Board-level optical interconnection and signal distribution using embedded thin-film optoelectronic devices

Optical interconnection and signal distribution at the backplane, board, and substrate level can be implemented using thin-film active optoelectronic devices embedded in polymer waveguide structures. These active embedded devices eliminate the need for optical beam turning to and from photodetectors and emitters, respectively, for inputs and outputs to the substrate waveguides. In this paper, optical interconnections using fully embedded thin-film metal-semiconductor-metal (MSM) photodetectors in polymer optical waveguides are demonstrated, and the experimental characterization of these thin-film MSMs embedded in polymer waveguides is reported. To illustrate the potential for high-level signal distribution at the backplane, board, and substrate levels, a 1/spl times/4 balanced multimode interference (MMI) coupler has also been demonstrated in a photoimageable polymer for the first time. Finally, a 1/spl times/4 thin-film MSM photodetector array has been embedded in the output arms of the a photoimageable polymer MMI for the first time, and the MSM array photocurrent outputs from the 4 arms show that highly balanced optical signal distribution has been achieved.     

Polymeric waveguides

Techniques for fabricating polymeric waveguides, which are of growing interest for telecommunications, data communications, and optical interconnects within computers at the backplane and multichip-module levels, are described. Fabrication without etching using diffusion techniques or localized reactions and electric field poling, is highlighted. An optical backplane interconnection that uses polyimide waveguide circuits on the daughterboards and motherboard of a multiprocessor system, fabricated as proof of concept, is reported     

Pluggable Optical Board Interconnection System With Flexible Polymeric Waveguides

Pluggable optical board interconnection system using flexible optical waveguide for direct-coupling to reduce the transmission loss is proposed and demonstrated. For the direct coupling between waveguides of boards, we use optical plug and adaptor with flexible polymeric waveguide and guide pins. Flexible polymeric optical waveguide is fabricated using hot embossing technique. Eye pattern and jitter characteristics of the backplane system is presented at 10 Gb/s.     

Performance analysis of 10-/spl mu/m-thick VCSEL array in fully embedded board level guided-wave optoelectronic interconnects

We introduce a simple and effective heat sink structure for thin-film vertical cavity surface emitting lasers (VCSELs) in fully embedded board level guided-wave interconnects. A 50% quantum efficiency increase is experimentally confirmed for the 10-/spl mu/m thin-film VCSELs. The thermal resistance of a 1 /spl times/ 12 embedded thin-film VCSEL array in printed circuit board (PCB) is further analyzed. The experimental results show an excellent match with the simulated results. The 10-/spl mu/m-thick VCSEL had the lowest thermal resistance and the highest differential efficiency compared to 250-, 200-, 150-, and 100-/spl mu/m-thick VCSELs. A substrate removed VCSEL can be used in fully embedded board level optical interconnects without special cooling techniques.     

Fully Embedded Board-Level Optical Interconnects From Waveguide Fabrication to Device Integration

This paper presents the latest progress toward fully embedded board-level optical interconnects in the aspect of waveguide fabrication and device integration. A one-step pattern transfer method is used to form a large cross-section multimode waveguide array with 45deg micromirrors by silicon hard molding method. Optimized by a novel spin-coating surface smoothing method for the master mold, the waveguide propagation loss is reduced to 0.09 dB/cm. The coupling efficiency of the metal-coated reflecting mirror, which is embedded in the thin-film waveguide, is simulated by an M² factor revised Gaussian beam method and is experimentally measured to be 85%. The active optoelectronic devices, vertical surface emitter lasers and p-i-n photodiodes, are integrated with the mirror-ended waveguide array and successfully demonstrate a 10 Gbps signal transmission over the embeddable optical layer.     

Integration of optical interconnects and optoelectronic elements on wafer-scale

The UV-reaction molding technology enabling for the fabrication of microoptical elements with rectangular, triangular or circular cross-sections (waveguides, prisms, lenses) in optical polymers is described. Multimode waveguide optical interconnects, coupling prisms and holding structures for fibers can be fabricated in one step. A three-dimensional monomode waveguide interconnection module is presented. Stability tests of the microoptical elements are reported.     

Optical signal distribution to MSM photodetector arrays viaintegrated polyimide waveguides

The integration of metal-semiconductor-metal (MSM) photodetector arrays with polyimide ridge waveguides is demonstrated. MSM detectors were fabricated using transparent indium tin oxide (ITO) interdigitated electrodes on semi-insulating GaAs substrates. An optical buffer layer of SiO₂ was deposited and patterned, and then polyimide ridge waveguides were fabricated on top by spin coating and photolithography. The guides were multimode with widths from 10 to 50 μm. Light at 830 nm was coupled efficiently from the waveguides through gaps in the SiO ₂ buffer layer into the underlying detector structures. Absolute responsivities of the integrated MSM devices were around 0.5 A/W and the 3 dB bandwidths of 5-6 GHz were measured. Division of the input signal between sets of two and four detectors under a single waveguide has been achieved, highlighting the potential for the fabrication of integrated optoelectronic switches     

Optical backplane system using waveguide-embedded PCBs and optical slots

As discussed in this paper, a practical optical backplane system was demonstrated, using a waveguide-embedded optical backplane board, processing boards, and optical slots for board-to-board interconnection. A metal optical bench was used as a packaging die for the optical devices and the integrated circuit chips in both the transmitter and the receiver processing boards. The polymer waveguide was produced by means of a hot-embossing technique and was then embedded following a conventional lamination processes. The average propagation loss of these waveguides was approximately 0.1 dB/cm at 850 nm. The dimension and optical properties of the waveguide in an optical backplane board were unchanged after lamination. As connection components between transmitter/receiver processing boards and an optical backplane board, optical slots were used for easy and repeatable insertion and extraction of the boards with a micrometer-scale precision. A 1/spl times/4 850-nm vertical-cavity surface-emitting laser array was used with 2 dBm of output power for the transmitter and a p-i-n photodiode array for the receiver. This paper successfully demonstrates 8 Gb/s of data transmission between the transmitter processing board and the optical backplane board.     

Polymer-Based Long-Range Surface Plasmon Polariton Waveguides for 10-Gbps Optical Signal Transmission Applications

We present characteristics of very thin Au strip waveguides based on long-range surface plasmon polaritons (LR-SPPs) along thin Au strips embedded in polymers. We also report a 10 Gbps optical signal transmission via LR-SPPs with the pig-tailed Au strip waveguide at a telecommunication wavelength of 1.55 mum. We limited the thickness, width, and length up to ~20 nm, ~ 10 mum, and ~5 cm, respectively, for practical applications. At 1.55 mum, loss properties of the Au strip waveguides were theoretically and experimentally evaluated with thickness, width and cladding material. The lowest propagation loss of ~1.4 dB/cm was experimentally obtained with the 14-nm-thick and 2-mum-wide Au strip. With a single-mode fiber, the lowest coupling loss of less than 0.1 dB/facet was achieved with the 14-nm-thick and 7.5-mum-wide Au strip. The lowest insertion loss was obtained 7.7 dB with the 14-nm-thick, 5-mum-wide, and 1.5-cm-long Au strip. The propagation loss was improved approximately 30% for the 17-nm-thick Au strip with lowering the refractive index of the cladding polymer by 0.01. In the 10 Gbps optical signal transmission experiment, the LR-SPP waveguide exhibits an excellent eye opening and a 2.2 dB power penalty at 10^-12 bit error rate. These all results indicate that the LR-SPP waveguide is a potential transmission line for optical interconnects to overcome inherent problems in electric interconnects.     

Chip-scale optical interconnects and optical data processing using silicon photonic devices

Recent advances in the density and complexity of photonic integrated circuits have facilitated possible implementation of chip-scale optical communication systems. Chip-scale optical interconnects and optical data processing are two important functions to transmit and process signal in the optical domain. Silicon photonics offers a promising platform to enable chip-scale optical interconnects and optical data processing using silicon photonic devices. In this paper, we review our recent progress in the design, modeling, and fabrication of silicon photonic devices and their applications in chip-scale optical interconnects and optical data processing with advanced modulation formats. For chip-scale optical interconnects, we experimentally demonstrate digital signal transmissions in silicon microring and silicon vertical slot waveguide. Terabit chip-scale optical interconnect is demonstrated in the experiment. Also, we experimentally demonstrate analog signal transmissions in silicon microring and silicon photonic crystal nanocavity. For chip-scale optical data processing, we experimentally demonstrate all-optical wavelength conversion using a silicon waveguide, simultaneous polarization and wavelength demultiplexing using 2D grating coupler connected with microrings, two-mode (de)multiplexing using a tapered asymmetrical grating-assisted contra-directional coupler, and two-/three-mode (de)multiplexing using asymmetrical directional converter. In addition, we propose and simulate chip-scale optical data exchange, chip-scale high-base optical computing, and chip-scale optical coding/decoding by using nonlinear interactions in a silicon-organic hybrid slot waveguide. The obtained theoretical and experimental results of chip-scale optical interconnects and optical data processing indicate possible integration of optical communication functions on a monolithic chip.     

Modellierungs- und Simulationsverfahren für die optische Verbindungstechnik auf elektrischen Leiterplatten

Optical interconnection technology on the printed circuit board level is a key technology for future microelectronic equipment. The consideration of functional, technological, and economical requirements results in a hybrid solution, where electrical and optical interconnects are integrated into one substrate called electrical optical printed circuit board. The significant part of the entire design process for electrical optical printed circuit boards is marked by the design supporting modelling and simulation of optical interconnects. Based on an abstract model for an entire optical interconnect a simulation model for optical multimode-waveguides is presented, taking into account all significant waveguide properties. Apart from that, the modeling of active components (laser- and photo-diodes) is addressed.     

Compact three-dimensional optical interconnects with largetolerance by stacked ARROW-type waveguides

A compact configuration of three-dimensional optical interconnects using stacked ARROW-B waveguides is developed. A short coupling length of 200 μm and a large tolerance to core thickness are demonstrated     

有机聚合物光波导制作工艺综述

有机聚合物光波导光互连已成为实现短距离计算通信设计目标的最佳解决方法。短距离光互连是未来互连方向,综合性能优良的聚合物多模光波导是光互连中的重要组成部分。有机聚合物光波导的制作工艺对光波导的性能具有重要影响,故此对有机聚合物光波导的制作工艺进行了综述,并提出了一些未来的研发方向。     

Fabrication of single-mode polymeric optical waveguides bylaser-beam writing

A laser-beam writing system is developed for large-area optical waveguide fabrication. Single-mode embedded channel optical waveguides are successfully fabricated on both 4- and 8-in silicon substrates using deuterated fluoromethacrylate polymers by laser-beam writing in photoresist and dry etching. The propagation loss of the waveguides is as low as 0.1 dB/cm at 1.3 μm     

Characterization of a 4 × 4 Gb/s Parallel Electronic Bus to WDM Optical Link Silicon Photonic Translator

A 4times4 Gb/s microring modulator cascade, which can directly convert data from a parallel electrical bus to a multiple-wavelength optical signal in a single silicon-on-insulator waveguide, is demonstrated and characterized. The integrity of the modulated optical signal is verified using Q-factor extrapolations. In addition, the frequency characteristics and crosstalk, in terms of total harmonic distortion, are quantified. A transparent translator from electronics to optics such as this is crucial for the development of large-scale high-bandwidth interconnects based on photonic integrated circuits     

Waveguide Interconnection in Silica-Based Planar Lightwave Circuit Using Femtosecond Laser

The interconnection of waveguides inside a silica- based planar lightwave circuit (PLC) is demonstrated both two- and three-dimensionally by using a femtosecond laser. The waveguides written with a femtosecond laser can be successfully connected to waveguides inside a PLC with low loss. Unlike previous work on the direct writing of 2-D and 3-D waveguides in bulk glass, the waveguide must be written a few tens of micrometers beneath the surface of a PLC composed of multilayers of different glasses. To realize a low-loss waveguide, we studied the sensitivity difference for femtosecond pulses in each layer in detail and developed a multiple-scanning technique with a femtosecond laser for writing waveguides. In addition, we investigated a mode-field (MF) diameter control technique to allow us to achieve the low-loss interconnection of PLC and written waveguides. We also studied particular problems caused by nonlinear optical effects, such as the positional displacement of written waveguides from the focal point. As a result, we achieved a low-loss waveguide with almost the same MF diameter as a PLC waveguide and performed the first demonstration of interconnection between PLC waveguides. The excess losses at 1550 nm were 1.4 and 2.3 dB for 2-D and 3-D interconnection, respectively.      

High sensitivity and submillimeter resolution optical time-domainreflectometry based on low-coherence interference

Characteristics of the low-coherence optical time-domain reflectometer (OTDR) are presented, and optical waveguide diagnosis using the OTDR is demonstrated. Ultrahigh sensitivity in the shot noise limited operation is discussed, and jagged-shaped Rayleigh-backscatter signals are predicted and observed experimentally. Signal smoothing by widening the resolution from 14 to 400 μm can drastically reduce the jagging. In the experiment, polarization-sensitive and insensitive OTDRs using a fiber-coiled piezoelectric phase modulator are proposed. Measurements of beat length and bending loss, quality characterization of low-loss waveguides by polarization-sensitive OTDR, and cancellations of polarization fading in discrete backreflection and polarization jagging in Rayleigh backscattering by polarization-insensitive OTDR are successfully demonstrated     

Realistic end-to-end simulation of the optoelectronic links andcomparison with the electrical interconnections for system-on-chipapplications

A detailed comparison of optoelectronic versus electrical interconnections for system-on-chip applications is performed in terms of signal latency and power consumption. Realistic end-to-end models of both interconnection schemes are employed in order to evaluate critical performance parameters. A variety of electrical and optoelectronic interconnection configurations are implemented and simulated using accurate optical device and electronic circuit models integrated under an integrated circuit (IC) design computer-aided design tool. Two commercial complementary metal-oxide-semiconductor (CMOS) technologies (0.8 μm and 0.25 μm) are used for the estimation of the signal latency and the power consumption as a function of the interconnection length for the different link configurations. It was found that optoelectronic interconnects outperform their electrical counterparts, under certain conditions, especially for relatively long lines and multichannel data links     

Fabrication of polymeric large-core waveguides for opticalinterconnects using a rubber molding process

Polymeric large-core (47 μm×41 μm) optical waveguides for optical interconnects have been fabricated by using a rubber molding process. For low-cost low-loss large-core waveguides, our newly developed thick-photoresist patterning process is used for a master fabrication. Also a low-loss thermocurable polymer, perfluorocyclobutane (PFCB), is used in fabricating optical waveguides by rubber molding for the first time. The propagation loss is measured to be 0.4 dB/cm at the wavelength of 1.3 μm, and 0.7 dB/cm at the wavelength of 1.55 μm     

Double-bonded InP-InGaAsP vertical coupler 1:8 beam splitter

A novel three-layer double-bonded InP-InGaAsP waveguide vertical coupler 1:8 beam splitter is demonstrated. The strongly coupled waveguides allow a 583-μm device length, more than 100 times shorter than that of the equivalent horizontal coupler. The device illustrates the use of multiple vertical-layer optical interconnects for three-dimensional routing of optical signals