are their two-cascade microaperture-per-channel counterparts. We also show that, for minimizing volume consumption, the optimum relative apertures F#(opt) for space-variant optical elements are, respectively, (5N)(1/2)/4 for a single microaperture-per-channel geometry and (5N)(1/2)/2 for a two-cascade microaperture-per-channel geometry. In guided-wave or fiber interconnect cases our study shows that the volume consumption for space-invariant and space-variant operations is O4(N), with O4 < O2, and O5(N(3/2)), respectively. Thus an important conclusion of the study is that free-space optics is less volume efficient than is guided-wave optics in both space-invariant and space-variant interconnect applications.

Thermo-optically tuned cascaded polymer waveguide taps

Polymer thermo-optic-waveguide taps have a potential application as light routers for guided-wave optical interconnects involving cascaded fanouts. The taps can guide light from an optical bus bar and direct it into other devices in a switching/modulation network. Thermo-optic waveguide taps are designed and fabricated on silicon wafers using standard very large-scale integrated fabrication techniques. Coupling of light into an adjacent waveguide tap is observed to increase by 12.3% from 38.7% to 51.0% with the application of 34 mW of power.

Path-reversed substrate- guided-wave optical interconnects for wavelength-division demultiplexing

A path-reversed substrate-guided-wave holographic interconnection scheme is investigated for a wavelength-division demultiplexing application. Using a beveled edge of a waveguiding plate allows optical signals to be coupled into the waveguiding plate and then to be coupled out of the plate by a waveguide hologram. Theoretical analyses are given for dispersion, bandwidth, and recording parameters of various guided-wave holographic gratings. A device is fabricated with a 45 degrees incident angle and a 45 degrees diffraction angle by use of a 20-microm photopolymer film. The 3-dB bandwidth of the device is measured to be 20 nm. Four-channel wavelength demultiplexing is demonstrated at 796, 798, 800, and 802 nm with no cross talk observed. A one-to-five cascaded four-channel wavelength-division demultiplexer with +/-5% energy uniformity under s polarization is also demonstrated to increase the user-sharing capacity. Twenty fan-out channels (5 x 4) are achieved experimentally.

Integrated-optic array illuminator: a new design for guided-wave optical interconnections

An integrated array illuminator can be used not only as an opticalpower distributor for an array of guided-wave optic devices but also asa key element for guided-wave optical interconnections. We presenta new design for an integrated-optic array illuminator with focusingwaveguide diffractive doublet arrays. This integrated arrayilluminator allows independent optimizations of efficient and uniformoptical power distribution and focusing performance. Furthermore, the device can be fabricated with all-optical lithographic technologyand hence has the advantages of mass production with lowcost.

Combination of free-space and guided-wave optical interconnects for angularly multiplexed multiwavelength holographic memory

We propose and test experimentally a new scheme to implement spatially multiplexed multiwavelength holographic memory. An electro-optically modulated phase grating array on LiNbO(3) substrate is used as a guided-wave interconnect to activate the reconfigurable reference beam. The object beam is provided by free-space interconnect. An electro-optic modulation efficiency of 18 +/- 2.5% is achieved with an applied voltage of 100 V. The reference beams with different diffraction angles can implement the angle-multiplexing holographic recording. We believe this is the first report of the implementation of guided-wave electro-optic interconnect together with free-space interconnect in holographic memory applications.

Cascaded energy-optimized linear volume hologram array for 1-to-many surface-normal even fan-outs

Optimization of fan-out energy distribution for substrate guided wave optical interconnects with a surface-normal configuration is addressed in this paper. Up to nine optimized waveguide holograms are independently fabricated on the same substrate. Energy fluctuation affected by the deviation of the designed diffraction efficiency is theoretically analysed. Using DuPont photopolymer film HRF-600X001-20, we demonstrate 1-to-5 and 1-to-9 surface-normal fan-out devices operating at 850 nm. The output non-uniformities of ±4% and ±10% are experimentally confirmed for the two devices, respectively.

Cross-link optimized cascaded volume hologram array with energy-equalized one-to-many surface-normal fan-outs

Achieving a uniform fan-out energy distribution is critical to the successful applications of substrate guided-wave optical interconnects. Using Dupont photopolymer film HRF-600X00120, we investigated the optimum recording beam intensity for obtaining a large dynamic region of diffraction efficiency relative to exposure dosage. Based on the experimental diffraction efficiency curve, 1-to-5 and 1-to-9 surface-normal fan-out devices were fabricated that operated at a wavelength of 850nm, and output nonuniformities of +/-4 % and +/-10 % were obtained for the two devices.

Implementation of optical perfect shuffle with substrate guided-wave optical interconnects

The vulnerability in optoelectronic packaging of free space optical interconnects fail to provide a reliable interconnection for highly parallel system. In this letter, we report, for the first time, a substrate-guided-wave-based perfect shuffle (PS) having an 8-to-8 interconnection, is demonstrated at 632.8-nm wavelength. Sixteen waveguide holograms are fabricated with the full functionality of the PS. The diffraction efficiencies of the waveguide holograms are all within 80%/spl plusmn/5%, The surface-normal configuration of the demonstrated PS makes the integration with vertical-cavity surface-emitting lasers (VCSELs) and other surface-mountable processing elements (PEs) highly feasible.

Guided-wave and free-space optical interconnects for parallel-processing systems: a comparison

Guided-wave and free-space optical interconnects are compared based on insertion loss, link efficiency, connection density, time delay, and power dissipation for three types of connection networks. Three types of free-space interconnect systems are analyzed that are representative of a wide variety of free-space systems: space-variant basis-set and space-invarient systems. Results indicate that the connection density of a space-variant free space system has a connection density roughly equivalent to a two level guided-wave system with a pitch of ~10 µm (for a 1-µm wavelength) and a core refractive index of 2.0. It is also shown that the connection density of basis-set and space-invariant free-space systems can be several orders of magnitude higher than fundamental limits on the connection density of dual-level guided-wave interconnect systems when large-scale highly connected networks are employed.

1-to-12 surface normal three-dimensional optical interconnects

We present a surface normal optical interconnect with a 1-to-12 collinear fan-out. Two types of polymer-based holograms were fabricated to provide a collinear 1-to-12 fan-out from guided mode to substrate modes and twelve 1-to-1 surface normal interconnects. Fluctuation of up to 7.2 dB for the 1-to-12 fan-out hologram was observed due to the oscillating and the film saturation effects of the transmission hologram. Diffraction efficiency better than 70% was observed for all the total internal reflection holograms. The result reported herein greatly enhanced optical signal processing capability of guided wave optical interconnects. The advantages of free space optical interconnect, such as global interconnect, three dimension, massive fan-out/fan-in capabilities, and surface normal optical interconnect, can be realized using the demonstrated architecture. The coupling from waveguide to fiber can be realized from the surface rather than the edge of a photonic integrated circuit.

Synthesis of guided wave optical interconnects

A guided wave optical interconnect has been designed which reduces or eliminates clock skew by ensuring simultaneous delivery of clock pulses to chips mounted on a wafer. The interconnect consists of a multimode trunk waveguide and a set of branch waveguides, one per chip, each of which couples one mode out of the trunk waveguide. The elimination of clock skew is accomplished by taking advantage of the different group velocities of the modes inherent in multimode waveguides and suitably tailoring the propagation constants of the trunk waveguide according to the location of the respective chip on the wafer. Inverse scattering theory, specifically, the method of Darboux transformations, is used to design the refractive index profiles of the trunk waveguides, using the set of propagation constants selected during the first stage of the design as input data. It is shown that, by using transverse coupling and suitable design of the trunk and branch waveguides, efficient coupling from the trunk to the branch waveguides can be ensured. Techniques for ensuring a symmetric trunk refractive index profile are investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Intraplane guided wave massive fanout optical interconnections

One-to-30 guided wave optical interconnections are demonstrated at 632.8 nm using a highly multiplexed waveguide volume hologram. This technology is capable of providing intrachip and intrawafer optical interconnections. The theoretical limit of the fanout number is addressed and experimentally confirmed. The measured data show that the diffracted beams have an average diffraction efficiency of 2.3% with ±0.2% variation. The demonstrated results can save surface space of electronic chips and also provide a large fanout capability due to the high index modulation of the volume hologram. Further applications based on this technology are very promising. Head-up display, high-speed optical data bus, surface enhanced Raman spectrometer, and optical sensors are some of the attractive ones.

Optical Interconnections Using A Silica-Based Waveguide On A Silicon Substrate

Guided-wave optical interconnections for interchip data transmis-sions and clock distributions are demonstrated. The optical interconnection circuit consists of a silica-based guided-wave circuit, laser diodes, and photodiodes. The interconnection topology adopts the star coupler network used in local area networks as a model. The laser diodes and photodiodes are assembled with the guided-wave circuit by the hybrid integration technique. Preliminary experiments on a four-chip interconnection circuit yield a 340 Mbps data rate and a 250 MHz clock frequency.

Guided-wave optical interconnects for VLSI systems : C T SULLIVAN, A HUSAIN (Honeywell Sensors & Signal Processing Lab., Bloomington, MN, USA) Proc. SPIE — Int. Soc. Opt. Eng. (USA), vol. 881, pp. 172–176 (1988). (Optical Computing and Nonlinear Materials, Los Angeles, CA, USA, 11–13 Jan. 1988)

Guided-wave optical interconnects for VLSI systems : C T SULLIVAN, A HUSAIN (Honeywell Sensors & Signal Processing Lab., Bloomington, MN, USA) Proc. SPIE — Int. Soc. Opt. Eng. (USA), vol. 881, pp. 172–176 (1988). (Optical Computing and Nonlinear Materials, Los Angeles, CA, USA, 11–13 Jan. 1988)