THERMAL MANAGEMENT AND EMC Cooling Optical Transceivers in


High-Speed Transmission Applications Andrew Dereka, thermoelectrics product director, Laird Thermal Solutions


H


igher data transfer rates along with energy consumption are being pushed to unprecedented levels with the increased data-driven demand and higher speed transmission rates. As a result, the optical transceiver market    smaller form factors. The current and future transceiver speeds are expected to progress from 800G to 1.6Tbps with emerging technology supporting next generation AI workloads.


The laser diodes inside pluggable optical transceivers are sensitive to temperature variations, which can lead to signal degradation and reduced reliability. Consequently, precise thermal control is crucial for maintaining optimal laser diode performance and signal integrity. Due to the small form factor and need to reduce power consumption, thermoelectric coolers (TECs) are the only feasible solution to provide reliable temperature and extending the operating life of optical transceivers.


Performance Challenges The operating temperature of a laser diode varies depending on several factors, such as the type of laser diode and package, the power of the laser diode and the operating conditions. Standard laser diodes designed for telecom applications operate within  -10°C and 85°C, although laser diodes in new optical devices can operate at even higher temperatures. Emerging telecom applications pursuing more than 400 Gb/s feature new optical devices and an expanded maximum temperature range. At temperatures outside the maximum operating range, the performance of a laser diode can degrade due to increased thermal resistance and reduced current gain. This can result in decreased laser output power and increased threshold current. High temperatures can also shift the wavelength of a laser diode, impacting its performance and reliability. For example, a distributed feedback (DFB) laser diode used in an optical communication application


36 APRIL 2025 | ELECTRONICS FOR ENGINEERS


typically emits light at a wavelength of around 1260-1650 nm. An increase in temperature causes a shift in the peak wavelength (toward the long wavelength) of around 0.1 nm/°C.


 in temperature is that of crosstalk. This can be seen in communication links that require high bandwidth and long distances. Hyperscale data centers are an example of this with optical transceivers that use wavelength-division multiplexing to  combining multiple data streams in parallel. Thermoelectric cooling provides the platform for a stable temperature of a laser diode to maintain a consistent wavelength, eliminate crosstalk and ensure reliable performance.


Cooling Challenges


More data transferring at higher speeds, increasing power densities and shrinking product form factors result in higher  transceivers, multiple lasers (up to eight) may be placed on a single TEC to achieve the desired data rates. For example, an 800G transceiver might use eight lasers, each capable of 100 Gigabits per second. Optimising the process focuses on customising the thermoelectric element geometry and the number of couples  each transceiver design. This customisation


allows for incremental improvements in  consumption in data centers.


The Need for Micro TECs Laser diodes generate more heat as data throughput speeds increase and the distance between connection points increases. As a result, laser diode packages require higher heat pumping capacity to move heat away from sensitive electronics and out of the package. To pump the heat out, micro TECs with higher packing fractions   control and temperature stabilisation. New thermoelectric materials and high-precision manufacturing processes have enabled the development of micro  diodes to be made in smaller form factors, as small as 1.6mm by 1.6mm, without compromising thermal stability. They  in temperature, which is important for  thermal control response, such as in optical  can improve the laser diode performance and reliability enabling higher data transmission rates. In addition, micro TECs can be manufactured inexpensively with high throughput, which can help reduce the overall cost of the laser diode system.


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