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Corporate InformationResearch & Development

December 7, 2015

Report from Presenter

The IEEE CPMT Symposium (ICSJ2015) was held in Kyoto, Japan on June 9 - July 11, 2015. Researchers from various areas such as China, Europe, USA and Japan attended this conference and discussed packaging technologies, optoelectronics and its applications animatedly.

Research and Development Group, Hitachi, Ltd., made 2 oral presentations and this report shows one of them. The title of the presentation is "A High-density 300-Gbit/s Parallel Optical Interconnect Module with Efficient Thermal Dissipation Characteristics".

Fig. 1 Demand for optical interconnect module size

Fig. 2 Structure of proposed OIM

Growing use of smart devices continues to drive mobile communications traffic growth at an annual rate of 140%. This trend calls for improvements at commensurate rates in communication performance and computing performance. However, Rack-to-rack interconnect transmission capacity is limited by the optical interconnect module (OIM) size. Therefore, To accommodate the front panel size within 1U height for over 5 Tb/s transmission capacity, high bandwidth and a compact optical interconnect modules are required to reduce the front panel height (Fig. 1). We proposed high-density and compact optical interconnect module with dual-inline electrical connector (Fig. 2).

However, reducing the module size causes a thermal issue. In a compact optical module, the heat generated from the IC transfers through the substrate and Wire bonding. Also, heat dissipation toward the case becomes difficult. Therefore, the VCSEL temperature increases, and then the optical waveform degrades. To solve this problem, we designed highly efficient heat dissipation structure that enabled maintaining low cost and small size by using a thermal via structure. In the conventional OIM (Optical Interconnect Module), the optical connector is placed on the IC upward. Directly diffusing the heat generated from the IC toward the OIM upwards is difficult. Meanwhile, in our OIM, the IC and optical connector are placed in the undersurface of the substrate. Accordingly, the heat generated from the IC can directly diffuse the upward OIM through the thermal via of the substrate (Fig. 3).

Fig. 3 Heat dissipation structure

Fig. 4 Thermal characteristics of OIM

To verify the characteristics of the proposed thermal structure, we fabricated a prototype OIM. It has a transmission data capacity of 300 Gbps with a 25 Gbps × 12 ch transceiver. The module size is 44.5 × 23 mm, and it has a high density of 50 Gbps/cm2. Especially, we focus on the heat dissipation. Our OIM can operate when the case temperature is 70℃ (Fig. 4). We will continue to develop high-density and compact optical interconnect module for future ICT systems.

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