Electro-optical Printed Circuit Board Research Articles

Research on composite manufacturing method of semi-buried 1×32 optical splitter

In this paper, a composite manufacturing method was proposed to reduce the inner surface roughness of silica groove. Firstly, femtosecond laser was used to ablate the silica groove, then, a 5% concentration hydrofluoric acid solution was used to corrode the inner surface of silica groove. Secondly, Su8 adhesive was filled with the groove to form a semi-buried 1×32 optical splitter by doctor blade. The test results showed that the surface roughness Ra was less than 0.2 µm, and average insertion loss of output ports was 21.34 dB, moreover, the uniformity was less than 1.44 dB. Compared with the traditional femtosecond laser ablating method, surface roughness reduced by at least 0.1 µm, and the average insertion loss of output ports was reduced by 1.22 dB, and the uniformity was reduced by 0.41 dB. So, the composite manufacturing method improved the communication performance. It is satisfied with the requirements for optical interconnection in the electro-optical printed circuit boards.

Manufacturing a 1 × 16 air-cladding polymeric optical splitter for electro-optical printed circuit boards by femtosecond laser

Based on the beam propagation method, a compact 1 × 16 polymeric optical splitter with center wavelength ∼1550 nm is designed for electro-optical printed circuit board (EOPCB). The length of the optical splitter is 20,000 μm. Spacing between each output port is 127 μm. The cross section of the optical splitter is 10 μm × 10 μm. The silicon glass is chosen as a substrate material of the optical splitter, the cladding material of the optical splitter is air, and the core material of the optical splitter is SU8 polymer. It is fabricated for a 1 × 16 chip-to-chips optical interconnect by femtosecond laser. The testing results show that average insertion loss per channel for the optical splitter is I L ≤ 20 dB and the uniformity for the optical splitter is C u ≈ 1.42 dB. It is very suitable for the optical interconnection of EOPCB.

Application-Oriented On-Board Optical Technologies for HPCs

The increased communication bandwidth demands of high performance computing (HPC) systems calling at the same time for reduced latency and increased power efficiency have designated optical interconnects as the key technology in order to achieve the target of exascale performance. In this realm, technology advances have to be accompanied by the development of corresponding design and simulation tools that support end-to-end system modeling in order to evaluate the performance benefits offered by optical components at system scale. In this paper, we present recent advances on electro-optical printed circuit boards (EOPCB) technology development pursued within the European FP7 PhoxTroT research program and directed toward system-scale performance benefits in real HPC workload applications. We report on high-density and multilayered EOPCBs together with all necessary building blocks for enabling true optical blade technology, including multimode polymer-based single- and dual-layer EOPCBs, a board-compatible optically interfaced router chip, and passive board-level connectors. We also demonstrate a complete optical blade design and evaluation software simulation framework called OptoHPC that tailors optical blade technology development toward optimized performance at HPC system scale, allowing for its validation with synthetic workload benchmark traffic profiles and for reliable comparison with existing HPC platforms. The OptoHPC simulator is finally utilized for evaluating and comparing a 384-node HPC system relying on optically enabled blades with the state-of-the-art Cray XK7 HPC network when performing with a range of synthetic workload traffic profiles, revealing the significant throughput and delay improvements that can be released through application-oriented optical blade technology.

International standards for optical circuit board fabrication, assembly and measurement

The commercial adoption of electro-optical printed circuit board (EOCB) technology will be accelerated by the development of industrial and conformity standards for high volume fabrication, connector assembly and waveguide measurement. In this paper, we introduce international standardisation activities surrounding EOCBs and report on industrial processes developed for the high volume fabrication of complex EOCBs with embedded multimode polymer waveguides including a first connector standard for polymer waveguide termination. We focus on solving a serious historic problem with the measurement of optical waveguide systems, namely the lack of harmonised measurement conditions for optical waveguides, which to this day gives rise to strong inconsistencies in the results of measurements by different parties on the same waveguide. We report on the development of a standard to ensure repeatable measurement of optical waveguides, whereby we demonstrate how the application of a measurement identification system and proposed reference measurement conditions can bring variation in measurement results to within 5%, thereby serving as the basis for a formal reliable optical waveguide measurement methodology.

High-Precision, Self-Aligned, Optical Fiber Connectivity Solution for Single-Mode Waveguides Embedded in Optical PCBs

A fully passive, optical fiber connectivity solution for polymer waveguides embedded in electro-optical printed circuit boards (EOCB) is described and its preliminary results for single-mode applications demonstrated. The connectivity solution is based on a pluggable glass-fiber connector interface and a self-alignment packaging technology using high-precision silicon V-grooves. The V-grooves provide precise positioning of the glass-fiber relative to the polymer waveguide through alignment structures on the EOCB, patterned in the same laser direct writing fabrication step as the waveguide core. We realized an EOCB module with an LC-connector pluggable adaptor interface assembled on one side of the EOCB. With this module, we were able to prove for the first time the usability of our connectivity solution for single-mode applications. Coupling losses as low as 1.2 dB between a standard LC-connector and the single-mode polymer waveguide embedded into the EOCB have been reached. This passive packaging solution provides a cost-effective optical connectivity to wave-guides in EOCBs, which will be required in future generations of optical interconnects.

Thermally Stable, Low Loss Optical Silicones: A Key Enabler for Electro-Optical Printed Circuit Boards

We report the development and characterization of a low loss polymer waveguide material with a polysiloxane backbone for enabling the new generation electrooptical printed circuit boards (PCBs). The polymer was designed to have low optical loss of <;0.05 dB/cm at 850 nm and low residual stress to withstand the harsh reliability requirements during PCB integration. The thermomechanical properties of the polymer were tuned to exhibit a residual stress of ~1 MPa over a temperature range of 25 °C to 200 °C in ambient air. Multimode polymer waveguides were fabricated using the polysiloxane polymer and embedded in a six-layer PCB architecture that was subjected to lamination, through-hole via drilling, plating, and IPC shock test (immersion) in solder bath at 288 °C. Eight channels of multimode polymer waveguide spirals of length 1.2 m were fabricated and the insertion loss measured after waveguide fabrication, lamination, and solder reflow. The deviation in insertion loss as a function of the PCB fabrication process was less than 3% with final insertion loss after solder reflow being 0.052 +/- 0.002 dB/cm. This finding presents an optical waveguide material which when embedded in a PCB fabricated using an industry standard process meets reliability requirements while maintaining optical performance.

FirstLight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers

The protocol data rate governing data storage devices will increase to over 12 Gb/s by 2013 thereby imposing unmanageable cost and performance burdens on future digital data storage systems. The resulting performance bottleneck can be substantially reduced by conveying high-speed data optically instead of electronically. A novel active pluggable 82.5 Gb/s aggregate bit rate optical connector technology, the design and fabrication of a compact electro-optical printed circuit board to meet exacting specifications, and a method for low cost, high precision, passive optical assembly are presented. A demonstration platform was constructed to assess the viability of embedded electro-optical midplane technology in such systems including the first ever demonstration of a pluggable active optical waveguide printed circuit board connector. High-speed optical data transfer at 10.3125 Gb/s was demonstrated through a complex polymer waveguide interconnect layer embedded into a 262 mm × 240 mm × 4.3 mm electro-optical midplane. Bit error rates of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> and optical losses as low as 6 dB were demonstrated through nine multimode polymer wave guides with an aggregate data bandwidth of 92.8125 Gb/s.

Metal-slotted hybrid optical waveguides for PCB-compatible optical interconnection

For development of electro-optical printed circuit board (PCB) systems, PCB-compatible metal-slotted hybrid optical waveguide was proposed and its optical characteristics are investigated at a wavelength of 1.31 μm. To confine light in a metallic multilayered structure, a metal film with a wide trench is inserted at the center of a dielectric medium that is sandwiched between metal films of infinite width. A circularly symmetric spot of the guided mode was measured at the center of the metal-slotted optical waveguide, which is a good agreement with the theoretical prediction by using the finite-element method. The measured propagation loss is about 1.5 dB/cm. Successful transmission of 2.5 Gbps optical signal without any distortion of the eye diagram confirms that the proposed hybrid optical waveguide holds a potential transmission line for the PCB-compatible optical interconnection.

Relative power loss of misalignment based on electro-optical printed circuit board

In this paper, the power loss values between 45° total internal reflecting waveguide mirror (TIRWM) and the polymer optical waveguide layer are obtained by vector finite element method. There are some misalignments during an actual fabrication of electro-optical printed circuit board (EOPCB). And, b , a , c correspond to the error value of alignment in the x-axis, y-axis and z-axis direction, respectively. Another, four effective refractive indices of the 45° TIRWM and polymer optical waveguide layer are calculated, separately. And, n eff1 = 1.425211 is uniquely chosen. Next, these relative power errors Δ are calculated, when a , b , c separately change. Moreover, these error values are plotted into some curved surface figures. By these figures, it is easy to find the relationship between a , b , c and Δ. Furthermore, it is beneficial for us to avoid the region of larger power loss during an actual fabrication of EOPCB.

Performance analysis of 45° coupled structure of optical waveguide based on electro-optical printed circuit board

In this paper, the non-ideal 45° coupled structure of the optical waveguide was simulated and analyzed by the finite element theory. Since the doctor-blade and grinding methods were used to product the electro-optical printed circuit board (EOPCB), the thickness of the core layer and the length of the 45° mirror side will be, respectively, in the variation of ±2 μm. In this case, output power values were calculated when the TE10 and TE20 were separately used as input signal; then they were individually compared with the ideal output power values. It can be seen that Δ% is not more than 0.45% by the TE10 wave, while Δ% is not more than 3.5% by the TE20 wave. The variation of output power compared with the input power is very small; this technology was more suitable for the actual EOPCB production.

Configuration of an optical waveguide interconnect mesh network based on EOPCB

An optical waveguide interconnect mesh network scheme for parallel multiprocessor systems based on an electro-optical printed circuit board (EOPCB) with multimode polymer waveguide is proposed. The system consists of 22 processor element chips interconnected in a mesh network configuration. An additional layer with optical waveguide structure is embedded in a conventional printed circuit board to construct the EOPCB. Vertical cavity surface emitting laser (VCSEL)/positive intrinsic-negative (PIN) arrays are applied as the optical transmitters/receivers. Three 112 VCSEL/PIN parallel optical transmitting/receiving modules are used to provide 32 input/output optical channels required by the 22 chip-to-chip optical mesh interconnect system. The data rate in each optical channel is 3.125 Gbps and thus 10 Gbps parallel optical interconnect link for each direction of a chip is obtained. The optical signals from a processor element chip can be transmitted to another chip through optical waveguide interconnect embedded in the board. Thus the optical interconnect mesh network for parallel multiprocessor system can be implemented.

Fabrication and performance analysis of polymer light waveguides in EOPCB

A new method, named as doctor-blading, is presented to fabricate light waveguides in electro-optical printed circuit board (EOPCB). This new technology is proven to be suitable for the fabrication of the large size waveguides. The performance parameters of the light waveguides fabricated by the proposed method as well as the influence of the parameters on the performance of the waveguides are analyzed and simulated. The results demonstrate the feasibility of the method to fabricate the polymer waveguides.

Characterization of organic multi‐mode optical waveguides for electro‐optical printed circuit boards (EOPCB)

Purpose – To characterise the optical performance of organic multi‐mode optical waveguides integrated with printed circuit board (PCB) and to demonstrate the feasibility of 2.5 and 10 Gbps optical interconnection in board‐level, respectively.Design/methodology/approach – This paper provides both qualitative and quantitative approaches for the characterization the wave guide performance, i.e. using loss measurement, optical beam profiling, ethernet verification, and eye‐diagram testing. In addition to wave guide loss measurement, the most significance part of the work reported in this paper is to evaluate optical wave guides with coupled VCSELs, by which a 3 dB coupling design budget can thus be identified. Furthermore, by artificially manipulating coupling conditions, practical concerns of EOPCB integration, including waveguide geometry, VCSEL driving power, alignment tolerance, coupling spacing, etc. are studied.Findings – Thermal stability studies related to PCB lamination processes show the feasibility...