As we all know, the internal temperature of the deposition tube is what matters, since the reaction is occurring on the inside. However, the process pyrometer is reading the external temperature. SG Controls offers a diameter control system, which controls and...
You do not need to purchase an expensive blackbody unit. Instead, purchase a hand-held standard that is calibrated with a blackbody standard. In addition, you could temporarily mount the hand-held pyrometer on the fire carriage to spot-check the process pyrometer...
Deposition tube temperature is critical, which means your process pyrometer must be calibrated. To ensure accuracy, I use a handheld calibration standard that is independent of the process pyrometer. Look through the pyrometer viewfinder, moving through
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Keeping your deposition temperature as low as possible prevents tube shrinkage AND prevents water from moving toward the core, which will cause absorptions in the final fiber measurements. Adding dopants such as phosphorous and fluorine reduce the required
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Calibration is critical. Let’s say you think your flow rate is 200 CC per minute, but you have not calibrated the mass flow controllers. You manufacture a large quantity of preforms, and one of your mass flow controllers fails. You buy and install a new controller...
Over the years, I have found chemical visibility to be a real advantage. In a glass bubbler, you can confirm proper chemical level, confirm a uniform bubble stream, and view the chemical color (A color change may indicate delivery system corrosion). Glass
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It takes a lot of work to generate gas streams that are uniform and reproducible, with no variation. But if your rotary seal leaks, this can introduce moisture and potential corrosion, and you may see a higher OH peak in measured fibers. Common rotary seal
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During my MCVD years, I actively sought out various add-on control devices to improve our process and fiber quality. In fact, some features were specifically designed for my needs. Here’s a brief overview of recommended options. Read more: “MCVD options: These
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Before you set up the preform, I recommend leak testing the rotary seal. I do this by flowing oxygen through the rotary seal. Start by plugging the end of the rotary seal with a solid quartz tube. Next, lower the regulated O2 pressure to ~ 5 psi, slightly above
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The tube-cleaning process is a critical part of preparation. I find that using the first cleaning step to remove metallic impurities works well. If you were to HF etch first, you may etch the glass around the metallic impurity, but not necessarily remove it. If you...
