Fiber Measures Behavior of Adhesives

Perry J. Greenbaum

At Corning Inc.'s Science and Technology Div. in Corning, N.Y., scientists have developed a technique that accurately predicts the photothermal behavior of the optical-path adhesives that connect photonic components in optical networks. With the model, they can estimate the temperature rise of the adhesive from such characteristics as its thermal conductivity and diffusivity, absorption coefficient and spot size at a particular operating wavelength.

The need for such a model is clear. "Organic adhesives could undergo photothermally induced degradation and cause a significant increase in insertion loss when exposed to high intensities," said Michael DeRosa, senior scientist at Corning. "Understanding the photothermal behavior of organic optical-path adhesives is important if [the adhesives] are to be seriously considered a viable photonic packaging technology."

The photonic components integrated into today's modern optical telecommunications networks must withstand higher power densities than they did even a few years ago. They often are assembled using an optical-path adhesive. In their study, the Corning scientists tested a commercially available adhesive, Master Bond Inc.'s UV15, to verify the predictive ability of the model.

The researchers monitored the photothermal response of the adhesive while it was exposed to 1550-nm continuous-wave (CW) and pulsed laser radiation. They used blooming and backreflectance techniques -- in a departure from traditional measurement approaches, such as an elaborate free-space optical setup. "That requires one to carefully overlap a focused pump and probe beam on the sample," DeRosa explained.

The adhesive withstood the test conditions. In good agreement with the model, it remained below its measured thermal degradation temperature even when exposed to 1-W CW or 130-W pulsed radiation.

Suitable for other adhesives

The new approach is also simpler to use. DeRosa noted that, because it more closely approximates what occurs to a component in use, the results can be extended to the optical performance of actual fiber optic devices.

The technique also may be suitable for use with other adhesives, he said. He added that the work could lead to the development of better materials. "Ultimately, it will better enable us to monitor and predict high power reliability of our products and to design future products with better high-power performance."