Using novel photonic circuit designs, researchers hope to reduce the power consumption of data centers.

Photonic integrated circuits, or PICs, are devices that allow data to be generated, transmitted and processed using light particles rather than electrons. While still in the experimental stage in alternative computing, PICs have long been the backbone of telecommunications, enabling today's high-speed fiber optic lines.

Due to traditional semiconductor manufacturing methods, silicon has become the primary platform for developing such chips, enabling engineers to design and mass produce them using existing electronics manufacturing facilities.

Although PICs are more efficient and have significantly higher bandwidths than electronic communication methods, there is still room for improvement, as silicon photonic chips require significant energy for temperature regulation to maintain their high data transmission performance.

In this paper, we will discuss a breakthrough in photonic IC efficiency that came from a joint study by engineers and scientists at Oregon State University and Baylor University aimed at cutting power consumption in data centers

To carry multiple optical frequencies through the same photonic medium and enable different signals to be transmitted simultaneously using a single fiber, engineers have devised a method called wavelength division multiplexing (WDM) that increases the technology's data channel capacity without hindering its extremely fast transmission rates.

In photonic integrated circuits, the structures used to perform WDM are called silicon micro-ring resonators or Si-MRRs, which act as optical waveguides to precisely measure an integer number of wavelengths by looping back on themselves in a way that resonates every time the length of the odd resonator's optical range occurs.

By using silicon resin to fabricate these types of ring resonators, WDM can be implemented on a very small scale and as part of an ultra-low energy system. However, a major challenge with Si-MRR technology is the sensitivity of resonant wavelengths due to temperature fluctuations and manufacturing process variations.

Until now, these devices have handled precise wavelength control by using free carrier injection with PIN diodes and thermal heaters that require large amounts of electrical power.

Now, researchers from Oregon State University and Baylor University have proposed a new method that can reduce this temperature control energy requirement by more than a million.

Back in March, a team led by Baylor professor Alan Wang published their findings on experiments with gate-driven Si-MRRs to develop efficient photonic integrated circuits.

To address the temperature challenges of this technique, Prof. Wang's team developed a special type of independently tunable on-chip WDM filter that uses four Si-MMR arrays of metal oxide semiconductor (MOS) capacitors made of indium tin oxide (ITiO), hafnium (IV) oxide (HfO2) { { <--SUBSCRIPT} and silica gel.

The MOS compound used in this study is a so-called high-mobility transparent conducting oxide (TCO), which has a higher electro-optical efficiency compared to PN junctions. This is what effectively produces the energy-saving properties of this breakthrough, because by using TCO materials, a large wavelength tuning range can be achieved with low gate voltage and negligible power consumption.

According to Professor John Conley of Oregon State University's College of Engineering, thanks to his knowledge of atomic layer deposition and electronic devices, and Professor Wang's expertise in photonics, their team was able to produce a working prototype PIC whose temperature is controlled by the gate voltage, which uses almost no current.

Professors Conley and Wang's research also included Oregon State University graduate students Wei-Che Hsu, Ben Kupp and Nabila Nujhat, and was supported by Intel, NASA and the National Science Foundation.

Because fiber optics and photonic circuits are critical to establishing fast and reliable physical interconnections in data centers, the research conducted by engineers at Oregon State University and Baylor University could have a significant impact on the industry today and in the foreseeable future, where demand is extremely high.

According to the U.S. Department of Energy, data centers provide critical computer and network infrastructure for many companies, including Google, Meta and Microsoft, and need to be operational at all times, accounting for about 2 percent of all electricity use in the United States.

While still in the experimental stage, the PIC research published by Professors Wang and Conley could play an important role in minimizing these energy demands, enabling engineers to create faster, more powerful tools without worrying about electricity costs and environmental impact.