Feature: Thermal management
operating at escalating power levels due to higher transmission speeds and parallelism. Multi-lane, multi-laser modules and faster pluggables oſten
contain up to eight lasers, semi-independent drivers and transimpedance amplifiers, driving thermal density higher. As module size remains constrained (QSFP-DD, OSFP), heat density increases, approaching practical limits for air cooling in server racks and prompting the need for advanced cooling techniques.
Sources of heat in rack enclosures With increasing transmission speeds, faster optical transceivers are among the fastest growing sources of rack heat. Te module’s optical and electrical power budget increases, leading to greater conversion losses in lasers, modulators and ICs. Faster DSPs – required for advanced modulation and error correction – push thermal consumption even further. More parallel data lanes within the same module size increases heat per square centimetre, creating a higher local heat flux, and thus calling for alternative cooling solutions in server racks. For a typical high-density switch using 32 × 800G pluggable
modules, the transceivers alone can dissipate over 500W within a small enclosure. Tis heat is added to that generated by switching ASICs or co-packaged optics. As a result, faster optical transceivers are a primary driver of increased heat dissipation in rack enclosures, with every generational leap compounding the thermal challenge and approaching the thermal density limit for air cooling in hyperscale setups; see Figure 2.
Laser diode behaviour and temperature sensitivity At the heart of every optical transceiver is the laser diode, tasked with converting electrical signals into coherent light at tightly controlled wavelengths. Temperature control is one of the most important factors in laser diode packaging, directly governing wavelength precision, output power, beam alignment but also the device’s lifetime. As hyperscale data centres and AI clusters use increasingly
larger models and interconnect more servers, the bandwidth required between compute and storage nodes is pushing transmission speeds from 800Gbps to 1.6Tbps per link. Tese higher-speed links produce more heat in smaller spaces, thus requiring increasingly compact, efficient and reliable thermal management to stabilise sensitive laser temperatures, mitigate crosstalk and preserve signal integrity over long-haul and multi-wavelength links. Effective miniaturised thermal management is critical to preventing signal degradation, maintaining laser wavelength stability and ensuring reliability. Temperature variations alter refractive index and physical
package dimensions, shiſting focus and impacting optical performance. Elevated temperatures accelerate wear mechanisms, defect growth, interdiffusion and corrosion, oſten cutting device lifetime in half for every 10°C temperature rise. Stabilising laser diode performance in pluggable transceivers
Figure 1: The continual push for higher data rates in pluggable transceivers parallels a dramatic rise in module power consumption
Figure 2: TEC designs shifting to higher heat pumping density for each generation
Figure 3: Robust thermoelectric cooling
www.electronicsworld.co.uk November 2025 31
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