What Makes Fused Silica Glass So Special?

In Part 1, we showed how AI’s “Copper Wall” is pushing data centers toward photonics and how ultra‑high‑purity fused silica glass quietly underpins that shift.

Part 2 zooms in on the material itself. What exactly is fused silica? How is it different from ordinary glass or quartz? And why is it so important for semiconductors, photonics and other high‑value technologies that Homerun is targeting with its silica platform?

Glass, Quartz and Fused Silica – Clearing Up the Basics

For many investors, “glass,” “quartz” and “fused silica” sound interchangeable. In practice, they sit on a spectrum.

•  Ordinary glass (e.g., window glass): Typically a soda‑lime or borosilicate glass, made by melting silica sand with additives (sodium, calcium, boron oxides, etc.) to lower the melting temperature and adjust properties. It’s affordable and versatile, but not pure or stable enough for the most demanding optical and semiconductor applications.
• Quartz: Naturally occurring crystalline silica (SiO₂). When melted and cooled, it can form fused quartz, which is essentially glass made from natural quartz feedstock.
• Fused silica: A very pure, glassy form of silica, typically produced from high‑purity silica sand or chemical precursors, melted above ~2,000 °C and cooled into an amorphous solid. Fused silica is often referred to as one of the purest types of glass.

In other words, fused silica is not “just glass.” It is a high‑performance, ultra‑pure form of silica glass with properties that ordinary glass cannot match.

The Properties That Matter

• Fused silica’s value comes from a combination of properties that line up very well with the needs of semiconductors, photonics and advanced electronics:
• Extreme purity – Commercial fused silica can reach >99.99% SiO₂ and even higher, with metallic impurities in the tens of parts per million or less. This low impurity level reduces absorption, scattering and defect‑related failures in optical and electronic systems.
• Wide optical transmission window – High‑grade fused silica transmits light from deep ultraviolet through visible and into the infrared, with very low optical loss. That makes it ideal for lenses, windows, prisms, waveguides and substrates in high‑performance optical systems and photonics.
• Very low thermal expansion and high thermal‑shock resistance – Fused silica expands and contracts very little with temperature changes, and can tolerate rapid heating and cooling without cracking. This stability is crucial for precision optics and semiconductor tools that operate under demanding thermal conditions.
• High softening point and temperature stability – It maintains its properties at temperatures where most conventional glasses deform or fail, which is important for high‑power lasers, lithography systems and high‑temperature industrial components.
• Chemical durability and electrical insulation – Fused silica is chemically resistant and an excellent electrical insulator, a combination that benefits advanced electronics, sensors and certain quantum applications.

For investors, the key takeaway is that fused silica sits at the intersection of purity and performance. It behaves more like a strategic advanced material than a commodity glass.

Why Purity Is Everything

In these applications, tiny amounts of the wrong impurities can have outsized effects.

• Optical performance: Transition metals and other impurities can create absorption bands, color centers or scattering sites that increase optical loss, degrade transmission at certain wavelengths or cause laser‑induced damage.
• Reliability: Defects and impurities can accelerate aging, cause local heating under high‑power laser irradiation, or reduce the lifetime of components in semiconductor and photonics tools.
• Process window: Tight impurity control allows equipment designers to rely on the material’s performance over long periods and across extreme operating conditions.

This is why “four nines” (99.99%) and “five nines” (99.999%) purity levels matter and why fused silica markets command premium pricing relative to ordinary glass.

Homerun’s R&D with UC Davis is directly aimed at this purity challenge: their femtosecond laser–based process has demonstrated upgrading SME silica from ~99.75% to above 99.99% purity, significantly reducing key impurities such as titanium, calcium, magnesium and iron, without the use of hazardous chemicals.

How Fused Silica Is Traditionally Made

Conventional fused silica production is technically sophisticated and capital‑intensive.

Two broad approaches are common:

• Synthetic fused silica: Often produced from high‑purity chemical precursors (such as silicon tetrachloride) that are oxidized and deposited in a flame or plasma, then consolidated into glass. This approach offers very tight control over purity and homogeneity, but involves complex equipment, energy‑intensive processing and corrosive chemicals.
• Fused quartz / fused silica from high‑purity sand or quartz: High‑purity silica sand or quartz is washed, refined, melted above ~2,000 °C and carefully cooled and annealed to produce glass, often followed by additional finishing steps (shaping, grinding, polishing).

In both cases, the combination of high purity, very high melting temperature and tight quality control makes fused silica more expensive and more specialized than ordinary glass. Supply is also relatively concentrated in a limited number of global producers.

This is where Homerun’s work is differentiated. Independent testing has already confirmed that Santa Maria Eterna silica sand is suitable as feedstock for fused silica production using conventional multi‑step methods. UC Davis, funded by Homerun, is now exploring new routes that aim to:

• Purify silica using femtosecond lasers (to ultra‑high purity)
• Convert sand directly into fused silica glass using a one‑step, thermoelectric Fast Joule Heating process at around 2,000 °C, without chemical reagents.

If successfully scaled, these processes could offer an alternative, potentially greener path into high‑value fused silica markets. The work is still at the R&D and scale‑up stage, and results have not yet been independently verified, but they point to a different way of thinking about fused silica supply.

Why This Matters in a Photonics World

As we discussed in Part 1, the move from copper to photonics in AI data centers and high‑performance computing is about moving more data, over longer distances, with less power and heat.

Fused silica shows up across that transition:

• In optical fibers and specialty waveguides carrying light between systems.
• In lenses, windows and prisms inside transceivers, lasers and photonic modules.
• In substrates and components for semiconductor tools that manufacture the chips and photonic devices.

As photonics scales, the demand signal for high‑purity fused silica is likely to grow in both volume and strategic importance. That is why Homerun sees fused silica not as an isolated niche, but as a core material in a broader silica‑driven strategy that also includes antimony‑free solar glass and other clean‑tech applications.

Looking Ahead to Part 3

Part 2 has focused on the “what” and “why” of fused silica glass: what it is, how it differs from ordinary glass, and why purity and performance matter so much.

In Part 3 – Inside Homerun’s UC Davis R&D: From Sand to Fused Silica, we will:

• Walk through the femtosecond laser purification and Fast Joule Heating processes in more detail.
• Highlight key results from the UC Davis lab program.
• Explain why partnering with a team that has been working in silica photonics for more than two decades matters for Homerun shareholders. Our aim with this series remains the same: to give Homerun investors a clear understanding of both the opportunity and the risks as we advance our silica‑based platform into high‑value markets.