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Beyond QSFP28 – transceivers to handle higher data rates

With the lowest power consumption and smallest form factor on the market, Quad Small Form-factor Pluggable (QSFP) has become the leading compact, hot-pluggable transceiver interconnection system used in data centers. The highest data rate module, known as QSFP28, is used for 100 Gb/s links, and has become popular for the simple reason that upgrading from 40Gb/s (QSFP+) to 100Gb/s (a 2.5x increase in bandwidth) requires minimal hardware changes – due to it having the same form factor and size as its predecessor – for less than double the cost.

Data center operators are demanding the next generation of modules, and all eyes are on QSFP and other package standards to deliver it. Leading transceiver makers are near to commercializing or already have QSFP56 products on the market, capable of delivering 200Gb/s, and back-compatible with previous QSFP standards so that data centers can reuse and easily refresh their system designs cost effectively.

Beyond this, QSFP-DD (‘DD’ standing for Double Density) and Octal Small Form Factor Pluggable (OSFP) standards are regarded as having the greatest potential to deliver next generation speed. QSFP-DD electrical interfaces will employ eight lanes that operate up to 25 Gb/s NRZ modulation or 50 Gb/s PAM4 modulation, providing solutions up to 200 Gb/s or 400 Gb/s aggregate.

With development being led by top companies who have joined the QSFP-DD and OSFP Multi Source Agreement (MSA) Groups, progress will be rapid. However, key to unlocking performance in these new standards will be fitting more complex optics and electronics into roughly the same space.

An important hurdle in achieving this ambition is the optical interface – current discrete fiber based interface solutions can take up too much real estate in the package. Simply put, the manufacturers need an alternative.

Monolithic 3D solutions are a promising option, capable of outperforming their discrete counterparts in terms of compactness, but also offering increased reliability and flexibility, less fragility, lower assembly costs, and more potential for high-volume automated assembly.

At this crucial time, when small form factor is constraining the industry’s ability to increase speed, bandwidth and channel density, transceiver manufacturers need compact components – and a monolithic 3D optical interface fits the bill perfectly.

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