Variation in waveguides fabricated by immersion of LiNbO3 in AgNO3 and TlNO3: The role of hydrogen

Abstract

Optical waveguides fabricated in LiNbO₃ by what has previously been described as silver‐lithium or thallium‐lithium ion exchange in the molten nitrates AgNO₃ or TlNO₃ have not generally been reproducible. We show that the large increases of the extraordinary index (Δn_e = 0.12), which are observed intermittently, result not from introduction of the heavy ions, Ag⁺ or Tl⁺, but from hydrogen‐lithium exchange, which occurs when hydrogen is present as an impurity in the melts.