Planar Optical Interconnect Research Articles

Chip-on-Flex Packaging of Optoelectronic Devices in Polymer-Based Planar Optical Interconnects

A variety of applications in the use of optical and optoelectronic devices as well as their integrated circuits are increasingly penetrating into our daily routine. One of the most demanding fields is the sensing engineering. Meanwhile, the demand for more mechanical flexibility of systems and lower manufacturing budgets is continuously growing. Since the optical transparency is desired for coupling and transmission of optical signals, cost-effective transparent polymeric films are the promising candidates as carrier substrates. In this work, we aim to establish short-distance planar optical interconnects consisting of light sources/detectors and waveguides on the flexible transparent polymeric films for optical sensing functions. To achieve a miniaturized structure and ensure the flexibility of interconnects, bare chips of optoelectronic light sources/detectors are employed. Here, packaging of these chips carries the burden of all responsibilities in terms of ensuring the mechanical strength, electrical connection, thermal stability as well as the optical performance. It leads to the concept of chip-on-flex (CoF) packaging of optoelectronic devices. We present CoF packaging of a bare edge-emitting laser diode using the previously developed novel optodic bonding. While operating CoF packages, the optical performance of an active diode is strongly impaired by inefficient heat dissipation due to the extremely low thermal conductivity of employed polymeric films. Addressing this challenge, different concepts of thermomanagement are implemented. We elaborate the characterization results that evaluate the performance of CoF packages in terms of mechanical, electrical, thermo-optical, and opto-electronic properties. Two prototypes of planar optical interconnects are presented, with multi- and single-mode polymeric waveguide.

On the Use of Terminal and Inline Conversion in Planar Optical Interconnection Networks

Optical wavelength converters (WCs) are used in the design of most optical interconnection networks to improve blocking performance. Typical network architectures make use of WCs at the terminal of the network (i.e., at the input and/or output ports). Recently, inline conversion has been introduced where WCs are deployed and shared between the stages of the network. Sharing conversion among stages can lead to architectures with reduced complexity and hence lower cost. However, sharing inline conversion requires crossovers of interstage links to enter and exit the shared inline converters. As a result, inline conversion can be difficult to implement in planar switching networks with no crossover between interstage links. In this paper, we study, for the first time to the best of our knowledge, the use of combined terminal and inline WCs in planar optical interconnection networks. In particular, we show that terminal conversion has limited scalability even when fixed-range WCs are used. Accordingly, we propose a new design approach that improves scalability while preserving the noncrossover property of planar interconnection networks. It is shown that all conversion processes in the new design are independent of the number of wavelengths in the network, and hence high scalability is achieved.

Capacity analysis of a simple integrated planar optical interconnects system

The analysis of capacity in a simple integrated planar optical interconnects (IPOIs) system, based on the Gaussian propagation model, is presented. The interconnects capacity is obtained as a function of signal-to-noise ratio (SNR), optical signal power, optical noise power, electrical noise equivalent power, and the geometrical constraints of the concept of integrated planar optics (IPO). The dependence of interconnects capacity on various system parameters is analysed and simulated. It is shown that the design of the IPOIs system can be optimized for maximum capacity using geometrical constraints as design parameters.

Optimization of signal-to-noise ratio in integrated planar optical interconnects packages

The signal-to-noise ratio (SNR) of integrated planar optical (IPO) board-to-board interconnections system is analyzed. The SNR is derived as a function of separation between the boards, beam spot size, optical system efficiency, receiver thermal noise, thickness of the substrate, and the angle of propagation of the beam. Based on the analyses and the results obtained it is shown that the design of optical interconnects system can be optimized for maximum SNR using at least one parameter, namely, angle of propagation.

Mechanical means for temperature compensation of planar diffractive optical interconnects: feasibility study

Planar diffractive optical interconnects have many advantages, however, their inherent chromaticity leads to temperature instability due to the wavelength shift of laser diodes' radiation. This shift can be compensated if the optical interconnect is bended in an appropriate direction with curvature proportional to the relative wavelength shift. The bending can be performed by attaching an additional plate to the element with a different thermal expansion coefficient. Theoretical analysis and ray tracing are reported.

Planar Lightwave Integrated Circuits With Embedded Actives for Board and Substrate Level Optical Signal Distribution

This paper explores design options for planar optical interconnections integrated onto boards, discusses fabrication options for both beam turning and embedded interconnections to optoelectronic devices, describes integration processes for creating embedded planar optical interconnections, and discusses measurement results for a number of integration schemes that have been demonstrated by the authors. In the area of optical interconnections with beams coupled to and from the board, the topics covered include integrated metal-coated polymer mirrors and volume holographic gratings for optical beam turning perpendicular to the board. Optical interconnections that utilize active thin film (approximately 1-5 /spl mu/m thick) optoelectronic components embedded in the board are also discussed, using both Si and high temperature FR-4 substrates. Both direct and evanescent coupling of optical signals into and out of the waveguide are discussed using embedded optical lasers and photodetectors.

Multichip module with free-space optical interconnects and VCSEL-solder-joints

The design of a multichip module with planar optical interconnects is presented. Electrical (local) interconnects for intra-chip communication and optical interconnects for chip-to-chip communication are implemented onto the same substrate of a planar-integrated free-space optical system. We suggest to integrate the optical emitter/detectors (VCSEL diodes) into solder balls; onto these solder balls IC carrying silicon chips can be flip-chip bonded like on a common ball grid array. With respect to the thermal load thermally conductive vias are incorporated into the package, too. We show that typical packaging errors can be tolerated by the optical system, which is designed for space variant interconnects and enables thin film replication techniques of temperature sensitive materials.

Fabrication of microprisms for planar optical interconnections by use of analog gray-scale lithography with high-energy-beam–sensitive glass

For an integrated free-space optical interconnection system we suggest the use of microprisms to achieve large coupling angles at low loss. Prisms were fabricated in photoresist and quartz glass by analog lithography. High-energy-beam-sensitive glass was used as the gray-tone mask. Optical testing of the prisms shows acceptable surface quality and high efficiency (95%).

Design and fabrication of binary slanted surface-relief gratings for a planar optical interconnection

We propose the use of binary slanted surface-relief gratings with parallel-groove walls as input and output couplers in a planar optical interconnect. Parametric optimization of cascaded output couplers is employed to design an interconnect consisting of N output couplers producing a uniform intensity distribution with a high efficiency that may be realized in one lithographic etching step. The sensitivity of a N = 4 interconnect to various fabrication errors is analyzed. We demonstrate the operation of a slanted surface-relief grating manufactured with electron-beam lithography and reactive-ion etching for an operating wavelength of lambda = 0.633 mum.

Parallel Optical Packet Address Detection Using Planar Optical Interconnections

We propose a novel planar optical interconnection scheme for 100 Gb/s optical packet address detection, which consists of wave guide grating couplers and a diffractive microlens integrated on a glass substrate 3-dimensionally. Length and duty cycle of the grating couplers have been determined on the bases of ray-optic propagation-mode analysis in a slab waveguide and of rigorous coupled-wave diffraction analysis for out-coupled radiation-modes. The 3-dimensionally integrated planar optics makes it possible to connect each address bit-signal of the TE0-waveguide mode to the detector with a power uniformity of 6.4% and a total coupling efficiency of 72.3%.

3-Dimensionally Integrated Planar Optics for 100 Gb/s Optical Packet Address Detection

We propose a novel planar optical interconnection scheme for 100 Gb/s optical packet address detection, which consists of waveguide grating couplers and a diffractive microlens integrated on a glass substrate 3-dimensionally. Length and duty cycle of the grating couplers have been determined on the bases of the rayoptic propagation-mode analysis in a slab waveguide and of the rigorous coupledwave diffraction analysis for out-coupled radiation-modes. The 3-dimensionally integrated planar optics makes it possible to connect each address bit-signals of TE 0-waveguide mode to the detector with a power uniformity of 6.4 % and a total coupling efficiency of 72.3 %.

Transverse holographic optical interconnect design

The design of A new type of planar optical interconnect, the transverse holographic waveguide, is described. With this type of interconnect a one-dimensional input light distribution is converted into a one-dimensional output light distribution by holographic patterning along the direction of the optical wave propagation.

Packaging considerations for planar optical interconnection systems

We discuss various aspects of building an integrated optoelectronic system that is based on the concept of planar optics. A particular optical interconnection system has been fabricated and demonstrated. It provides parallel interconnections with 1024 optical channels that could be useful as an optical backplane in an optoelectronic multichip module. We consider the design and the fabrication of the optical system, schemes for the hybrid integration with optoelectronic device arrays, and the thermal management of an integrated system. The proposed hybrid integration scheme is based on mature technologies such as thermal anodic bonding and flip-chip bonding. Possibilities for efficient heat sinking are described.

Optimization of alignability in integrated planar-optical interconnect packages

The efficiency of power transfer and the alignability of an integrated planar-optics holographic optical backplane for board-to-board interconnections are analyzed. Both the efficiency and the alignability are functions of lateral and angular offsets in the input, the error in the spatial frequency of the hologram, errors in the source wavelength, the distance between two boards, the thickness of the substrate, the sizes of the hologram and the beam spot, and the angle of propagation of the beam. From the analyses, design guidelines on integrated planar-optic interconnects are developed, and it is shown that the interconnect design can be optimized for maximum alignability. A design with optimum alignability may not have the highest possible peak efficiency, but it can tolerate greater offsets without a substantial efficiency decrease.

Optical perfect-shuffle interconnection using a computer-generated hologram

We propose the use of a computer-generated hologram that combines a fanout and focusing element that can be used to perform an optical perfect-shuffle interconnection. The hologram is designed by calculation of the interference fringes between diverging waves from four point sources and a reference plane wave. With this element we show experimentally the resulting perfect-shuffle pattern. The use of the computer-generated hologram makes it easy to implement a planar optical perfect-shuffle interconnect, which is compact, has low aberration, and is easy to align. The planar optics configuration for a perfect-shuffle interconnection network is also discussed.

Polymer waveguides: characterization through prism–film coupler method

Cr(VI) and Fe(III) doped polyvinyl alcohol) and poly(acrylic acid) polymers have been used as real-time holographic recording media as well as materials to fabricate planar waveguides. Planar wave guides were made of these metal ion doped polymer thin films. Changes in the absorption spectra of these polymer films due to irradiation with an intense illumination of 468 nm light were observed. Modifications in optical properties of dichromated poly(vinyl alcohol) (DCPVA), dichromated poly(acrylic acid) (DCPAA), and ferric chloride doped polyvinyl alcohol) (FePVA) were experimentally determined by the prism–film coupler (PFC) method for the first time. Changes in the refractive index at 632.8 nm were monitored for different exposure energies. Modification of the modal properties was observed and the refractive index of these films was also determined from the angular position of the guided modes. Optical losses in both exposed and unexposed films of DCPVA, DCPAA, and FePVA were measured employing a coupling set-up with two prisms. Observed results suggest that these materials can find successful applications in promising areas like integrated optics and planar optical interconnects.

Holographic interconnects: transverse Bragg waveguides

We propose a new type of planar optical interconnect, the transverse Bragg waveguide. With this interconnect, We propose a new type light distribution is converted into a one-dimensional output light distribution by means one-dimensional input of holographic patterning along the direction of propagation.

Planar optical implementation of crossover interconnects

We propose a planar optical configuration for implementation of crossover interconnects. The planar overlay allows two-dimensional pixel arrays located on a wafer-scale integrated circuit to be interconnected in a compact and vibrationally robust configuration. By using an acute-angle microprism array with apex angles of 70.52 deg fabricated on a silicon substrate, we show the experimental result of the crossover interconnections. Some practical limits of the planar optical crossover interconnections are also discussed.

Diffraction-limited blazed reflection diffractive microlenses for oblique incidence fabricated by electron-beam lithography

Blazed reflection diffractive microlenses potentially have many uses. The fabrication accuracy and the optical characteristics of these microlenses can be greatly improved compared with transmission diffractive microlenses. The reflection microlenses for oblique incidence can be flexibly used without a beam splitter. The functions of the electron-beam writing system that we developed have been expanded so that the diffraction-limited microlenses for oblique incidence can be fabricated. It is demonstrated that the fabricated microlens exhibits diffraction-limited focusing characteristics with 78% high efficiency at a large oblique angle of 30 degrees . These microlenses could be used as key devices in planar optics and optical interconnections.