A Very High-Dense on-Board Optical Module Realizing >1.3 Tb/s/Inch ^2

We demonstrate >1.3-Tb/s VCSEL-based on-board optical module for high-density optical interconnects. The optical module integrates 28-Gb/s × 24-channel transmitter and receiver into one package of 1-inch² footprint. Subsequently, the total data rate is as high as 1.34 Tb/s. As investigated the temperature distributions of an optical module in calculation and experiment, an operating case temperature of optical module is lower than the maximum case temperature of 70 degree C in a practical air-cooling environment with the total power consumption of 9.1 W when activating all CDR circuitries as the harshest condition. The module exhibits a total jitter margin of 0.48 U. I. at a BER of 10^-12 when operated by a 28.05-Gb/s NRZ PRBS bit stream for each channel. By bypassing CDR circuitries with a capable length of electrical transmission line of 30 mm, a jitter margin was degraded to 0.21 U. I. at a case temperature of 70 degree C. If a system accepts such a level of jitter margin, the total power consumption can be suppressed to 6.0 W and an operating case temperature can be decreased accordingly.

I. Introduction

Optical interconnects have been deployed as a promising solution for low-loss, long distance, and high-speed signal transmission in datacenters and high performance computing systems [1]. In rack-to-rack applications, active optical cables (AOCs) that have the same electrical interface as conventional electrical cables have been deployed to actual systems especially. On the other hand, to the next generation optical interconnects, on-board optical modules have been expected to realize a high data rate density [2]. So far, (i.e., 300 Gb/s) transceiver on-board optical modules have been demonstrated with a data rate density of 600 Gb/s/inch² [3]–[6]. To move on the next generation 400 Gigabit Ethernet and a higher data rate protocol, a very high-dense on-board optical module is demanded. We targeted realizing the doubled data rate density (i.e. 1200 Gb/s/inch²) with maintaining the size of footprint as large as 1 inch². We demonstrated vertical cavity surface emitting laser (VCSEL)-based transceiver optical module with a novel packaging structure to realize a data rate density of 1344 Gb/s/inch² (i.e. ) [7]. The total power consumption was as same as 9.1 W when operating all 24 channels simultaneously. The generated heat has to be efficiently dissipated to a heatsink. To suppress the temperature increase of the used optical and electronic devices, the top surface has a wide area of copper plane for thermal dissipation. To be adapted to actual applications, the optical module should accept an air-cooling environment. In our former work, a thermal simulation result shows that a case temperature is ∼68°C under an environmental condition of an ambient temperature of 40 °C and a wind velocity of 4.0 m/s [8]. In this report, we investigate the case temperature characteristics upon ambient temperature and wind velocity in simulation and experiment. In particular, we derive a case temperature characteristic in compliant with the OIF condition [9] as a practical environment requirement. To reduce an operating case temperature, it is capable to reduce the total power consumption (i.e., 6.0 W) by disabling CDR circuitries. Since such an on-board optical module can be located close to a host LSI, it may allow using a very short electrical transmission line to prevent the degradation of electrical signal quality. We investigate a case temperature characteristic when bypassing CDR circuitries. We also investigate a capable length of electrical transmission line by evaluating the loop-back optical link.