Optical Printed Circuit Board Research Articles

Optical printed circuit boards with multimode polymer waveguides and pluggable connectors for high-speed optical interconnects.

We demonstrate the development of optical printed circuit boards (OPCBs) containing multimode polymer waveguides and pluggable optical connectors. The basic optical characteristics of the PCB-embedded waveguides, waveguide connectors, and high-speed performance were comprehensively evaluated. The fabricated OPCB comprises eight electrical layers and one optical layer. Waveguides are terminated at both ends with MT/MPO connectors. The optical channels comprising 10 cm-long waveguides embedded in OPCBs with two connectors show an average insertion loss of 6.42 dB. The resulting coupling loss is 0.77 dB per interface, which is very low and to our knowledge is among the lowest reported to date for waveguides embedded in rigid PCBs. 30 Gbps per channel NRZ data transmission was demonstrated with a measured waveguide bandwidth of 23 GHz × m, which gives a possible data traffic of 720 Gb/s for such 24-channel parallel optical link. Our efforts lay the foundation for the further development of OPCBs with higher performance.

SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material.

Stepped laser-ablation fabrication of concave micromirrors in rectangular optical waveguides for low loss vertical coupling.

In this report, we present a stepped laser-ablation method for the fabrication of concave micromirrors in rectangular optical waveguides. The numerically simulated vertical coupling loss of the reflection of the concave micromirror can be reduced to 1.53 dB. The processing parameters of the utilized excimer laser, such as the step number, width, and depth, were optimized to fabricate the concave micromirrors. After the thermal reflow process, the measured curve of the circular concave micromirrors obtained using a 3D optical profiler agreed well with a standard circle with a surface roughness of 39.56 nm. Furthermore, vertical coupling for 62.5 µm MMF revealed that the loss of the circular concave micromirror coated with a 50 nm thick Au film is as low as 1.83 dB, corresponding to a high coupling efficiency of 65.61%. This new, convenient, and efficient fabrication technology for the fabrication of concave micromirrors can be applied to vertical coupling for optical printed circuit board (OPCB) interconnection technology.

Low-Loss 3-Dimensional Shuffling Graded-Index Polymer Optical Waveguides for Optical Printed Circuit Boards

Low-Loss 3-Dimensional Shuffling Graded-Index Polymer Optical Waveguides for Optical Printed Circuit Boards

Competitive Evaluation of Planar Embedded Glass and Polymer Waveguides in Data Center Environments

Optical printed circuit board (OPCB) waveguide materials and fabrication methods have advanced considerably over the past 15 years, giving rise to two classes of embedded planar graded index waveguide based on polymer and glass. We consider the performance of these two emerging waveguide classes in view of the anticipated deployment in data center environments of optical transceivers based on directly modulated multimode short wavelength VCSELs against those based on longer wavelength single-mode photonic integrated circuits. We describe the fabrication of graded index polymer waveguides, using the Mosquito and photo-addressing methods, and graded index glass waveguides, using ion diffusion on thin glass foils. A comparative characterization was carried out on the waveguide classes to show a clear reciprocal dependence of the performance of different waveguide classes on wavelength. Furthermore, the different waveguide types were connected into an optically disaggregated data switch and storage system to evaluate and validate their suitability for deployment in future data center environments.

Multipoint Architectures for On-Board Optical Interconnects

Optical technology offers a high-bandwidth, energy-efficient solution for the increased communication requirements of data center and high-performance computing environments and is expected to be gradually deployed at all levels of the packaging hierarchy: from board-toboard, to on-board, andeven on-chipcommunication. In this work we focus on the on-board architecture level, outlining layout strategies for multipoint networks, such as single buses as well as a mesh of buses (MB) on optical printed circuit boards (OPCBs). Driven by that, we discuss how related point-to-point topologies, such as ameshof fully connected networks (MFCN), can be realized using wavelength division multiplexing (WDM) and multipoint layouts. We also provide closed-form formulas for the network capacity and the average internodal distance of these two mesh-like topology families,MB and MFCN, and demonstrate how the proposed techniques and formulas can be used for designing reconfigurable mesh-like architectures on OPCBs.

面向光印刷电路板的聚合物光波导制备及性能研究

面向光印刷电路板的聚合物光波导制备及性能研究

Index-profile design for low-loss crossed multimode waveguide for optical printed circuit board.

We present an index profile design for remarkably low loss multimode optical crossed waveguide. In this paper, we theoretically calculate the light propagation loss in crossed waveguides with step-index (SI) and graded-index (GI) square cores utilizing a ray tracing simulation. In this simulation, we focus on the index exponent values for the GI profile, which allows low crossing loss even if the number of crossing is as large as 50 or even if the crossing angle is as low as 20°. It is revealed that an index exponent of 2.0 for the GI core strongly contributes to exhibit 35 times lower loss (0.072 dB after 50-perpendicular crosses) compared to the loss of the SI-core counterpart (2.58 dB after the same crossings). The GI cores with a smaller index exponent exhibit better loss in crossed waveguides with a wide range of crossing angles from 30° to 90°. Furthermore, we discuss the effect of the refractive index profile at the intersection on the optical loss of crossed waveguides.

Vertical waveguide structure optical printed circuit board based on a low-dielectric and transparent PCB materials

This paper suggests an optical printed circuit board (OPCB) having new optical coupling structures, including a laser-drilled and under-filled structure (LD-UFS) and a vertical waveguide structure (VWS). The suggested OPCB has the features of high-speed data transmission as well as highly efficient optical coupling because it was fabricated with low-dielectric and transparent electrical PCB materials through a PCB compatible process. To evaluate and compare the optical and electrical performances of the suggested OPCB with those of other OPCBs, the various types of OPCBs were fabricated and measured. The optical coupling losses of the LD-UFS and the VWS were measured with excellent results of 9.8 and 7.8 dB, respectively, which are lower than that of the basic structure. The electrical 3-dB bandwidth of the OPCB was also evaluated up to more than 40 GHz.

Polymer waveguides for electro-optical integration in data centers and high-performance computers.

To satisfy the intra- and inter-system bandwidth requirements of future data centers and high-performance computers, low-cost low-power high-throughput optical interconnects will become a key enabling technology. To tightly integrate optics with the computing hardware, particularly in the context of CMOS-compatible silicon photonics, optical printed circuit boards using polymer waveguides are considered as a formidable platform. IBM Research has already demonstrated the essential silicon photonics and interconnection building blocks. A remaining challenge is electro-optical packaging, i.e., the connection of the silicon photonics chips with the system. In this paper, we present a new single-mode polymer waveguide technology and a scalable method for building the optical interface between silicon photonics chips and single-mode polymer waveguides.

Industry Compatible Embossing Process for the Fabrication of Waveguide-Embedded Optical Printed Circuit Boards

We demonstrate a cost-effective embossing process for the fabrication of waveguide-embedded optical printed circuit boards (OPCBs). The process involves the application of a polydimethylsiloxane mold for the production of polymer waveguides on a copper-clad FR4 substrate followed by the conventional lamination process. The embossing process is carefully tailored for the commercial polymer materials that are developed specifically to withstand the high temperature and high pressure environment during lamination. With this process, we are able to produce high-quality waveguide-embedded OPCBs with good repeatability. Our typical OPCB samples, each of which consists of 12 130-mm long fully embedded channel waveguides with a core size of approximately 50 × 50 μm and a pitch of 250 μm, show an average optical loss in the range 0.16-0.22 dB/cm at the wavelength 850 nm. The OPCBs survive the reflow process at 245 °C with a small change in the optical loss. The embossing process can be readily integrated with the existing PCB manufacturing process and thus offers a practical solution to mass production of OPCBs.

Polymer Optical Waveguides With GI and W-Shaped Cores for High-Bandwidth-Density On-Board Interconnects

We fabricate polynorbornene-based graded-index (GI) core polymer optical waveguides using the photoaddressing method, and demonstrate that the GI-core polymer waveguides are capable of realizing high-bandwidth-density on-board optical interconnects. Because of the tight optical confinement effect of the parabolic refractive index profile, the fabricated GI-core polymer waveguides exhibit superior optical properties compared to step-index (SI) core polymer waveguides: low propagation loss, low connection loss with GI multimode fiber (MMF) with wide misalignment tolerance, and low interchannel crosstalk even under a small pitch size are experimentally confirmed. Furthermore, interchannel crosstalk due to multicore operation is experimentally evaluated, and a method to estimate the interchannel crosstalk in multimode polymer parallel optical waveguides under multicore operation is proposed for the first time, to the best of our knowledge. The photoaddressing method capable of fabricating even low-loss GI-core polymer waveguide circuits will pave the way for realizing low-cost and high-bandwidth-density optical printed circuit boards.

Research and Design of Optical-Fiber-Embedded Structure in Optical Printed Circuit Board under Thermal Shock

To improve the serviceability of embedded optical fiber in OPCB, the paper discussed the optical-fiber-embedded structure in OPCB from the aspects of stress. Firstly, discussed optical fiber, groove and whether to use filler and provided six kinds of embedded structures. Then, finite element models were built for thermal simulation and thermal stress in fiber was calculated. Finally, compared different embedded structures from the stress in fiber and gave some suggestion about the design of embedded structure. The study proved that glass fiber is a better selection for OPCB; the stress concentrate easily appears in the edge of glass fiber; using filler can protect uncoated glass fiber, but increase the thermal stress is in coated glass fiber; when embedding uncoated fiber, U-groove is a better choice; when embedding coated fiber, U-groove without filler is the best choice. The results are helpful to the application of glass fiber in OPCB.

Optical matching of single-mode fibres with planar waveguides as an application of nonlinear wave processes in photopolymerizable media

The possibility of optical matching of a standard single-mode fibre (core diameter 8.2 μm, Δn = 0.37%) and the planar waveguide of an optical printed circuit board (side 2.5 μm, Δn = 0.96%) is under investigation. The optical formation process of a polymeric waveguiding structure under the action of light beams propagating in opposite directions through a photopolymerizable composite was simulated. It was shown that the efficiency of radiation transmission through the connective unit synthesized by light can reach 70% even in the direction from the single-mode optical fibre (wider) into the planar waveguide (narrower).

Fabrication of a Graded-Index Circular-Core Polymer Parallel Optical Waveguide Using a Microdispenser for a High-Density Optical Printed Circuit Board

A simple fabrication method for multimode polymer optical waveguides with graded-index (GI) circular cores is introduced for use in optical printed circuit boards (O-PCBs). The new method, named “Mosquito method,” utilizes a microdispenser to dispense a viscous monomer directly onto the substrates. By optimizing the dispensing conditions, 12-channel parallel waveguides with circular GI-cores (core diameter of 40 μm) are successfully fabricated using the Mosquito method. The advantages of GI-core waveguides for O-PCB applications are discussed by comparing the optical characteristics of the fabricated waveguides with those of conventional step-index (SI) square-core polymer waveguides, and even with those of silica-based GI multimode fibers (MMFs), as an ideal case. To the best of our knowledge, this is the first comparison of SI- and GI-core multimode polymer waveguides that are composed of the same polymer materials and that have similar core and pitch sizes. We experimentally demonstrate that the GI circular-core polymer waveguides fabricated by the Mosquito method have sufficiently low propagation loss (0.033 dB/cm at 850 nm), low connection loss with GI-MMFs, and low interchannel crosstalk. We observe approximately -50 dB of interchannel crosstalk in the 250-μm pitch GI-core waveguide fabricated, which is almost 10 dB lower than in the SI counterpart. Furthermore, sufficiently low crosstalk is maintained in a half-pitch GI-core waveguide fabricated by the Mosquito method.

Ultra-thin and low-power optical interconnect module based on a flexible optical printed circuit board

We describe an ultra-thin and low-power optical interconnect module for mobile electronic devices such as mobile phones and notebooks. The module was fabricated by directly packaging optic and electronic components onto a thin and flexible optical printed circuit board having a size of 70×8×0.25 mm. The completed active module has features of thinness (0.5 mm), small size (7×5 mm), very low total power consumption (15.88 mW), and high data rate transmissions (2.5 Gbps).

A Low Power Consumption Architecture Model for Multiple Processors on Optical Printed Circuit Board

A Low Power Consumption Architecture Model for Multiple Processors on Optical Printed Circuit Board

Terabit/s-Class Optical PCB Links Incorporating 360-Gb/s Bidirectional 850 nm Parallel Optical Transceivers

We report here on the design, fabrication, and characterization of highly integrated parallel optical transceivers designed for Tb/s-class module-to-module data transfer through polymer waveguides integrated into optical printed circuit boards (o-PCBs). The parallel optical transceiver is based on a through-silicon-via silicon carrier as the platform for integration of 24-channel vertical cavity surface-emitting laser and photodiode arrays with CMOS ICs. The Si carrier also includes optical vias (holes) for optical access to conventional surface-emitting 850 nm optoelectronic devices. The 48-channel 3-D transceiver optochips are flip-chip soldered to organic carriers to form transceiver optomodules. Fully functional optomodules with 24 transmitter + 24 receiver channels were assembled and characterized with transmitters operating up to 20 Gb/s/ch and receivers up to 15 Gb/s/ch. At 15 Gb/s, the 48-channel optomodules provide a bidirectional aggregate bandwidth of 360 Gb/s. In addition, o-PCBs have been developed using a 48-channel flex waveguide assembly attached to FR4 electronic boards. Incorporation of waveguide turning mirrors and lens arrays facilitates optical coupling to/from the o-PCB. Assembly of optomodules to the o-PCB using a ball grid array process provides both electrical and optical interconnections. An initial demonstration of the full module-to-module optical link achieved >; 20 bidirectional links at 10 Gb/s. At 15 Gb/s, operation at a bit error ratio of <; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 12</sup> was demonstrated for 15 channels in each direction, realizing a record o-PCB link with a 225 Gb/s bidirectional aggregate data rate.

Design and analysis of a low loss and large-tolerance optical interface for large-area optical waveguides

An alternative interface structure design of a large-area optical waveguide for a large-area optical printed circuit board using a step-out fabrication technique is proposed. To investigate the misalignment tolerances and coupling excess losses, we simulated and compared our proposed structure to a typical straight core structure. As a result, the proposed structure was found to significantly improve the misalignment tolerance by more than 2 times and successfully conduct a data-link based on large area optical waveguide of 50 cm × 50 cm.

2.5-Gb/s/ch Long Wavelength Transmitter Modules for Chip-to-Chip Optical PCB Applications

We have fabricated 2.5-Gb/s/ch long wavelength optical transmitter modules in planar and multichip module structures for chip-to-chip optical printed-circuit board (OPCB) applications. Their performance has been analyzed and compared with two types of short wavelength structures. The long wavelength multichip module showed a 3-dB bandwidth of 2.46 GHz while the planar showed 2.16 GHz. The modules showed clear eye openings at 2.5 Gb/s with a bit-error rate less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> and can be used for optical interconnections in OPCBs.