MEMS Oscillators: The Complement to High Speed Optical Modules?
Since the first implementation of the 5G network in 2018, numerous countries worldwide have received access to quick and lossless network connectivity. Although individual users and small businesses may enjoy the various features associated with 5G network access, large data centers, such as those owned by Google and Amazon, stand to benefit the most from the novel technology. However, in order to achieve compatibility with such networks, data centers worldwide have had to upgrade and replace equipment to achieve next-generation standards. This modernization is not only costly, but it is also challenging to find products that can meet the standards without pulling enormous amounts of power and taking up space in a limited facility. In this blog, we will discuss the next generation of high-speed optical modules, which will play a significant role in facilitating network compatibility.
Optical modules are devices that are paired with a fiber optic cable to translate data into electric signals that may interface with data center components. Although optical modules are generally reliable and may last several years without issue, data centers have been recently challenged since 5G optical cables may transmit up to 1000mpbs. With constant network speed upgrades, it has become incumbent upon beneficiaries to stay up to date with current technologies.
One of the most significant limitations in upgrading optical modules is phase jitters. In order for modules to transmit data without error, they must effectively synchronize timing in an optical network with the processes occurring on the integrated circuit. This action is accomplished by a digital retimer, which essentially creates a copy of the original signal without loss. However, in order for a retimer to function appropriately, it requires a low-phase jitter reference clock. Phase jitter refers to the fluctuations of a signal over time. Therefore, jitter and signal stability are inversely proportional, meaning it should be kept at its nadir whenever possible. As data rates increase, so does the demand for phase jitter control.
Oscillators have long been used to create stable reference frequencies to help facilitate data transfer. For over 60 years, crystal oscillators dominated the market. These devices rely upon piezoelectric crystals, usually quartz, to resonate at a stable frequency and provide an accurate reference clock. Capable of resonating at frequencies as low as a few dozen kHz or as high as several MHz, quartz-based crystal oscillators offer utility in an endless number of applications. However, crystal oscillators have some limitations. Namely, as the crystals age, they experience a shift in resonance frequency due to mechanical stresses over time. They are also prone to slight frequency fluctuations caused by thermal noise, phonon scattering, and the removal of mechanical stress such as vibration.
Microelectromechanical system (MEMS) oscillators are devices that create much more stable resonance frequencies and have therefore become a major contributor to the feasibility of high data rates using optical modules. Although MEMS oscillators were first developed in the mid-20th century, they were not fit for widespread commercial use until the late 2000s. The most significant advancement in oscillator technology came from switching from traditional crystal materials to semiconductor materials such as polycrystalline silicon.
Building the next generation of optical modules has forced engineers to choose between the two classes of oscillators. While quartz oscillators are less expensive on average, they present several limitations, as mentioned before. Another critical factor that has influenced the push towards MEMS oscillators is relative size. The Circuit board footprint has always been a consideration, but even more so with the higher data rate demands. MEMS oscillators save space by being naturally designed smaller and by including on-chip voltage regulators. Clearly, MEMS oscillators will help support the increased demands placed upon optical modules by the 5G network revolution.
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