The function of the optical module is to realize the mutual conversion and transmission of photoelectric signals. They are mainly used in data center interconnection scenarios, telecom markets, passive WDM systems, etc.
Currently, the optical module packaging types used in China are especially 100G four-channel small form-factor pluggable QSFP28 optical module and 200G four-channel small form-factor pluggable double-density optical module QSFP-DD.
With the development of the visual communication industry, 400G QSFP-DD optical modules are gradually being applied to cloud computing and 5G networks.
The increase in communication rate inevitably brings large power consumption. The heat dissipation environment must be guaranteed to ensure the stable operation of data centers and base stations.
In the past, Microsoft built data centers on the seabed, and then Facebook made data centers in the Arctic Circle. It is enough to see that the heat dissipation of the optical module is significant.
To ensure that the high-speed communication optical module can still work stably in this extreme environment, it is necessary to add radical temperature cycle experiments in the module factory test to ensure that the optical module can work generally under extreme temperatures.
There are heat flow meters, a thermal shock test chamber, and a thermoelectric cooler (Thermoelectric cooler, TEC) to control the module’s temperature.
The temperature control efficiency of the heat flow meter is high, but it is large in size, high in cost, and loud in noise. Due to the limitation of the test fixture, the heat flow meter can only test a single module and cannot test multiple modules in parallel; the temperature control of the thermal shock test chamber is stable, but its volume is significant, and its efficiency is low, especially the cooling time is too long.
And due to the structure of the thermal shock test chamber, it is impossible to perform other optical module function tests while controlling the temperature. To facilitate the functional integration test of the optical module, the chassis size of the temperature control system needs to be less than 200mm500mm500mm, and the noise must be lower than 65 decibels.
In summary, neither the heat flow meter nor the thermal shock test chamber is suitable; TEC is selected as the thermal control system because of its lightweight, compact structure, small footprint, and zero noise, which is ideal for the integration test of optical modules.
Temperature control components. At the same time, according to the existing relevant theoretical research: the liquid cooling heat dissipation method has the advantages of ultra-quiet, fast heat dissipation, etc., although the heat pipe heat dissipation method is light in size and occupies a small area, it has the possibility of natural failure. , chemical building materials and other industries, and the electronics industry has fewer applications; combined with the experimental conclusions of the heat dissipation optimization design of the hot end, the liquid cooling method was finally selected to improve the temperature control efficiency of the TEC.
This paper combines liquid cooling and TEC to design a thermal control system for high-speed communication optical modules.
The thermoelectric cooler components in the system can be replaced with different test fixtures according to other package types of modules to be tested: it is possible to test a single QSFP-DD optical module or two QSFP28 optical modules in parallel.
Compared with the water cooler, the system’s heat dissipation system has the advantages of small size and low noise, which will promote the integration test of the optical module function in the later stage.
Hardware Composition of Thermal Control System
The high-speed communication optical module thermal control system mainly comprises a device under test (DUT) thermoelectric more excellent assembly, a DUT fixture, a TEC controller, and a TEC heat dissipation system. The TEC heat dissipation system consists of an outer and inner circulation waterway.
The external circulation waterway includes a cold plate, water pump, and TEC cold source; the inner circulation waterway consists of a cold plate, air exhaust, fan, and water pump.
How the Thermal Control System Works
The basic working principle of the system is that the TEC cooling surface in the thermoelectric more excellent assembly is in direct contact with the module to be measured through a heat sink to realize heat exchange to achieve the temperature control of the module to be measured.
Its heat dissipation surface is in contact with the surface of the water cooling head and exchanges heat through the cooled water cooling liquid to achieve the purpose of cooling; after the temperature of the water cooling liquid rises due to heat absorption, it flows into the external circulating water pump through the shallow circulating water channel of the heat dissipation system, and then pumped into the TEC cold source to cool down, and finally flow back to the cold plate in the thermoelectric cooling component through the water channel to continue heat exchange.
The TEC cold source in the heat dissipation system adopts liquid cooling to dissipate heat. Its primary purpose is to reduce the temperature difference between the two sides of the TEC in the cold source, thereby improving the cooling capacity and efficiency of the heat dissipation system.
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