Optical transceivers can beat the heat in the era of high-speed data centers

The rapid growth of artificial intelligence (AI) and large language models has led to a surge in demand for high-speed optical transceivers within data centers and AI cluster computers. With transceiver speeds scaling from 100 Gbps to 400 Gbps to 800 Gbps, and future roadmaps pointing beyond 1.6 Tbps, efficient thermal management is critical to ensure performance, reliability, and energy efficiency.

Optical transceivers are the backbone of high-speed communication between servers and network devices, facilitating the data transfer required for AI computations within modern data centers. As AI cloud computing and data-driven demand increase, higher data transfer rates and energy consumption are being pushed to unprecedented levels. Listed below are current and future transceiver speeds that represent the rapid progression from 100-Gbps to 1.6-Tbps transceivers due to AI and data center applications:

100 Gigabit (100G) transceivers for entry-level data center applications
400 Gigabit (400G) transceivers widely used in current AI clusters
800 Gigabit (800G) transceivers preferred in high-demand applications
1.6 Terabit (1.6T) transceivers emerging to support next-generation AI workloads

The recent AI boom has reinvigorated interest in optical transceiver technology, and is driving innovation and competition in the industry. Optical transceivers are categorized based on their transmission range (see Table 1).

TABLE 1. Optical transceiver types and cooling requirements.

As the transmission distance increases, the need for temperature stabilization becomes more critical, leading to the use of thermoelectric coolers (TECs) in longer-range transceivers. Optical transceivers, especially those designed for longer ranges, require precise temperature control to maintain laser stability and performance.

Importance of thermal management

Pluggable optical transceivers rely on laser diodes for data transmission. These lasers are sensitive to temperature variations, which can lead to signal degradation and reduced reliability. There are several thermal challenges facing optical transceiver manufacturers because of current AI and data center activities (see Fig. 1):

Increasing module power requirements
Constrained module size
Approaching module thermal limits
Tightening signal-to-noise ratio budgets as speeds increase from 400G to 3.2T
Need for cooling and temperature stability
Demand for power savings across all components

Precise thermal control is crucial to maintain optimal performance of the laser diodes and the entire optical transceiver.

Laser diode performance and temperature

The performance of a laser diode is influenced by various factors, including temperature, current, and optical power. Changes in temperature can affect the electrical and optical properties of the laser diode and impact its performance and lifespan. Below is a list of temperature effects on laser diodes:

Standard telecom laser diodes operate between -10°C and 85°C
New optical devices can operate at even higher temperatures
Outside the maximum operating range, performance degrades due to increased thermal resistance and reduced current gain
High temperatures can shift the wavelength of a laser diode, impacting performance and reliability
Wavelength shift can lead to significant crosstalk or even failure of the laser diode

For example, a distributed feedback (DFB) laser diode typically emits light at a wavelength of around 1260 to 1650 nm. An increase in temperature causes a shift in the peak wavelength of approximately 0.1 nm/°C. TECs can provide the reliable temperature stabilization by efficiently removing heat and maintaining a stable thermal environment. This improves signal integrity and extends the operating life of optical transceivers.

Another problem attributed to fluctuations 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 increase data throughput within optical fibers by combining multiple data streams in parallel.¹

Why ultrasmall or micro-TECs?

Advancements in laser diode technology also require advancements in thermal management solutions. Laser diodes generate more heat as data throughput speeds increase and the distance between connection points increases, so 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 and thinner profiles are required to improve efficiency and maintain precise wavelength control and temperature stabilization.

Benefits of micro-TECs include:

Lower profiles enable smaller laser diode form factors
More efficient response to temperature changes
Improved laser diode performance and reliability
Cost-effective manufacturing for high-volume production
Lower power consumption, which is a vital characteristic for data centers

New thermoelectric materials and high-precision manufacturing processes enabled the development of micro-TECs with lower profiles. This allows laser diodes to be made in smaller form factors without compromising thermal stability. They also respond more efficiently to changes in temperature, which is important for applications that require an efficient thermal control response, such as in optical communication systems. Higher efficiency can improve the laser diode performance and reliability to enable higher data transmission rates. Micro-TECs can also be manufactured inexpensively with high throughput, which helps reduce the overall cost of the laser diode system.

Micro-TECs like the new OptoTEC MBX series from Laird Thermal Systems are designed for laser diode temperature stabilization (see Fig. 2). The ultraminiature MBX series meets the requirements of modern laser diode applications including smaller size, lower power consumption, higher reliability, and lower cost in mass production. These factors can improve the performance and extend the reliability of the laser diode to enable innovation in next-gen telecom applications.

FIGURE 2. Micro-TEC shape-adaptable modules.

As optical transceiver modules evolve, TEC suppliers are designing smaller, thinner, and shape-adaptable modules to fit these tight geometries without sacrificing performance (see Table 2). This includes micro-TECs for on-chip cooling of specific hotspots, as an example. Engineered-to-order TECs are optimized to meet unique transmitter optical subassembly (TOSA) package requirements. This type of customized cooling solution for optical transceivers enables incremental improvements in efficiency, which is crucial to reduce overall power consumption within data centers.

TABLE 2. Typical micro-TECs for 800 Gbps transceivers.

Key design considerations for micro-TECs are:

Low power consumption due to high transceiver density within data centers
Sufficient cooling capacity to handle 1- to 3-watt range for optical transceivers
Compact form factor to fit within transceiver modules while providing efficient cooling
High-volume manufacturability for streamlined, scalable fabrication and assembly process to help reduce production costs and improve yield—ensuring TECs can be produced reliably and economically for large-scale deployments

As AI continues to drive demand for faster and more efficient data transfer, the optical transceiver market is expected to continue its growth and innovation. Customized thermoelectric cooling solutions will play a crucial role in enabling the performance and reliability of these critical components within the rapidly evolving landscape of AI and data center technologies.

The rapid advancement of AI and large language models has created a surge in demand for high-speed optical transceivers, particularly within data centers and for AI cluster computers. As the industry pushes toward even higher data transfer rates and greater power efficiency, advanced thermal management techniques and optimized TEC designs will remain key enablers of next-generation optical transceiver technology.

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