>1.3-Tb/s VCSEL-Based On-Board Parallel-Optical Transceiver Module for High-Density Optical Interconnects

This paper gives a detailed description of a >1.3-Tb/s VCSEL-based on-board parallel-optical transceiver module for high-density optical interconnects. The optical module integrates a 28-Gb/s × 24-channel transmitter and receiver into one package with a 1-in² footprint, thereby yielding a data rate density as high as 1.34 Tb/s/in². A unique module design is developed to utilize the whole top surface for thermal dissipation and the bottom surface for optical and electrical interfaces. The heat dissipation characteristics are studied in simulations and experiments. A test system of 24-channel optical loop-back link is built to evaluate the performance when operating all 24 channels by 28.05-Gb/s 2³¹-1 PRBS bit streams simultaneously. With a total power consumption of 9.1 W, the optical module can be operated within the operating case temperature under a practical air cooling condition. When operating all 24 channels simultaneously, a total jitter margin at BER of 10^-12 is larger than 0.4 U.I. at a monitor channel. The measured jitter margin is consistent regardless of any channel operation.

I. Introduction

On-Board optical modules have been developed to realize a high data rate density in next generation optical interconnects [1]. For instance, -channel on-board parallel-optical transceiver modules have been demonstrated with a total data rate of 0.6 Tb/s with a footprint of 1 in² [2]–[7]. Krishnamoorthy et al. demonstrated an engineered Spine and Leaf switches which integrate two-dimensionally allocated -channel on-board optical transceiver modules on a card [8]; the reported Spine switch employed eight optical modules for a card. The optical back plane has 12 slots to connect the optical module-mounted card. Therefore, the total data-rate capacity of the backplane is estimated to be as high as 43.2 Tb/s ( modules × 12 slots). As a study on a feasible total data-rate capacity using an existing small form factor (SFF) for a 19-in rack unit [9], the currently deployed 100-Gb/s QSFP28 [10] and a newly developed 200-Gb/s QSFP-DD [11] reach 3.0 Tb/s and 7.2 Tb/s, respectively. Whereas a very small and high-density 400-Gb/s solution using a proposed CFP16 form factor which has the same size as a 100-Gb/s CFP4 [12] is capable of reaching 12.8 Tb/s. Hence, it is obvious that on-board optical modules can realize a much higher data-rate capacity than that of SFF-based modules, and next generation 400 Gigabit Ethernet [13] and a higher data-rate protocol would require a higher-density on-board optical transceiver module. With the aim of doubling data rate of existing 300-Gb/s on-board optical modules, we have demonstrated a -channel parallel-optical transceiver module with 1-in² footprint based on vertical cavity surface-emitting laser (VCSEL) [14] and demonstrated a total data rate density as high as 1.34 Tb/s/in² at a total power consumption of 9.1 W when operating all 24 channels simultaneously [14]. The optical module has the same footprint of 1 in² with the reported -channel optical modules. A technical challenge for this optical module is capable of realizing an air-cooling system with a total power consumption of 9.1 W which is ∼65% higher than 5.5 W of the existing -channel optical module [5]. The optical module integrates 28-Gb/s VCSEL/photodiode (PD) arrays and clock data recovery (CDR)-integrated VCSEL driver (VD)/trans-impedance amplifier (TIA) in one package where a unique packaging structure enables the whole area of top surface to be used for thermal dissipation in an air-cooling environment. Experimental and numerical temperature correlation studies between the case and optical/electrical devices showed the VCSEL temperature is ∼5 °C and the VD/TIA temperature is ∼8 °C higher than the case temperature, respectively [15]. Under actual usage in an air cooling environment in a rack where the ambient temperature is 40 °C and air-flow velocity is 2.5 m/s, we concluded that the optical module can be operated within the maximum case temperature of 70 °C [16].