Optical Networking Best Practices Handbook

13.4. OPTICAL CONTACTING

Microoptic systems consisting of prisms, beamsplitters, and other optical components are used across a variety of industries from telecommunications to biophotonics. They can increase the efficiency of fiber-optic and endoscopic imaging systems in medical and biophotonic applications, lock the wavelength of telecommunications transmitters, or increase the lasing efficiency in high-power lasers. The optics in these microsystems is bonded together so that no extra fixturing is required. A variety of processes such as epoxy bonding, frit bonding, diffusion bonding, and optical contacting have been used. The quality of the bond and interface is judged on several criteria, including precision, mechanical strength, optical properties (scattering, absorption, index mismatch, and power handling), thermal properties, and chemical properties, along with the simplicity and manufacturability of the process itself [6].

One of the most common methods used to adhere two pieces of optical glass is epoxy bonding. The two pieces are coated with epoxy, brought together, and cured (time, temperature, or UV exposure). Epoxy bonding is reliable and manufacturable because it is an inexpensive process with high yield. However, because it leaves an often thick and variable film, it is inappropriate for applications requiring precision thickness control. Scattering can occur in these optically thick interfaces, introducing loss. And, because the epoxy is often made from organic ...